SM – Seismology
SM1.1 – General Contributions on Earthquakes, Earth Structure, Seismology
EGU21-1581 | vPICO presentations | SM1.1 | Highlight
The major (Mw=7.0) earthquake of 30th October 2020 north Samos Island, Greece: Analysis of seismological and geodetic dataAlexandra Moshou, Antonios Konstantaras, and Panagiotis Argyrakis
On 30th October 2020, at 11.51 (UTC), a very strong earthquake of magnitude Mw = 7.0 struck north of the Greek island of Samos in the Aegean coast of Turkey, south of Izmir. The epicentre was determined 17km north of Samos, in the Gulf of Ephesus and was felt in many parts of Greece and western Turkey. The geographical coordinates as calculated of the manual analysis of the National Observatory of Athens (http://bbnet.gein.noa.gr/Events/2020/10/noa2020vipzs_info.html) was determined as φ= 37.9001⁰N, λ=26.8167⁰E at a focal depth at 11.8km. The earthquake triggered a tsunami that flooded the coastal district of Seferihisar (Turkey), Cesme, Izmir and the port of Samos (Greece). In the next 8 minutes after the detection of the earthquake, tsunami bulletins were issued to national focal points by the Tsunami Service Providers accredited by UNESCO’s IOC Intergovernmental Coordination Group for the Tsunami Early Warning and Mitigation System in the North-eastern Atlantic, the Mediterranean and connected seas (ICG/NEAMTWS). Greece and Turkey were put on Tsunami Watch (highest level of alert). In Seferishar the tsunami swept away many boats in the marina and the water level reached 1.5 meters causing damage to shops.
Three hours later, 15:14 (UTC) a second strong event (Mw = 5.3) occurred in the same region some kilometres south of the main earthquake (φ=37.8223⁰N,λ=26.8652⁰E, http://bbnet.gein.noa.gr/Events/2020/10/noa2020viwsi_info.html). By the end of the same day that the earthquake took place, there were 65 aftershocks while a total of 576 aftershocks up to 31/12 with magnitude greater than 1.0. For the aftershocks with 3.7<ML<7.0 we applied the moment tensor inversion to determine the focal mechanism, the Seismic Moment (M0) and the Moment Magnitude (Mw). For this purpose, 3–component broadband seismological data from the Hellenic Unified Seismological Network (HUSN) at epicentral distances less than 3˚ were selected and analysed. The preparation of the data, includes the deconvolution of instrument response, following the velocity was integrated to displacement and finally the horizontal components rotated to radial and transverse. Finally, an extensive kinematic analysis from data provided by two private sector companies networks was done.
References:
Athanassios Ganas, Penelope Kourkouli, Pierre Briole, Alexandra Moshou, Panagiotis Elias and Isaak Parcharidis. Coseismic Displacements from Moderate-Size Earthquakes Mapped by Sentinel-1 Differential Interferometry: The Case of February 2017 Gulpinar Earthquake Sequence (Biga Peninsula, Turkey), Remote Sensing, 2018, pp. 237 – 248
Athanassios Ganas, Zafeiria Roumelioti, Vassilios Karastathis, Konstantinos Chousianitis, Alexandra Moshou, Evangelos Mouzakiotis. The Lemnos 8 January 2013 (Mw=5.7) earthquake: fault slip, aftershock properties and static stress transfer modeling in the north Aegean Sea J Seismol (2014) 18:433–455 DOI 10.1007/s10950-014-9418-3
Konstantaras A. Deep Learning and Parallel Processing Spatio-Temporal Clustering Unveil New Ionian Distinct Seismic Zone. Informatics, 7(4), 39, 2020
KONSTANTARAS, A. Expert knowledge-based algorithm for the dynamic discrimination of interactive natural clusters. Earth Science Informatics 9, (2016), 95-100
How to cite: Moshou, A., Konstantaras, A., and Argyrakis, P.: The major (Mw=7.0) earthquake of 30th October 2020 north Samos Island, Greece: Analysis of seismological and geodetic data , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1581, https://doi.org/10.5194/egusphere-egu21-1581, 2021.
On 30th October 2020, at 11.51 (UTC), a very strong earthquake of magnitude Mw = 7.0 struck north of the Greek island of Samos in the Aegean coast of Turkey, south of Izmir. The epicentre was determined 17km north of Samos, in the Gulf of Ephesus and was felt in many parts of Greece and western Turkey. The geographical coordinates as calculated of the manual analysis of the National Observatory of Athens (http://bbnet.gein.noa.gr/Events/2020/10/noa2020vipzs_info.html) was determined as φ= 37.9001⁰N, λ=26.8167⁰E at a focal depth at 11.8km. The earthquake triggered a tsunami that flooded the coastal district of Seferihisar (Turkey), Cesme, Izmir and the port of Samos (Greece). In the next 8 minutes after the detection of the earthquake, tsunami bulletins were issued to national focal points by the Tsunami Service Providers accredited by UNESCO’s IOC Intergovernmental Coordination Group for the Tsunami Early Warning and Mitigation System in the North-eastern Atlantic, the Mediterranean and connected seas (ICG/NEAMTWS). Greece and Turkey were put on Tsunami Watch (highest level of alert). In Seferishar the tsunami swept away many boats in the marina and the water level reached 1.5 meters causing damage to shops.
Three hours later, 15:14 (UTC) a second strong event (Mw = 5.3) occurred in the same region some kilometres south of the main earthquake (φ=37.8223⁰N,λ=26.8652⁰E, http://bbnet.gein.noa.gr/Events/2020/10/noa2020viwsi_info.html). By the end of the same day that the earthquake took place, there were 65 aftershocks while a total of 576 aftershocks up to 31/12 with magnitude greater than 1.0. For the aftershocks with 3.7<ML<7.0 we applied the moment tensor inversion to determine the focal mechanism, the Seismic Moment (M0) and the Moment Magnitude (Mw). For this purpose, 3–component broadband seismological data from the Hellenic Unified Seismological Network (HUSN) at epicentral distances less than 3˚ were selected and analysed. The preparation of the data, includes the deconvolution of instrument response, following the velocity was integrated to displacement and finally the horizontal components rotated to radial and transverse. Finally, an extensive kinematic analysis from data provided by two private sector companies networks was done.
References:
Athanassios Ganas, Penelope Kourkouli, Pierre Briole, Alexandra Moshou, Panagiotis Elias and Isaak Parcharidis. Coseismic Displacements from Moderate-Size Earthquakes Mapped by Sentinel-1 Differential Interferometry: The Case of February 2017 Gulpinar Earthquake Sequence (Biga Peninsula, Turkey), Remote Sensing, 2018, pp. 237 – 248
Athanassios Ganas, Zafeiria Roumelioti, Vassilios Karastathis, Konstantinos Chousianitis, Alexandra Moshou, Evangelos Mouzakiotis. The Lemnos 8 January 2013 (Mw=5.7) earthquake: fault slip, aftershock properties and static stress transfer modeling in the north Aegean Sea J Seismol (2014) 18:433–455 DOI 10.1007/s10950-014-9418-3
Konstantaras A. Deep Learning and Parallel Processing Spatio-Temporal Clustering Unveil New Ionian Distinct Seismic Zone. Informatics, 7(4), 39, 2020
KONSTANTARAS, A. Expert knowledge-based algorithm for the dynamic discrimination of interactive natural clusters. Earth Science Informatics 9, (2016), 95-100
How to cite: Moshou, A., Konstantaras, A., and Argyrakis, P.: The major (Mw=7.0) earthquake of 30th October 2020 north Samos Island, Greece: Analysis of seismological and geodetic data , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1581, https://doi.org/10.5194/egusphere-egu21-1581, 2021.
EGU21-9320 | vPICO presentations | SM1.1
Aftershock signature of the M7.5 Palu 2018 supershear rupture from a rapidly deployed nodal arrayKaren Lythgoe, Muzi Muzli, Win Oo, Hongyu Zeng, Rahmat Triyono, Phyo Maung Maung, Dwikorita Karnawati, and Shengji Wei
Supershear earthquakes have significant implications for seismic hazard, in terms of ground shaking and aftershock pattern. It has been suggested that supershear ruptures are associated with fewer aftershocks on the supershear rupture segment, however this needs to be tested using high resolution event locations. Current aftershock catalogues for the M7.5 Palu 2018 supershear rupture are not of sufficient resolution to identify any characteristic aftershock pattern. Additionally it is unclear whether the supershear rupture speed occurred from the time of earthquake initiation, or at a later time on a certain segment of the fault.
We deployed a nodal array to record aftershocks following the main event. The array comprised of twenty short-period nodes, which can be deployed rapidly, making them ideal for post-rupture investigations in areas of sparse coverage. We expand the earthquake catalogue by applying template matching to the nodal array data. We then relocate seismicity recorded by the array using a double difference method. We also relocate seismicity that occurred before the array was active, using a relative relocation method. To do this, we calibrate the more distant permanent stations using events well-located by the nodal array. We further derive moment tensors for the largest events by waveform modelling using short-period and broadband records.
Our results show that the aftershocks cluster at the northern and southern extents of rupture. There is a relative dearth of aftershocks in the middle part of the rupture, particularly in the Palu valley, where rupture terminated to the surface. The fault here is a long and straight distinctive geomorphic feature. Many secondary faults were triggered, particularly in the southern Sapu valley fault system. An earthquake swarm was triggered 1 month after the main event on a strike-slip fault 200km away.
How to cite: Lythgoe, K., Muzli, M., Oo, W., Zeng, H., Triyono, R., Maung Maung, P., Karnawati, D., and Wei, S.: Aftershock signature of the M7.5 Palu 2018 supershear rupture from a rapidly deployed nodal array , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9320, https://doi.org/10.5194/egusphere-egu21-9320, 2021.
Supershear earthquakes have significant implications for seismic hazard, in terms of ground shaking and aftershock pattern. It has been suggested that supershear ruptures are associated with fewer aftershocks on the supershear rupture segment, however this needs to be tested using high resolution event locations. Current aftershock catalogues for the M7.5 Palu 2018 supershear rupture are not of sufficient resolution to identify any characteristic aftershock pattern. Additionally it is unclear whether the supershear rupture speed occurred from the time of earthquake initiation, or at a later time on a certain segment of the fault.
We deployed a nodal array to record aftershocks following the main event. The array comprised of twenty short-period nodes, which can be deployed rapidly, making them ideal for post-rupture investigations in areas of sparse coverage. We expand the earthquake catalogue by applying template matching to the nodal array data. We then relocate seismicity recorded by the array using a double difference method. We also relocate seismicity that occurred before the array was active, using a relative relocation method. To do this, we calibrate the more distant permanent stations using events well-located by the nodal array. We further derive moment tensors for the largest events by waveform modelling using short-period and broadband records.
Our results show that the aftershocks cluster at the northern and southern extents of rupture. There is a relative dearth of aftershocks in the middle part of the rupture, particularly in the Palu valley, where rupture terminated to the surface. The fault here is a long and straight distinctive geomorphic feature. Many secondary faults were triggered, particularly in the southern Sapu valley fault system. An earthquake swarm was triggered 1 month after the main event on a strike-slip fault 200km away.
How to cite: Lythgoe, K., Muzli, M., Oo, W., Zeng, H., Triyono, R., Maung Maung, P., Karnawati, D., and Wei, S.: Aftershock signature of the M7.5 Palu 2018 supershear rupture from a rapidly deployed nodal array , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9320, https://doi.org/10.5194/egusphere-egu21-9320, 2021.
EGU21-10516 | vPICO presentations | SM1.1
Insights into seismic activity of Central Adriatic offshore (Italy) evidenced by the 2013-2014, Conero seismic sequenceGuido Maria Adinolfi, Elvira Battimelli, Ortensia Amoroso, and Paolo Capuano
The Adriatic region has always attracted the interests of researchers involved in the study of the tectonic processes that controlled the evolution of the Alpine-Mediterranean area. It has been considered as an undeformed area, an aseismic, rigid block located between two active orogenic belts, the Apennines and External Dinarides thrust belts. Nevertheless, new scientific evidences reveal a complex structural framework in which active faults are capable to produce seismic activity not only along the borders of Adriatic Sea, but also in the offshore areas. In fact, the outer thrusts of Apennines and Dinarides orogenic belts propagated from the coasts to the offshore areas originating active, NW-SE trending anticlines and thrust faults that affects the Plio-Quaternary sequences.
Defining the seismotectonics of Adriatic domain and studying the active tectonics of the area with its seismogenic potential represent a challenge because the sea prevents direct observation of main geological and structural lineaments and the deployment of standard seismic networks for a more accurate analysis of seismicity. Despite the existence of new evidences, derived from seismic profiles and borehole data, by hydrocarbon exploration, correct seismic hazard estimates of Adriatic Sea require original and accurate data on the seismic activity that can allow to depict the number, size and geometry of seismogenic sources.
In this work, we focused our attention on the seismic sequence, consisting of about 230 events, which occurred along the Central Adriatic coast, in the Conero offshore, during the 2013-2104, with a ML 4.9 mainshock located at 20 km far away from city of Ancona, the main city of Marche region. After a careful and innovative selection of the data recorded from the Italian National Seismic Network, operated by the Istituto Nazionale di Geofisica e Vulcanologia, the earthquakes were relocated according to a probabilistic approach. By the inversion of the polarity of the P-wave first arrivals, the focal mechanisms were estimated and finally the local magnitudes were re-calculated. Moreover, in order verify if there has been a migration of seismicity with the activation of different faults during the seismic sequence, the analysis of spatio-temporal evolution of the seismic sequence was performed. Preliminary results show that the seismic sequence was originated mainly at small depths (< 10 km) along NW-SE trending thrust fault structures as evidenced by fault plane solutions, consistent with NE-SW horizontal, maximum compression of the outer front of Apennines thrust belt, still active in the Central Adriatic offshore.
How to cite: Adinolfi, G. M., Battimelli, E., Amoroso, O., and Capuano, P.: Insights into seismic activity of Central Adriatic offshore (Italy) evidenced by the 2013-2014, Conero seismic sequence, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10516, https://doi.org/10.5194/egusphere-egu21-10516, 2021.
The Adriatic region has always attracted the interests of researchers involved in the study of the tectonic processes that controlled the evolution of the Alpine-Mediterranean area. It has been considered as an undeformed area, an aseismic, rigid block located between two active orogenic belts, the Apennines and External Dinarides thrust belts. Nevertheless, new scientific evidences reveal a complex structural framework in which active faults are capable to produce seismic activity not only along the borders of Adriatic Sea, but also in the offshore areas. In fact, the outer thrusts of Apennines and Dinarides orogenic belts propagated from the coasts to the offshore areas originating active, NW-SE trending anticlines and thrust faults that affects the Plio-Quaternary sequences.
Defining the seismotectonics of Adriatic domain and studying the active tectonics of the area with its seismogenic potential represent a challenge because the sea prevents direct observation of main geological and structural lineaments and the deployment of standard seismic networks for a more accurate analysis of seismicity. Despite the existence of new evidences, derived from seismic profiles and borehole data, by hydrocarbon exploration, correct seismic hazard estimates of Adriatic Sea require original and accurate data on the seismic activity that can allow to depict the number, size and geometry of seismogenic sources.
In this work, we focused our attention on the seismic sequence, consisting of about 230 events, which occurred along the Central Adriatic coast, in the Conero offshore, during the 2013-2104, with a ML 4.9 mainshock located at 20 km far away from city of Ancona, the main city of Marche region. After a careful and innovative selection of the data recorded from the Italian National Seismic Network, operated by the Istituto Nazionale di Geofisica e Vulcanologia, the earthquakes were relocated according to a probabilistic approach. By the inversion of the polarity of the P-wave first arrivals, the focal mechanisms were estimated and finally the local magnitudes were re-calculated. Moreover, in order verify if there has been a migration of seismicity with the activation of different faults during the seismic sequence, the analysis of spatio-temporal evolution of the seismic sequence was performed. Preliminary results show that the seismic sequence was originated mainly at small depths (< 10 km) along NW-SE trending thrust fault structures as evidenced by fault plane solutions, consistent with NE-SW horizontal, maximum compression of the outer front of Apennines thrust belt, still active in the Central Adriatic offshore.
How to cite: Adinolfi, G. M., Battimelli, E., Amoroso, O., and Capuano, P.: Insights into seismic activity of Central Adriatic offshore (Italy) evidenced by the 2013-2014, Conero seismic sequence, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10516, https://doi.org/10.5194/egusphere-egu21-10516, 2021.
EGU21-1759 | vPICO presentations | SM1.1
Rupture process of the 7 May 2020 Mw 5.0 Tehran earthquake and its relation with the Damavand stratovolcano, and Mosha FaultPınar Büyükakpınar, Mohammadreza Jamalreyhani, Mehdi Rezapour, Stefanie Donner, Nima Nooshiri, Mirali Hassanzadeh, Pouria Marzban, and Behnam Maleki Asayesh
In May 2020 an earthquake with Mw 5.0 struck at ~40 km east of Tehran metropolis and ~15 km south of the Damavand stratovolcano. It was responsible for 2 casualties and 23 injured. The mainshock was preceded by a foreshock with Ml 2.9 and followed by a significant aftershock sequence, including ten events with Ml 3+. The occurrence of this event raised the question of its relation with volcanic activities and/or concern about the occurrence of larger future earthquakes in the capital of Iran. Tehran megacity is surrounded by several inner-city and adjacent active faults that correspond to high-risk seismic sources in the area. The Mosha fault with ~150 km long is one of the major active faults in central Alborz and east of Tehran. It has hosted several historical earthquakes (i.e. 1665 Mw 6.5 and 1830 Mw 7.1 earthquakes) in the vicinity of the 2020 Mw 5.0 Tehran earthquake’s hypocenter. In this study, we evaluate the seismic sequence of the Tehran earthquake and obtain the full moment tensor inversion of this event and its larger aftershocks, which is a key tool to discriminate between tectonic and volcanic earthquakes. Furthermore, we obtain a robust characterization of the finite fault model of this event applying probabilistic earthquake source inversion framework using near-field strong-motion records and broadband seismograms, with an estimation of the uncertainties of source parameters. Due to the relatively weak magnitude and deeper centroid depth (~12 km), no static surface displacement was observed in the coseismic interferograms, and modeling performed by seismic records. Focal mechanism solution from waveform inversion, with a significant double-couple component, is compatible with the orientation of the sinistral north-dipping Mosha fault at the centroid location. The finite fault model suggests that the mainshock rupture propagated towards the northwest. This directivity enhanced the peak acceleration in the direction of rupture propagation, observed in strong-motion records. The 2020 moderate magnitude earthquake with 2 casualties, highlights the necessity of high-resolution seismic monitoring in the capital of Iran, which is exposed to a risk of destructive earthquakes with more than 10 million population. Our results are important for the hazard and risk assessment, and the forthcoming earthquake early warning system development in Tehran metropolis.
How to cite: Büyükakpınar, P., Jamalreyhani, M., Rezapour, M., Donner, S., Nooshiri, N., Hassanzadeh, M., Marzban, P., and Maleki Asayesh, B.: Rupture process of the 7 May 2020 Mw 5.0 Tehran earthquake and its relation with the Damavand stratovolcano, and Mosha Fault, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1759, https://doi.org/10.5194/egusphere-egu21-1759, 2021.
In May 2020 an earthquake with Mw 5.0 struck at ~40 km east of Tehran metropolis and ~15 km south of the Damavand stratovolcano. It was responsible for 2 casualties and 23 injured. The mainshock was preceded by a foreshock with Ml 2.9 and followed by a significant aftershock sequence, including ten events with Ml 3+. The occurrence of this event raised the question of its relation with volcanic activities and/or concern about the occurrence of larger future earthquakes in the capital of Iran. Tehran megacity is surrounded by several inner-city and adjacent active faults that correspond to high-risk seismic sources in the area. The Mosha fault with ~150 km long is one of the major active faults in central Alborz and east of Tehran. It has hosted several historical earthquakes (i.e. 1665 Mw 6.5 and 1830 Mw 7.1 earthquakes) in the vicinity of the 2020 Mw 5.0 Tehran earthquake’s hypocenter. In this study, we evaluate the seismic sequence of the Tehran earthquake and obtain the full moment tensor inversion of this event and its larger aftershocks, which is a key tool to discriminate between tectonic and volcanic earthquakes. Furthermore, we obtain a robust characterization of the finite fault model of this event applying probabilistic earthquake source inversion framework using near-field strong-motion records and broadband seismograms, with an estimation of the uncertainties of source parameters. Due to the relatively weak magnitude and deeper centroid depth (~12 km), no static surface displacement was observed in the coseismic interferograms, and modeling performed by seismic records. Focal mechanism solution from waveform inversion, with a significant double-couple component, is compatible with the orientation of the sinistral north-dipping Mosha fault at the centroid location. The finite fault model suggests that the mainshock rupture propagated towards the northwest. This directivity enhanced the peak acceleration in the direction of rupture propagation, observed in strong-motion records. The 2020 moderate magnitude earthquake with 2 casualties, highlights the necessity of high-resolution seismic monitoring in the capital of Iran, which is exposed to a risk of destructive earthquakes with more than 10 million population. Our results are important for the hazard and risk assessment, and the forthcoming earthquake early warning system development in Tehran metropolis.
How to cite: Büyükakpınar, P., Jamalreyhani, M., Rezapour, M., Donner, S., Nooshiri, N., Hassanzadeh, M., Marzban, P., and Maleki Asayesh, B.: Rupture process of the 7 May 2020 Mw 5.0 Tehran earthquake and its relation with the Damavand stratovolcano, and Mosha Fault, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1759, https://doi.org/10.5194/egusphere-egu21-1759, 2021.
EGU21-10625 | vPICO presentations | SM1.1
Analysis of background seismicity recorded at Mefite d’Ansato CO2 emission field in the framework of FURTHER project: first results.Paola Cusano, Pierdomenico Del Gaudio, Danilo Galluzzo, Guido Gaudiosi, Anna Gervasi, Mario La Rocca, Claudio Martino, Girolamo Milano, Lucia Nardone, Simona Petrosino, Vincenzo Torello, Luciano Zuccarello, and Francesca Di Luccio
FURTHER – “The role of FlUids in the pReparaTory pHase of EaRthquakes in Southern Apennines” is an INGV Departement Strategic Project devoted to define the role of fluids in earthquake genesis. One of the target areas of the multidisciplinary study is Mefite d’Ansanto, which is the largest area of non-volcanic low temperature CO2 emission field on the Earth. In particular, Work Package 1.4 is dedicated to the application of analysis methodologies in time and frequency domains, aimed to intercept eventual variations in fluid behavior before or in correspondence of local and regional earthquakes, using recordings from the INGV National Seismic Network (IV) and local networks. For this purpose, temporary acquisition surveys have been locally deployed.
On November 20, 2020, a stand-alone seismic station equipped with a Guralp CMG40T 60s broadband sensor, was installed close to the Mefite emission field. In this study we analyze some characteristics of the local seismicity, e.g., frequency content, energy temporal pattern (RMS) and polarization (Montalbetti et al., 1970), and estimate site effects (Nakamura, 1989; http://www.geopsy.org/). Here we present the first results of the ongoing investigation of the seismic noise wavefield in the Mefite area. The temporal pattern of the retrieved seismological observables is compared with the meteorological parameters, such as temperature and rainfall, to find possible relationships with exogenous factors.
Preliminary analysis of the waveforms acquired by the stations of the (IV) have been also performed. We selected the stations inside a radius of 30 km from Mefite area to eventually retrieve the fluid dynamics footprint in the recorded wavefield.
The identification of the wavefield and site characteristics will be useful to define the features of the next survey planned in the area.
References
Montalbetti, J. R., Kanasevich, E. R. (1970): Enhancement of teleseismic body phase with a polarization filter. Geophys. J. Int. 21 (2), 119–129.
Nakamura, Y. (1989). A method for dynamic characteristics estimation of subsurface using microtremor on the ground surface, Railway Technical Research Institute, Quarterly Reports, 30 (1), 25-33.
How to cite: Cusano, P., Del Gaudio, P., Galluzzo, D., Gaudiosi, G., Gervasi, A., La Rocca, M., Martino, C., Milano, G., Nardone, L., Petrosino, S., Torello, V., Zuccarello, L., and Di Luccio, F.: Analysis of background seismicity recorded at Mefite d’Ansato CO2 emission field in the framework of FURTHER project: first results., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10625, https://doi.org/10.5194/egusphere-egu21-10625, 2021.
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FURTHER – “The role of FlUids in the pReparaTory pHase of EaRthquakes in Southern Apennines” is an INGV Departement Strategic Project devoted to define the role of fluids in earthquake genesis. One of the target areas of the multidisciplinary study is Mefite d’Ansanto, which is the largest area of non-volcanic low temperature CO2 emission field on the Earth. In particular, Work Package 1.4 is dedicated to the application of analysis methodologies in time and frequency domains, aimed to intercept eventual variations in fluid behavior before or in correspondence of local and regional earthquakes, using recordings from the INGV National Seismic Network (IV) and local networks. For this purpose, temporary acquisition surveys have been locally deployed.
On November 20, 2020, a stand-alone seismic station equipped with a Guralp CMG40T 60s broadband sensor, was installed close to the Mefite emission field. In this study we analyze some characteristics of the local seismicity, e.g., frequency content, energy temporal pattern (RMS) and polarization (Montalbetti et al., 1970), and estimate site effects (Nakamura, 1989; http://www.geopsy.org/). Here we present the first results of the ongoing investigation of the seismic noise wavefield in the Mefite area. The temporal pattern of the retrieved seismological observables is compared with the meteorological parameters, such as temperature and rainfall, to find possible relationships with exogenous factors.
Preliminary analysis of the waveforms acquired by the stations of the (IV) have been also performed. We selected the stations inside a radius of 30 km from Mefite area to eventually retrieve the fluid dynamics footprint in the recorded wavefield.
The identification of the wavefield and site characteristics will be useful to define the features of the next survey planned in the area.
References
Montalbetti, J. R., Kanasevich, E. R. (1970): Enhancement of teleseismic body phase with a polarization filter. Geophys. J. Int. 21 (2), 119–129.
Nakamura, Y. (1989). A method for dynamic characteristics estimation of subsurface using microtremor on the ground surface, Railway Technical Research Institute, Quarterly Reports, 30 (1), 25-33.
How to cite: Cusano, P., Del Gaudio, P., Galluzzo, D., Gaudiosi, G., Gervasi, A., La Rocca, M., Martino, C., Milano, G., Nardone, L., Petrosino, S., Torello, V., Zuccarello, L., and Di Luccio, F.: Analysis of background seismicity recorded at Mefite d’Ansato CO2 emission field in the framework of FURTHER project: first results., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10625, https://doi.org/10.5194/egusphere-egu21-10625, 2021.
EGU21-15620 | vPICO presentations | SM1.1
Tectonic stress patterns along the Vrancea subcrustal zone from the inversion of focal mechanisms dataAndreea Craiu, Marius Craiu, Mariu Mihai, Elena Manea, and Alexandru Marmureanu
The Vrancea zone is an unique area with both crustal and intermediate-depth seismic activity and constitutes one of the most active seismic area in Europe. An intense and persistent seismicity is generated between 60 and 180 km depth, within a relic slab sinking nearly vertical in the Earth’s mantle due to the increasing of the stress state within this volume. At intermediate-depths, large magnitude events are frequent, i.e. four earthquakes with moment magnitudes (Mw) >7 occurred in the last century. An unique slab geometry, likely preserved until the present, causes stress localization due to the slab bending and subsequent stress release resulting in large mantle earthquakes in the region.
In this study, we evaluate the current stress field along the Vrancea subcrustal region by computing the fault plane solutions of 422 seismic events since January 2005. The continuous development of the National Seismic Network allows us to constrain the fault plane solutions and subsequently to evaluate the current stress field.
The main style of faulting for Vrancea subcrustal events presents a predominant reverse one, with two main earthquakes categories: the first one with the nodal planes oriented NE-SW parallel with the Carpathian Arc and the second one with the nodal planes oriented NW-SE perpendicular on the Carpathian Arc. The main axis of the moment tensor may indicate a predominant compressional stress field (Tpl>450 Ppl<450). Another characteristic of the Vrancea subcrustal zone is the tendency of the extension axis T to be almost vertical and the compression axis P being almost horizontal.
The results of stress inversion indicate a dominant reverse faulting style, with an average stress regime index of 2.9. Other tectonic regimes were observed in the present dataset as normal and strike-slip but they are retrieved for a restrained number of events.
The stress patterns obtained from formal stress inversion of focal mechanism solutions reveal many features of the current stress field that were not captured by large-scale numerical models.
How to cite: Craiu, A., Craiu, M., Mihai, M., Manea, E., and Marmureanu, A.: Tectonic stress patterns along the Vrancea subcrustal zone from the inversion of focal mechanisms data, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15620, https://doi.org/10.5194/egusphere-egu21-15620, 2021.
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The Vrancea zone is an unique area with both crustal and intermediate-depth seismic activity and constitutes one of the most active seismic area in Europe. An intense and persistent seismicity is generated between 60 and 180 km depth, within a relic slab sinking nearly vertical in the Earth’s mantle due to the increasing of the stress state within this volume. At intermediate-depths, large magnitude events are frequent, i.e. four earthquakes with moment magnitudes (Mw) >7 occurred in the last century. An unique slab geometry, likely preserved until the present, causes stress localization due to the slab bending and subsequent stress release resulting in large mantle earthquakes in the region.
In this study, we evaluate the current stress field along the Vrancea subcrustal region by computing the fault plane solutions of 422 seismic events since January 2005. The continuous development of the National Seismic Network allows us to constrain the fault plane solutions and subsequently to evaluate the current stress field.
The main style of faulting for Vrancea subcrustal events presents a predominant reverse one, with two main earthquakes categories: the first one with the nodal planes oriented NE-SW parallel with the Carpathian Arc and the second one with the nodal planes oriented NW-SE perpendicular on the Carpathian Arc. The main axis of the moment tensor may indicate a predominant compressional stress field (Tpl>450 Ppl<450). Another characteristic of the Vrancea subcrustal zone is the tendency of the extension axis T to be almost vertical and the compression axis P being almost horizontal.
The results of stress inversion indicate a dominant reverse faulting style, with an average stress regime index of 2.9. Other tectonic regimes were observed in the present dataset as normal and strike-slip but they are retrieved for a restrained number of events.
The stress patterns obtained from formal stress inversion of focal mechanism solutions reveal many features of the current stress field that were not captured by large-scale numerical models.
How to cite: Craiu, A., Craiu, M., Mihai, M., Manea, E., and Marmureanu, A.: Tectonic stress patterns along the Vrancea subcrustal zone from the inversion of focal mechanisms data, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15620, https://doi.org/10.5194/egusphere-egu21-15620, 2021.
EGU21-8209 | vPICO presentations | SM1.1
Focal mechanism of intermediate depth earthquakes in the Alboran Sea (Western Mediterranean)Carolina López-Sánchez, Elisa Buforn, Maurizio Mattesini, Simone Cesca, Juan Vicente Cantavella, Lucia Lozano, and Agustín Udías
One of the characteristics of the seismicity in the Ibero-Maghrebian region is the occurrence of intermediate depth earthquakes (50<h<100 km), their largest concentration located at the western part of the Alboran Sea, with epicenters following an NNE-SSW alignment. In this study, we have relocated over 200 intermediate depth earthquakes (M≥3) occurred in this region in the period 2000-2020, using a non-linear probabilistic approach (NonLinLoc algorithm) together with a recent regional 3D tomography lithospheric velocity model for the Alboran-Betic Rif Zone. Maximum likelihood hypocenters confirm the NNE-SSW distribution in a depth range between 50 and 100 km. We have determined the focal mechanisms of 26 of these earthquakes with magnitudes (mb) greater than 3.9. We first derived focal mechanisms using the P-wave first motion polarity method and then performed a moment tensor inversion, using a probabilistic inversion approach based on the simultaneous fit of waveforms and amplitude spectra of P and S phases. We performed an accurate resolution study, by repeating the inversion using different 1-D velocity models and testing different moment tensor (MT) constraints: a full moment tensor, a deviatoric moment tensor and a pure double couple (DC). Misfit values are similar for different MT constraints. Most solutions have a non-DC component larger than 30%. This may be due to the tectonic complexity of the region and the use on the inversion of 1-D Earth model. The DC components obtained from the inversion show different orientations of the nodal planes. A first group of events to the northern part with epicenters inland on south Spain have horizontal tension axes in NE-SW direction. A second group of earthquakes with epicenters off-shore, but close to the Spanish coast, presents near-vertical pressure axes. The third group, formed by deeper earthquakes, with epicenters on the center of the Alboran sea have dip slip focal mechanisms of either normal or reverse motion with planes either vertical or dipping 45º plane oriented in NNE-SSW direction, approximately the same orientation as the alignment of their epicenters. The distribution of these intermediate depth earthquakes and their focal mechanisms evidence the seismotectonic complexity of the region related with a possible subduction.
How to cite: López-Sánchez, C., Buforn, E., Mattesini, M., Cesca, S., Cantavella, J. V., Lozano, L., and Udías, A.: Focal mechanism of intermediate depth earthquakes in the Alboran Sea (Western Mediterranean), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8209, https://doi.org/10.5194/egusphere-egu21-8209, 2021.
One of the characteristics of the seismicity in the Ibero-Maghrebian region is the occurrence of intermediate depth earthquakes (50<h<100 km), their largest concentration located at the western part of the Alboran Sea, with epicenters following an NNE-SSW alignment. In this study, we have relocated over 200 intermediate depth earthquakes (M≥3) occurred in this region in the period 2000-2020, using a non-linear probabilistic approach (NonLinLoc algorithm) together with a recent regional 3D tomography lithospheric velocity model for the Alboran-Betic Rif Zone. Maximum likelihood hypocenters confirm the NNE-SSW distribution in a depth range between 50 and 100 km. We have determined the focal mechanisms of 26 of these earthquakes with magnitudes (mb) greater than 3.9. We first derived focal mechanisms using the P-wave first motion polarity method and then performed a moment tensor inversion, using a probabilistic inversion approach based on the simultaneous fit of waveforms and amplitude spectra of P and S phases. We performed an accurate resolution study, by repeating the inversion using different 1-D velocity models and testing different moment tensor (MT) constraints: a full moment tensor, a deviatoric moment tensor and a pure double couple (DC). Misfit values are similar for different MT constraints. Most solutions have a non-DC component larger than 30%. This may be due to the tectonic complexity of the region and the use on the inversion of 1-D Earth model. The DC components obtained from the inversion show different orientations of the nodal planes. A first group of events to the northern part with epicenters inland on south Spain have horizontal tension axes in NE-SW direction. A second group of earthquakes with epicenters off-shore, but close to the Spanish coast, presents near-vertical pressure axes. The third group, formed by deeper earthquakes, with epicenters on the center of the Alboran sea have dip slip focal mechanisms of either normal or reverse motion with planes either vertical or dipping 45º plane oriented in NNE-SSW direction, approximately the same orientation as the alignment of their epicenters. The distribution of these intermediate depth earthquakes and their focal mechanisms evidence the seismotectonic complexity of the region related with a possible subduction.
How to cite: López-Sánchez, C., Buforn, E., Mattesini, M., Cesca, S., Cantavella, J. V., Lozano, L., and Udías, A.: Focal mechanism of intermediate depth earthquakes in the Alboran Sea (Western Mediterranean), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8209, https://doi.org/10.5194/egusphere-egu21-8209, 2021.
EGU21-3020 | vPICO presentations | SM1.1
Focal parameter analysis of earthquakes of the S-SE of the Iberian Peninsula (1900-1923)Javier Fernandez Fraile, Elisa Buforn, Maurizio Mattesini, and Juan Vicente Cantavella
The aim of this study is to make a review, actualization and homogenization of the seismic parameters of the Seismic Catalogue of the National Seismic Network of Spain, which belongs to the National Geographic Institute. Our analysis focusses on the region that spans from 36.0 to 39.5° N and from 3.25° W to 1° E, which is a seismically very active region. The studied time period refers to earthquakes occurred between 1900 and 1923, where most information comes from macroseismic data and macroseismic effects.
The study begins by searching and collecting information from seismic bulletins and seismic catalogues, seismograms, seismic surveys, photographs, specific studies, historical newspapers and different digital archives. Then, the achieved information from all the different sources were reviewed and, whenever possible, the seismic parameters such as localization, seismic intensity and magnitude were recalculated.
The objective of this work is, from one hand, to establish the study methodology that allow to develop an overall review of all the earthquakes occurred in Spain from 1900 to date, and on the other hand, to provide good quality seismic data (improving the completeness and homogeneity of this seismic catalogue). Seismic data is important because it is used to make seismic hazard maps, studies of seismic risk, to update the seismic building standards and it is also used to make seismic characterization of the territory.
How to cite: Fernandez Fraile, J., Buforn, E., Mattesini, M., and Cantavella, J. V.: Focal parameter analysis of earthquakes of the S-SE of the Iberian Peninsula (1900-1923), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3020, https://doi.org/10.5194/egusphere-egu21-3020, 2021.
The aim of this study is to make a review, actualization and homogenization of the seismic parameters of the Seismic Catalogue of the National Seismic Network of Spain, which belongs to the National Geographic Institute. Our analysis focusses on the region that spans from 36.0 to 39.5° N and from 3.25° W to 1° E, which is a seismically very active region. The studied time period refers to earthquakes occurred between 1900 and 1923, where most information comes from macroseismic data and macroseismic effects.
The study begins by searching and collecting information from seismic bulletins and seismic catalogues, seismograms, seismic surveys, photographs, specific studies, historical newspapers and different digital archives. Then, the achieved information from all the different sources were reviewed and, whenever possible, the seismic parameters such as localization, seismic intensity and magnitude were recalculated.
The objective of this work is, from one hand, to establish the study methodology that allow to develop an overall review of all the earthquakes occurred in Spain from 1900 to date, and on the other hand, to provide good quality seismic data (improving the completeness and homogeneity of this seismic catalogue). Seismic data is important because it is used to make seismic hazard maps, studies of seismic risk, to update the seismic building standards and it is also used to make seismic characterization of the territory.
How to cite: Fernandez Fraile, J., Buforn, E., Mattesini, M., and Cantavella, J. V.: Focal parameter analysis of earthquakes of the S-SE of the Iberian Peninsula (1900-1923), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3020, https://doi.org/10.5194/egusphere-egu21-3020, 2021.
EGU21-3256 | vPICO presentations | SM1.1
Differences in the rupture process for very deep earthquakes at the Peru-Brazil and Peru-Bolivia bordersElisa Buforn, Carmen Pro, Hernando Tavera, Agustin Udias, and Maurizio Mattesini
We analyze the differences in the rupture process for twelve very deep earthquakes (h>500 km) at the Peruvian-Brazilian subduction zone. These earthquakes are produced by the contact between the Nazca and the South America Plates. We have estimated the focal mechanism from teleseismic waveforms, using the slip inversion over the rupture plane, testing rupture velocities ranging from 2.5 km/s to 4.5 km/s, and analyzing the slip distribution for each rupture velocity. The selected 12 earthquakes have occurred in the period 1994- 2016, with magnitudes between 5.9 and 8.2 and focal depth 500- 700 km. They can be separated in two groups attending to their epicentral location. The first group is formed by 9 events located, in the Peruvian-Brazil border, with epicenters following a NNW-SSE alignment, parallel to the trench. Their focal mechanisms present solutions of normal faulting with planes oriented in NS direction, dipping about 45 degrees and with vertical pressure axis. The second group is formed by three earthquakes located to the south of the first group in northern Bolivia. Their mechanisms show dip-slip motion with a near vertical plane, oriented in NW-SE direction and the pressure axis dipping 45º to the NE. The moment rate functions correspond to single ruptures with time durations from 6s to 12s, with the exception of the large 1994 Bolivian earthquake (Mw = 8.2) which presents a complex and longer STF. The different mechanisms for the two groups of earthquakes confirm the different dip of the subducting Nazca plate at the two areas, with the steeper part at the southern one.
How to cite: Buforn, E., Pro, C., Tavera, H., Udias, A., and Mattesini, M.: Differences in the rupture process for very deep earthquakes at the Peru-Brazil and Peru-Bolivia borders , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3256, https://doi.org/10.5194/egusphere-egu21-3256, 2021.
We analyze the differences in the rupture process for twelve very deep earthquakes (h>500 km) at the Peruvian-Brazilian subduction zone. These earthquakes are produced by the contact between the Nazca and the South America Plates. We have estimated the focal mechanism from teleseismic waveforms, using the slip inversion over the rupture plane, testing rupture velocities ranging from 2.5 km/s to 4.5 km/s, and analyzing the slip distribution for each rupture velocity. The selected 12 earthquakes have occurred in the period 1994- 2016, with magnitudes between 5.9 and 8.2 and focal depth 500- 700 km. They can be separated in two groups attending to their epicentral location. The first group is formed by 9 events located, in the Peruvian-Brazil border, with epicenters following a NNW-SSE alignment, parallel to the trench. Their focal mechanisms present solutions of normal faulting with planes oriented in NS direction, dipping about 45 degrees and with vertical pressure axis. The second group is formed by three earthquakes located to the south of the first group in northern Bolivia. Their mechanisms show dip-slip motion with a near vertical plane, oriented in NW-SE direction and the pressure axis dipping 45º to the NE. The moment rate functions correspond to single ruptures with time durations from 6s to 12s, with the exception of the large 1994 Bolivian earthquake (Mw = 8.2) which presents a complex and longer STF. The different mechanisms for the two groups of earthquakes confirm the different dip of the subducting Nazca plate at the two areas, with the steeper part at the southern one.
How to cite: Buforn, E., Pro, C., Tavera, H., Udias, A., and Mattesini, M.: Differences in the rupture process for very deep earthquakes at the Peru-Brazil and Peru-Bolivia borders , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3256, https://doi.org/10.5194/egusphere-egu21-3256, 2021.
EGU21-3305 | vPICO presentations | SM1.1
Methods for determining focal mechanisms in laboratory experimentsNatalia Shikhova and Andrey Patonin
In laboratory experiments, acoustic emission (AE) caused by the deformation of geomaterial reflects changes in the strength and stress state of the sample. By analogy with the solution of focal mechanisms of earthquake sources, there are several methods for determining the mechanisms and types of AE sources using the amplitudes and signs of the first arrival of an elastic wave on sensors that register acoustic signals. With 16 receiving acoustic sensors, the number of polarity determinations of the incoming wave usually does not exceed 5-10, while the sign determination on some sensors is often incorrect due to the omission of the first half-period of the weak signal by the automatic registration algorithm. This reduces the reliability of determining the mechanism of the focus in laboratory tests of rocks by wellknown methods based on the distribution of signs of the first arrival of the AE wave. We propose a method for determining the directions of the axes and the values of compression and tension in the AE source. The algorithm uses information about the coordinates of events and receivers, values of amplitudes and signs of the first half-period of P-waves coming to the receivers. In this case, the model of the AE source is assumed as a quadrupole with compression and tension axes. The source-receiver distance, the directional diagram of the receiver, and the emission diagram of the source are taken into account for each of the receivers to calculate the value of displacements in the source. To test the proposed algorithm and compare it with the known methods, there was developed a program for generating an acoustic signal source of a given type with random coordinates and directions of the compression and tension axes. An array of signs and amplitudes of the first arrivals coming to the receivers was calculated from simulated data. The high efficiency of the proposed algorithm was shown. The usage of this method together with the determination of AE event types [Zang et.al., 1998] in real laboratory experiments allows us to characterize the prevailing processes of destruction during separate phases of the experiment on triaxial loading of rocks in more detail. The developed algorithm makes it possible to determine the directions of the axes and the values of compression-tension with a minimum number of signs of the arrivals of P- waves, to estimate the components of the seismic moment tensor and obtain more complete information about the mechanism of the AE source.
The work was supported partly by the mega-grant program of the Russian Federation Ministry of Science and Education under the project no. 14.W03.31.0033 and partly by the state assignment of the Ministry to IPE RAS.
How to cite: Shikhova, N. and Patonin, A.: Methods for determining focal mechanisms in laboratory experiments, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3305, https://doi.org/10.5194/egusphere-egu21-3305, 2021.
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In laboratory experiments, acoustic emission (AE) caused by the deformation of geomaterial reflects changes in the strength and stress state of the sample. By analogy with the solution of focal mechanisms of earthquake sources, there are several methods for determining the mechanisms and types of AE sources using the amplitudes and signs of the first arrival of an elastic wave on sensors that register acoustic signals. With 16 receiving acoustic sensors, the number of polarity determinations of the incoming wave usually does not exceed 5-10, while the sign determination on some sensors is often incorrect due to the omission of the first half-period of the weak signal by the automatic registration algorithm. This reduces the reliability of determining the mechanism of the focus in laboratory tests of rocks by wellknown methods based on the distribution of signs of the first arrival of the AE wave. We propose a method for determining the directions of the axes and the values of compression and tension in the AE source. The algorithm uses information about the coordinates of events and receivers, values of amplitudes and signs of the first half-period of P-waves coming to the receivers. In this case, the model of the AE source is assumed as a quadrupole with compression and tension axes. The source-receiver distance, the directional diagram of the receiver, and the emission diagram of the source are taken into account for each of the receivers to calculate the value of displacements in the source. To test the proposed algorithm and compare it with the known methods, there was developed a program for generating an acoustic signal source of a given type with random coordinates and directions of the compression and tension axes. An array of signs and amplitudes of the first arrivals coming to the receivers was calculated from simulated data. The high efficiency of the proposed algorithm was shown. The usage of this method together with the determination of AE event types [Zang et.al., 1998] in real laboratory experiments allows us to characterize the prevailing processes of destruction during separate phases of the experiment on triaxial loading of rocks in more detail. The developed algorithm makes it possible to determine the directions of the axes and the values of compression-tension with a minimum number of signs of the arrivals of P- waves, to estimate the components of the seismic moment tensor and obtain more complete information about the mechanism of the AE source.
The work was supported partly by the mega-grant program of the Russian Federation Ministry of Science and Education under the project no. 14.W03.31.0033 and partly by the state assignment of the Ministry to IPE RAS.
How to cite: Shikhova, N. and Patonin, A.: Methods for determining focal mechanisms in laboratory experiments, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3305, https://doi.org/10.5194/egusphere-egu21-3305, 2021.
EGU21-12225 | vPICO presentations | SM1.1
Moment Magnitude Estimates in the Marmara Sea Region (NW Turkey) Using Coda Wave AnalysisBerkan Özkan, Tuna Eken, Peter Gaebler, and Tuncay Taymaz
Reliable magnitude estimates of the earthquakes are of utmost important for seismic hazard studies, particularly, in tectonically active areas such as the Marmara region of NW Turkey. The region is highly populated and contains a major fault associated with destructive earthquakes. In this study we apply a coda wave modelling approach based on acoustic radiative transfer theory to calculate the source displacement spectrum, and thus to obtain moment magnitudes of small earthquakes within the Marmara region. We examine three-component waveform data extracted from local earthquakes with magnitudes 2.5 ≤ ML ≤ 5.7 recorded in a radius of 150 km. For each event in the region, an inversion is performed in several different frequency bands. Our results indicate significant similarity with the local magnitude values reported by the KOERI. Consequently, we focus on establishing a novel relation between Mw and ML in the Marmara region.
How to cite: Özkan, B., Eken, T., Gaebler, P., and Taymaz, T.: Moment Magnitude Estimates in the Marmara Sea Region (NW Turkey) Using Coda Wave Analysis, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12225, https://doi.org/10.5194/egusphere-egu21-12225, 2021.
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Reliable magnitude estimates of the earthquakes are of utmost important for seismic hazard studies, particularly, in tectonically active areas such as the Marmara region of NW Turkey. The region is highly populated and contains a major fault associated with destructive earthquakes. In this study we apply a coda wave modelling approach based on acoustic radiative transfer theory to calculate the source displacement spectrum, and thus to obtain moment magnitudes of small earthquakes within the Marmara region. We examine three-component waveform data extracted from local earthquakes with magnitudes 2.5 ≤ ML ≤ 5.7 recorded in a radius of 150 km. For each event in the region, an inversion is performed in several different frequency bands. Our results indicate significant similarity with the local magnitude values reported by the KOERI. Consequently, we focus on establishing a novel relation between Mw and ML in the Marmara region.
How to cite: Özkan, B., Eken, T., Gaebler, P., and Taymaz, T.: Moment Magnitude Estimates in the Marmara Sea Region (NW Turkey) Using Coda Wave Analysis, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12225, https://doi.org/10.5194/egusphere-egu21-12225, 2021.
EGU21-14608 | vPICO presentations | SM1.1
High-precision, absolute earthquake location based on waveform similarity between events and application to imaging foreshocks, fault complexity and damage zones for recent western US earthquakes.Anthony Lomax, Pierre Henry, and Sophie Viseur
We present a high-precision, absolute earthquake location procedure (NLL-SSST-coherence) based on waveform similarity between events and using the probabilistic, global-search NonLinLoc (NLL) location algorithm. NLL defines a posterior probability density function (PDF) in 3D space for absolute hypocenter location and invokes the equal differential-time (EDT) likelihood function which is very robust in the presence of outlier data. For NLL-SSST-coherence location we take initial NLL locations and iteratively generate smooth, 3D, source-specific, station travel-time corrections (SSST) for each station and phase type and an updated set of locations. Next, we greatly reduce absolute location, aleatoric error by combining location information across events based on waveform coherency between the events. This absolute coherency relocation is based on the concept that if the waveforms at a station for two or more events are very similar (have high coherency) up to a given frequency, then the distance separating these “multiplet” events is small relative to the seismic wavelength at that frequency. The NLL coherency relocation for a target event is a stack over 3D space of the event’s SSST location PDF and the SSST PDF’s for other similar events, each weighted by the waveform coherency between the target event and the other event. Absolute coherency relocation requires waveforms from only one or a few stations, allowing precise relocation for sparse networks, and for foreshocks and early aftershocks of a mainshock sequence or swarm before temporary stations are installed.
We apply the NLL-SSST-coherence procedure to the Mw5.8 Lone Pine CA, Mw5.7 Magna UT and Mw6.4 Monte Cristo NV earthquake sequences in 2020 and compare with other absolute and relative seismicity catalogs for these events. The NLL-SSST-coherence relocations generally show increased organization, clustering and depth resolution over other absolute location catalogs. The NLL-SSST-coherence relocations reflect well smaller scale patterns and features in relative location catalogs, with evidence of improved depth precision and accuracy over relative location results when there are no stations over or near the seismicity.
For all three western US sequences in 2020 the NLL-SSST-coherence relocations show mainly sparse clusters of seismicity. We interpret these clusters as damage zones around patches of principal mainshock slip containing few events, larger scale damage zone and splay structures around main slip patches, and background seismicity reactivated by stress changes from mainshock rupture. The Monte Cristo Range seismicity (Lomax 2020) shows two, en-echelon primary slip surfaces and surrounding, characteristic shear-crack features such as edge, wall, tip, and linking damage zones, showing that this sequence ruptured a complete shear crack system. See presentation EGU21-13447 for more details.
Lomax (2020) The 2020 Mw6.5 Monte Cristo NV earthquake: relocated seismicity shows rupture of a complete shear-crack system. Preprint: https://eartharxiv.org/repository/view/1904
How to cite: Lomax, A., Henry, P., and Viseur, S.: High-precision, absolute earthquake location based on waveform similarity between events and application to imaging foreshocks, fault complexity and damage zones for recent western US earthquakes., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14608, https://doi.org/10.5194/egusphere-egu21-14608, 2021.
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We present a high-precision, absolute earthquake location procedure (NLL-SSST-coherence) based on waveform similarity between events and using the probabilistic, global-search NonLinLoc (NLL) location algorithm. NLL defines a posterior probability density function (PDF) in 3D space for absolute hypocenter location and invokes the equal differential-time (EDT) likelihood function which is very robust in the presence of outlier data. For NLL-SSST-coherence location we take initial NLL locations and iteratively generate smooth, 3D, source-specific, station travel-time corrections (SSST) for each station and phase type and an updated set of locations. Next, we greatly reduce absolute location, aleatoric error by combining location information across events based on waveform coherency between the events. This absolute coherency relocation is based on the concept that if the waveforms at a station for two or more events are very similar (have high coherency) up to a given frequency, then the distance separating these “multiplet” events is small relative to the seismic wavelength at that frequency. The NLL coherency relocation for a target event is a stack over 3D space of the event’s SSST location PDF and the SSST PDF’s for other similar events, each weighted by the waveform coherency between the target event and the other event. Absolute coherency relocation requires waveforms from only one or a few stations, allowing precise relocation for sparse networks, and for foreshocks and early aftershocks of a mainshock sequence or swarm before temporary stations are installed.
We apply the NLL-SSST-coherence procedure to the Mw5.8 Lone Pine CA, Mw5.7 Magna UT and Mw6.4 Monte Cristo NV earthquake sequences in 2020 and compare with other absolute and relative seismicity catalogs for these events. The NLL-SSST-coherence relocations generally show increased organization, clustering and depth resolution over other absolute location catalogs. The NLL-SSST-coherence relocations reflect well smaller scale patterns and features in relative location catalogs, with evidence of improved depth precision and accuracy over relative location results when there are no stations over or near the seismicity.
For all three western US sequences in 2020 the NLL-SSST-coherence relocations show mainly sparse clusters of seismicity. We interpret these clusters as damage zones around patches of principal mainshock slip containing few events, larger scale damage zone and splay structures around main slip patches, and background seismicity reactivated by stress changes from mainshock rupture. The Monte Cristo Range seismicity (Lomax 2020) shows two, en-echelon primary slip surfaces and surrounding, characteristic shear-crack features such as edge, wall, tip, and linking damage zones, showing that this sequence ruptured a complete shear crack system. See presentation EGU21-13447 for more details.
Lomax (2020) The 2020 Mw6.5 Monte Cristo NV earthquake: relocated seismicity shows rupture of a complete shear-crack system. Preprint: https://eartharxiv.org/repository/view/1904
How to cite: Lomax, A., Henry, P., and Viseur, S.: High-precision, absolute earthquake location based on waveform similarity between events and application to imaging foreshocks, fault complexity and damage zones for recent western US earthquakes., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14608, https://doi.org/10.5194/egusphere-egu21-14608, 2021.
EGU21-8035 | vPICO presentations | SM1.1
Analysis of Differences in Seismic Moment Tensors between Global CatalogsBoris Rösler and Seth Stein
Catalogs of moment tensors form the foundation for a wide variety of studies in seismology. Despite their importance, assessing the uncertainties in the moment tensors and the quantities derived from them is difficult. To gain insight, we compare 5000 moment tensors in catalogs of the USGS and the Global CMT Project for the period from September 2015 to December 2020. The GCMT Project generally reports larger scalar moments than the USGS, with the difference between the reported moments decreasing with magnitude. The effect of the different definitions of the scalar moment between catalogs, reflecting treatment of the non-double-couple component, is consistent with that expected. However, this effect is small and has a sign opposite to the differences in reported scalar moment. Hence the differences are intrinsic to the moment tensors in the two catalogs. The differences in the deviation from a double-couple source and in source geometry derived from the moment tensors also decrease with magnitude. The deviations from a double-couple source inferred from the two catalogs are moderately correlated, with the correlation stronger for larger deviations. However, we do not observe the expected correlation between the deviation from a double-couple source and the resulting differences in scalar moment due to the different definitions. There is essentially no correlation between the differences in source geometry, scalar moment, or fraction of the non-double-couple component, suggesting that the differences reflect aspects of the inversion rather than the source process. Despite the differences in moment tensors, the reported location and depth of the centroids are consistent between catalogs.
How to cite: Rösler, B. and Stein, S.: Analysis of Differences in Seismic Moment Tensors between Global Catalogs, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8035, https://doi.org/10.5194/egusphere-egu21-8035, 2021.
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Catalogs of moment tensors form the foundation for a wide variety of studies in seismology. Despite their importance, assessing the uncertainties in the moment tensors and the quantities derived from them is difficult. To gain insight, we compare 5000 moment tensors in catalogs of the USGS and the Global CMT Project for the period from September 2015 to December 2020. The GCMT Project generally reports larger scalar moments than the USGS, with the difference between the reported moments decreasing with magnitude. The effect of the different definitions of the scalar moment between catalogs, reflecting treatment of the non-double-couple component, is consistent with that expected. However, this effect is small and has a sign opposite to the differences in reported scalar moment. Hence the differences are intrinsic to the moment tensors in the two catalogs. The differences in the deviation from a double-couple source and in source geometry derived from the moment tensors also decrease with magnitude. The deviations from a double-couple source inferred from the two catalogs are moderately correlated, with the correlation stronger for larger deviations. However, we do not observe the expected correlation between the deviation from a double-couple source and the resulting differences in scalar moment due to the different definitions. There is essentially no correlation between the differences in source geometry, scalar moment, or fraction of the non-double-couple component, suggesting that the differences reflect aspects of the inversion rather than the source process. Despite the differences in moment tensors, the reported location and depth of the centroids are consistent between catalogs.
How to cite: Rösler, B. and Stein, S.: Analysis of Differences in Seismic Moment Tensors between Global Catalogs, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8035, https://doi.org/10.5194/egusphere-egu21-8035, 2021.
EGU21-7913 | vPICO presentations | SM1.1
A comprehensive quantification of error location uncertainties for the French earthquake catalogAndres Felipe Peña Castro, Sophie Lambotte, Marc Grunberg, Pierre Arroucau, Jessi Mayor, Guillaume Daniel, and Jean Letort
Locating earthquakes has been a longterm problem in seismology that depends on multiple parameters like station density and spacing, azimuthal gap, velocity models, and phase pick precision. Here, we analyze the current state of the earthquake French catalog for the time period between 2010 until 2018, which we divide into different regions: the Alps, Massif Central, the West, the Pyrenees, the Grand-East and the North. We perform multiple location synthetic tests using as benchmark the earthquake catalog and the evolution of the French seismic network to quantify the improvements in 1) earthquake location through time and 2) the error locations and their uncertainties. For such endeavors, we use NonLinLoc to perform the synthetic tests varying, as input, the stations, the number of stations and phase picks, 1D velocity models and 3D velocity models, and to understand the changes in 1) earthquake hypocenters, 2) ellipsoidal errors and 3) posterior density functions. Then, we relocate the entire catalog using NonLinLoc including 3D velocity models (where available) and compare the hypocentral location differences when we relocate the catalog with 1D velocity models. Additionally, we estimate a quality factor for each of the located earthquakes and report the changes on the quality factor with the temporal evolution of the national seismic network. The resulting catalog and its associated error location will help future seismic hazard estimations in the Metropolitan French area.
How to cite: Peña Castro, A. F., Lambotte, S., Grunberg, M., Arroucau, P., Mayor, J., Daniel, G., and Letort, J.: A comprehensive quantification of error location uncertainties for the French earthquake catalog, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7913, https://doi.org/10.5194/egusphere-egu21-7913, 2021.
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Locating earthquakes has been a longterm problem in seismology that depends on multiple parameters like station density and spacing, azimuthal gap, velocity models, and phase pick precision. Here, we analyze the current state of the earthquake French catalog for the time period between 2010 until 2018, which we divide into different regions: the Alps, Massif Central, the West, the Pyrenees, the Grand-East and the North. We perform multiple location synthetic tests using as benchmark the earthquake catalog and the evolution of the French seismic network to quantify the improvements in 1) earthquake location through time and 2) the error locations and their uncertainties. For such endeavors, we use NonLinLoc to perform the synthetic tests varying, as input, the stations, the number of stations and phase picks, 1D velocity models and 3D velocity models, and to understand the changes in 1) earthquake hypocenters, 2) ellipsoidal errors and 3) posterior density functions. Then, we relocate the entire catalog using NonLinLoc including 3D velocity models (where available) and compare the hypocentral location differences when we relocate the catalog with 1D velocity models. Additionally, we estimate a quality factor for each of the located earthquakes and report the changes on the quality factor with the temporal evolution of the national seismic network. The resulting catalog and its associated error location will help future seismic hazard estimations in the Metropolitan French area.
How to cite: Peña Castro, A. F., Lambotte, S., Grunberg, M., Arroucau, P., Mayor, J., Daniel, G., and Letort, J.: A comprehensive quantification of error location uncertainties for the French earthquake catalog, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7913, https://doi.org/10.5194/egusphere-egu21-7913, 2021.
EGU21-5436 | vPICO presentations | SM1.1
Multi-Array Multi-Phase Back-Projection: Improving the imaging of earthquake rupture complexitiesFelipe Vera, Frederik Tilmann, and Joachim Saul
We present a teleseismic earthquake back-projection method parameterized with multiple arrays and combined P and pP waveforms, improving the spatiotemporal resolvability of rupture complexity. The contribution of each array to the rupture image is weighted depending on the multi-array configuration. Depth phases also contribute effectively to earthquakes at 40 km depth or deeper.
We examine 31 large earthquakes with moment magnitude greater than 7.5 from 2010-2020, which were back-projected in the 0.5-2.0 Hz band, giving access to the high-frequency rupture propagation. An algorithm estimates rupture length, directivity, and speed based on the back-projection results.
Thrust and normal earthquakes showed similar magnitude-dependent lengths and consistent subshear ruptures, while strike-slip earthquakes presented longer ruptures (relative to their magnitude) and frequently reached supershear speeds. The back-projected lengths provided scaling relations to derive high-frequency rupture lengths from moment magnitudes. The results revealed complex rupture behavior, for example, bilateral ruptures (e.g., the 2017 Mw 7.8 Komandorsky Islands earthquake), evidence of dynamic triggering by a P wave (e.g., the 2016 Mw 7.9 Solomon Islands earthquake), and encircling asperity ruptures (e.g., the 2010 Mw 7.8 Mentawai and 2015 Mw 8.4 Illapel earthquakes). The latter is particularly prevalent in subduction megathrust earthquakes, with down-dip, up-dip, double encircling, and segmented patterns. The automated choice of array weighting and the extraction of basic rupture parameters makes the approach well suited for near-real-time earthquake monitoring.
How to cite: Vera, F., Tilmann, F., and Saul, J.: Multi-Array Multi-Phase Back-Projection: Improving the imaging of earthquake rupture complexities, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5436, https://doi.org/10.5194/egusphere-egu21-5436, 2021.
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We present a teleseismic earthquake back-projection method parameterized with multiple arrays and combined P and pP waveforms, improving the spatiotemporal resolvability of rupture complexity. The contribution of each array to the rupture image is weighted depending on the multi-array configuration. Depth phases also contribute effectively to earthquakes at 40 km depth or deeper.
We examine 31 large earthquakes with moment magnitude greater than 7.5 from 2010-2020, which were back-projected in the 0.5-2.0 Hz band, giving access to the high-frequency rupture propagation. An algorithm estimates rupture length, directivity, and speed based on the back-projection results.
Thrust and normal earthquakes showed similar magnitude-dependent lengths and consistent subshear ruptures, while strike-slip earthquakes presented longer ruptures (relative to their magnitude) and frequently reached supershear speeds. The back-projected lengths provided scaling relations to derive high-frequency rupture lengths from moment magnitudes. The results revealed complex rupture behavior, for example, bilateral ruptures (e.g., the 2017 Mw 7.8 Komandorsky Islands earthquake), evidence of dynamic triggering by a P wave (e.g., the 2016 Mw 7.9 Solomon Islands earthquake), and encircling asperity ruptures (e.g., the 2010 Mw 7.8 Mentawai and 2015 Mw 8.4 Illapel earthquakes). The latter is particularly prevalent in subduction megathrust earthquakes, with down-dip, up-dip, double encircling, and segmented patterns. The automated choice of array weighting and the extraction of basic rupture parameters makes the approach well suited for near-real-time earthquake monitoring.
How to cite: Vera, F., Tilmann, F., and Saul, J.: Multi-Array Multi-Phase Back-Projection: Improving the imaging of earthquake rupture complexities, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5436, https://doi.org/10.5194/egusphere-egu21-5436, 2021.
EGU21-9664 | vPICO presentations | SM1.1
A grid-based b-value approximation through Southern and Northern Norway: preliminary resultsRodrigo Estay and Claudia Pavez
The Gutenberg – Richter’s b-value is commonly used to analyze the frequency-magnitude distribution of earthquakes, describing the proportion of small and large seismic events as the first estimation of seismic hazard. Additionally, the b-value has been used as a stress meter, giving some insights into the stress regime in different regions around the world. In this research, a grid-based spatial distribution for the b – value was estimated in three different areas of Norway: northern (74°-81° N/ 12°-26° E), southern (57°-64°N/3°-12° E), and the ridge zones of Mohns and Knipovich. For this, we used a complete catalog from the years 2000 to 2019, which was obtained from the Norwegian National Seismic Network online database. The magnitude of completeness was estimated separately for each zone both in time and space, covering a total area of ~425,000 km2. Our results show a regional variation of the mean b-value for northern (bnorth = 0.79) and southern (bsouth = 1.03) Norway, and the Ridge (bridge = 0.73), which can be interpreted in terms of the predominant stress regime in the different zones. So far, a few calculations regarding the b-value were previously done in Norway to analyze local intraplate sequences. Then, according to our knowledge, this research corresponds to the first estimation of a regional spatial variation of the b – value in the country.
How to cite: Estay, R. and Pavez, C.: A grid-based b-value approximation through Southern and Northern Norway: preliminary results , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9664, https://doi.org/10.5194/egusphere-egu21-9664, 2021.
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The Gutenberg – Richter’s b-value is commonly used to analyze the frequency-magnitude distribution of earthquakes, describing the proportion of small and large seismic events as the first estimation of seismic hazard. Additionally, the b-value has been used as a stress meter, giving some insights into the stress regime in different regions around the world. In this research, a grid-based spatial distribution for the b – value was estimated in three different areas of Norway: northern (74°-81° N/ 12°-26° E), southern (57°-64°N/3°-12° E), and the ridge zones of Mohns and Knipovich. For this, we used a complete catalog from the years 2000 to 2019, which was obtained from the Norwegian National Seismic Network online database. The magnitude of completeness was estimated separately for each zone both in time and space, covering a total area of ~425,000 km2. Our results show a regional variation of the mean b-value for northern (bnorth = 0.79) and southern (bsouth = 1.03) Norway, and the Ridge (bridge = 0.73), which can be interpreted in terms of the predominant stress regime in the different zones. So far, a few calculations regarding the b-value were previously done in Norway to analyze local intraplate sequences. Then, according to our knowledge, this research corresponds to the first estimation of a regional spatial variation of the b – value in the country.
How to cite: Estay, R. and Pavez, C.: A grid-based b-value approximation through Southern and Northern Norway: preliminary results , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9664, https://doi.org/10.5194/egusphere-egu21-9664, 2021.
EGU21-9249 | vPICO presentations | SM1.1
Temporal b-value variation before and after ML ≥ 6.0 Taiwan earthquakes from 2012 to 2019Po-Yuan Chen, Sean Kuanhsiang Chen, and Yih-Min Wu
Recent studies show that earthquake b values gradually decrease before large earthquakes at the epicenters and then immediately increase after the earthquakes. Temporal b-value variations may result from crustal stress changes associated with a large earthquake. However, the physical process is rarely observed and remains unclear. Taiwan island is a young orogeny leading to frequent earthquakes with magnitudes greater than ML 6.0, which provides an excellent laboratory to examine the physical process. We calculated b-value variation before and after ML ≥ 6.0 Taiwan earthquakes at the epicenters from 2012 to 2019. The time period is based on an enhancement of earthquake detection capability from the Central Weather Bureau Seismic Network in Taiwan, which allows the magnitude of completeness (Mc) down to 1.5 in the inland region. We used a relocated earthquake catalog to precisely estimate b value and Mc by the maximum likelihood method and maximum curvature method, respectively. We designed three steps in our research. First, we calculated the b value and Mc at the epicenters of the ML ≥ 6.0 earthquakes in overall 8 years to know the background seismic activity. Based on this, second, we calculated b values and Mc per half year to test the sensitivity between the radius from epicenters (r) and the number of earthquakes with magnitudes greater than Mc (n). Finally, we will apply moving window approach with specific criteria to continuously calculate temporal b-value variations. Our results showed that spatial b values in Taiwan in overall 8 years have an average of 1.0. The b values are systematically lower in the epicenters of ML ≥ 6.0 earthquakes from 2012 to 2019. We have determined suitable r and n values for each earthquake at the epicenters and some epicenters share similar r and n values. We preliminarily observed temporal b-value decreases before the 2018 Mw 6.4 Hualien earthquake. Considering temporal b-value variation by moving windows, we aim to realize whether temporal b-value variation by a large earthquake can be frequently observed in Taiwan.
How to cite: Chen, P.-Y., Chen, S. K., and Wu, Y.-M.: Temporal b-value variation before and after ML ≥ 6.0 Taiwan earthquakes from 2012 to 2019, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9249, https://doi.org/10.5194/egusphere-egu21-9249, 2021.
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Recent studies show that earthquake b values gradually decrease before large earthquakes at the epicenters and then immediately increase after the earthquakes. Temporal b-value variations may result from crustal stress changes associated with a large earthquake. However, the physical process is rarely observed and remains unclear. Taiwan island is a young orogeny leading to frequent earthquakes with magnitudes greater than ML 6.0, which provides an excellent laboratory to examine the physical process. We calculated b-value variation before and after ML ≥ 6.0 Taiwan earthquakes at the epicenters from 2012 to 2019. The time period is based on an enhancement of earthquake detection capability from the Central Weather Bureau Seismic Network in Taiwan, which allows the magnitude of completeness (Mc) down to 1.5 in the inland region. We used a relocated earthquake catalog to precisely estimate b value and Mc by the maximum likelihood method and maximum curvature method, respectively. We designed three steps in our research. First, we calculated the b value and Mc at the epicenters of the ML ≥ 6.0 earthquakes in overall 8 years to know the background seismic activity. Based on this, second, we calculated b values and Mc per half year to test the sensitivity between the radius from epicenters (r) and the number of earthquakes with magnitudes greater than Mc (n). Finally, we will apply moving window approach with specific criteria to continuously calculate temporal b-value variations. Our results showed that spatial b values in Taiwan in overall 8 years have an average of 1.0. The b values are systematically lower in the epicenters of ML ≥ 6.0 earthquakes from 2012 to 2019. We have determined suitable r and n values for each earthquake at the epicenters and some epicenters share similar r and n values. We preliminarily observed temporal b-value decreases before the 2018 Mw 6.4 Hualien earthquake. Considering temporal b-value variation by moving windows, we aim to realize whether temporal b-value variation by a large earthquake can be frequently observed in Taiwan.
How to cite: Chen, P.-Y., Chen, S. K., and Wu, Y.-M.: Temporal b-value variation before and after ML ≥ 6.0 Taiwan earthquakes from 2012 to 2019, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9249, https://doi.org/10.5194/egusphere-egu21-9249, 2021.
EGU21-13895 | vPICO presentations | SM1.1
Correlation between earthquake b value and VP/VS ratio in JapanPei-Ying Wu, Sean Kuanhsiang Chen, and Yih-Min Wu
Earthquake b value is primarily controlled by differential stress in the crust. Pore pressure has also been reported influencing b value locally. In nature, the influence can only be observed in the subsurface crust by injection wells. It remains unclear whether the influence of pore pressure on b value can be observed in the scale of the entire crust. To this end, we assume that pore pressure increases proportionally with VP/VS ratio, which is derived from seismic tomography studies, to examine correlation between VP/VS ratio and b value. We investigated this correlation in Japan because it is one of the most earthquake-prone countries with dense seismic networks and high-quality earthquake catalogs. We used an earthquake catalog from the Japan Meteorological Agency from 1998 to 2011 Feb to calculate the b values in the inland region of Japan above the 30 km depth. The selected period is based on a stable completeness of magnitude (Mc) since 1998 and the strong clustering effects by the both 2011 Tohoku and 2016 Kumamoto earthquakes. We then calculated Mc and b value by maximum curvature method and maximum likelihood method, respectively, in the grids of 0.1 0.1 10 km with a radius of 30 km from the center of the grids. The b value determination requires the number of earthquakes with magnitudes greater than the Mc over 150 within the radius. For the VP/VS ratios, we used the latest data derived from the National Research Institute for Earth Science and Disaster Resilience, Japan, to resample them to the same grids as b values. We simply resampled the VP/VS ratios by either averaging them into the grids of b values, or weighting them through a triangular function to the grids center of b values in depths. We analyzed b value as a function of VP/VS ratio and binned the b values within every 0.01 VP/VS interval to calculate the means and medians for liner regressions. Our preliminarily results show that there is little correlation between entire b values and VP/VS ratios among different depth ranges (0-10 km, 10-20 km, 20-30 km). We observed a linear negative relation in the binned data at the 10-20 km depth, however, this relation is not likely observed in the other depths. It may imply that the influence of pore pressure on b value could vary with depths. We’ll calculate the b values using entire magnitude range method and compare the results to the other localized geophysical observations.
How to cite: Wu, P.-Y., Chen, S. K., and Wu, Y.-M.: Correlation between earthquake b value and VP/VS ratio in Japan, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13895, https://doi.org/10.5194/egusphere-egu21-13895, 2021.
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Earthquake b value is primarily controlled by differential stress in the crust. Pore pressure has also been reported influencing b value locally. In nature, the influence can only be observed in the subsurface crust by injection wells. It remains unclear whether the influence of pore pressure on b value can be observed in the scale of the entire crust. To this end, we assume that pore pressure increases proportionally with VP/VS ratio, which is derived from seismic tomography studies, to examine correlation between VP/VS ratio and b value. We investigated this correlation in Japan because it is one of the most earthquake-prone countries with dense seismic networks and high-quality earthquake catalogs. We used an earthquake catalog from the Japan Meteorological Agency from 1998 to 2011 Feb to calculate the b values in the inland region of Japan above the 30 km depth. The selected period is based on a stable completeness of magnitude (Mc) since 1998 and the strong clustering effects by the both 2011 Tohoku and 2016 Kumamoto earthquakes. We then calculated Mc and b value by maximum curvature method and maximum likelihood method, respectively, in the grids of 0.1 0.1 10 km with a radius of 30 km from the center of the grids. The b value determination requires the number of earthquakes with magnitudes greater than the Mc over 150 within the radius. For the VP/VS ratios, we used the latest data derived from the National Research Institute for Earth Science and Disaster Resilience, Japan, to resample them to the same grids as b values. We simply resampled the VP/VS ratios by either averaging them into the grids of b values, or weighting them through a triangular function to the grids center of b values in depths. We analyzed b value as a function of VP/VS ratio and binned the b values within every 0.01 VP/VS interval to calculate the means and medians for liner regressions. Our preliminarily results show that there is little correlation between entire b values and VP/VS ratios among different depth ranges (0-10 km, 10-20 km, 20-30 km). We observed a linear negative relation in the binned data at the 10-20 km depth, however, this relation is not likely observed in the other depths. It may imply that the influence of pore pressure on b value could vary with depths. We’ll calculate the b values using entire magnitude range method and compare the results to the other localized geophysical observations.
How to cite: Wu, P.-Y., Chen, S. K., and Wu, Y.-M.: Correlation between earthquake b value and VP/VS ratio in Japan, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13895, https://doi.org/10.5194/egusphere-egu21-13895, 2021.
EGU21-3511 | vPICO presentations | SM1.1
Direct P-Wave Travel Time Tomography of the Middle EastSusini Desilva, Ebru Bozdag, Guust Nolet, Rengin Gok, Ahmed Ali, and Yahya Tarabulsi
High-resolution seismic images of the crust and mantle beneath regions of complex surface geological structures are necessary to gain insights on the underlying geodynamical processes. One such region embodying various plate boundary motions and intraplate deformations is the Middle East, and consequently the region is prone to significant seismic activity. Hence a tomographic investigation using a more recent and reliable data set is vital in understanding the ongoing complicated deformation process driven by the African, Arabian and Eurasian plates. The purpose of our study is to retrieve a detailed model of the crust and mantle beneath the Middle Eastern region using teleseismic P arrival times from the ISC-EHB bulletin (Engdahl et al., 1998).
Starting with AK135 as the reference model we invert for tomographic models of compressional wavespeed perturbations down to lower mantle depths in an area bounded by longitudes 22E–66E and latitudes 8N–48N. The data set used in this study consists of regionally observed P-phase arrival times from over 1000 global events from 1996–2016 culminating in a larger dataset than other similar studies. Selection of a reliable data, ray tracing, preconditioning and inversion steps are carried out using the BD-soft software suite (https://www.geoazur.fr/GLOBALSEIS/Soft.html).
Preliminary inversion results are consistent with the previous regional tomographic studies. In checkerboard tests, cell sizes as low as ∼ 2.8° × 2.8° ( ∼ 240 × 240 km at surface) are generally well recovered down to a 1000 km depth beneath the Anatolian plateau where we currently have the densest coverage. Additionally the Caucasus region and northern parts of the Iranian plateau shows good recovery of ±4% Vp perturbation amplitudes at depths ∼ 70 – 135 km. There is fair recovery for a minimum cell size of ∼ 2.8° × 2.8° beneath the Iranian Plateau, Zagros mountain region, Persian gulf, and northeast Iraq, along with quite good recovery of cell amplitudes towards the Anatolian-Caucasus region at depth ranges 380 – 430 km, 650 – 700 km, and around 950 km. Tomographic inversions unveil a low P velocity zone stretching from the Afar region to Sinai Peninsula consistent with S wave velocity observations of a similar feature by Chang and van der Lee 2011.
We are able to further improve coverage especially down to lithospheric depths within the Arabian peninsula using first arrival times measured from waveform data collected from regional networks. Addition of first arrival time delays from waveforms highlights a prominent low velocity in the tomographic inversions beneath the volcanic fields of western Saudi Arabia. Our ultimate goal is to perform full-waveform inversion of the region constrained by the constructed P-wave model.
How to cite: Desilva, S., Bozdag, E., Nolet, G., Gok, R., Ali, A., and Tarabulsi, Y.: Direct P-Wave Travel Time Tomography of the Middle East, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3511, https://doi.org/10.5194/egusphere-egu21-3511, 2021.
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We are sorry, but presentations are only available for users who registered for the conference. Thank you.
High-resolution seismic images of the crust and mantle beneath regions of complex surface geological structures are necessary to gain insights on the underlying geodynamical processes. One such region embodying various plate boundary motions and intraplate deformations is the Middle East, and consequently the region is prone to significant seismic activity. Hence a tomographic investigation using a more recent and reliable data set is vital in understanding the ongoing complicated deformation process driven by the African, Arabian and Eurasian plates. The purpose of our study is to retrieve a detailed model of the crust and mantle beneath the Middle Eastern region using teleseismic P arrival times from the ISC-EHB bulletin (Engdahl et al., 1998).
Starting with AK135 as the reference model we invert for tomographic models of compressional wavespeed perturbations down to lower mantle depths in an area bounded by longitudes 22E–66E and latitudes 8N–48N. The data set used in this study consists of regionally observed P-phase arrival times from over 1000 global events from 1996–2016 culminating in a larger dataset than other similar studies. Selection of a reliable data, ray tracing, preconditioning and inversion steps are carried out using the BD-soft software suite (https://www.geoazur.fr/GLOBALSEIS/Soft.html).
Preliminary inversion results are consistent with the previous regional tomographic studies. In checkerboard tests, cell sizes as low as ∼ 2.8° × 2.8° ( ∼ 240 × 240 km at surface) are generally well recovered down to a 1000 km depth beneath the Anatolian plateau where we currently have the densest coverage. Additionally the Caucasus region and northern parts of the Iranian plateau shows good recovery of ±4% Vp perturbation amplitudes at depths ∼ 70 – 135 km. There is fair recovery for a minimum cell size of ∼ 2.8° × 2.8° beneath the Iranian Plateau, Zagros mountain region, Persian gulf, and northeast Iraq, along with quite good recovery of cell amplitudes towards the Anatolian-Caucasus region at depth ranges 380 – 430 km, 650 – 700 km, and around 950 km. Tomographic inversions unveil a low P velocity zone stretching from the Afar region to Sinai Peninsula consistent with S wave velocity observations of a similar feature by Chang and van der Lee 2011.
We are able to further improve coverage especially down to lithospheric depths within the Arabian peninsula using first arrival times measured from waveform data collected from regional networks. Addition of first arrival time delays from waveforms highlights a prominent low velocity in the tomographic inversions beneath the volcanic fields of western Saudi Arabia. Our ultimate goal is to perform full-waveform inversion of the region constrained by the constructed P-wave model.
How to cite: Desilva, S., Bozdag, E., Nolet, G., Gok, R., Ali, A., and Tarabulsi, Y.: Direct P-Wave Travel Time Tomography of the Middle East, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3511, https://doi.org/10.5194/egusphere-egu21-3511, 2021.
EGU21-507 | vPICO presentations | SM1.1
Quantifying Intrinsic and Extrinsic Contributions to Elastic Anisotropy Observed in Seismic Tomography ModelsJohn Keith Magali, Thomas Bodin, Navid Hedjazian, Yanick Ricard, and Yann Capdeville
Large-scale seismic anisotropy inferred from seismic observations has been loosely interpreted either in terms of intrinsic anisotropy due to Crystallographic Preferred Orientation (CPO) development of mantle minerals or extrinsic anisotropy due to rock-scale Shape Preferred Orientation (SPO). The coexistence of both contributions misconstrues the origins of seismic anisotropy observed in seismic tomography models. It is thus essential to discriminate CPO from SPO in the effective anisotropy of an upscaled/homogenized medium, that is, the best possible elastic model recovered using finite-frequency seismic data assuming perfect data coverage. In this work, we investigate the effects of upscaling an intrinsically-anisotropic and highly-heterogeneous Earth's mantle. The problem is applied to a 2-D marble cake model of the mantle with a binary composition in the presence of CPO obtained from a micro-mechanical model. We compute the long-wavelength effective equivalent of this mantle model using the 3D non-periodic elastic homogenization technique. Our numerical findings predict that overall, upscaling purely intrinsically anisotropic medium amounts to the convection-scale averaging of CPO. As a result, it always underestimates the anisotropy, and may only be overestimated due to the additive extrinsic anisotropy from SPO. Finally, we show analytically (in 1D) and numerically (in 2D) that the full effective radial anisotropy ξ* is approximately just the product of the effective intrinsic radial anisotropy ξ*CPO and the extrinsic radial anisotropy ξSPO:
ξ* = ξ*CPO × ξSPO
Based on the above relation, it is imperative to homogenize a texture evolution model first before drawing interpretations from existing anisotropic tomography models. Such a scaling law can therefore be used as a constraint to better estimate the separate contributions of CPO and SPO from the effective anisotropy observed in tomographic models.
How to cite: Magali, J. K., Bodin, T., Hedjazian, N., Ricard, Y., and Capdeville, Y.: Quantifying Intrinsic and Extrinsic Contributions to Elastic Anisotropy Observed in Seismic Tomography Models, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-507, https://doi.org/10.5194/egusphere-egu21-507, 2021.
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Large-scale seismic anisotropy inferred from seismic observations has been loosely interpreted either in terms of intrinsic anisotropy due to Crystallographic Preferred Orientation (CPO) development of mantle minerals or extrinsic anisotropy due to rock-scale Shape Preferred Orientation (SPO). The coexistence of both contributions misconstrues the origins of seismic anisotropy observed in seismic tomography models. It is thus essential to discriminate CPO from SPO in the effective anisotropy of an upscaled/homogenized medium, that is, the best possible elastic model recovered using finite-frequency seismic data assuming perfect data coverage. In this work, we investigate the effects of upscaling an intrinsically-anisotropic and highly-heterogeneous Earth's mantle. The problem is applied to a 2-D marble cake model of the mantle with a binary composition in the presence of CPO obtained from a micro-mechanical model. We compute the long-wavelength effective equivalent of this mantle model using the 3D non-periodic elastic homogenization technique. Our numerical findings predict that overall, upscaling purely intrinsically anisotropic medium amounts to the convection-scale averaging of CPO. As a result, it always underestimates the anisotropy, and may only be overestimated due to the additive extrinsic anisotropy from SPO. Finally, we show analytically (in 1D) and numerically (in 2D) that the full effective radial anisotropy ξ* is approximately just the product of the effective intrinsic radial anisotropy ξ*CPO and the extrinsic radial anisotropy ξSPO:
ξ* = ξ*CPO × ξSPO
Based on the above relation, it is imperative to homogenize a texture evolution model first before drawing interpretations from existing anisotropic tomography models. Such a scaling law can therefore be used as a constraint to better estimate the separate contributions of CPO and SPO from the effective anisotropy observed in tomographic models.
How to cite: Magali, J. K., Bodin, T., Hedjazian, N., Ricard, Y., and Capdeville, Y.: Quantifying Intrinsic and Extrinsic Contributions to Elastic Anisotropy Observed in Seismic Tomography Models, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-507, https://doi.org/10.5194/egusphere-egu21-507, 2021.
EGU21-9852 | vPICO presentations | SM1.1
A new 3-D mantle density model from recent normal-mode measurementsRûna van Tent, Arwen Deuss, Andreas Fichtner, Lars Gebraad, Simon Schneider, and Jeannot Trampert
Constraints on the 3-D density structure of Earth’s mantle provide important insights into the nature of seismically observed features, such as the Large Low Shear Velocity Provinces (LLSVPs) in the lower mantle under Africa and the Pacific. The only seismic data directly sensitive to density variations throughout the entire mantle are normal modes: whole Earth oscillations that are induced by large earthquakes (Mw > 7.5). However, their sensitivity to density is weak compared to the sensitivity to velocity and different studies have presented conflicting density models of the lower mantle. For example, Ishii & Tromp (1999) and Trampert et al. (2004) have found that the LLSVPs have a larger density than the surrounding mantle, while Koelemeijer et al. (2017) used additional Stoneley-mode observations, which are particularly sensitive to the core-mantle boundary region, to show that the LLSVPs have a lower density. Recently, Lau et al. (2017) have used tidal tomography to show that Earth's body tides prefer dense LLSVPs.
A large number of new normal-mode splitting function measurements has become available since the last density models of the entire mantle were published. Here, we show the models from our inversion of these recent data and compare our results to previous studies. We find areas of high as well as low density at the base of the LLSVPs and we find that inside the LLSVPs density varies on a smaller scale than velocity, indicating the presence of compositionally distinct material. In fact, we find low correlations between the density and velocity structure throughout the entire mantle, revealing that compositional variations are required at all depths inside the mantle.
How to cite: van Tent, R., Deuss, A., Fichtner, A., Gebraad, L., Schneider, S., and Trampert, J.: A new 3-D mantle density model from recent normal-mode measurements, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9852, https://doi.org/10.5194/egusphere-egu21-9852, 2021.
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Constraints on the 3-D density structure of Earth’s mantle provide important insights into the nature of seismically observed features, such as the Large Low Shear Velocity Provinces (LLSVPs) in the lower mantle under Africa and the Pacific. The only seismic data directly sensitive to density variations throughout the entire mantle are normal modes: whole Earth oscillations that are induced by large earthquakes (Mw > 7.5). However, their sensitivity to density is weak compared to the sensitivity to velocity and different studies have presented conflicting density models of the lower mantle. For example, Ishii & Tromp (1999) and Trampert et al. (2004) have found that the LLSVPs have a larger density than the surrounding mantle, while Koelemeijer et al. (2017) used additional Stoneley-mode observations, which are particularly sensitive to the core-mantle boundary region, to show that the LLSVPs have a lower density. Recently, Lau et al. (2017) have used tidal tomography to show that Earth's body tides prefer dense LLSVPs.
A large number of new normal-mode splitting function measurements has become available since the last density models of the entire mantle were published. Here, we show the models from our inversion of these recent data and compare our results to previous studies. We find areas of high as well as low density at the base of the LLSVPs and we find that inside the LLSVPs density varies on a smaller scale than velocity, indicating the presence of compositionally distinct material. In fact, we find low correlations between the density and velocity structure throughout the entire mantle, revealing that compositional variations are required at all depths inside the mantle.
How to cite: van Tent, R., Deuss, A., Fichtner, A., Gebraad, L., Schneider, S., and Trampert, J.: A new 3-D mantle density model from recent normal-mode measurements, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9852, https://doi.org/10.5194/egusphere-egu21-9852, 2021.
EGU21-2829 | vPICO presentations | SM1.1
Global observations of 3D mantle attenuation using normal modesSujania Talavera-Soza and Arwen Deuss
Seismic tomographic models based solely on wave velocities are unable to distinguish between a temperature or compositional origin for Earth’s 3D structure variations, such as the Large Low Shear Velocity Provinces (LLSVPs) beneath the lower mantle of Africa and the Pacific. Seismic attenuation or damping is able able to provide additional information that may help to unravel the origin of the LLSVPs, which is fundamental to understand mantle convection evolution. For example, a thermal origin for the LLSVPs will point to them being short-lived anomalies, whereas a compositional origin will point to them being long-lived, forming mantle 'anchors' and influencing the pattern of mantle convection for a large part of Earth’s history. Seismic attenuation is able to make that distinction, because it is directly sensitive to temperature variations. So far, global 3D attenuation models have only been available for the upper mantle, with only two regional body waves studies exploring the lower mantle (Lawrence and Wysession, 2006; Hwang and Ritsema, 2011).
Here, we use normal mode data to measure elastic splitting functions (dependent on velocity and density) and anelastic splitting functions (dependent on attenuation). The advantage of normal modes is that they allow us to include focussing and scattering due to the velocity structure without the need for approximations, because we measure the elastic splitting function jointly with the anelastic splitting function. In our measurements for upper mantle sensi- tive modes, we find anti-correlation between the elastic and anelastic splitting functions, suggesting a thermal origin for low velocity spreading ridges, and agreeing with previous studies. On the other hand, for lower mantle sensitive modes, we find correlation, suggesting the averagely attenuating LLSVPs are surrounded by strongly attenuating regions potentially due to the presence of post-perovskite.
How to cite: Talavera-Soza, S. and Deuss, A.: Global observations of 3D mantle attenuation using normal modes , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2829, https://doi.org/10.5194/egusphere-egu21-2829, 2021.
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Seismic tomographic models based solely on wave velocities are unable to distinguish between a temperature or compositional origin for Earth’s 3D structure variations, such as the Large Low Shear Velocity Provinces (LLSVPs) beneath the lower mantle of Africa and the Pacific. Seismic attenuation or damping is able able to provide additional information that may help to unravel the origin of the LLSVPs, which is fundamental to understand mantle convection evolution. For example, a thermal origin for the LLSVPs will point to them being short-lived anomalies, whereas a compositional origin will point to them being long-lived, forming mantle 'anchors' and influencing the pattern of mantle convection for a large part of Earth’s history. Seismic attenuation is able to make that distinction, because it is directly sensitive to temperature variations. So far, global 3D attenuation models have only been available for the upper mantle, with only two regional body waves studies exploring the lower mantle (Lawrence and Wysession, 2006; Hwang and Ritsema, 2011).
Here, we use normal mode data to measure elastic splitting functions (dependent on velocity and density) and anelastic splitting functions (dependent on attenuation). The advantage of normal modes is that they allow us to include focussing and scattering due to the velocity structure without the need for approximations, because we measure the elastic splitting function jointly with the anelastic splitting function. In our measurements for upper mantle sensi- tive modes, we find anti-correlation between the elastic and anelastic splitting functions, suggesting a thermal origin for low velocity spreading ridges, and agreeing with previous studies. On the other hand, for lower mantle sensitive modes, we find correlation, suggesting the averagely attenuating LLSVPs are surrounded by strongly attenuating regions potentially due to the presence of post-perovskite.
How to cite: Talavera-Soza, S. and Deuss, A.: Global observations of 3D mantle attenuation using normal modes , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2829, https://doi.org/10.5194/egusphere-egu21-2829, 2021.
EGU21-4843 | vPICO presentations | SM1.1
Lg wave propagation and attenuation characteristics of the NW HimalayaKaushik Kumar Pradhan and Supriyo Mitra
Lg waves are formed by the superposition of shear waves trapped within the crustal waveguide and are the most destructive at regional distances. Excitation of Lg waves, its propagation and lateral variability determine the intensity of ground shaking from regional earthquakes. Spatial decay of spectral amplitude of Lg waves have been used to quantify the attenuation characteristics of the crust. In this study we use regional waveform data from the Jammu and Kashmir Seismological NETwork (JAKSNET) to study Lg wave propagation across the Indian Peninsula, Himalaya, Tibetan Plateau and Hindu Kush regions. We compute Lg/Sn wave ratio to distinguish regions with efficient Lg propagation from those with Lg blockage. These results are categorised using earthquake magnitude and depth to study Lg wave excitation and propagation across these varying geological terrains. We further use the two-station method to study Lg wave quality factor and its frequency dependence for the NW Himalaya. Seismograms recorded at two stations of the network, which are aligned within 15 degrees of the event, are used for analysis. The spectral ratio of Lg wave amplitude recorded at the two stations will be used to estimate the Q (quality factor) as a function of frequency. This will provide Q0 along all inter-station paths, which will then be combined to form Q0 tomography maps for the region. Checkerboard tests will be performed to estimate the resolution of the tomographic maps and accordingly the results will be interpreted.
How to cite: Pradhan, K. K. and Mitra, S.: Lg wave propagation and attenuation characteristics of the NW Himalaya, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4843, https://doi.org/10.5194/egusphere-egu21-4843, 2021.
Lg waves are formed by the superposition of shear waves trapped within the crustal waveguide and are the most destructive at regional distances. Excitation of Lg waves, its propagation and lateral variability determine the intensity of ground shaking from regional earthquakes. Spatial decay of spectral amplitude of Lg waves have been used to quantify the attenuation characteristics of the crust. In this study we use regional waveform data from the Jammu and Kashmir Seismological NETwork (JAKSNET) to study Lg wave propagation across the Indian Peninsula, Himalaya, Tibetan Plateau and Hindu Kush regions. We compute Lg/Sn wave ratio to distinguish regions with efficient Lg propagation from those with Lg blockage. These results are categorised using earthquake magnitude and depth to study Lg wave excitation and propagation across these varying geological terrains. We further use the two-station method to study Lg wave quality factor and its frequency dependence for the NW Himalaya. Seismograms recorded at two stations of the network, which are aligned within 15 degrees of the event, are used for analysis. The spectral ratio of Lg wave amplitude recorded at the two stations will be used to estimate the Q (quality factor) as a function of frequency. This will provide Q0 along all inter-station paths, which will then be combined to form Q0 tomography maps for the region. Checkerboard tests will be performed to estimate the resolution of the tomographic maps and accordingly the results will be interpreted.
How to cite: Pradhan, K. K. and Mitra, S.: Lg wave propagation and attenuation characteristics of the NW Himalaya, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4843, https://doi.org/10.5194/egusphere-egu21-4843, 2021.
EGU21-5940 | vPICO presentations | SM1.1
Applying cluster analysis to seismic tomography models: Uncovering similarities and differences in the spatial and spectral domainsMoloud Rahimzadeh Bajgiran and Lorenzo Colli
In recent years, several types of Machine Learning (ML) methods have been employed by Earth scientists to extract patterns and structures from multi-dimensional feature spaces. In this regard, images of the mantle obtained by different seismic tomography (ST) models are diverse datasets with varying structures due to their different theoretical approximations and input data. In this work, we apply an unsupervised ML method, K-means clustering, on ST models to explore their similarities and differences to improve our physical understanding of the Earth’s interior. The K-means clustering method requires ST models to be standardized in a three-dimensional domain. For this purpose, we implement a weighted average technique to resample ST models to radial structural zones with uniform horizontal grid resolutions. However, the homogenized ST models still have 103-104 parameters, which need to be distilled into a small number of summary features. Feature selection is thus a key part of this study: features should be independent from unphysical effects of inversion choices (e.g., the damping factor) and should instead capture the essence of the geological structure. Preliminary results obtained using the center of mass as the attribute to represent the longest wavelength part of the mantle structure show that P-wave and S-wave models do not cluster separately. Therefore, compositional anomalies do not play an essential role at these spatial scales. We plan to expand our analysis by including more summary attributes from both the spatial as well as the frequency domain.
How to cite: Rahimzadeh Bajgiran, M. and Colli, L.: Applying cluster analysis to seismic tomography models: Uncovering similarities and differences in the spatial and spectral domains, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5940, https://doi.org/10.5194/egusphere-egu21-5940, 2021.
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In recent years, several types of Machine Learning (ML) methods have been employed by Earth scientists to extract patterns and structures from multi-dimensional feature spaces. In this regard, images of the mantle obtained by different seismic tomography (ST) models are diverse datasets with varying structures due to their different theoretical approximations and input data. In this work, we apply an unsupervised ML method, K-means clustering, on ST models to explore their similarities and differences to improve our physical understanding of the Earth’s interior. The K-means clustering method requires ST models to be standardized in a three-dimensional domain. For this purpose, we implement a weighted average technique to resample ST models to radial structural zones with uniform horizontal grid resolutions. However, the homogenized ST models still have 103-104 parameters, which need to be distilled into a small number of summary features. Feature selection is thus a key part of this study: features should be independent from unphysical effects of inversion choices (e.g., the damping factor) and should instead capture the essence of the geological structure. Preliminary results obtained using the center of mass as the attribute to represent the longest wavelength part of the mantle structure show that P-wave and S-wave models do not cluster separately. Therefore, compositional anomalies do not play an essential role at these spatial scales. We plan to expand our analysis by including more summary attributes from both the spatial as well as the frequency domain.
How to cite: Rahimzadeh Bajgiran, M. and Colli, L.: Applying cluster analysis to seismic tomography models: Uncovering similarities and differences in the spatial and spectral domains, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5940, https://doi.org/10.5194/egusphere-egu21-5940, 2021.
EGU21-11829 | vPICO presentations | SM1.1
Seismic attenuation analysis in the central part of the Leipzig-Regensburg fault zone using the Multiple Lapse Time Window Analysis and QopenMarcel van Laaten, Tom Eulenfeld, and Ulrich Wegler
Seismic attenuation provides valuable information about the structure of the crust. For the analysis of seismic attenuation in the central part of the Leipzig-Regensburg fault zone in Germany, where numerous areas of intracontinental earthquake swarms are located, we use 18 of the region's strongest earthquakes from the period 2008 to 2019 with a magnitude between 1.4 and 3.0 in the frequency range between 3 and 34 Hz. Two different methods were used to determine the frequency-dependent scattering and the intrinsic attenuation on one hand and to compare the two methods with respect to their results on the other hand. Both methods, the Multiple Lapse Time Windows Analysis (MLTWA) and the Qopen method use the acoustic radiative transfer theory for forward modelling to generate synthetic data and fit them to the observed data. As a by-product of Qopen, we also obtain the energy site amplifications of the stations used in the inversion, as well as the estimated moment magnitudes of the inverted earthquakes. In addition, factors that influence the inversion were investigated. Different combinations of inversion parameters were tested for the MLTWA, as well as the influence of the window length on the result of Qopen. The results from both methods provide similar results within their error bars, with intrinsic attenuation being stronger than scattering and overall, rather low attenuation values compared to other regions.
How to cite: van Laaten, M., Eulenfeld, T., and Wegler, U.: Seismic attenuation analysis in the central part of the Leipzig-Regensburg fault zone using the Multiple Lapse Time Window Analysis and Qopen, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11829, https://doi.org/10.5194/egusphere-egu21-11829, 2021.
Seismic attenuation provides valuable information about the structure of the crust. For the analysis of seismic attenuation in the central part of the Leipzig-Regensburg fault zone in Germany, where numerous areas of intracontinental earthquake swarms are located, we use 18 of the region's strongest earthquakes from the period 2008 to 2019 with a magnitude between 1.4 and 3.0 in the frequency range between 3 and 34 Hz. Two different methods were used to determine the frequency-dependent scattering and the intrinsic attenuation on one hand and to compare the two methods with respect to their results on the other hand. Both methods, the Multiple Lapse Time Windows Analysis (MLTWA) and the Qopen method use the acoustic radiative transfer theory for forward modelling to generate synthetic data and fit them to the observed data. As a by-product of Qopen, we also obtain the energy site amplifications of the stations used in the inversion, as well as the estimated moment magnitudes of the inverted earthquakes. In addition, factors that influence the inversion were investigated. Different combinations of inversion parameters were tested for the MLTWA, as well as the influence of the window length on the result of Qopen. The results from both methods provide similar results within their error bars, with intrinsic attenuation being stronger than scattering and overall, rather low attenuation values compared to other regions.
How to cite: van Laaten, M., Eulenfeld, T., and Wegler, U.: Seismic attenuation analysis in the central part of the Leipzig-Regensburg fault zone using the Multiple Lapse Time Window Analysis and Qopen, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11829, https://doi.org/10.5194/egusphere-egu21-11829, 2021.
EGU21-8183 | vPICO presentations | SM1.1
Crustal shear wave blockage in and around the Eastern Alps from the 2016 Alland earthquakePetr Spacek, Pavel Zacherle, Götz Bokelman, Sven Schippkus, Rita Meurers, Jana Pazdírková, and the AlpArray Working Group
Earthquakes in the Eastern Alps are characterized by strongly elongated isoseismals, documenting significantly more efficient propagation of seismic waves towards the foreland (F) than into the orogen (O). In an effort to understand this phenomenon we analysed the local to regional wavefield of a single earthquake with ML4.2 / mb3.6 and epicenter WSW of Vienna (Alland) using instrumental data with unprecedented dense coverage (including AlpArray) and rich macroseismic observations. This earthquake with characteristic asymmetry of isoseismals and with the source located in the basement of the European plate just beneath the frontal thin-skinned thrust of the Penninic units is considered a representative example of the stronger historical and potential future earthquakes from this regionally important seismogenic source area. The analysis of macroseismic intensities and PGA, PGV and spectral content within time windows tied to Sg+Lg wavetrains and other interpreted phases indicates a very good match of smoothed high precision instrumental and high resolution macroseismic wavefields, which allows their joint interpretation. In the F-direction, a very small decrease of intensity and PGA values at an epicentral distance range between 30-50 km and 130-180 km is well approximated by intensity prediction equations derived for central and eastern North America. On the other hand, a sudden drop of respective values is observed at a distance of 20-30 km in the O-direction, correlating with the seismically active fault zone of Mur-Mürz line. The geographic distribution of regional distance-corrected PGA perturbations (dPGA) reveals several well-defined domains with internally limited variance whose boundaries partly correlate with known major geologic structures. Special attention has been paid to description of contrasts between the Foreland domain (Bohemian Massif + autochthonous sediments), the North Alpine domain (between the frontal thrust and Mur-Mürz line + its WSW continuation, i.e. close to southern limits of stable European plate) and the South Alpine domain (south of the former to the southern limits of the region of interest at latitude 46.2°N). The ratio of mean dPGA values observed in these three neighbouring domains is 1.00 : 0.27 : 0.05, respectively. Furthermore, significant contrast between the three domains is observed in terms of spectral content. High frequency signal above 10Hz is characteristic for the Foreland domain and strongly reduced in the South Alpine domain, suggesting that the structures related to the margin of stable European plate act here as an efficient high-cut frequency filter. While map isolines of high frequency spectral amplitude are strongly elongated in F-direction, in agreement with PGA and macroseismic intensity, for frequencies below ~5Hz the isolines of spectral amplitude are quasi-isometric around the epicenter at least within distance of ~120 km. Combination of several mechanisms is considered to explain the wave energy propagation, including intrinsic attenuation at fault zones, blockage at waveguide inhomogeneities and Q(f) contrasts between the crustal domains. Numerous other interesting observations from the whole region including the Carpathian and Pannonian domains, demonstrate the strong potential of densely sampled earthquake wavefields for studies of crustal structure and seismic hazard in the generally low-rate seismicity areas.
How to cite: Spacek, P., Zacherle, P., Bokelman, G., Schippkus, S., Meurers, R., Pazdírková, J., and AlpArray Working Group, T.: Crustal shear wave blockage in and around the Eastern Alps from the 2016 Alland earthquake, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8183, https://doi.org/10.5194/egusphere-egu21-8183, 2021.
Earthquakes in the Eastern Alps are characterized by strongly elongated isoseismals, documenting significantly more efficient propagation of seismic waves towards the foreland (F) than into the orogen (O). In an effort to understand this phenomenon we analysed the local to regional wavefield of a single earthquake with ML4.2 / mb3.6 and epicenter WSW of Vienna (Alland) using instrumental data with unprecedented dense coverage (including AlpArray) and rich macroseismic observations. This earthquake with characteristic asymmetry of isoseismals and with the source located in the basement of the European plate just beneath the frontal thin-skinned thrust of the Penninic units is considered a representative example of the stronger historical and potential future earthquakes from this regionally important seismogenic source area. The analysis of macroseismic intensities and PGA, PGV and spectral content within time windows tied to Sg+Lg wavetrains and other interpreted phases indicates a very good match of smoothed high precision instrumental and high resolution macroseismic wavefields, which allows their joint interpretation. In the F-direction, a very small decrease of intensity and PGA values at an epicentral distance range between 30-50 km and 130-180 km is well approximated by intensity prediction equations derived for central and eastern North America. On the other hand, a sudden drop of respective values is observed at a distance of 20-30 km in the O-direction, correlating with the seismically active fault zone of Mur-Mürz line. The geographic distribution of regional distance-corrected PGA perturbations (dPGA) reveals several well-defined domains with internally limited variance whose boundaries partly correlate with known major geologic structures. Special attention has been paid to description of contrasts between the Foreland domain (Bohemian Massif + autochthonous sediments), the North Alpine domain (between the frontal thrust and Mur-Mürz line + its WSW continuation, i.e. close to southern limits of stable European plate) and the South Alpine domain (south of the former to the southern limits of the region of interest at latitude 46.2°N). The ratio of mean dPGA values observed in these three neighbouring domains is 1.00 : 0.27 : 0.05, respectively. Furthermore, significant contrast between the three domains is observed in terms of spectral content. High frequency signal above 10Hz is characteristic for the Foreland domain and strongly reduced in the South Alpine domain, suggesting that the structures related to the margin of stable European plate act here as an efficient high-cut frequency filter. While map isolines of high frequency spectral amplitude are strongly elongated in F-direction, in agreement with PGA and macroseismic intensity, for frequencies below ~5Hz the isolines of spectral amplitude are quasi-isometric around the epicenter at least within distance of ~120 km. Combination of several mechanisms is considered to explain the wave energy propagation, including intrinsic attenuation at fault zones, blockage at waveguide inhomogeneities and Q(f) contrasts between the crustal domains. Numerous other interesting observations from the whole region including the Carpathian and Pannonian domains, demonstrate the strong potential of densely sampled earthquake wavefields for studies of crustal structure and seismic hazard in the generally low-rate seismicity areas.
How to cite: Spacek, P., Zacherle, P., Bokelman, G., Schippkus, S., Meurers, R., Pazdírková, J., and AlpArray Working Group, T.: Crustal shear wave blockage in and around the Eastern Alps from the 2016 Alland earthquake, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8183, https://doi.org/10.5194/egusphere-egu21-8183, 2021.
EGU21-13043 | vPICO presentations | SM1.1
The Samos Mw6.9 event: Damage investigation in the town of Vathy incorporating a stochastic finite-fault source with site and structural informationGeorgia Giannaraki, Zafeiria Roumelioti, and Nikolaos S. Melis
The stochastic method is applied for the finite-fault modelling of strong ground motion from the October 30, 2020, shallow earthquake of Mw=6.9 which occurred offshore the northern part of Samos island in the Aegean Sea, Greece. The earthquake resulted to several human casualties and many injuries, to considerable infrastructure damage in Samos island and Western Turkey, especially in the city of Izmir, and a tsunami affecting both the Greek and Turkish coast. We focus this research on reproducing the ground motion field and damage pattern observed in Vathy, the capital of Samos Island. Different source representations, based on preliminary finite-fault slip distribution models, are tested against their capability to reproduce the two acceleration records available in Vathy. Site effects are incorporated in our modelling in the form of empirical amplification factors assigned according to a Vs30 distribution for the Samos island, which we constructed based on local geology and terrain-based proxies and on the Vs profiles at the sites of the two permanent accelerometric stations. The analysis further focuses on the empirical assessment of structural vulnerability for an estimated exposure model per building block in Vathy, which suffered structural damage due to the mainshock, mainly to a number of old and monumental buildings. The estimated exposure model in Vathy, when combined with the synthetic ground motion derived from the validated stochastic model, provides results in good agreement with available macroseismic intensities and damage reports. Our results contribute to better understanding the observed spatial distribution of damage in Vathy with respect to variations in the quality of buildings, the foundation soil and the frequency content of the excitation motion as radiated from the seismic source. The usefulness of our validated stochastic model is further demonstrated through blind predictions at sites of considerable earthquake effects, at which no record of the Mw=6.9 earthquake is available, such as in the town of Karlovasi in Samos and in the port of Chios Island.
How to cite: Giannaraki, G., Roumelioti, Z., and Melis, N. S.: The Samos Mw6.9 event: Damage investigation in the town of Vathy incorporating a stochastic finite-fault source with site and structural information, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13043, https://doi.org/10.5194/egusphere-egu21-13043, 2021.
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Please use the buttons below to download the presentation materials or to visit the external website where the presentation is linked. Regarding the external link, please note that Copernicus Meetings cannot accept any liability for the content and the website you will visit.
Forward to presentation link
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The stochastic method is applied for the finite-fault modelling of strong ground motion from the October 30, 2020, shallow earthquake of Mw=6.9 which occurred offshore the northern part of Samos island in the Aegean Sea, Greece. The earthquake resulted to several human casualties and many injuries, to considerable infrastructure damage in Samos island and Western Turkey, especially in the city of Izmir, and a tsunami affecting both the Greek and Turkish coast. We focus this research on reproducing the ground motion field and damage pattern observed in Vathy, the capital of Samos Island. Different source representations, based on preliminary finite-fault slip distribution models, are tested against their capability to reproduce the two acceleration records available in Vathy. Site effects are incorporated in our modelling in the form of empirical amplification factors assigned according to a Vs30 distribution for the Samos island, which we constructed based on local geology and terrain-based proxies and on the Vs profiles at the sites of the two permanent accelerometric stations. The analysis further focuses on the empirical assessment of structural vulnerability for an estimated exposure model per building block in Vathy, which suffered structural damage due to the mainshock, mainly to a number of old and monumental buildings. The estimated exposure model in Vathy, when combined with the synthetic ground motion derived from the validated stochastic model, provides results in good agreement with available macroseismic intensities and damage reports. Our results contribute to better understanding the observed spatial distribution of damage in Vathy with respect to variations in the quality of buildings, the foundation soil and the frequency content of the excitation motion as radiated from the seismic source. The usefulness of our validated stochastic model is further demonstrated through blind predictions at sites of considerable earthquake effects, at which no record of the Mw=6.9 earthquake is available, such as in the town of Karlovasi in Samos and in the port of Chios Island.
How to cite: Giannaraki, G., Roumelioti, Z., and Melis, N. S.: The Samos Mw6.9 event: Damage investigation in the town of Vathy incorporating a stochastic finite-fault source with site and structural information, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13043, https://doi.org/10.5194/egusphere-egu21-13043, 2021.
EGU21-8564 | vPICO presentations | SM1.1
High-frequency strong ground-motion simulation for the 2016 Mw 7.0 Kumamoto earthquakeJavier Ojeda, Sebastian Arriola, Christian Flores, Cristian Otarola, and Sergio Ruiz
The 2016 Kumamoto earthquake Mw 7.0 occurred in Japan reveal a multisegment shallow fault rupture that was well recorded by the KiK-net stations in accelerographs placed inside boreholes and on the surface. The numerous damaged buildings due to this earthquake reflect the critical implications for seismic hazard estimation and improvement of earthquake-resistant design for a shallower event. Here, we generate synthetic accelerograms at high frequencies implementing a stochastic method that allow us to simulate horizontal and vertical strong ground-motion accelerograms in azimuthal well-distributed stations. We included multisegment finite fault geometries estimated by independent authors as input for source model. From each sub-fault we calculated the incident and azimuthal angles arriving at each seismic station, we determined free surface effect, energy partition, radiation pattern and dynamic frequency corner for sources effect. Besides, we adopted region-specific attenuation parameters such as geometrical spreading and anelastic attenuation for path effect, and site effect parameters such as generic amplifications, soil amplification transfer functions for body waves, and high-frequency attenuation kappa filter. Our simulated acceleration time series show similarities in time and frequency with the observed records in the frequency band between 1 – 10 Hz. We obtained a good agreement between peak ground accelerations for both horizontal and vertical components, and we reproduce the amplitude and attenuation trend for the horizontal component of the GMPE models in the region. Finally, we are capable to simulate the high-frequency band of engineering interest using physics-based parameters to improve our knowledge about the source, path, and site effect and their impact on a seismic hazard assessment in earthquake-prone regions.
How to cite: Ojeda, J., Arriola, S., Flores, C., Otarola, C., and Ruiz, S.: High-frequency strong ground-motion simulation for the 2016 Mw 7.0 Kumamoto earthquake, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8564, https://doi.org/10.5194/egusphere-egu21-8564, 2021.
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The 2016 Kumamoto earthquake Mw 7.0 occurred in Japan reveal a multisegment shallow fault rupture that was well recorded by the KiK-net stations in accelerographs placed inside boreholes and on the surface. The numerous damaged buildings due to this earthquake reflect the critical implications for seismic hazard estimation and improvement of earthquake-resistant design for a shallower event. Here, we generate synthetic accelerograms at high frequencies implementing a stochastic method that allow us to simulate horizontal and vertical strong ground-motion accelerograms in azimuthal well-distributed stations. We included multisegment finite fault geometries estimated by independent authors as input for source model. From each sub-fault we calculated the incident and azimuthal angles arriving at each seismic station, we determined free surface effect, energy partition, radiation pattern and dynamic frequency corner for sources effect. Besides, we adopted region-specific attenuation parameters such as geometrical spreading and anelastic attenuation for path effect, and site effect parameters such as generic amplifications, soil amplification transfer functions for body waves, and high-frequency attenuation kappa filter. Our simulated acceleration time series show similarities in time and frequency with the observed records in the frequency band between 1 – 10 Hz. We obtained a good agreement between peak ground accelerations for both horizontal and vertical components, and we reproduce the amplitude and attenuation trend for the horizontal component of the GMPE models in the region. Finally, we are capable to simulate the high-frequency band of engineering interest using physics-based parameters to improve our knowledge about the source, path, and site effect and their impact on a seismic hazard assessment in earthquake-prone regions.
How to cite: Ojeda, J., Arriola, S., Flores, C., Otarola, C., and Ruiz, S.: High-frequency strong ground-motion simulation for the 2016 Mw 7.0 Kumamoto earthquake, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8564, https://doi.org/10.5194/egusphere-egu21-8564, 2021.
EGU21-3092 | vPICO presentations | SM1.1
Discrimination of earthquakes and quarry blasts in Mecsek Mountain region (Hungary) and its vicinity by using a linear discrimination functionMárta Kiszely, Bálint Süle, and István Bondár
Contamination of earthquake catalogues with anthropogenic events largely complicates seismotectonic interpretation. It is especially true for relatively low seismicity areas, such as Hungary. In the present study, we analyze the characteristics of earthquakes and blasts of quarries occurred between 2015 and 2020 in the Mecsek Mountains in southern Hungary within 120 km to MORH and KOVH stations.
The objective of this study was to determine the linear discrimination line between the two classes earthquakes and explosions. We investigated the effectiveness of P/S amplitude ratios using filtered waveforms at different ranges of frequencies. We applied waveform cross-correlation to build correlation matrices at both stations and performed hierarchical cluster analysis to identify event clusters. Because most of the quarry blasts were carried out by ripple-fire technology, we computed spectrograms and examined the spectral ratio between low and high frequencies and the steepness of spectra.
Classes of earthquakes and quarry blasts have separated well from each other by combining the amplitude ratio, waveform similarity and the different spectral methods. We compare the discrimination parameters and capability of both stations to identify the explosions in analyzed quarries that were misclassified as earthquakes in the Hungarian National Bulletins.
How to cite: Kiszely, M., Süle, B., and Bondár, I.: Discrimination of earthquakes and quarry blasts in Mecsek Mountain region (Hungary) and its vicinity by using a linear discrimination function , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3092, https://doi.org/10.5194/egusphere-egu21-3092, 2021.
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Contamination of earthquake catalogues with anthropogenic events largely complicates seismotectonic interpretation. It is especially true for relatively low seismicity areas, such as Hungary. In the present study, we analyze the characteristics of earthquakes and blasts of quarries occurred between 2015 and 2020 in the Mecsek Mountains in southern Hungary within 120 km to MORH and KOVH stations.
The objective of this study was to determine the linear discrimination line between the two classes earthquakes and explosions. We investigated the effectiveness of P/S amplitude ratios using filtered waveforms at different ranges of frequencies. We applied waveform cross-correlation to build correlation matrices at both stations and performed hierarchical cluster analysis to identify event clusters. Because most of the quarry blasts were carried out by ripple-fire technology, we computed spectrograms and examined the spectral ratio between low and high frequencies and the steepness of spectra.
Classes of earthquakes and quarry blasts have separated well from each other by combining the amplitude ratio, waveform similarity and the different spectral methods. We compare the discrimination parameters and capability of both stations to identify the explosions in analyzed quarries that were misclassified as earthquakes in the Hungarian National Bulletins.
How to cite: Kiszely, M., Süle, B., and Bondár, I.: Discrimination of earthquakes and quarry blasts in Mecsek Mountain region (Hungary) and its vicinity by using a linear discrimination function , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3092, https://doi.org/10.5194/egusphere-egu21-3092, 2021.
EGU21-14253 | vPICO presentations | SM1.1
Estimation Of High-Frequency Attenuation Parameter (Kappa) For Hard Rock Stations Of Turkish Strong Motion NetworkAtınç Özgün Akgün, Zeynep Gülerce, and Atilla Arda Özacar
Site-specific decay in the Fourier Amplitude Spectrum (FAS) at high frequencies, a.k.a. the zero-distance kappa (κ0), is frequently used in seismic analysis of critical infrastructure; especially for the host-to-target adjustment of the design spectrum and the site response analysis. The zero-distance kappa value for hard rock sites is more crucial but harder to constrain because the amount of strong-motion stations on hard-rock sites is limited in the global datasets. The objective of this study is to calculate the zero-distance kappa value for the hard rock strong-motion stations operated by the Disaster and Emergency Presidency of Turkey (AFAD). For this purpose, 6463 recordings from 22 strong-motion stations with measured average shear wave velocities at the first 30 meters (VS30) higher than 740m/s and having at least 100 records have been analyzed. The slope of the decay in the S-wave portion of the FAS (kappa) at high frequencies is determined for a carefully selected and record-specific frequency range. Variation of the kappa with epicentral distance is evaluated to determine the median zero-distance kappa and its uncertainty for each recording station. Estimated median zero-distance kappa values vary between 0.01s to 0.06s and are consistent with the limited amount of previously published data. Only a weak reduction in median zero-distance kappa is observed with increasing VS30 and a rather large scatter in kappa for the same VS30 values is observed. More robust results might be attained by isolating the site amplification effects of weak surficial layers and subcategorization based on available geological and geographical information.
How to cite: Akgün, A. Ö., Gülerce, Z., and Özacar, A. A.: Estimation Of High-Frequency Attenuation Parameter (Kappa) For Hard Rock Stations Of Turkish Strong Motion Network, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14253, https://doi.org/10.5194/egusphere-egu21-14253, 2021.
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Site-specific decay in the Fourier Amplitude Spectrum (FAS) at high frequencies, a.k.a. the zero-distance kappa (κ0), is frequently used in seismic analysis of critical infrastructure; especially for the host-to-target adjustment of the design spectrum and the site response analysis. The zero-distance kappa value for hard rock sites is more crucial but harder to constrain because the amount of strong-motion stations on hard-rock sites is limited in the global datasets. The objective of this study is to calculate the zero-distance kappa value for the hard rock strong-motion stations operated by the Disaster and Emergency Presidency of Turkey (AFAD). For this purpose, 6463 recordings from 22 strong-motion stations with measured average shear wave velocities at the first 30 meters (VS30) higher than 740m/s and having at least 100 records have been analyzed. The slope of the decay in the S-wave portion of the FAS (kappa) at high frequencies is determined for a carefully selected and record-specific frequency range. Variation of the kappa with epicentral distance is evaluated to determine the median zero-distance kappa and its uncertainty for each recording station. Estimated median zero-distance kappa values vary between 0.01s to 0.06s and are consistent with the limited amount of previously published data. Only a weak reduction in median zero-distance kappa is observed with increasing VS30 and a rather large scatter in kappa for the same VS30 values is observed. More robust results might be attained by isolating the site amplification effects of weak surficial layers and subcategorization based on available geological and geographical information.
How to cite: Akgün, A. Ö., Gülerce, Z., and Özacar, A. A.: Estimation Of High-Frequency Attenuation Parameter (Kappa) For Hard Rock Stations Of Turkish Strong Motion Network, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14253, https://doi.org/10.5194/egusphere-egu21-14253, 2021.
EGU21-8781 | vPICO presentations | SM1.1
Seismic shaking scenarios for city of Zagreb, CroatiaHelena Latečki, Josip Stipčević, and Irene Molinari
In order to assess the seismic shaking levels, following the strong Zagreb March 22nd 2020 earthquake, we compute broadband seismograms using a hybrid technique. In a hybrid technique, low frequency (LF, f < 1 Hz) and high frequency (HF, f = 1–10 Hz) seismograms are obtained separately and then merged into a single time series. The LF part of seismogram is computed using a deterministic approach while for the HF part, we adopt the semi-stochastic method following the work of Graves and Pitarka (2010). For the purposes of the simulation, we also assemble the 3D velocity and density model of the crust for the city of Zagreb and its surrounding region. The model consists of a detailed description of the main geologic structures that are observed in the upper crust and is embedded within a greater regional EPCrust crustal model (Molinari and Morelli, 2011). To test and evaluate its performance, we apply the hybrid technique to the Zagreb March 22nd 2020 Mw = 5.3 event and four smaller (3.0 < Mw < 5.0) events. We compare the measured seismograms with the synthetic data and validate our results by assessing the goodness of fit for the peak ground velocity values and the shaking duration. Furthermore, since the 1880 Mw = 6.2 historic earthquake significantly contributes to the hazard assessment for the wider Zagreb area, we compute synthetic seismograms for this event at two different hypocenter locations. We calculate broadband waveforms on a dense grid of points and from these we plot the shakemaps to determine if the main expected ground-motion features are well-represented by our approach. Lastly, due to the events that occured in the Petrinja epicentral area at the end of 2020, we decided to extend our 3D model to cover the area of interest. We will present the preliminary results of the simulation for the December 29th 2020 Mw = 6.4 strong earthquake, as well as our plans for further research.
How to cite: Latečki, H., Stipčević, J., and Molinari, I.: Seismic shaking scenarios for city of Zagreb, Croatia, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8781, https://doi.org/10.5194/egusphere-egu21-8781, 2021.
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In order to assess the seismic shaking levels, following the strong Zagreb March 22nd 2020 earthquake, we compute broadband seismograms using a hybrid technique. In a hybrid technique, low frequency (LF, f < 1 Hz) and high frequency (HF, f = 1–10 Hz) seismograms are obtained separately and then merged into a single time series. The LF part of seismogram is computed using a deterministic approach while for the HF part, we adopt the semi-stochastic method following the work of Graves and Pitarka (2010). For the purposes of the simulation, we also assemble the 3D velocity and density model of the crust for the city of Zagreb and its surrounding region. The model consists of a detailed description of the main geologic structures that are observed in the upper crust and is embedded within a greater regional EPCrust crustal model (Molinari and Morelli, 2011). To test and evaluate its performance, we apply the hybrid technique to the Zagreb March 22nd 2020 Mw = 5.3 event and four smaller (3.0 < Mw < 5.0) events. We compare the measured seismograms with the synthetic data and validate our results by assessing the goodness of fit for the peak ground velocity values and the shaking duration. Furthermore, since the 1880 Mw = 6.2 historic earthquake significantly contributes to the hazard assessment for the wider Zagreb area, we compute synthetic seismograms for this event at two different hypocenter locations. We calculate broadband waveforms on a dense grid of points and from these we plot the shakemaps to determine if the main expected ground-motion features are well-represented by our approach. Lastly, due to the events that occured in the Petrinja epicentral area at the end of 2020, we decided to extend our 3D model to cover the area of interest. We will present the preliminary results of the simulation for the December 29th 2020 Mw = 6.4 strong earthquake, as well as our plans for further research.
How to cite: Latečki, H., Stipčević, J., and Molinari, I.: Seismic shaking scenarios for city of Zagreb, Croatia, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8781, https://doi.org/10.5194/egusphere-egu21-8781, 2021.
EGU21-14796 | vPICO presentations | SM1.1
The TURNkey TB4 Achaia Array: Bridging School and Citizen Seismology through Earthquake AlertingNikolaos S. Melis, Eustratios Liadopoulos, Georgia Giannaraki, Ioannis Kalogeras, and Konstantinos Boukouras
An extended strong motion array comprised mainly of low cost sensors has been deployed in the Achaia region: the Patras city and the Aigion, Kalavrita towns, Greece. It combines: 4 standard accelerometric stations operated by the National Observatory of Athens, Institute of Geodynamics (NOA), 15 P-Alert MEMS acceleration devices, already deployed and operated in public sector buildings, schools and private dwellings (the Patras P-Alert Array) and 40 Raspberry Shake 4D sensors, which are deployed through the newly established Test Bed 4 region (TB4) for the H2020 financed TURNkey project. Principal aim, in an operational approach, to estimate rapidly the intensity of a felt event in a highly populated urban environment and inform local Civil Protection Agencies and through them the final responders and the general public. Moreover, the deployment of these low cost sensors, especially in schools of the Achaia region, aims to involve the pupils/students, in primary and secondary education, towards exploring School Seismology exercises, in a region where strong felt earthquakes are very frequent. Simple exercises in class, using the recorded data after a felt event have been completed such as: locating the event, estimating the magnitude, show the distribution of max PGA values in the region etc. Taking advantage of the school – local community link, the resilience increase has been already demonstrated in the local communities through happenings, popularized seminars and local press postings. A connection with the Municipalities and the Communal public sector allows the expansion of the citizen involvement (Citizen Seismology) through the use of dedicated smartphone app (i.e. LastQuake@EMSC). Citizens are informed and also pass their felt experience. This allows improved estimation and distribution of the shaking in a second phase, useful for Civil Protection Agencies. The increase of the resilience and public awareness are under monitoring with the collaboration of local media. All data will be also used as input to a TURNkey under development central platform, serving as an EEW system, mainly focusing to schools in an application for the TB4 project region in Greece.
How to cite: Melis, N. S., Liadopoulos, E., Giannaraki, G., Kalogeras, I., and Boukouras, K.: The TURNkey TB4 Achaia Array: Bridging School and Citizen Seismology through Earthquake Alerting, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14796, https://doi.org/10.5194/egusphere-egu21-14796, 2021.
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An extended strong motion array comprised mainly of low cost sensors has been deployed in the Achaia region: the Patras city and the Aigion, Kalavrita towns, Greece. It combines: 4 standard accelerometric stations operated by the National Observatory of Athens, Institute of Geodynamics (NOA), 15 P-Alert MEMS acceleration devices, already deployed and operated in public sector buildings, schools and private dwellings (the Patras P-Alert Array) and 40 Raspberry Shake 4D sensors, which are deployed through the newly established Test Bed 4 region (TB4) for the H2020 financed TURNkey project. Principal aim, in an operational approach, to estimate rapidly the intensity of a felt event in a highly populated urban environment and inform local Civil Protection Agencies and through them the final responders and the general public. Moreover, the deployment of these low cost sensors, especially in schools of the Achaia region, aims to involve the pupils/students, in primary and secondary education, towards exploring School Seismology exercises, in a region where strong felt earthquakes are very frequent. Simple exercises in class, using the recorded data after a felt event have been completed such as: locating the event, estimating the magnitude, show the distribution of max PGA values in the region etc. Taking advantage of the school – local community link, the resilience increase has been already demonstrated in the local communities through happenings, popularized seminars and local press postings. A connection with the Municipalities and the Communal public sector allows the expansion of the citizen involvement (Citizen Seismology) through the use of dedicated smartphone app (i.e. LastQuake@EMSC). Citizens are informed and also pass their felt experience. This allows improved estimation and distribution of the shaking in a second phase, useful for Civil Protection Agencies. The increase of the resilience and public awareness are under monitoring with the collaboration of local media. All data will be also used as input to a TURNkey under development central platform, serving as an EEW system, mainly focusing to schools in an application for the TB4 project region in Greece.
How to cite: Melis, N. S., Liadopoulos, E., Giannaraki, G., Kalogeras, I., and Boukouras, K.: The TURNkey TB4 Achaia Array: Bridging School and Citizen Seismology through Earthquake Alerting, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14796, https://doi.org/10.5194/egusphere-egu21-14796, 2021.
EGU21-6771 | vPICO presentations | SM1.1
Current status of design basis earthquake level for nuclear power plant sites in several countriesHoseon Choi and Seung Gyu Hyun
According to strict criteria step by step for site selection, design, construction and operation, the seismic safety of nuclear power plant (NPP) sites in South Korea are secured by considering design basis earthquake (DBE) level capable of withstanding the maximum ground motions that can occur on the site. Therefore, it is intended to summarize DBE level and its evaluation details for NPP sites in several countries.
Similar but different terms are used for DBE from country to country, i.e. safe shutdown earthquake (SSE), design earthquake (DE), SL2, Ss, and maximum calculated earthquake (MCE). They may differ when applied to actual seismic design process, and only refer to approximate comparisons. This script used DBE as a representative term, and DBE level was based on horizontal values.
The DBE level of NPP sites depends on seismic activity of the area. Japan and Western United States, where earthquakes occur more frequently than South Korea, have high DBE values. The DBE level of NPP sites in South Korea has been confirmed to be similar or higher compared to that of Central and Eastern Unites Sates and Europe, which have similar seismic activity.
How to cite: Choi, H. and Hyun, S. G.: Current status of design basis earthquake level for nuclear power plant sites in several countries, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6771, https://doi.org/10.5194/egusphere-egu21-6771, 2021.
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According to strict criteria step by step for site selection, design, construction and operation, the seismic safety of nuclear power plant (NPP) sites in South Korea are secured by considering design basis earthquake (DBE) level capable of withstanding the maximum ground motions that can occur on the site. Therefore, it is intended to summarize DBE level and its evaluation details for NPP sites in several countries.
Similar but different terms are used for DBE from country to country, i.e. safe shutdown earthquake (SSE), design earthquake (DE), SL2, Ss, and maximum calculated earthquake (MCE). They may differ when applied to actual seismic design process, and only refer to approximate comparisons. This script used DBE as a representative term, and DBE level was based on horizontal values.
The DBE level of NPP sites depends on seismic activity of the area. Japan and Western United States, where earthquakes occur more frequently than South Korea, have high DBE values. The DBE level of NPP sites in South Korea has been confirmed to be similar or higher compared to that of Central and Eastern Unites Sates and Europe, which have similar seismic activity.
How to cite: Choi, H. and Hyun, S. G.: Current status of design basis earthquake level for nuclear power plant sites in several countries, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6771, https://doi.org/10.5194/egusphere-egu21-6771, 2021.
EGU21-11008 | vPICO presentations | SM1.1
Persistent monochromatic seismic signals across central Europe: AlpArray data indicate a man-made seismic source for regional wave propagation studiesFlorian Fuchs, Götz Bokelmann, and AlpArray Working Group
Consistent and monochromatic signals appear as sharp peaks in frequency spectra or as continuous lines in spectrograms on many permanent and temporary seismic stations in Central Europe, especially in South-Eastern Germany, Austria and the Czech Republic. Similar observations have already puzzled the seismic community more than 20 years ago. Here we report on new observations of such monochromatic seismic signals within a 1 – 10 Hz range across central Europe using the dense AlpArray network.
We identify several monochromatic signals on both permanent and temporary stations. The respective frequencies of e.g. 1.72 Hz, 2.08 Hz, 2.77 Hz or 4.16 Hz are generally stable even over long time spans (months to years). Strikingly, all such signals at any given station show identical and simultaneous short-term (minutes to days) frequency variations of up to 0.4% of the central frequency. These variations precisely correspond to fluctuations of the frequency of the European electric power network, which is regulated to 50 Hz +/- 0.4%. In fact, all persistent seismic signals that follow this behavior have frequencies of 50 Hz / n with n being an integer number (50 Hz / 29 = 1.72 Hz, 50 Hz / 24 = 2.08 Hz, 50 Hz / 18 = 2.77 Hz, 50 Hz / 12 = 4.16 Hz). We show that if the frequency of an observed spectral line is an integer fraction of the power network frequency (and only in that case) it will perfectly follow the fluctuations of the power network. This obviously raises questions about the nature of the signal itself, in particular if it is of seismic or maybe electro-magnetic origin.
We confirm that the signals are of seismic origin and we have identified water turbines inside river power plants as the source. The observed frequencies correspond well to reported rotation frequencies of water turbines at several different river power plants in Southern Germany and Austria. The seismic signals may propagate to almost 100 km from the corresponding plant. We analyze the spatial distribution of signal amplitudes for a selected river power plant in Austria, and show that it is similar to expected isolines of seismic shaking for an earthquake in the region.
Knowing the source of those exotic signals potentially enables us to use them for seismo-tectonic purposes. The long-term (several years) stability and the permanent availability (24h operation of water turbines) render them very interesting sources e.g. for studying temporal seismic velocity variations in the shallow crust.
How to cite: Fuchs, F., Bokelmann, G., and Working Group, A.: Persistent monochromatic seismic signals across central Europe: AlpArray data indicate a man-made seismic source for regional wave propagation studies, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11008, https://doi.org/10.5194/egusphere-egu21-11008, 2021.
Consistent and monochromatic signals appear as sharp peaks in frequency spectra or as continuous lines in spectrograms on many permanent and temporary seismic stations in Central Europe, especially in South-Eastern Germany, Austria and the Czech Republic. Similar observations have already puzzled the seismic community more than 20 years ago. Here we report on new observations of such monochromatic seismic signals within a 1 – 10 Hz range across central Europe using the dense AlpArray network.
We identify several monochromatic signals on both permanent and temporary stations. The respective frequencies of e.g. 1.72 Hz, 2.08 Hz, 2.77 Hz or 4.16 Hz are generally stable even over long time spans (months to years). Strikingly, all such signals at any given station show identical and simultaneous short-term (minutes to days) frequency variations of up to 0.4% of the central frequency. These variations precisely correspond to fluctuations of the frequency of the European electric power network, which is regulated to 50 Hz +/- 0.4%. In fact, all persistent seismic signals that follow this behavior have frequencies of 50 Hz / n with n being an integer number (50 Hz / 29 = 1.72 Hz, 50 Hz / 24 = 2.08 Hz, 50 Hz / 18 = 2.77 Hz, 50 Hz / 12 = 4.16 Hz). We show that if the frequency of an observed spectral line is an integer fraction of the power network frequency (and only in that case) it will perfectly follow the fluctuations of the power network. This obviously raises questions about the nature of the signal itself, in particular if it is of seismic or maybe electro-magnetic origin.
We confirm that the signals are of seismic origin and we have identified water turbines inside river power plants as the source. The observed frequencies correspond well to reported rotation frequencies of water turbines at several different river power plants in Southern Germany and Austria. The seismic signals may propagate to almost 100 km from the corresponding plant. We analyze the spatial distribution of signal amplitudes for a selected river power plant in Austria, and show that it is similar to expected isolines of seismic shaking for an earthquake in the region.
Knowing the source of those exotic signals potentially enables us to use them for seismo-tectonic purposes. The long-term (several years) stability and the permanent availability (24h operation of water turbines) render them very interesting sources e.g. for studying temporal seismic velocity variations in the shallow crust.
How to cite: Fuchs, F., Bokelmann, G., and Working Group, A.: Persistent monochromatic seismic signals across central Europe: AlpArray data indicate a man-made seismic source for regional wave propagation studies, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11008, https://doi.org/10.5194/egusphere-egu21-11008, 2021.
EGU21-14708 | vPICO presentations | SM1.1
Orientation of broadband seismographs in the Kashmir Himalaya: Effect on vector-based studiesRamees Mir, Imtiyaz Parvez, and Vinod Gaur
We used regional as well as global Rayleigh wave signals (source-receiver distance: 5°-175°; M≥ 6, Depth ≤ 150 km) recorded at 12 broadband seismic stations in northwestern Himalaya to compute arrival angles of surface waves at each station, assuming orthogonality of the horizontal components, and error-free levelling of the instrument. The average of all measurements at a station with cross-correlation values > 0.8, between Hilbert transformed vertical and radial components, was interpreted as the degree of misalignment of the horizontal components in a geographic frame of reference.
Out of the 12 station data used in this analysis, 3 were found to have instrument misorientation errors between 5° and 10° w.r.t geographic north, 2 between 10° and 15° and the remaining 7 < 5°. The number of measurements at each of these stations ranged from 75 to 331, with 11 stations having more than 90 measurements, assuring high reliability. We also analysed data from two nearby broadband instruments located in Ladakh Himalaya. One of these (LEH) with 46 measurements showed a misorientation error of 14.87°±4.87° and the other (HNL) with 48 showed an error of 0.75°±3.48°. Since misorientation errors based on less than 90 data elements are considered to be unstable, these were not used for further analysis.
We evaluated the effect of seismograph misorientations on the inverted solutions for P-wave receiver functions (RFs) and core-refracted shear waves (SKS). The errors in Moho depths and those of other intra-crustal features were within ±2 km for instrument misorientations of up to ~15°, that is close to the resolution errors. But, the SKS results, notably the azimuths of the fast component, were, found to be quite sensitive to instrument misalignment. For example, a ~14° error in orientation was found to cause a shift of up to 20° in the calculated azimuth of the fast component. Corrections of misorientation errors in both cases showed reduction of variance in the inverted solutions.
How to cite: Mir, R., Parvez, I., and Gaur, V.: Orientation of broadband seismographs in the Kashmir Himalaya: Effect on vector-based studies, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14708, https://doi.org/10.5194/egusphere-egu21-14708, 2021.
We used regional as well as global Rayleigh wave signals (source-receiver distance: 5°-175°; M≥ 6, Depth ≤ 150 km) recorded at 12 broadband seismic stations in northwestern Himalaya to compute arrival angles of surface waves at each station, assuming orthogonality of the horizontal components, and error-free levelling of the instrument. The average of all measurements at a station with cross-correlation values > 0.8, between Hilbert transformed vertical and radial components, was interpreted as the degree of misalignment of the horizontal components in a geographic frame of reference.
Out of the 12 station data used in this analysis, 3 were found to have instrument misorientation errors between 5° and 10° w.r.t geographic north, 2 between 10° and 15° and the remaining 7 < 5°. The number of measurements at each of these stations ranged from 75 to 331, with 11 stations having more than 90 measurements, assuring high reliability. We also analysed data from two nearby broadband instruments located in Ladakh Himalaya. One of these (LEH) with 46 measurements showed a misorientation error of 14.87°±4.87° and the other (HNL) with 48 showed an error of 0.75°±3.48°. Since misorientation errors based on less than 90 data elements are considered to be unstable, these were not used for further analysis.
We evaluated the effect of seismograph misorientations on the inverted solutions for P-wave receiver functions (RFs) and core-refracted shear waves (SKS). The errors in Moho depths and those of other intra-crustal features were within ±2 km for instrument misorientations of up to ~15°, that is close to the resolution errors. But, the SKS results, notably the azimuths of the fast component, were, found to be quite sensitive to instrument misalignment. For example, a ~14° error in orientation was found to cause a shift of up to 20° in the calculated azimuth of the fast component. Corrections of misorientation errors in both cases showed reduction of variance in the inverted solutions.
How to cite: Mir, R., Parvez, I., and Gaur, V.: Orientation of broadband seismographs in the Kashmir Himalaya: Effect on vector-based studies, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14708, https://doi.org/10.5194/egusphere-egu21-14708, 2021.
SM2.1 – Sensing ground translation, rotation, and strain - instrumentation, theory and applications
EGU21-859 | vPICO presentations | SM2.1
Visualizing the Seismic Wavefield with AlpArrayOn Ki Angel Ling, Simon Stähler, Domenico Giardini, and the AlpArray Working Group
The AlpArray Seismic Network (AASN) is a large-scale multidisciplinary seismic network in Europe that consists of over 600 3-component (3C) broadband stations with mean inter-station distance of 30-40km. This dense array allows the recording of the seismic wave propagation of distant earthquakes at a resolution of typical body and surface waves.
By animating the spatially-dense seismic recordings of the AASN, we can visualize seismic waves propagating across the European Alps as a function of space and time. Our 3C ground motion animations illustrate the full spatial-temporal evolution of global body and surface waves and demonstrates how a dense array allows the transformation from translation measurements at single stations to spatial gradients of the wavefield at the surface, capturing both small- and large-scale wave propagation phenomena. The addition of travel-time estimation, ray path illustration, and array-specific information such as slowness vector of incoming waves facilitate identification of seismic phases and their arrival-angle deviations. We will highlight some interesting observations of different seismic wave types in the animations of a few example teleseismic events during the course of the AASN between 2016-2019. Application for future research and education will also be discussed.
How to cite: Ling, O. K. A., Stähler, S., Giardini, D., and Group, T. A. W.: Visualizing the Seismic Wavefield with AlpArray, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-859, https://doi.org/10.5194/egusphere-egu21-859, 2021.
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The AlpArray Seismic Network (AASN) is a large-scale multidisciplinary seismic network in Europe that consists of over 600 3-component (3C) broadband stations with mean inter-station distance of 30-40km. This dense array allows the recording of the seismic wave propagation of distant earthquakes at a resolution of typical body and surface waves.
By animating the spatially-dense seismic recordings of the AASN, we can visualize seismic waves propagating across the European Alps as a function of space and time. Our 3C ground motion animations illustrate the full spatial-temporal evolution of global body and surface waves and demonstrates how a dense array allows the transformation from translation measurements at single stations to spatial gradients of the wavefield at the surface, capturing both small- and large-scale wave propagation phenomena. The addition of travel-time estimation, ray path illustration, and array-specific information such as slowness vector of incoming waves facilitate identification of seismic phases and their arrival-angle deviations. We will highlight some interesting observations of different seismic wave types in the animations of a few example teleseismic events during the course of the AASN between 2016-2019. Application for future research and education will also be discussed.
How to cite: Ling, O. K. A., Stähler, S., Giardini, D., and Group, T. A. W.: Visualizing the Seismic Wavefield with AlpArray, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-859, https://doi.org/10.5194/egusphere-egu21-859, 2021.
EGU21-8817 | vPICO presentations | SM2.1
Spectral ratio comparison between translation and rotational records from induced seismic events.Dariusz Nawrocki, Maciej Mendecki, and Lesław Teper
The seismic observations of the rotational signals are a field of seismology that is constantly developed. The recent research concerns sensors technology and its potential application in seismic tests. This study presents the results of a comparative analysis of rotational and translational seismic records using the horizontal-to-vertical spectral ratio (HVSR) method. In terms of transitional signal ratio, we have used the name of HVSR, but in terms of rotational component spectra, we have introduced a torsion-to-rocking spectral ratio (TRSR) which corresponds to horizontal rotation spectrum to vertical rotation spectrum. It has to be noticed that rotation in the horizontal axes has a vertical character and rotation in the vertical axis has a horizontal character.
The comparison was carried out between velocity signals of translational and rotational records, as well as, between acceleration signals respectively. All seismic data were recorded by two independent sensors: the rotational seismometer and translational accelerometer at the Imielin station, located in the Upper Silesia Coal Basin (USCB), Poland. The seismic data composed of three-component seismic waveforms related to 56 recorded tremors which were located up to 1,5 km from the seismic station and they resulted from the coal extractions carried out in the neighboring coal mines. The rotational acceleration was obtained by numerical differentiation and the translational velocity was produced by numerical integration.
The conducted spectral analyses allowed to estimate the range of frequency in which the rotational HVSR and the corresponded translational HVSR are comparable. The analysis of HVSR/TRSR curves (in the selected frequency range of 1Hz to 10Hz) showed a strong correlation between the spectral ratios for the velocity signals (translational and rotational) in the frequency range of 1Hz to 2Hz. Respectively, the comparison of the accelerometer signals indicated the correlation between HVSR/TRSR curves in the frequency range of 1Hz to 3Hz. Moreover, both of the TRSR (for velocity and acceleration) showed additional maxima in the same frequency range of 3Hz to 5Hz. These relatively high-frequency maxima did not correspond to translational spectra.
How to cite: Nawrocki, D., Mendecki, M., and Teper, L.: Spectral ratio comparison between translation and rotational records from induced seismic events., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8817, https://doi.org/10.5194/egusphere-egu21-8817, 2021.
The seismic observations of the rotational signals are a field of seismology that is constantly developed. The recent research concerns sensors technology and its potential application in seismic tests. This study presents the results of a comparative analysis of rotational and translational seismic records using the horizontal-to-vertical spectral ratio (HVSR) method. In terms of transitional signal ratio, we have used the name of HVSR, but in terms of rotational component spectra, we have introduced a torsion-to-rocking spectral ratio (TRSR) which corresponds to horizontal rotation spectrum to vertical rotation spectrum. It has to be noticed that rotation in the horizontal axes has a vertical character and rotation in the vertical axis has a horizontal character.
The comparison was carried out between velocity signals of translational and rotational records, as well as, between acceleration signals respectively. All seismic data were recorded by two independent sensors: the rotational seismometer and translational accelerometer at the Imielin station, located in the Upper Silesia Coal Basin (USCB), Poland. The seismic data composed of three-component seismic waveforms related to 56 recorded tremors which were located up to 1,5 km from the seismic station and they resulted from the coal extractions carried out in the neighboring coal mines. The rotational acceleration was obtained by numerical differentiation and the translational velocity was produced by numerical integration.
The conducted spectral analyses allowed to estimate the range of frequency in which the rotational HVSR and the corresponded translational HVSR are comparable. The analysis of HVSR/TRSR curves (in the selected frequency range of 1Hz to 10Hz) showed a strong correlation between the spectral ratios for the velocity signals (translational and rotational) in the frequency range of 1Hz to 2Hz. Respectively, the comparison of the accelerometer signals indicated the correlation between HVSR/TRSR curves in the frequency range of 1Hz to 3Hz. Moreover, both of the TRSR (for velocity and acceleration) showed additional maxima in the same frequency range of 3Hz to 5Hz. These relatively high-frequency maxima did not correspond to translational spectra.
How to cite: Nawrocki, D., Mendecki, M., and Teper, L.: Spectral ratio comparison between translation and rotational records from induced seismic events., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8817, https://doi.org/10.5194/egusphere-egu21-8817, 2021.
EGU21-6446 | vPICO presentations | SM2.1
Simulation of High-Frequency Rotational Motion in a Two-Dimensional Laterally Heterogeneous Half-SpaceIvan Lokmer, Varun Kumar Singla, and John McCloskey
The seismic waves responsible for vibrating civil engineering structures undergo interference, focusing, scattering, and diffraction by the inhomogeneous medium encountered along the source-to-site propagation path. The subsurface heterogeneities at a site can particularly alter the local seismic wave field and amplify the ground rotations, thereby increasing the seismic hazard. The conventional techniques to carry out full wave field simulations (such as finite-difference or spectral finite element methods) at high frequencies (e.g., 15 Hz) are computationally expensive, particularly when the size of the heterogeneities is small (e.g., <100 m). This study proposes an alternative technique that is based on the first-order perturbation theory for wave propagation. In this technique, the total wave field due to a particular source is obtained as a superposition of the ‘mean’ and ‘scattered’ wave fields. Whereas the ‘mean’ wave field is the response of the background (i.e., heterogeneity-free) medium due to the given source, the ‘scattered’ wave is the response of the background medium excited by fictitious body forces. For a two-dimensional laterally heterogeneous elastic medium, these body forces can be conveniently evaluated as a function of the material properties of the heterogeneities and the mean wave field. Since the problem of simulating high-frequency rotations in a laterally heterogeneous medium reduces to that of calculating rotations in the background medium subjected to the (1) given seismic source and (2) body forces that mathematically replace the small-scale heterogeneities, the original problem can be easily solved in a computationally accurate and efficient manner by using the classical (analytical) wavenumber-integration method. The workflow is illustrated for the case of a laterally heterogenous layer embedded in a homogeneous half-space excited by plane body-waves.
How to cite: Lokmer, I., Singla, V. K., and McCloskey, J.: Simulation of High-Frequency Rotational Motion in a Two-Dimensional Laterally Heterogeneous Half-Space, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6446, https://doi.org/10.5194/egusphere-egu21-6446, 2021.
The seismic waves responsible for vibrating civil engineering structures undergo interference, focusing, scattering, and diffraction by the inhomogeneous medium encountered along the source-to-site propagation path. The subsurface heterogeneities at a site can particularly alter the local seismic wave field and amplify the ground rotations, thereby increasing the seismic hazard. The conventional techniques to carry out full wave field simulations (such as finite-difference or spectral finite element methods) at high frequencies (e.g., 15 Hz) are computationally expensive, particularly when the size of the heterogeneities is small (e.g., <100 m). This study proposes an alternative technique that is based on the first-order perturbation theory for wave propagation. In this technique, the total wave field due to a particular source is obtained as a superposition of the ‘mean’ and ‘scattered’ wave fields. Whereas the ‘mean’ wave field is the response of the background (i.e., heterogeneity-free) medium due to the given source, the ‘scattered’ wave is the response of the background medium excited by fictitious body forces. For a two-dimensional laterally heterogeneous elastic medium, these body forces can be conveniently evaluated as a function of the material properties of the heterogeneities and the mean wave field. Since the problem of simulating high-frequency rotations in a laterally heterogeneous medium reduces to that of calculating rotations in the background medium subjected to the (1) given seismic source and (2) body forces that mathematically replace the small-scale heterogeneities, the original problem can be easily solved in a computationally accurate and efficient manner by using the classical (analytical) wavenumber-integration method. The workflow is illustrated for the case of a laterally heterogenous layer embedded in a homogeneous half-space excited by plane body-waves.
How to cite: Lokmer, I., Singla, V. K., and McCloskey, J.: Simulation of High-Frequency Rotational Motion in a Two-Dimensional Laterally Heterogeneous Half-Space, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6446, https://doi.org/10.5194/egusphere-egu21-6446, 2021.
EGU21-13490 | vPICO presentations | SM2.1
Democratizing and Densifying Low Noise Long Period Broadband StationsGeoffrey Bainbridge, Valarie Hamilton, and Timothy Parker
The Streckeisen STS-1 set a very high performance and lasting broadband (VBB) sensor standard that has been hard to match by other instruments, but these sensors also required a very careful emplacement and shielding from environmental changes and conditions, along with the high costs of ensuring the conditions for this level of instrument performance. Recent developments have demonstrated equivalent and broader bandwidth sensors that enable deploying these types of sensors in most any terrestrial environment. These new instruments, in many types of form factors, all magnetically shielded, open up new opportunities for continuing and expanding these VBB observations, democratizing the observations of these long period signals and opening up the possibilities of better performance through deep boreholes and observations of less developed sites that have harsher environmental conditions, along with recapitalizations of sites where STS-1s are no longer supported. We will describe recent testing results of Trillium 360 GSN vault, borehole, and posthole sensors as well as the Horizon 360 from many observatories and new potential use cases, some in polar environments that were impractical until now, and discuss development of the new Horizon 360 OBS.
How to cite: Bainbridge, G., Hamilton, V., and Parker, T.: Democratizing and Densifying Low Noise Long Period Broadband Stations, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13490, https://doi.org/10.5194/egusphere-egu21-13490, 2021.
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The Streckeisen STS-1 set a very high performance and lasting broadband (VBB) sensor standard that has been hard to match by other instruments, but these sensors also required a very careful emplacement and shielding from environmental changes and conditions, along with the high costs of ensuring the conditions for this level of instrument performance. Recent developments have demonstrated equivalent and broader bandwidth sensors that enable deploying these types of sensors in most any terrestrial environment. These new instruments, in many types of form factors, all magnetically shielded, open up new opportunities for continuing and expanding these VBB observations, democratizing the observations of these long period signals and opening up the possibilities of better performance through deep boreholes and observations of less developed sites that have harsher environmental conditions, along with recapitalizations of sites where STS-1s are no longer supported. We will describe recent testing results of Trillium 360 GSN vault, borehole, and posthole sensors as well as the Horizon 360 from many observatories and new potential use cases, some in polar environments that were impractical until now, and discuss development of the new Horizon 360 OBS.
How to cite: Bainbridge, G., Hamilton, V., and Parker, T.: Democratizing and Densifying Low Noise Long Period Broadband Stations, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13490, https://doi.org/10.5194/egusphere-egu21-13490, 2021.
EGU21-12443 | vPICO presentations | SM2.1
On the use of Distributed Acoustic Sensing for seismic divergence and curl estimationsPascal Edme, Patrick Paitz, David Sollberger, Tjeerd Kiers, Vincent Perron, Cedric Schmelzbach, Andreas Fichtner, and Johan O.A. Robertsson
Distributed Acoustic Sensing (DAS) is becoming an established tool for seismological and geophysical applications. DAS is based on Rayleigh scattering of light pulses conveyed in fibre optic cables, enabling unprecedented strain rate measurements over kilometers with spatial resolution of less than a meter. The low cost, logistically easy deployment, and the broadband sensitivity make it a very attractive technology to investigate an increasing number of man-made or natural phenomena.
One key restriction however is that DAS collects axial strain rate instead of the vector of ground motion, resulting in a poor sensitivity to broadside events like (at the surface) vertically incident waves or surface waves impinging perpendicular to the cable. Helically wound cables partially mitigate the issue but still do not provide omni-directional response as the typical vertical component of seismometers or geophones.
The present study is about the potential of using unconventional DAS cable layouts to replace and/or complement traditional sensors. We investigate the possibility of estimating the divergence and the vertical rotational components of the wavefield from cables deployed in a square or circular shape. The impact of the size of the arrangement as well as that of the interrogation gauge length is discussed. Real data are shown and the results suggest that DAS has the potential to offer additional seismic component(s) useful for wave type identification and separation for example.
How to cite: Edme, P., Paitz, P., Sollberger, D., Kiers, T., Perron, V., Schmelzbach, C., Fichtner, A., and Robertsson, J. O. A.: On the use of Distributed Acoustic Sensing for seismic divergence and curl estimations, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12443, https://doi.org/10.5194/egusphere-egu21-12443, 2021.
Distributed Acoustic Sensing (DAS) is becoming an established tool for seismological and geophysical applications. DAS is based on Rayleigh scattering of light pulses conveyed in fibre optic cables, enabling unprecedented strain rate measurements over kilometers with spatial resolution of less than a meter. The low cost, logistically easy deployment, and the broadband sensitivity make it a very attractive technology to investigate an increasing number of man-made or natural phenomena.
One key restriction however is that DAS collects axial strain rate instead of the vector of ground motion, resulting in a poor sensitivity to broadside events like (at the surface) vertically incident waves or surface waves impinging perpendicular to the cable. Helically wound cables partially mitigate the issue but still do not provide omni-directional response as the typical vertical component of seismometers or geophones.
The present study is about the potential of using unconventional DAS cable layouts to replace and/or complement traditional sensors. We investigate the possibility of estimating the divergence and the vertical rotational components of the wavefield from cables deployed in a square or circular shape. The impact of the size of the arrangement as well as that of the interrogation gauge length is discussed. Real data are shown and the results suggest that DAS has the potential to offer additional seismic component(s) useful for wave type identification and separation for example.
How to cite: Edme, P., Paitz, P., Sollberger, D., Kiers, T., Perron, V., Schmelzbach, C., Fichtner, A., and Robertsson, J. O. A.: On the use of Distributed Acoustic Sensing for seismic divergence and curl estimations, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12443, https://doi.org/10.5194/egusphere-egu21-12443, 2021.
EGU21-8438 | vPICO presentations | SM2.1
The GIOTTO Project - Building Monitoring with 6DoF SensorsFelix Bernauer, Louisa Murray-Bergquist, Felix Strobel, Joachim Wassermann, Heiner Igel, Eva P.S. Eibl, Cun-Man Liao, Ernst Niederleithinger, Sneha Singh, and Celine Hadziioannou
Characterizing earthquake induced building damage in an efficient, automated and non-
invasive way is a crucial support for the decision on further usability of critical infras-
tructure. In the GIOTTO project (Gebäudeschwingungen: kombinierte Zustandsanalyse
mit innovativem Sensorkonzept) we propose to use 6 degrees of freedom sensors (6DoF)
to monitor the complete movement of a building structure in three rotational and three
translational degrees of freedom. On one side, we develop 6DoF sensor networks for
strong motion building monitoring on the basis of 20 inertial measurement units (IMU50
by iXblue, France) originally designed as north-finding gyroscopes, on the other side we
incorporate the new observable of rotational ground motions into the concept of coda wave
interferometry for continuous real-time structural health monitoring. In this contribution
we show first results (1) from laboratory experiments for sensor performance characteriza-
tion as well as (2) from a 6DoF active source experiment at a horizontal 24 m long concrete
beam (the BLEIB test structure hosted by the Bundesanstalt für Materialforschung und
-prüfung, south of Berlin, Germany).
How to cite: Bernauer, F., Murray-Bergquist, L., Strobel, F., Wassermann, J., Igel, H., Eibl, E. P. S., Liao, C.-M., Niederleithinger, E., Singh, S., and Hadziioannou, C.: The GIOTTO Project - Building Monitoring with 6DoF Sensors, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8438, https://doi.org/10.5194/egusphere-egu21-8438, 2021.
Characterizing earthquake induced building damage in an efficient, automated and non-
invasive way is a crucial support for the decision on further usability of critical infras-
tructure. In the GIOTTO project (Gebäudeschwingungen: kombinierte Zustandsanalyse
mit innovativem Sensorkonzept) we propose to use 6 degrees of freedom sensors (6DoF)
to monitor the complete movement of a building structure in three rotational and three
translational degrees of freedom. On one side, we develop 6DoF sensor networks for
strong motion building monitoring on the basis of 20 inertial measurement units (IMU50
by iXblue, France) originally designed as north-finding gyroscopes, on the other side we
incorporate the new observable of rotational ground motions into the concept of coda wave
interferometry for continuous real-time structural health monitoring. In this contribution
we show first results (1) from laboratory experiments for sensor performance characteriza-
tion as well as (2) from a 6DoF active source experiment at a horizontal 24 m long concrete
beam (the BLEIB test structure hosted by the Bundesanstalt für Materialforschung und
-prüfung, south of Berlin, Germany).
How to cite: Bernauer, F., Murray-Bergquist, L., Strobel, F., Wassermann, J., Igel, H., Eibl, E. P. S., Liao, C.-M., Niederleithinger, E., Singh, S., and Hadziioannou, C.: The GIOTTO Project - Building Monitoring with 6DoF Sensors, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8438, https://doi.org/10.5194/egusphere-egu21-8438, 2021.
EGU21-8551 | vPICO presentations | SM2.1
Application of a new type of six-component seismometer for underground anomaly detectionXinding Fang
A new type of portable six-component seismometer is invented and used in the development of a seismic imaging method for shallow subsurface anomaly detection. This new six-component seismometer contains a mini-MEMS-array for acceleration and rotational velocity measurements. The self-noise for acceleration measurement is about 8 µg/√Hz, and the self-noise for rotational velocity measurement is about 5 µrad/s/√Hz. The frequency band is DC-1000 Hz. Different from the traditional seismic imaging methods that require the deployment of an array of either one-component or three-component seismometers, our imaging method is established based on the data recorded at individual six-component seismometer. Because the rotational field (i.e., the curl field) gives information about the spatial gradient of a seismic wavefield, so the translational field together with the rotational field can be used to derive the frequency-dependent velocity (i.e., dispersion) of the formation right beneath a seismic station. This single station velocity inversion approach delivers localized subsurface velocity information, making it suitable for imaging of small-scale underground anomalies. Especially, the Rayleigh wave dispersion is used in our method as Rayleigh wave is generally the dominant signal in surface seismic data. An underground velocity model can be immediately constructed by consolidating the dispersion curves derived from individual receivers. In our study, we first demonstrate the accuracy of our imaging method through numerical modeling of various scenarios of subsurface anomalies and then conduct an experiment to further verify the performance of our self-invented six-component seismometer and the field applicability of our imaging method.
How to cite: Fang, X.: Application of a new type of six-component seismometer for underground anomaly detection, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8551, https://doi.org/10.5194/egusphere-egu21-8551, 2021.
Please decide on your access
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Forward to presentation link
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We are sorry, but presentations are only available for users who registered for the conference. Thank you.
A new type of portable six-component seismometer is invented and used in the development of a seismic imaging method for shallow subsurface anomaly detection. This new six-component seismometer contains a mini-MEMS-array for acceleration and rotational velocity measurements. The self-noise for acceleration measurement is about 8 µg/√Hz, and the self-noise for rotational velocity measurement is about 5 µrad/s/√Hz. The frequency band is DC-1000 Hz. Different from the traditional seismic imaging methods that require the deployment of an array of either one-component or three-component seismometers, our imaging method is established based on the data recorded at individual six-component seismometer. Because the rotational field (i.e., the curl field) gives information about the spatial gradient of a seismic wavefield, so the translational field together with the rotational field can be used to derive the frequency-dependent velocity (i.e., dispersion) of the formation right beneath a seismic station. This single station velocity inversion approach delivers localized subsurface velocity information, making it suitable for imaging of small-scale underground anomalies. Especially, the Rayleigh wave dispersion is used in our method as Rayleigh wave is generally the dominant signal in surface seismic data. An underground velocity model can be immediately constructed by consolidating the dispersion curves derived from individual receivers. In our study, we first demonstrate the accuracy of our imaging method through numerical modeling of various scenarios of subsurface anomalies and then conduct an experiment to further verify the performance of our self-invented six-component seismometer and the field applicability of our imaging method.
How to cite: Fang, X.: Application of a new type of six-component seismometer for underground anomaly detection, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8551, https://doi.org/10.5194/egusphere-egu21-8551, 2021.
EGU21-10927 | vPICO presentations | SM2.1
Performance of a rotational sensor at Etna, Italy focusing on back-azimuth estimations of volcano-seismic eventsMartina Rosskopf, Eva P. S. Eibl, Gilda Currenti, Philippe Jousset, Joachim Wassermann, Daniel Vollmer, Graziano Larocca, Daniele Pellegrino, Mario Pulvirenti, and Danilo Contrafatto
The field of rotational seismology has only recently emerged. Portable 3 component rotational sensors are commercially available since a few years which opens the pathway for a first use in volcano-seismology. The combination of rotational and translational components of the wavefield allows identifying and filtering for specific seismic wave types, estimating the back azimuth of an earthquake, and calculating local seismic phase velocities.
Our work focuses on back-azimuth calculations of volcano-tectonic and long-period events detected at Etna volcano in Italy. Therefore, a continuous full seismic wavefield of 30 days was recorded by a BlueSeis-3A, the first portable rotational sensor, and a broadband Trillium Compact seismometer located next to each other at Mount Etna in August and September of 2019. In this study, we applied two methods for back-azimuth calculations. The first one is based on the similarity of the vertical rotation rate to the horizontal acceleration and the second one uses a polarization analysis from the two horizontal components of the rotation rate. The estimated back-azimuths for volcano-tectonic events were compared to theoretical back-azimuths based on the INGV event catalog and the long-period event back-azimuths were analyzed for their dominant directions. We discuss the quality of our back azimuths with respect to event locations and evaluate the sensitivity and benefits of the rotational sensor focusing on volcano-seismic events on Etna regarding the signal to noise ratios, locations, distances, and magnitudes.
How to cite: Rosskopf, M., Eibl, E. P. S., Currenti, G., Jousset, P., Wassermann, J., Vollmer, D., Larocca, G., Pellegrino, D., Pulvirenti, M., and Contrafatto, D.: Performance of a rotational sensor at Etna, Italy focusing on back-azimuth estimations of volcano-seismic events, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10927, https://doi.org/10.5194/egusphere-egu21-10927, 2021.
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The field of rotational seismology has only recently emerged. Portable 3 component rotational sensors are commercially available since a few years which opens the pathway for a first use in volcano-seismology. The combination of rotational and translational components of the wavefield allows identifying and filtering for specific seismic wave types, estimating the back azimuth of an earthquake, and calculating local seismic phase velocities.
Our work focuses on back-azimuth calculations of volcano-tectonic and long-period events detected at Etna volcano in Italy. Therefore, a continuous full seismic wavefield of 30 days was recorded by a BlueSeis-3A, the first portable rotational sensor, and a broadband Trillium Compact seismometer located next to each other at Mount Etna in August and September of 2019. In this study, we applied two methods for back-azimuth calculations. The first one is based on the similarity of the vertical rotation rate to the horizontal acceleration and the second one uses a polarization analysis from the two horizontal components of the rotation rate. The estimated back-azimuths for volcano-tectonic events were compared to theoretical back-azimuths based on the INGV event catalog and the long-period event back-azimuths were analyzed for their dominant directions. We discuss the quality of our back azimuths with respect to event locations and evaluate the sensitivity and benefits of the rotational sensor focusing on volcano-seismic events on Etna regarding the signal to noise ratios, locations, distances, and magnitudes.
How to cite: Rosskopf, M., Eibl, E. P. S., Currenti, G., Jousset, P., Wassermann, J., Vollmer, D., Larocca, G., Pellegrino, D., Pulvirenti, M., and Contrafatto, D.: Performance of a rotational sensor at Etna, Italy focusing on back-azimuth estimations of volcano-seismic events, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10927, https://doi.org/10.5194/egusphere-egu21-10927, 2021.
EGU21-16524 | vPICO presentations | SM2.1
Short Review of True-North Alignment Method on the Field Demonstrating the benefits of the use of an Optical GyrocompassFrédéric Guattari, Pierrick Auregan, Elliot de Toldi, Theo Laudat, and Laurent Mattio
To install a seismometer with a properly defined orientation - inside a vault or into a borehole - as a single station including various instruments or as a part of an array - an ‘adequate’ tool and an ‘absolute’ reference are needed.
In the past, and sometimes it persists nowadays, magnetic North have been used as a reference for Z-orientation of seismic station. Several studies have extensively measured the orientation error that have been made with this method, using an optical gyrocompass providing True-North as a reference, and their work will be summarized here.
In these studies, optical Gyrocompass is said to be the good solution, even if it is too heavy, expensive, and difficult to export. This paper will explain how iXblue has overcome these limitations to design the new-born Seistans Optical Gyrocompass.
Moreover, to aim True-North with a reliable accuracy is not the only think you need to do on the field. The method to transfer the North-line from the gyrocompass to the instrument to aligned must not induce errors that ruined the accuracy obtained using state-of-the-art gyrocompass. So an exhaustive study of the different ways to transfer the orientation from the compass to the aligned sensor will be presented, and corresponding added uncertainty will be evaluated, which is a good way to promote good practice on the field.
Finally, some figures will be gathered and shared from literature to quantify the precision needed for the alignment of a seismic sensor. There are today so few papers about this important matter that it is worth to spread their information.
How to cite: Guattari, F., Auregan, P., de Toldi, E., Laudat, T., and Mattio, L.: Short Review of True-North Alignment Method on the Field Demonstrating the benefits of the use of an Optical Gyrocompass, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16524, https://doi.org/10.5194/egusphere-egu21-16524, 2021.
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To install a seismometer with a properly defined orientation - inside a vault or into a borehole - as a single station including various instruments or as a part of an array - an ‘adequate’ tool and an ‘absolute’ reference are needed.
In the past, and sometimes it persists nowadays, magnetic North have been used as a reference for Z-orientation of seismic station. Several studies have extensively measured the orientation error that have been made with this method, using an optical gyrocompass providing True-North as a reference, and their work will be summarized here.
In these studies, optical Gyrocompass is said to be the good solution, even if it is too heavy, expensive, and difficult to export. This paper will explain how iXblue has overcome these limitations to design the new-born Seistans Optical Gyrocompass.
Moreover, to aim True-North with a reliable accuracy is not the only think you need to do on the field. The method to transfer the North-line from the gyrocompass to the instrument to aligned must not induce errors that ruined the accuracy obtained using state-of-the-art gyrocompass. So an exhaustive study of the different ways to transfer the orientation from the compass to the aligned sensor will be presented, and corresponding added uncertainty will be evaluated, which is a good way to promote good practice on the field.
Finally, some figures will be gathered and shared from literature to quantify the precision needed for the alignment of a seismic sensor. There are today so few papers about this important matter that it is worth to spread their information.
How to cite: Guattari, F., Auregan, P., de Toldi, E., Laudat, T., and Mattio, L.: Short Review of True-North Alignment Method on the Field Demonstrating the benefits of the use of an Optical Gyrocompass, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16524, https://doi.org/10.5194/egusphere-egu21-16524, 2021.
EGU21-16525 | vPICO presentations | SM2.1
From prototypes to first production units: blueSeis-1C Fiber Optical Gyroscope industrial solution for broadband ground motion rotation measurement at the best self-noiseKevin Gautier, Pierrick Auregan, Theo Laudat, and Frédéric Guattari
SM2.2 – Advances in fibre-optic technologies for geophysical applications
EGU21-6445 | vPICO presentations | SM2.2 | Highlight
Towards multi-method geophysical sensing on submarine cablesZhongwen Zhan, Mattia Cantono, Jorge Castellanos, Miguel González Herráez, Zhensheng Jia, Valey Kamalov, Hugo Martins, Antonio Mecozzi, Rafael Müller, Zhichao Shen, Ethan Williams, and Shuang Yin
The oceans present a major gap in geophysical instrumentation, hindering fundamental research on submarine earthquakes and the Earth’s interior structure, as well as effective earthquake and tsunami warning for offshore events. Emerging fiber-optic sensing technologies that can leverage submarine telecommunication cables present an new opportunity in filling the data gap. Marra et al. (2018) turned a 96 km long submarine cable into a sensitive seismic sensor using ultra-stable laser interferometry of a round-tripped signal. Another technology, Distributed Acoustic Sensing (DAS), interrogates intrinsic Rayleigh backscattering and converts tens of kilometers of dedicated fiber into thousands of seismic strainmeters on the seafloor (e.g., Lindsey et al., 2019; Sladen et al., 2019; Williams et al., 2019; Spica et al., 2020). Zhan et al. (2021) successfully sensed seismic and water waves over a 10,000 km long submarine cable connecting Los Angeles and Valparaiso, by monitoring the polarization of regular optical telecommunication channels. However, these new technologies have substantially different levels of sensitivity, coverage, spatial resolution, and scalability. In this talk, we advocate that strategic combinations of the different sensing techniques (including conventional geophysical networks) are necessary to provide the broadest coverage of the seafloor while making high-fidelity, physically interpretable measurements. Strategic collaborations between the geophysics community and telecommunication community without burdening the telecomm operation (e.g., by multiplexing or using regular telecom signals) will be critical to the long term success.
Marra, G., C. Clivati, R. Luckett, A. Tampellini, J. Kronjäger, L. Wright, A. Mura, F. Levi, S. Robinson, A. Xuereb, B. Baptie, D. Calonico, 2018. Ultrastable laser interferometry for earthquake detection with terrestrial and submarine cables. Science, eaat4458.
Lindsey, N.J., T. C. Dawe, J. B. Ajo-Franklin, 2019. Illuminating seafloor faults and ocean dynamics with dark fiber distributed acoustic sensing. Science. 366, 1103–1107.
Sladen, A., D. Rivet, J. P. Ampuero, L. De Barros, Y. Hello, G. Calbris, P. Lamare, 2019. Distributed sensing of earthquakes and ocean-solid Earth interactions on seafloor telecom cables. Nat Commun. 10, 5777.
Spica, Z.J., Nishida, K., Akuhara, T., Pétrélis, F., Shinohara, M. and Yamada, T., 2020. Marine Sediment Characterized by Ocean‐Bottom Fiber‐Optic Seismology. Geophysical Research Letters, 47(16), p.e2020GL088360.
Williams, E.F., M. R. Fernández-Ruiz, R. Magalhaes, R. Vanthillo, Z. Zhan, M. González-Herráez, H. F. Martins, 2019. Distributed sensing of microseisms and teleseisms with submarine dark fibers. Nat Commun. 10, 5778.
Zhan, Z., M. Cantono, V. Kamalov, A. Mecozzi, R. Muller, S. Yin, J.C. Castellanos, 2021. Optical polarization-based seismic and water wave sensing on transoceanic cables. Science, in press.
How to cite: Zhan, Z., Cantono, M., Castellanos, J., González Herráez, M., Jia, Z., Kamalov, V., Martins, H., Mecozzi, A., Müller, R., Shen, Z., Williams, E., and Yin, S.: Towards multi-method geophysical sensing on submarine cables , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6445, https://doi.org/10.5194/egusphere-egu21-6445, 2021.
Please decide on your access
Please use the buttons below to download the presentation materials or to visit the external website where the presentation is linked. Regarding the external link, please note that Copernicus Meetings cannot accept any liability for the content and the website you will visit.
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We are sorry, but presentations are only available for users who registered for the conference. Thank you.
The oceans present a major gap in geophysical instrumentation, hindering fundamental research on submarine earthquakes and the Earth’s interior structure, as well as effective earthquake and tsunami warning for offshore events. Emerging fiber-optic sensing technologies that can leverage submarine telecommunication cables present an new opportunity in filling the data gap. Marra et al. (2018) turned a 96 km long submarine cable into a sensitive seismic sensor using ultra-stable laser interferometry of a round-tripped signal. Another technology, Distributed Acoustic Sensing (DAS), interrogates intrinsic Rayleigh backscattering and converts tens of kilometers of dedicated fiber into thousands of seismic strainmeters on the seafloor (e.g., Lindsey et al., 2019; Sladen et al., 2019; Williams et al., 2019; Spica et al., 2020). Zhan et al. (2021) successfully sensed seismic and water waves over a 10,000 km long submarine cable connecting Los Angeles and Valparaiso, by monitoring the polarization of regular optical telecommunication channels. However, these new technologies have substantially different levels of sensitivity, coverage, spatial resolution, and scalability. In this talk, we advocate that strategic combinations of the different sensing techniques (including conventional geophysical networks) are necessary to provide the broadest coverage of the seafloor while making high-fidelity, physically interpretable measurements. Strategic collaborations between the geophysics community and telecommunication community without burdening the telecomm operation (e.g., by multiplexing or using regular telecom signals) will be critical to the long term success.
Marra, G., C. Clivati, R. Luckett, A. Tampellini, J. Kronjäger, L. Wright, A. Mura, F. Levi, S. Robinson, A. Xuereb, B. Baptie, D. Calonico, 2018. Ultrastable laser interferometry for earthquake detection with terrestrial and submarine cables. Science, eaat4458.
Lindsey, N.J., T. C. Dawe, J. B. Ajo-Franklin, 2019. Illuminating seafloor faults and ocean dynamics with dark fiber distributed acoustic sensing. Science. 366, 1103–1107.
Sladen, A., D. Rivet, J. P. Ampuero, L. De Barros, Y. Hello, G. Calbris, P. Lamare, 2019. Distributed sensing of earthquakes and ocean-solid Earth interactions on seafloor telecom cables. Nat Commun. 10, 5777.
Spica, Z.J., Nishida, K., Akuhara, T., Pétrélis, F., Shinohara, M. and Yamada, T., 2020. Marine Sediment Characterized by Ocean‐Bottom Fiber‐Optic Seismology. Geophysical Research Letters, 47(16), p.e2020GL088360.
Williams, E.F., M. R. Fernández-Ruiz, R. Magalhaes, R. Vanthillo, Z. Zhan, M. González-Herráez, H. F. Martins, 2019. Distributed sensing of microseisms and teleseisms with submarine dark fibers. Nat Commun. 10, 5778.
Zhan, Z., M. Cantono, V. Kamalov, A. Mecozzi, R. Muller, S. Yin, J.C. Castellanos, 2021. Optical polarization-based seismic and water wave sensing on transoceanic cables. Science, in press.
How to cite: Zhan, Z., Cantono, M., Castellanos, J., González Herráez, M., Jia, Z., Kamalov, V., Martins, H., Mecozzi, A., Müller, R., Shen, Z., Williams, E., and Yin, S.: Towards multi-method geophysical sensing on submarine cables , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6445, https://doi.org/10.5194/egusphere-egu21-6445, 2021.
EGU21-2498 | vPICO presentations | SM2.2
First deployment of a 6-km long fiber-optic strain cable and a seafloor geodetic network, across an active submarine fault (offshore Catania, Sicily): The FOCUS experimentMarc-Andre Gutscher, Jean-Yves Royer, Shane Murphy, Frauke Klingelhoefer, Giovanni Barreca, Arnaud Gaillot, Lionel Quetel, Giorgio Riccobene, Salvatore Aurnia, Philippe Jousset, Charles Poitou, and Viorel Ciausu
For the first time, a 6-km long fiber-optic strain cable was deployed across an active fault on the seafloor with the aim to monitor possible tectonic movement using laser reflectometry, 25 km offshore Catania Sicily (an urban area of 1 million people). Brillouin Optical Time Domain Reflectometry (BOTDR) is commonly used for structural health monitoring (bridges, dams, etc.) and under ideal conditions, can measure small strains (10-6) along a fiber-optic cable, across very large distances (10 - 200 km), with a spatial resolution of 10 - 50 m. The FocusX1 expedition, (6-21 October 2020) onboard the R/V Pourquoi Pas? was the first experiment of the European funded FOCUS project (ERC Advanced Grant). We first performed micro-bathymetric mapping and a video camera survey using the ROV Victor6000 to select the best path for the cable track and for deployment sites for eight seafloor geodetic stations. Next we connected a custom designed 6-km long fiber-optic cable (manufactured by Nexans Norway) to the TSS (Test Site South) seafloor observatory in 2100 m water depth operated by INFN-LNS (Italian National Physics Institute) via a new Y-junction frame and cable-end module. Cable deployment was performed by means of a deep-water cable-laying system with an integrated plow (updated Deep Sea Net design Ifremer, Toulon) to bury the cable 20 cm in the soft sediments in order to increase coupling between the cable and the seafloor. The cable track crosses the North Alfeo Fault at four locations. Laser reflectometry measurements began on 18 October 2020 and are being calibrated by a 3 - 4 year deployment of eight seafloor geodetic instruments (Canopus acoustic beacons manufactured by iXblue) deployed on 15 October 2020. During a future marine expedition, tentatively scheduled for early 2022 (FocusX2) a passive seismological experiment is planned to record regional seismicity. This will involve deployment of a temporary network of Ocean Bottom Seismometers (OBS) on the seafloor and seismic stations on land, supplemented by INGV permanent land stations. The simultaneous use of laser reflectometry, seafloor geodetic stations as well as seismological land and sea stations will provide an integrated system for monitoring a wide range of slipping event types along the North Alfeo Fault (e.g. - creep, slow-slip, rupture). A long-term goal of the project is the development of dual-use telecom cables with industry partners.
How to cite: Gutscher, M.-A., Royer, J.-Y., Murphy, S., Klingelhoefer, F., Barreca, G., Gaillot, A., Quetel, L., Riccobene, G., Aurnia, S., Jousset, P., Poitou, C., and Ciausu, V.: First deployment of a 6-km long fiber-optic strain cable and a seafloor geodetic network, across an active submarine fault (offshore Catania, Sicily): The FOCUS experiment, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2498, https://doi.org/10.5194/egusphere-egu21-2498, 2021.
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We are sorry, but presentations are only available for users who registered for the conference. Thank you.
For the first time, a 6-km long fiber-optic strain cable was deployed across an active fault on the seafloor with the aim to monitor possible tectonic movement using laser reflectometry, 25 km offshore Catania Sicily (an urban area of 1 million people). Brillouin Optical Time Domain Reflectometry (BOTDR) is commonly used for structural health monitoring (bridges, dams, etc.) and under ideal conditions, can measure small strains (10-6) along a fiber-optic cable, across very large distances (10 - 200 km), with a spatial resolution of 10 - 50 m. The FocusX1 expedition, (6-21 October 2020) onboard the R/V Pourquoi Pas? was the first experiment of the European funded FOCUS project (ERC Advanced Grant). We first performed micro-bathymetric mapping and a video camera survey using the ROV Victor6000 to select the best path for the cable track and for deployment sites for eight seafloor geodetic stations. Next we connected a custom designed 6-km long fiber-optic cable (manufactured by Nexans Norway) to the TSS (Test Site South) seafloor observatory in 2100 m water depth operated by INFN-LNS (Italian National Physics Institute) via a new Y-junction frame and cable-end module. Cable deployment was performed by means of a deep-water cable-laying system with an integrated plow (updated Deep Sea Net design Ifremer, Toulon) to bury the cable 20 cm in the soft sediments in order to increase coupling between the cable and the seafloor. The cable track crosses the North Alfeo Fault at four locations. Laser reflectometry measurements began on 18 October 2020 and are being calibrated by a 3 - 4 year deployment of eight seafloor geodetic instruments (Canopus acoustic beacons manufactured by iXblue) deployed on 15 October 2020. During a future marine expedition, tentatively scheduled for early 2022 (FocusX2) a passive seismological experiment is planned to record regional seismicity. This will involve deployment of a temporary network of Ocean Bottom Seismometers (OBS) on the seafloor and seismic stations on land, supplemented by INGV permanent land stations. The simultaneous use of laser reflectometry, seafloor geodetic stations as well as seismological land and sea stations will provide an integrated system for monitoring a wide range of slipping event types along the North Alfeo Fault (e.g. - creep, slow-slip, rupture). A long-term goal of the project is the development of dual-use telecom cables with industry partners.
How to cite: Gutscher, M.-A., Royer, J.-Y., Murphy, S., Klingelhoefer, F., Barreca, G., Gaillot, A., Quetel, L., Riccobene, G., Aurnia, S., Jousset, P., Poitou, C., and Ciausu, V.: First deployment of a 6-km long fiber-optic strain cable and a seafloor geodetic network, across an active submarine fault (offshore Catania, Sicily): The FOCUS experiment, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2498, https://doi.org/10.5194/egusphere-egu21-2498, 2021.
EGU21-5042 | vPICO presentations | SM2.2
The Potential of DAS on Underwater Fiber Optic Cables for Deep-Sea Current MonitoringDaniel Mata Flores, Jean-Paul Ampuero, Diego Mercerat, Anthony Sladen, and Diane Rivet
Distributed Acoustic Sensing (DAS) enables the use of existing underwater telecommunication cables as multi-sensor arrays, allowing for detailed study of the seismic wavefield. Since underwater telecommunication cables were not deployed for seismological investigations, the coupling between the cable and the seafloor varies, dramatically reducing the usefulness of poorly coupled cable segments for seismological research. In particular, underwater cables include segments that are suspended in the water column across seafloor valleys or other bathymetry irregularities. Here, we propose that ocean bottom currents may be studied by monitoring the vibrations of suspended cable segments. We analyze DAS-strain recordings on three dark fibers deployed in the Mediterranean Sea. Several cable segments, presumably suspended, feature high-amplitude signals with harmonic spectra as expected from a theoretical model of in-plane vibration of hanging cables. The spatial shape of the vibration modes are determined by filtering and stacking. Their comparison to theory allows constraining the attenuation of longitudinal waves propagating along the cable in the non-suspended sections. The vibration frequencies change over time scales of tens of minutes. Assuming that oscillations of suspended sections are driven by deep sea currents, the temporal fluctuations of the vibration frequencies are related to changes of the cables tension which, in turn, are related to the drag force induced on the suspended cable by the shedding of Karman vortex. On this basis, we propose a method to infer changes of deep sea current speeds from the changes of fundamental frequency of cable vibrations. Submarine optical reconnaissance campaigns and controlled smaller-scale experiments are planned to validate the approach. The work aims at demonstrating the potential of using suspended telecommunication cables to monitor and investigate marine currents in deep ocean environments.
How to cite: Mata Flores, D., Ampuero, J.-P., Mercerat, D., Sladen, A., and Rivet, D.: The Potential of DAS on Underwater Fiber Optic Cables for Deep-Sea Current Monitoring , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5042, https://doi.org/10.5194/egusphere-egu21-5042, 2021.
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Distributed Acoustic Sensing (DAS) enables the use of existing underwater telecommunication cables as multi-sensor arrays, allowing for detailed study of the seismic wavefield. Since underwater telecommunication cables were not deployed for seismological investigations, the coupling between the cable and the seafloor varies, dramatically reducing the usefulness of poorly coupled cable segments for seismological research. In particular, underwater cables include segments that are suspended in the water column across seafloor valleys or other bathymetry irregularities. Here, we propose that ocean bottom currents may be studied by monitoring the vibrations of suspended cable segments. We analyze DAS-strain recordings on three dark fibers deployed in the Mediterranean Sea. Several cable segments, presumably suspended, feature high-amplitude signals with harmonic spectra as expected from a theoretical model of in-plane vibration of hanging cables. The spatial shape of the vibration modes are determined by filtering and stacking. Their comparison to theory allows constraining the attenuation of longitudinal waves propagating along the cable in the non-suspended sections. The vibration frequencies change over time scales of tens of minutes. Assuming that oscillations of suspended sections are driven by deep sea currents, the temporal fluctuations of the vibration frequencies are related to changes of the cables tension which, in turn, are related to the drag force induced on the suspended cable by the shedding of Karman vortex. On this basis, we propose a method to infer changes of deep sea current speeds from the changes of fundamental frequency of cable vibrations. Submarine optical reconnaissance campaigns and controlled smaller-scale experiments are planned to validate the approach. The work aims at demonstrating the potential of using suspended telecommunication cables to monitor and investigate marine currents in deep ocean environments.
How to cite: Mata Flores, D., Ampuero, J.-P., Mercerat, D., Sladen, A., and Rivet, D.: The Potential of DAS on Underwater Fiber Optic Cables for Deep-Sea Current Monitoring , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5042, https://doi.org/10.5194/egusphere-egu21-5042, 2021.
EGU21-7404 | vPICO presentations | SM2.2
Measuring floating ice thickness with optical fibers and DAS, a test case study on a frozen moutain lake.Olivier Coutant, Ludovic Moreau, Pierre Boué, Eric Larose, and Arnaud Cimolino
Accurate monitoring of floating ice thickness is an important safety issue for northern countries where lakes, fjords, and coasts are covered with ice in winter, and used by people to travel. For example in Finland, 15-20 fatal accidents occur every year due to ice-related drowning. We have explored the potential of fiber optics to measure the propagation of seismic waves guided in the ice layer, in order to infer its thickness via the inversion of the dispersion curves. An optical fiber was deployed on a frozen lake at Lacs Roberts (2400m) above Grenoble and we measured with a DAS the signal generated by active sources (hammer) and ambient noise. We demonstrate that we can retrieve the ice thickness. This monitoring method could be of interest since the deployment of a fiber on ice is quite simple (e.g. using a drone) compared to other techniques for ice thickness estimation such as seismic survey or manual drilling.
How to cite: Coutant, O., Moreau, L., Boué, P., Larose, E., and Cimolino, A.: Measuring floating ice thickness with optical fibers and DAS, a test case study on a frozen moutain lake., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7404, https://doi.org/10.5194/egusphere-egu21-7404, 2021.
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Please use the buttons below to download the presentation materials or to visit the external website where the presentation is linked. Regarding the external link, please note that Copernicus Meetings cannot accept any liability for the content and the website you will visit.
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Accurate monitoring of floating ice thickness is an important safety issue for northern countries where lakes, fjords, and coasts are covered with ice in winter, and used by people to travel. For example in Finland, 15-20 fatal accidents occur every year due to ice-related drowning. We have explored the potential of fiber optics to measure the propagation of seismic waves guided in the ice layer, in order to infer its thickness via the inversion of the dispersion curves. An optical fiber was deployed on a frozen lake at Lacs Roberts (2400m) above Grenoble and we measured with a DAS the signal generated by active sources (hammer) and ambient noise. We demonstrate that we can retrieve the ice thickness. This monitoring method could be of interest since the deployment of a fiber on ice is quite simple (e.g. using a drone) compared to other techniques for ice thickness estimation such as seismic survey or manual drilling.
How to cite: Coutant, O., Moreau, L., Boué, P., Larose, E., and Cimolino, A.: Measuring floating ice thickness with optical fibers and DAS, a test case study on a frozen moutain lake., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7404, https://doi.org/10.5194/egusphere-egu21-7404, 2021.
EGU21-8284 | vPICO presentations | SM2.2
A variety of surface waves in ocean-bottom DAS recordsZack Spica, Loïc Viens, Jorge Castillo Castellanos, Takeshi Akuhara, Kiwamu Nishida, Masanao Shinohara, and Tomoaki Yamada
Distributed acoustic sensing (DAS) can transform existing telecommunication fiber-optic cables into arrays of thousands of sensors, enabling meter-scale recordings over tens of kilometers. Recently, DAS has demonstrated its utility for many seismological applications onshore. However, the use of offshore cables for seismic exploration and monitoring is still in its infancy.
In this work, we introduce some new results and observations obtained from a fiber-optic cable offshore the coast of Sanriku, Japan. In particular, we focus on surface wave retrieved from various signals and show that ocean-bottom DAS can be used to extract dispersion curves (DC) over a wide range of frequencies. We show that multi-mode DC can be easily extracted from ambient seismo-acoustic noise cross-correlation functions or F-K analysis. Moderate magnitude earthquakes also contain multiple surface-wave packets that are buried within their coda. Fully-coupled 3-D numerical simulations suggest that these low-amplitude signals originate from the continuous reverberations of the acoustic waves in the ocean layer.
How to cite: Spica, Z., Viens, L., Castillo Castellanos, J., Akuhara, T., Nishida, K., Shinohara, M., and Yamada, T.: A variety of surface waves in ocean-bottom DAS records, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8284, https://doi.org/10.5194/egusphere-egu21-8284, 2021.
Distributed acoustic sensing (DAS) can transform existing telecommunication fiber-optic cables into arrays of thousands of sensors, enabling meter-scale recordings over tens of kilometers. Recently, DAS has demonstrated its utility for many seismological applications onshore. However, the use of offshore cables for seismic exploration and monitoring is still in its infancy.
In this work, we introduce some new results and observations obtained from a fiber-optic cable offshore the coast of Sanriku, Japan. In particular, we focus on surface wave retrieved from various signals and show that ocean-bottom DAS can be used to extract dispersion curves (DC) over a wide range of frequencies. We show that multi-mode DC can be easily extracted from ambient seismo-acoustic noise cross-correlation functions or F-K analysis. Moderate magnitude earthquakes also contain multiple surface-wave packets that are buried within their coda. Fully-coupled 3-D numerical simulations suggest that these low-amplitude signals originate from the continuous reverberations of the acoustic waves in the ocean layer.
How to cite: Spica, Z., Viens, L., Castillo Castellanos, J., Akuhara, T., Nishida, K., Shinohara, M., and Yamada, T.: A variety of surface waves in ocean-bottom DAS records, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8284, https://doi.org/10.5194/egusphere-egu21-8284, 2021.
EGU21-2502 | vPICO presentations | SM2.2
A self-supervised Deep Learning approach for improving signal coherence in Distributed Acoustic SensingMartijn van den Ende, Itzhak Lior, Jean Paul Ampuero, Anthony Sladen, and Cédric Richard
Fibre-optic Distributed Acoustic Sensing (DAS) is an emerging technology for vibration measurements with numerous applications in seismic signal analysis as well as in monitoring of urban and marine environments, including microseismicity detection, ambient noise tomography, traffic density monitoring, and maritime vessel tracking. A major advantage of DAS is its ability to turn fibre-optic cables into large and dense seismic arrays. As a cornerstone of seismic array analysis, beamforming relies on the relative arrival times of coherent signals along the optical fibre array to estimate the direction-of-arrival of the signals, and can hence be used to locate earthquakes as well as moving acoustic sources (e.g. maritime vessels). Naturally, this technique can only be applied to signals that are sufficiently coherent in space and time, and so beamforming benefits from signal processing methods that enhance the signal-to-noise ratio of the spatio-temporally coherent signal components. DAS measurements often suffer from waveform incoherence, and processing submarine DAS data is particularly challenging.
In this work, we adopt a self-supervised deep learning algorithm to extract locally-coherent signal components. Owing to the similarity of coherent signals along a DAS system, one can predict the coherent part of the signal at a given channel based on the signals recorded at other channels, referred to as "J-invariance". Following the recent approach proposed by Batson & Royer (2019), we leverage the J-invariant property of earthquake signals recorded by a submarine fibre-optic cable. A U-net auto-encoder is trained to reconstruct the earthquake waveforms recorded at one channel based on the waveforms recorded at neighbouring channels. Repeating this procedure for every measurement location along the cable yields a J-invariant reconstruction of the dataset that maximises the local coherence of the data. When we apply standard beamforming techniques to the output of the deep learning model, we indeed obtain higher-fidelity estimates of the direction-of-arrival of the seismic waves, and spurious solutions resulting from a lack of waveform coherence and local seismic scattering are suppressed.
While the present application focuses on earthquake signals, the deep learning method is completely general, self-supervised, and directly applicable to other DAS-recorded signals. This approach facilitates the analysis of signals with low signal-to-noise ratio that are spatio-temporally coherent, and can work in tandem with existing time-series analysis techniques.
References:
Batson J., Royer L. (2019), "Noise2Self: Blind Denoising by Self-Supervision", Proceedings of the 36th International Conference on Machine Learning (ICML), Long Beach, California
How to cite: van den Ende, M., Lior, I., Ampuero, J. P., Sladen, A., and Richard, C.: A self-supervised Deep Learning approach for improving signal coherence in Distributed Acoustic Sensing, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2502, https://doi.org/10.5194/egusphere-egu21-2502, 2021.
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Fibre-optic Distributed Acoustic Sensing (DAS) is an emerging technology for vibration measurements with numerous applications in seismic signal analysis as well as in monitoring of urban and marine environments, including microseismicity detection, ambient noise tomography, traffic density monitoring, and maritime vessel tracking. A major advantage of DAS is its ability to turn fibre-optic cables into large and dense seismic arrays. As a cornerstone of seismic array analysis, beamforming relies on the relative arrival times of coherent signals along the optical fibre array to estimate the direction-of-arrival of the signals, and can hence be used to locate earthquakes as well as moving acoustic sources (e.g. maritime vessels). Naturally, this technique can only be applied to signals that are sufficiently coherent in space and time, and so beamforming benefits from signal processing methods that enhance the signal-to-noise ratio of the spatio-temporally coherent signal components. DAS measurements often suffer from waveform incoherence, and processing submarine DAS data is particularly challenging.
In this work, we adopt a self-supervised deep learning algorithm to extract locally-coherent signal components. Owing to the similarity of coherent signals along a DAS system, one can predict the coherent part of the signal at a given channel based on the signals recorded at other channels, referred to as "J-invariance". Following the recent approach proposed by Batson & Royer (2019), we leverage the J-invariant property of earthquake signals recorded by a submarine fibre-optic cable. A U-net auto-encoder is trained to reconstruct the earthquake waveforms recorded at one channel based on the waveforms recorded at neighbouring channels. Repeating this procedure for every measurement location along the cable yields a J-invariant reconstruction of the dataset that maximises the local coherence of the data. When we apply standard beamforming techniques to the output of the deep learning model, we indeed obtain higher-fidelity estimates of the direction-of-arrival of the seismic waves, and spurious solutions resulting from a lack of waveform coherence and local seismic scattering are suppressed.
While the present application focuses on earthquake signals, the deep learning method is completely general, self-supervised, and directly applicable to other DAS-recorded signals. This approach facilitates the analysis of signals with low signal-to-noise ratio that are spatio-temporally coherent, and can work in tandem with existing time-series analysis techniques.
References:
Batson J., Royer L. (2019), "Noise2Self: Blind Denoising by Self-Supervision", Proceedings of the 36th International Conference on Machine Learning (ICML), Long Beach, California
How to cite: van den Ende, M., Lior, I., Ampuero, J. P., Sladen, A., and Richard, C.: A self-supervised Deep Learning approach for improving signal coherence in Distributed Acoustic Sensing, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2502, https://doi.org/10.5194/egusphere-egu21-2502, 2021.
EGU21-7869 | vPICO presentations | SM2.2
Parameterizing the gains in earthquake monitoring using submarine optical fiber telecom cablesLuis Matias, Fernando Carrilho, Vasco Sá, Manfred Niehus, Carlos Corela, and Yasser Omar
The need for submarine observatories to monitor offshore tectonic sources that can generate destructive earthquakes and tsunamis is widely recognized but the requirements of real-time communications and cost has hindered its Implementation. Only very few dedicated cables with sensors are in operation today. If the dozens of commercial telecommunication submarine cables that are deployed every year were instrumented, they could revolutionize the offshore earthquake monitoring. These cables, named as SMART (Science Monitoring And Reliable) have been advocated by the JTF of United Nations (Joint Task Force) for nearly a decade but none has been deployed today. However, there are several identified projects that should become the first pilots worldwide.
Fiber optic research have shown that the cable itself can be used as strain meters and useful for seismic monitoring.
One technology is DAS, Distributed Acoustic Sensing. DAS uses a single dedicated portion of (dark) fiber on a submarine cable, with a length about ~100 km. It can be modelled as a distributed strain sensor, with localization ability of a few meters. The DAS signal using OTDR (optical time domain reflectometry) and signal phase detection measures the fiber strain and record earthquakes with a resolution like broadband seismic sensors.
Another technology is LI (Laser Interferometry). LI may use a dark fiber or a single telecom wavelength channel in an optical fiber pair with commercial traffic, thousands km long. It relies on frequency stable laser sources and coherent detection. LI detects the changes of fiber optical transmission parameters over the whole cable. Using recording instruments on both ends, the arrival point of the first seismic waves is determined, and the azimuth to the epicenter estimated.
This work proposes and applies one methodology to assess the gain in earthquake source information using any of the three cable sensor technologies mentioned, against a background scenario that includes only land stations. We use a Monte-Carlo simulation to allow for picking uncertainties, local and regional variations of propagation velocity models. We parametrize the gain in information by measuring the epicenter uncertainty ellipse and the focal depth variability.
The proposed methodology is applied to the NE Atlantic domain, SW Iberia and the Azores archipelago, an area where the relative motion of the Nubia, Eurasia and North America plates can generate large and destructive earthquakes and tsunamis.
While the inclusion in the monitoring network of SMART observatories, placed inside cable repeaters, spaced every ±70 km, is straightforward, the use of DAS and LI is not. For DAS and LI we consider that observations can be decimated to virtual seismic stations every 5 km and 1 km respectively. To avoid using a set of very close stations, we implement different station selection algorithms.
The investigation presented in this work was conducted by LEA, Listening to the Earth under the Atlantic, a partnership between IT, IPMA and IDL. One of the main objectives of LEA is to promote research, development, training and outreach on geophysical and oceanographic phenomena using submarine cables, fostering its applications to Science and Civil Protection.
How to cite: Matias, L., Carrilho, F., Sá, V., Niehus, M., Corela, C., and Omar, Y.: Parameterizing the gains in earthquake monitoring using submarine optical fiber telecom cables, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7869, https://doi.org/10.5194/egusphere-egu21-7869, 2021.
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The need for submarine observatories to monitor offshore tectonic sources that can generate destructive earthquakes and tsunamis is widely recognized but the requirements of real-time communications and cost has hindered its Implementation. Only very few dedicated cables with sensors are in operation today. If the dozens of commercial telecommunication submarine cables that are deployed every year were instrumented, they could revolutionize the offshore earthquake monitoring. These cables, named as SMART (Science Monitoring And Reliable) have been advocated by the JTF of United Nations (Joint Task Force) for nearly a decade but none has been deployed today. However, there are several identified projects that should become the first pilots worldwide.
Fiber optic research have shown that the cable itself can be used as strain meters and useful for seismic monitoring.
One technology is DAS, Distributed Acoustic Sensing. DAS uses a single dedicated portion of (dark) fiber on a submarine cable, with a length about ~100 km. It can be modelled as a distributed strain sensor, with localization ability of a few meters. The DAS signal using OTDR (optical time domain reflectometry) and signal phase detection measures the fiber strain and record earthquakes with a resolution like broadband seismic sensors.
Another technology is LI (Laser Interferometry). LI may use a dark fiber or a single telecom wavelength channel in an optical fiber pair with commercial traffic, thousands km long. It relies on frequency stable laser sources and coherent detection. LI detects the changes of fiber optical transmission parameters over the whole cable. Using recording instruments on both ends, the arrival point of the first seismic waves is determined, and the azimuth to the epicenter estimated.
This work proposes and applies one methodology to assess the gain in earthquake source information using any of the three cable sensor technologies mentioned, against a background scenario that includes only land stations. We use a Monte-Carlo simulation to allow for picking uncertainties, local and regional variations of propagation velocity models. We parametrize the gain in information by measuring the epicenter uncertainty ellipse and the focal depth variability.
The proposed methodology is applied to the NE Atlantic domain, SW Iberia and the Azores archipelago, an area where the relative motion of the Nubia, Eurasia and North America plates can generate large and destructive earthquakes and tsunamis.
While the inclusion in the monitoring network of SMART observatories, placed inside cable repeaters, spaced every ±70 km, is straightforward, the use of DAS and LI is not. For DAS and LI we consider that observations can be decimated to virtual seismic stations every 5 km and 1 km respectively. To avoid using a set of very close stations, we implement different station selection algorithms.
The investigation presented in this work was conducted by LEA, Listening to the Earth under the Atlantic, a partnership between IT, IPMA and IDL. One of the main objectives of LEA is to promote research, development, training and outreach on geophysical and oceanographic phenomena using submarine cables, fostering its applications to Science and Civil Protection.
How to cite: Matias, L., Carrilho, F., Sá, V., Niehus, M., Corela, C., and Omar, Y.: Parameterizing the gains in earthquake monitoring using submarine optical fiber telecom cables, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7869, https://doi.org/10.5194/egusphere-egu21-7869, 2021.
EGU21-7601 | vPICO presentations | SM2.2
Strain to Ground Motion Conversion of DAS Data for Earthquake Magnitude and Stress Drop DeterminationItzhak Lior, Anthony Sladen, Diego Mercerat, Jean-Paul Ampuero, Diane Rivet, and Serge Sambolian
The use of Distributed Acoustic Sensing (DAS) presents unique advantages for earthquake monitoring compared with standard seismic networks: spatially dense measurements adapted for harsh environments and designed for remote operation. However, the ability to determine earthquake source parameters using DAS is yet to be fully established. In particular, resolving the magnitude and stress drop, is a fundamental objective for seismic monitoring and earthquake early warning. To apply existing methods for source parameter estimation to DAS signals, they must first be converted from strain to ground motions. This conversion can be achieved using the waves’ apparent phase velocity, which varies for different seismic phases ranging from fast body-waves to slow surface- and scattered-waves. To facilitate this conversion and improve its reliability, an algorithm for slowness determination is presented, based on the local slant-stack transform. This approach yields a unique slowness value at each time instance of a DAS time-series. The ability to convert strain-rate signals to ground accelerations is validated using simulated data and applied to several earthquakes recorded by dark fibers of three ocean-bottom telecommunication cables in the Mediterranean Sea. The conversion emphasizes fast body-waves compared to slow scattered-waves and ambient noise, and is robust even in the presence of correlated noise and varying wave propagation directions. Good agreement is found between source parameters determined using converted DAS waveforms and on-land seismometers for both P- and S-wave records. The demonstrated ability to resolve source parameters using P-waves on horizontal ocean-bottom fibers is key for the implementation of DAS based earthquake early warning, which will significantly improve hazard mitigation capabilities for offshore and tsunami earthquakes.
How to cite: Lior, I., Sladen, A., Mercerat, D., Ampuero, J.-P., Rivet, D., and Sambolian, S.: Strain to Ground Motion Conversion of DAS Data for Earthquake Magnitude and Stress Drop Determination, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7601, https://doi.org/10.5194/egusphere-egu21-7601, 2021.
Please decide on your access
Please use the buttons below to download the presentation materials or to visit the external website where the presentation is linked. Regarding the external link, please note that Copernicus Meetings cannot accept any liability for the content and the website you will visit.
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We are sorry, but presentations are only available for users who registered for the conference. Thank you.
The use of Distributed Acoustic Sensing (DAS) presents unique advantages for earthquake monitoring compared with standard seismic networks: spatially dense measurements adapted for harsh environments and designed for remote operation. However, the ability to determine earthquake source parameters using DAS is yet to be fully established. In particular, resolving the magnitude and stress drop, is a fundamental objective for seismic monitoring and earthquake early warning. To apply existing methods for source parameter estimation to DAS signals, they must first be converted from strain to ground motions. This conversion can be achieved using the waves’ apparent phase velocity, which varies for different seismic phases ranging from fast body-waves to slow surface- and scattered-waves. To facilitate this conversion and improve its reliability, an algorithm for slowness determination is presented, based on the local slant-stack transform. This approach yields a unique slowness value at each time instance of a DAS time-series. The ability to convert strain-rate signals to ground accelerations is validated using simulated data and applied to several earthquakes recorded by dark fibers of three ocean-bottom telecommunication cables in the Mediterranean Sea. The conversion emphasizes fast body-waves compared to slow scattered-waves and ambient noise, and is robust even in the presence of correlated noise and varying wave propagation directions. Good agreement is found between source parameters determined using converted DAS waveforms and on-land seismometers for both P- and S-wave records. The demonstrated ability to resolve source parameters using P-waves on horizontal ocean-bottom fibers is key for the implementation of DAS based earthquake early warning, which will significantly improve hazard mitigation capabilities for offshore and tsunami earthquakes.
How to cite: Lior, I., Sladen, A., Mercerat, D., Ampuero, J.-P., Rivet, D., and Sambolian, S.: Strain to Ground Motion Conversion of DAS Data for Earthquake Magnitude and Stress Drop Determination, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7601, https://doi.org/10.5194/egusphere-egu21-7601, 2021.
EGU21-7856 | vPICO presentations | SM2.2
Leveraging coherent wave field analysis and deep learning in fiber-optic seismologyBenjamin Schwarz, Korbinian Sager, Philippe Jousset, Gilda Currenti, Charlotte Krawczyk, and Victor Tsai
Fiber-optic cables form an integral part of modern telecommunications infrastructure and are ubiquitous in particular in regions where dedicated seismic instrumentation is traditionally sparse or lacking entirely. Fiber-optic seismology promises to enable affordable and time-extended observations of earth and environmental processes at an unprecedented temporal and spatial resolution. The method’s unique potential for combined large-N and large-T observations implies intriguing opportunities but also significant challenges in terms of data storage, data handling and computation.
Our goal is to enable real-time data enhancement, rapid signal detection and wave field characterization without the need for time-demanding user interaction. We therefore combine coherent wave field analysis, an optics-inspired processing framework developed in controlled-source seismology, with state-of-the-art deep convolutional neural network (CNN) architectures commonly used in visual perception. While conventional deep learning strategies have to rely on manually labeled or purely synthetic training datasets, coherent wave field analysis labels field data based on physical principles and enables large-scale and purely data-driven training of the CNN models. The shear amount of data already recorded in various settings makes artificial data generation by numerical modeling superfluous – a task that is often constrained by incomplete knowledge of the embedding medium and an insufficient description of processes at or close to the surface, which are challenging to capture in integrated simulations.
Applications to extensive field datasets acquired with dark-fiber infrastructure at a geothermal field in SW Iceland and in a town at the flank of Mt Etna, Italy, reveal that the suggested framework generalizes well across different observational scales and environments, and sheds new light on the origin of a broad range of physically distinct wave fields that can be sensed with fiber-optic technology. Owing to the real-time applicability with affordable computing infrastructure, our analysis lends itself well to rapid on-the-fly data enhancement, wave field separation and compression strategies, thereby promising to have a positive impact on the full processing chain currently in use in fiber-optic seismology.
How to cite: Schwarz, B., Sager, K., Jousset, P., Currenti, G., Krawczyk, C., and Tsai, V.: Leveraging coherent wave field analysis and deep learning in fiber-optic seismology, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7856, https://doi.org/10.5194/egusphere-egu21-7856, 2021.
Fiber-optic cables form an integral part of modern telecommunications infrastructure and are ubiquitous in particular in regions where dedicated seismic instrumentation is traditionally sparse or lacking entirely. Fiber-optic seismology promises to enable affordable and time-extended observations of earth and environmental processes at an unprecedented temporal and spatial resolution. The method’s unique potential for combined large-N and large-T observations implies intriguing opportunities but also significant challenges in terms of data storage, data handling and computation.
Our goal is to enable real-time data enhancement, rapid signal detection and wave field characterization without the need for time-demanding user interaction. We therefore combine coherent wave field analysis, an optics-inspired processing framework developed in controlled-source seismology, with state-of-the-art deep convolutional neural network (CNN) architectures commonly used in visual perception. While conventional deep learning strategies have to rely on manually labeled or purely synthetic training datasets, coherent wave field analysis labels field data based on physical principles and enables large-scale and purely data-driven training of the CNN models. The shear amount of data already recorded in various settings makes artificial data generation by numerical modeling superfluous – a task that is often constrained by incomplete knowledge of the embedding medium and an insufficient description of processes at or close to the surface, which are challenging to capture in integrated simulations.
Applications to extensive field datasets acquired with dark-fiber infrastructure at a geothermal field in SW Iceland and in a town at the flank of Mt Etna, Italy, reveal that the suggested framework generalizes well across different observational scales and environments, and sheds new light on the origin of a broad range of physically distinct wave fields that can be sensed with fiber-optic technology. Owing to the real-time applicability with affordable computing infrastructure, our analysis lends itself well to rapid on-the-fly data enhancement, wave field separation and compression strategies, thereby promising to have a positive impact on the full processing chain currently in use in fiber-optic seismology.
How to cite: Schwarz, B., Sager, K., Jousset, P., Currenti, G., Krawczyk, C., and Tsai, V.: Leveraging coherent wave field analysis and deep learning in fiber-optic seismology, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7856, https://doi.org/10.5194/egusphere-egu21-7856, 2021.
EGU21-7927 | vPICO presentations | SM2.2
Combining Distributed Acoustic Sensing and Beamforming in a Volcanic Environment on Mount Meager, British Columbia.Sara Klaasen, Patrick Paitz, Jan Dettmer, and Andreas Fichtner
We present one of the first applications of Distributed Acoustic Sensing (DAS) in a volcanic environment. The goals are twofold: First, we want to examine the feasibility of DAS in such a remote and extreme environment, and second, we search for active volcanic signals of Mount Meager in British Columbia (Canada).
The Mount Meager massif is an active volcanic complex that is estimated to have the largest geothermal potential in Canada and caused its largest recorded landslide in 2010. We installed a 3-km long fibre-optic cable at 2000 m elevation that crosses the ridge of Mount Meager and traverses the uppermost part of a glacier, yielding continuous measurements from 19 September to 17 October 2019.
We identify ~30 low-frequency (0.01-1 Hz) and 3000 high-frequency (5-45 Hz) events. The low-frequency events are not correlated with microseismic ocean or atmospheric noise sources and volcanic tremor remains a plausible origin. The frequency-power distribution of the high-frequency events indicates a natural origin, and beamforming on these events reveals distinct event clusters, predominantly in the direction of the main peaks of the volcanic complex. Numerical examples show that we can apply conventional beamforming to the data, and that the results are improved by taking the signal-to-noise ratio of individual channels into account.
The increased data quantity of DAS can outweigh the limitations due to the lower quality of individual channels in these hazardous and remote environments. We conclude that DAS is a promising tool in this setting that warrants further development.
How to cite: Klaasen, S., Paitz, P., Dettmer, J., and Fichtner, A.: Combining Distributed Acoustic Sensing and Beamforming in a Volcanic Environment on Mount Meager, British Columbia., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7927, https://doi.org/10.5194/egusphere-egu21-7927, 2021.
We present one of the first applications of Distributed Acoustic Sensing (DAS) in a volcanic environment. The goals are twofold: First, we want to examine the feasibility of DAS in such a remote and extreme environment, and second, we search for active volcanic signals of Mount Meager in British Columbia (Canada).
The Mount Meager massif is an active volcanic complex that is estimated to have the largest geothermal potential in Canada and caused its largest recorded landslide in 2010. We installed a 3-km long fibre-optic cable at 2000 m elevation that crosses the ridge of Mount Meager and traverses the uppermost part of a glacier, yielding continuous measurements from 19 September to 17 October 2019.
We identify ~30 low-frequency (0.01-1 Hz) and 3000 high-frequency (5-45 Hz) events. The low-frequency events are not correlated with microseismic ocean or atmospheric noise sources and volcanic tremor remains a plausible origin. The frequency-power distribution of the high-frequency events indicates a natural origin, and beamforming on these events reveals distinct event clusters, predominantly in the direction of the main peaks of the volcanic complex. Numerical examples show that we can apply conventional beamforming to the data, and that the results are improved by taking the signal-to-noise ratio of individual channels into account.
The increased data quantity of DAS can outweigh the limitations due to the lower quality of individual channels in these hazardous and remote environments. We conclude that DAS is a promising tool in this setting that warrants further development.
How to cite: Klaasen, S., Paitz, P., Dettmer, J., and Fichtner, A.: Combining Distributed Acoustic Sensing and Beamforming in a Volcanic Environment on Mount Meager, British Columbia., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7927, https://doi.org/10.5194/egusphere-egu21-7927, 2021.
EGU21-3858 | vPICO presentations | SM2.2
Beamforming Reliability of DAS Ambient Noise Data and Wave Modes IdentificationYumin Zhao and Yunyue Elita Li
Ambient noise generated by the anthropological activities in the urban environments may contain both Rayleigh and Love waves. Due to the differences in the physics of Rayleigh and Love waves, a pre-knowledge of the wave modes in the cross-correlogram is essential for an accurate inversion of the subsurface velocity model. Several studies (Martin and Biondi, 2017; Martin et al., 2017; Luo et al., 2020) demonstrated that only Rayleigh waves can be extracted by cross-correlation if the virtual source is colinear with the DAS array based on the assumption that the ambient noise sources are random and uniformly distributed. However, in realistic cases, ambient noise sources may come from a certain direction (e.g., Dou et al., 2017; Zhang et al., 2019). Moreover, the source propagation direction should be resolved and used to correct the apparent dispersion curves. Zhao et al. (2020) and van den Ende et al. (2020) proposed that beamforming results are not always reliable due to the measurements of DAS.
Based on the synthetic DAS ambient noise data recorded by a near “L” shape array (Source-West corner of the Stanford DAS-1 array), we prove that beamforming can resolve the source direction when the ambient sources are mainly coming from one direction. Two important processing procedures are that: check the polarity in the data and apply polarity flip on one part of the data; apply amplitude normalization on the data if strong amplitude difference exits in the data. Based on the source direction, the coordinate of the DAS array, and amplitude ratio of the data recorded by the two segments of the DAS array, we propose an inversion method to calculate the amplitude ratio of the Rayleigh and Love waves generated by the ambient sources.
We apply the method to two 100-second DAS ambient noise data recorded by the Stanford DAS-1 array. We first resolve the source propagation direction from the two data. The results indicate that the ambient noise in the data were mainly generated by the motor vehicles running on the Campus Drive in the northwest of the array. Then we invert for the Rayleigh and Love waves amplitude ratio using the proposed method. The ratios for the two data are 0.2 and 0.13, respectively. The results suggest that the ambient noise generated by motor vehicles running on the northwest corner of the Campus Drive mainly contain Love waves.
How to cite: Zhao, Y. and Li, Y. E.: Beamforming Reliability of DAS Ambient Noise Data and Wave Modes Identification, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3858, https://doi.org/10.5194/egusphere-egu21-3858, 2021.
Please decide on your access
Please use the buttons below to download the presentation materials or to visit the external website where the presentation is linked. Regarding the external link, please note that Copernicus Meetings cannot accept any liability for the content and the website you will visit.
Forward to presentation link
You are going to open an external link to the presentation as indicated by the authors. Copernicus Meetings cannot accept any liability for the content and the website you will visit.
We are sorry, but presentations are only available for users who registered for the conference. Thank you.
Ambient noise generated by the anthropological activities in the urban environments may contain both Rayleigh and Love waves. Due to the differences in the physics of Rayleigh and Love waves, a pre-knowledge of the wave modes in the cross-correlogram is essential for an accurate inversion of the subsurface velocity model. Several studies (Martin and Biondi, 2017; Martin et al., 2017; Luo et al., 2020) demonstrated that only Rayleigh waves can be extracted by cross-correlation if the virtual source is colinear with the DAS array based on the assumption that the ambient noise sources are random and uniformly distributed. However, in realistic cases, ambient noise sources may come from a certain direction (e.g., Dou et al., 2017; Zhang et al., 2019). Moreover, the source propagation direction should be resolved and used to correct the apparent dispersion curves. Zhao et al. (2020) and van den Ende et al. (2020) proposed that beamforming results are not always reliable due to the measurements of DAS.
Based on the synthetic DAS ambient noise data recorded by a near “L” shape array (Source-West corner of the Stanford DAS-1 array), we prove that beamforming can resolve the source direction when the ambient sources are mainly coming from one direction. Two important processing procedures are that: check the polarity in the data and apply polarity flip on one part of the data; apply amplitude normalization on the data if strong amplitude difference exits in the data. Based on the source direction, the coordinate of the DAS array, and amplitude ratio of the data recorded by the two segments of the DAS array, we propose an inversion method to calculate the amplitude ratio of the Rayleigh and Love waves generated by the ambient sources.
We apply the method to two 100-second DAS ambient noise data recorded by the Stanford DAS-1 array. We first resolve the source propagation direction from the two data. The results indicate that the ambient noise in the data were mainly generated by the motor vehicles running on the Campus Drive in the northwest of the array. Then we invert for the Rayleigh and Love waves amplitude ratio using the proposed method. The ratios for the two data are 0.2 and 0.13, respectively. The results suggest that the ambient noise generated by motor vehicles running on the northwest corner of the Campus Drive mainly contain Love waves.
How to cite: Zhao, Y. and Li, Y. E.: Beamforming Reliability of DAS Ambient Noise Data and Wave Modes Identification, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3858, https://doi.org/10.5194/egusphere-egu21-3858, 2021.
EGU21-12216 | vPICO presentations | SM2.2
Wave-selective beamforming with Distributed Acoustic SensingDaniel C. Bowden, Sara Klaasen, Eileen Martin, Patrick Paitz, and Andreas Fichtner
As fibre-optic DAS deployments become more common, researchers are turning to tried-and-true methods of locating or characterizing seismic sources such as beamforming. However, the strain measurement from DAS intrinsically carries its own sensitivities to both wave type and polarization (Martin et al. 2018, Paitz 2020 doctoral thesis). Additionally, a measurement along a conventional fibre-optic cable only provides one component of motion, and so certain azimuths may be blind to certain types of seismic sources, unless the cable layout can be designed to be oriented in multiple directions.
In this work, we explore the development and application of a beamforming algorithm that explicitly searches for multiple wavetypes. This builds on 3-component beamforming or Matched Field Processing (MFP) algorithms by Riahi et al. (2013), and Gal et al. (2018), where in addition to gridsearching over possible source azimuths, a distinct gridsearch is performed for each possible wavetype of interest. This does not solve the problem that a given cable orientation might be less sensitive to certain directions, but at least an array-response function can be robustly defined for each type of seismic excitation. This might help further distinguish whether beamforming observations are dominated by primary sources or by secondary scattering (van der Ende and Ampuero, 2020 preprint).
Much of this work uses analytic theory and synthetic examples. Time permitting, the enhanced algorithm will also be applied to data from the Mt. Meager experiment to explore its feasibility and efficacy with real data (EGU contribution from Klaasen et. al, 2021).
How to cite: Bowden, D. C., Klaasen, S., Martin, E., Paitz, P., and Fichtner, A.: Wave-selective beamforming with Distributed Acoustic Sensing, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12216, https://doi.org/10.5194/egusphere-egu21-12216, 2021.
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As fibre-optic DAS deployments become more common, researchers are turning to tried-and-true methods of locating or characterizing seismic sources such as beamforming. However, the strain measurement from DAS intrinsically carries its own sensitivities to both wave type and polarization (Martin et al. 2018, Paitz 2020 doctoral thesis). Additionally, a measurement along a conventional fibre-optic cable only provides one component of motion, and so certain azimuths may be blind to certain types of seismic sources, unless the cable layout can be designed to be oriented in multiple directions.
In this work, we explore the development and application of a beamforming algorithm that explicitly searches for multiple wavetypes. This builds on 3-component beamforming or Matched Field Processing (MFP) algorithms by Riahi et al. (2013), and Gal et al. (2018), where in addition to gridsearching over possible source azimuths, a distinct gridsearch is performed for each possible wavetype of interest. This does not solve the problem that a given cable orientation might be less sensitive to certain directions, but at least an array-response function can be robustly defined for each type of seismic excitation. This might help further distinguish whether beamforming observations are dominated by primary sources or by secondary scattering (van der Ende and Ampuero, 2020 preprint).
Much of this work uses analytic theory and synthetic examples. Time permitting, the enhanced algorithm will also be applied to data from the Mt. Meager experiment to explore its feasibility and efficacy with real data (EGU contribution from Klaasen et. al, 2021).
How to cite: Bowden, D. C., Klaasen, S., Martin, E., Paitz, P., and Fichtner, A.: Wave-selective beamforming with Distributed Acoustic Sensing, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12216, https://doi.org/10.5194/egusphere-egu21-12216, 2021.
EGU21-10943 | vPICO presentations | SM2.2
Signal analysis between DAS and geophones in a vertical borehole from active and passive sourcesMarius Paul Isken, Torsten Dahm, Sebastian Heimann, Christopher Wollin, Matthias Ohrnberger, Thomas Reinsch, and Charlotte M. Krawczyk
We present an analysis and qualitative comparison between acoustic data recorded on a distributed acoustic sensing (DAS) instrument (Silixa iDAS, version 2) and a three-component geophone chain colocated in a 400 m deep ICDP borehole in the magmatically active Vogtland area, Germany. A tight buffer single-mode fiber optic cable with a structured surface was installed and cemented behind casing down to total depth of the well. Additionally, a vertical array of 10 Hz geophones is suspended within the borehole.At the surface, further geophones were installed to shape a permanent three-dimensional seismic array. For this experiment the DAS system sampled strain-rate data at 10 m gauge length and 1 m spacing, yielding a high-resolution image of the wave field. Both seismic systems recorded data for 24 hours at 1 kHz sampling rate.
Within these 24 hours of recording, we shot a vertical seismic profile (VSP) with a 300 kg heavy and 2.4 m tall drop weight source moving up to a distance of 400 m away from the wellhead. Furthermore, passive seismic events at local and regional distances were recorded.
We compare the signal quality between the DAS system and the calibrated three-component geophones using the active and passive signals, to determine the sensitivity, signal-to-noise ratios and frequency response. Further we investigate the noise characteristics of both systems in this natural and remote environment, and evaluate the feasibility of borehole DAS behind casing for micro-earthquake monitoring. We give an outlook how dense DAS data can be utilized for VSP experiments with the aim to develop methods for fault detection and characterisation for application in DAS data recorded at the surface.
How to cite: Isken, M. P., Dahm, T., Heimann, S., Wollin, C., Ohrnberger, M., Reinsch, T., and Krawczyk, C. M.: Signal analysis between DAS and geophones in a vertical borehole from active and passive sources, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10943, https://doi.org/10.5194/egusphere-egu21-10943, 2021.
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We present an analysis and qualitative comparison between acoustic data recorded on a distributed acoustic sensing (DAS) instrument (Silixa iDAS, version 2) and a three-component geophone chain colocated in a 400 m deep ICDP borehole in the magmatically active Vogtland area, Germany. A tight buffer single-mode fiber optic cable with a structured surface was installed and cemented behind casing down to total depth of the well. Additionally, a vertical array of 10 Hz geophones is suspended within the borehole.At the surface, further geophones were installed to shape a permanent three-dimensional seismic array. For this experiment the DAS system sampled strain-rate data at 10 m gauge length and 1 m spacing, yielding a high-resolution image of the wave field. Both seismic systems recorded data for 24 hours at 1 kHz sampling rate.
Within these 24 hours of recording, we shot a vertical seismic profile (VSP) with a 300 kg heavy and 2.4 m tall drop weight source moving up to a distance of 400 m away from the wellhead. Furthermore, passive seismic events at local and regional distances were recorded.
We compare the signal quality between the DAS system and the calibrated three-component geophones using the active and passive signals, to determine the sensitivity, signal-to-noise ratios and frequency response. Further we investigate the noise characteristics of both systems in this natural and remote environment, and evaluate the feasibility of borehole DAS behind casing for micro-earthquake monitoring. We give an outlook how dense DAS data can be utilized for VSP experiments with the aim to develop methods for fault detection and characterisation for application in DAS data recorded at the surface.
How to cite: Isken, M. P., Dahm, T., Heimann, S., Wollin, C., Ohrnberger, M., Reinsch, T., and Krawczyk, C. M.: Signal analysis between DAS and geophones in a vertical borehole from active and passive sources, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10943, https://doi.org/10.5194/egusphere-egu21-10943, 2021.
EGU21-7868 | vPICO presentations | SM2.2
Urban DAS recording of a vibroseismic campaign with a 21km-long dark fibre in Potsdam, GermanyCharLotte Krawczyk, Christopher Wollin, Stefan Lüth, Martin Lipus, Christian Cunow, Ariane Siebert, Philippe Jousset, and Sven Fuchs
The de-carbonization strategy of the city of Potsdam, Germany, incorporates the utilization of its geothermal potential. As a first step of developing a deep geothermal project for district heating, an urban seismic exploration campaign of the Stadtwerke Potsdam took place in December 2020 in the city centre of Potsdam. Since urban measurements are often difficult to setup and a low-footprint alternative is sought for, we supplemented the contractor-performed Vibroseis survey along three profiles by distributed acoustic sensing (DAS). In close cooperation with the municipal utilities, we interrogated a 21 km-long dark telecommunication fibre whose trajectory followed the seismic lines as close as possible. This was accompanied by a network of 15 three-component geophones for further control and research.
In this contribution we present the data set, the approach for geo-referencing the fibre, and first results regarding DAS recording capabilities of vibroseismic signals in an urban environment. Following the paradigm that the high density of telecommunication networks in urban areas may facilitate the exploration of the often insufficiently known local geology, we strive to further shed light on the possibilities of their employment for urban exploration. In this respect we aim at tackling the question of the accuracy of fibre localization, recording sensitivity and range of active stimulation.
How to cite: Krawczyk, C., Wollin, C., Lüth, S., Lipus, M., Cunow, C., Siebert, A., Jousset, P., and Fuchs, S.: Urban DAS recording of a vibroseismic campaign with a 21km-long dark fibre in Potsdam, Germany, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7868, https://doi.org/10.5194/egusphere-egu21-7868, 2021.
The de-carbonization strategy of the city of Potsdam, Germany, incorporates the utilization of its geothermal potential. As a first step of developing a deep geothermal project for district heating, an urban seismic exploration campaign of the Stadtwerke Potsdam took place in December 2020 in the city centre of Potsdam. Since urban measurements are often difficult to setup and a low-footprint alternative is sought for, we supplemented the contractor-performed Vibroseis survey along three profiles by distributed acoustic sensing (DAS). In close cooperation with the municipal utilities, we interrogated a 21 km-long dark telecommunication fibre whose trajectory followed the seismic lines as close as possible. This was accompanied by a network of 15 three-component geophones for further control and research.
In this contribution we present the data set, the approach for geo-referencing the fibre, and first results regarding DAS recording capabilities of vibroseismic signals in an urban environment. Following the paradigm that the high density of telecommunication networks in urban areas may facilitate the exploration of the often insufficiently known local geology, we strive to further shed light on the possibilities of their employment for urban exploration. In this respect we aim at tackling the question of the accuracy of fibre localization, recording sensitivity and range of active stimulation.
How to cite: Krawczyk, C., Wollin, C., Lüth, S., Lipus, M., Cunow, C., Siebert, A., Jousset, P., and Fuchs, S.: Urban DAS recording of a vibroseismic campaign with a 21km-long dark fibre in Potsdam, Germany, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7868, https://doi.org/10.5194/egusphere-egu21-7868, 2021.
EGU21-14860 | vPICO presentations | SM2.2
Field Test of 12 serially connected FBG accelerometer parallelly with the vertical sensor of 4.5 -Hz geophones.Aarathy Ezhuthupally Reghuprasad, Alberto Godio, Davide Luca Janner, Chiara Colombero, and Diego Franco
Fibre Bragg Grating (FBG) sensors are widely used for measuring vibrations in the fields like seismology and civil engineering. FBG sensors possess several advantages when compared to the traditional vibration sensors like immunity to electromagnetic interference, multiplexing, miniature size, higher sensitivity. Highly sensitive systems are required for capturing the seismic vibrations with low magnitude of acceleration. In this work a cost-effective cantilever based FBG accelerometer is developed. The structure is modelled using the software Solid Works and fabricated with PLA by 3D printing. Finally, a comparison test was carried out by serially connecting 12 FBG accelerometers parallelly to common vertical 4.5-Hz geophones outside the lab environment. Hammer shots were acquired along the tested line and the experimental results from both the systems were analysed and compared. The FBG system demonstrated here is suitable for seismic field acquisitions with potential applications to seismic refraction surveys, surface-wave analyses and passive seismic recordings.
How to cite: Ezhuthupally Reghuprasad, A., Godio, A., Janner, D. L., Colombero, C., and Franco, D.: Field Test of 12 serially connected FBG accelerometer parallelly with the vertical sensor of 4.5 -Hz geophones., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14860, https://doi.org/10.5194/egusphere-egu21-14860, 2021.
Fibre Bragg Grating (FBG) sensors are widely used for measuring vibrations in the fields like seismology and civil engineering. FBG sensors possess several advantages when compared to the traditional vibration sensors like immunity to electromagnetic interference, multiplexing, miniature size, higher sensitivity. Highly sensitive systems are required for capturing the seismic vibrations with low magnitude of acceleration. In this work a cost-effective cantilever based FBG accelerometer is developed. The structure is modelled using the software Solid Works and fabricated with PLA by 3D printing. Finally, a comparison test was carried out by serially connecting 12 FBG accelerometers parallelly to common vertical 4.5-Hz geophones outside the lab environment. Hammer shots were acquired along the tested line and the experimental results from both the systems were analysed and compared. The FBG system demonstrated here is suitable for seismic field acquisitions with potential applications to seismic refraction surveys, surface-wave analyses and passive seismic recordings.
How to cite: Ezhuthupally Reghuprasad, A., Godio, A., Janner, D. L., Colombero, C., and Franco, D.: Field Test of 12 serially connected FBG accelerometer parallelly with the vertical sensor of 4.5 -Hz geophones., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14860, https://doi.org/10.5194/egusphere-egu21-14860, 2021.
SM2.3 – Improving seismic networks operations from site scouting to waveform services and products
EGU21-6119 | vPICO presentations | SM2.3
ORFEUS Services and Activities to Promote Observational Seismology in Europe and beyondCarlo Cauzzi, Jarek Bieńkowski, Susana Custódio, Sebastiano D'Amico, Christos Evangelidis, Philippe Guéguen, Christian Haberland, Florian Haslinger, Giovanni Lanzano, Lars Ottemöller, Stephane Rondenay, Reinoud Sleeman, and Angelo Strollo
ORFEUS (Observatories and Research Facilities for European Seismology; http://orfeus-eu.org/) is a non-profit foundation that promotes observational seismology in the Euro-Mediterranean area through the collection, archival and distribution of seismic waveform data, metadata, and closely related services and products. The data and services are collected or developed at national level by more than 60 contributing Institutions in Pan-Europe and further enhanced, integrated, standardized, homogenized and promoted through ORFEUS. Among the goals of ORFEUS are: (a) the development and coordination of waveform data products; (b) the coordination of a European data distribution system, and the support for seismic networks in archiving and exchanging digital seismic waveform data; (c) the encouragement of the adoption of best practices for seismic network operation, data quality control and FAIR data management; (d) the promotion of open access to seismic waveform data, products and services for the broader Earth science community. These goals are achieved through the development and maintenance of services targeted to a broad community of seismological data users, ranging from earth scientists to earthquake engineering practitioners. Two Service Management Committees (SMCs) are consolidated within ORFEUS devoted to managing, operating and developing (with the support of one or more Infrastructure Development Groups): (i) the European Integrated Data Archive (EIDA; https://www.orfeus-eu.org/data/eida/); and (ii) the European Strong-Motion databases (SM; https://www.orfeus-eu.org/data/strong/). New emerging groups within ORFEUS are focused on mobile pools and computational seismology. ORFEUS services currently provide access to the waveforms acquired by ~ 14,500 stations, including dense temporary experiments, with strong emphasis on open, high-quality data. Contributing to ORFEUS data archives means benefitting from long-term archival, state-of-the-art quality control, improved access, increased usage, and community participation. Access to data and products is ensured through state-of-the-art information and communication technologies, with strong emphasis on federated web services that considerably improve seamless user access to data gathered and/or distributed by the various ORFEUS institutions. Web services also facilitate the automation of downstream products. Particular attention is paid to adopting clear policies and licenses, and acknowledging the crucial role played by data providers / owners, who are part of the ORFEUS community. There are significant efforts by ORFEUS participating Institutions to enhance the existing services to tackle the challenges posed by the Big Data Era, with emphasis on data quality, improved user experience, and implementation of strategies for scalability, high-volume data access and archival. ORFEUS data and services are assessed and improved through the technical and scientific feedback of a User Advisory Group (UAG), which comprises European Earth scientists with expertise on a broad range of disciplines. All ORFEUS services are developed in coordination with EPOS and are largely integrated in the EPOS Data Access Portal, as ORFEUS is one of the founding Parties and fundamental contributors of the EPOS Thematic Core Service for Seismology (https://www.epos-eu.org/tcs/seismology). In this contribution, we selectively present the activities of ORFEUS, with the main aims of facilitating seismological data discovery and encouraging open data sharing and integration, as well as promoting best practice in observational seismology.
How to cite: Cauzzi, C., Bieńkowski, J., Custódio, S., D'Amico, S., Evangelidis, C., Guéguen, P., Haberland, C., Haslinger, F., Lanzano, G., Ottemöller, L., Rondenay, S., Sleeman, R., and Strollo, A.: ORFEUS Services and Activities to Promote Observational Seismology in Europe and beyond, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6119, https://doi.org/10.5194/egusphere-egu21-6119, 2021.
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Please use the buttons below to download the presentation materials or to visit the external website where the presentation is linked. Regarding the external link, please note that Copernicus Meetings cannot accept any liability for the content and the website you will visit.
Forward to presentation link
You are going to open an external link to the presentation as indicated by the authors. Copernicus Meetings cannot accept any liability for the content and the website you will visit.
We are sorry, but presentations are only available for users who registered for the conference. Thank you.
ORFEUS (Observatories and Research Facilities for European Seismology; http://orfeus-eu.org/) is a non-profit foundation that promotes observational seismology in the Euro-Mediterranean area through the collection, archival and distribution of seismic waveform data, metadata, and closely related services and products. The data and services are collected or developed at national level by more than 60 contributing Institutions in Pan-Europe and further enhanced, integrated, standardized, homogenized and promoted through ORFEUS. Among the goals of ORFEUS are: (a) the development and coordination of waveform data products; (b) the coordination of a European data distribution system, and the support for seismic networks in archiving and exchanging digital seismic waveform data; (c) the encouragement of the adoption of best practices for seismic network operation, data quality control and FAIR data management; (d) the promotion of open access to seismic waveform data, products and services for the broader Earth science community. These goals are achieved through the development and maintenance of services targeted to a broad community of seismological data users, ranging from earth scientists to earthquake engineering practitioners. Two Service Management Committees (SMCs) are consolidated within ORFEUS devoted to managing, operating and developing (with the support of one or more Infrastructure Development Groups): (i) the European Integrated Data Archive (EIDA; https://www.orfeus-eu.org/data/eida/); and (ii) the European Strong-Motion databases (SM; https://www.orfeus-eu.org/data/strong/). New emerging groups within ORFEUS are focused on mobile pools and computational seismology. ORFEUS services currently provide access to the waveforms acquired by ~ 14,500 stations, including dense temporary experiments, with strong emphasis on open, high-quality data. Contributing to ORFEUS data archives means benefitting from long-term archival, state-of-the-art quality control, improved access, increased usage, and community participation. Access to data and products is ensured through state-of-the-art information and communication technologies, with strong emphasis on federated web services that considerably improve seamless user access to data gathered and/or distributed by the various ORFEUS institutions. Web services also facilitate the automation of downstream products. Particular attention is paid to adopting clear policies and licenses, and acknowledging the crucial role played by data providers / owners, who are part of the ORFEUS community. There are significant efforts by ORFEUS participating Institutions to enhance the existing services to tackle the challenges posed by the Big Data Era, with emphasis on data quality, improved user experience, and implementation of strategies for scalability, high-volume data access and archival. ORFEUS data and services are assessed and improved through the technical and scientific feedback of a User Advisory Group (UAG), which comprises European Earth scientists with expertise on a broad range of disciplines. All ORFEUS services are developed in coordination with EPOS and are largely integrated in the EPOS Data Access Portal, as ORFEUS is one of the founding Parties and fundamental contributors of the EPOS Thematic Core Service for Seismology (https://www.epos-eu.org/tcs/seismology). In this contribution, we selectively present the activities of ORFEUS, with the main aims of facilitating seismological data discovery and encouraging open data sharing and integration, as well as promoting best practice in observational seismology.
How to cite: Cauzzi, C., Bieńkowski, J., Custódio, S., D'Amico, S., Evangelidis, C., Guéguen, P., Haberland, C., Haslinger, F., Lanzano, G., Ottemöller, L., Rondenay, S., Sleeman, R., and Strollo, A.: ORFEUS Services and Activities to Promote Observational Seismology in Europe and beyond, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6119, https://doi.org/10.5194/egusphere-egu21-6119, 2021.
EGU21-15558 | vPICO presentations | SM2.3
The EIDA federator – a one-stop access to EIDA seismic data holdingsPhilipp Kaestli, Daniel Armbruster, and The EIDA Technical Committee
With the setup of EIDA (the European Integrated Data Archive https://www.orfeus-eu.org/data/eida/) in the framework of ORFEUS, and the implementation of FDSN-standardized web services, seismic waveform data and instrumentation metadata of most seismic networks and data centers in Europe became accessible in a homogeneous way. EIDA has augmented this with the WFcatalog service for waveform quality metadata, and a routing service to find out which data center offers data of which network, region, and type. However, while a distributed data archive has clear advantages for maintenance and quality control of the holdings, it complicates the life of researchers who wish to collect data archived across different data centers. To tackle this, EIDA has implemented the “federator” as a one-stop transparent gateway service to access the entire data holdings of EIDA.
To its users the federator acts just like a standard FDSN dataselect, station, or EIDA WFcatalog service, except for the fact that it can (due to a fully qualified internal routing cache) directly answer data requests on virtual networks.
Technically, the federator fulfills a user request by decomposing it into single stream epoch requests targeted at a single data center, collecting them, and re-assemble them to a single result.
This implementation has several technical advantages:
- It avoids response size limitations of EIDA member services, reducing limitations to those imposed by assembling cache space of the federator instance itself.
- It allows easy merging of partial responses using request sorting and concatenation, and reducing needs to interpret them. This reduces computational needs of the federator and allows high throughput of parallel user requests.
- It reduces the variability of requests to end member services. Thus, the federator can implement a reverse loopback cache and protect end node services from delivering redundant information and reducing their load.
- As partial results are quick, and delivered in small subunits, they can be streamed to the user more or less continuously, avoiding both service timeouts and throughput bottlenecks.
The advantage of having a one-stop data access for entire EIDA still comes with some limitations and shortcomings. Having requests which ultimately map to a single data center performed by the federator can be slower by that data center directly. FDSN-defined standard error codes sent by end member services have limited utility as they refer to a part of the request only. Finally, the federator currently does not provide access to restricted data.
Nevertheless, we believe that the one-stop data access compensates these shortcomings in many use cases.
Further documentation of the service is available with ORFEUS at http://www.orfeus-eu.org/data/eida/nodes/FEDERATOR/
How to cite: Kaestli, P., Armbruster, D., and EIDA Technical Committee, T.: The EIDA federator – a one-stop access to EIDA seismic data holdings, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15558, https://doi.org/10.5194/egusphere-egu21-15558, 2021.
Please decide on your access
Please use the buttons below to download the presentation materials or to visit the external website where the presentation is linked. Regarding the external link, please note that Copernicus Meetings cannot accept any liability for the content and the website you will visit.
Forward to presentation link
You are going to open an external link to the presentation as indicated by the authors. Copernicus Meetings cannot accept any liability for the content and the website you will visit.
We are sorry, but presentations are only available for users who registered for the conference. Thank you.
With the setup of EIDA (the European Integrated Data Archive https://www.orfeus-eu.org/data/eida/) in the framework of ORFEUS, and the implementation of FDSN-standardized web services, seismic waveform data and instrumentation metadata of most seismic networks and data centers in Europe became accessible in a homogeneous way. EIDA has augmented this with the WFcatalog service for waveform quality metadata, and a routing service to find out which data center offers data of which network, region, and type. However, while a distributed data archive has clear advantages for maintenance and quality control of the holdings, it complicates the life of researchers who wish to collect data archived across different data centers. To tackle this, EIDA has implemented the “federator” as a one-stop transparent gateway service to access the entire data holdings of EIDA.
To its users the federator acts just like a standard FDSN dataselect, station, or EIDA WFcatalog service, except for the fact that it can (due to a fully qualified internal routing cache) directly answer data requests on virtual networks.
Technically, the federator fulfills a user request by decomposing it into single stream epoch requests targeted at a single data center, collecting them, and re-assemble them to a single result.
This implementation has several technical advantages:
- It avoids response size limitations of EIDA member services, reducing limitations to those imposed by assembling cache space of the federator instance itself.
- It allows easy merging of partial responses using request sorting and concatenation, and reducing needs to interpret them. This reduces computational needs of the federator and allows high throughput of parallel user requests.
- It reduces the variability of requests to end member services. Thus, the federator can implement a reverse loopback cache and protect end node services from delivering redundant information and reducing their load.
- As partial results are quick, and delivered in small subunits, they can be streamed to the user more or less continuously, avoiding both service timeouts and throughput bottlenecks.
The advantage of having a one-stop data access for entire EIDA still comes with some limitations and shortcomings. Having requests which ultimately map to a single data center performed by the federator can be slower by that data center directly. FDSN-defined standard error codes sent by end member services have limited utility as they refer to a part of the request only. Finally, the federator currently does not provide access to restricted data.
Nevertheless, we believe that the one-stop data access compensates these shortcomings in many use cases.
Further documentation of the service is available with ORFEUS at http://www.orfeus-eu.org/data/eida/nodes/FEDERATOR/
How to cite: Kaestli, P., Armbruster, D., and EIDA Technical Committee, T.: The EIDA federator – a one-stop access to EIDA seismic data holdings, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15558, https://doi.org/10.5194/egusphere-egu21-15558, 2021.
Recently a set of quality control procedures have been implemented at the data center of the BGR (Seismic Survey of Germany). Goal is to identify unusual deviations in amplitude, timing and waveform caused by data and metadata errors. One of the strategies applied is to evaluate long term observations of seismic noise at specific frequencies at many stations. Particularly at lower frequencies this analysis is quite sensitive to amplitude changes. Also useful is the characterization of station sites by looking at anthropogenic noise patterns in a frequency range of 4-14 Hz. The sites show fundamental differences when looking at daily and weekly noise patterns and some also have specific responses to local wind. Changes in the noise patterns indicate changes in the environment or uncompensated hardware or metadata changes. Furthermore, correlations of teleseismic signals reveal possible inconsistencies in waveform shape, travel time residuals and amplitudes within the station set. When applied systematically a statistical analysis of the correlation parameters indicates long term deviations in these three observables. Finally, a formal check of the transfer function given in the metadata is implemented to identify wrong settings in the normalization and illegal specifications in the poles and zeros (conjugate complex pairs and negative real part at poles). These implemented measures help us to keep our data at a high quality level and to react quickly on the occurrence of hardware and metadata errors.
How to cite: Stammler, K.: Waveform quality checks at German networks, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5889, https://doi.org/10.5194/egusphere-egu21-5889, 2021.
Please decide on your access
Please use the buttons below to download the presentation materials or to visit the external website where the presentation is linked. Regarding the external link, please note that Copernicus Meetings cannot accept any liability for the content and the website you will visit.
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We are sorry, but presentations are only available for users who registered for the conference. Thank you.
Recently a set of quality control procedures have been implemented at the data center of the BGR (Seismic Survey of Germany). Goal is to identify unusual deviations in amplitude, timing and waveform caused by data and metadata errors. One of the strategies applied is to evaluate long term observations of seismic noise at specific frequencies at many stations. Particularly at lower frequencies this analysis is quite sensitive to amplitude changes. Also useful is the characterization of station sites by looking at anthropogenic noise patterns in a frequency range of 4-14 Hz. The sites show fundamental differences when looking at daily and weekly noise patterns and some also have specific responses to local wind. Changes in the noise patterns indicate changes in the environment or uncompensated hardware or metadata changes. Furthermore, correlations of teleseismic signals reveal possible inconsistencies in waveform shape, travel time residuals and amplitudes within the station set. When applied systematically a statistical analysis of the correlation parameters indicates long term deviations in these three observables. Finally, a formal check of the transfer function given in the metadata is implemented to identify wrong settings in the normalization and illegal specifications in the poles and zeros (conjugate complex pairs and negative real part at poles). These implemented measures help us to keep our data at a high quality level and to react quickly on the occurrence of hardware and metadata errors.
How to cite: Stammler, K.: Waveform quality checks at German networks, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5889, https://doi.org/10.5194/egusphere-egu21-5889, 2021.
EGU21-12436 | vPICO presentations | SM2.3
Improving data, metadata and service quality within Résif-SIJonathan Schaeffer, Fabien Engels, Marc Grunberg, Christophe Maron, Constanza Pardo, Jean-Marie Saurel, David Wolyniec, Patrick Arnoul, Philippe Bollard, Jérôme Touvier, Jérôme Chèze, Fabrice Peix, and Catherine Pequegnat
Résif, the French seismological and geodetic network, was launched in 2009 in an effort to develop, modernize, and centralize geophysical observation of the Earth’s interior. This French research infrastructure uses both permanent and mobile instrument networks for continuous seismological, geodetic and gravimetric measurements.
Résif-SI is the Information System that manages, validates and distributes seismological data from Résif.
The construction of Résif-SI has lead to a federated organisation gathering several data and metadata producers (Nodes) and a national Seismological Data Centre.
The Résif Seismological Data Centre is one of 19 global centres distributing data and metadata in formats and using protocols which comply with International Federation of Digital Seismograph Networks (FDSN) standards. It is also one of the eleven nodes in EIDA, the European virtual data centre and seismic data portal in the European Plate Observing System (EPOS) framework.
Inside Résif-SI, each Node has it's specificities and dedicated procedures in order to manage and validate the data and metadata workflow from the station instruments to the Résif Seismological Data Centre.
To meet the expectations and needs of the end user in terms of data quality, metadata consistency and service availability, Résif-SI operates a complex set of quality enhancement operations.
This contribution will present the quality expectations that are in the core of Résif-SI, and show the methods and tools that help us meeting the expectations, and that could be of interest for the rest of the community.
We will then list some of our quality improvement projets and the expected results.
How to cite: Schaeffer, J., Engels, F., Grunberg, M., Maron, C., Pardo, C., Saurel, J.-M., Wolyniec, D., Arnoul, P., Bollard, P., Touvier, J., Chèze, J., Peix, F., and Pequegnat, C.: Improving data, metadata and service quality within Résif-SI, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12436, https://doi.org/10.5194/egusphere-egu21-12436, 2021.
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Résif, the French seismological and geodetic network, was launched in 2009 in an effort to develop, modernize, and centralize geophysical observation of the Earth’s interior. This French research infrastructure uses both permanent and mobile instrument networks for continuous seismological, geodetic and gravimetric measurements.
Résif-SI is the Information System that manages, validates and distributes seismological data from Résif.
The construction of Résif-SI has lead to a federated organisation gathering several data and metadata producers (Nodes) and a national Seismological Data Centre.
The Résif Seismological Data Centre is one of 19 global centres distributing data and metadata in formats and using protocols which comply with International Federation of Digital Seismograph Networks (FDSN) standards. It is also one of the eleven nodes in EIDA, the European virtual data centre and seismic data portal in the European Plate Observing System (EPOS) framework.
Inside Résif-SI, each Node has it's specificities and dedicated procedures in order to manage and validate the data and metadata workflow from the station instruments to the Résif Seismological Data Centre.
To meet the expectations and needs of the end user in terms of data quality, metadata consistency and service availability, Résif-SI operates a complex set of quality enhancement operations.
This contribution will present the quality expectations that are in the core of Résif-SI, and show the methods and tools that help us meeting the expectations, and that could be of interest for the rest of the community.
We will then list some of our quality improvement projets and the expected results.
How to cite: Schaeffer, J., Engels, F., Grunberg, M., Maron, C., Pardo, C., Saurel, J.-M., Wolyniec, D., Arnoul, P., Bollard, P., Touvier, J., Chèze, J., Peix, F., and Pequegnat, C.: Improving data, metadata and service quality within Résif-SI, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12436, https://doi.org/10.5194/egusphere-egu21-12436, 2021.
EGU21-263 | vPICO presentations | SM2.3
Continuous Improvement in the Performance and Operations of the Global Seismographic Network (GSN)Katrin Hafner, Dave Wilson, Rob Mellors, and Pete Davis
The decades long recordings of high-quality open data from the Global Seismographic Network have facilitated studies of earth structure and earthquake processes, as well as monitoring of earthquakes and explosions worldwide. These data have also enabled a wide range of transformative, cross-disciplinary research that far exceeded the original expectations and design goals of the network, including studies of slow earthquakes, landslides, the Earth’s “hum”, glacial earthquakes, sea-state, climate change, and induced seismicity.
The GSN continues to produce high quality waveform data, metadata, and multiple data quality metrics such as timing quality and noise levels. This requires encouraging equipment vendors to develop modern instrumentation, upgrading the stations with new seismic sensors and infrastructure, implementing consistent and well documented calibrations, and monitoring of noise performance. A Design Goals working group is convening to evaluate how well the GSN has met its original 1985 and 2002 goals, as well as how the network should evolve in order to be able to meet the requirements for enabling new research and monitoring capabilities.
In collaboration with GEOFON and GEOSCOPE the GSN is also reviewing the current global distribution and performance of very broadband and broadband stations that comprise these three networks. We are working to exchange our expertise and experience about new technologies and deployment techniques, and to identify regions where we could collaborate to make operations more efficient, where current efforts are overlapping or where we have similar needs for relocating stations.
How to cite: Hafner, K., Wilson, D., Mellors, R., and Davis, P.: Continuous Improvement in the Performance and Operations of the Global Seismographic Network (GSN), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-263, https://doi.org/10.5194/egusphere-egu21-263, 2021.
The decades long recordings of high-quality open data from the Global Seismographic Network have facilitated studies of earth structure and earthquake processes, as well as monitoring of earthquakes and explosions worldwide. These data have also enabled a wide range of transformative, cross-disciplinary research that far exceeded the original expectations and design goals of the network, including studies of slow earthquakes, landslides, the Earth’s “hum”, glacial earthquakes, sea-state, climate change, and induced seismicity.
The GSN continues to produce high quality waveform data, metadata, and multiple data quality metrics such as timing quality and noise levels. This requires encouraging equipment vendors to develop modern instrumentation, upgrading the stations with new seismic sensors and infrastructure, implementing consistent and well documented calibrations, and monitoring of noise performance. A Design Goals working group is convening to evaluate how well the GSN has met its original 1985 and 2002 goals, as well as how the network should evolve in order to be able to meet the requirements for enabling new research and monitoring capabilities.
In collaboration with GEOFON and GEOSCOPE the GSN is also reviewing the current global distribution and performance of very broadband and broadband stations that comprise these three networks. We are working to exchange our expertise and experience about new technologies and deployment techniques, and to identify regions where we could collaborate to make operations more efficient, where current efforts are overlapping or where we have similar needs for relocating stations.
How to cite: Hafner, K., Wilson, D., Mellors, R., and Davis, P.: Continuous Improvement in the Performance and Operations of the Global Seismographic Network (GSN), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-263, https://doi.org/10.5194/egusphere-egu21-263, 2021.
EGU21-8510 | vPICO presentations | SM2.3
The national seismic network for the Maltese islands: Update 2021Pauline Galea, Matthew Agius, George Bozionelos, Sebastiano D'Amico, and Daniela Farrugia
The Maltese islands are a small country 15 km wide by 30 km long located about 100 km south of Sicily, Italy. Since 2015 Malta has set up a national seismic network. The primary aim of this network is to monitor in real-time and to locate more accurately the seismicity close to the islands and the seismicity in the Sicily Channel, offshore between Sicily, Tunisia and Libya. This Channel presents a range of interesting and complex tectonic processes that have developed in response to various regional stress fields mainly as a result of the collision between the African plate with Europe. The Maltese islands are known to have been affected by a number of earthquakes originating in the Channel, with some of these events estimated to be very close to the islands.
The seismotectonic characteristics of the Sicily channel, particularly south of the Maltese islands, is not well understood. This situation is being partially addressed through an increase in the number of seismic stations on the Maltese archipelago. The Malta Seismic Network (FDSN code ML), managed by the Seismic Monitoring and Research Group, within the Department of Geosciences, University of Malta, currently comprises 8 broadband, 3-component stations over an area slightly exceeding 300 km2. We present a technical description of the MSN including quality control tests such as spectral analysis (Power Spectral Density and HVSR), station orientations and timings as well as examples of local and regional earthquakes recorded on the network. We describe the upgrades to real-time data transmission and archiving, and automated epicentre location for continuous seismic monitoring using the local network amalgamated with a virtual seismic network to monitor the seismicity in the extended Mediterranean region. Such a dense national network, besides improving epicentral location in the Sicily Channel, is providing valuable information on microearthquake activity known to occur in close proximity to the islands, which has been very difficult to study in the past. It also provides an important tool for analysing site response and site amplification related to underlying geology, which constitutes a major component of seismic hazard analysis on the islands. Furthermore, the increase in seismic stations to the seismic monitoring system provides more robust earthquake estimates for the tsunami monitoring/simulation system.
Funding for stations was provided by Interreg Italia-Malta projects (SIMIT and SIMIT-THARSY, Codes B1-2.19/11 and C1-3.2-57) and by Transport Malta.
How to cite: Galea, P., Agius, M., Bozionelos, G., D'Amico, S., and Farrugia, D.: The national seismic network for the Maltese islands: Update 2021, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8510, https://doi.org/10.5194/egusphere-egu21-8510, 2021.
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The Maltese islands are a small country 15 km wide by 30 km long located about 100 km south of Sicily, Italy. Since 2015 Malta has set up a national seismic network. The primary aim of this network is to monitor in real-time and to locate more accurately the seismicity close to the islands and the seismicity in the Sicily Channel, offshore between Sicily, Tunisia and Libya. This Channel presents a range of interesting and complex tectonic processes that have developed in response to various regional stress fields mainly as a result of the collision between the African plate with Europe. The Maltese islands are known to have been affected by a number of earthquakes originating in the Channel, with some of these events estimated to be very close to the islands.
The seismotectonic characteristics of the Sicily channel, particularly south of the Maltese islands, is not well understood. This situation is being partially addressed through an increase in the number of seismic stations on the Maltese archipelago. The Malta Seismic Network (FDSN code ML), managed by the Seismic Monitoring and Research Group, within the Department of Geosciences, University of Malta, currently comprises 8 broadband, 3-component stations over an area slightly exceeding 300 km2. We present a technical description of the MSN including quality control tests such as spectral analysis (Power Spectral Density and HVSR), station orientations and timings as well as examples of local and regional earthquakes recorded on the network. We describe the upgrades to real-time data transmission and archiving, and automated epicentre location for continuous seismic monitoring using the local network amalgamated with a virtual seismic network to monitor the seismicity in the extended Mediterranean region. Such a dense national network, besides improving epicentral location in the Sicily Channel, is providing valuable information on microearthquake activity known to occur in close proximity to the islands, which has been very difficult to study in the past. It also provides an important tool for analysing site response and site amplification related to underlying geology, which constitutes a major component of seismic hazard analysis on the islands. Furthermore, the increase in seismic stations to the seismic monitoring system provides more robust earthquake estimates for the tsunami monitoring/simulation system.
Funding for stations was provided by Interreg Italia-Malta projects (SIMIT and SIMIT-THARSY, Codes B1-2.19/11 and C1-3.2-57) and by Transport Malta.
How to cite: Galea, P., Agius, M., Bozionelos, G., D'Amico, S., and Farrugia, D.: The national seismic network for the Maltese islands: Update 2021, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8510, https://doi.org/10.5194/egusphere-egu21-8510, 2021.
EGU21-6195 | vPICO presentations | SM2.3
Residual analysis of large strong-motion flatfiles as a tool for detecting data error and anomaliesClaudia Mascandola, Giovanni Lanzano, and Francesca Pacor
The rapid increase of seismic waveforms, due to the increment of seismic stations and continuous real-time streaming to data centres, leads to the need for automatic procedures aimed at supporting data processing and data quality control. In this study, we propose a semi-automatic procedure for the consistency check of large strong-motion datasets, classifying the anomalies observed on the residuals analysis and identifying the possible causes.
The data collected in the strong-motion databases are usually arranged as parametric tables (called flatfiles), used to disseminate the Intensity Measures (IMs) and the associated metadata of the processed waveforms. This is the current practice for the ITalian ACcelerometric Archive (ITACA, D’Amico et al., 2020) and Engineering Strong Motion (ESM; Lanzano et al. 2019a) databases. The adopted criteria for flatfile compilation are designed to collect IMs and related metadata in a uniform, updated, and traceable way, with the aim of providing datasets useful to develop Ground Motion Models (GMMs) for Probabilistic Seismic Hazard Assessment (PSHA) and engineering applications. Therefore, the consistency check of the flatfiles is a crucial task to improve the quality of the products provided by the waveform services.
The proposed procedure is based on the residual distributions obtained from ad-hoc ground motion prediction equations for the ordinates of the 5% damped acceleration response spectra. In this study, we focus on the active shallow crust events in ITACA, considering the ITA18 ground motion model (Lanzano et al., 2019b) as a reference for Italy. The total residuals, computed as logarithm difference between observations and predictions, are decomposed in between-event, between-station and event-and-station corrected residuals by applying a mixed-effect regression (Bates et al., 2015). This is the common practice for the (partial) removal of the ergodic assumption in empirical GMMs (e.g., Stafford 2014), where the contribution of the systematic corrective effects of event and station on aleatory variability are identified and shifted to the epistemic uncertainty. Afterward, the proposed procedure is applied to raise a warning in case of anomalous residual values. Warnings are provided when the normalized residuals exceed a certain threshold, in three ranges of periods (i.e., 0.01-0.15 s, 0.15-1 s, 1-5 s). The causes of warnings may be several and may concern the event, the site, the waveform, or a combination of them. Among the possible sources of anomalous trends, the more common are: preliminary or inaccurate event localization or magnitude, wrong soil category assigned based on proxies, misleading tectonic regime assigned to the earthquake, and fault directivity that may cause strong-ground motion amplification in certain directions. Warnings may also raise for peculiarities in the site-response (e.g., large amplifications/de-amplifications at certain frequency-bands) and to the occurrence of near-source effects in the waveforms (see Pacor et al., 2018). Based on the raised warnings, a decision tree classifier is developed to identify the common anomaly sources and to support the consistency check of the semi-automatic procedure.
This study may help to enhance the waveform services and related products, besides reducing the variability of ground motion models and guiding decisions for site characterization studies and network maintenance.
How to cite: Mascandola, C., Lanzano, G., and Pacor, F.: Residual analysis of large strong-motion flatfiles as a tool for detecting data error and anomalies, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6195, https://doi.org/10.5194/egusphere-egu21-6195, 2021.
Please decide on your access
Please use the buttons below to download the presentation materials or to visit the external website where the presentation is linked. Regarding the external link, please note that Copernicus Meetings cannot accept any liability for the content and the website you will visit.
Forward to presentation link
You are going to open an external link to the presentation as indicated by the authors. Copernicus Meetings cannot accept any liability for the content and the website you will visit.
We are sorry, but presentations are only available for users who registered for the conference. Thank you.
The rapid increase of seismic waveforms, due to the increment of seismic stations and continuous real-time streaming to data centres, leads to the need for automatic procedures aimed at supporting data processing and data quality control. In this study, we propose a semi-automatic procedure for the consistency check of large strong-motion datasets, classifying the anomalies observed on the residuals analysis and identifying the possible causes.
The data collected in the strong-motion databases are usually arranged as parametric tables (called flatfiles), used to disseminate the Intensity Measures (IMs) and the associated metadata of the processed waveforms. This is the current practice for the ITalian ACcelerometric Archive (ITACA, D’Amico et al., 2020) and Engineering Strong Motion (ESM; Lanzano et al. 2019a) databases. The adopted criteria for flatfile compilation are designed to collect IMs and related metadata in a uniform, updated, and traceable way, with the aim of providing datasets useful to develop Ground Motion Models (GMMs) for Probabilistic Seismic Hazard Assessment (PSHA) and engineering applications. Therefore, the consistency check of the flatfiles is a crucial task to improve the quality of the products provided by the waveform services.
The proposed procedure is based on the residual distributions obtained from ad-hoc ground motion prediction equations for the ordinates of the 5% damped acceleration response spectra. In this study, we focus on the active shallow crust events in ITACA, considering the ITA18 ground motion model (Lanzano et al., 2019b) as a reference for Italy. The total residuals, computed as logarithm difference between observations and predictions, are decomposed in between-event, between-station and event-and-station corrected residuals by applying a mixed-effect regression (Bates et al., 2015). This is the common practice for the (partial) removal of the ergodic assumption in empirical GMMs (e.g., Stafford 2014), where the contribution of the systematic corrective effects of event and station on aleatory variability are identified and shifted to the epistemic uncertainty. Afterward, the proposed procedure is applied to raise a warning in case of anomalous residual values. Warnings are provided when the normalized residuals exceed a certain threshold, in three ranges of periods (i.e., 0.01-0.15 s, 0.15-1 s, 1-5 s). The causes of warnings may be several and may concern the event, the site, the waveform, or a combination of them. Among the possible sources of anomalous trends, the more common are: preliminary or inaccurate event localization or magnitude, wrong soil category assigned based on proxies, misleading tectonic regime assigned to the earthquake, and fault directivity that may cause strong-ground motion amplification in certain directions. Warnings may also raise for peculiarities in the site-response (e.g., large amplifications/de-amplifications at certain frequency-bands) and to the occurrence of near-source effects in the waveforms (see Pacor et al., 2018). Based on the raised warnings, a decision tree classifier is developed to identify the common anomaly sources and to support the consistency check of the semi-automatic procedure.
This study may help to enhance the waveform services and related products, besides reducing the variability of ground motion models and guiding decisions for site characterization studies and network maintenance.
How to cite: Mascandola, C., Lanzano, G., and Pacor, F.: Residual analysis of large strong-motion flatfiles as a tool for detecting data error and anomalies, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6195, https://doi.org/10.5194/egusphere-egu21-6195, 2021.
EGU21-459 | vPICO presentations | SM2.3
Evaluation of seismic sensor orientations in the full moment tensor inversion resultsMohammadreza Jamalreyhani, Mehdi Rezapour, and Pınar Büyükakpınar
Three-component seismograms recorded by seismic sensors are momentous data to study the source mechanism of earthquakes. Correct orientation of sensors relative to the true north is important for the waveform inversion techniques. Yet, the non-precise orientation of horizontal components of seismic sensors has been reported in many seismic networks worldwide. In this study, we evaluated the effect of sensor misorientations (deviations from the true north) on time-domain moment tensor inversion, relying on the recent sensor orientation studies on broadband seismic networks in Iran and Turkey. We selected several well-recorded countrywide local and regional moderate magnitude earthquakes, which are associated with the tectonic events, in the time period of 2012-2019. We calculated the moment tensor inversion of those events before and after applying the orientation correction using a Bayesian bootstrap-based probabilistic method. This leads to reaching the uncertainties and trade-offs of parameters and helps to stabilize the inversion. Our analysis shows that in the presence of misoriented sensors, an approximate solution is achievable. However, this includes the remarkable uncertainties in inverted parameters and makes the reliable determination of the moment tensor’s elements challenging. We also found an additional significant non-double couple component while using the misoriented radial and transverse components. Results show that the misfit and uncertainties decrease significantly when sensor orientation correction applied. We suggest that the evaluation of metadata should be part of data processing in seismic networks and data centers, to report more reliable moment tensor solutions.
How to cite: Jamalreyhani, M., Rezapour, M., and Büyükakpınar, P.: Evaluation of seismic sensor orientations in the full moment tensor inversion results, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-459, https://doi.org/10.5194/egusphere-egu21-459, 2021.
Please decide on your access
Please use the buttons below to download the presentation materials or to visit the external website where the presentation is linked. Regarding the external link, please note that Copernicus Meetings cannot accept any liability for the content and the website you will visit.
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We are sorry, but presentations are only available for users who registered for the conference. Thank you.
Three-component seismograms recorded by seismic sensors are momentous data to study the source mechanism of earthquakes. Correct orientation of sensors relative to the true north is important for the waveform inversion techniques. Yet, the non-precise orientation of horizontal components of seismic sensors has been reported in many seismic networks worldwide. In this study, we evaluated the effect of sensor misorientations (deviations from the true north) on time-domain moment tensor inversion, relying on the recent sensor orientation studies on broadband seismic networks in Iran and Turkey. We selected several well-recorded countrywide local and regional moderate magnitude earthquakes, which are associated with the tectonic events, in the time period of 2012-2019. We calculated the moment tensor inversion of those events before and after applying the orientation correction using a Bayesian bootstrap-based probabilistic method. This leads to reaching the uncertainties and trade-offs of parameters and helps to stabilize the inversion. Our analysis shows that in the presence of misoriented sensors, an approximate solution is achievable. However, this includes the remarkable uncertainties in inverted parameters and makes the reliable determination of the moment tensor’s elements challenging. We also found an additional significant non-double couple component while using the misoriented radial and transverse components. Results show that the misfit and uncertainties decrease significantly when sensor orientation correction applied. We suggest that the evaluation of metadata should be part of data processing in seismic networks and data centers, to report more reliable moment tensor solutions.
How to cite: Jamalreyhani, M., Rezapour, M., and Büyükakpınar, P.: Evaluation of seismic sensor orientations in the full moment tensor inversion results, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-459, https://doi.org/10.5194/egusphere-egu21-459, 2021.
EGU21-13999 | vPICO presentations | SM2.3
Determining OBS clock drift using ambient seismic noiseDavid Naranjo, Laura Parisi, Philippe Jousset, Cornelis Weemstra, and Sigurjón Jónsson
Accurate timing of seismic records is essential for almost all applications in seismology. Wrong timing of the waveforms may result in incorrect Earth models and/or inaccurate earthquake locations. As such, it may render interpretations of underground processes incorrect. Ocean bottom seismometers (OBSs) experience clock drifts due to their inability to synchronize with a GNSS signal (with the correct reference time), since electromagnetic signals are unable to propagate efficiently in water. As OBSs generally operate in relatively stable ambient temperature, the timing deviation is usually assumed to be linear. Therefore, the time corrections can be estimated through GPS synchronization before deployment and after recovery of the instrument. However, if the instrument has run out of power prior to recovery (i.e., due to the battery being dead at the time of recovery), the timing error at the end of the deployment cannot be determined. In addition, the drift may not be linear, e.g., due to rapid temperature drop while the OBS sinks to the seabed. Here we present an algorithm that recovers the linear clock drift, as well as a potential timing error at the onset.
The algorithm presented in this study exploits seismic interferometry (SI). Specifically, time-lapse (averaged) cross-correlations of ambient seismic noise are computed. As such, virtual-source responses, which are generally dominated by the recorded surface waves, are retrieved. These interferometric responses generate two virtual sources: a causal wave (arriving at a positive time) and an acausal wave (arriving at a negative time). Under favorable conditions, both interferometric responses approach the surface-wave part of the medium's Green's function. Therefore, it is possible to calculate the clock drift for each station by exploiting the time-symmetry between the causal and acausal waves. For this purpose, the clock drift is calculated by measuring the differential arrival times of the causal and acausal waves for a large number of receiver-receiver pairs and computing the drift by carrying-out a least-squares inversion. The methodology described is applied to time-lapse cross-correlations of ambient seismic noise recorded on and around the Reykjanes peninsula, SW Iceland. The stations used for the analysis were deployed in the context of IMAGE (Integrated Methods for Advanced Geothermal Exploration) and consisted of 30 on-land stations and 24 ocean bottom seismometers (OBSs). The seismic activity was recorded from spring 2014 until August 2015 on an area of around 100 km in diameter (from the tip of the Reykjanes peninsula).
How to cite: Naranjo, D., Parisi, L., Jousset, P., Weemstra, C., and Jónsson, S.: Determining OBS clock drift using ambient seismic noise , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13999, https://doi.org/10.5194/egusphere-egu21-13999, 2021.
Please decide on your access
Please use the buttons below to download the presentation materials or to visit the external website where the presentation is linked. Regarding the external link, please note that Copernicus Meetings cannot accept any liability for the content and the website you will visit.
Forward to presentation link
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We are sorry, but presentations are only available for users who registered for the conference. Thank you.
Accurate timing of seismic records is essential for almost all applications in seismology. Wrong timing of the waveforms may result in incorrect Earth models and/or inaccurate earthquake locations. As such, it may render interpretations of underground processes incorrect. Ocean bottom seismometers (OBSs) experience clock drifts due to their inability to synchronize with a GNSS signal (with the correct reference time), since electromagnetic signals are unable to propagate efficiently in water. As OBSs generally operate in relatively stable ambient temperature, the timing deviation is usually assumed to be linear. Therefore, the time corrections can be estimated through GPS synchronization before deployment and after recovery of the instrument. However, if the instrument has run out of power prior to recovery (i.e., due to the battery being dead at the time of recovery), the timing error at the end of the deployment cannot be determined. In addition, the drift may not be linear, e.g., due to rapid temperature drop while the OBS sinks to the seabed. Here we present an algorithm that recovers the linear clock drift, as well as a potential timing error at the onset.
The algorithm presented in this study exploits seismic interferometry (SI). Specifically, time-lapse (averaged) cross-correlations of ambient seismic noise are computed. As such, virtual-source responses, which are generally dominated by the recorded surface waves, are retrieved. These interferometric responses generate two virtual sources: a causal wave (arriving at a positive time) and an acausal wave (arriving at a negative time). Under favorable conditions, both interferometric responses approach the surface-wave part of the medium's Green's function. Therefore, it is possible to calculate the clock drift for each station by exploiting the time-symmetry between the causal and acausal waves. For this purpose, the clock drift is calculated by measuring the differential arrival times of the causal and acausal waves for a large number of receiver-receiver pairs and computing the drift by carrying-out a least-squares inversion. The methodology described is applied to time-lapse cross-correlations of ambient seismic noise recorded on and around the Reykjanes peninsula, SW Iceland. The stations used for the analysis were deployed in the context of IMAGE (Integrated Methods for Advanced Geothermal Exploration) and consisted of 30 on-land stations and 24 ocean bottom seismometers (OBSs). The seismic activity was recorded from spring 2014 until August 2015 on an area of around 100 km in diameter (from the tip of the Reykjanes peninsula).
How to cite: Naranjo, D., Parisi, L., Jousset, P., Weemstra, C., and Jónsson, S.: Determining OBS clock drift using ambient seismic noise , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13999, https://doi.org/10.5194/egusphere-egu21-13999, 2021.
EGU21-3195 | vPICO presentations | SM2.3
Detection of possible seismic station phase reversals using parametric data from seismological bulletinsKonstantinos Lentas
A simple and fast technique to detect systematic changes in the performance of seismic stations by using parametric data is being presented. The methodology is based on a simple principal, notably, quantifying the goodness of fit of first motion manually picked polarities from seismological bulletins versus available earthquake mechanism solutions over time. The probability of the reporting polarity data fitting (and not fitting) source mechanisms is quantified by calculating the probability distribution of several Bernoulli trials over a randomly perturbed set of hypocentres and velocity models for each earthquake mechanism - station polarity combination. The method was applied to the registered seismic stations in the bulletin of the International Seismological Centre (ISC) after grouping each polarity pick by reporting agency, using data from the past two decades. The overall agreement of first motion polarities against source mechanisms is found to be good with a few cases of seismic stations showing indications of systematic phase reversals over certain time periods. Specifically, results were obtained for 50% of the registered stations at the ISC, and from these stations 70% show reliable operation during the operational time period under investigation, with only 3% showing the opposite, and 7% showing evidence of systematic changes in the quality of the reported first motion polarities. The rest showed great variability over short periods of time, which does not allow one to draw any conclusions. Comparing waveform data with the associated reported polarities revealed a mixture of cases of either questionable picking or true station phase reversals.
How to cite: Lentas, K.: Detection of possible seismic station phase reversals using parametric data from seismological bulletins, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3195, https://doi.org/10.5194/egusphere-egu21-3195, 2021.
A simple and fast technique to detect systematic changes in the performance of seismic stations by using parametric data is being presented. The methodology is based on a simple principal, notably, quantifying the goodness of fit of first motion manually picked polarities from seismological bulletins versus available earthquake mechanism solutions over time. The probability of the reporting polarity data fitting (and not fitting) source mechanisms is quantified by calculating the probability distribution of several Bernoulli trials over a randomly perturbed set of hypocentres and velocity models for each earthquake mechanism - station polarity combination. The method was applied to the registered seismic stations in the bulletin of the International Seismological Centre (ISC) after grouping each polarity pick by reporting agency, using data from the past two decades. The overall agreement of first motion polarities against source mechanisms is found to be good with a few cases of seismic stations showing indications of systematic phase reversals over certain time periods. Specifically, results were obtained for 50% of the registered stations at the ISC, and from these stations 70% show reliable operation during the operational time period under investigation, with only 3% showing the opposite, and 7% showing evidence of systematic changes in the quality of the reported first motion polarities. The rest showed great variability over short periods of time, which does not allow one to draw any conclusions. Comparing waveform data with the associated reported polarities revealed a mixture of cases of either questionable picking or true station phase reversals.
How to cite: Lentas, K.: Detection of possible seismic station phase reversals using parametric data from seismological bulletins, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3195, https://doi.org/10.5194/egusphere-egu21-3195, 2021.
EGU21-7997 | vPICO presentations | SM2.3
Robust, an Earthquake Early Warning System in the Lower Rhine Embayment, GermanyBita Najdahmadi, Marco Pilz, Dino Bindi, Hoby Njara Tendrisoa Razafindrakoto, Adrien Oth, and Fabrice Cotton
The Lower Rhine Embayment in western Germany is one of the most important areas of earthquake recurrence north of the Alps, facing a moderate level of seismic hazard in the European context but a significant level of risk due to a large number of important industrial infrastructures. In this context, the project ROBUST aims at designing a user-oriented hybrid earthquake early warning and rapid response system where regional seismic monitoring is combined with smart, on-site sensors, resulting in the implementation of decentralized early warning procedures.
One of the research areas of this project deals with finding an optimal regional seismic network arrangement. With the optimally compacted network, strong ground movements can be detected quickly and reliably. In this work simulated scenario earthquakes in the area are used with an optimization approach in order to densify the existing sparse network through the installation of additional decentralized measuring stations. Genetic algorithms are used to design efficient EEW networks, computing optimal station locations and trigger thresholds in recorded ground acceleration. By minimizing the cost function, a comparison of the best earthquake early warning system designs is performed and the potential usefulness of existing stations in the region is considered as will be presented in the meeting.
How to cite: Najdahmadi, B., Pilz, M., Bindi, D., Njara Tendrisoa Razafindrakoto, H., Oth, A., and Cotton, F.: Robust, an Earthquake Early Warning System in the Lower Rhine Embayment, Germany, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7997, https://doi.org/10.5194/egusphere-egu21-7997, 2021.
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The Lower Rhine Embayment in western Germany is one of the most important areas of earthquake recurrence north of the Alps, facing a moderate level of seismic hazard in the European context but a significant level of risk due to a large number of important industrial infrastructures. In this context, the project ROBUST aims at designing a user-oriented hybrid earthquake early warning and rapid response system where regional seismic monitoring is combined with smart, on-site sensors, resulting in the implementation of decentralized early warning procedures.
One of the research areas of this project deals with finding an optimal regional seismic network arrangement. With the optimally compacted network, strong ground movements can be detected quickly and reliably. In this work simulated scenario earthquakes in the area are used with an optimization approach in order to densify the existing sparse network through the installation of additional decentralized measuring stations. Genetic algorithms are used to design efficient EEW networks, computing optimal station locations and trigger thresholds in recorded ground acceleration. By minimizing the cost function, a comparison of the best earthquake early warning system designs is performed and the potential usefulness of existing stations in the region is considered as will be presented in the meeting.
How to cite: Najdahmadi, B., Pilz, M., Bindi, D., Njara Tendrisoa Razafindrakoto, H., Oth, A., and Cotton, F.: Robust, an Earthquake Early Warning System in the Lower Rhine Embayment, Germany, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7997, https://doi.org/10.5194/egusphere-egu21-7997, 2021.
EGU21-13884 | vPICO presentations | SM2.3
A More Capable Array InfrastructureTim Parker, Val Hamilton, and Andrew Moores
A more capable infrastructure would enable greater monitoring capabilities. We propose a deeper grouted casing and using borehole best practices to ensure improved coupling and a better environment for reducing site and emplacement noise in both high and low frequencies and specifically the horizontal component recording. Casing emplacements should be a one to two day operation for installation. Stations using the new Trillium T120PH Slim or dual sensor Cascadia Slim in a single cased hole will have wider bandwidth, larger dynamic range, resiliency and low noise recording that would enable new observations along with higher sensitivity for local earthquake recording. Dry cased holes are the standard for long term geophysical observatories and a better investment when all the associated costs of operating observatories are considered. Facilities are both renewing old stations and trying to improve array performance through these new instruments. This line of Trillium borehole instruments are very robust with low SWaP (Size, Weight and Power), a 300 meter continuous immersion rating and of corrosion resistant construction. These sensors can be installed in bedding material or with a hole lock and are compatible with the ultimate installation, grouting it in!
How to cite: Parker, T., Hamilton, V., and Moores, A.: A More Capable Array Infrastructure, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13884, https://doi.org/10.5194/egusphere-egu21-13884, 2021.
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A more capable infrastructure would enable greater monitoring capabilities. We propose a deeper grouted casing and using borehole best practices to ensure improved coupling and a better environment for reducing site and emplacement noise in both high and low frequencies and specifically the horizontal component recording. Casing emplacements should be a one to two day operation for installation. Stations using the new Trillium T120PH Slim or dual sensor Cascadia Slim in a single cased hole will have wider bandwidth, larger dynamic range, resiliency and low noise recording that would enable new observations along with higher sensitivity for local earthquake recording. Dry cased holes are the standard for long term geophysical observatories and a better investment when all the associated costs of operating observatories are considered. Facilities are both renewing old stations and trying to improve array performance through these new instruments. This line of Trillium borehole instruments are very robust with low SWaP (Size, Weight and Power), a 300 meter continuous immersion rating and of corrosion resistant construction. These sensors can be installed in bedding material or with a hole lock and are compatible with the ultimate installation, grouting it in!
How to cite: Parker, T., Hamilton, V., and Moores, A.: A More Capable Array Infrastructure, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13884, https://doi.org/10.5194/egusphere-egu21-13884, 2021.
SM3.1 – Ambient seismic noise seismology: Topics, targets, tools & techniques
EGU21-14617 | vPICO presentations | SM3.1 | Highlight
The Polarization of Ambient Noise on MarsÉléonore Stutzmann, Martin Schimmel, Philippe Lognonné, Anna Horleston, Savas Ceylan, Martin van Driel, Simon Stahler, Bruce Banerdt, Marie Calvet, Constantinos Charalambous, John Clinton, Mélanie Drilleau, Lucile Fayon, Raphael Garcia, Alice Jacob, Taichi Kawamura, Balthazar Kenda, Ludovic Margerin, Naomie Murdoch, and Marc Panning and the Insight group
Seismic noise recorded at the surface of Mars has been monitored since February 2019, using the InSight seismometers.This noise can reach -200 dB and is 500 times lower than on Earth at night and it increases of 30 dB during the day. We analyze its polarization as a function of time and frequency in the band 0.03-1Hz. We use the degree of polarization to extract signals with stable polarization independent of their amplitude and type of polarization. We detect polarized signals at all frequencies and all times. Glitches correspond to linear polarized signals which are more abundant during the night. For signals with elliptical polarization, the ellipse is in the horizontal plane below 0.3 Hz (LF). Above 0.3 Hz (HF) and except in the evening, the ellipse is in the vertical plane and the major axis is tilted. While polarization azimuths are different in the two frequency bands, they both vary as a function of local hour and season. They are also correlated with wind direction, particularly during the daytime.
We investigate possible aseismic and seismic origins of the polarized signals. Lander or tether noise can be discarded. Pressure fluctuations transported by wind may explain part of the HF polarization but not the tilt of the ellipse. This tilt can be obtained if the source is an acoustic emission coming from high altitude at critical angle. Finally, in the evening when the wind is low, the polarized signals may correspond to the seismic wavefield of the Mars background noise.
How to cite: Stutzmann, É., Schimmel, M., Lognonné, P., Horleston, A., Ceylan, S., van Driel, M., Stahler, S., Banerdt, B., Calvet, M., Charalambous, C., Clinton, J., Drilleau, M., Fayon, L., Garcia, R., Jacob, A., Kawamura, T., Kenda, B., Margerin, L., Murdoch, N., and Panning, M. and the Insight group: The Polarization of Ambient Noise on Mars , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14617, https://doi.org/10.5194/egusphere-egu21-14617, 2021.
Seismic noise recorded at the surface of Mars has been monitored since February 2019, using the InSight seismometers.This noise can reach -200 dB and is 500 times lower than on Earth at night and it increases of 30 dB during the day. We analyze its polarization as a function of time and frequency in the band 0.03-1Hz. We use the degree of polarization to extract signals with stable polarization independent of their amplitude and type of polarization. We detect polarized signals at all frequencies and all times. Glitches correspond to linear polarized signals which are more abundant during the night. For signals with elliptical polarization, the ellipse is in the horizontal plane below 0.3 Hz (LF). Above 0.3 Hz (HF) and except in the evening, the ellipse is in the vertical plane and the major axis is tilted. While polarization azimuths are different in the two frequency bands, they both vary as a function of local hour and season. They are also correlated with wind direction, particularly during the daytime.
We investigate possible aseismic and seismic origins of the polarized signals. Lander or tether noise can be discarded. Pressure fluctuations transported by wind may explain part of the HF polarization but not the tilt of the ellipse. This tilt can be obtained if the source is an acoustic emission coming from high altitude at critical angle. Finally, in the evening when the wind is low, the polarized signals may correspond to the seismic wavefield of the Mars background noise.
How to cite: Stutzmann, É., Schimmel, M., Lognonné, P., Horleston, A., Ceylan, S., van Driel, M., Stahler, S., Banerdt, B., Calvet, M., Charalambous, C., Clinton, J., Drilleau, M., Fayon, L., Garcia, R., Jacob, A., Kawamura, T., Kenda, B., Margerin, L., Murdoch, N., and Panning, M. and the Insight group: The Polarization of Ambient Noise on Mars , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14617, https://doi.org/10.5194/egusphere-egu21-14617, 2021.
EGU21-12292 | vPICO presentations | SM3.1
Autocorrelation of the ground vibration recorded by the SEIS-InSight seismometer on Mars for imaging and monitoring applicationsNicolas Compaire, Ludovic Margerin, Raphaël F. Garcia, Marie Calvet, Baptiste Pinot, Guénolé Orhand-Mainsant, Doyeon Kim, Vedran Lekic, Benoit Tauzin, Martin Schimmel, Eléonore Stutzmann, Brigitte Knapmeyer-Endrun, Philippe Lognonné, William T. Pike, Nicholas Schmerr, Laurent Gizon, and Bruce Banerdt
Since early February 2019, the SEIS seismometer deployed at the surface of Mars in the framework of the NASA-InSight mission has been continuously recording the ground motion at Elysium Planitia. In this work, we take advantage of this exceptional dataset to put constraints on the crustal properties of Mars using seismic interferometry (SI). This method use the seismic waves, either from background vibrations of the planet or from quakes, that are scattered in the medium in order to recover the ground response between two seismic sensors. Applying the principles of SI to the single-station configuration of SEIS, we compute, for each Sol (martian day) and each local hour, all the components of the time-domain autocorrelation tensor of random ambient vibrations in various frequency bands. A similar computation is performed on the diffuse waveforms generated by more than a hundred Marsquakes. For imaging application a careful signal-to-noise ratio analysis and an inter-comparison between the two datasets are applied. These analyses suggest that the reconstructed ground responses are most reliable in a relatively narrow frequency band around 2.4Hz, where an amplification of both ambient vibrations and seismic events is observed. The average Auto-Correlation Functions (ACFs) from both ambient vibrations and seismic events contain well identifiable seismic arrivals, that are very consistent between the two datasets. We interpret the vertical and horizontal ACFs as the ground reflection response below InSight for the compressional waves and the shear waves respectively. We propose a simple stratified velocity model of the crust, which is most compatible with the arrival times of the detected phases, as well as with previous seismological studies of the SEIS record. The hourly computation of the ACFs over one martian year also allows us to study the diurnal and seasonal variations of the reconstructed ground response with a technique call Passive Image Interferometry (PII). In this study we present measurements of the relative stretching coefficient between consecutive ACF waveforms and discuss the potential origins of the observed temporal variations.
How to cite: Compaire, N., Margerin, L., Garcia, R. F., Calvet, M., Pinot, B., Orhand-Mainsant, G., Kim, D., Lekic, V., Tauzin, B., Schimmel, M., Stutzmann, E., Knapmeyer-Endrun, B., Lognonné, P., Pike, W. T., Schmerr, N., Gizon, L., and Banerdt, B.: Autocorrelation of the ground vibration recorded by the SEIS-InSight seismometer on Mars for imaging and monitoring applications, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12292, https://doi.org/10.5194/egusphere-egu21-12292, 2021.
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Since early February 2019, the SEIS seismometer deployed at the surface of Mars in the framework of the NASA-InSight mission has been continuously recording the ground motion at Elysium Planitia. In this work, we take advantage of this exceptional dataset to put constraints on the crustal properties of Mars using seismic interferometry (SI). This method use the seismic waves, either from background vibrations of the planet or from quakes, that are scattered in the medium in order to recover the ground response between two seismic sensors. Applying the principles of SI to the single-station configuration of SEIS, we compute, for each Sol (martian day) and each local hour, all the components of the time-domain autocorrelation tensor of random ambient vibrations in various frequency bands. A similar computation is performed on the diffuse waveforms generated by more than a hundred Marsquakes. For imaging application a careful signal-to-noise ratio analysis and an inter-comparison between the two datasets are applied. These analyses suggest that the reconstructed ground responses are most reliable in a relatively narrow frequency band around 2.4Hz, where an amplification of both ambient vibrations and seismic events is observed. The average Auto-Correlation Functions (ACFs) from both ambient vibrations and seismic events contain well identifiable seismic arrivals, that are very consistent between the two datasets. We interpret the vertical and horizontal ACFs as the ground reflection response below InSight for the compressional waves and the shear waves respectively. We propose a simple stratified velocity model of the crust, which is most compatible with the arrival times of the detected phases, as well as with previous seismological studies of the SEIS record. The hourly computation of the ACFs over one martian year also allows us to study the diurnal and seasonal variations of the reconstructed ground response with a technique call Passive Image Interferometry (PII). In this study we present measurements of the relative stretching coefficient between consecutive ACF waveforms and discuss the potential origins of the observed temporal variations.
How to cite: Compaire, N., Margerin, L., Garcia, R. F., Calvet, M., Pinot, B., Orhand-Mainsant, G., Kim, D., Lekic, V., Tauzin, B., Schimmel, M., Stutzmann, E., Knapmeyer-Endrun, B., Lognonné, P., Pike, W. T., Schmerr, N., Gizon, L., and Banerdt, B.: Autocorrelation of the ground vibration recorded by the SEIS-InSight seismometer on Mars for imaging and monitoring applications, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12292, https://doi.org/10.5194/egusphere-egu21-12292, 2021.
EGU21-516 | vPICO presentations | SM3.1 | Highlight
Simulations of gravitoelastic correlations for the Sardinian candidate site of the Einstein TelescopeTomislav Andric and Jan Harms
Gravity fluctuations produced by ambient seismic fields are predicted to limit the sensitivity of the next-generation, gravitational-wave detector Einstein Telescope at frequencies below 20 Hz. The detector will be hosted in an underground infrastructure to reduce seismic disturbances and associated gravity fluctuations. Additional mitigation might be required by monitoring the seismic field and using the data to estimate the associated gravity fluctuations and to subtract the estimate from the detector data, a technique called coherent noise cancellation. In this paper, we present a calculation of correlations between surface displacement of a seismic field and the associated gravitational fluctuations using the spectral-element SPECFEM3D Cartesian software. The model takes into account the local topography at a candidate site of the Einstein Telescope at Sardinia. This paper is a first demonstration of SPECFEM3D’s capabilities to provide estimates of gravitoelastic correlations, which are required for an optimized deployment of seismometers for gravity-noise cancellation.
How to cite: Andric, T. and Harms, J.: Simulations of gravitoelastic correlations for the Sardinian candidate site of the Einstein Telescope, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-516, https://doi.org/10.5194/egusphere-egu21-516, 2021.
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Gravity fluctuations produced by ambient seismic fields are predicted to limit the sensitivity of the next-generation, gravitational-wave detector Einstein Telescope at frequencies below 20 Hz. The detector will be hosted in an underground infrastructure to reduce seismic disturbances and associated gravity fluctuations. Additional mitigation might be required by monitoring the seismic field and using the data to estimate the associated gravity fluctuations and to subtract the estimate from the detector data, a technique called coherent noise cancellation. In this paper, we present a calculation of correlations between surface displacement of a seismic field and the associated gravitational fluctuations using the spectral-element SPECFEM3D Cartesian software. The model takes into account the local topography at a candidate site of the Einstein Telescope at Sardinia. This paper is a first demonstration of SPECFEM3D’s capabilities to provide estimates of gravitoelastic correlations, which are required for an optimized deployment of seismometers for gravity-noise cancellation.
How to cite: Andric, T. and Harms, J.: Simulations of gravitoelastic correlations for the Sardinian candidate site of the Einstein Telescope, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-516, https://doi.org/10.5194/egusphere-egu21-516, 2021.
EGU21-995 | vPICO presentations | SM3.1
Ambient seismic noise interferometry using rotational ground motionCéline Hadziioannou, Paul Neumann, Joachim Wassermann, Heiner Igel, Ulrich Schreiber, and the Romy Team
In seismology, new sensing technologies are currently emerging that can measure ground motion beyond the conventional seismic translation measurements. In particular, rotational motion sensors record an additional 3 components of ground motion and thus provide access to additional information about the seismic wavefield.
So far, most studies of rotational ground motion are mainly based on recordings of earthquakes or active sources. In this study, we push the limit towards the very weak motions associated with ocean-generated ambient seismic noise. Our aim is to show the potential of using these measurements in the context of ambient noise interferometry.
We use recordings from two ring lasers in Germany: the `G-Ring' at the Wettzell Geodetic Observatory, and `ROMY' at the Fürstenfeldbruck Observatory near Munich, at a distance of approximately 160 km. These are the most sensitive instruments to date which offer a local, direct measurement of rotational ground motion.
We demonstrate that the sensitivity of the Wettzell instrument has been sufficiently improved to detect Love waves in the primary microseismic frequency band. Both the G-Ring and ROMY ring lasers are also capable of detecting Love waves in the stronger secondary microseismic band. This latter frequency range is used to test the possibility of performing noise interferometry with rotational records.
The first results of rotational noise interferometry between the two ring lasers are promising. The correlation waveform is verified by comparison with interferometry carried out with co-located seismometer data at both locations, as well as with numerical simulations.
In conclusion, we show that ambient noise interferometry is in principle feasible using real rotational recordings of ocean-generated noise. This proof of concept study forms a first step towards noise interferometery of 6-component displacement data.
How to cite: Hadziioannou, C., Neumann, P., Wassermann, J., Igel, H., Schreiber, U., and Team, T. R.: Ambient seismic noise interferometry using rotational ground motion, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-995, https://doi.org/10.5194/egusphere-egu21-995, 2021.
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In seismology, new sensing technologies are currently emerging that can measure ground motion beyond the conventional seismic translation measurements. In particular, rotational motion sensors record an additional 3 components of ground motion and thus provide access to additional information about the seismic wavefield.
So far, most studies of rotational ground motion are mainly based on recordings of earthquakes or active sources. In this study, we push the limit towards the very weak motions associated with ocean-generated ambient seismic noise. Our aim is to show the potential of using these measurements in the context of ambient noise interferometry.
We use recordings from two ring lasers in Germany: the `G-Ring' at the Wettzell Geodetic Observatory, and `ROMY' at the Fürstenfeldbruck Observatory near Munich, at a distance of approximately 160 km. These are the most sensitive instruments to date which offer a local, direct measurement of rotational ground motion.
We demonstrate that the sensitivity of the Wettzell instrument has been sufficiently improved to detect Love waves in the primary microseismic frequency band. Both the G-Ring and ROMY ring lasers are also capable of detecting Love waves in the stronger secondary microseismic band. This latter frequency range is used to test the possibility of performing noise interferometry with rotational records.
The first results of rotational noise interferometry between the two ring lasers are promising. The correlation waveform is verified by comparison with interferometry carried out with co-located seismometer data at both locations, as well as with numerical simulations.
In conclusion, we show that ambient noise interferometry is in principle feasible using real rotational recordings of ocean-generated noise. This proof of concept study forms a first step towards noise interferometery of 6-component displacement data.
How to cite: Hadziioannou, C., Neumann, P., Wassermann, J., Igel, H., Schreiber, U., and Team, T. R.: Ambient seismic noise interferometry using rotational ground motion, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-995, https://doi.org/10.5194/egusphere-egu21-995, 2021.
EGU21-4440 | vPICO presentations | SM3.1
Incorporating spatial gradient observations into seismic noise interferometryPatrick Paitz, Korbinian Sager, Christian Boehm, and Andreas Fichtner
With an increasing availability of next-generation instruments in seismology such as Distributed Acoustic Sensing (DAS) interrogators and rotation sensors, as well as public datasets from these instruments, there is a demand for incorporating these new gradient observables into the workflows of seismic interferometry and noise source inversion.
Dropping the common assumption of Green’s function retrieval, we derive a generalized formulation for seismic interferometry that can utilize not only displacement measurements but also spatial and temporal gradients thereof – including velocity, strain and rotation.
Based on this formulation, we are able to simulate interferometric wavefields of displacement and gradient observations or arbitrary combinations of these observables, for heterogeneous visco-elastic media, and for arbitrary noise source distributions.
We demonstrate how to derive adjoint-based expressions for finite-frequency sensitivity kernels of the interferometric wavefields with respect to subsurface structure and noise source distributions, for a wide range of observed quantitates and combinations thereof. We provide numerical examples of such sensitivity kernels.
Especially in environments where the common assumption of a homogeneous noise source distribution is violated, our formulation enables correlation-wavefield based inversions, combining different seismic observables.
The discussed theoretical and numerical developments bring us one step closer to multi-observational full waveform ambient noise inversion, underlining the potential and possible impact of recent developments in seismic instrumentation to seismology across all scales.
How to cite: Paitz, P., Sager, K., Boehm, C., and Fichtner, A.: Incorporating spatial gradient observations into seismic noise interferometry, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4440, https://doi.org/10.5194/egusphere-egu21-4440, 2021.
With an increasing availability of next-generation instruments in seismology such as Distributed Acoustic Sensing (DAS) interrogators and rotation sensors, as well as public datasets from these instruments, there is a demand for incorporating these new gradient observables into the workflows of seismic interferometry and noise source inversion.
Dropping the common assumption of Green’s function retrieval, we derive a generalized formulation for seismic interferometry that can utilize not only displacement measurements but also spatial and temporal gradients thereof – including velocity, strain and rotation.
Based on this formulation, we are able to simulate interferometric wavefields of displacement and gradient observations or arbitrary combinations of these observables, for heterogeneous visco-elastic media, and for arbitrary noise source distributions.
We demonstrate how to derive adjoint-based expressions for finite-frequency sensitivity kernels of the interferometric wavefields with respect to subsurface structure and noise source distributions, for a wide range of observed quantitates and combinations thereof. We provide numerical examples of such sensitivity kernels.
Especially in environments where the common assumption of a homogeneous noise source distribution is violated, our formulation enables correlation-wavefield based inversions, combining different seismic observables.
The discussed theoretical and numerical developments bring us one step closer to multi-observational full waveform ambient noise inversion, underlining the potential and possible impact of recent developments in seismic instrumentation to seismology across all scales.
How to cite: Paitz, P., Sager, K., Boehm, C., and Fichtner, A.: Incorporating spatial gradient observations into seismic noise interferometry, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4440, https://doi.org/10.5194/egusphere-egu21-4440, 2021.
EGU21-3155 | vPICO presentations | SM3.1
Noise Correlations of Wavefield Gradients to Improve Sensitivity to (near surface, time-dependent) Structural HeterogeneityBetul Celik, Korbinian Sager, and Heiner Igel
We assess the potential of rotational ground motions to resolve time-dependent near surface structural heterogeneities using noise correlations. Recent studies reveal an increased sensitivity of gradient related observations to near surface structural heterogeneities (e.g., material contrast, cavities) compared to directly measured wavefields (and their time derivatives). The development of new sensing technologies, such as rotational ground motion sensors and distributing acoustic sensing (DAS), enable measurements of strain and rotations and motivate this study. Combining gradient related observations with ambient noise-based monitoring methods has the potential to increase both spatial and temporal resolution. In order to investigate the suggested benefits, we perform a numerical study in 2D, where we simulate seismic noise with random sources at random locations. We apply interferometric principles and calculate cross-correlations of the resulting noise traces recorded at different receiver locations for multiple realizations of the noise field. After analysing the convergence of the correlation functions in terms of simulation length and number of simulations, we compare noise correlations of acceleration and rotation rate for a homogenous reference and a perturbed model. Ultimately, we establish that noise correlations of wavefield gradients are more sensitive than noise correlations of wavefields to small-scale heterogeneity.
How to cite: Celik, B., Sager, K., and Igel, H.: Noise Correlations of Wavefield Gradients to Improve Sensitivity to (near surface, time-dependent) Structural Heterogeneity, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3155, https://doi.org/10.5194/egusphere-egu21-3155, 2021.
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We assess the potential of rotational ground motions to resolve time-dependent near surface structural heterogeneities using noise correlations. Recent studies reveal an increased sensitivity of gradient related observations to near surface structural heterogeneities (e.g., material contrast, cavities) compared to directly measured wavefields (and their time derivatives). The development of new sensing technologies, such as rotational ground motion sensors and distributing acoustic sensing (DAS), enable measurements of strain and rotations and motivate this study. Combining gradient related observations with ambient noise-based monitoring methods has the potential to increase both spatial and temporal resolution. In order to investigate the suggested benefits, we perform a numerical study in 2D, where we simulate seismic noise with random sources at random locations. We apply interferometric principles and calculate cross-correlations of the resulting noise traces recorded at different receiver locations for multiple realizations of the noise field. After analysing the convergence of the correlation functions in terms of simulation length and number of simulations, we compare noise correlations of acceleration and rotation rate for a homogenous reference and a perturbed model. Ultimately, we establish that noise correlations of wavefield gradients are more sensitive than noise correlations of wavefields to small-scale heterogeneity.
How to cite: Celik, B., Sager, K., and Igel, H.: Noise Correlations of Wavefield Gradients to Improve Sensitivity to (near surface, time-dependent) Structural Heterogeneity, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3155, https://doi.org/10.5194/egusphere-egu21-3155, 2021.
EGU21-2773 | vPICO presentations | SM3.1
Investigation of ambient noise seismological methods on a bridge modelChun-Man Liao, Franziska Mehrkens, Celine Hadziioannou, and Ernst Niederleithinger
The aim of this work is to investigate the application of seismological noise-based monitoring for bridge structures. A large-scale two-span concrete bridge model with a build-in post-tensioning system, which is exposed to environmental conditions, is chosen as our experimental test structure. Ambient seismic noise measurements were carried out under different pre-stressed conditions. Using the seismic interferometry technique, which is applied to the measurement data in the frequency domain, we reconstruct waveforms that relate to wave propagation in the structure. The coda wave interferometry technique is then implemented by comparing two waveforms recorded in two pre-stress states. Any relative seismic velocity changes are identified by determining the correlation coefficients and reveal the influence of the pre-stressing force. The decrease of the wave propagation velocity indicates the loss of the pre-stress and weakening stiffness due to opening or event extension of cracks. We conclude that the seismological methods used to estimate velocity change can be a promising tool for structural health monitoring of civil structures.
How to cite: Liao, C.-M., Mehrkens, F., Hadziioannou, C., and Niederleithinger, E.: Investigation of ambient noise seismological methods on a bridge model, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2773, https://doi.org/10.5194/egusphere-egu21-2773, 2021.
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The aim of this work is to investigate the application of seismological noise-based monitoring for bridge structures. A large-scale two-span concrete bridge model with a build-in post-tensioning system, which is exposed to environmental conditions, is chosen as our experimental test structure. Ambient seismic noise measurements were carried out under different pre-stressed conditions. Using the seismic interferometry technique, which is applied to the measurement data in the frequency domain, we reconstruct waveforms that relate to wave propagation in the structure. The coda wave interferometry technique is then implemented by comparing two waveforms recorded in two pre-stress states. Any relative seismic velocity changes are identified by determining the correlation coefficients and reveal the influence of the pre-stressing force. The decrease of the wave propagation velocity indicates the loss of the pre-stress and weakening stiffness due to opening or event extension of cracks. We conclude that the seismological methods used to estimate velocity change can be a promising tool for structural health monitoring of civil structures.
How to cite: Liao, C.-M., Mehrkens, F., Hadziioannou, C., and Niederleithinger, E.: Investigation of ambient noise seismological methods on a bridge model, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2773, https://doi.org/10.5194/egusphere-egu21-2773, 2021.
EGU21-1997 | vPICO presentations | SM3.1
Connecting velocity changes with complementary observations (fast and slow strain perturbations, temperature etc.): Insights from long-term (decades) monitoring in several Italian regionsPiero Poli
We present a set of studies on velocity variations (dv/v) measured from seismic noise correlation in the Italian region. By exploring the evolution of the dv/v as function of coda lapse time, and comparing with independent observations (e.g. dynamic and quasi-static strain, temperature induced strain, rain etc.) we are able to get new insights into the causes of velocity variations as function of space (depth). Out of our results we recognized depth dependence of coseismic velocity drop and recovery in the region of l’Aquila, and depth and spatial dependence of sensitivity to long period (years) small strain variation (~10e-6) induced by hydrological processes. In a similar way to dynamic acoustic-elastic testing in laboratory, we extract non-linear parameters of the crustal rocks. These measures are compared with laboratory results to get insights about the physical state of the rocks in the crust, in regions hosting seismogenic faults. A summary of frequency and strain dependent dv/v and sensitivity further permits to compare our results to laboratory experiments.
How to cite: Poli, P.: Connecting velocity changes with complementary observations (fast and slow strain perturbations, temperature etc.): Insights from long-term (decades) monitoring in several Italian regions, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1997, https://doi.org/10.5194/egusphere-egu21-1997, 2021.
We present a set of studies on velocity variations (dv/v) measured from seismic noise correlation in the Italian region. By exploring the evolution of the dv/v as function of coda lapse time, and comparing with independent observations (e.g. dynamic and quasi-static strain, temperature induced strain, rain etc.) we are able to get new insights into the causes of velocity variations as function of space (depth). Out of our results we recognized depth dependence of coseismic velocity drop and recovery in the region of l’Aquila, and depth and spatial dependence of sensitivity to long period (years) small strain variation (~10e-6) induced by hydrological processes. In a similar way to dynamic acoustic-elastic testing in laboratory, we extract non-linear parameters of the crustal rocks. These measures are compared with laboratory results to get insights about the physical state of the rocks in the crust, in regions hosting seismogenic faults. A summary of frequency and strain dependent dv/v and sensitivity further permits to compare our results to laboratory experiments.
How to cite: Poli, P.: Connecting velocity changes with complementary observations (fast and slow strain perturbations, temperature etc.): Insights from long-term (decades) monitoring in several Italian regions, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1997, https://doi.org/10.5194/egusphere-egu21-1997, 2021.
EGU21-1546 | vPICO presentations | SM3.1
Spatial Evaluation of Pore Pressure Variations Related to Rainfall from Seismic Velocity ChangesRezkia Dewi Andajani, Takeshi Tsuji, Roel Snieder, and Tatsunori Ikeda
Crustal pore pressure, which could trigger seismicity and volcanic activity, varies with fluid invasion. Various studies have discussed the potential of using seismic velocity changes from ambient noise to evaluate pore pressure conditions, especially due to rainfall perturbations. Although the influence of rainfall on seismic velocity changes has been reported, consideration of the spatial influence on rainfall towards seismic velocity and its mechanism have not been well understood. We investigated the mechanism of rainfall-induced pore pressure diffusion in southwestern Japan, using seismic velocity change (Vs) inferred from ambient noise. We modeled pore pressure changes from rainfall data based on a diffusion mechanism at the locations where infiltration is indicated. By calculating the correlation between Vs changes and the modeled pore pressure with various hydraulic diffusion parameters, the optimum hydraulic diffusion parameter was obtained. We estimated the diffusion parameters with the highest negative correlation between pore pressure and Vs change because a negative correlation indicates pore pressure increase due to diffusion induced by groundwater load. Furthermore, the spatial variation of the hydraulic diffusivity infers the heterogeneity of the rocks in different locations. This finding suggests that the response of pore pressure induced by rainfall percolation depends on location. We show that seismic velocity monitoring can be used to evaluate the status of pore pressure at different locations, which is useful for fluid injection, CO2 wellbore storage, and geothermal development.
How to cite: Andajani, R. D., Tsuji, T., Snieder, R., and Ikeda, T.: Spatial Evaluation of Pore Pressure Variations Related to Rainfall from Seismic Velocity Changes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1546, https://doi.org/10.5194/egusphere-egu21-1546, 2021.
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Crustal pore pressure, which could trigger seismicity and volcanic activity, varies with fluid invasion. Various studies have discussed the potential of using seismic velocity changes from ambient noise to evaluate pore pressure conditions, especially due to rainfall perturbations. Although the influence of rainfall on seismic velocity changes has been reported, consideration of the spatial influence on rainfall towards seismic velocity and its mechanism have not been well understood. We investigated the mechanism of rainfall-induced pore pressure diffusion in southwestern Japan, using seismic velocity change (Vs) inferred from ambient noise. We modeled pore pressure changes from rainfall data based on a diffusion mechanism at the locations where infiltration is indicated. By calculating the correlation between Vs changes and the modeled pore pressure with various hydraulic diffusion parameters, the optimum hydraulic diffusion parameter was obtained. We estimated the diffusion parameters with the highest negative correlation between pore pressure and Vs change because a negative correlation indicates pore pressure increase due to diffusion induced by groundwater load. Furthermore, the spatial variation of the hydraulic diffusivity infers the heterogeneity of the rocks in different locations. This finding suggests that the response of pore pressure induced by rainfall percolation depends on location. We show that seismic velocity monitoring can be used to evaluate the status of pore pressure at different locations, which is useful for fluid injection, CO2 wellbore storage, and geothermal development.
How to cite: Andajani, R. D., Tsuji, T., Snieder, R., and Ikeda, T.: Spatial Evaluation of Pore Pressure Variations Related to Rainfall from Seismic Velocity Changes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1546, https://doi.org/10.5194/egusphere-egu21-1546, 2021.
EGU21-2969 | vPICO presentations | SM3.1
Physics-based model relating seismic velocity variation to groundwater and pore pressure fluctuationEldert Fokker, Elmer Ruigrok, Rhys Hawkins, and Jeannot Trampert
Previous studies examining the relationship between the groundwater table and seismic velocities have provided contradictory results, sometimes reporting positive and sometimes negative correlations between seismic velocity and groundwater table changes. Here we introduce a physics-based model relating fluctuation in the groundwater table and the pore pressure to seismic velocity variation through change in effective stress. This model can be used to explain the contradictory results of previous studies and justifies the use of seismic velocity variation for monitoring of the pore pressure and the groundwater table. It further results in a new field method to measure the pressure dependency of the shear modulus. Using data acquired in Groningen, the Netherlands, we demonstrate that measurements of seismic velocity variation can be used to monitor the pore pressure.
How to cite: Fokker, E., Ruigrok, E., Hawkins, R., and Trampert, J.: Physics-based model relating seismic velocity variation to groundwater and pore pressure fluctuation, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2969, https://doi.org/10.5194/egusphere-egu21-2969, 2021.
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Previous studies examining the relationship between the groundwater table and seismic velocities have provided contradictory results, sometimes reporting positive and sometimes negative correlations between seismic velocity and groundwater table changes. Here we introduce a physics-based model relating fluctuation in the groundwater table and the pore pressure to seismic velocity variation through change in effective stress. This model can be used to explain the contradictory results of previous studies and justifies the use of seismic velocity variation for monitoring of the pore pressure and the groundwater table. It further results in a new field method to measure the pressure dependency of the shear modulus. Using data acquired in Groningen, the Netherlands, we demonstrate that measurements of seismic velocity variation can be used to monitor the pore pressure.
How to cite: Fokker, E., Ruigrok, E., Hawkins, R., and Trampert, J.: Physics-based model relating seismic velocity variation to groundwater and pore pressure fluctuation, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2969, https://doi.org/10.5194/egusphere-egu21-2969, 2021.
EGU21-7010 | vPICO presentations | SM3.1
Revealing seasonal crustal seismic velocity variations in Taiwan with single-station cross-component analysisKuan-Fu Feng, Hsin-Hua Huang, Ya-Ju Hsu, and Yih-Min Wu
Ambient noise interferometry is a promising technique for studying crustal behaviors, providing continuous measurements of seismic velocity changes (dv/v) in relation to physical processes in the crust over time. In addition to the tectonic-driven dv/v changes, dv/v is also known to be affected by environmental factors through rainfall-induced pore-pressure changes, air pressure loading changes, thermoelastic effects, and so forth. In this study, benefiting from the long-term continuous data of Broadband Array in Taiwan for Seismology (BATS) that has been operated since 1994, we analyze continuous seismic data from 1998 to 2019 by applying single-station cross-component (SC) technique to investigate the temporal variations of crust on seismic velocity. We process the continuous waveforms of BATS stations, construct the empirical Green’s functions, and compute daily seismic velocity changes by the stretching technique in a frequency band of 0.1 to 0.9 Hz. We observe co-seismic velocity drops associated with the inland moderate earthquakes. Furthermore, clear seasonal cycles, with a period of near one-year, are also revealed at most stations, but with different characteristics. Systematic spectral and time-series analyses with the weather data are conducted and show that the rainfall-induced pore-pressure change is likely the main cause to the seasonal variations with high correlations. The strong site-dependency of these seasonal variations also precludes air pressure and temperature which varies smoothly in space from being dominant sources and suggests spatially-varying complex hydro-mechanical interaction across the orogenic belt in Taiwan.
How to cite: Feng, K.-F., Huang, H.-H., Hsu, Y.-J., and Wu, Y.-M.: Revealing seasonal crustal seismic velocity variations in Taiwan with single-station cross-component analysis , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7010, https://doi.org/10.5194/egusphere-egu21-7010, 2021.
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Ambient noise interferometry is a promising technique for studying crustal behaviors, providing continuous measurements of seismic velocity changes (dv/v) in relation to physical processes in the crust over time. In addition to the tectonic-driven dv/v changes, dv/v is also known to be affected by environmental factors through rainfall-induced pore-pressure changes, air pressure loading changes, thermoelastic effects, and so forth. In this study, benefiting from the long-term continuous data of Broadband Array in Taiwan for Seismology (BATS) that has been operated since 1994, we analyze continuous seismic data from 1998 to 2019 by applying single-station cross-component (SC) technique to investigate the temporal variations of crust on seismic velocity. We process the continuous waveforms of BATS stations, construct the empirical Green’s functions, and compute daily seismic velocity changes by the stretching technique in a frequency band of 0.1 to 0.9 Hz. We observe co-seismic velocity drops associated with the inland moderate earthquakes. Furthermore, clear seasonal cycles, with a period of near one-year, are also revealed at most stations, but with different characteristics. Systematic spectral and time-series analyses with the weather data are conducted and show that the rainfall-induced pore-pressure change is likely the main cause to the seasonal variations with high correlations. The strong site-dependency of these seasonal variations also precludes air pressure and temperature which varies smoothly in space from being dominant sources and suggests spatially-varying complex hydro-mechanical interaction across the orogenic belt in Taiwan.
How to cite: Feng, K.-F., Huang, H.-H., Hsu, Y.-J., and Wu, Y.-M.: Revealing seasonal crustal seismic velocity variations in Taiwan with single-station cross-component analysis , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7010, https://doi.org/10.5194/egusphere-egu21-7010, 2021.
EGU21-14059 | vPICO presentations | SM3.1
Can land subsidence be monitored with ambient seismic auto-correlations?Laura Ermert, Marine Denolle, Enrique Cabral Cano, Estelle Chaussard, and Dario Solano Rojas
EGU21-12714 | vPICO presentations | SM3.1
Seismic velocity recovery following the 2015 Mw 7.8 Gorkha earthquake, Nepal: Towards a coupled vision of damage and hydrological-induced velocity variationsLuc Illien, Christoph Sens-Schönfelder, Christoff Andermann, Odin Marc, Kristen Cook, and Niels Hovius
Following the passage of seismic waves, most geomaterials experience non-linear mesoscopic elasticity (NLME). This is described by a drop in elastic moduli that precedes a subsequent recovery of physical properties over a relaxation timescale. Thanks to the development of seismic interferometry techniques that allows for the continuous monitoring of relative seismic velocity changes δv in the subsurface, observations of NLME (δvNLME) in the field are now numerous. In parallel, a growing community uses seismic interferometry to monitor velocity changes induced by seasonal hydrological variations (δvhydro). Monitoring of these variations are often independently done and a linear superposition of both effects is mostly assumed when decomposing the observed δv signal (δv = δvNLME + δvhydro). However, transient hydrological behaviour following co-seismic ground shaking has been widely reported in boreholes measurements and streamflow, which suggests that δvhydro may be impacted by the transient variation of material properties caused by NLME. In this presentation, we attempt to characterize the relative seismic velocity variations δv retrieved from a small dense seismic array in Nepal that was deployed in the aftermath of the 2015 Mw 7.8 Gorkha earthquake and that is prone to highly variable hydrological conditions. We first investigated the effect of aftershocks in computing δv at a 10-minute resolution centered around significant ground shaking events. After correcting δv for NLME caused by the Gorkha earthquake and its subsequent aftershocks, we test whether the corresponding residuals are in agreement with the background hydrological behaviour which we inferred from a calibrated hydrological model. This is not the case and we find that transient hydrological properties improve the data description in the early phase after the mainshock. We report three distinct relaxation time scales that are relevant for the recovery of seismic velocity at our field site: 1. A long time scale activated by the main shock of the Gorkha earthquake (~1 year) 2. A relatively short timescale (1-3 days) that occurs after moderate aftershocks. 3. An intermediate timescale (4-6 months) during the 2015 monsoon season that corresponds to the recovery of the hydrological system. This timescale could correspond to an enhanced permeability caused by Gorkha ground shaking. Our study demonstrates the capability of seismic interferometry to monitor transient hydrological properties after earthquakes at a spatial scale that is not available with classical hydrological measurements. This investigation demands calibrated hydrological models and a framework in which the different forcing of δv are coupled.
How to cite: Illien, L., Sens-Schönfelder, C., Andermann, C., Marc, O., Cook, K., and Hovius, N.: Seismic velocity recovery following the 2015 Mw 7.8 Gorkha earthquake, Nepal: Towards a coupled vision of damage and hydrological-induced velocity variations, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12714, https://doi.org/10.5194/egusphere-egu21-12714, 2021.
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Following the passage of seismic waves, most geomaterials experience non-linear mesoscopic elasticity (NLME). This is described by a drop in elastic moduli that precedes a subsequent recovery of physical properties over a relaxation timescale. Thanks to the development of seismic interferometry techniques that allows for the continuous monitoring of relative seismic velocity changes δv in the subsurface, observations of NLME (δvNLME) in the field are now numerous. In parallel, a growing community uses seismic interferometry to monitor velocity changes induced by seasonal hydrological variations (δvhydro). Monitoring of these variations are often independently done and a linear superposition of both effects is mostly assumed when decomposing the observed δv signal (δv = δvNLME + δvhydro). However, transient hydrological behaviour following co-seismic ground shaking has been widely reported in boreholes measurements and streamflow, which suggests that δvhydro may be impacted by the transient variation of material properties caused by NLME. In this presentation, we attempt to characterize the relative seismic velocity variations δv retrieved from a small dense seismic array in Nepal that was deployed in the aftermath of the 2015 Mw 7.8 Gorkha earthquake and that is prone to highly variable hydrological conditions. We first investigated the effect of aftershocks in computing δv at a 10-minute resolution centered around significant ground shaking events. After correcting δv for NLME caused by the Gorkha earthquake and its subsequent aftershocks, we test whether the corresponding residuals are in agreement with the background hydrological behaviour which we inferred from a calibrated hydrological model. This is not the case and we find that transient hydrological properties improve the data description in the early phase after the mainshock. We report three distinct relaxation time scales that are relevant for the recovery of seismic velocity at our field site: 1. A long time scale activated by the main shock of the Gorkha earthquake (~1 year) 2. A relatively short timescale (1-3 days) that occurs after moderate aftershocks. 3. An intermediate timescale (4-6 months) during the 2015 monsoon season that corresponds to the recovery of the hydrological system. This timescale could correspond to an enhanced permeability caused by Gorkha ground shaking. Our study demonstrates the capability of seismic interferometry to monitor transient hydrological properties after earthquakes at a spatial scale that is not available with classical hydrological measurements. This investigation demands calibrated hydrological models and a framework in which the different forcing of δv are coupled.
How to cite: Illien, L., Sens-Schönfelder, C., Andermann, C., Marc, O., Cook, K., and Hovius, N.: Seismic velocity recovery following the 2015 Mw 7.8 Gorkha earthquake, Nepal: Towards a coupled vision of damage and hydrological-induced velocity variations, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12714, https://doi.org/10.5194/egusphere-egu21-12714, 2021.
EGU21-12924 | vPICO presentations | SM3.1
Temporal seismic velocity changes during the 2020 rapid inflation at Mt. Thorbjorn-Svartsengi, Iceland, using ambient seismic noiseYesim Cubuk Sabuncu, Kristin Jonsdottir, Corentin Caudron, Thomas Lecocq, Michelle Maree Parks, Halldor Geirsson, and Aurelien Mordret
The Reykjanes peninsula, SW Iceland, was struck by intense earthquake swarm activity that occurred in January-July 2020 due to repeated magmatic intrusions in the Reykjanes-Svartsengi volcanic system. GPS and InSAR observations confirmed surface deformation centered near Mt. Thorbjorn, and during the unrest period, approximately ~14,000 earthquakes (-2≤M≤4.9) were reported at the Icelandic Meteorological Office (IMO). We investigate the behavior of the crust as a response to these repeated intrusions to provide insights into volcanic unrest in the Reykjanes peninsula. Our study presents temporal seismic wave velocity variations (dv/v, in percent) based on ambient noise seismic interferometry using continuous three-component waveforms collected by IMO, (http://www.vedur.is) for the period from April 2018 to November 2020. The state-of-the-art MSNoise software package (http://www.msnoise.org) is used to calculate cross-correlations of ambient seismic noise and to quantify the relative seismic velocity variations. We observe that magmatic intrusions in the vicinity of Mt. Thorbjorn-Svartsengi have considerably reduced the seismic wave velocities (dv/v, -1%) in the 1-2 Hz frequency band. Seismic velocity changes were compared with local seismicity, GPS and InSAR data recorded close to the repeated intrusions, and modelled volumetric strain changes. We found a good correlation between the dv/v variations and the available deformation data. The Rayleigh wave phase-velocity sensitivity kernels showed that the changes occurring at depths down to ~3-4 km in the crust were captured by our measurements. We interpret the relative seismic velocity decrease to be caused by crack opening induced by intrusive magmatic activity. Monitoring the Mt. Thorbjorn-Svartsengi volcanic unrest is crucial for successful early warning of volcanic hazards since the center of uplift is only 2km away from a fishing village and major infrastructure in the area, such as water supply and geothermal power. For the first time in Iceland, we have provided near-real-time dv/v variations to obtain a more complete picture of this magmatic activity. Our findings are supported by the analysis of other primary monitoring streams. We propose that this technique may be useful for early detection of future intrusions/increased magmatic activity. This study is supported by the Icelandic Research Fund, Rannis (Grant No: 185209-051).
How to cite: Cubuk Sabuncu, Y., Jonsdottir, K., Caudron, C., Lecocq, T., Parks, M. M., Geirsson, H., and Mordret, A.: Temporal seismic velocity changes during the 2020 rapid inflation at Mt. Thorbjorn-Svartsengi, Iceland, using ambient seismic noise, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12924, https://doi.org/10.5194/egusphere-egu21-12924, 2021.
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The Reykjanes peninsula, SW Iceland, was struck by intense earthquake swarm activity that occurred in January-July 2020 due to repeated magmatic intrusions in the Reykjanes-Svartsengi volcanic system. GPS and InSAR observations confirmed surface deformation centered near Mt. Thorbjorn, and during the unrest period, approximately ~14,000 earthquakes (-2≤M≤4.9) were reported at the Icelandic Meteorological Office (IMO). We investigate the behavior of the crust as a response to these repeated intrusions to provide insights into volcanic unrest in the Reykjanes peninsula. Our study presents temporal seismic wave velocity variations (dv/v, in percent) based on ambient noise seismic interferometry using continuous three-component waveforms collected by IMO, (http://www.vedur.is) for the period from April 2018 to November 2020. The state-of-the-art MSNoise software package (http://www.msnoise.org) is used to calculate cross-correlations of ambient seismic noise and to quantify the relative seismic velocity variations. We observe that magmatic intrusions in the vicinity of Mt. Thorbjorn-Svartsengi have considerably reduced the seismic wave velocities (dv/v, -1%) in the 1-2 Hz frequency band. Seismic velocity changes were compared with local seismicity, GPS and InSAR data recorded close to the repeated intrusions, and modelled volumetric strain changes. We found a good correlation between the dv/v variations and the available deformation data. The Rayleigh wave phase-velocity sensitivity kernels showed that the changes occurring at depths down to ~3-4 km in the crust were captured by our measurements. We interpret the relative seismic velocity decrease to be caused by crack opening induced by intrusive magmatic activity. Monitoring the Mt. Thorbjorn-Svartsengi volcanic unrest is crucial for successful early warning of volcanic hazards since the center of uplift is only 2km away from a fishing village and major infrastructure in the area, such as water supply and geothermal power. For the first time in Iceland, we have provided near-real-time dv/v variations to obtain a more complete picture of this magmatic activity. Our findings are supported by the analysis of other primary monitoring streams. We propose that this technique may be useful for early detection of future intrusions/increased magmatic activity. This study is supported by the Icelandic Research Fund, Rannis (Grant No: 185209-051).
How to cite: Cubuk Sabuncu, Y., Jonsdottir, K., Caudron, C., Lecocq, T., Parks, M. M., Geirsson, H., and Mordret, A.: Temporal seismic velocity changes during the 2020 rapid inflation at Mt. Thorbjorn-Svartsengi, Iceland, using ambient seismic noise, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12924, https://doi.org/10.5194/egusphere-egu21-12924, 2021.
EGU21-15222 | vPICO presentations | SM3.1
Temporal evolution of relative seismic velocity in the Golf of Corinth - Greece.Estelle Delouche and Laurent Stehly
Our aim is to monitor the temporal evolution of the crust in Greece, with a particular focus on the Gulf of Corinth. Indeed, Greece is one of the most exposed country to earthquakes in Europe. The Gulf of Corinth, is known for its fast extension rate of about 15 mm/yr in the western part and 10mm/yr in the eastern part. This fast extension is associated with recurrent seismic swarms and by a few destructive earthquakes. This seismicity is likely the result of a combination of multiple driving processes including fluid migration at depth.
In the present work, we use seismic noise recorded from 2010 to 2020 by all seismic stations deployed in Greece, and in particular by the dense Corinth Rift Laboratory network, to compute the seismic velocity variation (dv/v) in several subregions. By comparing the result obtained at different periods, we are able to distinguish the temporal evolution of the upper, mid and lower crust. This temporal evolution is compared to the seismicity of the Gulf of Corinth.
How to cite: Delouche, E. and Stehly, L.: Temporal evolution of relative seismic velocity in the Golf of Corinth - Greece., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15222, https://doi.org/10.5194/egusphere-egu21-15222, 2021.
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Our aim is to monitor the temporal evolution of the crust in Greece, with a particular focus on the Gulf of Corinth. Indeed, Greece is one of the most exposed country to earthquakes in Europe. The Gulf of Corinth, is known for its fast extension rate of about 15 mm/yr in the western part and 10mm/yr in the eastern part. This fast extension is associated with recurrent seismic swarms and by a few destructive earthquakes. This seismicity is likely the result of a combination of multiple driving processes including fluid migration at depth.
In the present work, we use seismic noise recorded from 2010 to 2020 by all seismic stations deployed in Greece, and in particular by the dense Corinth Rift Laboratory network, to compute the seismic velocity variation (dv/v) in several subregions. By comparing the result obtained at different periods, we are able to distinguish the temporal evolution of the upper, mid and lower crust. This temporal evolution is compared to the seismicity of the Gulf of Corinth.
How to cite: Delouche, E. and Stehly, L.: Temporal evolution of relative seismic velocity in the Golf of Corinth - Greece., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15222, https://doi.org/10.5194/egusphere-egu21-15222, 2021.
EGU21-3739 | vPICO presentations | SM3.1 | Highlight
Imaging the Hydrothermal Plumbing Architecture of Steamboat Geyser Using a Dense Nodal Array and Seismic InterferometrySin-Mei Wu, Fan-Chi Lin, and Jamie Farrell
The plumbing architecture of a hydrothermal feature (e.g., geyser and spring) exerts direct control over its eruption and recharge dynamics. During an active geyser’s recharge, in response to the evolution of temperature and hydrostatic pressure within the plumbing, this two-phase-flow system experiences intensive steam bubble nucleation and collapse throughout the eruption cycle. Such steam-liquid phase transitions generate seismic signals observed as hydrothermal tremor, thus the spatiotemporal pattern of its origin can depict the plumbing architecture and illuminate how the geyser operates internally. Steamboat, the tallest active geyser on Earth, is thought to have a complex architecture and dynamics owing to the hydrologic interaction with the nearby Cistern Spring, ~100 m SW of Steamboat. To study the system, in 2019 we deployed a dense array across the Steamboat-Cistern area with an aperture of ~250 m. The array was composed of 50 three-component geophones and had a spacing of 15–35 m. During the deployment, 6 eruption cycles with intervals ranging from 3 to 8 days were recorded. We observe distinct 1–5 Hz tremor emitted from Steamboat and Cistern, which are persistent and show no isolated events and discernable arrivals. To simultaneously locate the tremor from both features, we perform multicomponent cross-correlation to isolate and enhance the coherent signals of interest with each station as the virtual source. We apply the same normalization to the 3-component data so that the particle motion excited by each virtual source is retained. We observe prevalent seismic P waves at receivers near the source, with complex wavefield transition and interference at distant receivers. Using the P wave linearity, we back project the polarized directions to constrain the 3D source location. The results provide the first 4D view of the tremor throughout the eruption cycles with hourly resolution.
The 4D view reveals the conduit beneath Steamboat is vertical and extends down to ~120 m depth and the plumbing of Cistern includes a shallow vertical conduit connecting with a deep, large, and laterally offset reservoir ~60 m southeast of the surface pool. No direct connection between Steamboat and Cistern plumbing structures is found above ~120 m. The temporal variation of the tremor combined with in situ temperature and water depth measurements of Cistern, do reveal the interaction between Steamboat and Cistern throughout the eruption/recharge cycles. The observed delayed responses of Cistern in reaction to Steamboat eruptions and recharge suggest the two plumbing structures might be connected through a fractured/porous medium instead of a direct open channel, consistent with our inferred plumbing structure.
How to cite: Wu, S.-M., Lin, F.-C., and Farrell, J.: Imaging the Hydrothermal Plumbing Architecture of Steamboat Geyser Using a Dense Nodal Array and Seismic Interferometry, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3739, https://doi.org/10.5194/egusphere-egu21-3739, 2021.
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The plumbing architecture of a hydrothermal feature (e.g., geyser and spring) exerts direct control over its eruption and recharge dynamics. During an active geyser’s recharge, in response to the evolution of temperature and hydrostatic pressure within the plumbing, this two-phase-flow system experiences intensive steam bubble nucleation and collapse throughout the eruption cycle. Such steam-liquid phase transitions generate seismic signals observed as hydrothermal tremor, thus the spatiotemporal pattern of its origin can depict the plumbing architecture and illuminate how the geyser operates internally. Steamboat, the tallest active geyser on Earth, is thought to have a complex architecture and dynamics owing to the hydrologic interaction with the nearby Cistern Spring, ~100 m SW of Steamboat. To study the system, in 2019 we deployed a dense array across the Steamboat-Cistern area with an aperture of ~250 m. The array was composed of 50 three-component geophones and had a spacing of 15–35 m. During the deployment, 6 eruption cycles with intervals ranging from 3 to 8 days were recorded. We observe distinct 1–5 Hz tremor emitted from Steamboat and Cistern, which are persistent and show no isolated events and discernable arrivals. To simultaneously locate the tremor from both features, we perform multicomponent cross-correlation to isolate and enhance the coherent signals of interest with each station as the virtual source. We apply the same normalization to the 3-component data so that the particle motion excited by each virtual source is retained. We observe prevalent seismic P waves at receivers near the source, with complex wavefield transition and interference at distant receivers. Using the P wave linearity, we back project the polarized directions to constrain the 3D source location. The results provide the first 4D view of the tremor throughout the eruption cycles with hourly resolution.
The 4D view reveals the conduit beneath Steamboat is vertical and extends down to ~120 m depth and the plumbing of Cistern includes a shallow vertical conduit connecting with a deep, large, and laterally offset reservoir ~60 m southeast of the surface pool. No direct connection between Steamboat and Cistern plumbing structures is found above ~120 m. The temporal variation of the tremor combined with in situ temperature and water depth measurements of Cistern, do reveal the interaction between Steamboat and Cistern throughout the eruption/recharge cycles. The observed delayed responses of Cistern in reaction to Steamboat eruptions and recharge suggest the two plumbing structures might be connected through a fractured/porous medium instead of a direct open channel, consistent with our inferred plumbing structure.
How to cite: Wu, S.-M., Lin, F.-C., and Farrell, J.: Imaging the Hydrothermal Plumbing Architecture of Steamboat Geyser Using a Dense Nodal Array and Seismic Interferometry, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3739, https://doi.org/10.5194/egusphere-egu21-3739, 2021.
EGU21-15337 | vPICO presentations | SM3.1
Locating flowing conduits in Karst using passive seismic deploymentsHaleh Karbala Ali, Christopher J. Bean, Caoimhe Hickey, and Billy o'Keeffe
Karst is an important landscape in many locations incorporating many subterranean waterflow passages in the form of caves, conduits, and fractures. Although challenging, some karst structures can be imaged by active geophysical techniques however they generally cannot facilitate differentiation between flowing and non-flowing waterways. In this study, we aim to locate flowing conduits by passively capturing flow-induced seismic signals.
To gain a broad understanding of seismic source versus path effect in these complex structures and to help us design bespoke field experiments, we commence our study by undertaking 3D numerical simulation (using SPECFEM3D) for different cases of shallow and deep conduits. These choices are informed by known conduit geometries in Ireland (they have been dived). Spectral resonance, synthetic heat maps, and amplitude-based locations of synthetic data reveal interesting information regarding the conduit response.
Based on the results of these simulations, we designed the layout of a passive field experiment on karst on Pollnagran cave in County Roscommon, Ireland using 1Hz seismometers and 5 Hz Geophones. The karst deployment is also complemented by smaller experiments on surface rivers in order to help better understand observed signals. We also undertake an active hammer seismic survey at the site in order the build a model for future site-specific numerical simulations.
Consistent with numerical experiments, clear discrete frequencies associated with water flow are observed in the field data. A complex picture is emerging where the largest dived caves are not necessarily the flow structures with the largest seismic amplitudes.
How to cite: Karbala Ali, H., Bean, C. J., Hickey, C., and o'Keeffe, B.: Locating flowing conduits in Karst using passive seismic deployments, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15337, https://doi.org/10.5194/egusphere-egu21-15337, 2021.
Karst is an important landscape in many locations incorporating many subterranean waterflow passages in the form of caves, conduits, and fractures. Although challenging, some karst structures can be imaged by active geophysical techniques however they generally cannot facilitate differentiation between flowing and non-flowing waterways. In this study, we aim to locate flowing conduits by passively capturing flow-induced seismic signals.
To gain a broad understanding of seismic source versus path effect in these complex structures and to help us design bespoke field experiments, we commence our study by undertaking 3D numerical simulation (using SPECFEM3D) for different cases of shallow and deep conduits. These choices are informed by known conduit geometries in Ireland (they have been dived). Spectral resonance, synthetic heat maps, and amplitude-based locations of synthetic data reveal interesting information regarding the conduit response.
Based on the results of these simulations, we designed the layout of a passive field experiment on karst on Pollnagran cave in County Roscommon, Ireland using 1Hz seismometers and 5 Hz Geophones. The karst deployment is also complemented by smaller experiments on surface rivers in order to help better understand observed signals. We also undertake an active hammer seismic survey at the site in order the build a model for future site-specific numerical simulations.
Consistent with numerical experiments, clear discrete frequencies associated with water flow are observed in the field data. A complex picture is emerging where the largest dived caves are not necessarily the flow structures with the largest seismic amplitudes.
How to cite: Karbala Ali, H., Bean, C. J., Hickey, C., and o'Keeffe, B.: Locating flowing conduits in Karst using passive seismic deployments, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15337, https://doi.org/10.5194/egusphere-egu21-15337, 2021.
EGU21-15489 | vPICO presentations | SM3.1
Permanent, seasonal, and episodic seismic sources around Vatnajökull, Iceland from the analyses of correlogramsSylvain Nowé, Thomas Lecocq, Corentin Caudron, Kristín Jónsdóttir, and Frank Pattyn
This study aims at characterizing different seismic sources in the region of the Vatnajökull glacier using seismic interferometry. Vatnajökull is the largest Icelandic icecap, covering 4active volcanic systems. The seismic context is therefore very complex with glacial and volcanic events occurring simultaneously and a classification between the two can become cumbersome.
We used seismic interferometry or cross-correlation of seismic noise on seismic data from 2011 to 2019). Being based on continuous records, this passive monitoring method is not relying on earthquakes to locate seismic sources. We computed the cross-correlation functions between every pair of seismic stations using MSNoise for different frequency bands, from 0.5 to 8 Hz. The first step towards the location of seismic sources was to calculate the propagation velocities for each frequency range. The total range of velocities is between 1.39 km/s and 3.92 km/s. Then, we used two different location methods based on the calculated propagation velocities. The first method is based on hyperbole’s geometry and provides the location of seismic sources as the intersection between several hyperboles, while the second one, the Ballmer’s method (Ballmer et al. 2013), is based on the calculation of theoretical differential times and provides location probabilities for the seismic sources. We located and characterized persistent oceanic seismic noise located along the southern shoreline of Iceland potentially associated with waves activity and geometry of the shore, as well as a seasonal glacial tremor around outlet glaciers in the west part of the Vatnajökull icecap, potentially linked to glacial processes inside the glacier or in the glacial rivers. The uncertainty of a few kilometers is observed. Some limitations exist for these methods. For example, The Ballmer’s method (Ballmer et al. 2013) is reliable for seismic sources inside the seismic network but can only give an azimuthal direction for seismic sources located outside of it. When using hyperboles, slightly different propagation velocities between pairs of stations can affect the precision of the intersection. Therefore, the association of the two methods is important to diminish the impact of these limitations.
These results provide a better understanding of the seismic background of this region and will be compared and validated with other localization methods in the future.
How to cite: Nowé, S., Lecocq, T., Caudron, C., Jónsdóttir, K., and Pattyn, F.: Permanent, seasonal, and episodic seismic sources around Vatnajökull, Iceland from the analyses of correlograms, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15489, https://doi.org/10.5194/egusphere-egu21-15489, 2021.
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This study aims at characterizing different seismic sources in the region of the Vatnajökull glacier using seismic interferometry. Vatnajökull is the largest Icelandic icecap, covering 4active volcanic systems. The seismic context is therefore very complex with glacial and volcanic events occurring simultaneously and a classification between the two can become cumbersome.
We used seismic interferometry or cross-correlation of seismic noise on seismic data from 2011 to 2019). Being based on continuous records, this passive monitoring method is not relying on earthquakes to locate seismic sources. We computed the cross-correlation functions between every pair of seismic stations using MSNoise for different frequency bands, from 0.5 to 8 Hz. The first step towards the location of seismic sources was to calculate the propagation velocities for each frequency range. The total range of velocities is between 1.39 km/s and 3.92 km/s. Then, we used two different location methods based on the calculated propagation velocities. The first method is based on hyperbole’s geometry and provides the location of seismic sources as the intersection between several hyperboles, while the second one, the Ballmer’s method (Ballmer et al. 2013), is based on the calculation of theoretical differential times and provides location probabilities for the seismic sources. We located and characterized persistent oceanic seismic noise located along the southern shoreline of Iceland potentially associated with waves activity and geometry of the shore, as well as a seasonal glacial tremor around outlet glaciers in the west part of the Vatnajökull icecap, potentially linked to glacial processes inside the glacier or in the glacial rivers. The uncertainty of a few kilometers is observed. Some limitations exist for these methods. For example, The Ballmer’s method (Ballmer et al. 2013) is reliable for seismic sources inside the seismic network but can only give an azimuthal direction for seismic sources located outside of it. When using hyperboles, slightly different propagation velocities between pairs of stations can affect the precision of the intersection. Therefore, the association of the two methods is important to diminish the impact of these limitations.
These results provide a better understanding of the seismic background of this region and will be compared and validated with other localization methods in the future.
How to cite: Nowé, S., Lecocq, T., Caudron, C., Jónsdóttir, K., and Pattyn, F.: Permanent, seasonal, and episodic seismic sources around Vatnajökull, Iceland from the analyses of correlograms, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15489, https://doi.org/10.5194/egusphere-egu21-15489, 2021.
EGU21-1052 | vPICO presentations | SM3.1
A full-waveform inversion workflow for estimationing ambient seismic source distributions from Rayleigh-wave multicomponent crosscorrelationsZongbo Xu, T. Dylan Mikesell, Josefine Umlauft, and Gabriel Gribler
Estimation of ambient seismic source distributions (e.g. location and strength) is important for studies of seismic source mechanisms and subsurface structures. It is current state of the art to estimate the source distribution by applying full-waveform inversion (FWI) to seismic crosscorrelations. We previously theoretically demonstrated the advantage of Rayleigh-wave multicomponent crosscorrelations in the FWI estimation process. In this presentation, we utilize the crosscorrelations from real ambient seismic data acquired in Hartoušov, Czech Republic, where the seismic sources are CO2 degassing areas at Earth’s surface (i.e. fumaroles or mofettes). We develop a complete workflow from the raw data to the FWI estimation. We demonstrate that the multicomponent crosscorrelations can better constrain the source distribution than vertical-component crosscorrelations in both elastic media and anelastic media, even when we use an elastic forward model in the inversion process. Our inversion results indicate a strong seismic source near strong CO2 gas flux areas.
How to cite: Xu, Z., Mikesell, T. D., Umlauft, J., and Gribler, G.: A full-waveform inversion workflow for estimationing ambient seismic source distributions from Rayleigh-wave multicomponent crosscorrelations, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1052, https://doi.org/10.5194/egusphere-egu21-1052, 2021.
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Estimation of ambient seismic source distributions (e.g. location and strength) is important for studies of seismic source mechanisms and subsurface structures. It is current state of the art to estimate the source distribution by applying full-waveform inversion (FWI) to seismic crosscorrelations. We previously theoretically demonstrated the advantage of Rayleigh-wave multicomponent crosscorrelations in the FWI estimation process. In this presentation, we utilize the crosscorrelations from real ambient seismic data acquired in Hartoušov, Czech Republic, where the seismic sources are CO2 degassing areas at Earth’s surface (i.e. fumaroles or mofettes). We develop a complete workflow from the raw data to the FWI estimation. We demonstrate that the multicomponent crosscorrelations can better constrain the source distribution than vertical-component crosscorrelations in both elastic media and anelastic media, even when we use an elastic forward model in the inversion process. Our inversion results indicate a strong seismic source near strong CO2 gas flux areas.
How to cite: Xu, Z., Mikesell, T. D., Umlauft, J., and Gribler, G.: A full-waveform inversion workflow for estimationing ambient seismic source distributions from Rayleigh-wave multicomponent crosscorrelations, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1052, https://doi.org/10.5194/egusphere-egu21-1052, 2021.
EGU21-7515 | vPICO presentations | SM3.1
Imaging noise sources: comparing and combining a matched-field processing technique with finite-frequency noise source inversionsJonas Igel, Daniel Bowden, Korbinian Sager, and Andreas Fichtner
Imaging the spatio-temporal variations of ambient seismic noise sources can provide important information to improve near real-time monitoring and noise tomography. Various methods have been developed to tackle this problem. For example, Matched-Field Processing (MFP) offers an efficient data-driven approach by testing different noise source locations and subsequently correlating and stacking. A more rigorous approach is treating it as a finite-frequency full-waveform inversion problem. In contrast to the MFP technique, an inversion framework allows for the incorporation of prior information and subsequent iterative updates of the noise source distribution by numerically modelling correlations and source sensitivity kernels. Bowden et al. (2020) discuss the similarities between these two methods and how one can be derived from the other.
We aim to compare and contrast the two methods using real data from a regional to a global scale to locate the secondary microseismic sources in the ocean. Igel et al. (2021, in prep) use a logarithmic energy ratio as measurement for the sensitivity kernels, which is chosen due to its robustness with respect to unknown 3D Earth structures. However, some disadvantages of this type of measurement are not considering absolute amplitudes and discarding information outside of the expected surface wave arrival time window. By combining the two methods and first using MFP to create an initial model for the inversion, we are able to steer the inversion in the right direction, allowing us to use a more elaborate full-waveform measurement in the inversion and hence increasing the resolution and quality of the final model.
Results for noise source inversions in the ocean on a daily basis using the combination of the two methods will be presented. This work paves the way for publicly available, daily, multi-scale ambient noise source maps.
How to cite: Igel, J., Bowden, D., Sager, K., and Fichtner, A.: Imaging noise sources: comparing and combining a matched-field processing technique with finite-frequency noise source inversions, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7515, https://doi.org/10.5194/egusphere-egu21-7515, 2021.
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Imaging the spatio-temporal variations of ambient seismic noise sources can provide important information to improve near real-time monitoring and noise tomography. Various methods have been developed to tackle this problem. For example, Matched-Field Processing (MFP) offers an efficient data-driven approach by testing different noise source locations and subsequently correlating and stacking. A more rigorous approach is treating it as a finite-frequency full-waveform inversion problem. In contrast to the MFP technique, an inversion framework allows for the incorporation of prior information and subsequent iterative updates of the noise source distribution by numerically modelling correlations and source sensitivity kernels. Bowden et al. (2020) discuss the similarities between these two methods and how one can be derived from the other.
We aim to compare and contrast the two methods using real data from a regional to a global scale to locate the secondary microseismic sources in the ocean. Igel et al. (2021, in prep) use a logarithmic energy ratio as measurement for the sensitivity kernels, which is chosen due to its robustness with respect to unknown 3D Earth structures. However, some disadvantages of this type of measurement are not considering absolute amplitudes and discarding information outside of the expected surface wave arrival time window. By combining the two methods and first using MFP to create an initial model for the inversion, we are able to steer the inversion in the right direction, allowing us to use a more elaborate full-waveform measurement in the inversion and hence increasing the resolution and quality of the final model.
Results for noise source inversions in the ocean on a daily basis using the combination of the two methods will be presented. This work paves the way for publicly available, daily, multi-scale ambient noise source maps.
How to cite: Igel, J., Bowden, D., Sager, K., and Fichtner, A.: Imaging noise sources: comparing and combining a matched-field processing technique with finite-frequency noise source inversions, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7515, https://doi.org/10.5194/egusphere-egu21-7515, 2021.
EGU21-8752 | vPICO presentations | SM3.1
Source locations of microseisms in the North Atlantic from Matched Field Processing using full Green's Functions.Sven Schippkus and Céline Hadziioannou
Precise knowledge of the sources of seismic noise is fundamental to our understanding of the ambient seismic field and its generation mechanisms. Two approaches to locating such sources exist currently. One is based on minimizing the misfit between estimated Green's functions from cross-correlation of seismic noise and synthetically computed correlation functions. This approach is computationally expensive and not yet widely adopted. The other, more common approach is Beamforming, where a beam is computed by shifting waveforms in time corresponding to the slowness of a potentially arriving wave front. Beamforming allows fast computations, but is limited to the plane-wave assumption and sources outside of the array.
Matched Field Processing (MFP) is Beamforming in the spatial domain. By probing potential source locations directly, it allows for arbitrary wave propagation in the medium as well as sources inside of arrays. MFP has been successfully applied at local scale using a constant velocity for travel-time estimation, sufficient at that scale. At regional scale, travel times can be estimated from phase velocity maps, which are not yet available globally at microseism frequencies.
To expand MFP’s applicability to new regions and larger scales, we replace the replica vectors that contain only travel-time information with full synthetic Green's functions. This allows to capture the full complexity of wave propagation by including relative amplitude information between receivers and multiple phases. We apply the method to continuous recordings of stations surrounding the North Atlantic and locate seismic sources in the primary and secondary microseism band, using pre-computed databases of Green's functions for computational efficiency. The framework we introduce here can easily be adapted to a laterally homogeneous Earth once such Green’s function databases become available, hopefully in the near future.
How to cite: Schippkus, S. and Hadziioannou, C.: Source locations of microseisms in the North Atlantic from Matched Field Processing using full Green's Functions., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8752, https://doi.org/10.5194/egusphere-egu21-8752, 2021.
Precise knowledge of the sources of seismic noise is fundamental to our understanding of the ambient seismic field and its generation mechanisms. Two approaches to locating such sources exist currently. One is based on minimizing the misfit between estimated Green's functions from cross-correlation of seismic noise and synthetically computed correlation functions. This approach is computationally expensive and not yet widely adopted. The other, more common approach is Beamforming, where a beam is computed by shifting waveforms in time corresponding to the slowness of a potentially arriving wave front. Beamforming allows fast computations, but is limited to the plane-wave assumption and sources outside of the array.
Matched Field Processing (MFP) is Beamforming in the spatial domain. By probing potential source locations directly, it allows for arbitrary wave propagation in the medium as well as sources inside of arrays. MFP has been successfully applied at local scale using a constant velocity for travel-time estimation, sufficient at that scale. At regional scale, travel times can be estimated from phase velocity maps, which are not yet available globally at microseism frequencies.
To expand MFP’s applicability to new regions and larger scales, we replace the replica vectors that contain only travel-time information with full synthetic Green's functions. This allows to capture the full complexity of wave propagation by including relative amplitude information between receivers and multiple phases. We apply the method to continuous recordings of stations surrounding the North Atlantic and locate seismic sources in the primary and secondary microseism band, using pre-computed databases of Green's functions for computational efficiency. The framework we introduce here can easily be adapted to a laterally homogeneous Earth once such Green’s function databases become available, hopefully in the near future.
How to cite: Schippkus, S. and Hadziioannou, C.: Source locations of microseisms in the North Atlantic from Matched Field Processing using full Green's Functions., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8752, https://doi.org/10.5194/egusphere-egu21-8752, 2021.
EGU21-6350 | vPICO presentations | SM3.1 | Highlight
Seeking an eye using several ears: cyclonic storms as heard by seismic arrays.Julián Pelaez, Dirk Becker, and Céline Hadziioannou
Under certain conditions, ocean surface gravity waves (SGW) interact with the seafloor underneath to trigger relatively faint but measurable seismic waves known as ocean microseisms. Cyclonic storms (e.g. hurricanes, typhoons) wandering over the ocean are major (non-stationary) sources of the former, thus opening the possibility of tracking and studying cyclones by means of their corresponding microseims.
For this purpose, we identified storm-related microseisms hidden in the ambient seismic wavefield via array processing. Polarization beamforming, a robust and well-known technique is implemented. The analyses hinge on surface waves (Love and Rayleigh) which, in contrast to P-waves, are stronger but only constrain direction of arrival (without source remoteness). We use a few land-based virtual seismic arrays surrounding the North Atlantic to investigate the signatures of major hurricanes in the microseismic band (0.05-0.16 Hz), in a joint attempt to continuously triangulate their tracks.
In general, a better correlation with the tracks was observed for surface waves in comparison to P waves. At the same frequency band, there is a good agreement between storm-related Love and retrograde Rayleigh wave signatures, suggesting a common amplification mechanism and co-located excitation area. However, the Love wavefield appears to be comparatively more diffuse and weaker than that of Rayleigh waves, which in turn produced the sharpest and most accurate trackings.
Our findings show that storm microseisms are intermittently excited with modulated amplitude at localized oceanic regions, particularly over the shallow continental shelves and slopes, having maximum amplitudes virtually independent of storm category. In most cases no detection was possible over deep oceanic regions, nor at distant arrays. Additionally, the rear quadrants and trailing swells of the cyclone provide the optimum SGW spectrum for the generation of microseisms, often shifted more than 500 km off the "eye". Occasionally, the passage of a cyclone near an island appears to trigger strong stationary signals lasting for a couple of days.
As a result of the aforementioned and added to the strong attenuation of storm microseisms, the inversion of tracks or physical properties of storms using a few far-field arrays is discontinuous in most cases, being reliable only if benchmark atmospheric and/or oceanic data is available for comparison.
Even if challenging due to the complexity of the coupled phenomena responsible for microseisms, the inversion of site properties, such as bathymetric parameters (e.g. depth, seabed geomorphology), near-bottom geology or SGW spectrum might be possible if storms are treated as natural sources in time-lapse ambient noise investigations. This will likely require near-field (land and underwater) observations using optimal arrays or dense, widespread sensor networks. Improved detection and understanding of ocean microseisms carries a great potential to contribute to mechanically coupled atmosphere-ocean-earth models.
How to cite: Pelaez, J., Becker, D., and Hadziioannou, C.: Seeking an eye using several ears: cyclonic storms as heard by seismic arrays., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6350, https://doi.org/10.5194/egusphere-egu21-6350, 2021.
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Please use the buttons below to download the presentation materials or to visit the external website where the presentation is linked. Regarding the external link, please note that Copernicus Meetings cannot accept any liability for the content and the website you will visit.
Forward to presentation link
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We are sorry, but presentations are only available for users who registered for the conference. Thank you.
Under certain conditions, ocean surface gravity waves (SGW) interact with the seafloor underneath to trigger relatively faint but measurable seismic waves known as ocean microseisms. Cyclonic storms (e.g. hurricanes, typhoons) wandering over the ocean are major (non-stationary) sources of the former, thus opening the possibility of tracking and studying cyclones by means of their corresponding microseims.
For this purpose, we identified storm-related microseisms hidden in the ambient seismic wavefield via array processing. Polarization beamforming, a robust and well-known technique is implemented. The analyses hinge on surface waves (Love and Rayleigh) which, in contrast to P-waves, are stronger but only constrain direction of arrival (without source remoteness). We use a few land-based virtual seismic arrays surrounding the North Atlantic to investigate the signatures of major hurricanes in the microseismic band (0.05-0.16 Hz), in a joint attempt to continuously triangulate their tracks.
In general, a better correlation with the tracks was observed for surface waves in comparison to P waves. At the same frequency band, there is a good agreement between storm-related Love and retrograde Rayleigh wave signatures, suggesting a common amplification mechanism and co-located excitation area. However, the Love wavefield appears to be comparatively more diffuse and weaker than that of Rayleigh waves, which in turn produced the sharpest and most accurate trackings.
Our findings show that storm microseisms are intermittently excited with modulated amplitude at localized oceanic regions, particularly over the shallow continental shelves and slopes, having maximum amplitudes virtually independent of storm category. In most cases no detection was possible over deep oceanic regions, nor at distant arrays. Additionally, the rear quadrants and trailing swells of the cyclone provide the optimum SGW spectrum for the generation of microseisms, often shifted more than 500 km off the "eye". Occasionally, the passage of a cyclone near an island appears to trigger strong stationary signals lasting for a couple of days.
As a result of the aforementioned and added to the strong attenuation of storm microseisms, the inversion of tracks or physical properties of storms using a few far-field arrays is discontinuous in most cases, being reliable only if benchmark atmospheric and/or oceanic data is available for comparison.
Even if challenging due to the complexity of the coupled phenomena responsible for microseisms, the inversion of site properties, such as bathymetric parameters (e.g. depth, seabed geomorphology), near-bottom geology or SGW spectrum might be possible if storms are treated as natural sources in time-lapse ambient noise investigations. This will likely require near-field (land and underwater) observations using optimal arrays or dense, widespread sensor networks. Improved detection and understanding of ocean microseisms carries a great potential to contribute to mechanically coupled atmosphere-ocean-earth models.
How to cite: Pelaez, J., Becker, D., and Hadziioannou, C.: Seeking an eye using several ears: cyclonic storms as heard by seismic arrays., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6350, https://doi.org/10.5194/egusphere-egu21-6350, 2021.
EGU21-4709 | vPICO presentations | SM3.1 | Highlight
Secondary Microseisms generated by typhoons in the Northwestern Pacific OceanNassima Benbelkacem, Eléonore Stutzmann, Martin Schimmel, Véronique Farra, Fabrice Ardhuin, Guilhem Barruol, and Anne Mangeney
Secondary Microseisms (SM) are recorded by seismometers in the period band 3-10 s. They are generated by the interaction of ocean gravity waves of similar frequencies and coming from nearly opposite directions. Typhoons create such ocean waves, and the purpose of this study is to investigate the relationship between typhoons and microseism source characteristics. We focused our study on the Northwestern Pacific and we analyzed seismic signals recorded by the Alaska array and the corresponding storm catalog. While P body waves enable to characterize the amplitude and the localization of the sources, secondary microseisms are dominated by surface waves. Therefore, we apply beamforming technique to the vertical components in order to highlight the weaker body wave signals. This analysis permits us to track the localization of SM sources every 6 hours. Our results show three cases: In the case of one active typhoon, the positions of SM sources are localized close to the typhoon position. In the case of two nearby typhoons acting simultaneously, the SM sources are localized in between the typhoons. Finally, when the typhoon arrives close to the coast, we observe sources generated by ocean wave reflections. In conclusion, the three mechanisms proposed by Ardhuin et al., (2011) are necessary to explain secondary microseisms generated by typhoons.
How to cite: Benbelkacem, N., Stutzmann, E., Schimmel, M., Farra, V., Ardhuin, F., Barruol, G., and Mangeney, A.: Secondary Microseisms generated by typhoons in the Northwestern Pacific Ocean, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4709, https://doi.org/10.5194/egusphere-egu21-4709, 2021.
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Secondary Microseisms (SM) are recorded by seismometers in the period band 3-10 s. They are generated by the interaction of ocean gravity waves of similar frequencies and coming from nearly opposite directions. Typhoons create such ocean waves, and the purpose of this study is to investigate the relationship between typhoons and microseism source characteristics. We focused our study on the Northwestern Pacific and we analyzed seismic signals recorded by the Alaska array and the corresponding storm catalog. While P body waves enable to characterize the amplitude and the localization of the sources, secondary microseisms are dominated by surface waves. Therefore, we apply beamforming technique to the vertical components in order to highlight the weaker body wave signals. This analysis permits us to track the localization of SM sources every 6 hours. Our results show three cases: In the case of one active typhoon, the positions of SM sources are localized close to the typhoon position. In the case of two nearby typhoons acting simultaneously, the SM sources are localized in between the typhoons. Finally, when the typhoon arrives close to the coast, we observe sources generated by ocean wave reflections. In conclusion, the three mechanisms proposed by Ardhuin et al., (2011) are necessary to explain secondary microseisms generated by typhoons.
How to cite: Benbelkacem, N., Stutzmann, E., Schimmel, M., Farra, V., Ardhuin, F., Barruol, G., and Mangeney, A.: Secondary Microseisms generated by typhoons in the Northwestern Pacific Ocean, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4709, https://doi.org/10.5194/egusphere-egu21-4709, 2021.
EGU21-14837 | vPICO presentations | SM3.1 | Highlight
Inferring significant wave height from seismic data: A comparison between methods.Francisco Bolrão, Co Tran, Miguel Lima, Sheroze Sheriffdeen, Diogo Rodrigues, Graça Silveira, Tan Bui-Thanh, and Susana Custodio
The most pervasive seismic signal recorded on our planet – microseismic ambient noise -results from the coupling of energy between atmosphere, oceans and solid Earth. Because it carries information on ocean waves (source), the microseismic wavefield can be advantageously used to image ocean storms. This imaging is of interest both to climate studies – by extending the record of oceanic activity back into the early instrumental seismic record – and to real-time monitoring – where real-time seismic data can potentially be used to complement the spatially dense but temporally sparse satellite meteorological data.
In our work, we develop empirical transfer functions between seismic observations and ocean activity observations, in particular, significant wave height. We employ three different approaches: 1) The approach of Ferretti et al (2013), who compute a seismic significant wave height and invert only for the empirical conversion parameters between oceanic and seismic significant wave heights; 2) The classical approach of Bromirski et al (1999), who computed an empirical transfer function between ground-motion recorded at a coastal seismic station and significant wave height measured at a nearby ocean buoy; and 3) A novel recurrent neural-network (RNN) approach to infer significant wave height from seismic data.
We apply the three approaches to seismic and ocean buoy data recorded in the east coast of the United States. All three approaches are able to successfully predict ocean significant wave height from the seismic data. We compare the three approaches in terms of accuracy, computational effort and robustness. In addition, we investigate the regimes where each approach works best. The results show that the RNN approach is able to predict well the significant wave height recorded at the buoy. The prediction is improved if several nearby seismic stations are used rather than just one.
This work is supported by FCT through projects UIDB/50019/2020 – IDL and UTAP-EXPL/EAC/0056/2017 - STORM.
How to cite: Bolrão, F., Tran, C., Lima, M., Sheriffdeen, S., Rodrigues, D., Silveira, G., Bui-Thanh, T., and Custodio, S.: Inferring significant wave height from seismic data: A comparison between methods., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14837, https://doi.org/10.5194/egusphere-egu21-14837, 2021.
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The most pervasive seismic signal recorded on our planet – microseismic ambient noise -results from the coupling of energy between atmosphere, oceans and solid Earth. Because it carries information on ocean waves (source), the microseismic wavefield can be advantageously used to image ocean storms. This imaging is of interest both to climate studies – by extending the record of oceanic activity back into the early instrumental seismic record – and to real-time monitoring – where real-time seismic data can potentially be used to complement the spatially dense but temporally sparse satellite meteorological data.
In our work, we develop empirical transfer functions between seismic observations and ocean activity observations, in particular, significant wave height. We employ three different approaches: 1) The approach of Ferretti et al (2013), who compute a seismic significant wave height and invert only for the empirical conversion parameters between oceanic and seismic significant wave heights; 2) The classical approach of Bromirski et al (1999), who computed an empirical transfer function between ground-motion recorded at a coastal seismic station and significant wave height measured at a nearby ocean buoy; and 3) A novel recurrent neural-network (RNN) approach to infer significant wave height from seismic data.
We apply the three approaches to seismic and ocean buoy data recorded in the east coast of the United States. All three approaches are able to successfully predict ocean significant wave height from the seismic data. We compare the three approaches in terms of accuracy, computational effort and robustness. In addition, we investigate the regimes where each approach works best. The results show that the RNN approach is able to predict well the significant wave height recorded at the buoy. The prediction is improved if several nearby seismic stations are used rather than just one.
This work is supported by FCT through projects UIDB/50019/2020 – IDL and UTAP-EXPL/EAC/0056/2017 - STORM.
How to cite: Bolrão, F., Tran, C., Lima, M., Sheriffdeen, S., Rodrigues, D., Silveira, G., Bui-Thanh, T., and Custodio, S.: Inferring significant wave height from seismic data: A comparison between methods., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14837, https://doi.org/10.5194/egusphere-egu21-14837, 2021.
EGU21-8408 | vPICO presentations | SM3.1
Shear wave velocity from inter-source interferometryTom Eulenfeld
Ambient noise correlation uses the recordings of multiple, statistically distributed seismic sources (the noise sources) at two seismometers. By cross-correlating this signal, one obtains a wave traveling between two seismometers. Due to the principle of reciprocity it is possible to interchange the role of sources and receivers. This cannot be done with ambient noise, but another stochastic signal, the seismic coda is used. Using a cross-correlation of the seismic coda of two earthquakes recorded at multiple seismometers, it is possible to construct a seismic wave traveling between the two earthquakes in depth (inter-source interferometry). Here, I use the the time lag of the maxima in the cross-correlation of the coda wave field to measure the shear wave velocity in the source volume of swarm earthquakes. This technique is different from previous studies analyzing the decorrelation of the coda wave field of nearby events or using the cross-correlation for relocation purposes.
The technique is applied to five event clusters of the 2018 West Bohemia earthquake swarm. With the help of a high quality earthquake catalog, I was able to determine the shear wave velocity in the region of the five clusters separately. The shear wave velocities range between 3.5 km/s and 4.2 km/s. The resolution of this novel method is given by the extent of the clusters and better than for a comparable classical tomography. The method can be incorporated into a tomographic inversion to map the shear wave velocity in the source region with unprecedented resolution. The influence of focal mechanisms and the attenuation properties on the polarity and location of the maxima in the cross-correlation functions is discussed.
How to cite: Eulenfeld, T.: Shear wave velocity from inter-source interferometry, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8408, https://doi.org/10.5194/egusphere-egu21-8408, 2021.
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Ambient noise correlation uses the recordings of multiple, statistically distributed seismic sources (the noise sources) at two seismometers. By cross-correlating this signal, one obtains a wave traveling between two seismometers. Due to the principle of reciprocity it is possible to interchange the role of sources and receivers. This cannot be done with ambient noise, but another stochastic signal, the seismic coda is used. Using a cross-correlation of the seismic coda of two earthquakes recorded at multiple seismometers, it is possible to construct a seismic wave traveling between the two earthquakes in depth (inter-source interferometry). Here, I use the the time lag of the maxima in the cross-correlation of the coda wave field to measure the shear wave velocity in the source volume of swarm earthquakes. This technique is different from previous studies analyzing the decorrelation of the coda wave field of nearby events or using the cross-correlation for relocation purposes.
The technique is applied to five event clusters of the 2018 West Bohemia earthquake swarm. With the help of a high quality earthquake catalog, I was able to determine the shear wave velocity in the region of the five clusters separately. The shear wave velocities range between 3.5 km/s and 4.2 km/s. The resolution of this novel method is given by the extent of the clusters and better than for a comparable classical tomography. The method can be incorporated into a tomographic inversion to map the shear wave velocity in the source region with unprecedented resolution. The influence of focal mechanisms and the attenuation properties on the polarity and location of the maxima in the cross-correlation functions is discussed.
How to cite: Eulenfeld, T.: Shear wave velocity from inter-source interferometry, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8408, https://doi.org/10.5194/egusphere-egu21-8408, 2021.
EGU21-8007 | vPICO presentations | SM3.1 | Highlight
Humming trains as an opportune source for imaging the shallow crustLaura Pinzon-Rincon, François Lavoué, Aurélien Mordret, Pierre Boué, Florent Brenguier, Philippe Dales, Christopher J. Bean, and Daniel Hollis
How to cite: Pinzon-Rincon, L., Lavoué, F., Mordret, A., Boué, P., Brenguier, F., Dales, P., Bean, C. J., and Hollis, D.: Humming trains as an opportune source for imaging the shallow crust, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8007, https://doi.org/10.5194/egusphere-egu21-8007, 2021.
How to cite: Pinzon-Rincon, L., Lavoué, F., Mordret, A., Boué, P., Brenguier, F., Dales, P., Bean, C. J., and Hollis, D.: Humming trains as an opportune source for imaging the shallow crust, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8007, https://doi.org/10.5194/egusphere-egu21-8007, 2021.
EGU21-8708 | vPICO presentations | SM3.1
Deciphering train-induced body waves in correlation functions to promote fault monitoringKorbinian Sager, Florent Brenguier, Pierre Boué, Aurélien Mordret, and Victor C. Tsai
Continuous monitoring of active faults at seismogenic depths is key for the detection of potential precursors and to advance our understanding of earthquakes. In the context of the FaultScan project, we use seismic waves generated by freight trains – energetic and repetitive sources – recorded by two dense seismic arrays on both sides of the San Jacinto fault to directly observe transient deformation. Computing correlation functions for specific time segments corresponding to the passage of the trains reveals clear signals around the expected P-wave arrival time. The principle of Green’s function retrieval cannot be invoked for their interpretation, since the required assumption of a homogeneous source distribution is far from being met. To address this problem, we rely on correlation seismology, an emergent field of research that acknowledges the fact that correlations are shaped by both the distribution of ambient noise sources and Earth structure. Correlations are interpreted as self-consistent observables.
We first give a general introduction to (i) the forward problem of modeling correlation functions for arbitrary noise source distributions in space and frequency in potentially 3D heterogeneous and attenuating media, and to (ii) the computation of sensitivity kernels for noise sources and Earth structure. We then present an application of this framework to study the described problem of reconstructed body waves in the context of the FaultScan project. Studying structure kernels illustrates how signals are formed by the interaction of different P-wave phases and which parts should be used to monitor the fault. Forward modelling different source scenarios and structural changes further contributes to the understanding of the observed signals and highlights source-structure trade-offs.
Combining new and creative data-driven experiments with methodological developments is a promising way forward and has the potential to accelerate new discoveries.
How to cite: Sager, K., Brenguier, F., Boué, P., Mordret, A., and Tsai, V. C.: Deciphering train-induced body waves in correlation functions to promote fault monitoring, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8708, https://doi.org/10.5194/egusphere-egu21-8708, 2021.
Continuous monitoring of active faults at seismogenic depths is key for the detection of potential precursors and to advance our understanding of earthquakes. In the context of the FaultScan project, we use seismic waves generated by freight trains – energetic and repetitive sources – recorded by two dense seismic arrays on both sides of the San Jacinto fault to directly observe transient deformation. Computing correlation functions for specific time segments corresponding to the passage of the trains reveals clear signals around the expected P-wave arrival time. The principle of Green’s function retrieval cannot be invoked for their interpretation, since the required assumption of a homogeneous source distribution is far from being met. To address this problem, we rely on correlation seismology, an emergent field of research that acknowledges the fact that correlations are shaped by both the distribution of ambient noise sources and Earth structure. Correlations are interpreted as self-consistent observables.
We first give a general introduction to (i) the forward problem of modeling correlation functions for arbitrary noise source distributions in space and frequency in potentially 3D heterogeneous and attenuating media, and to (ii) the computation of sensitivity kernels for noise sources and Earth structure. We then present an application of this framework to study the described problem of reconstructed body waves in the context of the FaultScan project. Studying structure kernels illustrates how signals are formed by the interaction of different P-wave phases and which parts should be used to monitor the fault. Forward modelling different source scenarios and structural changes further contributes to the understanding of the observed signals and highlights source-structure trade-offs.
Combining new and creative data-driven experiments with methodological developments is a promising way forward and has the potential to accelerate new discoveries.
How to cite: Sager, K., Brenguier, F., Boué, P., Mordret, A., and Tsai, V. C.: Deciphering train-induced body waves in correlation functions to promote fault monitoring, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8708, https://doi.org/10.5194/egusphere-egu21-8708, 2021.
EGU21-5629 | vPICO presentations | SM3.1
On the Feasibility of Long-term Seismic Monitoring Using Freight Train SignalsYixiao Sheng, Florent Brenguier, Pierre Boué, Aurélien Mordret, Yehuda Ben-Zion, and Frank Vernon
How to cite: Sheng, Y., Brenguier, F., Boué, P., Mordret, A., Ben-Zion, Y., and Vernon, F.: On the Feasibility of Long-term Seismic Monitoring Using Freight Train Signals, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5629, https://doi.org/10.5194/egusphere-egu21-5629, 2021.
How to cite: Sheng, Y., Brenguier, F., Boué, P., Mordret, A., Ben-Zion, Y., and Vernon, F.: On the Feasibility of Long-term Seismic Monitoring Using Freight Train Signals, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5629, https://doi.org/10.5194/egusphere-egu21-5629, 2021.
EGU21-625 | vPICO presentations | SM3.1
Seismic interferometry from correlated noise sourcesDaniella Ayala, Andrew Curtis, and Michal Branicki
It is a well-established principle that cross-correlating seismic observations at different receiver locations yields new seismic responses that, under certain conditions, provide a useful estimate of the Green's function between the given receiver locations (that is, the medium response at one receiver location, had there been an impulsive source located at the other receiver). This principle, known as seismic interferometry, is a powerful technique that transforms previously discarded data such as seismic codas or background noise into useful signals that allow us to remotely illuminate subsurface Earth structures.
In practice it is often necessary and even desirable to rely on noise already present in the environment, since this type of seismic energy is freely and widely available in many regions around the globe. Across many applications of ambient noise interferometry there exists a persistent assumption that the noise sources in question are uncorrelated in space and time, and that energy arrives at the receiver array more-less equally from all directions. That this assumption is so tenaciously made comes as no surprise since the underlying theory unambiguously requires that the noise sources be uncorrelated for interferometry to work.
However, many real-world noise sources such as trains or highway traffic are inherently correlated both in space and time, in direct contradiction to these theoretical foundations. Violating the uncorrelatedness condition makes the Green’s function and associated phases liable to estimation errors that so far have not been accounted for. We show that these errors are indeed significant for commonly used noise sources, in some cases completely obscuring the phase one wishes to retrieve. Furthermore, we perform analysis that explains why stacking has the potential to reduce these errors in the interferometric estimate, as well as some limitations of this approach. This analytical insight allowed us to develop a novel workflow that mitigates or even completely removes the spurious effects arising from the use of correlated noise sources. Our methodology can be used in conjunction with already existing approaches, and hence we expect it to be widely applicable in real life ambient noise studies.
How to cite: Ayala, D., Curtis, A., and Branicki, M.: Seismic interferometry from correlated noise sources, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-625, https://doi.org/10.5194/egusphere-egu21-625, 2021.
It is a well-established principle that cross-correlating seismic observations at different receiver locations yields new seismic responses that, under certain conditions, provide a useful estimate of the Green's function between the given receiver locations (that is, the medium response at one receiver location, had there been an impulsive source located at the other receiver). This principle, known as seismic interferometry, is a powerful technique that transforms previously discarded data such as seismic codas or background noise into useful signals that allow us to remotely illuminate subsurface Earth structures.
In practice it is often necessary and even desirable to rely on noise already present in the environment, since this type of seismic energy is freely and widely available in many regions around the globe. Across many applications of ambient noise interferometry there exists a persistent assumption that the noise sources in question are uncorrelated in space and time, and that energy arrives at the receiver array more-less equally from all directions. That this assumption is so tenaciously made comes as no surprise since the underlying theory unambiguously requires that the noise sources be uncorrelated for interferometry to work.
However, many real-world noise sources such as trains or highway traffic are inherently correlated both in space and time, in direct contradiction to these theoretical foundations. Violating the uncorrelatedness condition makes the Green’s function and associated phases liable to estimation errors that so far have not been accounted for. We show that these errors are indeed significant for commonly used noise sources, in some cases completely obscuring the phase one wishes to retrieve. Furthermore, we perform analysis that explains why stacking has the potential to reduce these errors in the interferometric estimate, as well as some limitations of this approach. This analytical insight allowed us to develop a novel workflow that mitigates or even completely removes the spurious effects arising from the use of correlated noise sources. Our methodology can be used in conjunction with already existing approaches, and hence we expect it to be widely applicable in real life ambient noise studies.
How to cite: Ayala, D., Curtis, A., and Branicki, M.: Seismic interferometry from correlated noise sources, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-625, https://doi.org/10.5194/egusphere-egu21-625, 2021.
EGU21-10931 | vPICO presentations | SM3.1
Sensitivity enhancement of the ambient noise tomography and analysis of seasonal variations of noise sources to refine velocities in the lower crust in central EuropeJiri Kvapil, Jaroslava Plomerova, and AlpArray Working Group
The capability of the ambient noise tomography (ANT) to image subtle regional-scale velocity variations in the lower crust is limited by strong directionality of ambient noise sources in central Europe, which affects the quality of dispersion curves. Significant decrease of sensitivity kernels and sparse coverage of long interstation ray-pathes result in lower resolution at longer periods and thus increase uncertainty of the inversion solution in depth. If these well-known ANT limitations are properly addressed, the ANT is able to retrieve reliable high-resolution 3‑D shear velocities of the lower crust.
In this study we focus on seasonal variations of ambient noise sources in selected sites in different tectonic settings. We analyse ambient noise sources on continusly recorded wavefields from permanent observatories and temporary stations of AlpArray passive experiment with its complementary experiment and PACASE. These seismic networks with densely-spaced stations are well-suited for detailed analysis of period-dependent directionality of ambient noise sources and their effects on FTAN appearance and consequently on the quality of dispersion curves. In the second part of this study, we advocate a concept of layer-stripping during the stochastic inversion (enhanced ANT). It proved to be an efficient technique to explore the model space, particularly in the lower part of the crust. We discuss the sensitivity of the enhanced ANT to the imaged small-scale velocity features in the lower part of the crust, as well as the sensitivity to the sharp or gradational Moho in the models.
How to cite: Kvapil, J., Plomerova, J., and Working Group, A.: Sensitivity enhancement of the ambient noise tomography and analysis of seasonal variations of noise sources to refine velocities in the lower crust in central Europe, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10931, https://doi.org/10.5194/egusphere-egu21-10931, 2021.
Please decide on your access
Please use the buttons below to download the presentation materials or to visit the external website where the presentation is linked. Regarding the external link, please note that Copernicus Meetings cannot accept any liability for the content and the website you will visit.
Forward to presentation link
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We are sorry, but presentations are only available for users who registered for the conference. Thank you.
The capability of the ambient noise tomography (ANT) to image subtle regional-scale velocity variations in the lower crust is limited by strong directionality of ambient noise sources in central Europe, which affects the quality of dispersion curves. Significant decrease of sensitivity kernels and sparse coverage of long interstation ray-pathes result in lower resolution at longer periods and thus increase uncertainty of the inversion solution in depth. If these well-known ANT limitations are properly addressed, the ANT is able to retrieve reliable high-resolution 3‑D shear velocities of the lower crust.
In this study we focus on seasonal variations of ambient noise sources in selected sites in different tectonic settings. We analyse ambient noise sources on continusly recorded wavefields from permanent observatories and temporary stations of AlpArray passive experiment with its complementary experiment and PACASE. These seismic networks with densely-spaced stations are well-suited for detailed analysis of period-dependent directionality of ambient noise sources and their effects on FTAN appearance and consequently on the quality of dispersion curves. In the second part of this study, we advocate a concept of layer-stripping during the stochastic inversion (enhanced ANT). It proved to be an efficient technique to explore the model space, particularly in the lower part of the crust. We discuss the sensitivity of the enhanced ANT to the imaged small-scale velocity features in the lower part of the crust, as well as the sensitivity to the sharp or gradational Moho in the models.
How to cite: Kvapil, J., Plomerova, J., and Working Group, A.: Sensitivity enhancement of the ambient noise tomography and analysis of seasonal variations of noise sources to refine velocities in the lower crust in central Europe, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10931, https://doi.org/10.5194/egusphere-egu21-10931, 2021.
EGU21-4516 | vPICO presentations | SM3.1
Passive seismic matrix imaging of La Soufrière of Guadeloupe volcanoElsa Giraudat, Arnaud Burtin, and Alexandre Aubry
Volcanoes are among the most challenging media for seismic imaging given their highly localized and abrupt variations in physical parameters, extreme landforms, fractures, and the presence of magma and other fluids. Because of this high level of heterogeneity and the resulting difficulty to access the wave velocity distribution in the medium, reflection seismic imaging of volcanoes usually suffers from a loss of resolution and contrast. Here, we present a passive seismic imaging technique applied to the case of La Soufrière of Guadeloupe volcano. Inspired by previous works in optics (Badon et al., 2020), in acoustics (Lambert et al., 2020), and recently introduced in seismology (Touma et al., 2020), this technique relies on a matrix approach of passive reflection imaging, which requires only a rough approximation about the medium background velocity. This makes it robust even applied to extreme environments as volcanoes or fault zones. In this approach, the Green’s functions between an array of 76 geophones placed at the surface of the volcano are retrieved by cross-correlation of ambient seismic noise. This set of 2850 inter-element impulse responses forms a reflection matrix. Focusing operations are applied to this reflection matrix at emission and reception to project it in–depth. The focusing process allows to extract body wave components from seismic noise and thus, to retrieve information about reflectivity of in-depth structures. However, at this point, reflectivity images of the subsurface still suffer from phase distortions induced by long-range variations of the seismic velocity. This results in blurred images and hinders appropriate imaging. To overcome these issues, a novel operator is introduced: the distortion matrix. This operator is derived from the focused reflection matrix and connects any point in the medium with the distortion that a wavefront emitted from that point would experience due to heterogeneity. A time-reversal analysis of the distortion matrix allows to retrieve aberrations phase laws and hence to compensate for phase distortions. This correction enables to recover 3D-images of the volcano’s subsurface for the first 10km below the summit with optimized contrast and with an increased resolution. Interestingly, the restored resolution is even at least one half below the diffraction limit imposed by the geophone array angular aperture at the surface. The obtained gain in resolution and contrast allows to unveil internal structures of La Soufrière as hypothetical volcanic vents, magma reservoirs and lateral drainage conduits.
References
[Badon et al., 2020] Badon, A., Barolle, V., Irsch, K., Boccara, A. C., Fink, M., and Aubry, A. (2020). Distortion matrix concept for deep optical imaging in scattering media. Science Advances, 6(30).
[Lambert et al., 2020] Lambert, W., Cobus, L. A., Frappart, T., Fink, M., and Aubry, A. (2020). Distortion matrix approach for ultrasound imaging of random scattering media. Proceedings of the National Academy of Sciences, 117(26):14645-14656.
[Touma et al., 2020] Touma, R., Blondel, T., Derode, A., Campillo, M., & Aubry, A. (2020). A Distortion Matrix Framework for High-Resolution Passive Seismic 3D Imaging: Application to the San Jacinto Fault Zone, California. arXiv preprint arXiv:2008.01608.
How to cite: Giraudat, E., Burtin, A., and Aubry, A.: Passive seismic matrix imaging of La Soufrière of Guadeloupe volcano, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4516, https://doi.org/10.5194/egusphere-egu21-4516, 2021.
Volcanoes are among the most challenging media for seismic imaging given their highly localized and abrupt variations in physical parameters, extreme landforms, fractures, and the presence of magma and other fluids. Because of this high level of heterogeneity and the resulting difficulty to access the wave velocity distribution in the medium, reflection seismic imaging of volcanoes usually suffers from a loss of resolution and contrast. Here, we present a passive seismic imaging technique applied to the case of La Soufrière of Guadeloupe volcano. Inspired by previous works in optics (Badon et al., 2020), in acoustics (Lambert et al., 2020), and recently introduced in seismology (Touma et al., 2020), this technique relies on a matrix approach of passive reflection imaging, which requires only a rough approximation about the medium background velocity. This makes it robust even applied to extreme environments as volcanoes or fault zones. In this approach, the Green’s functions between an array of 76 geophones placed at the surface of the volcano are retrieved by cross-correlation of ambient seismic noise. This set of 2850 inter-element impulse responses forms a reflection matrix. Focusing operations are applied to this reflection matrix at emission and reception to project it in–depth. The focusing process allows to extract body wave components from seismic noise and thus, to retrieve information about reflectivity of in-depth structures. However, at this point, reflectivity images of the subsurface still suffer from phase distortions induced by long-range variations of the seismic velocity. This results in blurred images and hinders appropriate imaging. To overcome these issues, a novel operator is introduced: the distortion matrix. This operator is derived from the focused reflection matrix and connects any point in the medium with the distortion that a wavefront emitted from that point would experience due to heterogeneity. A time-reversal analysis of the distortion matrix allows to retrieve aberrations phase laws and hence to compensate for phase distortions. This correction enables to recover 3D-images of the volcano’s subsurface for the first 10km below the summit with optimized contrast and with an increased resolution. Interestingly, the restored resolution is even at least one half below the diffraction limit imposed by the geophone array angular aperture at the surface. The obtained gain in resolution and contrast allows to unveil internal structures of La Soufrière as hypothetical volcanic vents, magma reservoirs and lateral drainage conduits.
References
[Badon et al., 2020] Badon, A., Barolle, V., Irsch, K., Boccara, A. C., Fink, M., and Aubry, A. (2020). Distortion matrix concept for deep optical imaging in scattering media. Science Advances, 6(30).
[Lambert et al., 2020] Lambert, W., Cobus, L. A., Frappart, T., Fink, M., and Aubry, A. (2020). Distortion matrix approach for ultrasound imaging of random scattering media. Proceedings of the National Academy of Sciences, 117(26):14645-14656.
[Touma et al., 2020] Touma, R., Blondel, T., Derode, A., Campillo, M., & Aubry, A. (2020). A Distortion Matrix Framework for High-Resolution Passive Seismic 3D Imaging: Application to the San Jacinto Fault Zone, California. arXiv preprint arXiv:2008.01608.
How to cite: Giraudat, E., Burtin, A., and Aubry, A.: Passive seismic matrix imaging of La Soufrière of Guadeloupe volcano, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4516, https://doi.org/10.5194/egusphere-egu21-4516, 2021.
EGU21-9179 | vPICO presentations | SM3.1
Retrieving reflection arrivals from passive seismic data using Radon correlationDiako Hariri Naghadeh, Christopher J Bean, Patrick Smith, Sergei Lebedev, and Huda Mohamed
Since explosive and impulsive seismic sources such as dynamite, air guns, gas guns, or even vibroseis can have a big impact on the environment, some companies have decided to record ambient seismic noise and use it to estimate the physical properties of the subsurface. Big challenges arise when the aim is extracting body-waves from recorded passive signals, especially in the presence of strong surface waves. In passive seismic signals, such body-waves are usually weak in comparison to surface waves which are much more prominent. To understand the characteristics of passive signals and the effect of natural source locations, three simple synthetic models were created. To extract body-waves from simulated passive signals we propose and test a Radon-correlation method. This is a time-spatial correlation of amplitudes with a train of time-shifted Dirac delta functions through different hyperbolic paths. It is tested on a two-layer horizontal model, three-layer model which includes a dipping layer (with and without lateral heterogeneity) and also on synthetic Marmousi model data sets. Synthetic tests show that the introduced method is able to reconstruct reflection events at the correct time-offset positions which are hidden in results obtained by the general cross-correlation method. Also, a depth migrated section shows a good match between imaged-horizons and the true model. It is possible to generate off-end virtual gathers by applying the method to a linear array of receivers and to construct a velocity model by semblance velocity analysis of individually extracted gathers.
How to cite: Hariri Naghadeh, D., J Bean, C., Smith, P., Lebedev, S., and Mohamed, H.: Retrieving reflection arrivals from passive seismic data using Radon correlation , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9179, https://doi.org/10.5194/egusphere-egu21-9179, 2021.
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Since explosive and impulsive seismic sources such as dynamite, air guns, gas guns, or even vibroseis can have a big impact on the environment, some companies have decided to record ambient seismic noise and use it to estimate the physical properties of the subsurface. Big challenges arise when the aim is extracting body-waves from recorded passive signals, especially in the presence of strong surface waves. In passive seismic signals, such body-waves are usually weak in comparison to surface waves which are much more prominent. To understand the characteristics of passive signals and the effect of natural source locations, three simple synthetic models were created. To extract body-waves from simulated passive signals we propose and test a Radon-correlation method. This is a time-spatial correlation of amplitudes with a train of time-shifted Dirac delta functions through different hyperbolic paths. It is tested on a two-layer horizontal model, three-layer model which includes a dipping layer (with and without lateral heterogeneity) and also on synthetic Marmousi model data sets. Synthetic tests show that the introduced method is able to reconstruct reflection events at the correct time-offset positions which are hidden in results obtained by the general cross-correlation method. Also, a depth migrated section shows a good match between imaged-horizons and the true model. It is possible to generate off-end virtual gathers by applying the method to a linear array of receivers and to construct a velocity model by semblance velocity analysis of individually extracted gathers.
How to cite: Hariri Naghadeh, D., J Bean, C., Smith, P., Lebedev, S., and Mohamed, H.: Retrieving reflection arrivals from passive seismic data using Radon correlation , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9179, https://doi.org/10.5194/egusphere-egu21-9179, 2021.
EGU21-937 | vPICO presentations | SM3.1
High-frequency seismic interferometry: broadband measurements of surface-wave phase velocities using “large-N” arraysYihe Xu, Sergei Lebedev, Raffaele Bonadio, Thomas Meier, and Christopher Bean
High-frequency seismic surface waves sample the top few tens of meters to the top few kilometres of the subsurface. They can be used to determine three-dimensional distributions of shear-wave velocities and to map the depths of discontinuities (interfaces) within the crust. Passive seismic imaging, using ambient noise as the source of signal, can thus be an effective tool of exploration for mineral, geothermal and other resources, provided that sufficient high-frequency signal is available in the ambient noise wavefield and that accurate, high-frequency measurements can be performed on this signal. Ambient noise imaging using the ocean-generated noise at 5-30 s periods is now a standard method, but less signal is available at frequencies high enough for deposit-scale imaging (0.2-30 Hz), and few studies have reported successful measurements in broad frequency bands. Here, we develop a workflow for the measurement of high-frequency, surface-wave phase velocities in very broad frequency ranges. Our workflow comprises (1) a new noise cross-correlation procedure that accounts for the non-stationary properties of the high frequency noise sources, removes bandpass filtering, replaces temporal normalization with short time window stacking, and drops the explicit spectral normalization by adopting cross-coherence; (2) a new phase-velocity measurement method that extends the bandwidth of reliable measurements by exploiting the (resolved) 2π ambiguity of phase-velocity measurements; (3) interstation-distance-dependent quality control that uses the similarity of subgroups of dispersion curves to reject outliers and identify the frequency ranges with accurate measurements. The workflow is highly automated and applicable to large arrays. Applying our method to data from a large-N array that operated for one month near Marathon, Ontario, Canada, we use rectangular subarrays with 150-m station spacing and, typically, 1 hour of data and obtain Rayleigh-wave phase-velocity measurements in a 0.55-23.8 Hz frequency range, spanning over 5.4 octaves, nearly twice the typical frequency range of 1.5-3 octaves in previous studies. Phase-velocity maps and the subregion-average 1D velocity models they constrain show a high-velocity anomaly consistent with the known, west-dipping gabbro intrusions beneath the area. The new structural information can improve our understanding of the geometry of the gabbro intrusions, hosting the Cu-PGE Marathon deposit.
How to cite: Xu, Y., Lebedev, S., Bonadio, R., Meier, T., and Bean, C.: High-frequency seismic interferometry: broadband measurements of surface-wave phase velocities using “large-N” arrays, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-937, https://doi.org/10.5194/egusphere-egu21-937, 2021.
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High-frequency seismic surface waves sample the top few tens of meters to the top few kilometres of the subsurface. They can be used to determine three-dimensional distributions of shear-wave velocities and to map the depths of discontinuities (interfaces) within the crust. Passive seismic imaging, using ambient noise as the source of signal, can thus be an effective tool of exploration for mineral, geothermal and other resources, provided that sufficient high-frequency signal is available in the ambient noise wavefield and that accurate, high-frequency measurements can be performed on this signal. Ambient noise imaging using the ocean-generated noise at 5-30 s periods is now a standard method, but less signal is available at frequencies high enough for deposit-scale imaging (0.2-30 Hz), and few studies have reported successful measurements in broad frequency bands. Here, we develop a workflow for the measurement of high-frequency, surface-wave phase velocities in very broad frequency ranges. Our workflow comprises (1) a new noise cross-correlation procedure that accounts for the non-stationary properties of the high frequency noise sources, removes bandpass filtering, replaces temporal normalization with short time window stacking, and drops the explicit spectral normalization by adopting cross-coherence; (2) a new phase-velocity measurement method that extends the bandwidth of reliable measurements by exploiting the (resolved) 2π ambiguity of phase-velocity measurements; (3) interstation-distance-dependent quality control that uses the similarity of subgroups of dispersion curves to reject outliers and identify the frequency ranges with accurate measurements. The workflow is highly automated and applicable to large arrays. Applying our method to data from a large-N array that operated for one month near Marathon, Ontario, Canada, we use rectangular subarrays with 150-m station spacing and, typically, 1 hour of data and obtain Rayleigh-wave phase-velocity measurements in a 0.55-23.8 Hz frequency range, spanning over 5.4 octaves, nearly twice the typical frequency range of 1.5-3 octaves in previous studies. Phase-velocity maps and the subregion-average 1D velocity models they constrain show a high-velocity anomaly consistent with the known, west-dipping gabbro intrusions beneath the area. The new structural information can improve our understanding of the geometry of the gabbro intrusions, hosting the Cu-PGE Marathon deposit.
How to cite: Xu, Y., Lebedev, S., Bonadio, R., Meier, T., and Bean, C.: High-frequency seismic interferometry: broadband measurements of surface-wave phase velocities using “large-N” arrays, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-937, https://doi.org/10.5194/egusphere-egu21-937, 2021.
EGU21-4547 | vPICO presentations | SM3.1
Assessment of seismic ambient noise parameter estimation and wavefield decomposition in WaveDecMehrdad Fotouhimehr and Elham Shabani
Knowledge about seismic ambient noise wavefield through decomposition into different participant waves is of special importance in geophysical studies. In this study, WaveDec technique (Maranò et al., 2012) as an array statistical signal processing technique was used to decompose seismic ambient noise wavefield and to estimate wavefield parameters. In this method, the measurements from all components of stations and parameters of interest are modeled jointly which leads to significant improvement in extracting characteristics of surface waves. Considering the contribution of both Love and Rayleigh waves in the wavefield, the method estimates the desired parameters including amplitude, phase, azimuth, wave number and the ellipticity angle (for the Rayleigh wave only) based on the Maximum Likelihood Estimation method. One of the main characteristic of WaveDec is estimating the ellipticity angle of Rayleigh waves. This is very beneficial in determining retrograde and prograde particle motion and also in mode distinction.
In the WaveDec algorithm, the Truncated Newton method is used to optimize likelihood functions with respect to wavefield parameters. Furthermore, Bayesian Information Criterion (BIC) is used to select the best model and wave type determination (Rayleigh, Love, body wave or noise). Regarding a group of generated models for different wave types, the one with the smallest BIC is chosen.
We examined consistency of WaveDec algorithm by applying different numerical optimization methods; Truncated Newton, L-BFGS-B quasi-Newton and simplex-based Nelder-Mead methods. Furthermore, different model selection criteria; BIC, Akaike Information Criterion (AIC) and Hannan–Quinn Information Criterion (HQC) were examined to study the quality of generated models. They possess different penalty terms to avoid overfitting the models on data. All possible pairs of optimization methods and model selection criteria were utilized and replaced in WaveDec algorithm. In order to compare the resultant dispersion curves of surface waves and ellipticity angle curves of Rayleigh waves, SESAME model M2.1 synthetic data and some seismic ambient noise measurements in Colfiorito basin in Italy (Array B) were analyzed.
How to cite: Fotouhimehr, M. and Shabani, E.: Assessment of seismic ambient noise parameter estimation and wavefield decomposition in WaveDec, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4547, https://doi.org/10.5194/egusphere-egu21-4547, 2021.
Knowledge about seismic ambient noise wavefield through decomposition into different participant waves is of special importance in geophysical studies. In this study, WaveDec technique (Maranò et al., 2012) as an array statistical signal processing technique was used to decompose seismic ambient noise wavefield and to estimate wavefield parameters. In this method, the measurements from all components of stations and parameters of interest are modeled jointly which leads to significant improvement in extracting characteristics of surface waves. Considering the contribution of both Love and Rayleigh waves in the wavefield, the method estimates the desired parameters including amplitude, phase, azimuth, wave number and the ellipticity angle (for the Rayleigh wave only) based on the Maximum Likelihood Estimation method. One of the main characteristic of WaveDec is estimating the ellipticity angle of Rayleigh waves. This is very beneficial in determining retrograde and prograde particle motion and also in mode distinction.
In the WaveDec algorithm, the Truncated Newton method is used to optimize likelihood functions with respect to wavefield parameters. Furthermore, Bayesian Information Criterion (BIC) is used to select the best model and wave type determination (Rayleigh, Love, body wave or noise). Regarding a group of generated models for different wave types, the one with the smallest BIC is chosen.
We examined consistency of WaveDec algorithm by applying different numerical optimization methods; Truncated Newton, L-BFGS-B quasi-Newton and simplex-based Nelder-Mead methods. Furthermore, different model selection criteria; BIC, Akaike Information Criterion (AIC) and Hannan–Quinn Information Criterion (HQC) were examined to study the quality of generated models. They possess different penalty terms to avoid overfitting the models on data. All possible pairs of optimization methods and model selection criteria were utilized and replaced in WaveDec algorithm. In order to compare the resultant dispersion curves of surface waves and ellipticity angle curves of Rayleigh waves, SESAME model M2.1 synthetic data and some seismic ambient noise measurements in Colfiorito basin in Italy (Array B) were analyzed.
How to cite: Fotouhimehr, M. and Shabani, E.: Assessment of seismic ambient noise parameter estimation and wavefield decomposition in WaveDec, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4547, https://doi.org/10.5194/egusphere-egu21-4547, 2021.
EGU21-4226 | vPICO presentations | SM3.1
Seismic surface wave focal spot imaging: resolution tests using time-reversal simulationsBruno Giammarinaro, Gregor Hillers, Leonard Seydoux, Christina Tsarsitalidou, Stefan Catheline, Michel Campillo, Philippe Roux, and Julien de Rosny
Converging surface wave fields create a large-amplitude feature at the origin referred to as focal spot. Its properties are governed by local medium properties and have long been used in medical imaging approaches such as passive elastography. Modern dense seismic arrays consisting of many hundreds of sensors allow now the application of noise correlation-based focal spot imaging in seismology. Here we use numerical experiments to study the resolution properties of focal spots to explore the limits of seismological data applications. Focal spot imaging is based on the correlation of diffuse isotropic wavefields. Here, however, we perform numerical experiments using an equivalent time-reversal approach to synthesize Rayleigh wave focal spots in an elastic half-space from Green’s functions computed with the AXITRA solver. Simulations are performed using an 85 x 85 receiver grid separated by 8 m and 72 time-reversal mirrors in the far field. The Rayleigh wave speed is 2 km/s near the surface and increases with depth for multi-layered media. The mirrors are located at the surface, on a circle at 12 km distance from the origin to simulate refocusing surface waves. Mirrors located inside the medium are used to simulate the contribution of biasing body waves. The 2D focal spot amplitude fields obtained under these conditions are compared, for frequencies between 2 and 15 Hz, to a theoretical near-field surface wave Green’s tensor parametrization using non-linear least square fitting techniques to demonstrate the feasibility of estimating the dispersion curve in multi-layered media. The set-up is further used to study effects of azimuthally variable energy fluxes on the dispersion estimates. Data from different distance ranges from the origin in the regression process to estimate dispersion mimics the effect of variable wavelength-to-aperture ratios. We find that the vertical-radial component is more sensitive to non-isotropic wavefields compared to the vertical-vertical component. However, the results for impinging P-waves energy shows that the vertical-radial component-based estimates are more stable and accurate. The tool can thus be used to test different filtering methods to account for anisotropic fluxes and P-wave energy to efficiently use each component. These results inform the focal spot imaging study using USArray data discussed in an accompanying abstract.
How to cite: Giammarinaro, B., Hillers, G., Seydoux, L., Tsarsitalidou, C., Catheline, S., Campillo, M., Roux, P., and de Rosny, J.: Seismic surface wave focal spot imaging: resolution tests using time-reversal simulations , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4226, https://doi.org/10.5194/egusphere-egu21-4226, 2021.
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Converging surface wave fields create a large-amplitude feature at the origin referred to as focal spot. Its properties are governed by local medium properties and have long been used in medical imaging approaches such as passive elastography. Modern dense seismic arrays consisting of many hundreds of sensors allow now the application of noise correlation-based focal spot imaging in seismology. Here we use numerical experiments to study the resolution properties of focal spots to explore the limits of seismological data applications. Focal spot imaging is based on the correlation of diffuse isotropic wavefields. Here, however, we perform numerical experiments using an equivalent time-reversal approach to synthesize Rayleigh wave focal spots in an elastic half-space from Green’s functions computed with the AXITRA solver. Simulations are performed using an 85 x 85 receiver grid separated by 8 m and 72 time-reversal mirrors in the far field. The Rayleigh wave speed is 2 km/s near the surface and increases with depth for multi-layered media. The mirrors are located at the surface, on a circle at 12 km distance from the origin to simulate refocusing surface waves. Mirrors located inside the medium are used to simulate the contribution of biasing body waves. The 2D focal spot amplitude fields obtained under these conditions are compared, for frequencies between 2 and 15 Hz, to a theoretical near-field surface wave Green’s tensor parametrization using non-linear least square fitting techniques to demonstrate the feasibility of estimating the dispersion curve in multi-layered media. The set-up is further used to study effects of azimuthally variable energy fluxes on the dispersion estimates. Data from different distance ranges from the origin in the regression process to estimate dispersion mimics the effect of variable wavelength-to-aperture ratios. We find that the vertical-radial component is more sensitive to non-isotropic wavefields compared to the vertical-vertical component. However, the results for impinging P-waves energy shows that the vertical-radial component-based estimates are more stable and accurate. The tool can thus be used to test different filtering methods to account for anisotropic fluxes and P-wave energy to efficiently use each component. These results inform the focal spot imaging study using USArray data discussed in an accompanying abstract.
How to cite: Giammarinaro, B., Hillers, G., Seydoux, L., Tsarsitalidou, C., Catheline, S., Campillo, M., Roux, P., and de Rosny, J.: Seismic surface wave focal spot imaging: resolution tests using time-reversal simulations , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4226, https://doi.org/10.5194/egusphere-egu21-4226, 2021.
EGU21-9045 | vPICO presentations | SM3.1
Seismic imaging with focusing surface waves obtained from USArray noise correlation functionsChristina Tsarsitalidou, Pierre Boué, Gregor Hillers, Bruno Giammarinaro, Michel Campillo, Leonard Seydoux, and Laurent Stehly
Dense seismic arrays are equivalent to medical ultrasound transducers in the sense that both “devices” allow the reconstruction of refocusing wave fields at near-field distances. In this work we explore the imaging potential of refocusing surface waves constructed from USArray noise correlation functions using sensors located between the US west coast and -90 degrees West. So-called focal spots---a term adopted from elastography---are constructed from the noise correlation amplitude field at zero lag time around the origin, i.e., each sensor in the array. Similar to the related SPAC method, properties of the Bessel-function-shaped focal spot are controlled by the local medium properties, which underpins the local imaging approach. Unlike USArray SPAC applications in the 5 – 40 s period range, however, we proceed in the spirit of elastographic local measurements and demonstrate the possibility to estimate properties of Rayleigh wave propagation between 80 – 300 s period using the vertical-vertical and vertical-radial focal spot components of the Green’s tensor. Clearly, the up to five-fold extension of the period range compared to noise- based USArray surface wave tomography studies are an intriguing asset of the approach that suggests a significantly increased depth resolution. In addition to demonstrating the general applicability of the focal spot method using dense array data, we address the biasing effects of less-than-ideal ambient wave field properties on our measurements. Impinging body wave energy and non- isotropic surface wave energy flux contribute to focal spot shapes and properties that are not compatible with the theoretical assumptions and used model functions and parametrizations. We show the space and period dependent distributions of these biasing components based on the focal spot representation in the wave number domain. Numerical and theoretical work discussed in an accompanying abstract is used to assess the impact on the dispersion measurements, and to test the effectiveness of filtering strategies for making improved estimates.
How to cite: Tsarsitalidou, C., Boué, P., Hillers, G., Giammarinaro, B., Campillo, M., Seydoux, L., and Stehly, L.: Seismic imaging with focusing surface waves obtained from USArray noise correlation functions, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9045, https://doi.org/10.5194/egusphere-egu21-9045, 2021.
Please decide on your access
Please use the buttons below to download the presentation materials or to visit the external website where the presentation is linked. Regarding the external link, please note that Copernicus Meetings cannot accept any liability for the content and the website you will visit.
Forward to presentation link
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We are sorry, but presentations are only available for users who registered for the conference. Thank you.
Dense seismic arrays are equivalent to medical ultrasound transducers in the sense that both “devices” allow the reconstruction of refocusing wave fields at near-field distances. In this work we explore the imaging potential of refocusing surface waves constructed from USArray noise correlation functions using sensors located between the US west coast and -90 degrees West. So-called focal spots---a term adopted from elastography---are constructed from the noise correlation amplitude field at zero lag time around the origin, i.e., each sensor in the array. Similar to the related SPAC method, properties of the Bessel-function-shaped focal spot are controlled by the local medium properties, which underpins the local imaging approach. Unlike USArray SPAC applications in the 5 – 40 s period range, however, we proceed in the spirit of elastographic local measurements and demonstrate the possibility to estimate properties of Rayleigh wave propagation between 80 – 300 s period using the vertical-vertical and vertical-radial focal spot components of the Green’s tensor. Clearly, the up to five-fold extension of the period range compared to noise- based USArray surface wave tomography studies are an intriguing asset of the approach that suggests a significantly increased depth resolution. In addition to demonstrating the general applicability of the focal spot method using dense array data, we address the biasing effects of less-than-ideal ambient wave field properties on our measurements. Impinging body wave energy and non- isotropic surface wave energy flux contribute to focal spot shapes and properties that are not compatible with the theoretical assumptions and used model functions and parametrizations. We show the space and period dependent distributions of these biasing components based on the focal spot representation in the wave number domain. Numerical and theoretical work discussed in an accompanying abstract is used to assess the impact on the dispersion measurements, and to test the effectiveness of filtering strategies for making improved estimates.
How to cite: Tsarsitalidou, C., Boué, P., Hillers, G., Giammarinaro, B., Campillo, M., Seydoux, L., and Stehly, L.: Seismic imaging with focusing surface waves obtained from USArray noise correlation functions, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9045, https://doi.org/10.5194/egusphere-egu21-9045, 2021.
EGU21-7106 | vPICO presentations | SM3.1
Passive estimation of scattering and intrinsic absorption parameters at 18 active volcanoes in Japan using envelopes of seismic ambient noise cross-correlation functionsTakashi Hirose, Hideki Ueda, and Eisuke Fujita
Estimating seismic scattering and intrinsic absorption parameters, which are measures of medium heterogeneity, is important for understanding the complex structure in shallow regions of volcanoes. In recent years, seismic ambient noise cross-correlation functions (CCFs) have been used instead of records of natural earthquakes or active seismic experiments to estimate those parameters (e.g., Hirose et al., 2019; Hirose et al., 2020; van Dinther et al., 2020). This passive approach possibly allows us to estimate scattering and intrinsic absorption parameters in previously unmeasured regions and frequency bands. In this study, we apply the passive estimation method proposed by Hirose et al. (2019) to 18 active volcanoes in Japan and measure those parameters of Rayleigh waves. We used three-component seismic ambient noise data in the frequency bands of 0.5-1 Hz, 1-2 Hz, and 2-4 Hz at seismic stations of NIED, JMA, HSRI, and MFRI. Before computing CCFs, the temporal flattening technique (Weaver, 2011) was applied to ambient noise data for reducing the effect of temporal fluctuations in noise levels with retaining relative amplitudes among the stations. Daily CCFs of three components (ZZ, ZR, ZT) were computed by stacking 10-minutes-CCFs. We stacked daily CCFs over 1 year and computed mean squared envelopes by smoothing squared amplitude with 4 s (0.5-1 Hz), 2 s (1-2 Hz), or 1 s (2-4 Hz) long time windows. Scattering and intrinsic absorption parameters were estimated by modeling the space-time distributions of energy densities calculated from CCFs with 2D radiative transfer theory. Best-fit values of scattering mean free path at the 18 active volcanoes range between 1.0-4.6 km at 0.5-1Hz band, 0.7-2.9 km at 1-2 Hz band, and 0.9-2.9 km at 2-4 Hz band, respectively. These values are 2 orders of magnitude shorter than those in non-volcanic regions (e.g., Sato et al., 2012). Those of intrinsic absorption parameter range between 0.05-0.26 s-1 at the 0.5-1 Hz band, 0.06-0.24 s-1 at the 1-2 Hz band, and 0.06-0.32 s-1 at the 2-4 Hz band, respectively. They are at most one order of magnitude larger than those in the non-volcanic regions. Especially strong intrinsic attenuations are estimated at volcanic islands. Water-bearing layers at a depth of several hundred meters below these islands may cause such strong intrinsic attenuations. The frequency dependence of scattering attenuations is also strong at these volcanic islands, suggesting non-uniform structures that largely fluctuate along depths. The results of this study suggest that the passive estimation method of scattering and intrinsic absorption parameters proposed by Hirose et al. (2019) is applicable to various volcanoes. Comparing estimated values of these parameters at various volcanoes will improve our understanding of complex structure at the shallow regions of volcanoes. Moreover, the parameters estimated in this study will boost locating spatial distributions of seismic velocity and/or scattering property changes associated with volcanic activities at the 18 volcanoes.
Acknowledgments: We used seismograms recorded by Japan Meteorological Agency (JMA), Hot Springs Research Institute (HSRI) of Kanagawa Prefecture, and Mount Fuji Research Institute (MFRI), Yamanashi Prefectural Government.
How to cite: Hirose, T., Ueda, H., and Fujita, E.: Passive estimation of scattering and intrinsic absorption parameters at 18 active volcanoes in Japan using envelopes of seismic ambient noise cross-correlation functions, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7106, https://doi.org/10.5194/egusphere-egu21-7106, 2021.
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Estimating seismic scattering and intrinsic absorption parameters, which are measures of medium heterogeneity, is important for understanding the complex structure in shallow regions of volcanoes. In recent years, seismic ambient noise cross-correlation functions (CCFs) have been used instead of records of natural earthquakes or active seismic experiments to estimate those parameters (e.g., Hirose et al., 2019; Hirose et al., 2020; van Dinther et al., 2020). This passive approach possibly allows us to estimate scattering and intrinsic absorption parameters in previously unmeasured regions and frequency bands. In this study, we apply the passive estimation method proposed by Hirose et al. (2019) to 18 active volcanoes in Japan and measure those parameters of Rayleigh waves. We used three-component seismic ambient noise data in the frequency bands of 0.5-1 Hz, 1-2 Hz, and 2-4 Hz at seismic stations of NIED, JMA, HSRI, and MFRI. Before computing CCFs, the temporal flattening technique (Weaver, 2011) was applied to ambient noise data for reducing the effect of temporal fluctuations in noise levels with retaining relative amplitudes among the stations. Daily CCFs of three components (ZZ, ZR, ZT) were computed by stacking 10-minutes-CCFs. We stacked daily CCFs over 1 year and computed mean squared envelopes by smoothing squared amplitude with 4 s (0.5-1 Hz), 2 s (1-2 Hz), or 1 s (2-4 Hz) long time windows. Scattering and intrinsic absorption parameters were estimated by modeling the space-time distributions of energy densities calculated from CCFs with 2D radiative transfer theory. Best-fit values of scattering mean free path at the 18 active volcanoes range between 1.0-4.6 km at 0.5-1Hz band, 0.7-2.9 km at 1-2 Hz band, and 0.9-2.9 km at 2-4 Hz band, respectively. These values are 2 orders of magnitude shorter than those in non-volcanic regions (e.g., Sato et al., 2012). Those of intrinsic absorption parameter range between 0.05-0.26 s-1 at the 0.5-1 Hz band, 0.06-0.24 s-1 at the 1-2 Hz band, and 0.06-0.32 s-1 at the 2-4 Hz band, respectively. They are at most one order of magnitude larger than those in the non-volcanic regions. Especially strong intrinsic attenuations are estimated at volcanic islands. Water-bearing layers at a depth of several hundred meters below these islands may cause such strong intrinsic attenuations. The frequency dependence of scattering attenuations is also strong at these volcanic islands, suggesting non-uniform structures that largely fluctuate along depths. The results of this study suggest that the passive estimation method of scattering and intrinsic absorption parameters proposed by Hirose et al. (2019) is applicable to various volcanoes. Comparing estimated values of these parameters at various volcanoes will improve our understanding of complex structure at the shallow regions of volcanoes. Moreover, the parameters estimated in this study will boost locating spatial distributions of seismic velocity and/or scattering property changes associated with volcanic activities at the 18 volcanoes.
Acknowledgments: We used seismograms recorded by Japan Meteorological Agency (JMA), Hot Springs Research Institute (HSRI) of Kanagawa Prefecture, and Mount Fuji Research Institute (MFRI), Yamanashi Prefectural Government.
How to cite: Hirose, T., Ueda, H., and Fujita, E.: Passive estimation of scattering and intrinsic absorption parameters at 18 active volcanoes in Japan using envelopes of seismic ambient noise cross-correlation functions, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7106, https://doi.org/10.5194/egusphere-egu21-7106, 2021.
EGU21-8296 | vPICO presentations | SM3.1
Adjoint tomography with full envelope for scattering and intrinsic attenuation - resolution and trade-offTuo Zhang and Christoph Sens-Schönfelder
A rigorous framework exists for deterministic imaging the subsurface seismic velocity structure. Full-waveform inversion (FWI) that combines the forward simulation of waveforms with an adjoint (backward) simulation of the data misfit provides the gradient of the model misfit with respect to the changes in the model parameters. This gradient is used for iterative improvements of the model to minimize the data misfit. To investigate the small scale heterogeneity of the medium below the resolution limits the waveform tomography the envelopes of high-frequency seismic waves have been used to derive a statistical description of the small scale structure. Such studies employed a variety of misfit measures or empirical parameters and various assumptions about the spatial sensitivity of the measurements to derive some information about the spatial distribution of the high-frequency attenuation and scattering properties. A rigorous framework for the inversion of seismogram envelopes for the spatial imaging of heterogeneity and attenuation has been missing so far. Here we present a mathematical framework for the full envelope inversion that is based on a forward simulation of seismogram envelopes and an adjoint (backward) simulation of the envelope misfit, in full analogy to FWI.
Different from FWI that works with the wave equation, our approach is based on the Radiative Transfer Equation. In this study, the forward problem is solved by modelling the 2-D multiple nonisotropic scattering in a random elastic medium with spatially variable heterogeneity and attenuation using the Monte-Carlo method. The fluctuation strength ε and intrinsic quality factors QP-1 and QS-1 in the random medium are used to describe the spatial variability of attenuation and scattering. The misfit function is defined as the differences between the full observed and modelled envelopes.
We derived the sensitivity kernels corresponding to this misfit function that is minimized during the iterative adjoint inversion with the L-BFGS method. We have applied this algorithm in some numerical tests in the acoustic approximation. We show that it is possible in a rigorous way to image the spatial distribution of small scale heterogeneity and attenuation separately using seismogram envelopes. The resolution and the trade-off between scattering and intrinsic attenuation are discussed. Our analysis shows that relative importance of scattering and attenuation anomalies need to be considered when the model resolution is assessed. The inversions confirm, that the early coda is important for imaging the distribution of heterogeneity while later coda waves are more sensitive to intrinsic attenuation.
How to cite: Zhang, T. and Sens-Schönfelder, C.: Adjoint tomography with full envelope for scattering and intrinsic attenuation - resolution and trade-off, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8296, https://doi.org/10.5194/egusphere-egu21-8296, 2021.
A rigorous framework exists for deterministic imaging the subsurface seismic velocity structure. Full-waveform inversion (FWI) that combines the forward simulation of waveforms with an adjoint (backward) simulation of the data misfit provides the gradient of the model misfit with respect to the changes in the model parameters. This gradient is used for iterative improvements of the model to minimize the data misfit. To investigate the small scale heterogeneity of the medium below the resolution limits the waveform tomography the envelopes of high-frequency seismic waves have been used to derive a statistical description of the small scale structure. Such studies employed a variety of misfit measures or empirical parameters and various assumptions about the spatial sensitivity of the measurements to derive some information about the spatial distribution of the high-frequency attenuation and scattering properties. A rigorous framework for the inversion of seismogram envelopes for the spatial imaging of heterogeneity and attenuation has been missing so far. Here we present a mathematical framework for the full envelope inversion that is based on a forward simulation of seismogram envelopes and an adjoint (backward) simulation of the envelope misfit, in full analogy to FWI.
Different from FWI that works with the wave equation, our approach is based on the Radiative Transfer Equation. In this study, the forward problem is solved by modelling the 2-D multiple nonisotropic scattering in a random elastic medium with spatially variable heterogeneity and attenuation using the Monte-Carlo method. The fluctuation strength ε and intrinsic quality factors QP-1 and QS-1 in the random medium are used to describe the spatial variability of attenuation and scattering. The misfit function is defined as the differences between the full observed and modelled envelopes.
We derived the sensitivity kernels corresponding to this misfit function that is minimized during the iterative adjoint inversion with the L-BFGS method. We have applied this algorithm in some numerical tests in the acoustic approximation. We show that it is possible in a rigorous way to image the spatial distribution of small scale heterogeneity and attenuation separately using seismogram envelopes. The resolution and the trade-off between scattering and intrinsic attenuation are discussed. Our analysis shows that relative importance of scattering and attenuation anomalies need to be considered when the model resolution is assessed. The inversions confirm, that the early coda is important for imaging the distribution of heterogeneity while later coda waves are more sensitive to intrinsic attenuation.
How to cite: Zhang, T. and Sens-Schönfelder, C.: Adjoint tomography with full envelope for scattering and intrinsic attenuation - resolution and trade-off, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8296, https://doi.org/10.5194/egusphere-egu21-8296, 2021.
EGU21-14056 | vPICO presentations | SM3.1
Seismic Imaging Using Auto- and Cross-correlation of seismic noise in the Quito (Ecuador) basinDaniel Pacheco, Diego Mercerat, Françoise Courboulex, Fabián Bonilla, Aurore Laurendeau, and Alexandra Alvarado
Temporary seismic networks installed in urban areas provide a powerful tool for investigating shallow geological structures and assessing the seismic hazard using passive seismic methods, including auto- and cross-correlation of seismic noise. To examine the feasibility of the methods to image the uppermost geological structures, 20 broad- and mid-band seismological stations were deployed progressively throughout Quito in an irregular array to record ambient seismic noise between May 2016 and July 2018.
Quito, the capital of Ecuador, is located in a high seismic zone, 180 km from the Pacific subduction zone and surrounded by crustal-faults prone to generate significant earthquakes.
The city is built on a sedimentary basin, located on the hanging wall of a system of active reverse faults. The high population density (around 2.5 million inhabitants) and the lack of planning of most of its buildings, make Quito a metropolis exposed to high seismic risk. In Quito, the basin's filling has been described as volcano-sedimentary sequences consisting of lavas, lahars, lacustrine, and pyroclastic deposits (Alvarado et al., 2014). However, the thickness of the in-fill material, its spatial arrangement, and the basin's deep structure remain poorly known.
This study presents the results of ambient noise auto- and cross-correlation of simultaneous operating seismic stations to retrieve: 1) zero-offset high frequency body-wave crustal reflections, and 2) inter-station, surface-wave Green's functions in the frequency band 0.1 - 2 Hz.
Auto-correlation of seismic noise indicated at least one reflection within the first 2.5 s from the surface.
Careful analyses of day-night variations in noise spectral power were carried out to select optimal time windows for the cross-correlation. Additionally, Rayleigh and Love phase-velocity dispersion curves were inverted to obtain shear wave velocity profiles throughout the city. Love wave trains traveling in the longitudinal direction of the basin (NNE-SSW) are much clearer than Rayleigh wave trains.
The surface-wave Green’s functions and their inversions suggest a clear difference in the basin's structure between the northern and southern parts. In the north, we detect the seismic basement at a depth of about 300 meters, whereas in the south, it appears much deeper at around 1000 meters. This significant difference could be the main explanation for the low-frequency amplification (at 0.3 Hz) highlighted in the southern part of the basin from earthquake recordings (e.g., the Mw 7.8 Pedernales earthquake on April 2016) and by the analysis of spectral ratios (Laurendeau et al., 2017).
References:
Alvarado, A., et al. (2014). Active tectonics in Quito, Ecuador, assessed by geomorphological studies, GPS data, and crustal seismicity, DOI: 10.1002/2012TC003224.
Laurendeau, A., et al. (2017). Low-frequency seismic amplification in the Quito basin (Ecuador) revealed by accelerometric recordings of the RENAC network, DOI: 10.1785/0120170134.
How to cite: Pacheco, D., Mercerat, D., Courboulex, F., Bonilla, F., Laurendeau, A., and Alvarado, A.: Seismic Imaging Using Auto- and Cross-correlation of seismic noise in the Quito (Ecuador) basin, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14056, https://doi.org/10.5194/egusphere-egu21-14056, 2021.
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Temporary seismic networks installed in urban areas provide a powerful tool for investigating shallow geological structures and assessing the seismic hazard using passive seismic methods, including auto- and cross-correlation of seismic noise. To examine the feasibility of the methods to image the uppermost geological structures, 20 broad- and mid-band seismological stations were deployed progressively throughout Quito in an irregular array to record ambient seismic noise between May 2016 and July 2018.
Quito, the capital of Ecuador, is located in a high seismic zone, 180 km from the Pacific subduction zone and surrounded by crustal-faults prone to generate significant earthquakes.
The city is built on a sedimentary basin, located on the hanging wall of a system of active reverse faults. The high population density (around 2.5 million inhabitants) and the lack of planning of most of its buildings, make Quito a metropolis exposed to high seismic risk. In Quito, the basin's filling has been described as volcano-sedimentary sequences consisting of lavas, lahars, lacustrine, and pyroclastic deposits (Alvarado et al., 2014). However, the thickness of the in-fill material, its spatial arrangement, and the basin's deep structure remain poorly known.
This study presents the results of ambient noise auto- and cross-correlation of simultaneous operating seismic stations to retrieve: 1) zero-offset high frequency body-wave crustal reflections, and 2) inter-station, surface-wave Green's functions in the frequency band 0.1 - 2 Hz.
Auto-correlation of seismic noise indicated at least one reflection within the first 2.5 s from the surface.
Careful analyses of day-night variations in noise spectral power were carried out to select optimal time windows for the cross-correlation. Additionally, Rayleigh and Love phase-velocity dispersion curves were inverted to obtain shear wave velocity profiles throughout the city. Love wave trains traveling in the longitudinal direction of the basin (NNE-SSW) are much clearer than Rayleigh wave trains.
The surface-wave Green’s functions and their inversions suggest a clear difference in the basin's structure between the northern and southern parts. In the north, we detect the seismic basement at a depth of about 300 meters, whereas in the south, it appears much deeper at around 1000 meters. This significant difference could be the main explanation for the low-frequency amplification (at 0.3 Hz) highlighted in the southern part of the basin from earthquake recordings (e.g., the Mw 7.8 Pedernales earthquake on April 2016) and by the analysis of spectral ratios (Laurendeau et al., 2017).
References:
Alvarado, A., et al. (2014). Active tectonics in Quito, Ecuador, assessed by geomorphological studies, GPS data, and crustal seismicity, DOI: 10.1002/2012TC003224.
Laurendeau, A., et al. (2017). Low-frequency seismic amplification in the Quito basin (Ecuador) revealed by accelerometric recordings of the RENAC network, DOI: 10.1785/0120170134.
How to cite: Pacheco, D., Mercerat, D., Courboulex, F., Bonilla, F., Laurendeau, A., and Alvarado, A.: Seismic Imaging Using Auto- and Cross-correlation of seismic noise in the Quito (Ecuador) basin, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14056, https://doi.org/10.5194/egusphere-egu21-14056, 2021.
SM3.2 – New seismic data analysis methods for automatic characterization of seismicity
EGU21-309 | vPICO presentations | SM3.2
Data-In-Image: a novel concept for data manipulation and encryption implementationMohamed Abdelwahed
Conventionally, the way of storing and exchange numerical data depends mainly on binary data files in compressible form. In this era of the Big Data and machine learning systems and with the accumulation of data with different forms and types, it is important to find an alternative way for handling the data. The binary data are software dependent which does not exhibit its content and type without accessing the data by the proper software. In addition, it does not have any encryption ability. To solve this issue, we propose a new concept to handle the digital data in a descriptive, encrypted, compressed form, and able to be previewed. The idea is to pack the binary bits into a bitmap image with specific coding scheme. This approach employs the Steim scheme as a primary compression tool with a 128-bit encryption method then packs the encrypted codes into a WebP image file. The WebP image is featured by being an independent, web friendly, and highly compressed file. In order to make the file describing its contents, we reserved some pixels as coded descriptive pixels. By this way, the now packed data exhibits its contents and type during image preview.
It is proven that the Data-In-Image format, regardless of being encrypted, occupies the least amount of storage space among other image formats that can be easily handled, stored, and shared through clouds and devices safely with a lower cost. For seismic data, the size of the WebP image comprises ~20% of the corresponding binary size with a bit-rate of ~5.6 b/s which is smaller than that of the Steim form, 27% and 8.9 b/s, respectively. Regarding the compression speed, it is found that the code compresses data with a rate of ~11,118 samples/s or ~ 44 Kbytes/s in average.
In addition, the data image is able to be digitally scanned and with some modifications can be remotely accessed like the quick response code, the thing that is not possible in the binary form. Moreover, the descriptive pixels in the image allow the implementations of smart tools to archive and classify data by machine learning and recognition algorithms.
How to cite: Abdelwahed, M.: Data-In-Image: a novel concept for data manipulation and encryption implementation, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-309, https://doi.org/10.5194/egusphere-egu21-309, 2021.
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We are sorry, but presentations are only available for users who registered for the conference. Thank you.
Conventionally, the way of storing and exchange numerical data depends mainly on binary data files in compressible form. In this era of the Big Data and machine learning systems and with the accumulation of data with different forms and types, it is important to find an alternative way for handling the data. The binary data are software dependent which does not exhibit its content and type without accessing the data by the proper software. In addition, it does not have any encryption ability. To solve this issue, we propose a new concept to handle the digital data in a descriptive, encrypted, compressed form, and able to be previewed. The idea is to pack the binary bits into a bitmap image with specific coding scheme. This approach employs the Steim scheme as a primary compression tool with a 128-bit encryption method then packs the encrypted codes into a WebP image file. The WebP image is featured by being an independent, web friendly, and highly compressed file. In order to make the file describing its contents, we reserved some pixels as coded descriptive pixels. By this way, the now packed data exhibits its contents and type during image preview.
It is proven that the Data-In-Image format, regardless of being encrypted, occupies the least amount of storage space among other image formats that can be easily handled, stored, and shared through clouds and devices safely with a lower cost. For seismic data, the size of the WebP image comprises ~20% of the corresponding binary size with a bit-rate of ~5.6 b/s which is smaller than that of the Steim form, 27% and 8.9 b/s, respectively. Regarding the compression speed, it is found that the code compresses data with a rate of ~11,118 samples/s or ~ 44 Kbytes/s in average.
In addition, the data image is able to be digitally scanned and with some modifications can be remotely accessed like the quick response code, the thing that is not possible in the binary form. Moreover, the descriptive pixels in the image allow the implementations of smart tools to archive and classify data by machine learning and recognition algorithms.
How to cite: Abdelwahed, M.: Data-In-Image: a novel concept for data manipulation and encryption implementation, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-309, https://doi.org/10.5194/egusphere-egu21-309, 2021.
EGU21-16378 | vPICO presentations | SM3.2
Tools for monitoring the spatio-temporal evolution of seismic sequences: An application to the Azores triple junctionAnaldyne Soares, Susana Custodio, and Simone Cesca
In the last decades, the discovery of seismic signals other than those known as classical earthquakes have changed our understanding of the dynamic process of lithosphere fracturing with implications for seismic monitoring. These signals are hypothesized to be generated by slow slip on faults and/or by the motion of fluids in the crust. The earthquakes that occur in the Azores archipelago are thought to result from the interaction between a tectonic triple junction and a low-velocity (possibly hot) anomalous mantle. Although most of the seismic activity in this region is tectonic, there is also evidence of seismic activity related to hydrothermal and magmatic activity, which makes the Azores region a privileged natural observatory for studying different types of seismic signals. In this work we will then focus on the spatio-temporal evolution of the February 2018 seismic sequence which occurred in the island of São Miguel. We will carry out detection and preliminary location of seismic events using Lassie, an open-source software for earthquake detection. We will also perform waveform similarity and clustering analysis to understand the detailed spatio-temporal evolution of the crisis.
This work is funded by FCT through projects UIDB/50019/2020 – IDL and PTDC/CTAGEF/ 6674/2020 (RESTLESS).
How to cite: Soares, A., Custodio, S., and Cesca, S.: Tools for monitoring the spatio-temporal evolution of seismic sequences: An application to the Azores triple junction, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16378, https://doi.org/10.5194/egusphere-egu21-16378, 2021.
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In the last decades, the discovery of seismic signals other than those known as classical earthquakes have changed our understanding of the dynamic process of lithosphere fracturing with implications for seismic monitoring. These signals are hypothesized to be generated by slow slip on faults and/or by the motion of fluids in the crust. The earthquakes that occur in the Azores archipelago are thought to result from the interaction between a tectonic triple junction and a low-velocity (possibly hot) anomalous mantle. Although most of the seismic activity in this region is tectonic, there is also evidence of seismic activity related to hydrothermal and magmatic activity, which makes the Azores region a privileged natural observatory for studying different types of seismic signals. In this work we will then focus on the spatio-temporal evolution of the February 2018 seismic sequence which occurred in the island of São Miguel. We will carry out detection and preliminary location of seismic events using Lassie, an open-source software for earthquake detection. We will also perform waveform similarity and clustering analysis to understand the detailed spatio-temporal evolution of the crisis.
This work is funded by FCT through projects UIDB/50019/2020 – IDL and PTDC/CTAGEF/ 6674/2020 (RESTLESS).
How to cite: Soares, A., Custodio, S., and Cesca, S.: Tools for monitoring the spatio-temporal evolution of seismic sequences: An application to the Azores triple junction, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16378, https://doi.org/10.5194/egusphere-egu21-16378, 2021.
EGU21-6950 | vPICO presentations | SM3.2
Seismicity Detection in Skopje Region Using Tomographic Methods and 3-D ModellingCvetan Sinadinovski, Lazo Pekevski, Dragana Cernih, Katerina Drogreska, and Jasmina Najdovska
A novel geotomography technique has been applied at the epicentral area around capitol of Macedonia - Skopje, using selected earthquakes that occurred over a period of 57 years and were recorded on temporary and permanent seismograph stations. This study will test the tomography method for the first time in investigation of the crustal shape and structures in our tectonic environment using specially designed datasets covering 1964-1967 and 2016-2020 periods.
In the initial phase, the analysis will show the potential of the geotomography application in revealing detailed velocity perturbation in the lithosphere. Then, the events are relocated in the 3-D models and new cross-sections of the crust produced by a simultaneous approach. The images can help in constraining the velocity vs depth relationship and thus can contribute towards redefinition of the earthquake zones. The results are discussed in terms of general stress and seismic regime and their temporal changes.
Better understanding of the seismicity and tectonics processes in the Skopje region will lead to an overall improvement of the earthquake hazard assessment at local and national level, as well as further integration in research programs with other geophysical methods.
How to cite: Sinadinovski, C., Pekevski, L., Cernih, D., Drogreska, K., and Najdovska, J.: Seismicity Detection in Skopje Region Using Tomographic Methods and 3-D Modelling , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6950, https://doi.org/10.5194/egusphere-egu21-6950, 2021.
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Please use the buttons below to download the presentation materials or to visit the external website where the presentation is linked. Regarding the external link, please note that Copernicus Meetings cannot accept any liability for the content and the website you will visit.
Forward to presentation link
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We are sorry, but presentations are only available for users who registered for the conference. Thank you.
A novel geotomography technique has been applied at the epicentral area around capitol of Macedonia - Skopje, using selected earthquakes that occurred over a period of 57 years and were recorded on temporary and permanent seismograph stations. This study will test the tomography method for the first time in investigation of the crustal shape and structures in our tectonic environment using specially designed datasets covering 1964-1967 and 2016-2020 periods.
In the initial phase, the analysis will show the potential of the geotomography application in revealing detailed velocity perturbation in the lithosphere. Then, the events are relocated in the 3-D models and new cross-sections of the crust produced by a simultaneous approach. The images can help in constraining the velocity vs depth relationship and thus can contribute towards redefinition of the earthquake zones. The results are discussed in terms of general stress and seismic regime and their temporal changes.
Better understanding of the seismicity and tectonics processes in the Skopje region will lead to an overall improvement of the earthquake hazard assessment at local and national level, as well as further integration in research programs with other geophysical methods.
How to cite: Sinadinovski, C., Pekevski, L., Cernih, D., Drogreska, K., and Najdovska, J.: Seismicity Detection in Skopje Region Using Tomographic Methods and 3-D Modelling , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6950, https://doi.org/10.5194/egusphere-egu21-6950, 2021.
EGU21-3310 | vPICO presentations | SM3.2
Velocity models for routine earthquake monitoring at volcanoes: from deterministic to BayesianJeremy Pesicek, Trond Ryberg, Roger Machacca, and Jaime Raigosa
Earthquake location is a primary function of volcano observatories worldwide and the resulting catalogs of seismicity are integral to interpretations and forecasts of volcanic activity. Ensuring earthquake location accuracy is therefore of critical importance. However, accurate earthquake locations require accurate velocity models, which are not always available. In addition, difficulties involved in applying traditional velocity modeling methods often mean that earthquake locations are computed at volcanoes using velocity models not specific to the local volcano.
Traditional linearized methods that jointly invert for earthquake locations, velocity structure, and station corrections depend critically on having reasonable starting values for the unknown parameters, which are then iteratively updated to minimize the data misfit. However, these deterministic methods are susceptible to local minima and divergence, issues exacerbated by sparse seismic networks and/or poor data quality common at volcanoes. In cases where independent prior constraints on local velocity structure are not available, these methods may result in systematic errors in velocity models and hypocenters, especially if the full range of possible starting values is not explored. Furthermore, such solutions depend on subjective choices for model regularization and parameterization.
In contrast, Bayesian methods promise to avoid all these pitfalls. Although these methods traditionally have been difficult to implement due to additional computational burdens, the increasing use and availability of High-Performance Computing resources mean widespread application of these methods is no longer prohibitively expensive. In this presentation, we apply a Bayesian, hierarchical, trans-dimensional Markov chain Monte Carlo method to jointly solve for hypocentral parameters, 1D velocity structure, and station corrections using data from monitoring networks of varying quality at several volcanoes in the U.S. and South America. We compare the results with those from a more traditional deterministic approach and show that the resulting velocity models produce more accurate earthquake locations. Finally, we chart a path forward for more widespread adoption of the Bayesian approach, which may improve catalogs of volcanic seismicity at observatories worldwide.
How to cite: Pesicek, J., Ryberg, T., Machacca, R., and Raigosa, J.: Velocity models for routine earthquake monitoring at volcanoes: from deterministic to Bayesian, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3310, https://doi.org/10.5194/egusphere-egu21-3310, 2021.
Earthquake location is a primary function of volcano observatories worldwide and the resulting catalogs of seismicity are integral to interpretations and forecasts of volcanic activity. Ensuring earthquake location accuracy is therefore of critical importance. However, accurate earthquake locations require accurate velocity models, which are not always available. In addition, difficulties involved in applying traditional velocity modeling methods often mean that earthquake locations are computed at volcanoes using velocity models not specific to the local volcano.
Traditional linearized methods that jointly invert for earthquake locations, velocity structure, and station corrections depend critically on having reasonable starting values for the unknown parameters, which are then iteratively updated to minimize the data misfit. However, these deterministic methods are susceptible to local minima and divergence, issues exacerbated by sparse seismic networks and/or poor data quality common at volcanoes. In cases where independent prior constraints on local velocity structure are not available, these methods may result in systematic errors in velocity models and hypocenters, especially if the full range of possible starting values is not explored. Furthermore, such solutions depend on subjective choices for model regularization and parameterization.
In contrast, Bayesian methods promise to avoid all these pitfalls. Although these methods traditionally have been difficult to implement due to additional computational burdens, the increasing use and availability of High-Performance Computing resources mean widespread application of these methods is no longer prohibitively expensive. In this presentation, we apply a Bayesian, hierarchical, trans-dimensional Markov chain Monte Carlo method to jointly solve for hypocentral parameters, 1D velocity structure, and station corrections using data from monitoring networks of varying quality at several volcanoes in the U.S. and South America. We compare the results with those from a more traditional deterministic approach and show that the resulting velocity models produce more accurate earthquake locations. Finally, we chart a path forward for more widespread adoption of the Bayesian approach, which may improve catalogs of volcanic seismicity at observatories worldwide.
How to cite: Pesicek, J., Ryberg, T., Machacca, R., and Raigosa, J.: Velocity models for routine earthquake monitoring at volcanoes: from deterministic to Bayesian, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3310, https://doi.org/10.5194/egusphere-egu21-3310, 2021.
EGU21-6592 | vPICO presentations | SM3.2 | Highlight
Towards automatic microseismic cluster localization with DASKatinka Tuinstra, Federica Lanza, Francesco Grigoli, Antonio Pio Rinaldi, Andreas Fichtner, and Stefan Wiemer
Currently the capability of detecting earthquakes with decreasing magnitudes demands efficient source localization, especially in seismic monitoring. This work is a step towards automatic high-resolution earthquake localization in a seismic monitoring setup that makes use of Distributed Acoustic Sensing (DAS) as its primary measuring technique. With DAS, the dense spatial sampling of the seismic wavefield leads to an improvement of both event detection and localization of earthquakes. The advantage of DAS is easy and cost-effective deployment compared to traditional seismic instruments (especially in boreholes). However, the single-component nature and the large storage requirements of DAS data demand novel methods for efficient analysis of the recorded events.
We apply a new seismic event location method to DAS data, based on a distance geometry problem in biochemistry for protein structure determination (HADES1). From the distances between individual earthquakes and a seismic station, the relative distance between the events can be computed. This approach allows us to first determine the relative location of earthquakes within a seismic cluster, and subsequently position the cluster in its correct absolute location. The technique has already been successfully applied for a single traditional seismometer. The densely spaced channels in DAS measurements accommodate accurate relative distance computation, without the ability to constrain the azimuth of the seismic cluster. Therefore, after finding the relative locations within the cluster, the position and orientation of the cluster with respect to the fiber-optic cable is calculated by minimizing the difference between observed and calculated P- and S-wave first arrival times, using a grid search approach (multi-event location). In this way, the absolute locations of all earthquakes present in the cluster are found efficiently. We first test this DAS-adapted method on synthetics, then we will move towards a real data application.
1 HADES: https://github.com/wulwife/HADES
How to cite: Tuinstra, K., Lanza, F., Grigoli, F., Rinaldi, A. P., Fichtner, A., and Wiemer, S.: Towards automatic microseismic cluster localization with DAS, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6592, https://doi.org/10.5194/egusphere-egu21-6592, 2021.
Currently the capability of detecting earthquakes with decreasing magnitudes demands efficient source localization, especially in seismic monitoring. This work is a step towards automatic high-resolution earthquake localization in a seismic monitoring setup that makes use of Distributed Acoustic Sensing (DAS) as its primary measuring technique. With DAS, the dense spatial sampling of the seismic wavefield leads to an improvement of both event detection and localization of earthquakes. The advantage of DAS is easy and cost-effective deployment compared to traditional seismic instruments (especially in boreholes). However, the single-component nature and the large storage requirements of DAS data demand novel methods for efficient analysis of the recorded events.
We apply a new seismic event location method to DAS data, based on a distance geometry problem in biochemistry for protein structure determination (HADES1). From the distances between individual earthquakes and a seismic station, the relative distance between the events can be computed. This approach allows us to first determine the relative location of earthquakes within a seismic cluster, and subsequently position the cluster in its correct absolute location. The technique has already been successfully applied for a single traditional seismometer. The densely spaced channels in DAS measurements accommodate accurate relative distance computation, without the ability to constrain the azimuth of the seismic cluster. Therefore, after finding the relative locations within the cluster, the position and orientation of the cluster with respect to the fiber-optic cable is calculated by minimizing the difference between observed and calculated P- and S-wave first arrival times, using a grid search approach (multi-event location). In this way, the absolute locations of all earthquakes present in the cluster are found efficiently. We first test this DAS-adapted method on synthetics, then we will move towards a real data application.
1 HADES: https://github.com/wulwife/HADES
How to cite: Tuinstra, K., Lanza, F., Grigoli, F., Rinaldi, A. P., Fichtner, A., and Wiemer, S.: Towards automatic microseismic cluster localization with DAS, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6592, https://doi.org/10.5194/egusphere-egu21-6592, 2021.
EGU21-2672 | vPICO presentations | SM3.2
Automatic swarm analyzer based on matched filtering algorithms: El Hierro 2011 and Torreperogil 2012-2013Eduardo Andrés Díaz Suárez, Itahiza Francisco Domínguez Cerdeña, Carmen Del Fresno Rodríguez-Portugal, Juan Vicente Cantavella Nadal, and Jaime Barco De La Torre
Dense seismic swarms usually show a high number of earthquakes per hour, the events may overlap and in most of the cases seismic records are characterized by a low signal-to-noise ratio. As a result, the manual characterization performed by seismic and volcanic observatories can become very complicated or impossible to perform. In order to solve this problem, we have developed a set of algorithms whose purpose is to detect the events, pick their phases and give a location (in an absolute and relative way) of the earthquakes associated with a known swarm.
These algorithms have been tested in two different tectonic environments: the volcano-tectonic pre-eruptive swarm of El Hierro, Spain (2011) and the tectonic seismic series of Torreperogil, Spain (2012-2013). Both crises mainly differ in the distances from the seismic stations to the hypocentres of the swarms: in the case of El Hierro, data corresponds to local epicentral distances (5-20Km) while the case of Torreperogil seismic series deals with regional distances (10-180km). Otherwise, both series present a similar evolution of the seismic network: as the number of earthquakes increased, more stations were deployed and the network became denser.
To analyze these series, we have used two sets of well relocated earthquakes of both swarms as masters, considering manually analyzed events by National Geographic Institute (IGN) with magnitude mbLg greater than 1.5. After the application of the new algorithms, we have increased the number of earthquakes of the IGN seismic catalog by a factor of 4.5 for Torreperogil and 2.9 for El Hierro. Similarly, the number of picked phases for these two series has been increased by a factor of 4.5 and 3.5, respectively.
How to cite: Díaz Suárez, E. A., Domínguez Cerdeña, I. F., Del Fresno Rodríguez-Portugal, C., Cantavella Nadal, J. V., and Barco De La Torre, J.: Automatic swarm analyzer based on matched filtering algorithms: El Hierro 2011 and Torreperogil 2012-2013, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2672, https://doi.org/10.5194/egusphere-egu21-2672, 2021.
Dense seismic swarms usually show a high number of earthquakes per hour, the events may overlap and in most of the cases seismic records are characterized by a low signal-to-noise ratio. As a result, the manual characterization performed by seismic and volcanic observatories can become very complicated or impossible to perform. In order to solve this problem, we have developed a set of algorithms whose purpose is to detect the events, pick their phases and give a location (in an absolute and relative way) of the earthquakes associated with a known swarm.
These algorithms have been tested in two different tectonic environments: the volcano-tectonic pre-eruptive swarm of El Hierro, Spain (2011) and the tectonic seismic series of Torreperogil, Spain (2012-2013). Both crises mainly differ in the distances from the seismic stations to the hypocentres of the swarms: in the case of El Hierro, data corresponds to local epicentral distances (5-20Km) while the case of Torreperogil seismic series deals with regional distances (10-180km). Otherwise, both series present a similar evolution of the seismic network: as the number of earthquakes increased, more stations were deployed and the network became denser.
To analyze these series, we have used two sets of well relocated earthquakes of both swarms as masters, considering manually analyzed events by National Geographic Institute (IGN) with magnitude mbLg greater than 1.5. After the application of the new algorithms, we have increased the number of earthquakes of the IGN seismic catalog by a factor of 4.5 for Torreperogil and 2.9 for El Hierro. Similarly, the number of picked phases for these two series has been increased by a factor of 4.5 and 3.5, respectively.
How to cite: Díaz Suárez, E. A., Domínguez Cerdeña, I. F., Del Fresno Rodríguez-Portugal, C., Cantavella Nadal, J. V., and Barco De La Torre, J.: Automatic swarm analyzer based on matched filtering algorithms: El Hierro 2011 and Torreperogil 2012-2013, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2672, https://doi.org/10.5194/egusphere-egu21-2672, 2021.
EGU21-1583 | vPICO presentations | SM3.2
Bayesian multiple rupture plane inversion to assess rupture complexity: application to the 2018 Mw 7.9 Alaska earthquakeAngela Carrillo Ponce, Torsten Dahm, Simone Cesca, Frederik Tilmann, Andrey Babeyko, and Sebastian Heimann
When the earthquake rupture is complex and ruptures of multiple fault segments contribute to the total energy release, the produced wavefield is the superposition of individual signals produced by single subevents. Resolving source complexity for large, shallow earthquakes can be used to improve ground shaking and surface slip estimations, and thus tsunami models. The 2018 Mw 7.9 Alaska earthquake showed such complexity: according to previous studies, the rupture initiated as a right-lateral strike-slip fault on a N-S oriented fault plane, but then jumped onto a left-lateral strike-slip fault oriented westward. Rupture complexity and presence of multiple subevents may characterize a number of other earthquakes. However, even when individual subevents are spatially and/or temporally separated, it is very difficult to identify them from far field recordings. In order to model complex earthquakes we have implemented a multiple double couple inversion scheme within Grond, a tool devoted to the robust characterization of earthquake source parameters included in the Pyrocko software. Given the large magnitude of the target earthquake, we perform our source inversions using broadband body waves data (P and S phases) at teleseismic distances. Our approach starts with a standard moment tensor inversion, which allows to get more insights about the centroid location and overall moment release. These values can then be used to constrain the double source inversion. We discuss the performance of the inversion for the Alaska earthquake, using synthetic and real data. First, we generated realistic synthetic waveforms for a two-subevents source, assuming double couple sources with the strike-slip mechanisms proposed for the Alaska earthquake. We model the synthetic dataset both using a moment tensor and a double double couple source, and demonstrate the stability of the double double couple inversion, which is able to reconstruct the two focal mechanisms, the moment ratio and the relative centroid locations of the two subevents. Synthetic tests show that the inversion accuracy can be in some cases reduced, in presence of noisy data and when the interevent time between subevents is short. A larger noise addition affects the retrieval of the focal mechanism orientations only in some cases, but in general all the parameters were well retrieved. Then, we test our tool using real data for the earthquake. The single source inversion shows that the centroid is shifted 27 s in time and 40 km towards NE with respect to the original assumed location retrieved from the gCMT catalogue. The following double double couple source inversion resolves two subevents with right-lateral and left-lateral strike-slip focal mechanisms and Mw 7.6 and 7.8 respectively. The subevent centroids are separated by less than 40 km in space and less than 20 s in time.
How to cite: Carrillo Ponce, A., Dahm, T., Cesca, S., Tilmann, F., Babeyko, A., and Heimann, S.: Bayesian multiple rupture plane inversion to assess rupture complexity: application to the 2018 Mw 7.9 Alaska earthquake , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1583, https://doi.org/10.5194/egusphere-egu21-1583, 2021.
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When the earthquake rupture is complex and ruptures of multiple fault segments contribute to the total energy release, the produced wavefield is the superposition of individual signals produced by single subevents. Resolving source complexity for large, shallow earthquakes can be used to improve ground shaking and surface slip estimations, and thus tsunami models. The 2018 Mw 7.9 Alaska earthquake showed such complexity: according to previous studies, the rupture initiated as a right-lateral strike-slip fault on a N-S oriented fault plane, but then jumped onto a left-lateral strike-slip fault oriented westward. Rupture complexity and presence of multiple subevents may characterize a number of other earthquakes. However, even when individual subevents are spatially and/or temporally separated, it is very difficult to identify them from far field recordings. In order to model complex earthquakes we have implemented a multiple double couple inversion scheme within Grond, a tool devoted to the robust characterization of earthquake source parameters included in the Pyrocko software. Given the large magnitude of the target earthquake, we perform our source inversions using broadband body waves data (P and S phases) at teleseismic distances. Our approach starts with a standard moment tensor inversion, which allows to get more insights about the centroid location and overall moment release. These values can then be used to constrain the double source inversion. We discuss the performance of the inversion for the Alaska earthquake, using synthetic and real data. First, we generated realistic synthetic waveforms for a two-subevents source, assuming double couple sources with the strike-slip mechanisms proposed for the Alaska earthquake. We model the synthetic dataset both using a moment tensor and a double double couple source, and demonstrate the stability of the double double couple inversion, which is able to reconstruct the two focal mechanisms, the moment ratio and the relative centroid locations of the two subevents. Synthetic tests show that the inversion accuracy can be in some cases reduced, in presence of noisy data and when the interevent time between subevents is short. A larger noise addition affects the retrieval of the focal mechanism orientations only in some cases, but in general all the parameters were well retrieved. Then, we test our tool using real data for the earthquake. The single source inversion shows that the centroid is shifted 27 s in time and 40 km towards NE with respect to the original assumed location retrieved from the gCMT catalogue. The following double double couple source inversion resolves two subevents with right-lateral and left-lateral strike-slip focal mechanisms and Mw 7.6 and 7.8 respectively. The subevent centroids are separated by less than 40 km in space and less than 20 s in time.
How to cite: Carrillo Ponce, A., Dahm, T., Cesca, S., Tilmann, F., Babeyko, A., and Heimann, S.: Bayesian multiple rupture plane inversion to assess rupture complexity: application to the 2018 Mw 7.9 Alaska earthquake , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1583, https://doi.org/10.5194/egusphere-egu21-1583, 2021.
EGU21-2000 | vPICO presentations | SM3.2
Toward implementing a grid search moment tensor (GRiD MT) tool for the rapid detection and characterization of seismic events in Metropolitan FranceMarine Menager, Aurélie Trilla, and Bertrand Delouis
The aim of this study is to implement at the CEA a grid search moment tensor inversion scheme (GRiD MT) for the rapid detection and characterization of seismic events, to monitor low to moderate magnitude earthquakes in France. Given the heterogeneity of the seismic network and of the crustal geology over the country, we propose to use a combination of source grids focusing on specific regions. The GRiD MT approach requires an extensive preliminary analysis to define the different inversion parameters (velocity model, frequency band, and stations) and grid spacing (in latitude, longitude and depth). Here, we present the advances made towards the GRiD MT implementation for France. Using recent earthquakes, such as the 2019 ML 5.4 Le Teil earthquake, near Montelimar in Southern France, we discuss the validity of this detection and characterization tool for earthquake routine. The GRiD MT results applied in the South-East region for moderate earthquakes are close to those published by other agencies (USGS, IPGP, OCA, INGV) in terms of location, magnitude and focal mechanism. Nonetheless, more care is needed for the smallest events. We also discuss the precision and the uncertainties in constraining the source parameters using this method, especially when considering the goodness of fit as the unique criterion to identify a potential source, and different Earth’s structures. In the end, we show that the GRiD MT approach may be an interesting tool to analyze seismic events in France within only a few minutes after their occurrence. However, their low magnitude range raises some challenging questions to be answered.
How to cite: Menager, M., Trilla, A., and Delouis, B.: Toward implementing a grid search moment tensor (GRiD MT) tool for the rapid detection and characterization of seismic events in Metropolitan France, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2000, https://doi.org/10.5194/egusphere-egu21-2000, 2021.
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Forward to presentation link
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The aim of this study is to implement at the CEA a grid search moment tensor inversion scheme (GRiD MT) for the rapid detection and characterization of seismic events, to monitor low to moderate magnitude earthquakes in France. Given the heterogeneity of the seismic network and of the crustal geology over the country, we propose to use a combination of source grids focusing on specific regions. The GRiD MT approach requires an extensive preliminary analysis to define the different inversion parameters (velocity model, frequency band, and stations) and grid spacing (in latitude, longitude and depth). Here, we present the advances made towards the GRiD MT implementation for France. Using recent earthquakes, such as the 2019 ML 5.4 Le Teil earthquake, near Montelimar in Southern France, we discuss the validity of this detection and characterization tool for earthquake routine. The GRiD MT results applied in the South-East region for moderate earthquakes are close to those published by other agencies (USGS, IPGP, OCA, INGV) in terms of location, magnitude and focal mechanism. Nonetheless, more care is needed for the smallest events. We also discuss the precision and the uncertainties in constraining the source parameters using this method, especially when considering the goodness of fit as the unique criterion to identify a potential source, and different Earth’s structures. In the end, we show that the GRiD MT approach may be an interesting tool to analyze seismic events in France within only a few minutes after their occurrence. However, their low magnitude range raises some challenging questions to be answered.
How to cite: Menager, M., Trilla, A., and Delouis, B.: Toward implementing a grid search moment tensor (GRiD MT) tool for the rapid detection and characterization of seismic events in Metropolitan France, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2000, https://doi.org/10.5194/egusphere-egu21-2000, 2021.
EGU21-15888 | vPICO presentations | SM3.2
Gisola: Real-Time Moment Tensor computation optimized for multicore and manycore architecturesNikolaos Triantafyllis, Ioannis Venetis, Ioannis Fountoulakis, Erion-Vasilis Pikoulis, Efthimios Sokos, and Christos Evangelidis
Automatic Moment Tensor (MT) determination for regional areas is essential for real-time seismological applications such as stress inversion, shakemap generation, and tsunami warning. In recent years, the combination of two powerful tools, SeisComP and ISOLA (Sokos and Zahradník, 2008), paved the way for the release of Scisola (Triantafyllis et al., 2016), an open-source Python-based software for automatic MT calculation of seismic events provided by SeisComP -a well-known software package-, in real-time. ISOLA is an extensively used manual MT retrieval utility, based on multiple-point source representation and iterative deconvolution, full wavefield is taken into consideration and Green's functions are calculated with the discrete wavenumber method as implemented in the Axitra Fortran code (Cotton and Coutant, 1997). MT of subevents is found by least-square minimization of misfit between observed and synthetic waveforms, while position and time of subevents is optimized through grid search. Scisola monitors SeisComP and passes the event information, the respective waveform data and the station information to the ISOLA software for the Green’s Functions and MT computation. Gisola is a highly evolved version of Scisola software, oriented for High-Performance Computing. Unlike Scisola, the new program applies enhanced algorithms for waveform data filtering via quality metrics such as signal-to-noise ratio, waveform clipping, data and meta-data inconsistency, long-period (“mouse”) disturbances, and current station evaluation based on comparison between its daily Power Spectral Density (PSD) and various reference metrics for the frequency bands of interest, featuring a CPU multiprocessing implementation for faster calculations. Concerning the Green’s Functions computation, Gisola operates a newer version of the Axitra, highlighting the power of simultaneous processing in the CPU domain. Likewise, the inversion procedure code has been intensively improved by exploiting the performance efficiency of GPU-based multiprocessing implementation (with an automatic fallback to CPU-based multiprocessing in case of GPU hardware absence) and by unifying sub-programs to minimize I/O operations. In addition, a fine-grained 4D (space-time) adjustable source grid search is available for more accurate MT solutions. Moreover, Gisola expands its seismic data input resources by interconnecting to the FDSN Web Services. Furthermore, the new software has the ability to export the results in the well-known QuakeML standard, and in this way, provide clients -such as SeisComP- with MT results attached to the seismic event information. Finally, the operator has full control of all calculation aspects, with an extensive and adapted to regional data, configuration. The program can be installed on any computer that operates a Linux OS and has access to the FDSN Web Services, while the source code will be open and free to the scientific community.
Cotton F. and Coutant O., 1997, Dynamic stress variations due to shear faults in a plane-layered medium, GEOPHYSICAL JOURNAL INTERNATIONAL,Vol 128, 676-688, doi: 10.1111/j.1365-246X.1997.tb05328.x.
Sokos, E. N., and J. Zahradník (2008). ISOLA a FORTRAN code and a MATLAB GUI to perform multiple-point source inversion of seismic data, Comp. Geosci. 34, no. 8, 967–977, doi: 10.1016/j.cageo.2007.07.005.
Triantafyllis, N., Sokos, E., Ilias, A., & Zahradník, J. (2016). Scisola: automatic moment tensor solution for SeisComP3. Seismological Research Letters, 87(1), 157-163, doi: 10.1785/0220150065.
How to cite: Triantafyllis, N., Venetis, I., Fountoulakis, I., Pikoulis, E.-V., Sokos, E., and Evangelidis, C.: Gisola: Real-Time Moment Tensor computation optimized for multicore and manycore architectures, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15888, https://doi.org/10.5194/egusphere-egu21-15888, 2021.
Please decide on your access
Please use the buttons below to download the presentation materials or to visit the external website where the presentation is linked. Regarding the external link, please note that Copernicus Meetings cannot accept any liability for the content and the website you will visit.
Forward to presentation link
You are going to open an external link to the presentation as indicated by the authors. Copernicus Meetings cannot accept any liability for the content and the website you will visit.
We are sorry, but presentations are only available for users who registered for the conference. Thank you.
Automatic Moment Tensor (MT) determination for regional areas is essential for real-time seismological applications such as stress inversion, shakemap generation, and tsunami warning. In recent years, the combination of two powerful tools, SeisComP and ISOLA (Sokos and Zahradník, 2008), paved the way for the release of Scisola (Triantafyllis et al., 2016), an open-source Python-based software for automatic MT calculation of seismic events provided by SeisComP -a well-known software package-, in real-time. ISOLA is an extensively used manual MT retrieval utility, based on multiple-point source representation and iterative deconvolution, full wavefield is taken into consideration and Green's functions are calculated with the discrete wavenumber method as implemented in the Axitra Fortran code (Cotton and Coutant, 1997). MT of subevents is found by least-square minimization of misfit between observed and synthetic waveforms, while position and time of subevents is optimized through grid search. Scisola monitors SeisComP and passes the event information, the respective waveform data and the station information to the ISOLA software for the Green’s Functions and MT computation. Gisola is a highly evolved version of Scisola software, oriented for High-Performance Computing. Unlike Scisola, the new program applies enhanced algorithms for waveform data filtering via quality metrics such as signal-to-noise ratio, waveform clipping, data and meta-data inconsistency, long-period (“mouse”) disturbances, and current station evaluation based on comparison between its daily Power Spectral Density (PSD) and various reference metrics for the frequency bands of interest, featuring a CPU multiprocessing implementation for faster calculations. Concerning the Green’s Functions computation, Gisola operates a newer version of the Axitra, highlighting the power of simultaneous processing in the CPU domain. Likewise, the inversion procedure code has been intensively improved by exploiting the performance efficiency of GPU-based multiprocessing implementation (with an automatic fallback to CPU-based multiprocessing in case of GPU hardware absence) and by unifying sub-programs to minimize I/O operations. In addition, a fine-grained 4D (space-time) adjustable source grid search is available for more accurate MT solutions. Moreover, Gisola expands its seismic data input resources by interconnecting to the FDSN Web Services. Furthermore, the new software has the ability to export the results in the well-known QuakeML standard, and in this way, provide clients -such as SeisComP- with MT results attached to the seismic event information. Finally, the operator has full control of all calculation aspects, with an extensive and adapted to regional data, configuration. The program can be installed on any computer that operates a Linux OS and has access to the FDSN Web Services, while the source code will be open and free to the scientific community.
Cotton F. and Coutant O., 1997, Dynamic stress variations due to shear faults in a plane-layered medium, GEOPHYSICAL JOURNAL INTERNATIONAL,Vol 128, 676-688, doi: 10.1111/j.1365-246X.1997.tb05328.x.
Sokos, E. N., and J. Zahradník (2008). ISOLA a FORTRAN code and a MATLAB GUI to perform multiple-point source inversion of seismic data, Comp. Geosci. 34, no. 8, 967–977, doi: 10.1016/j.cageo.2007.07.005.
Triantafyllis, N., Sokos, E., Ilias, A., & Zahradník, J. (2016). Scisola: automatic moment tensor solution for SeisComP3. Seismological Research Letters, 87(1), 157-163, doi: 10.1785/0220150065.
How to cite: Triantafyllis, N., Venetis, I., Fountoulakis, I., Pikoulis, E.-V., Sokos, E., and Evangelidis, C.: Gisola: Real-Time Moment Tensor computation optimized for multicore and manycore architectures, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15888, https://doi.org/10.5194/egusphere-egu21-15888, 2021.
EGU21-12686 | vPICO presentations | SM3.2
Towards Real-Time Moment Tensor Inversions in a Data Rich Micro-Seismic Environment using Deep LearningNima Nooshiri, Christopher J. Bean, Francesco Grigoli, and Torsten Dahm
Despite advanced seismological methods, source characterization for micro-seismic events remains challenging since current inversion and modelling of high-frequency waveforms are complex and time consuming. For a real-time application like induced-seismicity monitoring, these methods are slow for true real-time information because they require repeated evaluation of the often computationally expensive forward operation. Moreover, because of the low amplitude and high-frequency content of the recorded micro-seismic signals, routine inversion procedure can become unstable and manual parameter tuning is often required. Therefore, real-time and automatic source inversion procedures are difficult and not standard. A more promising alternative to the current inversion methods for rapid source parameter inversion is to use a deep-learning neural network model that is calibrated on a data set of past and/or possible future observations. Such data-driven model, once trained, offers the potential for rapid real-time information on seismic sources in a monitoring context.
In this study, we investigate how a supervised deep-learning model trained on a data set of synthetic seismograms can be used to rapidly invert for source parameters. The inversion is represented in compact form by a convolutional neural network which yields seismic moment tensor. In other words, a neural-network algorithm is trained to encapsulate the information about the relationship between observations and underlying point-source models. The learning-based model allows rapid inversion once seismic waveforms are available. Moreover, we find that the method is robust with respect to perturbations such as observational noise and missing data. In this study, we seek to demonstrate that this approach is viable for micro-seismicity real-time estimation of source parameters. As a demonstration test, we plan to apply the new approach to data collected at the geothermal field system in the Hengill area, Iceland, within the framework of the COSEISMIQ project funded through the EU GEOTHERMICA programme.
How to cite: Nooshiri, N., Bean, C. J., Grigoli, F., and Dahm, T.: Towards Real-Time Moment Tensor Inversions in a Data Rich Micro-Seismic Environment using Deep Learning, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12686, https://doi.org/10.5194/egusphere-egu21-12686, 2021.
Despite advanced seismological methods, source characterization for micro-seismic events remains challenging since current inversion and modelling of high-frequency waveforms are complex and time consuming. For a real-time application like induced-seismicity monitoring, these methods are slow for true real-time information because they require repeated evaluation of the often computationally expensive forward operation. Moreover, because of the low amplitude and high-frequency content of the recorded micro-seismic signals, routine inversion procedure can become unstable and manual parameter tuning is often required. Therefore, real-time and automatic source inversion procedures are difficult and not standard. A more promising alternative to the current inversion methods for rapid source parameter inversion is to use a deep-learning neural network model that is calibrated on a data set of past and/or possible future observations. Such data-driven model, once trained, offers the potential for rapid real-time information on seismic sources in a monitoring context.
In this study, we investigate how a supervised deep-learning model trained on a data set of synthetic seismograms can be used to rapidly invert for source parameters. The inversion is represented in compact form by a convolutional neural network which yields seismic moment tensor. In other words, a neural-network algorithm is trained to encapsulate the information about the relationship between observations and underlying point-source models. The learning-based model allows rapid inversion once seismic waveforms are available. Moreover, we find that the method is robust with respect to perturbations such as observational noise and missing data. In this study, we seek to demonstrate that this approach is viable for micro-seismicity real-time estimation of source parameters. As a demonstration test, we plan to apply the new approach to data collected at the geothermal field system in the Hengill area, Iceland, within the framework of the COSEISMIQ project funded through the EU GEOTHERMICA programme.
How to cite: Nooshiri, N., Bean, C. J., Grigoli, F., and Dahm, T.: Towards Real-Time Moment Tensor Inversions in a Data Rich Micro-Seismic Environment using Deep Learning, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12686, https://doi.org/10.5194/egusphere-egu21-12686, 2021.
EGU21-9627 | vPICO presentations | SM3.2
An application of automatic event detection based on neural network at St Gallen (Switzerland) deep geothermal fieldPaola Forlenza, Silvia Scarpetta, Ortensia Amoroso, Paolo Capuano, and Roberto Scarpa
In seismology, when dealing with low signal-to-noise recordings, traditional event detection methods are often unable to recognise all the weak events hidden within the seismic noise. We are interested in investigating how machine learning techniques can be a useful tool to improve automatic event detection by recognising the similarity between events. We are interested in studying areas where anthropogenic activity, related to the exploitation of subsoil resources, can generate induced seismicity. Therefore, it is essential to increase the detection of weak events to improve knowledge about the seismicity of the area and its related consequences.
The SOM (Self-Organizing Map) is an unsupervised machine learning approach that is widely used for clustering, visualization and data-exploration tasks in various applications. The SOM carries out a nonlinear mapping of data onto a two-dimensional map, preserving the most important topological and metric relationships of the data. One of the reasons for using SOM for clustering indeed is to benefit from its topological structure when interpreting the data clusters.
In the preprocessing stage, features extraction is done by using both the linear prediction coding (LPC) technique for coding the spectrograms, and a waveform parameterization for characterizing amplitude characteristics in the time domain, for each of the three components.
The SOM was trained on dataset, recorded at the St Gallen geothermal site, composed of 388 records of seismic noise and 347 earthquakes with magnitude (MLcorr) between -1.2 and 3.5 collected by the Swiss Seismological Service in 2013 while realizing well control measures after drilling and acidizing the GT-1 well.
We obtained promising first results as SOM strategy correctly discriminates all known earthquakes events, clustering them into different nodes, distant from the group of nodes where noise falls. We also jointly tested synthetic traces in which we have hidden events traces within seismic noise or noise artificially generated. We studied the signals of each cluster individually, assessing the similarities of the waveform and spectral characteristics for the three components. In addition, the results are also evaluated in terms of events location, hypocentral distance, magnitude, and origin time.
This work has been supported by PRIN-2017 MATISSE project, No 20177EPPN2, funded by the Italian Ministry of Education and Research.
How to cite: Forlenza, P., Scarpetta, S., Amoroso, O., Capuano, P., and Scarpa, R.: An application of automatic event detection based on neural network at St Gallen (Switzerland) deep geothermal field, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9627, https://doi.org/10.5194/egusphere-egu21-9627, 2021.
In seismology, when dealing with low signal-to-noise recordings, traditional event detection methods are often unable to recognise all the weak events hidden within the seismic noise. We are interested in investigating how machine learning techniques can be a useful tool to improve automatic event detection by recognising the similarity between events. We are interested in studying areas where anthropogenic activity, related to the exploitation of subsoil resources, can generate induced seismicity. Therefore, it is essential to increase the detection of weak events to improve knowledge about the seismicity of the area and its related consequences.
The SOM (Self-Organizing Map) is an unsupervised machine learning approach that is widely used for clustering, visualization and data-exploration tasks in various applications. The SOM carries out a nonlinear mapping of data onto a two-dimensional map, preserving the most important topological and metric relationships of the data. One of the reasons for using SOM for clustering indeed is to benefit from its topological structure when interpreting the data clusters.
In the preprocessing stage, features extraction is done by using both the linear prediction coding (LPC) technique for coding the spectrograms, and a waveform parameterization for characterizing amplitude characteristics in the time domain, for each of the three components.
The SOM was trained on dataset, recorded at the St Gallen geothermal site, composed of 388 records of seismic noise and 347 earthquakes with magnitude (MLcorr) between -1.2 and 3.5 collected by the Swiss Seismological Service in 2013 while realizing well control measures after drilling and acidizing the GT-1 well.
We obtained promising first results as SOM strategy correctly discriminates all known earthquakes events, clustering them into different nodes, distant from the group of nodes where noise falls. We also jointly tested synthetic traces in which we have hidden events traces within seismic noise or noise artificially generated. We studied the signals of each cluster individually, assessing the similarities of the waveform and spectral characteristics for the three components. In addition, the results are also evaluated in terms of events location, hypocentral distance, magnitude, and origin time.
This work has been supported by PRIN-2017 MATISSE project, No 20177EPPN2, funded by the Italian Ministry of Education and Research.
How to cite: Forlenza, P., Scarpetta, S., Amoroso, O., Capuano, P., and Scarpa, R.: An application of automatic event detection based on neural network at St Gallen (Switzerland) deep geothermal field, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9627, https://doi.org/10.5194/egusphere-egu21-9627, 2021.
EGU21-10646 | vPICO presentations | SM3.2
Implementation of a new real time seismicity detector for the Mayotte crisisJean-Marie Saurel, Lise Retailleau, Weiqiang Zhu, Simon Issartel, Claudio Satriano, and Gregory C. Beroza
Seismology is one of the main techniques used to monitor volcanic activity worldwide. Seismicity analysis through several seismic sensor deployments has been used to monitor Mayotte volcano crisis since its beginning in May 2018. Because volcanic activity can evolve rapidly, efficient and accurate seismicity detectors are crucial to assess in real-time the activity level of the volcano and, if needed, to issue timely warnings.
Traditional real-time seismic processing software, such as EarthWorm or SeisComP, use phase onset pickers followed by a phase association algorithm to declare an event and proceed with its location. Real-time phase pickers usually cannot identify whether the detected phase is a P or S arrival and this decision or assumption is made by the associator. The lack of S arrival has an obvious impact on the hypocentral location quality. S-phases can also help detection on small earthquakes where weak P-phases can be missed.
We implemented the deep neural network-based method PhaseNet to identify in real-time seismic P and S waves on 3-component seismometers deployed on Mayotte island. We also built an interface to subsequently process PhaseNet results and send pick objects to EarthWorm. We use EarthWorm binder_ew associator module specifically tuned for PhaseNet a priori phase identification to detect and locate the events, which are finally archived in a SeisComP database. We implemented this innovative real-time processing system for the REVOSIMA (Reseau de surveillance Volcanologique et Sismologique de Mayotte) hosted at OVPF (Observatoire Volcanologique du Piton de la Fournaise). We assess the robustness of the algorithm by comparing the results to existing automatic and manually detected seismicity catalogs.
We show that the existing SeisComP automatic system is outperformed by our new algorithm, both in number of earthquake detections and location reliability. Our implementation also detects more events than the daily manual data screening. While this promising new processing system was first applied to study the Mayotte seismicity, it can be used in any seismic active zone, of volcanic or tectonic origin. Indeed, it will be installed at Martinique volcanic and seismic observatory later this year.
How to cite: Saurel, J.-M., Retailleau, L., Zhu, W., Issartel, S., Satriano, C., and Beroza, G. C.: Implementation of a new real time seismicity detector for the Mayotte crisis, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10646, https://doi.org/10.5194/egusphere-egu21-10646, 2021.
Seismology is one of the main techniques used to monitor volcanic activity worldwide. Seismicity analysis through several seismic sensor deployments has been used to monitor Mayotte volcano crisis since its beginning in May 2018. Because volcanic activity can evolve rapidly, efficient and accurate seismicity detectors are crucial to assess in real-time the activity level of the volcano and, if needed, to issue timely warnings.
Traditional real-time seismic processing software, such as EarthWorm or SeisComP, use phase onset pickers followed by a phase association algorithm to declare an event and proceed with its location. Real-time phase pickers usually cannot identify whether the detected phase is a P or S arrival and this decision or assumption is made by the associator. The lack of S arrival has an obvious impact on the hypocentral location quality. S-phases can also help detection on small earthquakes where weak P-phases can be missed.
We implemented the deep neural network-based method PhaseNet to identify in real-time seismic P and S waves on 3-component seismometers deployed on Mayotte island. We also built an interface to subsequently process PhaseNet results and send pick objects to EarthWorm. We use EarthWorm binder_ew associator module specifically tuned for PhaseNet a priori phase identification to detect and locate the events, which are finally archived in a SeisComP database. We implemented this innovative real-time processing system for the REVOSIMA (Reseau de surveillance Volcanologique et Sismologique de Mayotte) hosted at OVPF (Observatoire Volcanologique du Piton de la Fournaise). We assess the robustness of the algorithm by comparing the results to existing automatic and manually detected seismicity catalogs.
We show that the existing SeisComP automatic system is outperformed by our new algorithm, both in number of earthquake detections and location reliability. Our implementation also detects more events than the daily manual data screening. While this promising new processing system was first applied to study the Mayotte seismicity, it can be used in any seismic active zone, of volcanic or tectonic origin. Indeed, it will be installed at Martinique volcanic and seismic observatory later this year.
How to cite: Saurel, J.-M., Retailleau, L., Zhu, W., Issartel, S., Satriano, C., and Beroza, G. C.: Implementation of a new real time seismicity detector for the Mayotte crisis, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10646, https://doi.org/10.5194/egusphere-egu21-10646, 2021.
EGU21-1285 | vPICO presentations | SM3.2 | Highlight
Discrimination of quarry blasts from earthquakes using artificial neural networksDeniz Ertuncay, Andrea De Lorenzo, and Giovanni Costa
Seismic networks record vibrations that are captured by their stations. These vibrations can be coming from various sources, such as tectonic tremors, quarry blasts and anthropogenic sources. Separation of earthquakes from other sources may require human intervention and it can be a labor-intensive work. In case of lack of such a separation, seismic hazard may be miscalculated. Our goal is to discriminate earthquakes from quarry blasts by using artificial neural networks. To do that, we used two different databases for earthquake signals and quarry blasts. Neither of them have data from our study of interest, which is North-East of Italy. We used three channel signals from the stations as an input for the neural networks. Signals are used as both time series and their spectral characteristics and are fed to the neural networks with this information. We then separated earthquakes from quarry blasts in North-East Italy by using our algorithm. We conclude that our algorithm is able to discriminate earthquakes from quarry blasts with high accuracy and the database can be used in different regions with different earthquake and quarry blast sources in a large variety of distances.
How to cite: Ertuncay, D., De Lorenzo, A., and Costa, G.: Discrimination of quarry blasts from earthquakes using artificial neural networks, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1285, https://doi.org/10.5194/egusphere-egu21-1285, 2021.
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Seismic networks record vibrations that are captured by their stations. These vibrations can be coming from various sources, such as tectonic tremors, quarry blasts and anthropogenic sources. Separation of earthquakes from other sources may require human intervention and it can be a labor-intensive work. In case of lack of such a separation, seismic hazard may be miscalculated. Our goal is to discriminate earthquakes from quarry blasts by using artificial neural networks. To do that, we used two different databases for earthquake signals and quarry blasts. Neither of them have data from our study of interest, which is North-East of Italy. We used three channel signals from the stations as an input for the neural networks. Signals are used as both time series and their spectral characteristics and are fed to the neural networks with this information. We then separated earthquakes from quarry blasts in North-East Italy by using our algorithm. We conclude that our algorithm is able to discriminate earthquakes from quarry blasts with high accuracy and the database can be used in different regions with different earthquake and quarry blast sources in a large variety of distances.
How to cite: Ertuncay, D., De Lorenzo, A., and Costa, G.: Discrimination of quarry blasts from earthquakes using artificial neural networks, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1285, https://doi.org/10.5194/egusphere-egu21-1285, 2021.
EGU21-707 | vPICO presentations | SM3.2
Estimating Seismic Moment Tensors based on Bayesian Machine LearningAndreas Steinberg, Hannes Vasyura-Bathke, Peter Gaebler, and Lars Ceranna
Estimating fast earthquakes’ source mechanism is essential for near real time hazard assessments, which are based on shakemaps and further downstream analysis such as physics based aftershock probability calculations. The model and data uncertainties associated to the estimated source mechanism are also crucial. We propose a Baysian Machine Learning algorithm trained on normalized synthetic waveforms for estimating the full moment tensor of earthquakes almost instantaneously with associated source parameter uncertainties.
A prior assumption is an appropriate location of the earthquakes along with its associated uncertainties. Here, this is obtained by already established Machine learning based algorithms, where the training data set is computed by forward calculations of synthetic waveforms based on Green’s functions calculated for a specified 1-D velocity model using the Pyrocko software package. The learned labels, which are the information learned by the Machine Learning algorithm associated to the data, are the moment tensor components, described with only five unique parameters. For predefined locations in an area of interest we train a full independent Bayesian Convolutional Neural Network (BNN).
With variational inference the weights of the network are not scalar but represent a distribution of weights for the activation of neurons. Each evaluation of input data into our BNN yields therefore to a set of predictions with associated probabilities. This allows us to evaluate an ensemble of possible source mechanisms for each evaluation of input waveform data.
As a test set, we trained our models for an area south of the Coso geothermal field in California for a fixed set of broadband stations at maximum 150 km distance. We validate our approach with a subset of earthquakes from the Ridgecrest 2019-2020 sequence. For this data set we compare the results of the estimates of our Machine Learning based approach with independently determined focal mechanism and moment tensors. Overall, we benchmark our approach with data unseen during the training process of the Machine Learning models and show its capabilities for generating similar source mechanism estimations as independent studies within only a few seconds processing time per earthquake. We finally apply the method to seismic data of a research network monitoring the area around two south-german geothermal power plants. Our approach demonstrates the potential of Machine Learning for being implemented in operational frameworks for fast earthquake source mechanism estimation with associated uncertainties.
How to cite: Steinberg, A., Vasyura-Bathke, H., Gaebler, P., and Ceranna, L.: Estimating Seismic Moment Tensors based on Bayesian Machine Learning, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-707, https://doi.org/10.5194/egusphere-egu21-707, 2021.
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Estimating fast earthquakes’ source mechanism is essential for near real time hazard assessments, which are based on shakemaps and further downstream analysis such as physics based aftershock probability calculations. The model and data uncertainties associated to the estimated source mechanism are also crucial. We propose a Baysian Machine Learning algorithm trained on normalized synthetic waveforms for estimating the full moment tensor of earthquakes almost instantaneously with associated source parameter uncertainties.
A prior assumption is an appropriate location of the earthquakes along with its associated uncertainties. Here, this is obtained by already established Machine learning based algorithms, where the training data set is computed by forward calculations of synthetic waveforms based on Green’s functions calculated for a specified 1-D velocity model using the Pyrocko software package. The learned labels, which are the information learned by the Machine Learning algorithm associated to the data, are the moment tensor components, described with only five unique parameters. For predefined locations in an area of interest we train a full independent Bayesian Convolutional Neural Network (BNN).
With variational inference the weights of the network are not scalar but represent a distribution of weights for the activation of neurons. Each evaluation of input data into our BNN yields therefore to a set of predictions with associated probabilities. This allows us to evaluate an ensemble of possible source mechanisms for each evaluation of input waveform data.
As a test set, we trained our models for an area south of the Coso geothermal field in California for a fixed set of broadband stations at maximum 150 km distance. We validate our approach with a subset of earthquakes from the Ridgecrest 2019-2020 sequence. For this data set we compare the results of the estimates of our Machine Learning based approach with independently determined focal mechanism and moment tensors. Overall, we benchmark our approach with data unseen during the training process of the Machine Learning models and show its capabilities for generating similar source mechanism estimations as independent studies within only a few seconds processing time per earthquake. We finally apply the method to seismic data of a research network monitoring the area around two south-german geothermal power plants. Our approach demonstrates the potential of Machine Learning for being implemented in operational frameworks for fast earthquake source mechanism estimation with associated uncertainties.
How to cite: Steinberg, A., Vasyura-Bathke, H., Gaebler, P., and Ceranna, L.: Estimating Seismic Moment Tensors based on Bayesian Machine Learning, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-707, https://doi.org/10.5194/egusphere-egu21-707, 2021.
EGU21-12218 | vPICO presentations | SM3.2
SeisBench: A toolbox for benchmarking and applying machine learning in seismology.Jack Woollam, Jannes Münchmeyer, Carlo Giunchi, Dario Jozinovic, Tobias Diehl, Joachim Saul, Alberto Michelini, Florian Haslinger, Dietrich Lange, Frederik Tilmann, and Andreas Rietbrock
Machine learning methods have seen widespread adoption within the seismological community in recent years due to their ability to effectively process large amounts of data, while equalling or surpassing the performance of human analysts or classic algorithms. In the wider machine learning world, for example in imaging applications, the open availability of extensive high-quality datasets for training, validation, and the benchmarking of competing algorithms is seen as a vital ingredient to the rapid progress observed throughout the last decade. Within seismology, vast catalogues of labelled data are readily available, but collecting the waveform data for millions of records and assessing the quality of training examples is a time-consuming, tedious process. The natural variability in source processes and seismic wave propagation also presents a critical problem during training. The performance of models trained on different regions, distance and magnitude ranges are not easily comparable. The inability to easily compare and contrast state-of-the-art machine learning-based detection techniques on varying seismic data sets is currently a barrier to further progress within this emerging field. We present SeisBench, an extensible open-source framework for training, benchmarking, and applying machine learning algorithms. SeisBench provides access to various benchmark data sets and models from literature, along with pre-trained model weights, through a unified API. Built to be extensible, and modular, SeisBench allows for the simple addition of new models and data sets, which can be easily interchanged with existing pre-trained models and benchmark data. Standardising the access of varying quality data, and metadata simplifies comparison workflows, enabling the development of more robust machine learning algorithms. We initially focus on phase detection, identification and picking, but the framework is designed to be extended for other purposes, for example direct estimation of event parameters. Users will be able to contribute their own benchmarks and (trained) models. In the future, it will thus be much easier to compare both the performance of new algorithms against published machine learning models/architectures and to check the performance of established algorithms against new data sets. We hope that the ease of validation and inter-model comparison enabled by SeisBench will serve as a catalyst for the development of the next generation of machine learning techniques within the seismological community. The SeisBench source code will be published with an open license and explicitly encourages community involvement.
How to cite: Woollam, J., Münchmeyer, J., Giunchi, C., Jozinovic, D., Diehl, T., Saul, J., Michelini, A., Haslinger, F., Lange, D., Tilmann, F., and Rietbrock, A.: SeisBench: A toolbox for benchmarking and applying machine learning in seismology., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12218, https://doi.org/10.5194/egusphere-egu21-12218, 2021.
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Machine learning methods have seen widespread adoption within the seismological community in recent years due to their ability to effectively process large amounts of data, while equalling or surpassing the performance of human analysts or classic algorithms. In the wider machine learning world, for example in imaging applications, the open availability of extensive high-quality datasets for training, validation, and the benchmarking of competing algorithms is seen as a vital ingredient to the rapid progress observed throughout the last decade. Within seismology, vast catalogues of labelled data are readily available, but collecting the waveform data for millions of records and assessing the quality of training examples is a time-consuming, tedious process. The natural variability in source processes and seismic wave propagation also presents a critical problem during training. The performance of models trained on different regions, distance and magnitude ranges are not easily comparable. The inability to easily compare and contrast state-of-the-art machine learning-based detection techniques on varying seismic data sets is currently a barrier to further progress within this emerging field. We present SeisBench, an extensible open-source framework for training, benchmarking, and applying machine learning algorithms. SeisBench provides access to various benchmark data sets and models from literature, along with pre-trained model weights, through a unified API. Built to be extensible, and modular, SeisBench allows for the simple addition of new models and data sets, which can be easily interchanged with existing pre-trained models and benchmark data. Standardising the access of varying quality data, and metadata simplifies comparison workflows, enabling the development of more robust machine learning algorithms. We initially focus on phase detection, identification and picking, but the framework is designed to be extended for other purposes, for example direct estimation of event parameters. Users will be able to contribute their own benchmarks and (trained) models. In the future, it will thus be much easier to compare both the performance of new algorithms against published machine learning models/architectures and to check the performance of established algorithms against new data sets. We hope that the ease of validation and inter-model comparison enabled by SeisBench will serve as a catalyst for the development of the next generation of machine learning techniques within the seismological community. The SeisBench source code will be published with an open license and explicitly encourages community involvement.
How to cite: Woollam, J., Münchmeyer, J., Giunchi, C., Jozinovic, D., Diehl, T., Saul, J., Michelini, A., Haslinger, F., Lange, D., Tilmann, F., and Rietbrock, A.: SeisBench: A toolbox for benchmarking and applying machine learning in seismology., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12218, https://doi.org/10.5194/egusphere-egu21-12218, 2021.
SM5.1 – Imaging, modelling and inversion to explore the Earth’s lithosphere
EGU21-10058 | vPICO presentations | SM5.1
Imaging the Earth’s small structures: AI-driven, Bayesian inference of microstructure descriptors from finite-frequency wavesIvan Vasconcelos, Wouter Klessens, Yang Jiao, Andre Niemeijer, and Suzanne Hangx
More often than not, important geologic processes occur at micro-scales, e.g., fluid flow, mineral-phase changes, chemically-induced alteration, rock-frame compaction, or even mechanical ruptures/instabilities leading to large earthquakes. However, reliably imaging material properties at such scales from remote long-wavelength information contained in either seismic or EM fields has long been a challenge to the geophysical, engineering and material science communities. In this talk, we present a general framework for the estimation of sub-wavelength material properties from long-scale waves, building on recent advances on statistical microstructure descriptors (SMDs) within the field of material science.
In geoscience, traditional approaches to describing material microheterogeneity rely on either analytical inclusion-based models, or in sample-based digital rocks: each of these having their pros and cons. Here, we instead rely on SMDs, namely two-point correlation and polytope functions, to describe microheterogeneous geo-materials in a manner that is capable of generalizing complex geometrical information hidden in microstructures, while also retaining realism and sample fidelity. Using SMDs, we rely on wave-equation-based Strong Contrast Expansions (SCEs) to predict frequency/scale-dependent effective wave properties for acoustic, elastic and EM waves. We briefly discuss how SMD-described microstructures affect long-wave properties – and in particular how they not only predict frequency-dependent attenuation due to sub-wavelength scattering, but that attenuation is particularly sensitive to microstructure when compared to effective wavespeeds.
When it comes to the estimation of microstructure properties from wave observations, the problem becomes substantially more difficult because realistic microscale parameters could in principle have far too many degrees of freedom than what is observable from finite-frequency wave data. As such, it is key that any method that aims at realistically retrieving microstructure information from long-scale wave data accounts for uncertainty, while also handling the highly nonlinear nature of microstructure-dependent effective wave properties. To that end, we combine our SMD and SCE approaches for effective wave properties with the supervised machine-learning method of Random Forests to construct a Bayesian approach to infer microstructure properties from effective wave parameters as observables. This method yields full posterior distributions for microstructure parameters (e.g., property contrast, volume fraction, and geometry information) from frequency-dependent observations of wave velocities and attenuation. We present several examples of inference scenarios, showing, for example, that i) attenuation is key to microstructure imaging, and ii) microgeometry information can only be reliably retrieved if contrast and volume fraction are relatively well known a priori. We illustrate of inference approach with several examples of analytical and real microstructures, including data from a laboratory compaction experiment controlled by microscale CT imaging.
How to cite: Vasconcelos, I., Klessens, W., Jiao, Y., Niemeijer, A., and Hangx, S.: Imaging the Earth’s small structures: AI-driven, Bayesian inference of microstructure descriptors from finite-frequency waves, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10058, https://doi.org/10.5194/egusphere-egu21-10058, 2021.
Please decide on your access
Please use the buttons below to download the presentation materials or to visit the external website where the presentation is linked. Regarding the external link, please note that Copernicus Meetings cannot accept any liability for the content and the website you will visit.
Forward to presentation link
You are going to open an external link to the presentation as indicated by the authors. Copernicus Meetings cannot accept any liability for the content and the website you will visit.
We are sorry, but presentations are only available for users who registered for the conference. Thank you.
More often than not, important geologic processes occur at micro-scales, e.g., fluid flow, mineral-phase changes, chemically-induced alteration, rock-frame compaction, or even mechanical ruptures/instabilities leading to large earthquakes. However, reliably imaging material properties at such scales from remote long-wavelength information contained in either seismic or EM fields has long been a challenge to the geophysical, engineering and material science communities. In this talk, we present a general framework for the estimation of sub-wavelength material properties from long-scale waves, building on recent advances on statistical microstructure descriptors (SMDs) within the field of material science.
In geoscience, traditional approaches to describing material microheterogeneity rely on either analytical inclusion-based models, or in sample-based digital rocks: each of these having their pros and cons. Here, we instead rely on SMDs, namely two-point correlation and polytope functions, to describe microheterogeneous geo-materials in a manner that is capable of generalizing complex geometrical information hidden in microstructures, while also retaining realism and sample fidelity. Using SMDs, we rely on wave-equation-based Strong Contrast Expansions (SCEs) to predict frequency/scale-dependent effective wave properties for acoustic, elastic and EM waves. We briefly discuss how SMD-described microstructures affect long-wave properties – and in particular how they not only predict frequency-dependent attenuation due to sub-wavelength scattering, but that attenuation is particularly sensitive to microstructure when compared to effective wavespeeds.
When it comes to the estimation of microstructure properties from wave observations, the problem becomes substantially more difficult because realistic microscale parameters could in principle have far too many degrees of freedom than what is observable from finite-frequency wave data. As such, it is key that any method that aims at realistically retrieving microstructure information from long-scale wave data accounts for uncertainty, while also handling the highly nonlinear nature of microstructure-dependent effective wave properties. To that end, we combine our SMD and SCE approaches for effective wave properties with the supervised machine-learning method of Random Forests to construct a Bayesian approach to infer microstructure properties from effective wave parameters as observables. This method yields full posterior distributions for microstructure parameters (e.g., property contrast, volume fraction, and geometry information) from frequency-dependent observations of wave velocities and attenuation. We present several examples of inference scenarios, showing, for example, that i) attenuation is key to microstructure imaging, and ii) microgeometry information can only be reliably retrieved if contrast and volume fraction are relatively well known a priori. We illustrate of inference approach with several examples of analytical and real microstructures, including data from a laboratory compaction experiment controlled by microscale CT imaging.
How to cite: Vasconcelos, I., Klessens, W., Jiao, Y., Niemeijer, A., and Hangx, S.: Imaging the Earth’s small structures: AI-driven, Bayesian inference of microstructure descriptors from finite-frequency waves, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10058, https://doi.org/10.5194/egusphere-egu21-10058, 2021.
EGU21-5859 | vPICO presentations | SM5.1
What does the 2A Event observed in the oceanic crust actually represent?Richard Hobbs and Christine Peirce
The transition zone between the more porous upper extrusive layer (2A) and the less porous lower dyke layer (2B) within the oceanic crust is characterised by a high velocity gradient based on inversion of controlled-source, long-offset refraction data. In these data the phase associated with this high velocity gradient, termed the 2A Event, has an anomalously high amplitude over a limited range of offsets and appears to form a triplication with refractions from layer 2A above and 2B below. These characteristics fit the accepted model that this event is a caustic or retrograde phase, generated by a distinct layer whose thickness and velocity gradient can be determined by ray-trace modelling. Hence, a velocity model for Layer 2 (derived from seismic data acquired near ODP 504B) consists of a ~500 m-thick 2A with a velocity gradient of ~1.0 s-1; a ~200 m-thick transition zone with a high velocity gradient of ~4.0 s-1; and a ~1300 m-thick 2B with a velocity gradient of ~0.3 s-1. However, this model is at odds with observation of Layer 2 lithology obtained from coring and ophiolites where the 2A is composed of a mixture of higher velocity basalt flows and lower velocity pillow lavas and breccia, with the transition zone represented by an increasing number of dykes which eventually make up 100% of the section in layer 2B combined and the effects of high-temperature alteration. Starting with a simplified but plausible geologically-based model, we show that it is possible to synthetically generate the observed 2A Event, and gain insight into what controls its visibility and variability in refraction data. Our primary findings show that the 2A Event will only form and propagate in the base of layer 2A, above the level where the higher velocities dominate. We also show that the amplitude of the 2A Event is sensitive to the local velocity structure of the extrusive layer and is most visible when seismic energy is focused by a low velocity layer. Hence, we conclude that the 2A Event is not a simple caustic, as defined by geometrical optics, but instead caused by the incident seismic energy being briefly concentrated in a leaky waveguide close to, but above, the mean depth of the dykes and the onset of high temperature alteration.
How to cite: Hobbs, R. and Peirce, C.: What does the 2A Event observed in the oceanic crust actually represent?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5859, https://doi.org/10.5194/egusphere-egu21-5859, 2021.
The transition zone between the more porous upper extrusive layer (2A) and the less porous lower dyke layer (2B) within the oceanic crust is characterised by a high velocity gradient based on inversion of controlled-source, long-offset refraction data. In these data the phase associated with this high velocity gradient, termed the 2A Event, has an anomalously high amplitude over a limited range of offsets and appears to form a triplication with refractions from layer 2A above and 2B below. These characteristics fit the accepted model that this event is a caustic or retrograde phase, generated by a distinct layer whose thickness and velocity gradient can be determined by ray-trace modelling. Hence, a velocity model for Layer 2 (derived from seismic data acquired near ODP 504B) consists of a ~500 m-thick 2A with a velocity gradient of ~1.0 s-1; a ~200 m-thick transition zone with a high velocity gradient of ~4.0 s-1; and a ~1300 m-thick 2B with a velocity gradient of ~0.3 s-1. However, this model is at odds with observation of Layer 2 lithology obtained from coring and ophiolites where the 2A is composed of a mixture of higher velocity basalt flows and lower velocity pillow lavas and breccia, with the transition zone represented by an increasing number of dykes which eventually make up 100% of the section in layer 2B combined and the effects of high-temperature alteration. Starting with a simplified but plausible geologically-based model, we show that it is possible to synthetically generate the observed 2A Event, and gain insight into what controls its visibility and variability in refraction data. Our primary findings show that the 2A Event will only form and propagate in the base of layer 2A, above the level where the higher velocities dominate. We also show that the amplitude of the 2A Event is sensitive to the local velocity structure of the extrusive layer and is most visible when seismic energy is focused by a low velocity layer. Hence, we conclude that the 2A Event is not a simple caustic, as defined by geometrical optics, but instead caused by the incident seismic energy being briefly concentrated in a leaky waveguide close to, but above, the mean depth of the dykes and the onset of high temperature alteration.
How to cite: Hobbs, R. and Peirce, C.: What does the 2A Event observed in the oceanic crust actually represent?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5859, https://doi.org/10.5194/egusphere-egu21-5859, 2021.
EGU21-9743 | vPICO presentations | SM5.1
3D seismic imaging of the Alpine Fault and the glacial valley at Whataroa, New ZealandVera Lay, Stefan Buske, Franz Kleine, John Townend, Richard Kellett, Martha Savage, Douglas R. Schmitt, Alexis Constantinou, Jennifer Eccles, Donald Lawton, Malcolm Bertram, Kevin Hall, Randolph Kofman, and Andrew Gorman
The Alpine Fault at the West Coast of the South Island (New Zealand) is a major plate boundary that is expected to rupture in the next 50 years, likely as a magnitude 8 earthquake. The Deep Fault Drilling Project (DFDP) aimed to deliver insight into the geological structure of this fault zone and its evolution by drilling and sampling the Alpine Fault at depth. Here we present results from a seismic survey around the DFDP-2 drill site in the Whataroa Valley where the drillhole almost reached the fault plane. This unique 3D seismic survey includes several 2D lines and a 3D array at the surface as well as borehole recordings. Within the borehole, the unique option to compare two measurement systems is used: conventional three-component borehole geophones and a fibre optic cable (heterodyne Distributed Vibration Sensing system (hDVS)). Both systems show coherent signals but only the hDVS system allowed a recording along the complete length of the borehole.
Despite the challenging conditions for seismic imaging within a glacial valley filled with sediments and steeply dipping valley flanks, several structures related to the valley itself as well as the tectonic fault system are imaged. The pre-processing of the seismic data also includes wavefield separation for the zero-offset borehole data. Seismic images are obtained by prestack depth migration approaches.
Within the glacial valley, particularly steep valley flanks are imaged directly and correlate well with results from the P-wave velocity model obtained by first arrival travel-time tomography. Additionally, a glacially over-deepened trough with nearly horizontally layered sediments is identified about 0.5 km south of the DFDP-2B borehole.
With regard to the expected Alpine fault zone, a set of several reflectors dipping 40-56° to the southeast are identified in a ~600 m wide zone between depths of 0.2 and 1.2 km that is interpreted to be the minimum extent of the damage zone. Different approaches image one distinct reflector dipping at 40°, which is interpreted to be the main Alpine Fault reflector. This reflector is only ~100 m ahead from the lower end of the borehole. At shallower depths (z<0.5 km), additional reflectors are identified as fault segments and generally have steeper dips up to 56°. About 1 km south of the drill site, a major fault is identified at a depth of 0.1-0.5 km that might be caused by the regional tectonics interacting with local valley structures. A good correlation is observed among the separate seismic data sets and with geological results such as the borehole stratigraphy and the expected surface trace of the fault.
In conclusion, several structural details of the fault zone and its environment are seismically imaged and show the complexity of the Alpine Fault at the Whataroa Valley. Thus, a detailed seismic characterization clarifies the subsurface structures, which is crucial to understand the transpressive fault’s tectonic processes.
How to cite: Lay, V., Buske, S., Kleine, F., Townend, J., Kellett, R., Savage, M., Schmitt, D. R., Constantinou, A., Eccles, J., Lawton, D., Bertram, M., Hall, K., Kofman, R., and Gorman, A.: 3D seismic imaging of the Alpine Fault and the glacial valley at Whataroa, New Zealand, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9743, https://doi.org/10.5194/egusphere-egu21-9743, 2021.
The Alpine Fault at the West Coast of the South Island (New Zealand) is a major plate boundary that is expected to rupture in the next 50 years, likely as a magnitude 8 earthquake. The Deep Fault Drilling Project (DFDP) aimed to deliver insight into the geological structure of this fault zone and its evolution by drilling and sampling the Alpine Fault at depth. Here we present results from a seismic survey around the DFDP-2 drill site in the Whataroa Valley where the drillhole almost reached the fault plane. This unique 3D seismic survey includes several 2D lines and a 3D array at the surface as well as borehole recordings. Within the borehole, the unique option to compare two measurement systems is used: conventional three-component borehole geophones and a fibre optic cable (heterodyne Distributed Vibration Sensing system (hDVS)). Both systems show coherent signals but only the hDVS system allowed a recording along the complete length of the borehole.
Despite the challenging conditions for seismic imaging within a glacial valley filled with sediments and steeply dipping valley flanks, several structures related to the valley itself as well as the tectonic fault system are imaged. The pre-processing of the seismic data also includes wavefield separation for the zero-offset borehole data. Seismic images are obtained by prestack depth migration approaches.
Within the glacial valley, particularly steep valley flanks are imaged directly and correlate well with results from the P-wave velocity model obtained by first arrival travel-time tomography. Additionally, a glacially over-deepened trough with nearly horizontally layered sediments is identified about 0.5 km south of the DFDP-2B borehole.
With regard to the expected Alpine fault zone, a set of several reflectors dipping 40-56° to the southeast are identified in a ~600 m wide zone between depths of 0.2 and 1.2 km that is interpreted to be the minimum extent of the damage zone. Different approaches image one distinct reflector dipping at 40°, which is interpreted to be the main Alpine Fault reflector. This reflector is only ~100 m ahead from the lower end of the borehole. At shallower depths (z<0.5 km), additional reflectors are identified as fault segments and generally have steeper dips up to 56°. About 1 km south of the drill site, a major fault is identified at a depth of 0.1-0.5 km that might be caused by the regional tectonics interacting with local valley structures. A good correlation is observed among the separate seismic data sets and with geological results such as the borehole stratigraphy and the expected surface trace of the fault.
In conclusion, several structural details of the fault zone and its environment are seismically imaged and show the complexity of the Alpine Fault at the Whataroa Valley. Thus, a detailed seismic characterization clarifies the subsurface structures, which is crucial to understand the transpressive fault’s tectonic processes.
How to cite: Lay, V., Buske, S., Kleine, F., Townend, J., Kellett, R., Savage, M., Schmitt, D. R., Constantinou, A., Eccles, J., Lawton, D., Bertram, M., Hall, K., Kofman, R., and Gorman, A.: 3D seismic imaging of the Alpine Fault and the glacial valley at Whataroa, New Zealand, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9743, https://doi.org/10.5194/egusphere-egu21-9743, 2021.
EGU21-14388 | vPICO presentations | SM5.1
A high-resolution seismic survey across the Balmuccia Peridotite, Ivrea Zone, Italy - Project DIVE phase two, site investigationDamian Pasiecznik, Andrew Greenwood, Ludovic Baron, Florian Bleibinhaus, and György Hetényi
The Ivrea Verbano Zone (IVZ) is one of the most complete crust–upper mantle geological references in the world, and the Drilling the Ivrea-Verbano zone project (DIVE) aims to unravel the uncertainties below this area. Geophysical anomalies detected across the IVZ indicate that dense, mantle-like rocks are located at depths as shallow as ca. 3km. Thus, several geological, geochemical and geophysical studies are planned, including the drilling of a 4km deep borehole that will penetrate the Balmuccia Peridotite (Val Sesia, Italy) to approach and possibly cross the crust–mantle transition zone, and provide, for the first time, geophysical in-situ measurements of the IVZ.
One of the primary requirements before drilling is a seismic site characterization, to define with precision the correct positioning and orientation of the borehole, to assess potential drilling hazards and to allow for the spatial extrapolation of the borehole logs. For that goal, two joint geophysical surveys were performed in October 2020 in a collaboration of GFZ Potsdam, Université de Lausanne and Montanuniversität Leoben. First: a deep seismic survey, entitled SEIZE (SEismic imaging of the Ivrea ZonE), consisting of two approximately 15km-long seismic lines performed by GFZ Potsdam, that aim to resolve the deeper structure of the IVZ in the area, and second: a static seismic survey at the proposed drill site, entitled HiSEIZE (High-resolution SEismic imaging of the Ivrea ZonE), geared towards providing high-resolution seismic images of the uppermost few km at the proposed drill site.
The HiSEIZE survey, the subject of this study, was performed with a fixed spread of 200 vertical geophones and 160 3C-sensors, spaced at ca. 11m along three sub-parallel lines spaced 50-80m apart. Vibroseis source points were at 22m stations along a 2.4km line utilizing a high-frequency (12-140 Hz) 10s linear sweep with 3s listening time. In addition to this, the HiSEIZE receiver spread was active during the deep SEIZE survey, information that may be useful in determination of a velocity model through the Balmuccia Peridotite.
This project will not only provide site characterization for the DIVE project, but also contribute to understanding the structure of the Balmuccia Peridotite, its changes in depth and its relationship with the crustal-mantle transition.
Here we present the data and discuss the challenges of 3D pre-stack-imaging in an area of extreme topography.
How to cite: Pasiecznik, D., Greenwood, A., Baron, L., Bleibinhaus, F., and Hetényi, G.: A high-resolution seismic survey across the Balmuccia Peridotite, Ivrea Zone, Italy - Project DIVE phase two, site investigation, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14388, https://doi.org/10.5194/egusphere-egu21-14388, 2021.
The Ivrea Verbano Zone (IVZ) is one of the most complete crust–upper mantle geological references in the world, and the Drilling the Ivrea-Verbano zone project (DIVE) aims to unravel the uncertainties below this area. Geophysical anomalies detected across the IVZ indicate that dense, mantle-like rocks are located at depths as shallow as ca. 3km. Thus, several geological, geochemical and geophysical studies are planned, including the drilling of a 4km deep borehole that will penetrate the Balmuccia Peridotite (Val Sesia, Italy) to approach and possibly cross the crust–mantle transition zone, and provide, for the first time, geophysical in-situ measurements of the IVZ.
One of the primary requirements before drilling is a seismic site characterization, to define with precision the correct positioning and orientation of the borehole, to assess potential drilling hazards and to allow for the spatial extrapolation of the borehole logs. For that goal, two joint geophysical surveys were performed in October 2020 in a collaboration of GFZ Potsdam, Université de Lausanne and Montanuniversität Leoben. First: a deep seismic survey, entitled SEIZE (SEismic imaging of the Ivrea ZonE), consisting of two approximately 15km-long seismic lines performed by GFZ Potsdam, that aim to resolve the deeper structure of the IVZ in the area, and second: a static seismic survey at the proposed drill site, entitled HiSEIZE (High-resolution SEismic imaging of the Ivrea ZonE), geared towards providing high-resolution seismic images of the uppermost few km at the proposed drill site.
The HiSEIZE survey, the subject of this study, was performed with a fixed spread of 200 vertical geophones and 160 3C-sensors, spaced at ca. 11m along three sub-parallel lines spaced 50-80m apart. Vibroseis source points were at 22m stations along a 2.4km line utilizing a high-frequency (12-140 Hz) 10s linear sweep with 3s listening time. In addition to this, the HiSEIZE receiver spread was active during the deep SEIZE survey, information that may be useful in determination of a velocity model through the Balmuccia Peridotite.
This project will not only provide site characterization for the DIVE project, but also contribute to understanding the structure of the Balmuccia Peridotite, its changes in depth and its relationship with the crustal-mantle transition.
Here we present the data and discuss the challenges of 3D pre-stack-imaging in an area of extreme topography.
How to cite: Pasiecznik, D., Greenwood, A., Baron, L., Bleibinhaus, F., and Hetényi, G.: A high-resolution seismic survey across the Balmuccia Peridotite, Ivrea Zone, Italy - Project DIVE phase two, site investigation, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14388, https://doi.org/10.5194/egusphere-egu21-14388, 2021.
EGU21-12246 | vPICO presentations | SM5.1
Forward Modelling of Bouguer Anomalies along a transect of the Southern Apennines and the Tyrrhenian back-arc basin.Assel Akimbekova, Paolo Mancinelli, Massimiliano Rinaldo Barchi, Cristina Pauselli, and Giorgio Minelli
Abstract
In the present study, starting from original measurement stations, we created the Bouguer anomaly map of Southern Italy with a reduction density of 2670 kg m-3. We perform a regional gravity modelling at crustal scale along the trace of the CROP-04 (on-shore) and MB6 (off-shore) deep seismic reflection profiles crossing the Southern Apennines and the Southern Tyrrhenian Sea. Along the 320 km-long modelled profile, we investigate crustal-scale sources for the observed gravity anomalies.
After a compelling review of the published Moho geometries in the area, that were retrieved from either active or passive seismic methods, we test them in the observed gravity field through forward modeling of the Bouguer gravity anomalies. The comparison between the different Moho interpretations shows that the steepness of the subducting slab, the position of the step between the western (Tyrrhenian) and the eastern (Adriatic) Moho and Moho depth represent the main features influencing the observed Bouguer anomalies at crustal scale.
Finally, we provide a best-fitting model across both onshore and offshore areas. In the proposed best-fitting model, the wide wavelength and strong regional Bouguer anomalies correlate with the geometry of the Moho discontinuity and deep tectonic structures. On the other hand, the small-amplitude oscillations of the gravity anomalies were attributed to the low-density values of the Pliocene-Quaternary deposits both on- (e.g. the Bradanic trough) and off-shore (e.g. recent deposits in the Tyrrhenian sea bottom). Gravity minima correspond to the crustal doubling underneath the Southern Apennines where the Tyrrhenian Moho (~27 km depth) overlies the deeper Adriatic Moho (~50 km depth). The positive trend of the observed anomaly toward NE is related to the shallowing of the Adriatic Moho to depths of ~28 km in the Adriatic. Similarly, towards SW, the observed anomaly follows a positive trend towards the maxima located in the Central Tyrrhenian Sea. We model this trend as representative of crustal thinning and shallowing to values of ~12 km depth of the Tyrrhenian Moho. We also model a crustal transition from geometries and density values typical of a continental crust in the Adriatic domain towards a more oceanic structure and composition in the Tyrrhenian domain. This crustal model locates the westward flexure of the Adriatic Moho, mimicking the subduction of the Adriatic lithosphere beneath the Peri-Tyrrhenian block and locates step between the western (Tyrrhenian) and the eastern (Adriatic) Moho beneath the Apennines range.
The resulted gravity forward model provide contributions to the tectonic settings understanding of the area by providing a robust crustal model ranging from the Tyrrhenian Sea to the Apulian foreland.
Finally, we believe that the proposed model can serve as a starting point for future studies investigating the upper crustal geometries in the area and addressing open questions about its relations with seismicity distribution.
How to cite: Akimbekova, A., Mancinelli, P., Rinaldo Barchi, M., Pauselli, C., and Minelli, G.: Forward Modelling of Bouguer Anomalies along a transect of the Southern Apennines and the Tyrrhenian back-arc basin., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12246, https://doi.org/10.5194/egusphere-egu21-12246, 2021.
Abstract
In the present study, starting from original measurement stations, we created the Bouguer anomaly map of Southern Italy with a reduction density of 2670 kg m-3. We perform a regional gravity modelling at crustal scale along the trace of the CROP-04 (on-shore) and MB6 (off-shore) deep seismic reflection profiles crossing the Southern Apennines and the Southern Tyrrhenian Sea. Along the 320 km-long modelled profile, we investigate crustal-scale sources for the observed gravity anomalies.
After a compelling review of the published Moho geometries in the area, that were retrieved from either active or passive seismic methods, we test them in the observed gravity field through forward modeling of the Bouguer gravity anomalies. The comparison between the different Moho interpretations shows that the steepness of the subducting slab, the position of the step between the western (Tyrrhenian) and the eastern (Adriatic) Moho and Moho depth represent the main features influencing the observed Bouguer anomalies at crustal scale.
Finally, we provide a best-fitting model across both onshore and offshore areas. In the proposed best-fitting model, the wide wavelength and strong regional Bouguer anomalies correlate with the geometry of the Moho discontinuity and deep tectonic structures. On the other hand, the small-amplitude oscillations of the gravity anomalies were attributed to the low-density values of the Pliocene-Quaternary deposits both on- (e.g. the Bradanic trough) and off-shore (e.g. recent deposits in the Tyrrhenian sea bottom). Gravity minima correspond to the crustal doubling underneath the Southern Apennines where the Tyrrhenian Moho (~27 km depth) overlies the deeper Adriatic Moho (~50 km depth). The positive trend of the observed anomaly toward NE is related to the shallowing of the Adriatic Moho to depths of ~28 km in the Adriatic. Similarly, towards SW, the observed anomaly follows a positive trend towards the maxima located in the Central Tyrrhenian Sea. We model this trend as representative of crustal thinning and shallowing to values of ~12 km depth of the Tyrrhenian Moho. We also model a crustal transition from geometries and density values typical of a continental crust in the Adriatic domain towards a more oceanic structure and composition in the Tyrrhenian domain. This crustal model locates the westward flexure of the Adriatic Moho, mimicking the subduction of the Adriatic lithosphere beneath the Peri-Tyrrhenian block and locates step between the western (Tyrrhenian) and the eastern (Adriatic) Moho beneath the Apennines range.
The resulted gravity forward model provide contributions to the tectonic settings understanding of the area by providing a robust crustal model ranging from the Tyrrhenian Sea to the Apulian foreland.
Finally, we believe that the proposed model can serve as a starting point for future studies investigating the upper crustal geometries in the area and addressing open questions about its relations with seismicity distribution.
How to cite: Akimbekova, A., Mancinelli, P., Rinaldo Barchi, M., Pauselli, C., and Minelli, G.: Forward Modelling of Bouguer Anomalies along a transect of the Southern Apennines and the Tyrrhenian back-arc basin., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12246, https://doi.org/10.5194/egusphere-egu21-12246, 2021.
EGU21-1545 | vPICO presentations | SM5.1
3D tomographic imaging of the Cayman Trough lithosphere: challenges, ongoing work and first resultsLaura Gómez de la Peña, Ingo Grevemeyer, Anke Dannowsky, Adrià Meléndez, Christine Peirce, and Harm van Avendonk
About 25% of the Earth’s mid-ocean ridges spread at ultraslow rates of less than 20 mm/yr. However, most of these ultraslow spreading ridges are located in geographically remote areas, which hamper investigation. Consequently, how the crust forms and ages at such spreading centres, which traditional models predict to be magma-starved and cold, remains poorly understood.
CAYSEIS project was proposed to survey the Cayman Trough area in order to obtain new data that constraints the nature of the crust, tectonic structures, lithologies outcropping and hydrothermal processes taking place in this area, which includes the Mid Cayman ultra-slow spreading centre (MSCS) with spreading rates of ~15-17 mm/yr. Understanding the sub-seabed geophysical structure of the MCSC is key to understanding not only the lithologies and structures exposed at the seabed, but more fundamentally, how they are related at depth and what role hydrothermal fluid flow plays in the geodynamics of ultraslow spreading. CAYSEIS was a joint and multidisciplinary programme of German, British and US American top tier scientists designed for the obtaining of a new high-quality dataset, including 3D Wide-Angle Seismic (WAS), magnetic, gravimetric and seismological data.
We took leverage of the CAYSEIS dataset to invert a 3D velocity model of the Cayman Trough lithosphere using the Tomo3D code (Meléndez et al., 2015; 2019). This is one of the first times that the Tomo3D code is used for 3D inversion of real datasets. Thus, we are checking our results comparing them with travel time tomographic inversions of 2D lines and testing the different parameters to obtain the more accurate and higher resolution model as possible. The results of this experiment show not only the lithospheric structure along and across the MSCS, including the exhumed Ocean Core Complexes in the surrounding areas, but the 3D lithospheric configuration of the region which is important to understand the crustal formation processes and evolution of ultra-slow spreading settings.
How to cite: Gómez de la Peña, L., Grevemeyer, I., Dannowsky, A., Meléndez, A., Peirce, C., and van Avendonk, H.: 3D tomographic imaging of the Cayman Trough lithosphere: challenges, ongoing work and first results, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1545, https://doi.org/10.5194/egusphere-egu21-1545, 2021.
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About 25% of the Earth’s mid-ocean ridges spread at ultraslow rates of less than 20 mm/yr. However, most of these ultraslow spreading ridges are located in geographically remote areas, which hamper investigation. Consequently, how the crust forms and ages at such spreading centres, which traditional models predict to be magma-starved and cold, remains poorly understood.
CAYSEIS project was proposed to survey the Cayman Trough area in order to obtain new data that constraints the nature of the crust, tectonic structures, lithologies outcropping and hydrothermal processes taking place in this area, which includes the Mid Cayman ultra-slow spreading centre (MSCS) with spreading rates of ~15-17 mm/yr. Understanding the sub-seabed geophysical structure of the MCSC is key to understanding not only the lithologies and structures exposed at the seabed, but more fundamentally, how they are related at depth and what role hydrothermal fluid flow plays in the geodynamics of ultraslow spreading. CAYSEIS was a joint and multidisciplinary programme of German, British and US American top tier scientists designed for the obtaining of a new high-quality dataset, including 3D Wide-Angle Seismic (WAS), magnetic, gravimetric and seismological data.
We took leverage of the CAYSEIS dataset to invert a 3D velocity model of the Cayman Trough lithosphere using the Tomo3D code (Meléndez et al., 2015; 2019). This is one of the first times that the Tomo3D code is used for 3D inversion of real datasets. Thus, we are checking our results comparing them with travel time tomographic inversions of 2D lines and testing the different parameters to obtain the more accurate and higher resolution model as possible. The results of this experiment show not only the lithospheric structure along and across the MSCS, including the exhumed Ocean Core Complexes in the surrounding areas, but the 3D lithospheric configuration of the region which is important to understand the crustal formation processes and evolution of ultra-slow spreading settings.
How to cite: Gómez de la Peña, L., Grevemeyer, I., Dannowsky, A., Meléndez, A., Peirce, C., and van Avendonk, H.: 3D tomographic imaging of the Cayman Trough lithosphere: challenges, ongoing work and first results, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1545, https://doi.org/10.5194/egusphere-egu21-1545, 2021.
EGU21-11115 | vPICO presentations | SM5.1
Small-scale lithospheric heterogeneity characterization using Bayesian inferenceItahisa González Álvarez, Sebastian Rost, Andy Nowacki, and Neil Selby
Heterogeneities on the scale of the seismic wavelength in the Earth's crust and mantle cause complex wavefield fluctuations in time and amplitude which are known to affect velocity and source inversions, as well as other seismic characterisations. However, many seismic models ignore these heterogeneities for simplicity. As part of our longer-term goal to account for these, we attempt to rigorously and probabilistically characterise these lithospheric small-scale heterogeneities by combining a single-layer and a multi-layer energy flux models with a new Bayesian inference algorithm. The first technique characterizes energy losses to the ballistic arrival as intrinsic, diffusion and scattering quality factors, which allows us to compare the effects of these attenuation mechanisms on our data. With the second method, we can obtain synthetic coda envelopes for 1- and 2- layer models with different values of the correlation length and fractional velocity fluctuations in each layer. We then use the Metropolis-Hastings algorithm to sample the likelihood space and obtain the posterior probability distributions for each parameter and layer in the model. Our thorough testing of these methods reveals complicated trade-offs between the parameters and highly non-unique solutions, thus highlighting the importance of the Bayesian approach for scattering studies. Previous studies applying these methods used a more traditional grid search for their coda inversion, which may have affected their results. We applied this approach to a data set of over 300 events from three seismic arrays in Australia: Alice Springs array (ASAR), Warramunga Array (WRA) and Pilbara Seismic Array (PSA). The results from the single-layer energy flux model show that all quality factors take higher values for PSA than for the other two arrays, indicating that the structure beneath this array is less attenuating and heterogeneous than for the other arrays. Intrinsic and diffusion attenuation are strongest for ASAR, while scattering and total attenuation are similarly strong for ASAR and WRA. Our multi-layer model results show the crust is more heterogeneous than the lithospheric mantle for all arrays, with crustal values of the correlation length and velocity fluctuations being lower for PSA than for the other arrays, indicating the presence of weaker and smaller scale heterogeneity beneath this array. We attribute these differences and similarities in the attenuation and heterogeneity structure beneath the arrays to variations in the tectonic history of the areas they are located on. This new Bayesian approach to the multi-layer energy flux model, in combination with the single-layer model, not only allows us to determine and compare the different quality factors, but also gives us detailed information about the trade-offs and uncertainties in the determination of the scattering parameters, making it a useful tool for future scattering and small-scale structure studies.
How to cite: González Álvarez, I., Rost, S., Nowacki, A., and Selby, N.: Small-scale lithospheric heterogeneity characterization using Bayesian inference , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11115, https://doi.org/10.5194/egusphere-egu21-11115, 2021.
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Heterogeneities on the scale of the seismic wavelength in the Earth's crust and mantle cause complex wavefield fluctuations in time and amplitude which are known to affect velocity and source inversions, as well as other seismic characterisations. However, many seismic models ignore these heterogeneities for simplicity. As part of our longer-term goal to account for these, we attempt to rigorously and probabilistically characterise these lithospheric small-scale heterogeneities by combining a single-layer and a multi-layer energy flux models with a new Bayesian inference algorithm. The first technique characterizes energy losses to the ballistic arrival as intrinsic, diffusion and scattering quality factors, which allows us to compare the effects of these attenuation mechanisms on our data. With the second method, we can obtain synthetic coda envelopes for 1- and 2- layer models with different values of the correlation length and fractional velocity fluctuations in each layer. We then use the Metropolis-Hastings algorithm to sample the likelihood space and obtain the posterior probability distributions for each parameter and layer in the model. Our thorough testing of these methods reveals complicated trade-offs between the parameters and highly non-unique solutions, thus highlighting the importance of the Bayesian approach for scattering studies. Previous studies applying these methods used a more traditional grid search for their coda inversion, which may have affected their results. We applied this approach to a data set of over 300 events from three seismic arrays in Australia: Alice Springs array (ASAR), Warramunga Array (WRA) and Pilbara Seismic Array (PSA). The results from the single-layer energy flux model show that all quality factors take higher values for PSA than for the other two arrays, indicating that the structure beneath this array is less attenuating and heterogeneous than for the other arrays. Intrinsic and diffusion attenuation are strongest for ASAR, while scattering and total attenuation are similarly strong for ASAR and WRA. Our multi-layer model results show the crust is more heterogeneous than the lithospheric mantle for all arrays, with crustal values of the correlation length and velocity fluctuations being lower for PSA than for the other arrays, indicating the presence of weaker and smaller scale heterogeneity beneath this array. We attribute these differences and similarities in the attenuation and heterogeneity structure beneath the arrays to variations in the tectonic history of the areas they are located on. This new Bayesian approach to the multi-layer energy flux model, in combination with the single-layer model, not only allows us to determine and compare the different quality factors, but also gives us detailed information about the trade-offs and uncertainties in the determination of the scattering parameters, making it a useful tool for future scattering and small-scale structure studies.
How to cite: González Álvarez, I., Rost, S., Nowacki, A., and Selby, N.: Small-scale lithospheric heterogeneity characterization using Bayesian inference , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11115, https://doi.org/10.5194/egusphere-egu21-11115, 2021.
EGU21-15749 | vPICO presentations | SM5.1
Coda-attenuation imaging of the North Anatolian Fault Zone, northern TurkeyPanayiota Sketsiou, Luca De Siena, and David G. Cornwell
The North Anatolian Fault (NAF), a right-lateral strike-slip fault spanning 1500 km in length, stretches across northern Turkey and it marks the boundary between the Eurasian and Anatolian plates. Nucleating in the east, at the Karliova triple junction and reaching the Aegean Sea at the west, it is a particularly active fault zone with a series of migrating high-magnitude earthquakes. Using 6445 Z-component waveforms from a temporary seismic network in the area (Dense Array for North Anatolia – DANA), this study aims to investigate the western part of the NAF, which splays into a northern and southern branch. Coda attenuation imaging is utilised for imaging the absorption characteristics of the area, as it can be used as a marker for source and dynamic Earth processes due to its higher sensitivity to small variations of lithospheric properties compared to seismic velocity. The absorption structure is recovered by inverting for the coda attenuation quality factor, Qc, at frequencies between 3-18 Hz, using sensitivity kernels. The extensive seismicity in the area, as well as the density of the seismic stations, provide high-resolution models of 0.04-0.05 degrees in spacing. The scattering structure of the region is imaged using peak-delay time, which is used as a direct measure for multiple forward scattering. Preliminary results show a clear change in scattering between the Istanbul and Sakarya zones, north and south of the fault respectively, with the scattering increasing from north to south at lower frequencies and decreasing at higher frequencies. At a smaller scale, absorption and scattering anomalies appear to outline contrasting geological units beneath the DANA network.
How to cite: Sketsiou, P., De Siena, L., and Cornwell, D. G.: Coda-attenuation imaging of the North Anatolian Fault Zone, northern Turkey, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15749, https://doi.org/10.5194/egusphere-egu21-15749, 2021.
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The North Anatolian Fault (NAF), a right-lateral strike-slip fault spanning 1500 km in length, stretches across northern Turkey and it marks the boundary between the Eurasian and Anatolian plates. Nucleating in the east, at the Karliova triple junction and reaching the Aegean Sea at the west, it is a particularly active fault zone with a series of migrating high-magnitude earthquakes. Using 6445 Z-component waveforms from a temporary seismic network in the area (Dense Array for North Anatolia – DANA), this study aims to investigate the western part of the NAF, which splays into a northern and southern branch. Coda attenuation imaging is utilised for imaging the absorption characteristics of the area, as it can be used as a marker for source and dynamic Earth processes due to its higher sensitivity to small variations of lithospheric properties compared to seismic velocity. The absorption structure is recovered by inverting for the coda attenuation quality factor, Qc, at frequencies between 3-18 Hz, using sensitivity kernels. The extensive seismicity in the area, as well as the density of the seismic stations, provide high-resolution models of 0.04-0.05 degrees in spacing. The scattering structure of the region is imaged using peak-delay time, which is used as a direct measure for multiple forward scattering. Preliminary results show a clear change in scattering between the Istanbul and Sakarya zones, north and south of the fault respectively, with the scattering increasing from north to south at lower frequencies and decreasing at higher frequencies. At a smaller scale, absorption and scattering anomalies appear to outline contrasting geological units beneath the DANA network.
How to cite: Sketsiou, P., De Siena, L., and Cornwell, D. G.: Coda-attenuation imaging of the North Anatolian Fault Zone, northern Turkey, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15749, https://doi.org/10.5194/egusphere-egu21-15749, 2021.
EGU21-8802 | vPICO presentations | SM5.1
Spatio-temporal variation of Anaelastic and Scattering Seismic Attenuation during the 2016-2017 Central Italy Seismic SequenceSimona Gabrielli, Aybige Akinci, Ferdinando Napolitano, Luca De Siena, Edoardo Del Pezzo, and Guido Ventura
Between August and October 2016, the Central Apennines in Italy have been struck by a long-lasting seismic sequence, known as the Amatrice (Mw 6.0) - Visso (Mw 5.9) - Norcia (Mw 6.5) sequence. The cascading ruptures occurred in this sequence have been considered connected to the fluid migration in the fault network, as suggested by previous studies. The behaviour of fluids in the crust is crucial to understand earthquakes occurrence and stress changes since fluids reduce fault stability. It has long been understood that the seismic attenuation is strongly controlled by the structural irregularity and heterogeneities; micro-cracks and cavities, either fluid-filled or dry, temperature and pressure variations cause a decrease in seismic wave amplitude and pulse broadening. Hence seismic attenuation imagining is a powerful tool to be a relevant provenance of information about the influence and abundance of fluids in a seismic sequence.
The aim of this work is to separate scattering and absorption contributions to the total attenuation of coda waves and to provide their spatial and temporal variations at different frequency bands of these quantities using two datasets: the first one comprising 592 earthquakes occurred before the sequence (March 2013-August 2016) and the second one comprising 763 events (ML > 2.8) from the Amatrice-Visso-Norcia sequence. Scattering and absorption have been measured through peak-delay and coda-wave attenuation parameters (the latter inverted using frequency-dependent sensitivity kernels).
The preliminary results show a clear difference between the pre-sequence and sequence images, mainly at low frequencies (1.5 Hz), where we can define a spatial increase of scattering with time attributed to rock fracturing and fluid circulation. The coda attenuation tomography also demonstrates a clear variation between the pre-sequence and the sequence over series of time windows being before and after the largest main shocks of the seismic sequence, with an increase of the attenuation in space with decreasing time. The peak delay indicates a high scattering area corresponding to the Gran Sasso massif and L’Aquila zone, where an important seismic sequence (Mw 6.3) occurred in 2009.
How to cite: Gabrielli, S., Akinci, A., Napolitano, F., De Siena, L., Del Pezzo, E., and Ventura, G.: Spatio-temporal variation of Anaelastic and Scattering Seismic Attenuation during the 2016-2017 Central Italy Seismic Sequence, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8802, https://doi.org/10.5194/egusphere-egu21-8802, 2021.
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Between August and October 2016, the Central Apennines in Italy have been struck by a long-lasting seismic sequence, known as the Amatrice (Mw 6.0) - Visso (Mw 5.9) - Norcia (Mw 6.5) sequence. The cascading ruptures occurred in this sequence have been considered connected to the fluid migration in the fault network, as suggested by previous studies. The behaviour of fluids in the crust is crucial to understand earthquakes occurrence and stress changes since fluids reduce fault stability. It has long been understood that the seismic attenuation is strongly controlled by the structural irregularity and heterogeneities; micro-cracks and cavities, either fluid-filled or dry, temperature and pressure variations cause a decrease in seismic wave amplitude and pulse broadening. Hence seismic attenuation imagining is a powerful tool to be a relevant provenance of information about the influence and abundance of fluids in a seismic sequence.
The aim of this work is to separate scattering and absorption contributions to the total attenuation of coda waves and to provide their spatial and temporal variations at different frequency bands of these quantities using two datasets: the first one comprising 592 earthquakes occurred before the sequence (March 2013-August 2016) and the second one comprising 763 events (ML > 2.8) from the Amatrice-Visso-Norcia sequence. Scattering and absorption have been measured through peak-delay and coda-wave attenuation parameters (the latter inverted using frequency-dependent sensitivity kernels).
The preliminary results show a clear difference between the pre-sequence and sequence images, mainly at low frequencies (1.5 Hz), where we can define a spatial increase of scattering with time attributed to rock fracturing and fluid circulation. The coda attenuation tomography also demonstrates a clear variation between the pre-sequence and the sequence over series of time windows being before and after the largest main shocks of the seismic sequence, with an increase of the attenuation in space with decreasing time. The peak delay indicates a high scattering area corresponding to the Gran Sasso massif and L’Aquila zone, where an important seismic sequence (Mw 6.3) occurred in 2009.
How to cite: Gabrielli, S., Akinci, A., Napolitano, F., De Siena, L., Del Pezzo, E., and Ventura, G.: Spatio-temporal variation of Anaelastic and Scattering Seismic Attenuation during the 2016-2017 Central Italy Seismic Sequence, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8802, https://doi.org/10.5194/egusphere-egu21-8802, 2021.
EGU21-1745 | vPICO presentations | SM5.1
Finite difference forward modelling across the Tyrrhenian basinChiara Nardoni, Luca De Siena, Fabio Cammarano, Elisabetta Mattei, and Fabrizio Magrini
Strong lateral variations in medium properties affect the response of seismic wavefields. The Tyrrhenian Sea is ideally suited to explore these effects in a mixed continental-oceanic crust that comprises magmatic systems. The study aims at investigating the effects of crustal thinning and sedimentary layers on wave propagation, especially the reverberating (e.g., Lg) phases, across the oceanic basin. We model regional seismograms (600-800 km) using the software tool OpenSWPC (Maeda et al., 2017, EPS) based on the finite difference simulation of the wave equation. The code simulates the seismic wave propagation in heterogeneous viscoelastic media including the statistical velocity fluctuations as well as heterogeneous topography, typical of mixed settings. This approach allows to evaluate the role of interfaces and layer thicknesses on phase arrivals and direct and coda attenuation measurements. The results are compared with previous simulations of the radiative-transfer equations. They provide an improved understanding of the complex wave attenuation and energy leakage in the mantle characterizing the southern part of the Tyrrhenian Sea and the Italian peninsula. The forward modelling is to be embedded in future applications of attenuation, absorption and scattering tomography performed with MuRAT (the Multi-Resolution Attenuation Tomography code – De Siena et al. 2014, JVGR) available at https://github.com/LucaDeSiena/MuRAT.
How to cite: Nardoni, C., De Siena, L., Cammarano, F., Mattei, E., and Magrini, F.: Finite difference forward modelling across the Tyrrhenian basin, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1745, https://doi.org/10.5194/egusphere-egu21-1745, 2021.
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Strong lateral variations in medium properties affect the response of seismic wavefields. The Tyrrhenian Sea is ideally suited to explore these effects in a mixed continental-oceanic crust that comprises magmatic systems. The study aims at investigating the effects of crustal thinning and sedimentary layers on wave propagation, especially the reverberating (e.g., Lg) phases, across the oceanic basin. We model regional seismograms (600-800 km) using the software tool OpenSWPC (Maeda et al., 2017, EPS) based on the finite difference simulation of the wave equation. The code simulates the seismic wave propagation in heterogeneous viscoelastic media including the statistical velocity fluctuations as well as heterogeneous topography, typical of mixed settings. This approach allows to evaluate the role of interfaces and layer thicknesses on phase arrivals and direct and coda attenuation measurements. The results are compared with previous simulations of the radiative-transfer equations. They provide an improved understanding of the complex wave attenuation and energy leakage in the mantle characterizing the southern part of the Tyrrhenian Sea and the Italian peninsula. The forward modelling is to be embedded in future applications of attenuation, absorption and scattering tomography performed with MuRAT (the Multi-Resolution Attenuation Tomography code – De Siena et al. 2014, JVGR) available at https://github.com/LucaDeSiena/MuRAT.
How to cite: Nardoni, C., De Siena, L., Cammarano, F., Mattei, E., and Magrini, F.: Finite difference forward modelling across the Tyrrhenian basin, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1745, https://doi.org/10.5194/egusphere-egu21-1745, 2021.
EGU21-8226 | vPICO presentations | SM5.1
Crustal velocity structure beneath the NW Dinarides from 1-D hypocenter-velocity inversionGregor Rajh, Josip Stipčević, Mladen Živčić, Marijan Herak, and Andrej Gosar
The investigated area of the NW Dinarides is bordered by the Adriatic foreland, the Southern Alps, and the Pannonian basin at the NE corner of the Adriatic Sea. Its complex crustal structure is the result of interactions among different tectonic units. Despite numerous seismic studies taking place in this region, there still exists a need for a detailed, smaller scale study focusing mainly on the brittle part of the Earth's crust. Therefore, we decided to investigate the velocity structure of the crust using concepts of local earthquake tomography (LET) and minimum 1-D velocity model. Here, we present the results of the 1-D velocity modeling and the catalogue of the relocated seismicity. A minimum 1-D velocity model is computed by simultaneous inversion for hypocentral and velocity parameters together with seismic station corrections and represents the best fit to the observed arrival times.
We used 15,579 routinely picked P wave arrival times from 631 well-located earthquakes that occurred in Slovenia and in its immediate surroundings (mainly NW Croatia). Various initial 1-D velocity models, differing in velocity and layering, were used as input for velocity inversion in the VELEST program. We also varied several inversion parameters during the inversion runs. Most of the computed 1-D velocity models converged to a stable solution in the depth range between 0 and 25 km. We evaluated the inversion results using rigorous testing procedures and selected two best performing velocity models. Each of these models will be used independently as the initial model in the simultaneous hypocenter-velocity inversion for a 3-D velocity structure in LET. Based on the results of the 1-D velocity modeling, seismicity distribution, and tectonics, we divided the study area into three parts, redefined the earthquake-station geometry, and performed the inversion for each part separately. This way, we gained a better insight into the shallow velocity structure of each subregion and were able to demonstrate the differences among them.
Besides general structural implications and a potential to improve the results of LET, the new 1-D velocity models along with station corrections can also be used in fast routine earthquake location and to detect systematic travel time errors in seismological bulletins, as already shown by some studies using similar methods.
How to cite: Rajh, G., Stipčević, J., Živčić, M., Herak, M., and Gosar, A.: Crustal velocity structure beneath the NW Dinarides from 1-D hypocenter-velocity inversion, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8226, https://doi.org/10.5194/egusphere-egu21-8226, 2021.
The investigated area of the NW Dinarides is bordered by the Adriatic foreland, the Southern Alps, and the Pannonian basin at the NE corner of the Adriatic Sea. Its complex crustal structure is the result of interactions among different tectonic units. Despite numerous seismic studies taking place in this region, there still exists a need for a detailed, smaller scale study focusing mainly on the brittle part of the Earth's crust. Therefore, we decided to investigate the velocity structure of the crust using concepts of local earthquake tomography (LET) and minimum 1-D velocity model. Here, we present the results of the 1-D velocity modeling and the catalogue of the relocated seismicity. A minimum 1-D velocity model is computed by simultaneous inversion for hypocentral and velocity parameters together with seismic station corrections and represents the best fit to the observed arrival times.
We used 15,579 routinely picked P wave arrival times from 631 well-located earthquakes that occurred in Slovenia and in its immediate surroundings (mainly NW Croatia). Various initial 1-D velocity models, differing in velocity and layering, were used as input for velocity inversion in the VELEST program. We also varied several inversion parameters during the inversion runs. Most of the computed 1-D velocity models converged to a stable solution in the depth range between 0 and 25 km. We evaluated the inversion results using rigorous testing procedures and selected two best performing velocity models. Each of these models will be used independently as the initial model in the simultaneous hypocenter-velocity inversion for a 3-D velocity structure in LET. Based on the results of the 1-D velocity modeling, seismicity distribution, and tectonics, we divided the study area into three parts, redefined the earthquake-station geometry, and performed the inversion for each part separately. This way, we gained a better insight into the shallow velocity structure of each subregion and were able to demonstrate the differences among them.
Besides general structural implications and a potential to improve the results of LET, the new 1-D velocity models along with station corrections can also be used in fast routine earthquake location and to detect systematic travel time errors in seismological bulletins, as already shown by some studies using similar methods.
How to cite: Rajh, G., Stipčević, J., Živčić, M., Herak, M., and Gosar, A.: Crustal velocity structure beneath the NW Dinarides from 1-D hypocenter-velocity inversion, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8226, https://doi.org/10.5194/egusphere-egu21-8226, 2021.
EGU21-8079 | vPICO presentations | SM5.1
Improved three-dimensional image of the tomographic inversion of the Arraiolos aftershock sequence.Ines Hamak, Piedade Wachilala, José Borges, Nuno Dias, Inês Rio, and Mourad Bezzeghoud
This work puts in light the several steps followed to obtain a 3D velocity model in Arraiolos, a region located in central Portugal. After the earthquake of January 2018 occurred, a set of stations were deployed around the main shock area and has recorded the aftershock sequence during a period of six months.
The first stage of this study used a set of data recorded along the 1st month by 21 temporary seismological stations. 317 aftershocks were used to invert a 3D P and S velocity model, using LOTOS program, and showing an agglomeration of events in one local point leading to a poor resolution. Therefore, we added more stations and data to the second stage of study by integrating 437 aftershocks recorded during a period of 6 months by a set of 34 stations. The tomographic inversion of this extended aftershock sequence has shown a significant improvement of the 3D velocity model resolution and suggesting an alignment of the seismic events cluster. However, the imaged crustal volume was still too small and possessing low resolution on the edges of the area. To fix this issue, additional data and seismological stations were integrated to the study in order to increase the area of interest and cover it entirely in terms of ray density.
The step which we are currently conducting concerns the location of new events followed by their integration to the tomographic study using IPMA and DOCTAR station network records. Since the later phases PmP and SmS has the potential to increase the ray coverage as similarly as the resolution of an area, we will hopefully obtain, after their integration, significant improvements in terms of accuracy and reliability of the crustal image. The main purpose of this new stage of study is to finally provide significant interpretations and figure out precisely the tectonic processes having generated the Arraiolos seismicity.
Thanks are due to FCT for the financial support to the ICT project (UID/GEO/04683/2013) with the reference POCI-01- 0145-FEDER-007690, to the IDL project (UIDB/50019/2020 – IDL).
How to cite: Hamak, I., Wachilala, P., Borges, J., Dias, N., Rio, I., and Bezzeghoud, M.: Improved three-dimensional image of the tomographic inversion of the Arraiolos aftershock sequence., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8079, https://doi.org/10.5194/egusphere-egu21-8079, 2021.
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We are sorry, but presentations are only available for users who registered for the conference. Thank you.
This work puts in light the several steps followed to obtain a 3D velocity model in Arraiolos, a region located in central Portugal. After the earthquake of January 2018 occurred, a set of stations were deployed around the main shock area and has recorded the aftershock sequence during a period of six months.
The first stage of this study used a set of data recorded along the 1st month by 21 temporary seismological stations. 317 aftershocks were used to invert a 3D P and S velocity model, using LOTOS program, and showing an agglomeration of events in one local point leading to a poor resolution. Therefore, we added more stations and data to the second stage of study by integrating 437 aftershocks recorded during a period of 6 months by a set of 34 stations. The tomographic inversion of this extended aftershock sequence has shown a significant improvement of the 3D velocity model resolution and suggesting an alignment of the seismic events cluster. However, the imaged crustal volume was still too small and possessing low resolution on the edges of the area. To fix this issue, additional data and seismological stations were integrated to the study in order to increase the area of interest and cover it entirely in terms of ray density.
The step which we are currently conducting concerns the location of new events followed by their integration to the tomographic study using IPMA and DOCTAR station network records. Since the later phases PmP and SmS has the potential to increase the ray coverage as similarly as the resolution of an area, we will hopefully obtain, after their integration, significant improvements in terms of accuracy and reliability of the crustal image. The main purpose of this new stage of study is to finally provide significant interpretations and figure out precisely the tectonic processes having generated the Arraiolos seismicity.
Thanks are due to FCT for the financial support to the ICT project (UID/GEO/04683/2013) with the reference POCI-01- 0145-FEDER-007690, to the IDL project (UIDB/50019/2020 – IDL).
How to cite: Hamak, I., Wachilala, P., Borges, J., Dias, N., Rio, I., and Bezzeghoud, M.: Improved three-dimensional image of the tomographic inversion of the Arraiolos aftershock sequence., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8079, https://doi.org/10.5194/egusphere-egu21-8079, 2021.
EGU21-12696 | vPICO presentations | SM5.1
Regional fast-marching tomography in intracontinental settings: preliminary analysis of limitations and potentialDonato Talone, Rita de Nardis, Giusy Lavecchia, and Luca De Siena
Seismic tomography can be applied to different scales. Over the last two decades, monitoring systems, technical innovations and methodologies have substantially improved, resulting in accurate tomographic images at the global and local scales. Nowadays it is easy to perform travel-time tomography with local seismicity thanks to the increasing density of seismic stations. Nevertheless, it is unlikely to have earthquakes that properly cover the whole studied area at the requested depths. For this reason, many tomographic images are obtained with teleseisms and both far and local earthquakes.
Here, we realized a Local Earthquake Tomography (LET) in an area of high seismic hazard in central-southern Italy, extending from L’Aquila to Benevento, to benchmark the iterative non-linear Fast-Marching code FMTOMO (Rawlinson and Sambridge, 2004) at intracontinental scale. The primary aim is to analyse and discuss the influence of both the inversion parameters and the grid sizes on the inversion results. Special attention was devoted to setting damping factors and smoothing parameters and to study how they can affect the tomographic images and their reliability.
We used 5712 local events (0.2<ML<5.1) recorded by 38 stations of the Italian Seismic network; we jointly inverted 71221 P and S arrival times to obtain Vp and Vs model. We selected earthquakes having: (1) a root-mean-square (RMS) residual less than 0.5 s, (2) more than 10 phases (P and S), (3) azimuth gap less than 180, (4) residual of each phase less than 0.5 s, (5) a depth between 0.5 and 30 km. We used a single layer of 35 km in depth and a grid area extending 162 km in latitude and 245 km in longitude with a node spacing of about 5 km in each direction. As a starting velocity model, we chose a mono-dimensional one of Trionfera et al. (2020).
Using these well-localized earthquakes, we observed low residuals variability despite a full investigation of damping and smoothing parameters. Furthermore, the regularization parameters we obtained are one or two order of magnitude lower than those estimated at the wider scales.
Because of the uncertainties in the depth of events, the fast-marching code needs several nodes above and below the grid set for earthquakes to move sources during each hypocentral inversion. As a consequence, when inverting for both velocity and hypocentral location, FMTOMO performs the calculation even for a wide boundary area without earthquakes, which causes a loss of computational speed.
After properly tuning the inversion parameters, FMTOMO gives reliable and high-resolution tomographic images. We found a good agreement with surface geology and regional tectonic structures, demonstrating that the code works well in areas with such complex geology.
How to cite: Talone, D., de Nardis, R., Lavecchia, G., and De Siena, L.: Regional fast-marching tomography in intracontinental settings: preliminary analysis of limitations and potential, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12696, https://doi.org/10.5194/egusphere-egu21-12696, 2021.
Seismic tomography can be applied to different scales. Over the last two decades, monitoring systems, technical innovations and methodologies have substantially improved, resulting in accurate tomographic images at the global and local scales. Nowadays it is easy to perform travel-time tomography with local seismicity thanks to the increasing density of seismic stations. Nevertheless, it is unlikely to have earthquakes that properly cover the whole studied area at the requested depths. For this reason, many tomographic images are obtained with teleseisms and both far and local earthquakes.
Here, we realized a Local Earthquake Tomography (LET) in an area of high seismic hazard in central-southern Italy, extending from L’Aquila to Benevento, to benchmark the iterative non-linear Fast-Marching code FMTOMO (Rawlinson and Sambridge, 2004) at intracontinental scale. The primary aim is to analyse and discuss the influence of both the inversion parameters and the grid sizes on the inversion results. Special attention was devoted to setting damping factors and smoothing parameters and to study how they can affect the tomographic images and their reliability.
We used 5712 local events (0.2<ML<5.1) recorded by 38 stations of the Italian Seismic network; we jointly inverted 71221 P and S arrival times to obtain Vp and Vs model. We selected earthquakes having: (1) a root-mean-square (RMS) residual less than 0.5 s, (2) more than 10 phases (P and S), (3) azimuth gap less than 180, (4) residual of each phase less than 0.5 s, (5) a depth between 0.5 and 30 km. We used a single layer of 35 km in depth and a grid area extending 162 km in latitude and 245 km in longitude with a node spacing of about 5 km in each direction. As a starting velocity model, we chose a mono-dimensional one of Trionfera et al. (2020).
Using these well-localized earthquakes, we observed low residuals variability despite a full investigation of damping and smoothing parameters. Furthermore, the regularization parameters we obtained are one or two order of magnitude lower than those estimated at the wider scales.
Because of the uncertainties in the depth of events, the fast-marching code needs several nodes above and below the grid set for earthquakes to move sources during each hypocentral inversion. As a consequence, when inverting for both velocity and hypocentral location, FMTOMO performs the calculation even for a wide boundary area without earthquakes, which causes a loss of computational speed.
After properly tuning the inversion parameters, FMTOMO gives reliable and high-resolution tomographic images. We found a good agreement with surface geology and regional tectonic structures, demonstrating that the code works well in areas with such complex geology.
How to cite: Talone, D., de Nardis, R., Lavecchia, G., and De Siena, L.: Regional fast-marching tomography in intracontinental settings: preliminary analysis of limitations and potential, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12696, https://doi.org/10.5194/egusphere-egu21-12696, 2021.
EGU21-2001 | vPICO presentations | SM5.1
Crustal seismic structure of Red-River shear zone and surrounding areaHa Vinh Long, Hsin-Hua Huang, Le Minh Nguyen, Van Duong Nguyen, Quang Khoi Le, Thi Giang Ha, Dinh Quoc Van, Bor-Shouh Huang, and Tu Son Le
The collision between the Eurasian and Indian plates since about 65 Ma caused extensive deformation in the Tibetan Plateau and surrounding areas. Northern Vietnam located in the southeastern Himalayan syntaxis is directly influenced by the collision and extrusion through the Red River shear zone that runs from southeastern Tibet to the South China Sea. Knowledge of crustal structure characteristics in northern Vietnam and across the Red River shear zone is crucial to improve our understanding not only of seismic hazards in the region but also of the regional Himalayan tectonic evolution as a whole. Seismic tomography is one of few methods that allows to study the subsurface structures effectively. In this study, we perform a joint tomographic inversion for northern Vietnam integrating the P- and S-direct waves traveling in the crust and the head waves along the Moho waves arrival time from more than 1000 earthquakes observed by Vietnamese networks. The obtained velocity model shows a good correlation with shallow geological features but also some complexity at crustal-scale. Several velocity anomalies bounded by and across the fault zones are revealed and discussed
Keyword: Traveltime tomography, Northern Vietnam, VpVs ratio, crustal structure, Vietnam seismic network
How to cite: Long, H. V., Huang, H.-H., Nguyen, L. M., Nguyen, V. D., Le, Q. K., Ha, T. G., Van, D. Q., Huang, B.-S., and Le, T. S.: Crustal seismic structure of Red-River shear zone and surrounding area, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2001, https://doi.org/10.5194/egusphere-egu21-2001, 2021.
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The collision between the Eurasian and Indian plates since about 65 Ma caused extensive deformation in the Tibetan Plateau and surrounding areas. Northern Vietnam located in the southeastern Himalayan syntaxis is directly influenced by the collision and extrusion through the Red River shear zone that runs from southeastern Tibet to the South China Sea. Knowledge of crustal structure characteristics in northern Vietnam and across the Red River shear zone is crucial to improve our understanding not only of seismic hazards in the region but also of the regional Himalayan tectonic evolution as a whole. Seismic tomography is one of few methods that allows to study the subsurface structures effectively. In this study, we perform a joint tomographic inversion for northern Vietnam integrating the P- and S-direct waves traveling in the crust and the head waves along the Moho waves arrival time from more than 1000 earthquakes observed by Vietnamese networks. The obtained velocity model shows a good correlation with shallow geological features but also some complexity at crustal-scale. Several velocity anomalies bounded by and across the fault zones are revealed and discussed
Keyword: Traveltime tomography, Northern Vietnam, VpVs ratio, crustal structure, Vietnam seismic network
How to cite: Long, H. V., Huang, H.-H., Nguyen, L. M., Nguyen, V. D., Le, Q. K., Ha, T. G., Van, D. Q., Huang, B.-S., and Le, T. S.: Crustal seismic structure of Red-River shear zone and surrounding area, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2001, https://doi.org/10.5194/egusphere-egu21-2001, 2021.
EGU21-9882 | vPICO presentations | SM5.1
Joint receiver function and gravity inversion for new constraints on the Ivrea body structure: a 2D high-resolution view along the Val Sesia profile (N. Italy).Matteo Scarponi, György Hetényi, Jaroslava Plomerová, and Stefano Solarino
We present results from a joint inversion study of new seismic and gravity data to constrain a 2D high-resolution image of one of the most prominent geophysical anomalies of the European Alps: the Ivrea geophysical body (IGB). Our work exploits both new data and multidisciplinary a priori constraints, to better resolve the shallow crustal structure in the Ivrea-Verbano zone (IVZ), where the IGB is known to reach anomalously shallow depths and partially outcrop at the surface.
A variety of previous studies, ranging from gravity surveys to vintage refraction seismics and recent local earthquake tomographies (Solarino et al. 2018, Diehl et al. 2009), provide comprehensive but spatially sparse information on the IGB structure, which we aim at investigating at higher resolution, along a linear profile crossing the IVZ. To this purpose, we deployed 10 broadband seismic stations (MOBNET pool, IG CAS Prague), 5 km spaced along a linear West-East profile, along Val Sesia and crossing Lago Maggiore. This network operated for 27 months and allowed us to produce a new database of ca. 1000 seismic high-quality receiver functions (RFs). In addition, we collected new gravity data in the IVZ, with a data coverage of 1 gravity point every 1-2 km along the seismic profile. The newly collected data was used to set up an inversion scheme, in which RFs and gravity anomalies are jointly used to constrain the shape and the physical property contrasts across the IGB interface.
We model the IGB as a single interface between far-field constraints, whose geometry is defined by the coordinates of four nodes which may vary in space, and density and VS shear-wave velocity contrasts associated with the interface itself, varying independently. A Markov chain Monte Carlo (MCMC) sampling method with Metropolis-Hastings selection rule was implemented to efficiently explore the model space, directing the search towards better fitting areas.
For each model, we perform ray-tracing and RFs migration using the actual velocity structure both for migration and computation of synthetic RFs, to be compared with the observations via cross-correlation of the migration images. Similarly, forward gravity modelling for a 2D density distribution is implemented and the synthetic gravity anomaly is compared with the observations along the profile. The joint inversion performance is the product of these two misfits.
The inversion results show that the IGB reaches the shallowest depths in the western part of the profile, preferentially locating the IGB interface between 3 and 7 km depth over a horizontal distance of ca. 20 km (between Boccioleto and Civiasco, longitudes 8.1 and 8.3). Within this segment, the shallowest point reaches up to 1 km below sea level. The found density and velocity contrasts are in agreement with rock physics properties of various units observed in the field and characterized in earlier studies.
How to cite: Scarponi, M., Hetényi, G., Plomerová, J., and Solarino, S.: Joint receiver function and gravity inversion for new constraints on the Ivrea body structure: a 2D high-resolution view along the Val Sesia profile (N. Italy)., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9882, https://doi.org/10.5194/egusphere-egu21-9882, 2021.
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We present results from a joint inversion study of new seismic and gravity data to constrain a 2D high-resolution image of one of the most prominent geophysical anomalies of the European Alps: the Ivrea geophysical body (IGB). Our work exploits both new data and multidisciplinary a priori constraints, to better resolve the shallow crustal structure in the Ivrea-Verbano zone (IVZ), where the IGB is known to reach anomalously shallow depths and partially outcrop at the surface.
A variety of previous studies, ranging from gravity surveys to vintage refraction seismics and recent local earthquake tomographies (Solarino et al. 2018, Diehl et al. 2009), provide comprehensive but spatially sparse information on the IGB structure, which we aim at investigating at higher resolution, along a linear profile crossing the IVZ. To this purpose, we deployed 10 broadband seismic stations (MOBNET pool, IG CAS Prague), 5 km spaced along a linear West-East profile, along Val Sesia and crossing Lago Maggiore. This network operated for 27 months and allowed us to produce a new database of ca. 1000 seismic high-quality receiver functions (RFs). In addition, we collected new gravity data in the IVZ, with a data coverage of 1 gravity point every 1-2 km along the seismic profile. The newly collected data was used to set up an inversion scheme, in which RFs and gravity anomalies are jointly used to constrain the shape and the physical property contrasts across the IGB interface.
We model the IGB as a single interface between far-field constraints, whose geometry is defined by the coordinates of four nodes which may vary in space, and density and VS shear-wave velocity contrasts associated with the interface itself, varying independently. A Markov chain Monte Carlo (MCMC) sampling method with Metropolis-Hastings selection rule was implemented to efficiently explore the model space, directing the search towards better fitting areas.
For each model, we perform ray-tracing and RFs migration using the actual velocity structure both for migration and computation of synthetic RFs, to be compared with the observations via cross-correlation of the migration images. Similarly, forward gravity modelling for a 2D density distribution is implemented and the synthetic gravity anomaly is compared with the observations along the profile. The joint inversion performance is the product of these two misfits.
The inversion results show that the IGB reaches the shallowest depths in the western part of the profile, preferentially locating the IGB interface between 3 and 7 km depth over a horizontal distance of ca. 20 km (between Boccioleto and Civiasco, longitudes 8.1 and 8.3). Within this segment, the shallowest point reaches up to 1 km below sea level. The found density and velocity contrasts are in agreement with rock physics properties of various units observed in the field and characterized in earlier studies.
How to cite: Scarponi, M., Hetényi, G., Plomerová, J., and Solarino, S.: Joint receiver function and gravity inversion for new constraints on the Ivrea body structure: a 2D high-resolution view along the Val Sesia profile (N. Italy)., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9882, https://doi.org/10.5194/egusphere-egu21-9882, 2021.
EGU21-16456 | vPICO presentations | SM5.1
Seismic Structure and Tectonic Evolution of Borneo and SulawesiHarry Telajan Linang, Amy Gilligan, Jennifer Jenkins, Tim Greenfield, Felix Tongkul, Sri Widiyantoro, and Nick Rawlinson
Borneo is located at the centre of Southeast Asia, which is one of the most active tectonic regions on Earth due to the subduction of the Indo-Australian plate in the south and the Philippines Sea plate in the east. Borneo resides on the leading edge of the Sundaland block of the Eurasian plate and exhibits lower rates of seismicity when compared to the surrounding regions due to its intraplate setting. Sulawesi, an island which lies just southeast of Borneo, is characterised by intense seismicity due to multiple subduction zones in its vicinity. The tectonic relationship between the two islands is poorly understood, including the provenance of their respective lithospheres, which may have Eurasian and/or East Gondwana origin.
Here, we present recent receiver function (RF) results from temporary and permanent broadband seismic stations in the region, which can be used to help improve our understanding of the crust and mantle lithosphere beneath Borneo and Sulawesi. We applied H-K stacking, receiver function migration and inversion to obtain reliable estimates of the crustal thickness beneath the seismic stations. Our preliminary results indicate that the crust beneath Sabah (in northern Borneo), which is a post-subduction setting, appears to be much more complex and is overall thicker (more than 35 km) than the rest of the island. In addition, we find that crustal thickness varies between different tectonic blocks defined from previous surface mapping, with the thinnest crust (23 to 25 km) occurring beneath Sarawak in the west-northwest as well as in the east of Kalimantan.
We also present preliminary results from Virtual Deep Seismic Sounding (VDSS) in northern Borneo, where from the RF results we know that there is thick and complex crust. VDSS is able to produce well constrained crustal thickness results in regions where the RF analysis has difficulty recovering the Moho, likely due to complexities such as thick sedimentary basins and obducted ophiolite sequences.
How to cite: Linang, H. T., Gilligan, A., Jenkins, J., Greenfield, T., Tongkul, F., Widiyantoro, S., and Rawlinson, N.: Seismic Structure and Tectonic Evolution of Borneo and Sulawesi, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16456, https://doi.org/10.5194/egusphere-egu21-16456, 2021.
Borneo is located at the centre of Southeast Asia, which is one of the most active tectonic regions on Earth due to the subduction of the Indo-Australian plate in the south and the Philippines Sea plate in the east. Borneo resides on the leading edge of the Sundaland block of the Eurasian plate and exhibits lower rates of seismicity when compared to the surrounding regions due to its intraplate setting. Sulawesi, an island which lies just southeast of Borneo, is characterised by intense seismicity due to multiple subduction zones in its vicinity. The tectonic relationship between the two islands is poorly understood, including the provenance of their respective lithospheres, which may have Eurasian and/or East Gondwana origin.
Here, we present recent receiver function (RF) results from temporary and permanent broadband seismic stations in the region, which can be used to help improve our understanding of the crust and mantle lithosphere beneath Borneo and Sulawesi. We applied H-K stacking, receiver function migration and inversion to obtain reliable estimates of the crustal thickness beneath the seismic stations. Our preliminary results indicate that the crust beneath Sabah (in northern Borneo), which is a post-subduction setting, appears to be much more complex and is overall thicker (more than 35 km) than the rest of the island. In addition, we find that crustal thickness varies between different tectonic blocks defined from previous surface mapping, with the thinnest crust (23 to 25 km) occurring beneath Sarawak in the west-northwest as well as in the east of Kalimantan.
We also present preliminary results from Virtual Deep Seismic Sounding (VDSS) in northern Borneo, where from the RF results we know that there is thick and complex crust. VDSS is able to produce well constrained crustal thickness results in regions where the RF analysis has difficulty recovering the Moho, likely due to complexities such as thick sedimentary basins and obducted ophiolite sequences.
How to cite: Linang, H. T., Gilligan, A., Jenkins, J., Greenfield, T., Tongkul, F., Widiyantoro, S., and Rawlinson, N.: Seismic Structure and Tectonic Evolution of Borneo and Sulawesi, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16456, https://doi.org/10.5194/egusphere-egu21-16456, 2021.
EGU21-13610 | vPICO presentations | SM5.1
A Pseudo-3D Vs Velocity Model of Ischia Island (Italy) by HVSR spectral ratio inversionRoberto Manzo, Lucia Nardone, Guido Gaudiosi, Claudio Martino, Danilo Galluzzo, Francesca Bianco, and Rosa Di Maio
Following the MD4.0 (Mw3.9) earthquake of August 21 2017 which occurred on the Ischia island (Naples, southern Italy), the local monitoring seismic network was significantly improved in terms of both number of stations and instrumentation performance. Due to the considerable amount of collected data, in particular of seismic noise recorded at broadband stations, some efforts have been addressed in particular to the definition of a 1D average velocity model effective for the whole island. This is an important scientific step because, in complex volcanic areas, the use of reliable velocity models is essential for an accurate localization of local earthquakes. In this work, the main target is to retrieve a pseudo-3D velocity model of the Ischia island. Specifically, we inverted H/V curves and frequency peaks evaluated at about twenty sites to obtain a velocity profile for each of the investigated measurement points. Taking into account that the H/V frequency peak depends on both velocity and thickness of layers, for each site we applied an inversion process fixing the velocities and modifying the thicknesses in order to obtain the corresponding 1D velocity models. We are quite enough confident about the robustness of models, since during the inversion process, we achieved a good convergence towards the best-fit solutions. Then, a pseudo-3D velocity model was obtained by contouring the 1D models of each station site to highlight possible lateral variations of the layer thicknesses and to reconstruct the morphology of the deeper interface characterized by a high impedance contrast. A good correspondence between the pseudo-3D model and the geological features of the island was observed, especially in the northern sector where most of the stations is installed. In particular, the top of the high-impedance contrast interface appears deeper in the northern coastal areas and shallower in the central sector. This is in agreement with the structural setting of the island likely due to the resurgence of Mount Epomeo.
How to cite: Manzo, R., Nardone, L., Gaudiosi, G., Martino, C., Galluzzo, D., Bianco, F., and Di Maio, R.: A Pseudo-3D Vs Velocity Model of Ischia Island (Italy) by HVSR spectral ratio inversion, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13610, https://doi.org/10.5194/egusphere-egu21-13610, 2021.
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Following the MD4.0 (Mw3.9) earthquake of August 21 2017 which occurred on the Ischia island (Naples, southern Italy), the local monitoring seismic network was significantly improved in terms of both number of stations and instrumentation performance. Due to the considerable amount of collected data, in particular of seismic noise recorded at broadband stations, some efforts have been addressed in particular to the definition of a 1D average velocity model effective for the whole island. This is an important scientific step because, in complex volcanic areas, the use of reliable velocity models is essential for an accurate localization of local earthquakes. In this work, the main target is to retrieve a pseudo-3D velocity model of the Ischia island. Specifically, we inverted H/V curves and frequency peaks evaluated at about twenty sites to obtain a velocity profile for each of the investigated measurement points. Taking into account that the H/V frequency peak depends on both velocity and thickness of layers, for each site we applied an inversion process fixing the velocities and modifying the thicknesses in order to obtain the corresponding 1D velocity models. We are quite enough confident about the robustness of models, since during the inversion process, we achieved a good convergence towards the best-fit solutions. Then, a pseudo-3D velocity model was obtained by contouring the 1D models of each station site to highlight possible lateral variations of the layer thicknesses and to reconstruct the morphology of the deeper interface characterized by a high impedance contrast. A good correspondence between the pseudo-3D model and the geological features of the island was observed, especially in the northern sector where most of the stations is installed. In particular, the top of the high-impedance contrast interface appears deeper in the northern coastal areas and shallower in the central sector. This is in agreement with the structural setting of the island likely due to the resurgence of Mount Epomeo.
How to cite: Manzo, R., Nardone, L., Gaudiosi, G., Martino, C., Galluzzo, D., Bianco, F., and Di Maio, R.: A Pseudo-3D Vs Velocity Model of Ischia Island (Italy) by HVSR spectral ratio inversion, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13610, https://doi.org/10.5194/egusphere-egu21-13610, 2021.
EGU21-7188 | vPICO presentations | SM5.1
Ambient noise surface wave inversion using OBS data from the north Atlantic, north of the Gloria fault.Juan Pinzon, Susana Custódio, Graça Silveira, Luis Matias, and Frank Krüger
The Gloria fault is a strike-slip oceanic plate boundary fault, which has remained poorly studied due mostly to its remote location in the north Atlantic Ocean. The fault has hosted some of the largest strike-slip earthquakes in the oceanic domain, notably the 1941 M8.3 and the 1975 M8.1 earthquakes, and generating tsunamis is the surrounding areas.
The seismic data used for this study was recorded by 12 broadband ocean bottom seismometers (OBSs) located about 100 km north of the Gloria fault during a 10-month experiment. The dataset has been used before to image crustal and mantle discontinuities using receiver function analysis and to infer the S-wave velocity structure of the oceanic lithosphere north of the Gloria fault from P-wave polarization. These studies indicate a slight crustal thickening towards the Gloria fault, as well as an increase in uppermost mantle S-wave velocities towards the fault.
In this study, we use ambient noise surface wave tomography to find the velocity structure beneath the OBS deployment. First, we present a 1D shear-velocity model obtained from inversion of the average fundamental mode Rayleigh and Love wave group and phase velocities. In addition, the hydrophone is also used to better constrain the inversion at shallow depths, because the hydrophone shows a clear fundamental mode without interference of the first higher mode. Because of the short interstation distances of the array, it is not possible to extract the dispersion curves at periods longer than ~16 s. To compute the Vs inversions, we used the code SURF96 (Herrmann and Ammon, 2004) and consider a water layer in the initial model for Rayleigh waves, because these waves are affected by the water layer. Our results show an upper mantle low-velocity zone, which may be related to serpentinization due to the proximity of the Gloria Fault. Finally, we present the lateral variations of group and phase velocities, as a function of period obtained using FMST (Rawlinson and Sambridge, 2005), which show strong contrast velocity anomalies at the center of the array at short periods (shallow depths).
The authors acknowledge support from the Portuguese FCT – Fundação para a Ciência e a Tecnologia, I.P., within the scope of project UTAP-EXPL/EAC/0056/2017 and with the FCT grant PD/BD/135069/2017 - IDL.
How to cite: Pinzon, J., Custódio, S., Silveira, G., Matias, L., and Krüger, F.: Ambient noise surface wave inversion using OBS data from the north Atlantic, north of the Gloria fault., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7188, https://doi.org/10.5194/egusphere-egu21-7188, 2021.
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The Gloria fault is a strike-slip oceanic plate boundary fault, which has remained poorly studied due mostly to its remote location in the north Atlantic Ocean. The fault has hosted some of the largest strike-slip earthquakes in the oceanic domain, notably the 1941 M8.3 and the 1975 M8.1 earthquakes, and generating tsunamis is the surrounding areas.
The seismic data used for this study was recorded by 12 broadband ocean bottom seismometers (OBSs) located about 100 km north of the Gloria fault during a 10-month experiment. The dataset has been used before to image crustal and mantle discontinuities using receiver function analysis and to infer the S-wave velocity structure of the oceanic lithosphere north of the Gloria fault from P-wave polarization. These studies indicate a slight crustal thickening towards the Gloria fault, as well as an increase in uppermost mantle S-wave velocities towards the fault.
In this study, we use ambient noise surface wave tomography to find the velocity structure beneath the OBS deployment. First, we present a 1D shear-velocity model obtained from inversion of the average fundamental mode Rayleigh and Love wave group and phase velocities. In addition, the hydrophone is also used to better constrain the inversion at shallow depths, because the hydrophone shows a clear fundamental mode without interference of the first higher mode. Because of the short interstation distances of the array, it is not possible to extract the dispersion curves at periods longer than ~16 s. To compute the Vs inversions, we used the code SURF96 (Herrmann and Ammon, 2004) and consider a water layer in the initial model for Rayleigh waves, because these waves are affected by the water layer. Our results show an upper mantle low-velocity zone, which may be related to serpentinization due to the proximity of the Gloria Fault. Finally, we present the lateral variations of group and phase velocities, as a function of period obtained using FMST (Rawlinson and Sambridge, 2005), which show strong contrast velocity anomalies at the center of the array at short periods (shallow depths).
The authors acknowledge support from the Portuguese FCT – Fundação para a Ciência e a Tecnologia, I.P., within the scope of project UTAP-EXPL/EAC/0056/2017 and with the FCT grant PD/BD/135069/2017 - IDL.
How to cite: Pinzon, J., Custódio, S., Silveira, G., Matias, L., and Krüger, F.: Ambient noise surface wave inversion using OBS data from the north Atlantic, north of the Gloria fault., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7188, https://doi.org/10.5194/egusphere-egu21-7188, 2021.
EGU21-6132 | vPICO presentations | SM5.1
Passive seismic interferometry of the ultraslow-spreading Southwest Indian RidgeMohamadhasan Mohamadian Sarvandani, Emanuel Kästle, Lapo Boschi, Sylvie Leroy, and Mathilde Cannat
Passive seismic interferometry (ambient-noise seismology) is an increasingly popular, eco-friendly, relatively inexpensive exploration geophysics tool, to map S-wave velocity in the Earth’s crust. This method has not yet been applied widely to marine exploration. The purpose of this study is to investigate the crustal structure of a quasi-amagmatic portion of the Southwest Indian Ridge by interferometry, and to examine the performance and reliability of interferometry in marine exploration. To achieve this goal, continuous vertical-component recordings from 43 ocean bottom seismometers (OBS) deployed during the SISMO-SMOOTH cruise (2014) were utilized. Recorded signals span frequencies between 0.1Hz and 3Hz. We show that reliable estimates of the Green’s function are obtained for many station pairs, by cross-correlation in the frequency domain. The comparison of the cross-correlations with the theoretical Green’s (Bessel) function provides one Rayleigh-wave dispersion curve per station pair; dispersion curves are then averaged, and inverted through a conditional neighborhood algorithm to determine a 1D S-wave velocity model, that we estimate to be well constrained within the crust. Our S-wave velocity model is analyzed and interpreted with geological information, and independent geophysical studies in the region of interest, as well as other areas characterized by similar tectonically-dominated, quasi amagmatic spreadings.
How to cite: Mohamadian Sarvandani, M., Kästle, E., Boschi, L., Leroy, S., and Cannat, M.: Passive seismic interferometry of the ultraslow-spreading Southwest Indian Ridge , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6132, https://doi.org/10.5194/egusphere-egu21-6132, 2021.
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Please use the buttons below to download the presentation materials or to visit the external website where the presentation is linked. Regarding the external link, please note that Copernicus Meetings cannot accept any liability for the content and the website you will visit.
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We are sorry, but presentations are only available for users who registered for the conference. Thank you.
Passive seismic interferometry (ambient-noise seismology) is an increasingly popular, eco-friendly, relatively inexpensive exploration geophysics tool, to map S-wave velocity in the Earth’s crust. This method has not yet been applied widely to marine exploration. The purpose of this study is to investigate the crustal structure of a quasi-amagmatic portion of the Southwest Indian Ridge by interferometry, and to examine the performance and reliability of interferometry in marine exploration. To achieve this goal, continuous vertical-component recordings from 43 ocean bottom seismometers (OBS) deployed during the SISMO-SMOOTH cruise (2014) were utilized. Recorded signals span frequencies between 0.1Hz and 3Hz. We show that reliable estimates of the Green’s function are obtained for many station pairs, by cross-correlation in the frequency domain. The comparison of the cross-correlations with the theoretical Green’s (Bessel) function provides one Rayleigh-wave dispersion curve per station pair; dispersion curves are then averaged, and inverted through a conditional neighborhood algorithm to determine a 1D S-wave velocity model, that we estimate to be well constrained within the crust. Our S-wave velocity model is analyzed and interpreted with geological information, and independent geophysical studies in the region of interest, as well as other areas characterized by similar tectonically-dominated, quasi amagmatic spreadings.
How to cite: Mohamadian Sarvandani, M., Kästle, E., Boschi, L., Leroy, S., and Cannat, M.: Passive seismic interferometry of the ultraslow-spreading Southwest Indian Ridge , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6132, https://doi.org/10.5194/egusphere-egu21-6132, 2021.
EGU21-9357 | vPICO presentations | SM5.1
Adjoint Seismic Tomography of the Antarctic Continent Incorporating Green's Functions from Ambient Noise CorrelationZhengyang Zhou, Douglas Wiens, and Andrew Lloyd
The Antarctic continent with its large ice sheets provides a unique environment to investigate the response of the solid Earth to ice mass change. A key requirement of such studies is high-resolution seismic images of the crust and upper mantle, which can be used to estimate the region’s viscous structure. Likewise, these images are key to understanding the region’s geologic history and underlying geodynamic processes. Although the existing transverse isotropic seismic model ANT-20(Lloyd et al., 2020) and azimuthally anisotropic seismic model ANT-30 (Lloyd et al., in prep) have regional-scale resolution from the upper mantle to the transition zone, there is a need for higher resolution within the uppermost mantle (< 75 km) and crust of Antarctica. In this study, we use the ANT-30 model (Lloyd et al., in prep), a 3D seismic model from earthquake data, as a starting model. We seek to improve its resolution within the upper ~100 km of the Antarctic mantle by fitting three-component ambient noise correlograms computed from broadband records collected in Antarctica over the past 20 years. This includes data from recent temporary arrays such as TAMSEIS, AGAP, TAMNNET, RIS, POLENET/ANET, and UKANET. The three-component cross-correlations of station pairs are calculated and properly rotated to extract ambient noise surface waves that include both Rayleigh and Love waves, which show excellent signal-to-noise ratio between 15 to 70 seconds. The benefit of including this data is twofold: (1) it provides surface wave observations down to 15 s, as opposed to 25 s and (2) it provides shorter intercontinental paths, which were absent due to the region’s earthquake distribution. We then use the software package SPECFEM3D_GLOBE to iteratively improve the 3-D earth model, minimizing the nondimensionalized traveltime phase misfit between the observed and synthetic waveforms. The preliminary results indicate a stronger positive radial anisotropy (VSH > VSV) in the lower crust and uppermost mantle for West Antarctica and part of East Antarctica. With more iterations, smaller-scale detail can be revealed by the new ambient noise data, resulting in a more reliable uppermost mantle and crustal structure.
How to cite: Zhou, Z., Wiens, D., and Lloyd, A.: Adjoint Seismic Tomography of the Antarctic Continent Incorporating Green's Functions from Ambient Noise Correlation, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9357, https://doi.org/10.5194/egusphere-egu21-9357, 2021.
The Antarctic continent with its large ice sheets provides a unique environment to investigate the response of the solid Earth to ice mass change. A key requirement of such studies is high-resolution seismic images of the crust and upper mantle, which can be used to estimate the region’s viscous structure. Likewise, these images are key to understanding the region’s geologic history and underlying geodynamic processes. Although the existing transverse isotropic seismic model ANT-20(Lloyd et al., 2020) and azimuthally anisotropic seismic model ANT-30 (Lloyd et al., in prep) have regional-scale resolution from the upper mantle to the transition zone, there is a need for higher resolution within the uppermost mantle (< 75 km) and crust of Antarctica. In this study, we use the ANT-30 model (Lloyd et al., in prep), a 3D seismic model from earthquake data, as a starting model. We seek to improve its resolution within the upper ~100 km of the Antarctic mantle by fitting three-component ambient noise correlograms computed from broadband records collected in Antarctica over the past 20 years. This includes data from recent temporary arrays such as TAMSEIS, AGAP, TAMNNET, RIS, POLENET/ANET, and UKANET. The three-component cross-correlations of station pairs are calculated and properly rotated to extract ambient noise surface waves that include both Rayleigh and Love waves, which show excellent signal-to-noise ratio between 15 to 70 seconds. The benefit of including this data is twofold: (1) it provides surface wave observations down to 15 s, as opposed to 25 s and (2) it provides shorter intercontinental paths, which were absent due to the region’s earthquake distribution. We then use the software package SPECFEM3D_GLOBE to iteratively improve the 3-D earth model, minimizing the nondimensionalized traveltime phase misfit between the observed and synthetic waveforms. The preliminary results indicate a stronger positive radial anisotropy (VSH > VSV) in the lower crust and uppermost mantle for West Antarctica and part of East Antarctica. With more iterations, smaller-scale detail can be revealed by the new ambient noise data, resulting in a more reliable uppermost mantle and crustal structure.
How to cite: Zhou, Z., Wiens, D., and Lloyd, A.: Adjoint Seismic Tomography of the Antarctic Continent Incorporating Green's Functions from Ambient Noise Correlation, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9357, https://doi.org/10.5194/egusphere-egu21-9357, 2021.
EGU21-6124 | vPICO presentations | SM5.1
Crustal structure, seasonal and directional variations of ambient seismic noise in SE Canada and the NE USAomid Bagherpur Mojaver and Fiona Darbyshire
Long-duration stacks of ambient seismic noise cross-correlation can be used to generate high-resolution images of the lithosphere. In this study, we investigate the crustal structure beneath southeastern Canada and the northeastern USA, using an ambient noise tomography technique. Our study area covers the Phanerozoic northern Appalachians and the Proterozoic eastern Grenville Province, recording a complex tectonic history since ~1 Ga. Our datasets include continuous records of vertical component time series, recorded by 69 stations belonging to 7 seismograph networks over a more than two-year period. The ambient seismic noise directionality and seasonality variations of our datasets are analyzed in detail, and possible noise source locations are proposed in the Atlantic and Pacific oceans. Our analysis suggests strong variations of dominant seismic noise sources at both Primary (11-20 s) and Secondary (5-10 s) bands in various months, with different observed patterns at these passband periods. Our tomographic models indicate complex and strong variations of Rayleigh wave phase velocities across the study area, providing us evidence to discuss tectonic implications. The resulting Rayleigh wave phase velocity maps suggest generally slower velocities beneath the Appalachians than the Grenville province. A sharp velocity contrast is observed across the Grenville Province-Appalachian domain boundary at periods sensitive to the lower crust, suggesting a step-like geometry of the Moho interface beneath this area.
How to cite: Bagherpur Mojaver, O. and Darbyshire, F.: Crustal structure, seasonal and directional variations of ambient seismic noise in SE Canada and the NE USA, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6124, https://doi.org/10.5194/egusphere-egu21-6124, 2021.
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Long-duration stacks of ambient seismic noise cross-correlation can be used to generate high-resolution images of the lithosphere. In this study, we investigate the crustal structure beneath southeastern Canada and the northeastern USA, using an ambient noise tomography technique. Our study area covers the Phanerozoic northern Appalachians and the Proterozoic eastern Grenville Province, recording a complex tectonic history since ~1 Ga. Our datasets include continuous records of vertical component time series, recorded by 69 stations belonging to 7 seismograph networks over a more than two-year period. The ambient seismic noise directionality and seasonality variations of our datasets are analyzed in detail, and possible noise source locations are proposed in the Atlantic and Pacific oceans. Our analysis suggests strong variations of dominant seismic noise sources at both Primary (11-20 s) and Secondary (5-10 s) bands in various months, with different observed patterns at these passband periods. Our tomographic models indicate complex and strong variations of Rayleigh wave phase velocities across the study area, providing us evidence to discuss tectonic implications. The resulting Rayleigh wave phase velocity maps suggest generally slower velocities beneath the Appalachians than the Grenville province. A sharp velocity contrast is observed across the Grenville Province-Appalachian domain boundary at periods sensitive to the lower crust, suggesting a step-like geometry of the Moho interface beneath this area.
How to cite: Bagherpur Mojaver, O. and Darbyshire, F.: Crustal structure, seasonal and directional variations of ambient seismic noise in SE Canada and the NE USA, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6124, https://doi.org/10.5194/egusphere-egu21-6124, 2021.
EGU21-15238 | vPICO presentations | SM5.1
Seismic radial anisotropy in Central-Western Mediterranean and Italian peninsula from ambient noise recordingsGiovanni Diaferia, Fabrizio Magrini, Matthew Agius, and Fabio Cammarano
The dynamics of crustal extension and the crust-mantle interaction in the Central-Western Mediterranean and Italian peninsula (i.e. Liguro-Provençal and Tyrrhenian Basin), and plate convergence (i.e. Alpine and Apennines chains) are key for the understating of the current geodynamics setting and its evolution in the region. However, open questions such as the style, depth and extent of the deformation still exist despite the wealth of seismological and non-seismological data acquired in the past decades. In this context, it is necessary to provide improved subsurface models in terms of seismic velocities, from which better constraints on the geodynamic models can be derived.
We use seismic ambient noise for retrieving phase velocities of Rayleigh and Love waves in the 4-35 s period range, using private (LiSard network in Sardinia island) and publicly available continuous recordings from more than 500 seismic stations. Considering the excellent coverage and the short period of recovered phase velocities, our study aims to provide an unprecedented, high-resolution image of the shallow crust and uppermost mantle.
We employ a Bayesian trans-dimensional, Monte Carlo Markov chain inversion approach that requires no a-priori model nor a fixed parametrization. In addition to the (isotropic) shear wave velocity structure, we also recover the values of radial anisotropy (ξ=(VSH/VSV)2) as a function of depth, thanks to the joint inversion of both Rayleigh and Love phase velocities.
Focusing on radial anisotropy, this appears clearly uncoupled with respect to the shear wave velocity structure. The largest negative anisotropy anomalies (VSH<VSV, ξ<0.9) are found in the Liguro-Provençal and western Tyrrhenian basins in the top 10-15 km, suggesting a common structural imprint inherited during the extensional phases of such basins. Conversely, the eastern Tyrrhenian basin shows positive radial anisotropy (VSH>VSV, ξ>1.1) within the same depth range. This evidence, combined with the observed shear wave velocities typical of the uppermost mantle, corroborates the presence of a sub-horizontal asthenospheric flow driving the current extension and oceanization of the eastern Tyrrhenian basins.
Moving towards the Italian mainland, a strong anomaly of negative anisotropy appears in the eastern portion of the Apennines chain. We relate such an anisotropic signal with the ongoing compressive regime affecting the area. Here, the high-angle thrust faults and folds, that accommodates the horizontal shortening, obliterate the horizontal layering of the sedimentary deposits, currently constituting the flanks of the fold system.
Our results suggest that the combination of radial anisotropy and shear wave velocities can unravel key characteristics of the crust and uppermost mantle, such as inherited or currently active structures resulting from past or ongoing geodynamic processes.
How to cite: Diaferia, G., Magrini, F., Agius, M., and Cammarano, F.: Seismic radial anisotropy in Central-Western Mediterranean and Italian peninsula from ambient noise recordings, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15238, https://doi.org/10.5194/egusphere-egu21-15238, 2021.
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The dynamics of crustal extension and the crust-mantle interaction in the Central-Western Mediterranean and Italian peninsula (i.e. Liguro-Provençal and Tyrrhenian Basin), and plate convergence (i.e. Alpine and Apennines chains) are key for the understating of the current geodynamics setting and its evolution in the region. However, open questions such as the style, depth and extent of the deformation still exist despite the wealth of seismological and non-seismological data acquired in the past decades. In this context, it is necessary to provide improved subsurface models in terms of seismic velocities, from which better constraints on the geodynamic models can be derived.
We use seismic ambient noise for retrieving phase velocities of Rayleigh and Love waves in the 4-35 s period range, using private (LiSard network in Sardinia island) and publicly available continuous recordings from more than 500 seismic stations. Considering the excellent coverage and the short period of recovered phase velocities, our study aims to provide an unprecedented, high-resolution image of the shallow crust and uppermost mantle.
We employ a Bayesian trans-dimensional, Monte Carlo Markov chain inversion approach that requires no a-priori model nor a fixed parametrization. In addition to the (isotropic) shear wave velocity structure, we also recover the values of radial anisotropy (ξ=(VSH/VSV)2) as a function of depth, thanks to the joint inversion of both Rayleigh and Love phase velocities.
Focusing on radial anisotropy, this appears clearly uncoupled with respect to the shear wave velocity structure. The largest negative anisotropy anomalies (VSH<VSV, ξ<0.9) are found in the Liguro-Provençal and western Tyrrhenian basins in the top 10-15 km, suggesting a common structural imprint inherited during the extensional phases of such basins. Conversely, the eastern Tyrrhenian basin shows positive radial anisotropy (VSH>VSV, ξ>1.1) within the same depth range. This evidence, combined with the observed shear wave velocities typical of the uppermost mantle, corroborates the presence of a sub-horizontal asthenospheric flow driving the current extension and oceanization of the eastern Tyrrhenian basins.
Moving towards the Italian mainland, a strong anomaly of negative anisotropy appears in the eastern portion of the Apennines chain. We relate such an anisotropic signal with the ongoing compressive regime affecting the area. Here, the high-angle thrust faults and folds, that accommodates the horizontal shortening, obliterate the horizontal layering of the sedimentary deposits, currently constituting the flanks of the fold system.
Our results suggest that the combination of radial anisotropy and shear wave velocities can unravel key characteristics of the crust and uppermost mantle, such as inherited or currently active structures resulting from past or ongoing geodynamic processes.
How to cite: Diaferia, G., Magrini, F., Agius, M., and Cammarano, F.: Seismic radial anisotropy in Central-Western Mediterranean and Italian peninsula from ambient noise recordings, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15238, https://doi.org/10.5194/egusphere-egu21-15238, 2021.
EGU21-6028 | vPICO presentations | SM5.1
Geodynamics of the Central Mediterranean (GEOMED) inferred from ambient seismic noiseMatthew Agius, Fabrizio Magrini, Giovanni Diaferia, Fabio Cammarano, Claudio Faccenna, Francesca Funiciello, Emanuel Kästle, and Mark van der Meijde
The Central Mediterranean, the area encompassing Italy, Sardinia, Tunisia and Libya, is characterised by multiple tectonic processes (plate convergence, subduction, and backarc extension). The evolution and interaction of the plate margins within this relatively small area are still being unravelled particularly at the adjacent region known as the Sicily Channel located between Sicily, Tunisia, Libya and Malta. This Channel is characterised by a seismically and volcanically active rift zone. Much of the observations we have today for the southern parts of the Calabrian arc are either limited to the surface and the upper crust, or are broader and deeper from regional seismic tomography, missing important details about the lithospheric structure and dynamics. The project GEOMED (https://geomed-msca.eu) addresses this issue by processing all the seismic data available in the region in order to understand better the geodynamics of the Central Mediterranean.
We measure Rayleigh- and Love-wave phase velocities from ambient seismic noise recordings to infer the structures of the Central Mediterranean, from the Central Apennines to the African foreland, with a special focus on the Sicily Channel Rift Zone (SCRZ). The phase-velocity dispersion curves have periods ranging from 5 to 100 seconds and sample through the entire lithosphere. We invert the dispersion data for isotropic and polarised shear velocities with depth and infer crustal thickness and patterns of radial anisotropy. We find that continental blocks have thick crust (30-50 km), whereas beneath the SCRZ the crust is thin (<25 km), and thinner beneath the Tyrrhenian Sea. Beneath the SCRZ and the Tyrrhenian Sea, the crustal shear velocities are characterised by positive radial anisotropy (VSH>VSV) indicative of horizontal flow or extension, whereas the uppermost mantle is characterised by slow shear velocities indicative of warmer temperatures and strong negative radial anisotropy (VSH>VSV) indicative of vertical flow. We discuss the relevance of these findings together with other geophysical studies such as the regional seismicity and GPS velocity vectors to identify the rifting process type of the SCRZ.
This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 843696.
How to cite: Agius, M., Magrini, F., Diaferia, G., Cammarano, F., Faccenna, C., Funiciello, F., Kästle, E., and van der Meijde, M.: Geodynamics of the Central Mediterranean (GEOMED) inferred from ambient seismic noise, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6028, https://doi.org/10.5194/egusphere-egu21-6028, 2021.
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The Central Mediterranean, the area encompassing Italy, Sardinia, Tunisia and Libya, is characterised by multiple tectonic processes (plate convergence, subduction, and backarc extension). The evolution and interaction of the plate margins within this relatively small area are still being unravelled particularly at the adjacent region known as the Sicily Channel located between Sicily, Tunisia, Libya and Malta. This Channel is characterised by a seismically and volcanically active rift zone. Much of the observations we have today for the southern parts of the Calabrian arc are either limited to the surface and the upper crust, or are broader and deeper from regional seismic tomography, missing important details about the lithospheric structure and dynamics. The project GEOMED (https://geomed-msca.eu) addresses this issue by processing all the seismic data available in the region in order to understand better the geodynamics of the Central Mediterranean.
We measure Rayleigh- and Love-wave phase velocities from ambient seismic noise recordings to infer the structures of the Central Mediterranean, from the Central Apennines to the African foreland, with a special focus on the Sicily Channel Rift Zone (SCRZ). The phase-velocity dispersion curves have periods ranging from 5 to 100 seconds and sample through the entire lithosphere. We invert the dispersion data for isotropic and polarised shear velocities with depth and infer crustal thickness and patterns of radial anisotropy. We find that continental blocks have thick crust (30-50 km), whereas beneath the SCRZ the crust is thin (<25 km), and thinner beneath the Tyrrhenian Sea. Beneath the SCRZ and the Tyrrhenian Sea, the crustal shear velocities are characterised by positive radial anisotropy (VSH>VSV) indicative of horizontal flow or extension, whereas the uppermost mantle is characterised by slow shear velocities indicative of warmer temperatures and strong negative radial anisotropy (VSH>VSV) indicative of vertical flow. We discuss the relevance of these findings together with other geophysical studies such as the regional seismicity and GPS velocity vectors to identify the rifting process type of the SCRZ.
This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 843696.
How to cite: Agius, M., Magrini, F., Diaferia, G., Cammarano, F., Faccenna, C., Funiciello, F., Kästle, E., and van der Meijde, M.: Geodynamics of the Central Mediterranean (GEOMED) inferred from ambient seismic noise, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6028, https://doi.org/10.5194/egusphere-egu21-6028, 2021.
EGU21-15143 | vPICO presentations | SM5.1
Full-waveform inversion with wavefield gradientsSneha Singh, Yann Capdeville, Heiner Igel, Navid Hedjazian, and Thomas Bodin
Wavefield gradient instruments, such as rotational sensors and DAS systems, are becoming more and more accessible in seismology. Their usage for Full Waveform Inversion (FWI) is in sight. Nevertheless, local small-scale heterogeneities, like geological inhomogeneities, surface topographies, and cavities are known to affect wavefield gradients. This effect is in fact measurable with current instruments. For example, the agreement between data and synthetics computed in a tomographic model is often not as good for rotation as it is for displacement.
The theory of homogenization can help us understand why small-scale heterogeneities strongly affect wavefield gradients, but not the wavefield itself. It tells us that at any receiver measuring wavefield gradient, small-scale heterogeneities cause the wavefield gradient to couple with strain through a coupling tensor J. Furthermore, this J is 1) independent of source, 2) independent of time, but 3) only dependent on the receiver location. Consequently, we can invert for J based on an effective model for which synthetics fit displacement data reasonably well. Once inverted, J can be used to correct all other wavefield gradients at that receiver.
Here, we aim to understand the benefits and drawbacks of wavefield gradient sensors in a FWI context. We show that FWIs performed with rotations and strains are equivalent to that performed with displacements provided that 1) the number of data is sufficient, and 2) the receivers are placed far away from heterogeneities. In the case that receivers are placed near heterogeneities, we find that due to the effect of these heterogeneities, an incorrect model is recovered from inversion. In this case therefore, the coupling tensor J needs to be taken into account for each receiver to get rid of the effect.
How to cite: Singh, S., Capdeville, Y., Igel, H., Hedjazian, N., and Bodin, T.: Full-waveform inversion with wavefield gradients, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15143, https://doi.org/10.5194/egusphere-egu21-15143, 2021.
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Wavefield gradient instruments, such as rotational sensors and DAS systems, are becoming more and more accessible in seismology. Their usage for Full Waveform Inversion (FWI) is in sight. Nevertheless, local small-scale heterogeneities, like geological inhomogeneities, surface topographies, and cavities are known to affect wavefield gradients. This effect is in fact measurable with current instruments. For example, the agreement between data and synthetics computed in a tomographic model is often not as good for rotation as it is for displacement.
The theory of homogenization can help us understand why small-scale heterogeneities strongly affect wavefield gradients, but not the wavefield itself. It tells us that at any receiver measuring wavefield gradient, small-scale heterogeneities cause the wavefield gradient to couple with strain through a coupling tensor J. Furthermore, this J is 1) independent of source, 2) independent of time, but 3) only dependent on the receiver location. Consequently, we can invert for J based on an effective model for which synthetics fit displacement data reasonably well. Once inverted, J can be used to correct all other wavefield gradients at that receiver.
Here, we aim to understand the benefits and drawbacks of wavefield gradient sensors in a FWI context. We show that FWIs performed with rotations and strains are equivalent to that performed with displacements provided that 1) the number of data is sufficient, and 2) the receivers are placed far away from heterogeneities. In the case that receivers are placed near heterogeneities, we find that due to the effect of these heterogeneities, an incorrect model is recovered from inversion. In this case therefore, the coupling tensor J needs to be taken into account for each receiver to get rid of the effect.
How to cite: Singh, S., Capdeville, Y., Igel, H., Hedjazian, N., and Bodin, T.: Full-waveform inversion with wavefield gradients, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15143, https://doi.org/10.5194/egusphere-egu21-15143, 2021.
EGU21-279 | vPICO presentations | SM5.1
Efficacy of Seismic Interferometry in Removing Surface Waves from Active Seismic RecordsVarun Kumar Singla and Ivan Lokmer
While there are seismic techniques which make use of surface waves in imaging the subsurface, there are also those where these types of waves are considered coherent noise. Important examples where the surface waves may significantly degrade the obtained images include different types of reflection seismic surveys (e.g., shallow surveys for engineering, environmental and groundwater investigations, and deep surveys for imaging hydrocarbon reservoirs). In a strongly heterogeneous medium (encountered typically in onshore surveys), the conventional methods for attenuating these waves (such as f-k "velocity" filtering) often do not give satisfactory results.
Seismic interferometry is a data-driven approach that offers a viable alternative for removal of surface waves from active seismic records. In this approach, the reflection data of several sources is considered and for each source, the seismic signals at a pair of receivers are cross-correlated to produce the surface wavefield between the receivers. The cross-correlated waveforms are then summed over all the sources to obtain the "interferometric" signal for the considered receiver pair. During this summation, the reflection and non-physical events cancel out due to the variable differences in the travel times to the considered receiver pair from different sources. The "interferometric" signal consequently contains predominantly the surface waves and this makes it conducive for adaptive subtraction (or filtering) from the original records. This study investigates the efficacy of the commonly used filtering techniques in interferometry to remove the surface waves from active seismic records. For this, the reflection data of a complex 2-D elastic medium is simulated and the filtering techniques are applied to this data. The limitations of these techniques inferred from the quality of the filtered data are discussed and possible remedies to overcome them are suggested.
How to cite: Singla, V. K. and Lokmer, I.: Efficacy of Seismic Interferometry in Removing Surface Waves from Active Seismic Records, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-279, https://doi.org/10.5194/egusphere-egu21-279, 2021.
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While there are seismic techniques which make use of surface waves in imaging the subsurface, there are also those where these types of waves are considered coherent noise. Important examples where the surface waves may significantly degrade the obtained images include different types of reflection seismic surveys (e.g., shallow surveys for engineering, environmental and groundwater investigations, and deep surveys for imaging hydrocarbon reservoirs). In a strongly heterogeneous medium (encountered typically in onshore surveys), the conventional methods for attenuating these waves (such as f-k "velocity" filtering) often do not give satisfactory results.
Seismic interferometry is a data-driven approach that offers a viable alternative for removal of surface waves from active seismic records. In this approach, the reflection data of several sources is considered and for each source, the seismic signals at a pair of receivers are cross-correlated to produce the surface wavefield between the receivers. The cross-correlated waveforms are then summed over all the sources to obtain the "interferometric" signal for the considered receiver pair. During this summation, the reflection and non-physical events cancel out due to the variable differences in the travel times to the considered receiver pair from different sources. The "interferometric" signal consequently contains predominantly the surface waves and this makes it conducive for adaptive subtraction (or filtering) from the original records. This study investigates the efficacy of the commonly used filtering techniques in interferometry to remove the surface waves from active seismic records. For this, the reflection data of a complex 2-D elastic medium is simulated and the filtering techniques are applied to this data. The limitations of these techniques inferred from the quality of the filtered data are discussed and possible remedies to overcome them are suggested.
How to cite: Singla, V. K. and Lokmer, I.: Efficacy of Seismic Interferometry in Removing Surface Waves from Active Seismic Records, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-279, https://doi.org/10.5194/egusphere-egu21-279, 2021.
EGU21-7231 | vPICO presentations | SM5.1
Permo-Triassic Oceanic and Adjacent Continental Lithosphere in the Eastern Mediterranean, from surface-wave and wide-angle imagingAmr El-Sharkawy, Thomas Meier, Christian Hübscher, Sergei Lebedev, Anke Dannowski, Heidrun Kopp, Jan H. Behrmann, Andrew McGrandle, and Mona Hamada
The Earth’s oldest oceanic lithosphere preserved in-situ is in the eastern Mediterranean Sea. It can offer essential information on the oceanic plate evolution. Yet, its thickness and other properties have been difficult to determine by means of seismic imaging due to the high heterogeneity of the region. Here, we combine a large, new surface wave dataset with published wide-angle data in order to map the properties and lateral variability of the oceanic lithosphere, as well as the ocean-continent transition in the easternmost Mediterranean beneath the Levant Basin. We use stochastic joint inversion of broad band, phase-velocity dispersion measurements and seismic refraction P-wave velocity models to obtain 1-D, shear wave velocity models down to 300 km depth and compare the structure beneath the Ionian Sea and the Levant Basin. The thickness of the crust is about 16.4 ± 3 km and 22.3 ± 2 km beneath the chosen locations within the Ionian Sea and the Levant Basin, respectively. The Poisson’s ratio of about 0.32 and Vp/Vs of about 1.93 in the crystalline crust, yielded by the inversion, confirm the presence of oceanic crust beneath the Ionian Sea. The thickness of the Ionian oceanic lithosphere is around 180 km, whereas the continental lithosphere beneath the eastern Levant Basin is ~70 km thick, with low crustal Vp/Vs (~1.7) and Poisson’s (~0.24) ratios. According to 3-D shear wave velocity tomography using the surface wave data, the thickness of the oceanic lithosphere increases from the Triassic Ionian Sea towards the Permian-Carboniferous Libyan Sea and Herodotus Basin. Thicknesses of the Permo-Triassic oceanic lithosphere considerably larger than 100 km indicate that oceanic lithosphere can thicken by cooling substantially beyond the limits suggested by the plate cooling model. The transition from oceanic to continental lithosphere occurs at about 31°E in the crust, as indicated by magnetic and gravity measurements. The continental mantle lithosphere further to the east of this boundary is ~150 km thick beneath the westernmost Levant Basin, as indicated by shear wave velocity tomography and long wavelength gravity anomalies, and strongly thins eastward towards the area of the Levantine Coast and the Dead Sea Fault. The localization of the lithospheric deformation and crustal seismicity along the Dead Sea Fault correlates spatially with the thinning of the underlying continental lithosphere.
Key words: surface wave tomography, wide angle seismic imaging, joint inversion, Vp/Vs and Poisson’s ratios, eastern Mediterranean, Oceanic Lithosphere, Continental Lithosphere, Dead Sea Fault.
How to cite: El-Sharkawy, A., Meier, T., Hübscher, C., Lebedev, S., Dannowski, A., Kopp, H., Behrmann, J. H., McGrandle, A., and Hamada, M.: Permo-Triassic Oceanic and Adjacent Continental Lithosphere in the Eastern Mediterranean, from surface-wave and wide-angle imaging, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7231, https://doi.org/10.5194/egusphere-egu21-7231, 2021.
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The Earth’s oldest oceanic lithosphere preserved in-situ is in the eastern Mediterranean Sea. It can offer essential information on the oceanic plate evolution. Yet, its thickness and other properties have been difficult to determine by means of seismic imaging due to the high heterogeneity of the region. Here, we combine a large, new surface wave dataset with published wide-angle data in order to map the properties and lateral variability of the oceanic lithosphere, as well as the ocean-continent transition in the easternmost Mediterranean beneath the Levant Basin. We use stochastic joint inversion of broad band, phase-velocity dispersion measurements and seismic refraction P-wave velocity models to obtain 1-D, shear wave velocity models down to 300 km depth and compare the structure beneath the Ionian Sea and the Levant Basin. The thickness of the crust is about 16.4 ± 3 km and 22.3 ± 2 km beneath the chosen locations within the Ionian Sea and the Levant Basin, respectively. The Poisson’s ratio of about 0.32 and Vp/Vs of about 1.93 in the crystalline crust, yielded by the inversion, confirm the presence of oceanic crust beneath the Ionian Sea. The thickness of the Ionian oceanic lithosphere is around 180 km, whereas the continental lithosphere beneath the eastern Levant Basin is ~70 km thick, with low crustal Vp/Vs (~1.7) and Poisson’s (~0.24) ratios. According to 3-D shear wave velocity tomography using the surface wave data, the thickness of the oceanic lithosphere increases from the Triassic Ionian Sea towards the Permian-Carboniferous Libyan Sea and Herodotus Basin. Thicknesses of the Permo-Triassic oceanic lithosphere considerably larger than 100 km indicate that oceanic lithosphere can thicken by cooling substantially beyond the limits suggested by the plate cooling model. The transition from oceanic to continental lithosphere occurs at about 31°E in the crust, as indicated by magnetic and gravity measurements. The continental mantle lithosphere further to the east of this boundary is ~150 km thick beneath the westernmost Levant Basin, as indicated by shear wave velocity tomography and long wavelength gravity anomalies, and strongly thins eastward towards the area of the Levantine Coast and the Dead Sea Fault. The localization of the lithospheric deformation and crustal seismicity along the Dead Sea Fault correlates spatially with the thinning of the underlying continental lithosphere.
Key words: surface wave tomography, wide angle seismic imaging, joint inversion, Vp/Vs and Poisson’s ratios, eastern Mediterranean, Oceanic Lithosphere, Continental Lithosphere, Dead Sea Fault.
How to cite: El-Sharkawy, A., Meier, T., Hübscher, C., Lebedev, S., Dannowski, A., Kopp, H., Behrmann, J. H., McGrandle, A., and Hamada, M.: Permo-Triassic Oceanic and Adjacent Continental Lithosphere in the Eastern Mediterranean, from surface-wave and wide-angle imaging, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7231, https://doi.org/10.5194/egusphere-egu21-7231, 2021.
EGU21-11916 | vPICO presentations | SM5.1
CNN-based Multi-Scale Gradient Optimization for Full-Waveform InversionSenlin Yang, Peng Jiang, Yuxiao Ren, and Xinji Xu
The seismic full waveform inversion (FWI), as one of important ways to obtain the seismic wave velocity, has made rapid development in the last decade. In response to problems of cycle-skipping artifacts, dependence on the initial model, and low-frequency information in FWI, researchers have made many improvements, such as multi-scale envelope inversion and low-frequency extension. Recently, deep learning has been also adopted seismic data processing and interpretation, because of its strong nonlinear mapping ability. However, these works depend on labels used for training heavily, especially for the velocity model in the inversion, which prevents them from real application. Referring to these studies, this work combines low-frequency extension commonly as well as multiscale inversion with deep learning, and proposes a multi-scale FWI gradient optimization method based on CNN. CNN we designed is trained to predict the inversion gradient corresponding to the low-frequency band data in FWI, so that multi-scale gradient optimization can be directly used in multi-scale inversion, expanding the low-frequency information in the actual data and reducing the calculation in FWI. With a specially designed dataset, CNN is trained to optimize the gradients computed from the high-frequency band data by predicting the gradients corresponding to the low-frequency band data and the gradients corresponding to the mid-frequency band data, respectively. The predicted gradients are used in different stages of the multi-scale inversion. The low-frequency gradients are used to invert the initial structural construction so as not to rely on a good initial model, and the high-frequency gradients are used to improve the accuracy of the inversion results. In this way, low-frequency expansion and multiscale inversion can be achieved simultaneously. Our method achieves good results on the initial model for a given uniform wave velocity, effectively alleviating the reliance on the initial model in FWI. This study provides a new idea of combining deep learning and full waveform inversion, which will be effectively used in seismic data processing.
How to cite: Yang, S., Jiang, P., Ren, Y., and Xu, X.: CNN-based Multi-Scale Gradient Optimization for Full-Waveform Inversion, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11916, https://doi.org/10.5194/egusphere-egu21-11916, 2021.
The seismic full waveform inversion (FWI), as one of important ways to obtain the seismic wave velocity, has made rapid development in the last decade. In response to problems of cycle-skipping artifacts, dependence on the initial model, and low-frequency information in FWI, researchers have made many improvements, such as multi-scale envelope inversion and low-frequency extension. Recently, deep learning has been also adopted seismic data processing and interpretation, because of its strong nonlinear mapping ability. However, these works depend on labels used for training heavily, especially for the velocity model in the inversion, which prevents them from real application. Referring to these studies, this work combines low-frequency extension commonly as well as multiscale inversion with deep learning, and proposes a multi-scale FWI gradient optimization method based on CNN. CNN we designed is trained to predict the inversion gradient corresponding to the low-frequency band data in FWI, so that multi-scale gradient optimization can be directly used in multi-scale inversion, expanding the low-frequency information in the actual data and reducing the calculation in FWI. With a specially designed dataset, CNN is trained to optimize the gradients computed from the high-frequency band data by predicting the gradients corresponding to the low-frequency band data and the gradients corresponding to the mid-frequency band data, respectively. The predicted gradients are used in different stages of the multi-scale inversion. The low-frequency gradients are used to invert the initial structural construction so as not to rely on a good initial model, and the high-frequency gradients are used to improve the accuracy of the inversion results. In this way, low-frequency expansion and multiscale inversion can be achieved simultaneously. Our method achieves good results on the initial model for a given uniform wave velocity, effectively alleviating the reliance on the initial model in FWI. This study provides a new idea of combining deep learning and full waveform inversion, which will be effectively used in seismic data processing.
How to cite: Yang, S., Jiang, P., Ren, Y., and Xu, X.: CNN-based Multi-Scale Gradient Optimization for Full-Waveform Inversion, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11916, https://doi.org/10.5194/egusphere-egu21-11916, 2021.
EGU21-11754 | vPICO presentations | SM5.1
Optimal resolution seismic tomography with error tracking: imaging the upper mantle beneath Ireland and BritainRaffaele Bonadio, Sergei Lebedev, Thomas Meier, Pierre Arroucau, Andrew Schaeffer, Andrea Licciardi, Matthew Agius, Clare Horan, Louise Collins, Brian O'Reilly, Peter Readman, and the Ireland Array Working Group
Spatial resolution, as the ability to distinguish different features that are close together, is a fundamental concept in seismic tomography and other imaging fields. In contrast with microscopy or telescopy, seismic tomography’s images are computed, and their resolution has a complex, non-linear dependence on the data sampling and errors. Linear inverse theory provides a useful resolution-analysis approach, defining resolution in terms of the closeness of the resolution matrix to the identity matrix. This definition is similar to the universal, multi-disciplinary one in some contexts but diverges from it markedly in others. In this work, we adopt the universal definition of resolution (the minimum distance at which two spike anomalies can be resolved). The highest achievable resolution of a tomographic model then varies spatially and depends on the data sampling and errors in the data. We show that the propagation of systematic errors is resistant to data redundancy and results in models dominated by noise if the target resolution is too high. This forces one to look for smoother models and effectively limits the resolution. Here, we develop a surface-wave tomography method that finds optimal lateral resolution at every point by means of error tracking.
We first measure interstation phase velocities at simultaneously recording station pairs and compute phase-velocity maps at densely, logarithmically spaced periods. Multiple versions of the maps with varying smoothness are computed, ranging from very rough to very smooth. Phase-velocity curves extracted from the maps at every point are then inverted for shear-velocity (VS) profiles. As we show, errors in these phase-velocity curves increase nearly monotonically with the map roughness. Very smooth VS models computed from very smooth phase-velocity maps will be the most accurate, but at a cost of a loss of most structural information. At the other extreme, models that are too rough will be dominated by noise. We define the optimal resolution at a point such that the error of the local phase-velocity curve is below an empirical threshold. The error is estimated by isolating the roughness of the phase-velocity curve that cannot be explained by any Earth structure.
A 3D VS model is then computed by the inversion of the phase-velocity maps with the optimal resolution at every point. The estimated optimal resolution shows smooth lateral variations, confirming the robustness of the procedure. Importantly, optimal resolution does not scale with the density of the data coverage: some of the best-sampled locations require relatively low lateral resolution, probably due to systematic errors in the data.
We apply the method to image the lithosphere and underlying mantle beneath Ireland and Britain, using 11238 newly measured, broadband, inter-station dispersion curves. The lateral resolution of the 3D model is computed explicitly and varies from 39 km in central Ireland to over 800 km at the region boundaries, where the data coverage declines. Our tomography reveals pronounced, previously unknown variations in the lithospheric thickness beneath the region, with implications for the Caledonian assembly of the islands’ landmass and the mechanism of the magmatism of the British Tertiary Igneous Province.
How to cite: Bonadio, R., Lebedev, S., Meier, T., Arroucau, P., Schaeffer, A., Licciardi, A., Agius, M., Horan, C., Collins, L., O'Reilly, B., Readman, P., and Ireland Array Working Group, T.: Optimal resolution seismic tomography with error tracking: imaging the upper mantle beneath Ireland and Britain, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11754, https://doi.org/10.5194/egusphere-egu21-11754, 2021.
Spatial resolution, as the ability to distinguish different features that are close together, is a fundamental concept in seismic tomography and other imaging fields. In contrast with microscopy or telescopy, seismic tomography’s images are computed, and their resolution has a complex, non-linear dependence on the data sampling and errors. Linear inverse theory provides a useful resolution-analysis approach, defining resolution in terms of the closeness of the resolution matrix to the identity matrix. This definition is similar to the universal, multi-disciplinary one in some contexts but diverges from it markedly in others. In this work, we adopt the universal definition of resolution (the minimum distance at which two spike anomalies can be resolved). The highest achievable resolution of a tomographic model then varies spatially and depends on the data sampling and errors in the data. We show that the propagation of systematic errors is resistant to data redundancy and results in models dominated by noise if the target resolution is too high. This forces one to look for smoother models and effectively limits the resolution. Here, we develop a surface-wave tomography method that finds optimal lateral resolution at every point by means of error tracking.
We first measure interstation phase velocities at simultaneously recording station pairs and compute phase-velocity maps at densely, logarithmically spaced periods. Multiple versions of the maps with varying smoothness are computed, ranging from very rough to very smooth. Phase-velocity curves extracted from the maps at every point are then inverted for shear-velocity (VS) profiles. As we show, errors in these phase-velocity curves increase nearly monotonically with the map roughness. Very smooth VS models computed from very smooth phase-velocity maps will be the most accurate, but at a cost of a loss of most structural information. At the other extreme, models that are too rough will be dominated by noise. We define the optimal resolution at a point such that the error of the local phase-velocity curve is below an empirical threshold. The error is estimated by isolating the roughness of the phase-velocity curve that cannot be explained by any Earth structure.
A 3D VS model is then computed by the inversion of the phase-velocity maps with the optimal resolution at every point. The estimated optimal resolution shows smooth lateral variations, confirming the robustness of the procedure. Importantly, optimal resolution does not scale with the density of the data coverage: some of the best-sampled locations require relatively low lateral resolution, probably due to systematic errors in the data.
We apply the method to image the lithosphere and underlying mantle beneath Ireland and Britain, using 11238 newly measured, broadband, inter-station dispersion curves. The lateral resolution of the 3D model is computed explicitly and varies from 39 km in central Ireland to over 800 km at the region boundaries, where the data coverage declines. Our tomography reveals pronounced, previously unknown variations in the lithospheric thickness beneath the region, with implications for the Caledonian assembly of the islands’ landmass and the mechanism of the magmatism of the British Tertiary Igneous Province.
How to cite: Bonadio, R., Lebedev, S., Meier, T., Arroucau, P., Schaeffer, A., Licciardi, A., Agius, M., Horan, C., Collins, L., O'Reilly, B., Readman, P., and Ireland Array Working Group, T.: Optimal resolution seismic tomography with error tracking: imaging the upper mantle beneath Ireland and Britain, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11754, https://doi.org/10.5194/egusphere-egu21-11754, 2021.
EGU21-14319 | vPICO presentations | SM5.1
Lithospheric structure of the North American Craton constrained by full waveform inversionTong Zhou, Min Chen, Ziyi Xi, and Jiaqi Li
Cratonic lithosphere is believed to be rigid and less deformed during a long period of time. However, the detailed structure of Cratons may bring information of the complex formation and assemblage process of the continental lithosphere. Here, we present the seismic radial anisotropic structure of the North American Craton (NAC) constrained by a regional full-waveform inversion (FWI) with 465,422 high-quality frequency-dependent travel time misfit measurements with the shortest period of 15 s from both the body wave and surface wave recordings of 5,120 stations and 160 earthquakes located in the contiguous U.S and surrounding regions. Started from an initial model constructed by combining US.2016 and Crust1.0 in the crust and S40RTS (isotropic) in the mantle, we are able to have the optimized crustal structure in terms of initial waveform similarity and get rid of existing features from other radially anisotropic mantle models.
Our new model reveals the NAC lithosphere with about +2% voigt shear wave speed anomaly and an average thickness of 200–250 km beneath the Superior Craton, and becomes thinner towards the eastern, the southern, and the southwestern margins with a thickness decreased to 100–150 km. The radial anisotropy manifests a layer of higher horizontal shear wave speed VSH (ξ=VSH2/VSV2>1) beneath the core of Superior Craton down to around 160 km, where the higher vertical shear wave speed VSV (ξ<1) is observed beneath 160 km. Such radial anisotropy layering is also observed in the margin of continental lithosphere but with shallower depth. The radial anisotropic layer matches the receiver function results of mid-lithosphere discontinuities of the Craton cores, and the lithosphere conductivity result. The radial anisotropy layering observation confirms the two-layered lithosphere structure of the NAC, where the upper layer likely represents the original radial anisotropy fabric related to the cooling of the craton core, while the lower layer might be related to the tectonic processes more recently, e.g., accretion . The lithospheric thinning beneath the NAC margins indicates the deformation of the lithosphere and is likely controlled by the large-scale mantle convection, therefore relates to the further modification process of the NAC.
How to cite: Zhou, T., Chen, M., Xi, Z., and Li, J.: Lithospheric structure of the North American Craton constrained by full waveform inversion, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14319, https://doi.org/10.5194/egusphere-egu21-14319, 2021.
Cratonic lithosphere is believed to be rigid and less deformed during a long period of time. However, the detailed structure of Cratons may bring information of the complex formation and assemblage process of the continental lithosphere. Here, we present the seismic radial anisotropic structure of the North American Craton (NAC) constrained by a regional full-waveform inversion (FWI) with 465,422 high-quality frequency-dependent travel time misfit measurements with the shortest period of 15 s from both the body wave and surface wave recordings of 5,120 stations and 160 earthquakes located in the contiguous U.S and surrounding regions. Started from an initial model constructed by combining US.2016 and Crust1.0 in the crust and S40RTS (isotropic) in the mantle, we are able to have the optimized crustal structure in terms of initial waveform similarity and get rid of existing features from other radially anisotropic mantle models.
Our new model reveals the NAC lithosphere with about +2% voigt shear wave speed anomaly and an average thickness of 200–250 km beneath the Superior Craton, and becomes thinner towards the eastern, the southern, and the southwestern margins with a thickness decreased to 100–150 km. The radial anisotropy manifests a layer of higher horizontal shear wave speed VSH (ξ=VSH2/VSV2>1) beneath the core of Superior Craton down to around 160 km, where the higher vertical shear wave speed VSV (ξ<1) is observed beneath 160 km. Such radial anisotropy layering is also observed in the margin of continental lithosphere but with shallower depth. The radial anisotropic layer matches the receiver function results of mid-lithosphere discontinuities of the Craton cores, and the lithosphere conductivity result. The radial anisotropy layering observation confirms the two-layered lithosphere structure of the NAC, where the upper layer likely represents the original radial anisotropy fabric related to the cooling of the craton core, while the lower layer might be related to the tectonic processes more recently, e.g., accretion . The lithospheric thinning beneath the NAC margins indicates the deformation of the lithosphere and is likely controlled by the large-scale mantle convection, therefore relates to the further modification process of the NAC.
How to cite: Zhou, T., Chen, M., Xi, Z., and Li, J.: Lithospheric structure of the North American Craton constrained by full waveform inversion, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14319, https://doi.org/10.5194/egusphere-egu21-14319, 2021.
EGU21-13665 | vPICO presentations | SM5.1
Imaging the East Asia using waveform tomography with massive datasetsHui Dou, Sergei Lebedev, Bruna Chagas de Melo, Baoshan Wang, and Weitao Wang
We present a new shear-wave velocity model of the upper mantle beneath the East Asia, ASIA2021, derived using the Automatic Multimode Inversion technique. We use waveform fits of over 1.3 million seismograms, comprising waveforms of surface waves, S and multiple S waves. In total, data from 9351 stations and 23344 events constrain ASIA2021, which maps in detail the structure of the lithosphere and underlying mantle beneath the region. Our model reveals deep structure beneath the tectonic units that make up East Asia. It shows agreement with previous models at larger scales and, also, sharper and stronger velocity anomalies at smaller regional scales. High-velocity continent roots are mapped in detail beneath the Sichuan Basin, Tarim Basin, Ordos Block, and Siberian Craton, extending to over 200 km depths. The lack of a high-velocity continental root beneath the Eastern North China Craton (ENCC), underlain, instead, by a low-velocity anomaly, is consistent with the destruction of this Archean nucleus. Strong low-velocity anomalies are mapped within the top 100 km beneath Tibet, Pamir, Altay-Sayan area, and back-arc basins. At greater depths, ASIA2021 shows high-velocity anomalies related to the subducted and underthrusted lithosphere of India beneath Tibet and the subduction of the Pacific and other plates in the upper mantle. In the mantle transition zone (MTZ), we find high-velocity anomalies probably related to deflected subducted slabs or detached portions of ancient continent cratons. In particularly, ASIA2021 reveals separate bodies, probably originating from the Indian Plate lithosphere beneath central Tibet, with one at 100-200 km beneath Songpan-Ganzi Block (SGFB) and the other in the MTZ. A strong low-velocity anomaly extending from the surface to the lower mantle beneath Hainan volcano and South China Sea is consistent with the hypothesis of the Hainan mantle plume. The high-velocity anomaly beneath ENCC in MTZ can be interpreted as a detached Archean continent root. The Pacific Plate subducts beneath the eastern margin of Asia into the MTZ and appears to deflect and extend horizontally as far west as the Songliao Basin. The absence of major gaps in the stagnant slab is consistent with the origin of Changbaishan volcano above being related to the Big Mantle Wedge, proposed previously. The low-velocity anomalies down to ~ 700 km depth beneath the Lake Baikal area suggest a hot upwelling (mantle plume) feeding the widely distributed Cenozoic volcanoes in central and western Mongolia.
How to cite: Dou, H., Lebedev, S., Chagas de Melo, B., Wang, B., and Wang, W.: Imaging the East Asia using waveform tomography with massive datasets , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13665, https://doi.org/10.5194/egusphere-egu21-13665, 2021.
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We present a new shear-wave velocity model of the upper mantle beneath the East Asia, ASIA2021, derived using the Automatic Multimode Inversion technique. We use waveform fits of over 1.3 million seismograms, comprising waveforms of surface waves, S and multiple S waves. In total, data from 9351 stations and 23344 events constrain ASIA2021, which maps in detail the structure of the lithosphere and underlying mantle beneath the region. Our model reveals deep structure beneath the tectonic units that make up East Asia. It shows agreement with previous models at larger scales and, also, sharper and stronger velocity anomalies at smaller regional scales. High-velocity continent roots are mapped in detail beneath the Sichuan Basin, Tarim Basin, Ordos Block, and Siberian Craton, extending to over 200 km depths. The lack of a high-velocity continental root beneath the Eastern North China Craton (ENCC), underlain, instead, by a low-velocity anomaly, is consistent with the destruction of this Archean nucleus. Strong low-velocity anomalies are mapped within the top 100 km beneath Tibet, Pamir, Altay-Sayan area, and back-arc basins. At greater depths, ASIA2021 shows high-velocity anomalies related to the subducted and underthrusted lithosphere of India beneath Tibet and the subduction of the Pacific and other plates in the upper mantle. In the mantle transition zone (MTZ), we find high-velocity anomalies probably related to deflected subducted slabs or detached portions of ancient continent cratons. In particularly, ASIA2021 reveals separate bodies, probably originating from the Indian Plate lithosphere beneath central Tibet, with one at 100-200 km beneath Songpan-Ganzi Block (SGFB) and the other in the MTZ. A strong low-velocity anomaly extending from the surface to the lower mantle beneath Hainan volcano and South China Sea is consistent with the hypothesis of the Hainan mantle plume. The high-velocity anomaly beneath ENCC in MTZ can be interpreted as a detached Archean continent root. The Pacific Plate subducts beneath the eastern margin of Asia into the MTZ and appears to deflect and extend horizontally as far west as the Songliao Basin. The absence of major gaps in the stagnant slab is consistent with the origin of Changbaishan volcano above being related to the Big Mantle Wedge, proposed previously. The low-velocity anomalies down to ~ 700 km depth beneath the Lake Baikal area suggest a hot upwelling (mantle plume) feeding the widely distributed Cenozoic volcanoes in central and western Mongolia.
How to cite: Dou, H., Lebedev, S., Chagas de Melo, B., Wang, B., and Wang, W.: Imaging the East Asia using waveform tomography with massive datasets , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13665, https://doi.org/10.5194/egusphere-egu21-13665, 2021.
EGU21-1586 | vPICO presentations | SM5.1
Towards 3D Multiscale Adjoint Waveform Tomography of the Lithosphere and Underlying Mantle beneath Southeast AsiaDeborah Wehner, Nienke Blom, Nicholas Rawlinson, Meghan Miller, Sri Widiyantoro, and Mr Daryono
Southeast Asia is one of the most complex tectonic regions on Earth. This is mainly a result of its location within the triple junction of the Australian, Eurasian and Philippine Sea plates which has created a complicated configuration of active plate tectonic boundaries. Adjoint waveform tomography is especially suitable for imaging such complex regions. By simulating the 3D wavefield, it is possible to directly compare observed and simulated seismograms, thereby taking into account both body and surface waves. The method can account for the effects of anisotropy, anelasticity, wavefront healing, interference and (de)focusing that can hamper other seismological methods.
To date, sparse instrument coverage in the region has contributed to a heterogeneous path coverage. In this project, we make use of publicly available data as well as our recently deployed networks of broadband seismometers on Borneo and Sulawesi. This, in addition to access to national permanent networks, provides data from over 300 stations which promises a significant improvement in data coverage around the Banda Arc, Borneo and Sulawesi. We employ a geographical weighting scheme to minimise the effect of dense regional arrays and compile a catalogue of 118 well-constrained earthquakes, optimising for coverage, signal-to-noise ratio and data availability. An optimised window selection algorithm allows us to balance amplitude differences and include as much signal as possible while avoiding noisy data.
Here, we present a seismic waveform tomography for upper mantle structure in Southeast Asia, imaging radially anisotropic S velocity, P velocity and density. We use a gradient-based optimisation scheme (L-BFGS) and adjoint methods to obtain sensitivity kernels as the corresponding gradients. In the first part of the inversion, periods down to 50 s are used to update a 1D initial model, adapting a multi-scale approach in which long periods are inverted for first to avoid cycle skipping. In our long-period results, we observe a strong regional low S-velocity structure with an underlying high-velocity anomaly. The results are consistent with the global S40RTS model.
How to cite: Wehner, D., Blom, N., Rawlinson, N., Miller, M., Widiyantoro, S., and Daryono, M.: Towards 3D Multiscale Adjoint Waveform Tomography of the Lithosphere and Underlying Mantle beneath Southeast Asia, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1586, https://doi.org/10.5194/egusphere-egu21-1586, 2021.
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Southeast Asia is one of the most complex tectonic regions on Earth. This is mainly a result of its location within the triple junction of the Australian, Eurasian and Philippine Sea plates which has created a complicated configuration of active plate tectonic boundaries. Adjoint waveform tomography is especially suitable for imaging such complex regions. By simulating the 3D wavefield, it is possible to directly compare observed and simulated seismograms, thereby taking into account both body and surface waves. The method can account for the effects of anisotropy, anelasticity, wavefront healing, interference and (de)focusing that can hamper other seismological methods.
To date, sparse instrument coverage in the region has contributed to a heterogeneous path coverage. In this project, we make use of publicly available data as well as our recently deployed networks of broadband seismometers on Borneo and Sulawesi. This, in addition to access to national permanent networks, provides data from over 300 stations which promises a significant improvement in data coverage around the Banda Arc, Borneo and Sulawesi. We employ a geographical weighting scheme to minimise the effect of dense regional arrays and compile a catalogue of 118 well-constrained earthquakes, optimising for coverage, signal-to-noise ratio and data availability. An optimised window selection algorithm allows us to balance amplitude differences and include as much signal as possible while avoiding noisy data.
Here, we present a seismic waveform tomography for upper mantle structure in Southeast Asia, imaging radially anisotropic S velocity, P velocity and density. We use a gradient-based optimisation scheme (L-BFGS) and adjoint methods to obtain sensitivity kernels as the corresponding gradients. In the first part of the inversion, periods down to 50 s are used to update a 1D initial model, adapting a multi-scale approach in which long periods are inverted for first to avoid cycle skipping. In our long-period results, we observe a strong regional low S-velocity structure with an underlying high-velocity anomaly. The results are consistent with the global S40RTS model.
How to cite: Wehner, D., Blom, N., Rawlinson, N., Miller, M., Widiyantoro, S., and Daryono, M.: Towards 3D Multiscale Adjoint Waveform Tomography of the Lithosphere and Underlying Mantle beneath Southeast Asia, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1586, https://doi.org/10.5194/egusphere-egu21-1586, 2021.
EGU21-5272 | vPICO presentations | SM5.1
The Australian Plate and underlying mantle from waveform tomography with massive datasetsJanneke de Laat, Sergei Lebedev, Bruna Chagas de Melo, Nicolas Celli, and Raffaele Bonadio
We present a new S-wave velocity tomographic model of the Australian Plate, Aus21. It is constrained by waveforms of 0.9 million seismograms with both the corresponding sources and stations located within the half-hemisphere centred at the Australian continent. Waveform inversion extracts structural information from surface, S- and multiple S-waves on the seismograms in the form of a set of linear equations. These equations are then combined in a large linear system and inverted jointly to obtain a tomographic model of S- and P-wave speeds and S-wave azimuthal anisotropy of the crust and upper mantle. The model has been validated by resolution tests and, for particular locations in Australia with notable differences with previous models, by independent inter-station measurements of surface-wave phase velocities, which we performed using available array data.
Aus21 offers new insights into the structure and evolution of the Australian Plate and its boundaries. The Australian cratonic lithosphere occupies nearly all of the western and central Australia but shows substantial lateral heterogeneity. It extends up to the northern edge of the plate, where it is colliding with island arcs, without subducting. The rugged eastern boundary of the cratonic lithosphere provides a lithospheric definition of the Tasman Line. The thin, warm lithosphere below the eastern part of the continent, east of the Tasman Line, underlies the Cenozoic volcanism locations in the area. The lithosphere is also thin and warm below much of the Tasman Sea, underlying the Lord Howe hotspot and the submerged part of western Zealandia. A low velocity anomaly that may indicate the single source of the Lord Howe and Tasmanid hotspots is observed in the transition zone offshore the Australian continent, possibly also sourcing the East Australia hotspot. Another potential hotspot source is identified below the Kermadec Trench, causing an apparent slab gap in the overlying slab and possibly related to the Samoa Hotspot to the north. Below a portion of the South East Indian Ridge (the southern boundary of the Australian Plate) a pronounced high velocity anomaly is present in the 200-400 km depth range just east of the Australian-Antarctic Discordance (AAD), probably linked to the evolution of this chaotic ridge system.
How to cite: de Laat, J., Lebedev, S., Chagas de Melo, B., Celli, N., and Bonadio, R.: The Australian Plate and underlying mantle from waveform tomography with massive datasets , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5272, https://doi.org/10.5194/egusphere-egu21-5272, 2021.
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We present a new S-wave velocity tomographic model of the Australian Plate, Aus21. It is constrained by waveforms of 0.9 million seismograms with both the corresponding sources and stations located within the half-hemisphere centred at the Australian continent. Waveform inversion extracts structural information from surface, S- and multiple S-waves on the seismograms in the form of a set of linear equations. These equations are then combined in a large linear system and inverted jointly to obtain a tomographic model of S- and P-wave speeds and S-wave azimuthal anisotropy of the crust and upper mantle. The model has been validated by resolution tests and, for particular locations in Australia with notable differences with previous models, by independent inter-station measurements of surface-wave phase velocities, which we performed using available array data.
Aus21 offers new insights into the structure and evolution of the Australian Plate and its boundaries. The Australian cratonic lithosphere occupies nearly all of the western and central Australia but shows substantial lateral heterogeneity. It extends up to the northern edge of the plate, where it is colliding with island arcs, without subducting. The rugged eastern boundary of the cratonic lithosphere provides a lithospheric definition of the Tasman Line. The thin, warm lithosphere below the eastern part of the continent, east of the Tasman Line, underlies the Cenozoic volcanism locations in the area. The lithosphere is also thin and warm below much of the Tasman Sea, underlying the Lord Howe hotspot and the submerged part of western Zealandia. A low velocity anomaly that may indicate the single source of the Lord Howe and Tasmanid hotspots is observed in the transition zone offshore the Australian continent, possibly also sourcing the East Australia hotspot. Another potential hotspot source is identified below the Kermadec Trench, causing an apparent slab gap in the overlying slab and possibly related to the Samoa Hotspot to the north. Below a portion of the South East Indian Ridge (the southern boundary of the Australian Plate) a pronounced high velocity anomaly is present in the 200-400 km depth range just east of the Australian-Antarctic Discordance (AAD), probably linked to the evolution of this chaotic ridge system.
How to cite: de Laat, J., Lebedev, S., Chagas de Melo, B., Celli, N., and Bonadio, R.: The Australian Plate and underlying mantle from waveform tomography with massive datasets , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5272, https://doi.org/10.5194/egusphere-egu21-5272, 2021.
EGU21-1186 | vPICO presentations | SM5.1
Crustal structure of Khorasan (E-NE Iran) using the Rayleigh wave tomographyMaryam Rezaei and Taghi Shirzad
Classical surface wave tomography based on waveform scattering through seismic data has an important role in studying the structure of the Earth‘s crust and upper mantle on regional and global scale. The shallow crustal velocity structure is studied using earthquake waveforms in Khorasan/E-NE Iran. For this purpose, 522 local recorded waveforms with M≥4, which occurred between 53°-63°E and 30°-42°N, were selected. Therefore, all available vertical components of waveforms recorded at the stations in the Iranian Seismological Center (IrSC), the International Institute of Earthquake Engineering and Seismology (IIEES), and the IRIS global network collected in the period between January 2006 to October 2020. Then, some data selection criteria were applied for each waveform, including (i)SNR>4, (ii) the gap time less than 2 s within the expected signal window (1.5-4.5 km/s), (iii) epicentral distance greater than 20 km. The multiple-filter analysis technique was then applied by the computer program in seismology Hermann and Ammon (2013) to measure Rayleigh wave dispersion curves in the period range of 3-50 s. Finally, Rayleigh wave 2D horizontal group velocity maps are calculated by the fast marching surface wave tomography method. Our tomographic results indicate some local low velocity anomalies appeared in the W-NW of the study area where it connected with the East-Alborz tectonic structure. Also, the Doruneh Fault System clearly separates Kopeh-Dagh tectonic zone and Central Iran micro-plateau. However, a high velocity anomaly appears in Kopeh-Dagh tectonic zone at periods larger than 16 s and 30 s.
How to cite: Rezaei, M. and Shirzad, T.: Crustal structure of Khorasan (E-NE Iran) using the Rayleigh wave tomography, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1186, https://doi.org/10.5194/egusphere-egu21-1186, 2021.
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Classical surface wave tomography based on waveform scattering through seismic data has an important role in studying the structure of the Earth‘s crust and upper mantle on regional and global scale. The shallow crustal velocity structure is studied using earthquake waveforms in Khorasan/E-NE Iran. For this purpose, 522 local recorded waveforms with M≥4, which occurred between 53°-63°E and 30°-42°N, were selected. Therefore, all available vertical components of waveforms recorded at the stations in the Iranian Seismological Center (IrSC), the International Institute of Earthquake Engineering and Seismology (IIEES), and the IRIS global network collected in the period between January 2006 to October 2020. Then, some data selection criteria were applied for each waveform, including (i)SNR>4, (ii) the gap time less than 2 s within the expected signal window (1.5-4.5 km/s), (iii) epicentral distance greater than 20 km. The multiple-filter analysis technique was then applied by the computer program in seismology Hermann and Ammon (2013) to measure Rayleigh wave dispersion curves in the period range of 3-50 s. Finally, Rayleigh wave 2D horizontal group velocity maps are calculated by the fast marching surface wave tomography method. Our tomographic results indicate some local low velocity anomalies appeared in the W-NW of the study area where it connected with the East-Alborz tectonic structure. Also, the Doruneh Fault System clearly separates Kopeh-Dagh tectonic zone and Central Iran micro-plateau. However, a high velocity anomaly appears in Kopeh-Dagh tectonic zone at periods larger than 16 s and 30 s.
How to cite: Rezaei, M. and Shirzad, T.: Crustal structure of Khorasan (E-NE Iran) using the Rayleigh wave tomography, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1186, https://doi.org/10.5194/egusphere-egu21-1186, 2021.
EGU21-5381 | vPICO presentations | SM5.1
Imaging the temperature beneath Ireland and Britain using massive, broadband surface-wave datasets and petrological inversionEmma L. Chambers, Raffaele Bonadio, Sergei Lebedev, Javier Fullea, Duygu Kiyan, Christopher Bean, Brian O'Reilly, and Patrick Meere
Deep geothermal resources in low- to medium-temperature settings remain poorly understood and untapped in Ireland and much of Europe. Our new project DIG (De-risking Ireland’s Geothermal Potential) integrates multi-disciplinary, multi-scale datasets in order to investigate Ireland’s low-enthalpy geothermal energy potential. Seismic measurements constrain the distributions of seismic velocities and, through them, the composition and temperature within the lithosphere and underlying mantle. Recent deployments of broadband seismic stations and the surface-wave measurements using the new data yield an unprecedentedly dense data sampling of the crust and upper mantle beneath Ireland and neighbouring Britain. These data form a foundation for the region-scale, multi-parameter modelling of the thermal state of the lithosphere.
We use the recently assembled dataset of over 11,000 Rayleigh-wave, phase-velocity curves, measured for pairs of stations across Ireland and Britain (Bonadio et al. 2021) and complement it with new interstation measurements of Love-wave phase velocities. The measurements were performed using two methods with complementary period ranges, the teleseismic cross-correlation method and waveform inversion. Spanning a very broad period range (from as short as 4 s to as long as 500 s), the phase velocities provide resolution from the upper-middle crust to the asthenosphere. The joint analysis of Rayleigh and Love measurements constrains the isotropic-average shear-wave velocity, relatable to temperature and composition. The optimal-resolution, phase-velocity maps of Bonadio et al. (2021) for Rayleigh waves and the new maps for Love waves computed in this study provide essential constraints on the thermal structure of the region’s lithosphere. We demonstrate this by inverting the data using an integrated geophysical-petrological thermodynamically self-consistent approach (Fullea et al., 2021). The multi-parameter models produced by the integrated inversions fit the surface-wave and surface-elevation data and reveal the temperatures and geothermal gradients within the crust.
Bonadio, R., Lebedev, S., Meier, T., Arroucau, P., Schaeffer, A. J., Licciardi, A., Agius, M. R., Horan, C., Collins, L., O'Reilly, B. M., Readman, P. and the Ireland Array Working Group (2021). Optimal resolution tomography with error tracking: imaging the upper mantle beneath Ireland and Britain. Geophys. J. Int., in revision.
Fullea, J., Lebedev, S., Martinec, Z., & Celli, N. L. (2021). WINTERC-G: mapping the upper mantle thermochemical heterogeneity from coupled geophysical-petrological inversion of seismic waveforms, heat flow, surface elevation and gravity satellite data. Geophys. J. Int., revised version under evaluation.
How to cite: Chambers, E. L., Bonadio, R., Lebedev, S., Fullea, J., Kiyan, D., Bean, C., O'Reilly, B., and Meere, P.: Imaging the temperature beneath Ireland and Britain using massive, broadband surface-wave datasets and petrological inversion, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5381, https://doi.org/10.5194/egusphere-egu21-5381, 2021.
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Deep geothermal resources in low- to medium-temperature settings remain poorly understood and untapped in Ireland and much of Europe. Our new project DIG (De-risking Ireland’s Geothermal Potential) integrates multi-disciplinary, multi-scale datasets in order to investigate Ireland’s low-enthalpy geothermal energy potential. Seismic measurements constrain the distributions of seismic velocities and, through them, the composition and temperature within the lithosphere and underlying mantle. Recent deployments of broadband seismic stations and the surface-wave measurements using the new data yield an unprecedentedly dense data sampling of the crust and upper mantle beneath Ireland and neighbouring Britain. These data form a foundation for the region-scale, multi-parameter modelling of the thermal state of the lithosphere.
We use the recently assembled dataset of over 11,000 Rayleigh-wave, phase-velocity curves, measured for pairs of stations across Ireland and Britain (Bonadio et al. 2021) and complement it with new interstation measurements of Love-wave phase velocities. The measurements were performed using two methods with complementary period ranges, the teleseismic cross-correlation method and waveform inversion. Spanning a very broad period range (from as short as 4 s to as long as 500 s), the phase velocities provide resolution from the upper-middle crust to the asthenosphere. The joint analysis of Rayleigh and Love measurements constrains the isotropic-average shear-wave velocity, relatable to temperature and composition. The optimal-resolution, phase-velocity maps of Bonadio et al. (2021) for Rayleigh waves and the new maps for Love waves computed in this study provide essential constraints on the thermal structure of the region’s lithosphere. We demonstrate this by inverting the data using an integrated geophysical-petrological thermodynamically self-consistent approach (Fullea et al., 2021). The multi-parameter models produced by the integrated inversions fit the surface-wave and surface-elevation data and reveal the temperatures and geothermal gradients within the crust.
Bonadio, R., Lebedev, S., Meier, T., Arroucau, P., Schaeffer, A. J., Licciardi, A., Agius, M. R., Horan, C., Collins, L., O'Reilly, B. M., Readman, P. and the Ireland Array Working Group (2021). Optimal resolution tomography with error tracking: imaging the upper mantle beneath Ireland and Britain. Geophys. J. Int., in revision.
Fullea, J., Lebedev, S., Martinec, Z., & Celli, N. L. (2021). WINTERC-G: mapping the upper mantle thermochemical heterogeneity from coupled geophysical-petrological inversion of seismic waveforms, heat flow, surface elevation and gravity satellite data. Geophys. J. Int., revised version under evaluation.
How to cite: Chambers, E. L., Bonadio, R., Lebedev, S., Fullea, J., Kiyan, D., Bean, C., O'Reilly, B., and Meere, P.: Imaging the temperature beneath Ireland and Britain using massive, broadband surface-wave datasets and petrological inversion, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5381, https://doi.org/10.5194/egusphere-egu21-5381, 2021.
EGU21-6456 | vPICO presentations | SM5.1
Thermochemical structure of the lithosphere and upper mantle beneath Superior craton: Results from multi-observable probabilistic inversionRiddhi Dave, Fiona Ann Darbyshire, Juan Carlos Afonso, and Khaled Ali
We present new thermochemical models of the lithosphere and upper mantle beneath the Superior craton and surrounding regions. The study area is dominated by the Archean Superior Province, surrounded by Proterozoic orogenic belts such as the Trans-Hudson Orogen (THO) to the north and the Grenville Orogen to the southeast. Portions of the Rae and Hearne cratons north of the THO are also studied, as is the Mid-continent Rift to the south. Over a period of ∼3 Ga, the region has seen assembly and modification by accretionary and orogenic events, periods of rifting, and the influence of a number of mantle hotspots. Here, we use a probabilistic inverse method to jointly invert Rayleigh wave dispersion data, Vp data, geoid anomalies, surface heat flow, and absolute elevation. The output is a 3D model of the seismic, temperature, bulk density, and compositional structure of the whole lithosphere beneath the Superior craton.
The resulting model will provide new opportunities for joint studies of the structure of the upper mantle and will shed light on the thermal and compositional variations beneath the region. In this presentation, we will discuss the results from our model and several robust features that carry important geological and geodynamical implications for this region.
How to cite: Dave, R., Darbyshire, F. A., Afonso, J. C., and Ali, K.: Thermochemical structure of the lithosphere and upper mantle beneath Superior craton: Results from multi-observable probabilistic inversion, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6456, https://doi.org/10.5194/egusphere-egu21-6456, 2021.
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We present new thermochemical models of the lithosphere and upper mantle beneath the Superior craton and surrounding regions. The study area is dominated by the Archean Superior Province, surrounded by Proterozoic orogenic belts such as the Trans-Hudson Orogen (THO) to the north and the Grenville Orogen to the southeast. Portions of the Rae and Hearne cratons north of the THO are also studied, as is the Mid-continent Rift to the south. Over a period of ∼3 Ga, the region has seen assembly and modification by accretionary and orogenic events, periods of rifting, and the influence of a number of mantle hotspots. Here, we use a probabilistic inverse method to jointly invert Rayleigh wave dispersion data, Vp data, geoid anomalies, surface heat flow, and absolute elevation. The output is a 3D model of the seismic, temperature, bulk density, and compositional structure of the whole lithosphere beneath the Superior craton.
The resulting model will provide new opportunities for joint studies of the structure of the upper mantle and will shed light on the thermal and compositional variations beneath the region. In this presentation, we will discuss the results from our model and several robust features that carry important geological and geodynamical implications for this region.
How to cite: Dave, R., Darbyshire, F. A., Afonso, J. C., and Ali, K.: Thermochemical structure of the lithosphere and upper mantle beneath Superior craton: Results from multi-observable probabilistic inversion, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6456, https://doi.org/10.5194/egusphere-egu21-6456, 2021.
EGU21-7553 | vPICO presentations | SM5.1
3-D Heterogeneous Elastic Crustal Structure for Deformation Models in the Hengill Area, SW IcelandCécile Ducrocq, Halldór Geirsson, Alex Hobé, Gylfi Páll Hersir, Thóra Árnadóttir, Freysteinn Sigmundsson, Ari Tryggvason, and Vincent Drouin
Crustal deformation in volcanic areas relates ground motions, measured by geodetic techniques, to physical (e.g. pressure or volumetric) changes of magmatic sources below the surface. These measurements contribute to studies of ongoing processes at the source of possible unrest, and are thus key for hazard assessment in active volcanic areas around the globe. However, such assessments often rely on geodetic-based models with quite simplistic assumptions of the physical structure of the volcanic complex. Particularly, constant values of elastic parameters (e.g. Poisson’s ratio and shear moduli) are commonly used for entire active volcanic areas, thus overlooking the spatial effects of lithological properties, depth-dependant compression and temperature variations on those parameters. These simplifications may lead to inaccurate interpretation of the location, shape, and volume change of deformation sources.
In this study we ask how the 3-D heterogeneities of the elastic crustal structure beneath the Hengill volcanic system, SW Iceland, affects models of deformation sources in the area. The Hengill area hosts two active volcanic systems (Hengill and Hrómundartindur), and two high-enthalpy geothermal power plants (Nesjavellir and Hellisheiði), which provide thermal and electrical power to Reykjavík, the capital of Iceland, only 30 km away. To retrieve information on the spatial heterogeneities in the shear moduli and Poisson’s ratio beneath the Hengill area, we first estimate the 3-D shallow density structure of the area using results from regional and local gravimetric surveys. We implement this structure, along with seismic tomographic studies of the SW Iceland, in a Finite Element Model to solve, using forward models, for the 3-D heterogeneities in the shear moduli and Poisson’s ratio beneath the Hengill area. Furthermore, we discuss the difference between static and kinematic elastic moduli, which is important when building deformation models from seismic tomography. The new 3-D inferred elastic model is then used to re-estimate parameters for different sources of deformation causing uplift and subsidence in the area in the past decades. This study shows the importance of accounting for heterogeneities in the crustal elastic structure to estimate with higher accuracy the sources of deformation in volcanic areas around the world.
How to cite: Ducrocq, C., Geirsson, H., Hobé, A., Hersir, G. P., Árnadóttir, T., Sigmundsson, F., Tryggvason, A., and Drouin, V.: 3-D Heterogeneous Elastic Crustal Structure for Deformation Models in the Hengill Area, SW Iceland, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7553, https://doi.org/10.5194/egusphere-egu21-7553, 2021.
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Crustal deformation in volcanic areas relates ground motions, measured by geodetic techniques, to physical (e.g. pressure or volumetric) changes of magmatic sources below the surface. These measurements contribute to studies of ongoing processes at the source of possible unrest, and are thus key for hazard assessment in active volcanic areas around the globe. However, such assessments often rely on geodetic-based models with quite simplistic assumptions of the physical structure of the volcanic complex. Particularly, constant values of elastic parameters (e.g. Poisson’s ratio and shear moduli) are commonly used for entire active volcanic areas, thus overlooking the spatial effects of lithological properties, depth-dependant compression and temperature variations on those parameters. These simplifications may lead to inaccurate interpretation of the location, shape, and volume change of deformation sources.
In this study we ask how the 3-D heterogeneities of the elastic crustal structure beneath the Hengill volcanic system, SW Iceland, affects models of deformation sources in the area. The Hengill area hosts two active volcanic systems (Hengill and Hrómundartindur), and two high-enthalpy geothermal power plants (Nesjavellir and Hellisheiði), which provide thermal and electrical power to Reykjavík, the capital of Iceland, only 30 km away. To retrieve information on the spatial heterogeneities in the shear moduli and Poisson’s ratio beneath the Hengill area, we first estimate the 3-D shallow density structure of the area using results from regional and local gravimetric surveys. We implement this structure, along with seismic tomographic studies of the SW Iceland, in a Finite Element Model to solve, using forward models, for the 3-D heterogeneities in the shear moduli and Poisson’s ratio beneath the Hengill area. Furthermore, we discuss the difference between static and kinematic elastic moduli, which is important when building deformation models from seismic tomography. The new 3-D inferred elastic model is then used to re-estimate parameters for different sources of deformation causing uplift and subsidence in the area in the past decades. This study shows the importance of accounting for heterogeneities in the crustal elastic structure to estimate with higher accuracy the sources of deformation in volcanic areas around the world.
How to cite: Ducrocq, C., Geirsson, H., Hobé, A., Hersir, G. P., Árnadóttir, T., Sigmundsson, F., Tryggvason, A., and Drouin, V.: 3-D Heterogeneous Elastic Crustal Structure for Deformation Models in the Hengill Area, SW Iceland, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7553, https://doi.org/10.5194/egusphere-egu21-7553, 2021.
EGU21-14135 | vPICO presentations | SM5.1
Extreme variability of Tibetan thermal lithosphereBing Xia, Irina Artemieva, and Hans Thybo
We present a thermal model for the lithosphere in Tibet and adjacent regions based on the new thermal isostasy method and our compilation of the Moho depth based on published seismic models. The predicted surface heat flow is in agreement with the few available, reliable borehole measurements. Cratonic-type cold and thick lithosphere (200-240 km) with a surface heat flow of 40-50 mW/m2 typifies the Tarim craton, the north-western Yangtze craton, and most of the Lhasa Block that is possibly refrigerated by underthrusting Indian lithosphere. The thick lithosphere of the Lhasa block extends further north in its western and eastern segments than in its central section. We identify a North Tibet anomaly with a thin (<80 km) lithosphere and high surface heat flow (>80-100 mW/m2), possibly associated with the removal of lithospheric mantle and asthenospheric upwelling. Other parts of Tibet have an intermediate lithosphere thickness of 120-160 km and a surface heat flow of 45-60 mW/m2, with a patchy style in eastern Tibet. In the Qaidam deep sedimentary basin the lithosphere is about 100-120 km thick. The heterogeneous thermal lithosphere beneath Tibet suggests an interplay of several mechanisms as the driver of the observed uplift.
How to cite: Xia, B., Artemieva, I., and Thybo, H.: Extreme variability of Tibetan thermal lithosphere , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14135, https://doi.org/10.5194/egusphere-egu21-14135, 2021.
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We present a thermal model for the lithosphere in Tibet and adjacent regions based on the new thermal isostasy method and our compilation of the Moho depth based on published seismic models. The predicted surface heat flow is in agreement with the few available, reliable borehole measurements. Cratonic-type cold and thick lithosphere (200-240 km) with a surface heat flow of 40-50 mW/m2 typifies the Tarim craton, the north-western Yangtze craton, and most of the Lhasa Block that is possibly refrigerated by underthrusting Indian lithosphere. The thick lithosphere of the Lhasa block extends further north in its western and eastern segments than in its central section. We identify a North Tibet anomaly with a thin (<80 km) lithosphere and high surface heat flow (>80-100 mW/m2), possibly associated with the removal of lithospheric mantle and asthenospheric upwelling. Other parts of Tibet have an intermediate lithosphere thickness of 120-160 km and a surface heat flow of 45-60 mW/m2, with a patchy style in eastern Tibet. In the Qaidam deep sedimentary basin the lithosphere is about 100-120 km thick. The heterogeneous thermal lithosphere beneath Tibet suggests an interplay of several mechanisms as the driver of the observed uplift.
How to cite: Xia, B., Artemieva, I., and Thybo, H.: Extreme variability of Tibetan thermal lithosphere , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14135, https://doi.org/10.5194/egusphere-egu21-14135, 2021.
EGU21-13988 | vPICO presentations | SM5.1
A sparsity-based adaptive filtering approach to Shear Wave SplittingHamzeh Mohammadigheymasi, Mohammad Reza Ebrahimi, Graça Silveira, and David schlaphorst
Shear wave splitting analysis is a frequently used tool to study elastic anisotropy from the lower mantle to the crust. Several methods have been developed to evaluate the splitting parameters, Φ (fast axis) and δt (delay time), including the correlation of wave components, minimization of covariance matrix eigenvalues, and minimizing energy on the transverse component. Despite massive progress in introducing sophisticated methods, still fundamental problems, related mainly to noisy data, interfering phases, length of the analyzed waveform, and stability and reliability of results, remain. This study presents a sparsity-based adaptive filtering method to magnify the SKS waveforms and suppress the unwanted noise and interfering phases. The study is an extension of Jurkevics (1988), computing the semi-minor and semi-minor axis of the polarized motion in the time-frequency domain using a regularized inversion-based approach imposing a sparsity constraint. Afterward, the elliptical particle motion caused by the split shear waves and correspond to high semi-minor amplitude is derived in the time-frequency domain. The information is used to design an adaptive filter in the time domain to amplify the SKS phase and suppress the noise and other phases having non-elliptical polarization. The regularized inversion-based approach enables obtaining a sparse time-frequency semi-minor map while handling noise problems in the time-frequency decomposition. Conducting synthetic simulations, we show that the proposed method increases the signal-to-noise ratio of the SKS phase in radial and transverse components, giving a better estimation of anisotropy parameters in the presence of noise and other interfering phases. Future work involves implementing the processing algorithm on real data recorded in São Tomé and Prı́ncipe, Madeira, and Canary islands. This research contributes to the FCT-funded SHAZAM (Ref. PTDC/CTA-GEO/31475/2017) and SIGHT (Ref. PTDC/CTA-GEF/30264/2017) projects.
How to cite: Mohammadigheymasi, H., Ebrahimi, M. R., Silveira, G., and schlaphorst, D.: A sparsity-based adaptive filtering approach to Shear Wave Splitting, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13988, https://doi.org/10.5194/egusphere-egu21-13988, 2021.
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Shear wave splitting analysis is a frequently used tool to study elastic anisotropy from the lower mantle to the crust. Several methods have been developed to evaluate the splitting parameters, Φ (fast axis) and δt (delay time), including the correlation of wave components, minimization of covariance matrix eigenvalues, and minimizing energy on the transverse component. Despite massive progress in introducing sophisticated methods, still fundamental problems, related mainly to noisy data, interfering phases, length of the analyzed waveform, and stability and reliability of results, remain. This study presents a sparsity-based adaptive filtering method to magnify the SKS waveforms and suppress the unwanted noise and interfering phases. The study is an extension of Jurkevics (1988), computing the semi-minor and semi-minor axis of the polarized motion in the time-frequency domain using a regularized inversion-based approach imposing a sparsity constraint. Afterward, the elliptical particle motion caused by the split shear waves and correspond to high semi-minor amplitude is derived in the time-frequency domain. The information is used to design an adaptive filter in the time domain to amplify the SKS phase and suppress the noise and other phases having non-elliptical polarization. The regularized inversion-based approach enables obtaining a sparse time-frequency semi-minor map while handling noise problems in the time-frequency decomposition. Conducting synthetic simulations, we show that the proposed method increases the signal-to-noise ratio of the SKS phase in radial and transverse components, giving a better estimation of anisotropy parameters in the presence of noise and other interfering phases. Future work involves implementing the processing algorithm on real data recorded in São Tomé and Prı́ncipe, Madeira, and Canary islands. This research contributes to the FCT-funded SHAZAM (Ref. PTDC/CTA-GEO/31475/2017) and SIGHT (Ref. PTDC/CTA-GEF/30264/2017) projects.
How to cite: Mohammadigheymasi, H., Ebrahimi, M. R., Silveira, G., and schlaphorst, D.: A sparsity-based adaptive filtering approach to Shear Wave Splitting, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13988, https://doi.org/10.5194/egusphere-egu21-13988, 2021.
SM5.2 – Advances in geophysical imaging of near-surface structures and processes
EGU21-3508 | vPICO presentations | SM5.2
Closing a scale-gap in Earth observation using regional-scale airborne geophysics in the lower Mississippi ValleyBurke Minsley, James Rigby, Stephanie James, Bethany Burton, Katherine Knierim, Michael Pace, Paul Bedrosian, and Wade Kress
Critical groundwater resources and hidden seismic hazards underly much of the Mississippi Alluvial Plain. Spanning nearly 100,000 square kilometers across seven states, this region hosts one of the most prolific shallow aquifer systems in the United States that supports a $12 billion agricultural economy amidst chronic groundwater decline. Further, underlying fault structures of the Reelfoot Rift and New Madrid Seismic Zone represent an important and poorly understood hazard with a complex pattern of historical impacts. Despite its societal and economic importance, mapping of shallow subsurface architecture with spatial resolution needed for effective management is insufficient. Here, we report the results of 40,000 flight-line-kilometers of electromagnetic, magnetic, and radiometric data collectively providing a system-scale snapshot of an entire aquifer system, the first such effort in the United States. This survey enables new understanding of the regional hydrogeology while also revealing previously unseen large vertical displacements (exceeding 50 m) in the uppermost Tertiary units within the New Madrid Seismic Zone.
How to cite: Minsley, B., Rigby, J., James, S., Burton, B., Knierim, K., Pace, M., Bedrosian, P., and Kress, W.: Closing a scale-gap in Earth observation using regional-scale airborne geophysics in the lower Mississippi Valley, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3508, https://doi.org/10.5194/egusphere-egu21-3508, 2021.
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Critical groundwater resources and hidden seismic hazards underly much of the Mississippi Alluvial Plain. Spanning nearly 100,000 square kilometers across seven states, this region hosts one of the most prolific shallow aquifer systems in the United States that supports a $12 billion agricultural economy amidst chronic groundwater decline. Further, underlying fault structures of the Reelfoot Rift and New Madrid Seismic Zone represent an important and poorly understood hazard with a complex pattern of historical impacts. Despite its societal and economic importance, mapping of shallow subsurface architecture with spatial resolution needed for effective management is insufficient. Here, we report the results of 40,000 flight-line-kilometers of electromagnetic, magnetic, and radiometric data collectively providing a system-scale snapshot of an entire aquifer system, the first such effort in the United States. This survey enables new understanding of the regional hydrogeology while also revealing previously unseen large vertical displacements (exceeding 50 m) in the uppermost Tertiary units within the New Madrid Seismic Zone.
How to cite: Minsley, B., Rigby, J., James, S., Burton, B., Knierim, K., Pace, M., Bedrosian, P., and Kress, W.: Closing a scale-gap in Earth observation using regional-scale airborne geophysics in the lower Mississippi Valley, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3508, https://doi.org/10.5194/egusphere-egu21-3508, 2021.
EGU21-7372 | vPICO presentations | SM5.2
A multi-scale ground and drone-borne magnetic survey approach for the detection and investigation of archaeological structuresBruno Gavazzi, Hugo Reiller, Marc Munschy, Gilles Pierrevelcin, Florian Basoge, Jeanne Mercier de Lépinay, and Tristan Fréville
Ground magnetic surveys are commonly used for imaging near-surface structures in archaeological studies. Usually, surveys are conducted using vertical component gradiometers or scalar gradiometers to produce a vertical pseudo-gradient map. Scalar magnetometers can also be used, albeit less frequently, to produce maps of the total magnetic anomaly. In all these cases, the equipment is pushed or pulled by an operator or carried behind a vehicle. Here we present a third approach made available by the use of three-component fluxgate magnetometers: fast surveys over large areas using a compact lightweight drone flying automatically 1 to 2 m above the ground and high precision surveys acquired by an operator 0,2 to 1 m above the ground. A case study on the gallo-roman site of Oedenburg, located along the Rhine River in its upper valley, illustrates the results that can be obtained with the approach. A comparison with previously acquired pseudo-gradient surveys shows that the presented method allows a faster coverage, a greater resolution for the imaging of short wavelength structures (such as walls) and a better capacity of imaging large wavelength structures (such as pathways, palaeochannels or soil composition variations). As the site is crossed by a high voltage electric power line, a method to suppress the high-amplitude 50 Hz frequency magnetic field is presented.
How to cite: Gavazzi, B., Reiller, H., Munschy, M., Pierrevelcin, G., Basoge, F., Mercier de Lépinay, J., and Fréville, T.: A multi-scale ground and drone-borne magnetic survey approach for the detection and investigation of archaeological structures, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7372, https://doi.org/10.5194/egusphere-egu21-7372, 2021.
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Ground magnetic surveys are commonly used for imaging near-surface structures in archaeological studies. Usually, surveys are conducted using vertical component gradiometers or scalar gradiometers to produce a vertical pseudo-gradient map. Scalar magnetometers can also be used, albeit less frequently, to produce maps of the total magnetic anomaly. In all these cases, the equipment is pushed or pulled by an operator or carried behind a vehicle. Here we present a third approach made available by the use of three-component fluxgate magnetometers: fast surveys over large areas using a compact lightweight drone flying automatically 1 to 2 m above the ground and high precision surveys acquired by an operator 0,2 to 1 m above the ground. A case study on the gallo-roman site of Oedenburg, located along the Rhine River in its upper valley, illustrates the results that can be obtained with the approach. A comparison with previously acquired pseudo-gradient surveys shows that the presented method allows a faster coverage, a greater resolution for the imaging of short wavelength structures (such as walls) and a better capacity of imaging large wavelength structures (such as pathways, palaeochannels or soil composition variations). As the site is crossed by a high voltage electric power line, a method to suppress the high-amplitude 50 Hz frequency magnetic field is presented.
How to cite: Gavazzi, B., Reiller, H., Munschy, M., Pierrevelcin, G., Basoge, F., Mercier de Lépinay, J., and Fréville, T.: A multi-scale ground and drone-borne magnetic survey approach for the detection and investigation of archaeological structures, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7372, https://doi.org/10.5194/egusphere-egu21-7372, 2021.
EGU21-15788 | vPICO presentations | SM5.2
Using uncrewed aerial vehicles for wider coverage for geophysical observationsJouni Envall and Eija Tanskanen
Sodankylä Geophysical Observatory (SGO) has conducted research and provided high quality data series for numerous geophysical disciplines for more than a hundred years. As the next step in developing SGO’s measurement network, we are developing capabilities to operate uncrewed aerial vehicles (UAV’s), which can be equipped with a wide variety of geophysical measurement instruments, such as magnetometers, radars or imaging devices. During the first phase we will build a fleet of multirotor drones with variable characteristics. Any individual aircraft can be optimized for e.g. covering wide areas, covering high altitudes, or lifting heavy instrument payloads. In the next phase the coverage of the measurements will be further expanded by use of fixed-wing aircraft, helium balloons and rockets. In this presentation we will give an overview of the current status of the aircraft and supporting instrumentation. Also, future plans and objectives are discussed.
How to cite: Envall, J. and Tanskanen, E.: Using uncrewed aerial vehicles for wider coverage for geophysical observations, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15788, https://doi.org/10.5194/egusphere-egu21-15788, 2021.
Sodankylä Geophysical Observatory (SGO) has conducted research and provided high quality data series for numerous geophysical disciplines for more than a hundred years. As the next step in developing SGO’s measurement network, we are developing capabilities to operate uncrewed aerial vehicles (UAV’s), which can be equipped with a wide variety of geophysical measurement instruments, such as magnetometers, radars or imaging devices. During the first phase we will build a fleet of multirotor drones with variable characteristics. Any individual aircraft can be optimized for e.g. covering wide areas, covering high altitudes, or lifting heavy instrument payloads. In the next phase the coverage of the measurements will be further expanded by use of fixed-wing aircraft, helium balloons and rockets. In this presentation we will give an overview of the current status of the aircraft and supporting instrumentation. Also, future plans and objectives are discussed.
How to cite: Envall, J. and Tanskanen, E.: Using uncrewed aerial vehicles for wider coverage for geophysical observations, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15788, https://doi.org/10.5194/egusphere-egu21-15788, 2021.
EGU21-9857 | vPICO presentations | SM5.2
The potential of Self-Organising maps clustering to characterise a harvested peatland using airborne radiometric data and OS digital elevation model.Eve daly and David O Leary
Peatlands are becoming recognized as important carbon sequestration centres. Through restoration projects of peatlands in which the water table is raised, they may become carbon neutral or possibly carbon negative. Restoration projects require a knowledge of intra-peat variation across potentially large spatial areas. This is often difficult with traditional in-situ point measurements. The integration of multidimensional geophysical datasets and digital elevation models, combined with modern data analytical techniques, may provide a rapid means of accessing intra-peat variation. In this study, an airborne radiometric survey, being flown nationally over the Republic of Ireland, combined with a digital elevation model, is used to delineate areas within an industrial peatland where peat thickness is less than 1m. Radiometric data are particularly suited to peat studies as they are sensitive to water content and peat thickness and require relatively little expert knowledge to utilise. Peat, as a mostly organic material, acts as a low signal environment where variations in the signal are linked to intra-peat variation of thickness, density and/or water content. This study uses an unsupervised machine learning, self-organizing map clustering methodology to group the study site into three zones interpreted as 1) the edge of the bog where peat layer is thinning or there is influence on the radiometric signal from non-peat soils outside of the bog, 2) the normal peat conditions where thickness and saturation appear as a relative constant in the radiometric response, and 3) areas where the peat is either thinner or drier. A ground geophysical survey was conducted to verify this interpretation. The delineation of such spatial variations in the radiometric response could aid any restoration project in the initial stages or act as a baseline study to monitor changes to the peatland during and after a restoration project is complete. Future work will see this methodology extended to other peatland types such as blanket bogs and natural raised bogs, as well as the integration of concurrent airborne electromagnetic data to link the near-surface radiometric response to the deeper vadose zone and define a more comprehensive classification scheme for these peatland sites.
How to cite: daly, E. and O Leary, D.: The potential of Self-Organising maps clustering to characterise a harvested peatland using airborne radiometric data and OS digital elevation model., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9857, https://doi.org/10.5194/egusphere-egu21-9857, 2021.
Peatlands are becoming recognized as important carbon sequestration centres. Through restoration projects of peatlands in which the water table is raised, they may become carbon neutral or possibly carbon negative. Restoration projects require a knowledge of intra-peat variation across potentially large spatial areas. This is often difficult with traditional in-situ point measurements. The integration of multidimensional geophysical datasets and digital elevation models, combined with modern data analytical techniques, may provide a rapid means of accessing intra-peat variation. In this study, an airborne radiometric survey, being flown nationally over the Republic of Ireland, combined with a digital elevation model, is used to delineate areas within an industrial peatland where peat thickness is less than 1m. Radiometric data are particularly suited to peat studies as they are sensitive to water content and peat thickness and require relatively little expert knowledge to utilise. Peat, as a mostly organic material, acts as a low signal environment where variations in the signal are linked to intra-peat variation of thickness, density and/or water content. This study uses an unsupervised machine learning, self-organizing map clustering methodology to group the study site into three zones interpreted as 1) the edge of the bog where peat layer is thinning or there is influence on the radiometric signal from non-peat soils outside of the bog, 2) the normal peat conditions where thickness and saturation appear as a relative constant in the radiometric response, and 3) areas where the peat is either thinner or drier. A ground geophysical survey was conducted to verify this interpretation. The delineation of such spatial variations in the radiometric response could aid any restoration project in the initial stages or act as a baseline study to monitor changes to the peatland during and after a restoration project is complete. Future work will see this methodology extended to other peatland types such as blanket bogs and natural raised bogs, as well as the integration of concurrent airborne electromagnetic data to link the near-surface radiometric response to the deeper vadose zone and define a more comprehensive classification scheme for these peatland sites.
How to cite: daly, E. and O Leary, D.: The potential of Self-Organising maps clustering to characterise a harvested peatland using airborne radiometric data and OS digital elevation model., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9857, https://doi.org/10.5194/egusphere-egu21-9857, 2021.
EGU21-5809 | vPICO presentations | SM5.2
Capturing Glacier-Wide Cryoseismicity With Distributed Acoustic SensingFabian Walter, Patrick Paitz, Andreas Fichtner, Pascal Edme, Wojciech Gajek, Bradly P. Lipovsky, and Eileen Martin
Over the past 1-2 decades, seismological measurements have provided new and unique insights into glacier and ice sheet dynamics. At the same time, sensor coverage is typically limited in harsh glacial environments with littile or no access. Turning kilometer-long fiber optic cables placed on the Earth’s surface into thousands of seismic sensors, Distributed Acoustic Sensing (DAS) may overcome the limitation of sensor coverage in the cryosphere.
First DAS applications on the Greenland and Antarctic ice sheets and on Alpine glacier ice have highlighted the technique’s superiority. Signals of natural and man-made seismic sources can be resolved with an unrivaled level of detail. This offers glaciologists new perspectives to interpret their seismograms in terms of ice structure, basal boundary conditions and source locations. However, previous studies employed only relatively small network scales with a point-like borehole deployment or < 1 km cable aperture at the ice surface.
Here we present a DAS installation, which aims to cover the majority of an Alpine glacier catchment: For one month in summer 2020 we deployed a 9 km long fiber optic cable on Rhonegletscher, Switzerland, and gathered continuous DAS data. The cable followed the glacier’s central flow line starting in the lowest kilometer of the ablation zone and extending well into the accumulation area. Even for a relatively small mountain glacier such as Rhonegletscher, cable deployment was a considerable logistical challenge. However, initial data analysis illustrates the benefit compared to conventional cryoseismological instrumentation: DAS measurements capture ground deformation over many octaves, including typical high-frequency englacial sources (10s to 100s of Hz) related to crevasse formation and basal sliding as well as long period signals (10s to 100s of seconds) of ice deformation. Depending on the presence of a snow cover, DAS records contain strong environmental noise (wind, meltwater flow, precipitation) and thus exhibit lower signal-to-noise ratios compared to conventional on-ice seismic installations. This is nevertheless outweighed by the advantage of monitoring ground unrest and ice deformation of nearly an entire glacier. We present a first compilation of signal and noise records and discuss future directions to leverage DAS data sets in glaciological research.
How to cite: Walter, F., Paitz, P., Fichtner, A., Edme, P., Gajek, W., Lipovsky, B. P., and Martin, E.: Capturing Glacier-Wide Cryoseismicity With Distributed Acoustic Sensing, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5809, https://doi.org/10.5194/egusphere-egu21-5809, 2021.
Please decide on your access
Please use the buttons below to download the presentation materials or to visit the external website where the presentation is linked. Regarding the external link, please note that Copernicus Meetings cannot accept any liability for the content and the website you will visit.
Forward to presentation link
You are going to open an external link to the presentation as indicated by the authors. Copernicus Meetings cannot accept any liability for the content and the website you will visit.
We are sorry, but presentations are only available for users who registered for the conference. Thank you.
Over the past 1-2 decades, seismological measurements have provided new and unique insights into glacier and ice sheet dynamics. At the same time, sensor coverage is typically limited in harsh glacial environments with littile or no access. Turning kilometer-long fiber optic cables placed on the Earth’s surface into thousands of seismic sensors, Distributed Acoustic Sensing (DAS) may overcome the limitation of sensor coverage in the cryosphere.
First DAS applications on the Greenland and Antarctic ice sheets and on Alpine glacier ice have highlighted the technique’s superiority. Signals of natural and man-made seismic sources can be resolved with an unrivaled level of detail. This offers glaciologists new perspectives to interpret their seismograms in terms of ice structure, basal boundary conditions and source locations. However, previous studies employed only relatively small network scales with a point-like borehole deployment or < 1 km cable aperture at the ice surface.
Here we present a DAS installation, which aims to cover the majority of an Alpine glacier catchment: For one month in summer 2020 we deployed a 9 km long fiber optic cable on Rhonegletscher, Switzerland, and gathered continuous DAS data. The cable followed the glacier’s central flow line starting in the lowest kilometer of the ablation zone and extending well into the accumulation area. Even for a relatively small mountain glacier such as Rhonegletscher, cable deployment was a considerable logistical challenge. However, initial data analysis illustrates the benefit compared to conventional cryoseismological instrumentation: DAS measurements capture ground deformation over many octaves, including typical high-frequency englacial sources (10s to 100s of Hz) related to crevasse formation and basal sliding as well as long period signals (10s to 100s of seconds) of ice deformation. Depending on the presence of a snow cover, DAS records contain strong environmental noise (wind, meltwater flow, precipitation) and thus exhibit lower signal-to-noise ratios compared to conventional on-ice seismic installations. This is nevertheless outweighed by the advantage of monitoring ground unrest and ice deformation of nearly an entire glacier. We present a first compilation of signal and noise records and discuss future directions to leverage DAS data sets in glaciological research.
How to cite: Walter, F., Paitz, P., Fichtner, A., Edme, P., Gajek, W., Lipovsky, B. P., and Martin, E.: Capturing Glacier-Wide Cryoseismicity With Distributed Acoustic Sensing, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5809, https://doi.org/10.5194/egusphere-egu21-5809, 2021.
EGU21-12118 | vPICO presentations | SM5.2
Passive seismic investigations of subaquatic permafrostChristian Rasmussen, Paul Overduin, Julia Boike, Trond Ryberg, and Christian Haberland
Large quantities of organic carbon are known to be sequestered within subaquatic permafrost as gas hydrates. Therefore, knowledge of the extent and thaw rate is of critical importance to our understanding of global climate change. Investigations of sub-aquatic permafrost have focussed on its physical characteristics via drilling or probing, and through the limited application of geophysical methods. Active seismic methods have been most widely employed, especially for petroleum exploration, but recently passive methods have been used to investigate the seabed using ambient noise. The Horizontal-to-Vertical Spectral Ratio (HVSR) method has previously been shown to accurately determine permafrost thaw depth below the sea floor in marine and lacustrine environments, based on the collection of seismic data over a period of weeks. In this study, we test the use of short-term seabed HVSR seismic surveys and explore possibilities for optimizing the method in a wide variety of subaquatic environments.
The method was successfully used in a thermokarst lake, a lagoon and river channels of the Lena Delta (Russia), as well as in marine shelf environments in the Laptev Sea (Russia) and Tuktoyaktuk Island (NW Canada). Study areas where validation data was available were preferred and selected when possible. A passive seismic measuring device, consisting of a watertight metal cannister containing three-component broad-band seismometers, was lowered down to the sea floor from a small boat and left to collect data for 3-4 minutes. The data was recorded at a sample rate of 100Hz.
Post-processing and analysis were done with MATLAB. The three seismic signals were individually detrended, the offset was removed and the power spectral density was calculated. The smoothing function proposed by Konno and Ohmachi (1998) was applied to each signal with a smoothing coefficient of 40. Lastly the H/V (Horizontal / Vertical) amplitude was calculated. The H/V amplitude was plotted against signal frequencies from 0 to 50 Hz. The peak resonance frequency is believed to indicate the ice-bonded permafrost table (IBPT) thereby enabling us to determine thaw depth from the H/V plots, assuming a simple 2-layer model: thawed layer over frozen ground, characterized by low and high wave speeds, respectively.
Results generally display a good correlation, on average within 0.6 meters, between the thaw depth determined from HVSR and from physical validation, although HVSR often generates a thaw depth deeper than indicated by validation data. This may be a result of complex permafrost systems where several “zones” of frozen and unfrozen ground, of varying thickness, is present below the water bodies.
We conclude that the method has the potential to be an effective (fast) non-invasive tool for investigating the extent and, if repeated, the thaw rate of subaquatic permafrost. Further field testing is planned in order to continue the development and optimization of the method.
How to cite: Rasmussen, C., Overduin, P., Boike, J., Ryberg, T., and Haberland, C.: Passive seismic investigations of subaquatic permafrost, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12118, https://doi.org/10.5194/egusphere-egu21-12118, 2021.
Large quantities of organic carbon are known to be sequestered within subaquatic permafrost as gas hydrates. Therefore, knowledge of the extent and thaw rate is of critical importance to our understanding of global climate change. Investigations of sub-aquatic permafrost have focussed on its physical characteristics via drilling or probing, and through the limited application of geophysical methods. Active seismic methods have been most widely employed, especially for petroleum exploration, but recently passive methods have been used to investigate the seabed using ambient noise. The Horizontal-to-Vertical Spectral Ratio (HVSR) method has previously been shown to accurately determine permafrost thaw depth below the sea floor in marine and lacustrine environments, based on the collection of seismic data over a period of weeks. In this study, we test the use of short-term seabed HVSR seismic surveys and explore possibilities for optimizing the method in a wide variety of subaquatic environments.
The method was successfully used in a thermokarst lake, a lagoon and river channels of the Lena Delta (Russia), as well as in marine shelf environments in the Laptev Sea (Russia) and Tuktoyaktuk Island (NW Canada). Study areas where validation data was available were preferred and selected when possible. A passive seismic measuring device, consisting of a watertight metal cannister containing three-component broad-band seismometers, was lowered down to the sea floor from a small boat and left to collect data for 3-4 minutes. The data was recorded at a sample rate of 100Hz.
Post-processing and analysis were done with MATLAB. The three seismic signals were individually detrended, the offset was removed and the power spectral density was calculated. The smoothing function proposed by Konno and Ohmachi (1998) was applied to each signal with a smoothing coefficient of 40. Lastly the H/V (Horizontal / Vertical) amplitude was calculated. The H/V amplitude was plotted against signal frequencies from 0 to 50 Hz. The peak resonance frequency is believed to indicate the ice-bonded permafrost table (IBPT) thereby enabling us to determine thaw depth from the H/V plots, assuming a simple 2-layer model: thawed layer over frozen ground, characterized by low and high wave speeds, respectively.
Results generally display a good correlation, on average within 0.6 meters, between the thaw depth determined from HVSR and from physical validation, although HVSR often generates a thaw depth deeper than indicated by validation data. This may be a result of complex permafrost systems where several “zones” of frozen and unfrozen ground, of varying thickness, is present below the water bodies.
We conclude that the method has the potential to be an effective (fast) non-invasive tool for investigating the extent and, if repeated, the thaw rate of subaquatic permafrost. Further field testing is planned in order to continue the development and optimization of the method.
How to cite: Rasmussen, C., Overduin, P., Boike, J., Ryberg, T., and Haberland, C.: Passive seismic investigations of subaquatic permafrost, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12118, https://doi.org/10.5194/egusphere-egu21-12118, 2021.
EGU21-12883 | vPICO presentations | SM5.2
Development of Low Cost Autonomous Electrical Resistivity Monitoring Systems for continuous active-layer monitoring in harsh environmentFernando Acácio Monteiro dos Santos, Mohammad Farzamian, Miguel Esteves, Gonçalo Vieira, and Christian Hauck
Development of Low Cost Autonomous Electrical Resistivity Monitoring Systems for continuous active-layer monitoring in harsh environment
Fernando A. Monteiro Santos (1), Mohammad Farzamian (1), Miguel Esteves (1), Gonçalo Vieira (2), Christian Hauck (4)
(1) Universidade de Lisboa, IDL, Portugal
(2) Centre for Geographical Studies, IGOT, Universidade de Lisboa, Portugal
(3) Department of Geosciences, University of Fribourg, Switzerland
The last overview of the thermal state in the Western Antarctic Peninsula shows that permafrost is close to 0oC in the region. This fact reinforces the importance to study the evolution of permafrost and active layer in the region. However, monitoring of the active layer and permafrost dynamics in Antarctica is generally conducted using only 1-dimensional borehole and meteorological data, which restricts the analysis to point information that often lack representatives at the field scale. In addition, being an invasive technique, the drilling of boreholes disturbs the subsurface and is not feasible to conduct over large areas, especially in environmentally sensitive ecosystems such as the Antarctic.
In this context, we developed automated electrical resistivity tomography (A-ERT) systems using a 4POINTLIGHT_10W (Lippmann) instrument with a solar panel-driven battery and multi-electrode configuration for autonomous and non-invasive monitoring of active layer and permafrost in Antarctica. The A-ERT measurements are sensitive to the electrical conductivity of materials, allowing to distinguish between frozen and unfrozen soil and thus to monitor the active layer dynamics including freezing, thawing, water infiltration and refreezing processes in a spatial context. We deployed the system in two monitoring sites at Deception and Livingstone Islands (South Shetland Islands, Maritime Antarctica) for quasi-continuous measurements at 6h interval from early 2019 and 2020 respectively.
Detailed investigation of the A-ERT data and obtained models reveals that the A-ERT system can detect the seasonal active-layer freezing and thawing events with very high resolution. In addition, the brief surficial refreezing and thawing of the active layer during summer and winter respectively were well resolved by A-ERT data, highlighting the significance of the continuous A-ERT monitoring setup which enables detecting fast changes in the active layer during short-lived extreme meteorological event. This suggests that the A-ERT measurements can provide valuable subsurface information to improve the spatio-temporal understanding of active layer and permafrost dynamics with very high resolution and minimal environmental disturbance in Antarctica. The set-up is very flexible and can be used with different configurations to investigate different depth ranges for site-specific detailed investigation.
Publication supported by FCT- project UID/GEO/50019/2020 - Instituto Dom Luiz
How to cite: Monteiro dos Santos, F. A., Farzamian, M., Esteves, M., Vieira, G., and Hauck, C.: Development of Low Cost Autonomous Electrical Resistivity Monitoring Systems for continuous active-layer monitoring in harsh environment , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12883, https://doi.org/10.5194/egusphere-egu21-12883, 2021.
Please decide on your access
Please use the buttons below to download the presentation materials or to visit the external website where the presentation is linked. Regarding the external link, please note that Copernicus Meetings cannot accept any liability for the content and the website you will visit.
Forward to presentation link
You are going to open an external link to the presentation as indicated by the authors. Copernicus Meetings cannot accept any liability for the content and the website you will visit.
We are sorry, but presentations are only available for users who registered for the conference. Thank you.
Development of Low Cost Autonomous Electrical Resistivity Monitoring Systems for continuous active-layer monitoring in harsh environment
Fernando A. Monteiro Santos (1), Mohammad Farzamian (1), Miguel Esteves (1), Gonçalo Vieira (2), Christian Hauck (4)
(1) Universidade de Lisboa, IDL, Portugal
(2) Centre for Geographical Studies, IGOT, Universidade de Lisboa, Portugal
(3) Department of Geosciences, University of Fribourg, Switzerland
The last overview of the thermal state in the Western Antarctic Peninsula shows that permafrost is close to 0oC in the region. This fact reinforces the importance to study the evolution of permafrost and active layer in the region. However, monitoring of the active layer and permafrost dynamics in Antarctica is generally conducted using only 1-dimensional borehole and meteorological data, which restricts the analysis to point information that often lack representatives at the field scale. In addition, being an invasive technique, the drilling of boreholes disturbs the subsurface and is not feasible to conduct over large areas, especially in environmentally sensitive ecosystems such as the Antarctic.
In this context, we developed automated electrical resistivity tomography (A-ERT) systems using a 4POINTLIGHT_10W (Lippmann) instrument with a solar panel-driven battery and multi-electrode configuration for autonomous and non-invasive monitoring of active layer and permafrost in Antarctica. The A-ERT measurements are sensitive to the electrical conductivity of materials, allowing to distinguish between frozen and unfrozen soil and thus to monitor the active layer dynamics including freezing, thawing, water infiltration and refreezing processes in a spatial context. We deployed the system in two monitoring sites at Deception and Livingstone Islands (South Shetland Islands, Maritime Antarctica) for quasi-continuous measurements at 6h interval from early 2019 and 2020 respectively.
Detailed investigation of the A-ERT data and obtained models reveals that the A-ERT system can detect the seasonal active-layer freezing and thawing events with very high resolution. In addition, the brief surficial refreezing and thawing of the active layer during summer and winter respectively were well resolved by A-ERT data, highlighting the significance of the continuous A-ERT monitoring setup which enables detecting fast changes in the active layer during short-lived extreme meteorological event. This suggests that the A-ERT measurements can provide valuable subsurface information to improve the spatio-temporal understanding of active layer and permafrost dynamics with very high resolution and minimal environmental disturbance in Antarctica. The set-up is very flexible and can be used with different configurations to investigate different depth ranges for site-specific detailed investigation.
Publication supported by FCT- project UID/GEO/50019/2020 - Instituto Dom Luiz
How to cite: Monteiro dos Santos, F. A., Farzamian, M., Esteves, M., Vieira, G., and Hauck, C.: Development of Low Cost Autonomous Electrical Resistivity Monitoring Systems for continuous active-layer monitoring in harsh environment , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12883, https://doi.org/10.5194/egusphere-egu21-12883, 2021.
EGU21-4509 | vPICO presentations | SM5.2
Ice or rock matrix? Improved quantitative imaging of Alpine permafrost evolution through time-lapse petrophysical joint inversionJohanna Klahold, Christian Hauck, and Florian Wagner
Quantitative estimation of pore fractions filled with liquid water, ice and air is one of the prerequisites in many permafrost studies and forms the basis for a process-based understanding of permafrost and the hazard potential of its degradation in the context of global warming. The volumetric ice content is however difficult to retrieve, since standard borehole temperature monitoring is unable to provide any ice content estimation. Geophysical methods offer opportunities to image distributions of permafrost constituents in a non-invasive manner. A petrophysical joint inversion was recently developed to determine volumetric water, ice, air and rock contents from seismic refraction and electrical resistivity data. This approach benefits from the complementary sensitivities of seismic and electrical data to the phase change between ice and liquid water. A remaining weak point was the unresolved petrophysical ambiguity between ice and rock matrix. Within this study, the petrophysical joint inversion approach is extended along the time axis and respective temporal constraints are introduced. If the porosity (and other time-invariant properties like pore water resistivity or Archie exponents) can be assumed invariant over the considered time period, water, ice and air contents can be estimated together with a temporally constant (but spatially variable) porosity distribution. It is hypothesized that including multiple time steps in the inverse problem increases the ratio of data and parameters and leads to a more accurate distinction between ice and rock content. Based on a synthetic example and a field data set from an Alpine permafrost site (Schilthorn, Swiss Alps) it is demonstrated that the developed time-lapse petrophysical joint inversion provides physically plausible solutions, in particular improved estimates for the volumetric fractions of ice and rock. The field application is evaluated with independent validation data including thaw depths derived from borehole temperature measurements and shows generally good agreement. As opposed to the conventional petrophysical joint inversion, its time-lapse extension succeeds in providing reasonable estimates of permafrost degradation at the Schilthorn monitoring site without a priori constraints on the porosity model.
How to cite: Klahold, J., Hauck, C., and Wagner, F.: Ice or rock matrix? Improved quantitative imaging of Alpine permafrost evolution through time-lapse petrophysical joint inversion, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4509, https://doi.org/10.5194/egusphere-egu21-4509, 2021.
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Quantitative estimation of pore fractions filled with liquid water, ice and air is one of the prerequisites in many permafrost studies and forms the basis for a process-based understanding of permafrost and the hazard potential of its degradation in the context of global warming. The volumetric ice content is however difficult to retrieve, since standard borehole temperature monitoring is unable to provide any ice content estimation. Geophysical methods offer opportunities to image distributions of permafrost constituents in a non-invasive manner. A petrophysical joint inversion was recently developed to determine volumetric water, ice, air and rock contents from seismic refraction and electrical resistivity data. This approach benefits from the complementary sensitivities of seismic and electrical data to the phase change between ice and liquid water. A remaining weak point was the unresolved petrophysical ambiguity between ice and rock matrix. Within this study, the petrophysical joint inversion approach is extended along the time axis and respective temporal constraints are introduced. If the porosity (and other time-invariant properties like pore water resistivity or Archie exponents) can be assumed invariant over the considered time period, water, ice and air contents can be estimated together with a temporally constant (but spatially variable) porosity distribution. It is hypothesized that including multiple time steps in the inverse problem increases the ratio of data and parameters and leads to a more accurate distinction between ice and rock content. Based on a synthetic example and a field data set from an Alpine permafrost site (Schilthorn, Swiss Alps) it is demonstrated that the developed time-lapse petrophysical joint inversion provides physically plausible solutions, in particular improved estimates for the volumetric fractions of ice and rock. The field application is evaluated with independent validation data including thaw depths derived from borehole temperature measurements and shows generally good agreement. As opposed to the conventional petrophysical joint inversion, its time-lapse extension succeeds in providing reasonable estimates of permafrost degradation at the Schilthorn monitoring site without a priori constraints on the porosity model.
How to cite: Klahold, J., Hauck, C., and Wagner, F.: Ice or rock matrix? Improved quantitative imaging of Alpine permafrost evolution through time-lapse petrophysical joint inversion, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4509, https://doi.org/10.5194/egusphere-egu21-4509, 2021.
EGU21-974 | vPICO presentations | SM5.2
Inversion of electromagnetic induction data using a novel wavelet-based and scale-dependent regularization termWouter Deleersnyder, Benjamin Maveau, David Dudal, and Thomas Hermans
In frequency domain Electromagnetic Induction (EMI) surveys, an image of the electrical conductivity of the subsurface is obtained non-invasively. The electrical conductivity can be related to important subsurface properties such as the porosity, saturation or water conductivity via Archie’s law. The advantage of geophysical EMI surveys is its cost-effectiveness because it is a non-contacting method, one can easily walk with the device or mount in on a vehicle or a helicopter (AEM).
The process of finding the conductivity profile from the collected field data is an ill-posed inverse problem. Regularization improves the stability of the inversion and, based on Occam’s razor principle, a smoothing constraint is typically used with a very large number of thin layers. However, the conductivity profiles are not always expected to be smooth. Another alternative is to use a predefined number of layers and to invert for their conductivity and thickness. This can yield sharp contrasts in conductivity. In practice however, the real underground might be either blocky or smooth, or somewhere in between. Those standard constraints are thus not always appropriate.
We develop a new minimum-structure inversion scheme in which we transform the model into the wavelet space and impose a sparsity constraint. This sparsity constrained inversion scheme minimizes an objective function with a least-squares data misfit and a sparsity measure of the model in the wavelet domain. With a solid understanding of wavelet theory, a novel and intuitive model misfit term was developed, allowing for both smooth and blocky models, depending on the chosen wavelet basis. A model in the wavelet domain has both temporal (i.e. low and high frequencies) and spatial resolution, and penalizing small-scale coefficients effectively reduces the complexity of the model.
Comparing the novel scale-dependent wavelet-based regularization scheme with wavelet-based regularization with no scale-dependence, revealed significantly better results (Figure A and B) w.r.t. the true model. Comparing with standard Tikhonov regularization (Figure C and D) shows that our scheme can recover high amplitude anomalies in combination with globally smooth profiles. Furthermore, the adaptive nature of the inversion method (due to the choice of wavelet) allows for high flexibility because the shape of the wavelet can be exploited to generate multiple representations (smooth, blocky or intermediate) of the inverse model.
We have introduced an alternative inversion scheme for EMI surveys that can be extended to any other 1D geophysical method. It involves a new model misfit or regularization term based on the wavelet transform and scale-dependent weighting which can easily be combined with the existing framework of deterministic inversion (gradient-based optimization methods, L-curve criterion for optimal regularization parameter). A challenge remains to select the optimal wavelet, however, the ensemble of inversion results with different wavelets can also be used to qualitatively assess uncertainty.
How to cite: Deleersnyder, W., Maveau, B., Dudal, D., and Hermans, T.: Inversion of electromagnetic induction data using a novel wavelet-based and scale-dependent regularization term, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-974, https://doi.org/10.5194/egusphere-egu21-974, 2021.
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In frequency domain Electromagnetic Induction (EMI) surveys, an image of the electrical conductivity of the subsurface is obtained non-invasively. The electrical conductivity can be related to important subsurface properties such as the porosity, saturation or water conductivity via Archie’s law. The advantage of geophysical EMI surveys is its cost-effectiveness because it is a non-contacting method, one can easily walk with the device or mount in on a vehicle or a helicopter (AEM).
The process of finding the conductivity profile from the collected field data is an ill-posed inverse problem. Regularization improves the stability of the inversion and, based on Occam’s razor principle, a smoothing constraint is typically used with a very large number of thin layers. However, the conductivity profiles are not always expected to be smooth. Another alternative is to use a predefined number of layers and to invert for their conductivity and thickness. This can yield sharp contrasts in conductivity. In practice however, the real underground might be either blocky or smooth, or somewhere in between. Those standard constraints are thus not always appropriate.
We develop a new minimum-structure inversion scheme in which we transform the model into the wavelet space and impose a sparsity constraint. This sparsity constrained inversion scheme minimizes an objective function with a least-squares data misfit and a sparsity measure of the model in the wavelet domain. With a solid understanding of wavelet theory, a novel and intuitive model misfit term was developed, allowing for both smooth and blocky models, depending on the chosen wavelet basis. A model in the wavelet domain has both temporal (i.e. low and high frequencies) and spatial resolution, and penalizing small-scale coefficients effectively reduces the complexity of the model.
Comparing the novel scale-dependent wavelet-based regularization scheme with wavelet-based regularization with no scale-dependence, revealed significantly better results (Figure A and B) w.r.t. the true model. Comparing with standard Tikhonov regularization (Figure C and D) shows that our scheme can recover high amplitude anomalies in combination with globally smooth profiles. Furthermore, the adaptive nature of the inversion method (due to the choice of wavelet) allows for high flexibility because the shape of the wavelet can be exploited to generate multiple representations (smooth, blocky or intermediate) of the inverse model.
We have introduced an alternative inversion scheme for EMI surveys that can be extended to any other 1D geophysical method. It involves a new model misfit or regularization term based on the wavelet transform and scale-dependent weighting which can easily be combined with the existing framework of deterministic inversion (gradient-based optimization methods, L-curve criterion for optimal regularization parameter). A challenge remains to select the optimal wavelet, however, the ensemble of inversion results with different wavelets can also be used to qualitatively assess uncertainty.
How to cite: Deleersnyder, W., Maveau, B., Dudal, D., and Hermans, T.: Inversion of electromagnetic induction data using a novel wavelet-based and scale-dependent regularization term, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-974, https://doi.org/10.5194/egusphere-egu21-974, 2021.
EGU21-16130 | vPICO presentations | SM5.2
Geostatistical FDEM inversion: a three-dimensional real case applicationLeonardo Azevedo, João Narciso, and Ellen Van De Vijver
The near surface is a complex and often highly heterogeneous system as its current status results from interacting processes of both natural and anthropogenic origin. Effective sustainable management and land use planning, especially in urban environments, demands high-resolution subsurface property models enabling to capture small-scale processes of interest. The modelling methods based only on discrete direct observations from conventional invasive sampling techniques have limitations with respect to capturing the spatial variability of these systems. Near-surface geophysical surveys are emerging as powerful techniques to provide indirect measurements of subsurface properties. Their integration with direct observations has the potential for better predicting the spatial distribution of the subsurface physical properties of interest and capture the heterogeneities of the near-surface systems.
Within the most common geophysical techniques, frequency-domain electromagnetic (FDEM) induction methods have demonstrated their potential and efficiency to characterize heterogeneous deposits due to their simultaneous sensitivity to electrical conductivity (EC) and magnetic susceptibility (MS). The inverse modelling of FDEM data based on geostatistical techniques allows to go beyond conventional analyses of FDEM data. This geostatistical FDEM inversion method uses stochastic sequential simulation and co-simulation to perturbate the model parameter space and the corresponding FDEM forward model solutions, including both the synthetic FDEM responses and their sensitivity to changes on the physical properties of interest. A stochastic optimization driven by the misfit between true and synthetic FDEM data is applied to iterative towards a final subsurface model. This method not only improve the confidence of the obtained EC and MS inverted models but also allows to quantify the uncertainty related to them. Furthermore, taking into account spatial correlations enables more accurate prediction of the spatial distribution of subsurface properties and a more realistic reconstruction of small-scale spatial variations, even when considering highly heterogeneous near surface systems. Moreover, a main advantage of this iterative geostatistical FDEM inversion method is its ability to flexibly integrate data with different resolution in the same framework.
In this work, we apply this iterative geostatistical FDEM inversion technique, which has already been successfully demonstrated for one- and two-dimensional applications, to invert a real case FDEM data set in three dimensions. The FDEM survey data set was collected on a site located near Knowlton (Dorset, UK), which is geologically characterized by Cretaceous chalk overlain by Quaternary siliciclastic sand deposits. The subsurface at the site is known to contain several archaeological features, which produces strong local in-phase anomalies in the FDEM survey data. We discuss the particular challenges involved in the three-dimensional application of the inversion method to a real case data set and compare our results against previously obtained ones for one- and two-dimensional approximations.
How to cite: Azevedo, L., Narciso, J., and Van De Vijver, E.: Geostatistical FDEM inversion: a three-dimensional real case application, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16130, https://doi.org/10.5194/egusphere-egu21-16130, 2021.
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The near surface is a complex and often highly heterogeneous system as its current status results from interacting processes of both natural and anthropogenic origin. Effective sustainable management and land use planning, especially in urban environments, demands high-resolution subsurface property models enabling to capture small-scale processes of interest. The modelling methods based only on discrete direct observations from conventional invasive sampling techniques have limitations with respect to capturing the spatial variability of these systems. Near-surface geophysical surveys are emerging as powerful techniques to provide indirect measurements of subsurface properties. Their integration with direct observations has the potential for better predicting the spatial distribution of the subsurface physical properties of interest and capture the heterogeneities of the near-surface systems.
Within the most common geophysical techniques, frequency-domain electromagnetic (FDEM) induction methods have demonstrated their potential and efficiency to characterize heterogeneous deposits due to their simultaneous sensitivity to electrical conductivity (EC) and magnetic susceptibility (MS). The inverse modelling of FDEM data based on geostatistical techniques allows to go beyond conventional analyses of FDEM data. This geostatistical FDEM inversion method uses stochastic sequential simulation and co-simulation to perturbate the model parameter space and the corresponding FDEM forward model solutions, including both the synthetic FDEM responses and their sensitivity to changes on the physical properties of interest. A stochastic optimization driven by the misfit between true and synthetic FDEM data is applied to iterative towards a final subsurface model. This method not only improve the confidence of the obtained EC and MS inverted models but also allows to quantify the uncertainty related to them. Furthermore, taking into account spatial correlations enables more accurate prediction of the spatial distribution of subsurface properties and a more realistic reconstruction of small-scale spatial variations, even when considering highly heterogeneous near surface systems. Moreover, a main advantage of this iterative geostatistical FDEM inversion method is its ability to flexibly integrate data with different resolution in the same framework.
In this work, we apply this iterative geostatistical FDEM inversion technique, which has already been successfully demonstrated for one- and two-dimensional applications, to invert a real case FDEM data set in three dimensions. The FDEM survey data set was collected on a site located near Knowlton (Dorset, UK), which is geologically characterized by Cretaceous chalk overlain by Quaternary siliciclastic sand deposits. The subsurface at the site is known to contain several archaeological features, which produces strong local in-phase anomalies in the FDEM survey data. We discuss the particular challenges involved in the three-dimensional application of the inversion method to a real case data set and compare our results against previously obtained ones for one- and two-dimensional approximations.
How to cite: Azevedo, L., Narciso, J., and Van De Vijver, E.: Geostatistical FDEM inversion: a three-dimensional real case application, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16130, https://doi.org/10.5194/egusphere-egu21-16130, 2021.
EGU21-6149 | vPICO presentations | SM5.2
Vertical multi-frequency FDEM loop-loop soundings for sub-surface conductivity imaging: comparison of HCP and PERP configurations for different environmentsJulien Guillemoteau, Mauricio Arboleda Zapata, François-Xavier Simon, Guillaume Hulin, Laurent Deschodt, and Jens Tronicke
Frequency domain loop-loop electromagnetic induction (FDEM) soundings using decametric coil-separations and multi-frequency sources have been used for decades to investigate the electrical conductivity of top 100 m of the subsurface. The most common coil configurations include horizontal and vertical co-planar (HCP and VCP) setups, and the data recorded with a rather large station spacing are typically processed assuming 1D layered media. In many geological situations, the subsurface shows significant lateral contrasts in the electrical material properties, especially, in regoliths close to earth’s surface. Here, the HCP and VCP 2D/3D sensitivity functions show complex and rather extended lateral sensitivity patterns. Therefore, in presence of high lateral variations in the uppermost layers, assuming 1D layered media for interpreting HCP and VCP profiles is often not valid. Furthermore, using rather large lateral station spacings often hinders the identification (and removal) of 2D/3D effects. In consequence, the overall 1D FDEM profiling procedure is often considered to be less robust than other electrical imaging techniques (e.g., DC tomography) to depict near-surface horizontal variations of the subsurface.
In shallower FDEM applications focusing on the characterization of the uppermost soil layers, portable loop-loop FDEM sensors (e.g. rigid boom systems with coil separations < 6 m) are used to explore the subsurface electrical properties. Here, it is commonly known that the PERP configuration shows better lateral resolution and apparent conductivity maps closer to the actual conductivity distribution. The latter feature is in fact crucial for the validity and applicability of the 1D approximation. The robustness of the PERP configuration regarding the 1D assumption can be explained by its sensitivity pattern showing a preponderant sign and a rather focused pattern, centered approximately below the receiver.
In order to evaluate the benefit of the PERP configuration for systems with decametric coil separation, we present two case studies, where densely sampled profiles of 1D inversions of multi-frequency FDEM HCP and PERP data are compared to 2D ERT inverted models and additional independent borehole and rigid-boom FDEM sensor data. In the first case study, we explore a coastal environment near Bourbourg, France, where only minor lateral variations in the subsurface are expected. Here, our results demonstrate that a 1D inversion of HCP and PERP data result in similar models. In the second case study, we explore debris flow deposits close to Braunsbach, Germany, which are characterized by significant near-surface lateral variability. In this case, only the 1D inversion of our PERP data results in a pseudo 2D model being in agreement with the inverted 2D ERT data. These two case studies confirm that the 1D inversion of PERP data (only) yields results that are more robust regarding 2D/3D artifacts than the 1D inversion of HCP data, or a joint inversion of HCP/PERP data. In conclusion, we propose that the 1D inversion of spatially densely sampled multi-frequency PERP data should be further evaluated in view of characterizing the lateral variations within the first 20 m of the subsurface because it could represent an efficient alternative to ERT methods in selected applications.
How to cite: Guillemoteau, J., Arboleda Zapata, M., Simon, F.-X., Hulin, G., Deschodt, L., and Tronicke, J.: Vertical multi-frequency FDEM loop-loop soundings for sub-surface conductivity imaging: comparison of HCP and PERP configurations for different environments , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6149, https://doi.org/10.5194/egusphere-egu21-6149, 2021.
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Please use the buttons below to download the presentation materials or to visit the external website where the presentation is linked. Regarding the external link, please note that Copernicus Meetings cannot accept any liability for the content and the website you will visit.
Forward to presentation link
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Frequency domain loop-loop electromagnetic induction (FDEM) soundings using decametric coil-separations and multi-frequency sources have been used for decades to investigate the electrical conductivity of top 100 m of the subsurface. The most common coil configurations include horizontal and vertical co-planar (HCP and VCP) setups, and the data recorded with a rather large station spacing are typically processed assuming 1D layered media. In many geological situations, the subsurface shows significant lateral contrasts in the electrical material properties, especially, in regoliths close to earth’s surface. Here, the HCP and VCP 2D/3D sensitivity functions show complex and rather extended lateral sensitivity patterns. Therefore, in presence of high lateral variations in the uppermost layers, assuming 1D layered media for interpreting HCP and VCP profiles is often not valid. Furthermore, using rather large lateral station spacings often hinders the identification (and removal) of 2D/3D effects. In consequence, the overall 1D FDEM profiling procedure is often considered to be less robust than other electrical imaging techniques (e.g., DC tomography) to depict near-surface horizontal variations of the subsurface.
In shallower FDEM applications focusing on the characterization of the uppermost soil layers, portable loop-loop FDEM sensors (e.g. rigid boom systems with coil separations < 6 m) are used to explore the subsurface electrical properties. Here, it is commonly known that the PERP configuration shows better lateral resolution and apparent conductivity maps closer to the actual conductivity distribution. The latter feature is in fact crucial for the validity and applicability of the 1D approximation. The robustness of the PERP configuration regarding the 1D assumption can be explained by its sensitivity pattern showing a preponderant sign and a rather focused pattern, centered approximately below the receiver.
In order to evaluate the benefit of the PERP configuration for systems with decametric coil separation, we present two case studies, where densely sampled profiles of 1D inversions of multi-frequency FDEM HCP and PERP data are compared to 2D ERT inverted models and additional independent borehole and rigid-boom FDEM sensor data. In the first case study, we explore a coastal environment near Bourbourg, France, where only minor lateral variations in the subsurface are expected. Here, our results demonstrate that a 1D inversion of HCP and PERP data result in similar models. In the second case study, we explore debris flow deposits close to Braunsbach, Germany, which are characterized by significant near-surface lateral variability. In this case, only the 1D inversion of our PERP data results in a pseudo 2D model being in agreement with the inverted 2D ERT data. These two case studies confirm that the 1D inversion of PERP data (only) yields results that are more robust regarding 2D/3D artifacts than the 1D inversion of HCP data, or a joint inversion of HCP/PERP data. In conclusion, we propose that the 1D inversion of spatially densely sampled multi-frequency PERP data should be further evaluated in view of characterizing the lateral variations within the first 20 m of the subsurface because it could represent an efficient alternative to ERT methods in selected applications.
How to cite: Guillemoteau, J., Arboleda Zapata, M., Simon, F.-X., Hulin, G., Deschodt, L., and Tronicke, J.: Vertical multi-frequency FDEM loop-loop soundings for sub-surface conductivity imaging: comparison of HCP and PERP configurations for different environments , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6149, https://doi.org/10.5194/egusphere-egu21-6149, 2021.
EGU21-1131 | vPICO presentations | SM5.2
Applying BEL1D for transient electromagnetic sounding inversionArsalan Ahmed, Hadrien Michel, Wouter Deleersnyder, David Dudal, and Thomas Hermans
Accurate subsurface imaging through geophysics is of prime importance for many geological and hydrogeological applications. Recently, airborne electromagnetic methods have become more popular because of their potential to quickly acquire large data sets at relevant depths for hydrogeological applications. However, the solution of inversion of airborne EM data is not unique, so that many electrical conductivity models can explain the data. Two families of methods can be applied for inversion: deterministic and stochastic methods. Deterministic (or regularized) approaches are limited in terms of uncertainty quantification as they propose one unique solution according to the chosen regularization term. In contrast, stochastic methods are able to generate many models fitting the data. The most common approach is to use Markov chain Monte Carlo (McMC) Methods. However, the application of stochastic methods, even though more informative than deterministic ones, is rare due to a quite high computational cost.
In this research, the newly developed approach named Bayesian Evidential Learning 1D imaging (BEL1D) is used to efficiently and stochastically solve the inverse problem. BEL1D is combined to SimPEG: an open source python package, for solving the electromagnetic forward problem. BEL1D bypasses the inversion step, by generating random samples from the prior distribution with defined ranges for the thickness and electrical conductivity of the different layers, simulating the corresponding data and learning a direct statistical relationship between data and model parameters. From this relationship, BEL1D can generate posterior models fitting the field observed data, without additional forward model computations. The output of BEL1D shows the range of uncertainty for subsurface models. It enables to identify which model parameters are the most sensitive and can be accurately estimated from the electromagnetic data.
The application of BEL1D together with SimPEG for stochastic transient electromagnetic inversion is a very efficient approach, as it allows to estimate the uncertainty at a limited cost. Indeed, only a limited number of training models (typically a few thousands) is required for an accurate prediction. Moreover, the computed training models can be reused for other predictions, considerably reducing the computation cost when dealing with similar data sets. It is thus a promising approach for the inversion of dense data set (such as those collected in airborne surveys). In the future, we plan on relaxing constraints on the model parameters to go towards interpretation of EM data in coastal environment, where transition can be smooth due to salinity variations.
Keywords : EM, Uncertainty, 1D imaging, BEL1D, SimPEG
How to cite: Ahmed, A., Michel, H., Deleersnyder, W., Dudal, D., and Hermans, T.: Applying BEL1D for transient electromagnetic sounding inversion, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1131, https://doi.org/10.5194/egusphere-egu21-1131, 2021.
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Please use the buttons below to download the presentation materials or to visit the external website where the presentation is linked. Regarding the external link, please note that Copernicus Meetings cannot accept any liability for the content and the website you will visit.
Forward to presentation link
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We are sorry, but presentations are only available for users who registered for the conference. Thank you.
Accurate subsurface imaging through geophysics is of prime importance for many geological and hydrogeological applications. Recently, airborne electromagnetic methods have become more popular because of their potential to quickly acquire large data sets at relevant depths for hydrogeological applications. However, the solution of inversion of airborne EM data is not unique, so that many electrical conductivity models can explain the data. Two families of methods can be applied for inversion: deterministic and stochastic methods. Deterministic (or regularized) approaches are limited in terms of uncertainty quantification as they propose one unique solution according to the chosen regularization term. In contrast, stochastic methods are able to generate many models fitting the data. The most common approach is to use Markov chain Monte Carlo (McMC) Methods. However, the application of stochastic methods, even though more informative than deterministic ones, is rare due to a quite high computational cost.
In this research, the newly developed approach named Bayesian Evidential Learning 1D imaging (BEL1D) is used to efficiently and stochastically solve the inverse problem. BEL1D is combined to SimPEG: an open source python package, for solving the electromagnetic forward problem. BEL1D bypasses the inversion step, by generating random samples from the prior distribution with defined ranges for the thickness and electrical conductivity of the different layers, simulating the corresponding data and learning a direct statistical relationship between data and model parameters. From this relationship, BEL1D can generate posterior models fitting the field observed data, without additional forward model computations. The output of BEL1D shows the range of uncertainty for subsurface models. It enables to identify which model parameters are the most sensitive and can be accurately estimated from the electromagnetic data.
The application of BEL1D together with SimPEG for stochastic transient electromagnetic inversion is a very efficient approach, as it allows to estimate the uncertainty at a limited cost. Indeed, only a limited number of training models (typically a few thousands) is required for an accurate prediction. Moreover, the computed training models can be reused for other predictions, considerably reducing the computation cost when dealing with similar data sets. It is thus a promising approach for the inversion of dense data set (such as those collected in airborne surveys). In the future, we plan on relaxing constraints on the model parameters to go towards interpretation of EM data in coastal environment, where transition can be smooth due to salinity variations.
Keywords : EM, Uncertainty, 1D imaging, BEL1D, SimPEG
How to cite: Ahmed, A., Michel, H., Deleersnyder, W., Dudal, D., and Hermans, T.: Applying BEL1D for transient electromagnetic sounding inversion, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1131, https://doi.org/10.5194/egusphere-egu21-1131, 2021.
EGU21-13373 | vPICO presentations | SM5.2
Multiple-point geostatistical reconstruction of GPR reflection dataChongmin Zhang, Mathieu Gravey, James Irving, and Gregoire Mariethoz
A common challenge in reflection GPR data processing and analysis is the reconstruction of missing traces. Gap filling, for example, may be needed to fill-in data where they could not be recorded in the field in order to produce a uniform trace spacing that is important for Fourier- or finite-difference-based migration methods. Similarly, field GPR data recorded in continuous mode with an uneven trace spacing are usually needed at a regular spacing for subsequent visualization and imaging. Finally, we may wish to increase the spatial resolution of a GPR dataset through “super-resolution”, whereby new traces are simulated between the existing ones in order to improve the interpretability of the data. A common challenge in these various applications is the need to interpolate a variable that has a complex, non-smooth behavior.
A number of interpolation methods have been proposed for filling in missing GPR traces over the past decades. The majority of these, however, tend to produce overly smooth and unrealistic results. Here, we present a data reconstruction strategy based on the QuickSampling (QS) multiple-point geostatistical method. With this approach, GPR traces are simulated via sequential conditional simulation based on patterns that are observed in nearby high-resolution data (training images). To evaluate the potential of our approach, we apply it to a variety of field 2D GPR datasets. Results indicate that the QS method provides an effective means of simulating missing GPR traces in a highly realistic manner.
How to cite: Zhang, C., Gravey, M., Irving, J., and Mariethoz, G.: Multiple-point geostatistical reconstruction of GPR reflection data, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13373, https://doi.org/10.5194/egusphere-egu21-13373, 2021.
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Please use the buttons below to download the presentation materials or to visit the external website where the presentation is linked. Regarding the external link, please note that Copernicus Meetings cannot accept any liability for the content and the website you will visit.
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A common challenge in reflection GPR data processing and analysis is the reconstruction of missing traces. Gap filling, for example, may be needed to fill-in data where they could not be recorded in the field in order to produce a uniform trace spacing that is important for Fourier- or finite-difference-based migration methods. Similarly, field GPR data recorded in continuous mode with an uneven trace spacing are usually needed at a regular spacing for subsequent visualization and imaging. Finally, we may wish to increase the spatial resolution of a GPR dataset through “super-resolution”, whereby new traces are simulated between the existing ones in order to improve the interpretability of the data. A common challenge in these various applications is the need to interpolate a variable that has a complex, non-smooth behavior.
A number of interpolation methods have been proposed for filling in missing GPR traces over the past decades. The majority of these, however, tend to produce overly smooth and unrealistic results. Here, we present a data reconstruction strategy based on the QuickSampling (QS) multiple-point geostatistical method. With this approach, GPR traces are simulated via sequential conditional simulation based on patterns that are observed in nearby high-resolution data (training images). To evaluate the potential of our approach, we apply it to a variety of field 2D GPR datasets. Results indicate that the QS method provides an effective means of simulating missing GPR traces in a highly realistic manner.
How to cite: Zhang, C., Gravey, M., Irving, J., and Mariethoz, G.: Multiple-point geostatistical reconstruction of GPR reflection data, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13373, https://doi.org/10.5194/egusphere-egu21-13373, 2021.
EGU21-9492 | vPICO presentations | SM5.2
Enhancement of 3D GPR datasets using singular value decomposition applied in 2D the spectral domain for clutter noise removalRui Jorge Oliveira, Bento Caldeira, Teresa Teixidó, and José Fernando Borges
The ground-penetrating radar (GPR) datasets obtained in archaeological environments have substantial problems related the presence of clutter noise. These noisy reflections are generated by the heterogeneities of the ground and by the collapses of structures buried in the ground, that can prevent a good assessment of the subsurface with this method. The classic filtering operations available can fail to remove it effectively. This work presents an approach to filtering the GPR data in the 2D spectral domain through the singular value decomposition (SVD) factorization technique. The spectral domain present advantages such as the circular symmetry of the transformed data that turns easy the filter parametrisation and the constant computational effort whatever the amount of data considered. SVD allows the decreasing of the user dependency to parametrize the filter. The main propose of this method is to classify automatically the datasets into useful information, corresponding to buried structures, and noise, to remove the last. This approach was conceived based on the study of the GPR signal in the 2D spectral domain and the manual filter design. The tests were performed with different datasets, one from a laboratory experiment (controlled environment) and the other from a field acquisition in an archaeological site (uncontrolled environment) with subsequent excavation to proof the results. The proposed approach is effective to remove the clutter noise in the GPR datasets and constitutes a complementary operation to those already existing in the commercial software.
Acknowledgment: The work was supported by the Portuguese Foundation for Science and Technology (FCT) project UIDB/04683/2020 - ICT (Institute of Earth Sciences) and by the INTERREG 2014-2020 Program, through the "Innovación abierta e inteligente en la EUROACE" Project, with the reference 0049_INNOACE_4_E.
How to cite: Oliveira, R. J., Caldeira, B., Teixidó, T., and Borges, J. F.: Enhancement of 3D GPR datasets using singular value decomposition applied in 2D the spectral domain for clutter noise removal, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9492, https://doi.org/10.5194/egusphere-egu21-9492, 2021.
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The ground-penetrating radar (GPR) datasets obtained in archaeological environments have substantial problems related the presence of clutter noise. These noisy reflections are generated by the heterogeneities of the ground and by the collapses of structures buried in the ground, that can prevent a good assessment of the subsurface with this method. The classic filtering operations available can fail to remove it effectively. This work presents an approach to filtering the GPR data in the 2D spectral domain through the singular value decomposition (SVD) factorization technique. The spectral domain present advantages such as the circular symmetry of the transformed data that turns easy the filter parametrisation and the constant computational effort whatever the amount of data considered. SVD allows the decreasing of the user dependency to parametrize the filter. The main propose of this method is to classify automatically the datasets into useful information, corresponding to buried structures, and noise, to remove the last. This approach was conceived based on the study of the GPR signal in the 2D spectral domain and the manual filter design. The tests were performed with different datasets, one from a laboratory experiment (controlled environment) and the other from a field acquisition in an archaeological site (uncontrolled environment) with subsequent excavation to proof the results. The proposed approach is effective to remove the clutter noise in the GPR datasets and constitutes a complementary operation to those already existing in the commercial software.
Acknowledgment: The work was supported by the Portuguese Foundation for Science and Technology (FCT) project UIDB/04683/2020 - ICT (Institute of Earth Sciences) and by the INTERREG 2014-2020 Program, through the "Innovación abierta e inteligente en la EUROACE" Project, with the reference 0049_INNOACE_4_E.
How to cite: Oliveira, R. J., Caldeira, B., Teixidó, T., and Borges, J. F.: Enhancement of 3D GPR datasets using singular value decomposition applied in 2D the spectral domain for clutter noise removal, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9492, https://doi.org/10.5194/egusphere-egu21-9492, 2021.
EGU21-12073 | vPICO presentations | SM5.2
Characterization of a solid waste landfill through geophysical data fusionMatthias Steiner, Timea Katona, Johann Fellner, and Adrián Flores Orozco
A detailed characterization of the landfill geometry, the waste volume and composition, and the water saturation within and outside the landfill body is critical for an adequate environmental management. To overcome the limited spatial resolution of direct investigations into landfills, geophysical methods have proven to resolve subsurface properties with high spatial resolution in a non-invasive and cost-efficient manner. The joint inversion of different geophysical datasets became increasingly popular in various fields of application since it solves quantitatively for the parameters of interest. Built upon a recently developed framework considering Archie’s law and a time-averaging equation for the seismic slowness, we present here the petrophysical joint inversion (PJI) of electrical and seismic data collected along three profiles at the “Heferlbach” landfill located close to Vienna (Austria). We use the PJI framework to simultaneously invert apparent electrical resistivities and seismic traveltimes to solve for quantitative estimates for porosity, water saturation and air content. Our results show that the shallow geometry of the landfill with an average thickness of 3.5 m is clearly resolved by subsurface areas characterized by an air content of approximately 40 %. Based on the resolved saturation, we were able to identify the known aquifer underneath the landfill (average saturation of 25 %) that is lying on top of an aquiclude formed by tertiary sands. Within the landfill body, the saturation is approximately 10 to 15 %, which is in agreement with available data from the site. The resolved porosity model shows significant lateral variations (between 40 and 60 %) at shallow depths (< 3 m) suggesting a varying degree of compaction of the waste and different types of waste. Our results demonstrate the potential of the proposed PJI to enhance geophysical investigations of landfills by providing plausible quantitative estimates for parameters of interest with an adequate spatial resolution.
How to cite: Steiner, M., Katona, T., Fellner, J., and Flores Orozco, A.: Characterization of a solid waste landfill through geophysical data fusion, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12073, https://doi.org/10.5194/egusphere-egu21-12073, 2021.
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A detailed characterization of the landfill geometry, the waste volume and composition, and the water saturation within and outside the landfill body is critical for an adequate environmental management. To overcome the limited spatial resolution of direct investigations into landfills, geophysical methods have proven to resolve subsurface properties with high spatial resolution in a non-invasive and cost-efficient manner. The joint inversion of different geophysical datasets became increasingly popular in various fields of application since it solves quantitatively for the parameters of interest. Built upon a recently developed framework considering Archie’s law and a time-averaging equation for the seismic slowness, we present here the petrophysical joint inversion (PJI) of electrical and seismic data collected along three profiles at the “Heferlbach” landfill located close to Vienna (Austria). We use the PJI framework to simultaneously invert apparent electrical resistivities and seismic traveltimes to solve for quantitative estimates for porosity, water saturation and air content. Our results show that the shallow geometry of the landfill with an average thickness of 3.5 m is clearly resolved by subsurface areas characterized by an air content of approximately 40 %. Based on the resolved saturation, we were able to identify the known aquifer underneath the landfill (average saturation of 25 %) that is lying on top of an aquiclude formed by tertiary sands. Within the landfill body, the saturation is approximately 10 to 15 %, which is in agreement with available data from the site. The resolved porosity model shows significant lateral variations (between 40 and 60 %) at shallow depths (< 3 m) suggesting a varying degree of compaction of the waste and different types of waste. Our results demonstrate the potential of the proposed PJI to enhance geophysical investigations of landfills by providing plausible quantitative estimates for parameters of interest with an adequate spatial resolution.
How to cite: Steiner, M., Katona, T., Fellner, J., and Flores Orozco, A.: Characterization of a solid waste landfill through geophysical data fusion, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12073, https://doi.org/10.5194/egusphere-egu21-12073, 2021.
EGU21-14522 | vPICO presentations | SM5.2
Dense 3D electrical resistivity tomography to understand complex deep landslide structuresJulien Gance, Orlando Leite, Myriam Lajaunie, Kusnahadi Susanto, Catherine Truffert, Olivier Maillard, Catherine Bertrand, Gilbert Ferhat, and Jean-Philippe Malet
Large scale slope instabilities are complex objects controlled by multiple parameters. The underground and superficial structure of the slope plays a major role as it often controls water circulations, potentially causing weathering and damaging processes, and permits the local storage of water masses, causing temporary overload. In addition, the structure of the subsurface often delineates rock-volumes with variable mechanical properties, whose spatial distribution greatly influences the behavior of the slope. This work illustrates how Dense 3D Electrical Resistivity Tomography can provide relevant constraints on these parameters.
The village of Viella, in France (Hautes-Pyrénées), is affected by strong slope movement since 2018, when a massive rockslide above the village modified the stress conditions of the entire slope and, potentially, the hydrogeological context. As a consequence, some houses and infrastructures are progressively damaged, leading to heavy measures (houses evacuation). This complex, deep-seated (> 80 m), slope instability covers an area of ca. 650 000 m², is primarily composed of altered shists, colluviums, and non-consolidated alluvial deposits, forming several kinematic units with surface velocities in the range [0.5 – 5] mm.month-1.
A 3D dense electrical resistivity tomography was realized using the FullWaver system, to characterize the structure and the forcing factors of this unstable slope. 55 V-FullWavers receivers (3 -electrodes, 2 channels sensors) were quasi-evenly distributed over a surface area of 400 x 500 m² with an interval of 90 m, apart from the village area, where no electrode could be grounded. Each V-FullWaver recorded signals through two orthogonal dipoles of 25 m length. Current injections were realized with a high-power transmitter (6 kW, 16 A, 3000 V). 235 injection dipoles were used. The system injected current between a fixed remote electrode (more than 1 km away from the site to increase the investigation depth) and a local mobile electrode, moved all over the investigated area in between the V-Fullwaver receivers, with an interval of approximately 40 m, except in the village area.
The resulting 3D resistivity model presents a high spatial variability until 100 to 150 m depth approximately, that highly relates to the complex strain dynamics of the slope and the hydrogeological observations. It highlights the relation between the most active kinematic compartments and the large-scale structure of the slope.
It provides a first understanding of the role of local compacted rocks in the buildup of surface deformation but also on the localization of heterogeneities (fissures, scarps) which may relate to water circulation paths.
. This 3D image of the slope is the first structural reference model for future hydrogeological and geomechanical studies aiming at deducing the possible evolution of the slope.
How to cite: Gance, J., Leite, O., Lajaunie, M., Susanto, K., Truffert, C., Maillard, O., Bertrand, C., Ferhat, G., and Malet, J.-P.: Dense 3D electrical resistivity tomography to understand complex deep landslide structures, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14522, https://doi.org/10.5194/egusphere-egu21-14522, 2021.
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Large scale slope instabilities are complex objects controlled by multiple parameters. The underground and superficial structure of the slope plays a major role as it often controls water circulations, potentially causing weathering and damaging processes, and permits the local storage of water masses, causing temporary overload. In addition, the structure of the subsurface often delineates rock-volumes with variable mechanical properties, whose spatial distribution greatly influences the behavior of the slope. This work illustrates how Dense 3D Electrical Resistivity Tomography can provide relevant constraints on these parameters.
The village of Viella, in France (Hautes-Pyrénées), is affected by strong slope movement since 2018, when a massive rockslide above the village modified the stress conditions of the entire slope and, potentially, the hydrogeological context. As a consequence, some houses and infrastructures are progressively damaged, leading to heavy measures (houses evacuation). This complex, deep-seated (> 80 m), slope instability covers an area of ca. 650 000 m², is primarily composed of altered shists, colluviums, and non-consolidated alluvial deposits, forming several kinematic units with surface velocities in the range [0.5 – 5] mm.month-1.
A 3D dense electrical resistivity tomography was realized using the FullWaver system, to characterize the structure and the forcing factors of this unstable slope. 55 V-FullWavers receivers (3 -electrodes, 2 channels sensors) were quasi-evenly distributed over a surface area of 400 x 500 m² with an interval of 90 m, apart from the village area, where no electrode could be grounded. Each V-FullWaver recorded signals through two orthogonal dipoles of 25 m length. Current injections were realized with a high-power transmitter (6 kW, 16 A, 3000 V). 235 injection dipoles were used. The system injected current between a fixed remote electrode (more than 1 km away from the site to increase the investigation depth) and a local mobile electrode, moved all over the investigated area in between the V-Fullwaver receivers, with an interval of approximately 40 m, except in the village area.
The resulting 3D resistivity model presents a high spatial variability until 100 to 150 m depth approximately, that highly relates to the complex strain dynamics of the slope and the hydrogeological observations. It highlights the relation between the most active kinematic compartments and the large-scale structure of the slope.
It provides a first understanding of the role of local compacted rocks in the buildup of surface deformation but also on the localization of heterogeneities (fissures, scarps) which may relate to water circulation paths.
. This 3D image of the slope is the first structural reference model for future hydrogeological and geomechanical studies aiming at deducing the possible evolution of the slope.
How to cite: Gance, J., Leite, O., Lajaunie, M., Susanto, K., Truffert, C., Maillard, O., Bertrand, C., Ferhat, G., and Malet, J.-P.: Dense 3D electrical resistivity tomography to understand complex deep landslide structures, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14522, https://doi.org/10.5194/egusphere-egu21-14522, 2021.
EGU21-10012 | vPICO presentations | SM5.2
Geoelectrical imaging of subsurface discontinuities and heterogeneities using low-dimensional parameterizationsAaron Förderer, Florian Wellmann, and Florian Wagner
Geophysical imaging is subject to inherent non-uniqueness due to the ill-posed nature of the inverse problem. To mitigate this, the solution is commonly subjected to regularization. Smoothing regularization is widely used in practice, but produces high-dimensional images without sharp contrasts between geological units. These tomograms stand in contrast to current implicit geological models, which are able to produce sharp subsurface interfaces with complex geometries using low-dimensional parametrizations. This work aims to bring together modelling concepts from geophysics and geology using the example of electrical resistivity tomography (ERT).
An implicit geological model is used as the centerpiece of a 2D ERT inversion within a deterministic Gauss-Newton framework. The points that define the surfaces of the geological model are included into the model vector of the inverse problem along with a low-dimensional pilot point parametrization of the subsurface electrical resistivity. The point-based parameterization is translated to a triangular finite-element mesh to solve the geoelectrical forward problem. Sensitivities for the geological interfaces and resistivity parameters are efficiently calculated based on finite-differences and the reciprocity theorem, respectively. Each iteration step produces an update of both the geological interface as well as the parameter fields.
The approach converges to an updated geological model and a distribution of subsurface resistivity, which are in accordance with the measured data. The tomograms show sharply localized and realistic subsurface interfaces that are described by only a few parameters. While the imaging of small-scale heterogeneities is challenging and would require a locally increased number of pilot points, the current approach allows for the estimation of smoothly distributed heterogeneities. Further advantages of the approach lie in the improved integration of a-priori geological knowledge, the straightforward extension to 3D, and the applicability to other geophysical methods as well as joint inversion.
How to cite: Förderer, A., Wellmann, F., and Wagner, F.: Geoelectrical imaging of subsurface discontinuities and heterogeneities using low-dimensional parameterizations, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10012, https://doi.org/10.5194/egusphere-egu21-10012, 2021.
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Geophysical imaging is subject to inherent non-uniqueness due to the ill-posed nature of the inverse problem. To mitigate this, the solution is commonly subjected to regularization. Smoothing regularization is widely used in practice, but produces high-dimensional images without sharp contrasts between geological units. These tomograms stand in contrast to current implicit geological models, which are able to produce sharp subsurface interfaces with complex geometries using low-dimensional parametrizations. This work aims to bring together modelling concepts from geophysics and geology using the example of electrical resistivity tomography (ERT).
An implicit geological model is used as the centerpiece of a 2D ERT inversion within a deterministic Gauss-Newton framework. The points that define the surfaces of the geological model are included into the model vector of the inverse problem along with a low-dimensional pilot point parametrization of the subsurface electrical resistivity. The point-based parameterization is translated to a triangular finite-element mesh to solve the geoelectrical forward problem. Sensitivities for the geological interfaces and resistivity parameters are efficiently calculated based on finite-differences and the reciprocity theorem, respectively. Each iteration step produces an update of both the geological interface as well as the parameter fields.
The approach converges to an updated geological model and a distribution of subsurface resistivity, which are in accordance with the measured data. The tomograms show sharply localized and realistic subsurface interfaces that are described by only a few parameters. While the imaging of small-scale heterogeneities is challenging and would require a locally increased number of pilot points, the current approach allows for the estimation of smoothly distributed heterogeneities. Further advantages of the approach lie in the improved integration of a-priori geological knowledge, the straightforward extension to 3D, and the applicability to other geophysical methods as well as joint inversion.
How to cite: Förderer, A., Wellmann, F., and Wagner, F.: Geoelectrical imaging of subsurface discontinuities and heterogeneities using low-dimensional parameterizations, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10012, https://doi.org/10.5194/egusphere-egu21-10012, 2021.
EGU21-16358 | vPICO presentations | SM5.2
Efficient multi-scale imaging of subsurface resistivity with uncertainty quantification using ensemble Kalman inversionAndrew Binley, Michael Tso, Marco Iglesias, Paul Wilkinson, Oliver Kuras, and Jonathan Chambers
Electrical resistivity tomography (ERT) is widely used to image the Earth's subsurface and has proven to be an extremely useful tool in application to hydrological problems. Conventional smoothness-constrained inversion of ERT data is efficient and robust, and consequently very popular. However, it does not resolve well sharp interfaces of a resistivity field and tends to reduce and smooth resistivity variations. These issues can be problematic in a range of hydrological or near-surface studies, e.g. mapping regolith-bedrock interfaces. While fully Bayesian approaches, such as those employing Markov chain Monte Carlo sampling, can address the above issues, their very high computation cost makes them impractical for many applications. Ensemble Kalman Inversion (EKI) offers a computationally efficient alternative by approximating the Bayesian posterior distribution in a derivative-free manner, which means only a relatively small number of 'black-box' model runs are required. Although common limitations for ensemble Kalman filter-type methods apply to EKI, it is both efficient and generally captures uncertainty patterns correctly. We propose the use of a new EKI-based framework for ERT which estimates a resistivity model and its uncertainty at a modest computational cost. Our EKI framework uses a level-set parameterization of the unknown resistivity to allow efficient estimation of discontinuous resistivity fields. Instead of estimating level-set parameters directly, we introduce a second step to characterize the spatial variability of the resistivity field and infer length scale hyper-parameters directly. We demonstrate these features by applying the method to a series of synthetic and field examples. We also benchmark our results by comparing them to those obtained from standard smoothness-constrained inversion. Resultant resistivity images from EKI successfully capture arbitrarily shaped interfaces between resistivity zones and the inverted resistivities are close to the true values in synthetic cases. We highlight its readiness and applicability to similar problems in geophysics.
How to cite: Binley, A., Tso, M., Iglesias, M., Wilkinson, P., Kuras, O., and Chambers, J.: Efficient multi-scale imaging of subsurface resistivity with uncertainty quantification using ensemble Kalman inversion, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16358, https://doi.org/10.5194/egusphere-egu21-16358, 2021.
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Electrical resistivity tomography (ERT) is widely used to image the Earth's subsurface and has proven to be an extremely useful tool in application to hydrological problems. Conventional smoothness-constrained inversion of ERT data is efficient and robust, and consequently very popular. However, it does not resolve well sharp interfaces of a resistivity field and tends to reduce and smooth resistivity variations. These issues can be problematic in a range of hydrological or near-surface studies, e.g. mapping regolith-bedrock interfaces. While fully Bayesian approaches, such as those employing Markov chain Monte Carlo sampling, can address the above issues, their very high computation cost makes them impractical for many applications. Ensemble Kalman Inversion (EKI) offers a computationally efficient alternative by approximating the Bayesian posterior distribution in a derivative-free manner, which means only a relatively small number of 'black-box' model runs are required. Although common limitations for ensemble Kalman filter-type methods apply to EKI, it is both efficient and generally captures uncertainty patterns correctly. We propose the use of a new EKI-based framework for ERT which estimates a resistivity model and its uncertainty at a modest computational cost. Our EKI framework uses a level-set parameterization of the unknown resistivity to allow efficient estimation of discontinuous resistivity fields. Instead of estimating level-set parameters directly, we introduce a second step to characterize the spatial variability of the resistivity field and infer length scale hyper-parameters directly. We demonstrate these features by applying the method to a series of synthetic and field examples. We also benchmark our results by comparing them to those obtained from standard smoothness-constrained inversion. Resultant resistivity images from EKI successfully capture arbitrarily shaped interfaces between resistivity zones and the inverted resistivities are close to the true values in synthetic cases. We highlight its readiness and applicability to similar problems in geophysics.
How to cite: Binley, A., Tso, M., Iglesias, M., Wilkinson, P., Kuras, O., and Chambers, J.: Efficient multi-scale imaging of subsurface resistivity with uncertainty quantification using ensemble Kalman inversion, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16358, https://doi.org/10.5194/egusphere-egu21-16358, 2021.
EGU21-12578 | vPICO presentations | SM5.2
Diffraction imaging and depth-velocity inversion with 3D P-Cable seismic dataAlexander Bauer, Benjamin Schwarz, and Dirk Gajewski
Most established methods for the estimation of subsurface velocity models rely on the measurements of reflected or diving waves and therefore require data with sufficiently large source-receiver offsets. For seismic data that lacks these offsets, such as vintage data, low-fold academic data or near zero-offset P-Cable data, these methods fail. Building on recent studies, we apply a workflow that exploits the diffracted wavefield for depth-velocity-model building. This workflow consists of three principal steps: (1) revealing the diffracted wavefield by modeling and adaptively subtracting reflections from the raw data, (2) characterizing the diffractions with physically meaningful wavefront attributes, (3) estimating depth-velocity models with wavefront tomography. We propose a hybrid 2D/3D approach, in which we apply the well-established and automated 2D workflow to numerous inlines of a high-resolution 3D P-Cable dataset acquired near Ritter Island, a small volcanic island located north-east of New Guinea known for a catastrophic flank collapse in 1888. We use the obtained set of parallel 2D velocity models to interpolate a 3D velocity model for the whole data cube, thus overcoming possible issues such as varying data quality in inline and crossline direction and the high computational cost of 3D data analysis. Even though the 2D workflow may suffer from out-of-plane effects, we obtain a smooth 3D velocity model that is consistent with the data.
How to cite: Bauer, A., Schwarz, B., and Gajewski, D.: Diffraction imaging and depth-velocity inversion with 3D P-Cable seismic data, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12578, https://doi.org/10.5194/egusphere-egu21-12578, 2021.
Most established methods for the estimation of subsurface velocity models rely on the measurements of reflected or diving waves and therefore require data with sufficiently large source-receiver offsets. For seismic data that lacks these offsets, such as vintage data, low-fold academic data or near zero-offset P-Cable data, these methods fail. Building on recent studies, we apply a workflow that exploits the diffracted wavefield for depth-velocity-model building. This workflow consists of three principal steps: (1) revealing the diffracted wavefield by modeling and adaptively subtracting reflections from the raw data, (2) characterizing the diffractions with physically meaningful wavefront attributes, (3) estimating depth-velocity models with wavefront tomography. We propose a hybrid 2D/3D approach, in which we apply the well-established and automated 2D workflow to numerous inlines of a high-resolution 3D P-Cable dataset acquired near Ritter Island, a small volcanic island located north-east of New Guinea known for a catastrophic flank collapse in 1888. We use the obtained set of parallel 2D velocity models to interpolate a 3D velocity model for the whole data cube, thus overcoming possible issues such as varying data quality in inline and crossline direction and the high computational cost of 3D data analysis. Even though the 2D workflow may suffer from out-of-plane effects, we obtain a smooth 3D velocity model that is consistent with the data.
How to cite: Bauer, A., Schwarz, B., and Gajewski, D.: Diffraction imaging and depth-velocity inversion with 3D P-Cable seismic data, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12578, https://doi.org/10.5194/egusphere-egu21-12578, 2021.
EGU21-9354 | vPICO presentations | SM5.2
Shallow Crustal Structure in the DehDasht Region (SW Iran) from Ambient Seismic Noise TomographyNastaran Shakeri, Taghi Shirzad, Shobeir Ashkpour Motlagh, and Siavash Norouzi
Zagros continental collision zone (S-SW Iran) is tectonically active and extends over 1800 km contained most part of hydrocarbon reservoirs worldwide. The DehDasht region is located in the southeast of the Dezful embayment in the Zagros fold-and-thrust belt. The existence of an evaporation layer with high velocity features is the main challenge to apply classical seismic exploration in this region. However, ambient seismic noise carries valuable information about the propagation path; hence it could be a useful tool for studying crustal structure in the DehDasht region. For this purpose, we used up to 9 months of continuous data recorded by 107 stations in the area with ~16 × ~24 km2. All stations are equipped with broadband (120s) sensors recording at 100 sps. The standard ambient seismic noise processing was done as outlined by Bensen et al. (2007), and optimize empirical Green’s function (EGF) was retrieved based on the WRMS stacking method. Afterward, Rayleigh wave dispersion measurements were calculated using the FTAN approach in the period range of 0.1-5.0 s, then the inversion procedure was performed by the Fast-Marching Method with an inversion cell size of 2×2 km. Our group velocity tomographic maps show a high velocity anomaly in the Khaviz Mountain belt (west part of the study area) is generally linked to the older, consolidated bodies while two low velocity anomalies are related to the presence of fluids and or younger structures.
How to cite: Shakeri, N., Shirzad, T., Ashkpour Motlagh, S., and Norouzi, S.: Shallow Crustal Structure in the DehDasht Region (SW Iran) from Ambient Seismic Noise Tomography, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9354, https://doi.org/10.5194/egusphere-egu21-9354, 2021.
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Zagros continental collision zone (S-SW Iran) is tectonically active and extends over 1800 km contained most part of hydrocarbon reservoirs worldwide. The DehDasht region is located in the southeast of the Dezful embayment in the Zagros fold-and-thrust belt. The existence of an evaporation layer with high velocity features is the main challenge to apply classical seismic exploration in this region. However, ambient seismic noise carries valuable information about the propagation path; hence it could be a useful tool for studying crustal structure in the DehDasht region. For this purpose, we used up to 9 months of continuous data recorded by 107 stations in the area with ~16 × ~24 km2. All stations are equipped with broadband (120s) sensors recording at 100 sps. The standard ambient seismic noise processing was done as outlined by Bensen et al. (2007), and optimize empirical Green’s function (EGF) was retrieved based on the WRMS stacking method. Afterward, Rayleigh wave dispersion measurements were calculated using the FTAN approach in the period range of 0.1-5.0 s, then the inversion procedure was performed by the Fast-Marching Method with an inversion cell size of 2×2 km. Our group velocity tomographic maps show a high velocity anomaly in the Khaviz Mountain belt (west part of the study area) is generally linked to the older, consolidated bodies while two low velocity anomalies are related to the presence of fluids and or younger structures.
How to cite: Shakeri, N., Shirzad, T., Ashkpour Motlagh, S., and Norouzi, S.: Shallow Crustal Structure in the DehDasht Region (SW Iran) from Ambient Seismic Noise Tomography, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9354, https://doi.org/10.5194/egusphere-egu21-9354, 2021.
EGU21-10124 | vPICO presentations | SM5.2
Seismic structure of the Cheb Basin from high resolution surveying – data quality assessment and first resultsNatalia Banasiak and Florian Bleibinhaus
In this study we present data and preliminary results from several shallow high-resolution seismic surveys in the Cheb Basin, CR, a small intracontinental basin in the North-West Bohemian Massif, located at the Western end of the Cenozoic Eger Rift. The area is well known for its intense earthquake activity, with the largest instrumentally recorded magnitude of ML=4.6. Macroseismic reports of local seismicity date back to the early 19th century, with magnitudes possibly above 5. Quaternary volcanoes, CO2-rich moffettes, and the swarm-like occurrence of the earthquakes suggest they are being triggered by crustal fluids. In contrast, most focal mechanisms show a dominant strike-slip component, indicative of tectonics. Investigating the role of fluids in triggering those earthquakes is one of the objectives of an ongoing ICDP program.
We expect high-resolution images of the basin structure to provide additional constraints regarding the importance of tectonic faulting. To that end, we surveyed several up to 3-km-long reflection and refraction profiles in the basin center across the putative Počátky-Plesná Fault, and at its edge, across the basin-bounding Mariánské Lázně Fault. The up to 350-m-thick basin sediments are mostly of Miocene and Quaternary origin, overlying Paleozoic Variscan units and post-Variscan granites. The main reflectors are around 200-400 ms. The data were collected with a 500-m-long split-spread of single geophones at 2 m spacing, and the raw shots are dominated by ground roll. In this presentation, we will show an overview of the field campaigns and present first results.
How to cite: Banasiak, N. and Bleibinhaus, F.: Seismic structure of the Cheb Basin from high resolution surveying – data quality assessment and first results, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10124, https://doi.org/10.5194/egusphere-egu21-10124, 2021.
In this study we present data and preliminary results from several shallow high-resolution seismic surveys in the Cheb Basin, CR, a small intracontinental basin in the North-West Bohemian Massif, located at the Western end of the Cenozoic Eger Rift. The area is well known for its intense earthquake activity, with the largest instrumentally recorded magnitude of ML=4.6. Macroseismic reports of local seismicity date back to the early 19th century, with magnitudes possibly above 5. Quaternary volcanoes, CO2-rich moffettes, and the swarm-like occurrence of the earthquakes suggest they are being triggered by crustal fluids. In contrast, most focal mechanisms show a dominant strike-slip component, indicative of tectonics. Investigating the role of fluids in triggering those earthquakes is one of the objectives of an ongoing ICDP program.
We expect high-resolution images of the basin structure to provide additional constraints regarding the importance of tectonic faulting. To that end, we surveyed several up to 3-km-long reflection and refraction profiles in the basin center across the putative Počátky-Plesná Fault, and at its edge, across the basin-bounding Mariánské Lázně Fault. The up to 350-m-thick basin sediments are mostly of Miocene and Quaternary origin, overlying Paleozoic Variscan units and post-Variscan granites. The main reflectors are around 200-400 ms. The data were collected with a 500-m-long split-spread of single geophones at 2 m spacing, and the raw shots are dominated by ground roll. In this presentation, we will show an overview of the field campaigns and present first results.
How to cite: Banasiak, N. and Bleibinhaus, F.: Seismic structure of the Cheb Basin from high resolution surveying – data quality assessment and first results, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10124, https://doi.org/10.5194/egusphere-egu21-10124, 2021.
EGU21-9185 | vPICO presentations | SM5.2
Near-Surface High Resolution Characterization of the Seismogenic Alhama de Murcia Strike-slip FaultHandoyo Handoyo, Imma Palomeras, Juan Alcalde, Irene de Felipe, David Martí, Julian García-Mayordomo, Jose Jesus Martínez-Díaz, Teresa Teixidor, Juan Miguel Insúa-Arevalo, and Ramon Carbonell
In Spring 2011 (11th of May), the vicinity of Lorca city (Murcia, SE Iberian Peninsula) was hit by two main seismic shocks that reach a maximum magnitude of 5.2 Mw. The earthquake caused serious widespread damage in the city and its surroundings. Similar events have affected the area regularly in the past (for example: on May 6,1977, 4.2 mg). These events are distributed along a relatively broad band (roughly NE-SW oriented) parallel to the coast, associated to the activation of the Alhama de Murcia Fault (AMF), an oblique-slip (reverse-strike-slip) fault system located in the Eastern Betics Shear Zone. The current study aims to characterize the shallow subsurface across some of the surface outcrop of a few of the main faults that lie within this seismogenic strike-slip fault system. Six normal-incidence seismic reflection profiles were acquired in the area crossing the AMF and the Carrascoy fault, among others). This study focuses on the determination of the shear-wave velocity depth model by applying Multichannel Analysis of Surface Waves (MASW), using the shot records of the seismic reflection profiles. The 1D velocity-depth functions acquired were pasted together to obtain the final 2D velocity models. The hand-picked dispersion curves were inverted using two different approaches to address the consistency of the inversion schemes. The final models reveal relevant differences across the different fault zones, reflecting the heterogeneity and lateral variability that characterizes a complex seismogenic zone, a most probably, diffuse plate boundary.
This research is supported by: Generalitat de Catalunya (AGAUR) grant 2017SGR1022 (GREG); EU (H2020) 871121 (EPOS-SP); EIT-RawMaterials 17024 (SIT4ME), CGL2013-47412-C2-1-P.
How to cite: Handoyo, H., Palomeras, I., Alcalde, J., de Felipe, I., Martí, D., García-Mayordomo, J., Martínez-Díaz, J. J., Teixidor, T., Insúa-Arevalo, J. M., and Carbonell, R.: Near-Surface High Resolution Characterization of the Seismogenic Alhama de Murcia Strike-slip Fault , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9185, https://doi.org/10.5194/egusphere-egu21-9185, 2021.
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In Spring 2011 (11th of May), the vicinity of Lorca city (Murcia, SE Iberian Peninsula) was hit by two main seismic shocks that reach a maximum magnitude of 5.2 Mw. The earthquake caused serious widespread damage in the city and its surroundings. Similar events have affected the area regularly in the past (for example: on May 6,1977, 4.2 mg). These events are distributed along a relatively broad band (roughly NE-SW oriented) parallel to the coast, associated to the activation of the Alhama de Murcia Fault (AMF), an oblique-slip (reverse-strike-slip) fault system located in the Eastern Betics Shear Zone. The current study aims to characterize the shallow subsurface across some of the surface outcrop of a few of the main faults that lie within this seismogenic strike-slip fault system. Six normal-incidence seismic reflection profiles were acquired in the area crossing the AMF and the Carrascoy fault, among others). This study focuses on the determination of the shear-wave velocity depth model by applying Multichannel Analysis of Surface Waves (MASW), using the shot records of the seismic reflection profiles. The 1D velocity-depth functions acquired were pasted together to obtain the final 2D velocity models. The hand-picked dispersion curves were inverted using two different approaches to address the consistency of the inversion schemes. The final models reveal relevant differences across the different fault zones, reflecting the heterogeneity and lateral variability that characterizes a complex seismogenic zone, a most probably, diffuse plate boundary.
This research is supported by: Generalitat de Catalunya (AGAUR) grant 2017SGR1022 (GREG); EU (H2020) 871121 (EPOS-SP); EIT-RawMaterials 17024 (SIT4ME), CGL2013-47412-C2-1-P.
How to cite: Handoyo, H., Palomeras, I., Alcalde, J., de Felipe, I., Martí, D., García-Mayordomo, J., Martínez-Díaz, J. J., Teixidor, T., Insúa-Arevalo, J. M., and Carbonell, R.: Near-Surface High Resolution Characterization of the Seismogenic Alhama de Murcia Strike-slip Fault , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9185, https://doi.org/10.5194/egusphere-egu21-9185, 2021.
EGU21-8750 | vPICO presentations | SM5.2
Applicability and performance of seismic sources in clayBritta Wawerzinek, Stefan Lüth, Roman Esefelder, Rüdiger Giese, and Charlotte M. Krawczyk
Since clay formations are heterogeneous and anisotropic, their seismic characterization at the meso scale is challenging. To tackle this problem, experiments using different seismic sources were undertaken in the Mont Terri Underground Rock Laboratory (URL). The first experiment was carried out using impact and vibroseis sources which were particularly designed for seismic exploration in the underground. The second experiment was conducted using an ELVIS vibration source (Polom et al. 2011) which was mainly designed for near-surface investigations on roads or in open terrain.
The first experiment focused on the applicability and performance of the modular underground system (Borm & Giese 2003) in clay. It demonstrates the successful application of impact and vibroseis source in Opalinus clay. The impact source generates signals with high signal-to-noise ratios and strong lower frequencies (above 100 Hz). Due to that, the impact source is preferred for applications at large offsets. In contrast the vibroseis source has more control of the frequency generation and is able to excite higher frequencies (up to 12 kHz) than the impact source. Therefore, the vibroseis source is preferred for high-resolution applications at near offsets.
Both sources are also suitable for clay characterization and reflection imaging. Travel time analyses resulted in average P- and S-wave velocities that show a clear azimuthal dependence. The carbonate-rich sandy and the sandy facies are characterized by faster velocities than the shaly facies which is stronger anisotropic than the sandy facies. Our findings are in good agreement with seismic velocities and anisotropy determined by Schuster et al. (2017), Popp & Salzer (2007) and Siegesmund et al. (2014). Although the sparse acquisition geometry was not optimal for reflection imaging of the geological conditions around the URL, later arriving shear wave reflections could be extracted from the impact data. A 3D migration focuses these reflections at a distance of ~50 m at the transition from the lower sandy facies to the upper shaly facies.
The second experiment of our pilot survey focused on seismic reflection measurements using near-surface equipment to evaluate its applicability in URLs. Since the ELVIS source was combined with the 3-C geophones of the main experiment, the acquisition geometry was not optimal to image settings beneath the URL. The acquired ELVIS data were dominated by strong surface waves. After their removal, surface wave reflections appeared which mainly map the structural elements of the URL. The test measurements confirmed a general applicability of ELVIS in the tunnel, however it also indicates the need to improve the acquisition geometry.
How to cite: Wawerzinek, B., Lüth, S., Esefelder, R., Giese, R., and Krawczyk, C. M.: Applicability and performance of seismic sources in clay, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8750, https://doi.org/10.5194/egusphere-egu21-8750, 2021.
Since clay formations are heterogeneous and anisotropic, their seismic characterization at the meso scale is challenging. To tackle this problem, experiments using different seismic sources were undertaken in the Mont Terri Underground Rock Laboratory (URL). The first experiment was carried out using impact and vibroseis sources which were particularly designed for seismic exploration in the underground. The second experiment was conducted using an ELVIS vibration source (Polom et al. 2011) which was mainly designed for near-surface investigations on roads or in open terrain.
The first experiment focused on the applicability and performance of the modular underground system (Borm & Giese 2003) in clay. It demonstrates the successful application of impact and vibroseis source in Opalinus clay. The impact source generates signals with high signal-to-noise ratios and strong lower frequencies (above 100 Hz). Due to that, the impact source is preferred for applications at large offsets. In contrast the vibroseis source has more control of the frequency generation and is able to excite higher frequencies (up to 12 kHz) than the impact source. Therefore, the vibroseis source is preferred for high-resolution applications at near offsets.
Both sources are also suitable for clay characterization and reflection imaging. Travel time analyses resulted in average P- and S-wave velocities that show a clear azimuthal dependence. The carbonate-rich sandy and the sandy facies are characterized by faster velocities than the shaly facies which is stronger anisotropic than the sandy facies. Our findings are in good agreement with seismic velocities and anisotropy determined by Schuster et al. (2017), Popp & Salzer (2007) and Siegesmund et al. (2014). Although the sparse acquisition geometry was not optimal for reflection imaging of the geological conditions around the URL, later arriving shear wave reflections could be extracted from the impact data. A 3D migration focuses these reflections at a distance of ~50 m at the transition from the lower sandy facies to the upper shaly facies.
The second experiment of our pilot survey focused on seismic reflection measurements using near-surface equipment to evaluate its applicability in URLs. Since the ELVIS source was combined with the 3-C geophones of the main experiment, the acquisition geometry was not optimal to image settings beneath the URL. The acquired ELVIS data were dominated by strong surface waves. After their removal, surface wave reflections appeared which mainly map the structural elements of the URL. The test measurements confirmed a general applicability of ELVIS in the tunnel, however it also indicates the need to improve the acquisition geometry.
How to cite: Wawerzinek, B., Lüth, S., Esefelder, R., Giese, R., and Krawczyk, C. M.: Applicability and performance of seismic sources in clay, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8750, https://doi.org/10.5194/egusphere-egu21-8750, 2021.
EGU21-3573 | vPICO presentations | SM5.2
Modeling ambient noise distributions for surface wave imaging based on full waveform inversionChangjiang Zhou, Jianghai Xia, Feng Cheng, Jingyin Pang, and Xinhua Chen
Abundant noise sources in urban area has been widely utilized for subsurface investigations based on the seiemic interferometry. Reliable dispersion extraction between two seismic stations is an essential basis of surface wave imaging. Noise source directivity has become an inescapable obstacle and a main concern for passive seismic surveys: it basically breaks the physics of Green’s function retrieval in travel-time tomography; Moreover, the azimuthal effect of ambient noise sources would inherently cause different levels of early arrival on cross-correlation functions, so that the apparent velocity of surface wave could be overestimated in multichannel slant stackings.
Instead of the conventional frequency-time analysis, which aims to extract the apparent dispersions of phase/group velocity between seismic stations, we proposed a method to jointly invert noise source distributions and the corresponding unbiased surface wave velocities based on the theoretical framework of full waveform ambient noise inversion. Waveform itself could intrinsically contains the features of travel-time, energy and asymmetry of ambient noise cross correlation functions (NCF). And they could in return map the resulted NCF into the noise source distributions and velocity structures. The L2 norm of cross-correlating waveform misfits was taken as the objective function to conduct gradient based inversion (i.e. the L-BFGS algorithm). We parametrized the noise source distributions as a temporally ensemble averaged model, which was discretized as a spatially plane grid of normalized source strength. The surface wave velocity model was approximated as the straight-ray interstation velocity. The two kinds of variants were decoupled in waveform misfit function by their corresponding partial derivatives to iteratively update the model space.
The effectiveness of source-velocity joint imaging using above full waveform inversion work flow was qualified by both the synthetic test and the applied research in Hangzhou urban area. The inverted noise source model was comparable with the urban traffic- and construction- noise distributions. And the truthful surface wave velocities were achieved considering the constraint of noise source distributions, they were also prior constrained and later verified by local borehole datasets.
How to cite: Zhou, C., Xia, J., Cheng, F., Pang, J., and Chen, X.: Modeling ambient noise distributions for surface wave imaging based on full waveform inversion , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3573, https://doi.org/10.5194/egusphere-egu21-3573, 2021.
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We are sorry, but presentations are only available for users who registered for the conference. Thank you.
Abundant noise sources in urban area has been widely utilized for subsurface investigations based on the seiemic interferometry. Reliable dispersion extraction between two seismic stations is an essential basis of surface wave imaging. Noise source directivity has become an inescapable obstacle and a main concern for passive seismic surveys: it basically breaks the physics of Green’s function retrieval in travel-time tomography; Moreover, the azimuthal effect of ambient noise sources would inherently cause different levels of early arrival on cross-correlation functions, so that the apparent velocity of surface wave could be overestimated in multichannel slant stackings.
Instead of the conventional frequency-time analysis, which aims to extract the apparent dispersions of phase/group velocity between seismic stations, we proposed a method to jointly invert noise source distributions and the corresponding unbiased surface wave velocities based on the theoretical framework of full waveform ambient noise inversion. Waveform itself could intrinsically contains the features of travel-time, energy and asymmetry of ambient noise cross correlation functions (NCF). And they could in return map the resulted NCF into the noise source distributions and velocity structures. The L2 norm of cross-correlating waveform misfits was taken as the objective function to conduct gradient based inversion (i.e. the L-BFGS algorithm). We parametrized the noise source distributions as a temporally ensemble averaged model, which was discretized as a spatially plane grid of normalized source strength. The surface wave velocity model was approximated as the straight-ray interstation velocity. The two kinds of variants were decoupled in waveform misfit function by their corresponding partial derivatives to iteratively update the model space.
The effectiveness of source-velocity joint imaging using above full waveform inversion work flow was qualified by both the synthetic test and the applied research in Hangzhou urban area. The inverted noise source model was comparable with the urban traffic- and construction- noise distributions. And the truthful surface wave velocities were achieved considering the constraint of noise source distributions, they were also prior constrained and later verified by local borehole datasets.
How to cite: Zhou, C., Xia, J., Cheng, F., Pang, J., and Chen, X.: Modeling ambient noise distributions for surface wave imaging based on full waveform inversion , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3573, https://doi.org/10.5194/egusphere-egu21-3573, 2021.
EGU21-2500 | vPICO presentations | SM5.2
An evaluation of generated source signals from machinery in conventional tunnelling and their possible application in a tunnel seismic while drilling (TSWD) systemIrene Hartl, Ingrid Schlögel, Robert Wenighofer, and Jakob Gallistl
Geological conditions and their uncertainties are a major risk factor in underground construction projects. To ensure a fast, smooth and save completion of the excavation, a prediction of the geological conditions in front of the working face during tunnelling is a topic of great importance.
Various geophysical methods for a prediction of the conditions ahead of the tunnel face have been developed over the past years, yet, most of them being seismic techniques, which require a short interruption of the excavation to minimise noise interference. However, there is also the approach with TSWD which uses the working TBM (Tunnel Boring Machine) as a source signal and can thus work simultaneously with the excavation. Up to now, this concept has been applied primarily in mechanised tunnelling and there are hardly any applications in conventional tunnelling.
In the course of several practical experiments at the “Zentrum am Berg” in Eisenerz (Austria), different concepts for a transfer of TSWD from mechanised to conventional tunnelling were developed and tested at scale in an underground research facility. Three machines were used for these tests, an excavator with a hydraulic hammer attached as well as two different drilling jumbos. The devices were equipped with an accelerometer to pick up the source signal at its origin (pilot signal). Different sensor positions were tested using a sledge hammer as a source and evaluated in detail. Moreover, omnidirectional geophones of different sensitivities (4.5 Hz and 27 Hz) were tested and compared as transducers in the adjacent rock mass.
An essential part of the experiment analysis consisted of the evaluation of the source characteristics as well as the generated spectral bandwidth of the source signal from typical construction machines in conventional tunnelling. Consequently, the outcomes will be another step forward in the development of a TSWD exploration system also applicable to conventional tunnelling projects.
How to cite: Hartl, I., Schlögel, I., Wenighofer, R., and Gallistl, J.: An evaluation of generated source signals from machinery in conventional tunnelling and their possible application in a tunnel seismic while drilling (TSWD) system, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2500, https://doi.org/10.5194/egusphere-egu21-2500, 2021.
Geological conditions and their uncertainties are a major risk factor in underground construction projects. To ensure a fast, smooth and save completion of the excavation, a prediction of the geological conditions in front of the working face during tunnelling is a topic of great importance.
Various geophysical methods for a prediction of the conditions ahead of the tunnel face have been developed over the past years, yet, most of them being seismic techniques, which require a short interruption of the excavation to minimise noise interference. However, there is also the approach with TSWD which uses the working TBM (Tunnel Boring Machine) as a source signal and can thus work simultaneously with the excavation. Up to now, this concept has been applied primarily in mechanised tunnelling and there are hardly any applications in conventional tunnelling.
In the course of several practical experiments at the “Zentrum am Berg” in Eisenerz (Austria), different concepts for a transfer of TSWD from mechanised to conventional tunnelling were developed and tested at scale in an underground research facility. Three machines were used for these tests, an excavator with a hydraulic hammer attached as well as two different drilling jumbos. The devices were equipped with an accelerometer to pick up the source signal at its origin (pilot signal). Different sensor positions were tested using a sledge hammer as a source and evaluated in detail. Moreover, omnidirectional geophones of different sensitivities (4.5 Hz and 27 Hz) were tested and compared as transducers in the adjacent rock mass.
An essential part of the experiment analysis consisted of the evaluation of the source characteristics as well as the generated spectral bandwidth of the source signal from typical construction machines in conventional tunnelling. Consequently, the outcomes will be another step forward in the development of a TSWD exploration system also applicable to conventional tunnelling projects.
How to cite: Hartl, I., Schlögel, I., Wenighofer, R., and Gallistl, J.: An evaluation of generated source signals from machinery in conventional tunnelling and their possible application in a tunnel seismic while drilling (TSWD) system, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2500, https://doi.org/10.5194/egusphere-egu21-2500, 2021.
EGU21-8312 | vPICO presentations | SM5.2
An application of induced event interferometry approach at The Geysers Geothermal Field, California, USATaghi Shirzad, Stanisław Lasocki, and Beata Orlecka‐Sikora
While the classical tomography approaches, e.g., P-, S-, and/or surface-wave traveltime tomography, provide a general structure of the Earth’s interior, new developments in signal processing of interferometry approaches are needed to obtain a high-resolution velocity structure. If the number of earthquakes is adequate, the virtual seismometer method may be a solution in regions with sparse instrumental coverage. Theoretically, the empirical Green’s functions between a pair of events can be retrieved using earthquake’s cross-correlations. Here, an event interferometry approach was used on a very small scale around Prati-9 and Prati-29 injection wells in the NW of The Geysers Geothermal Field. The study region experienced intense injection-induced seismicity. We selected all events with location uncertainties less than 50 m in a cuboid of the horizontal side ~1 × ~2 km and the vertical edge at depths between 1.0 and 2.0 km. The cuboid was cut into 100m thick layers, and we applied to events from each layer criteria enabling a quasi 2D approach. After calculating the Rayleigh wave group velocity dispersion curves, further processing was performed at a 0.2s period, selected based on the sensitivity kernel criterion. Finally, the relative velocity model of each layer at the depth z was obtained by subtracting the velocity model of the just overlying layer (at the depth z-100m) from the model of this layer. Our resultant velocity model in the study area indicated four low-velocity anomalies. The first one can be linked by the two layers interface topography variation at the top of the cuboid (depth 1000 m). The secondary faults can cause the second low-velocity anomaly. The other two anomalies look to result from fluid injection into Prati-9 and Prati-29 wells.
This work was supported under the S4CE: "Science for Clean Energy" project, which has received funding from the European Union’s Horizon 2020 research and innovation program, under grant agreement No 764810.
How to cite: Shirzad, T., Lasocki, S., and Orlecka‐Sikora, B.: An application of induced event interferometry approach at The Geysers Geothermal Field, California, USA, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8312, https://doi.org/10.5194/egusphere-egu21-8312, 2021.
While the classical tomography approaches, e.g., P-, S-, and/or surface-wave traveltime tomography, provide a general structure of the Earth’s interior, new developments in signal processing of interferometry approaches are needed to obtain a high-resolution velocity structure. If the number of earthquakes is adequate, the virtual seismometer method may be a solution in regions with sparse instrumental coverage. Theoretically, the empirical Green’s functions between a pair of events can be retrieved using earthquake’s cross-correlations. Here, an event interferometry approach was used on a very small scale around Prati-9 and Prati-29 injection wells in the NW of The Geysers Geothermal Field. The study region experienced intense injection-induced seismicity. We selected all events with location uncertainties less than 50 m in a cuboid of the horizontal side ~1 × ~2 km and the vertical edge at depths between 1.0 and 2.0 km. The cuboid was cut into 100m thick layers, and we applied to events from each layer criteria enabling a quasi 2D approach. After calculating the Rayleigh wave group velocity dispersion curves, further processing was performed at a 0.2s period, selected based on the sensitivity kernel criterion. Finally, the relative velocity model of each layer at the depth z was obtained by subtracting the velocity model of the just overlying layer (at the depth z-100m) from the model of this layer. Our resultant velocity model in the study area indicated four low-velocity anomalies. The first one can be linked by the two layers interface topography variation at the top of the cuboid (depth 1000 m). The secondary faults can cause the second low-velocity anomaly. The other two anomalies look to result from fluid injection into Prati-9 and Prati-29 wells.
This work was supported under the S4CE: "Science for Clean Energy" project, which has received funding from the European Union’s Horizon 2020 research and innovation program, under grant agreement No 764810.
How to cite: Shirzad, T., Lasocki, S., and Orlecka‐Sikora, B.: An application of induced event interferometry approach at The Geysers Geothermal Field, California, USA, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8312, https://doi.org/10.5194/egusphere-egu21-8312, 2021.
EGU21-6904 | vPICO presentations | SM5.2
Numerical and Theoretical Investigation on the Origin of the Multiple Peaks of the H/V Ratio CurveWanbo Xiao, Siqi Lu, and Yanbin Wang
Despite the popularity of the horizontal to vertical spectral ratio (HVSR) method in site effect studies, the origin of the H/V peaks has been controversial since this method was proposed. Many previous studies mainly focused on the explanation of the first or single peak of the H/V ratio, trying to distinguish between the two hypotheses — the S-wave resonance and ellipticity of Rayleigh wave. However, it is common both in numerical simulations and practical experiments that the H/V ratio exhibits multiple peaks, which is essential to explore the origin of the H/V peaks.
The cause for the multiple H/V peaks has not been clearly figured out, and once was simply explained as the result of multi subsurface layers. Therefore, we adopted numerical method to simulate the ambient noise in various layered half-space models and calculated the H/V ratio curves for further comparisons. The peak frequencies of the H/V curves accord well with the theoretical frequencies of S-wave resonance in two-layer models, whose frequencies only depend on the S wave velocity and the thickness of the subsurface layer. The same is true for models with varying model parameters. Besides, the theoretical formula of the S-wave resonance in multiple-layer models is proposed and then supported by numerical investigations as in the cases of two-layer models. We also extended the S-wave resonance to P-wave resonance and found that its theoretical frequencies fit well with the V/H peaks, which could be an evidence to support the S-wave resonance theory from a new perspective. By contrast, there are obvious differences between the higher orders of the H/V ratio peaks and the higher orders of Rayleigh wave ellipticity curves both in two-layer and multiple-layer models. The Rayleigh wave ellipticity curves are found to be sensitive to the Poisson’s ratio and the thickness of the subsurface layer, so the variation of the P wave velocity can affect the peak frequencies of the Rayleigh wave ellipticity curves while the H/V peaks show slight change. The Rayleigh wave ellipticity theory is thus proved to be inappropriate for the explanation of the multiple H/V peaks, while the possible effects of the Rayleigh wave on the fundamental H/V peak still cannot be excluded.
Based on the analyses above, we proposed a new evidence to support the claim that the peak frequencies of the H/V ratio curve, except the fundamental peaks, are caused by S-wave resonance. The relationship between the P-wave resonance and the V/H peaks may also find further application.
How to cite: Xiao, W., Lu, S., and Wang, Y.: Numerical and Theoretical Investigation on the Origin of the Multiple Peaks of the H/V Ratio Curve, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6904, https://doi.org/10.5194/egusphere-egu21-6904, 2021.
Despite the popularity of the horizontal to vertical spectral ratio (HVSR) method in site effect studies, the origin of the H/V peaks has been controversial since this method was proposed. Many previous studies mainly focused on the explanation of the first or single peak of the H/V ratio, trying to distinguish between the two hypotheses — the S-wave resonance and ellipticity of Rayleigh wave. However, it is common both in numerical simulations and practical experiments that the H/V ratio exhibits multiple peaks, which is essential to explore the origin of the H/V peaks.
The cause for the multiple H/V peaks has not been clearly figured out, and once was simply explained as the result of multi subsurface layers. Therefore, we adopted numerical method to simulate the ambient noise in various layered half-space models and calculated the H/V ratio curves for further comparisons. The peak frequencies of the H/V curves accord well with the theoretical frequencies of S-wave resonance in two-layer models, whose frequencies only depend on the S wave velocity and the thickness of the subsurface layer. The same is true for models with varying model parameters. Besides, the theoretical formula of the S-wave resonance in multiple-layer models is proposed and then supported by numerical investigations as in the cases of two-layer models. We also extended the S-wave resonance to P-wave resonance and found that its theoretical frequencies fit well with the V/H peaks, which could be an evidence to support the S-wave resonance theory from a new perspective. By contrast, there are obvious differences between the higher orders of the H/V ratio peaks and the higher orders of Rayleigh wave ellipticity curves both in two-layer and multiple-layer models. The Rayleigh wave ellipticity curves are found to be sensitive to the Poisson’s ratio and the thickness of the subsurface layer, so the variation of the P wave velocity can affect the peak frequencies of the Rayleigh wave ellipticity curves while the H/V peaks show slight change. The Rayleigh wave ellipticity theory is thus proved to be inappropriate for the explanation of the multiple H/V peaks, while the possible effects of the Rayleigh wave on the fundamental H/V peak still cannot be excluded.
Based on the analyses above, we proposed a new evidence to support the claim that the peak frequencies of the H/V ratio curve, except the fundamental peaks, are caused by S-wave resonance. The relationship between the P-wave resonance and the V/H peaks may also find further application.
How to cite: Xiao, W., Lu, S., and Wang, Y.: Numerical and Theoretical Investigation on the Origin of the Multiple Peaks of the H/V Ratio Curve, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6904, https://doi.org/10.5194/egusphere-egu21-6904, 2021.
SM5.3 – Shallow shear-wave and multi-component seismic techniques – methodical capability, technical developments, data processing, and case studies
EGU21-10170 | vPICO presentations | SM5.3
Shear and compressive wave data acquisition using multicomponent vibrating source and landstreamerAndre Pugin, Barbara Dietiker, Kevin Brewer, and Timothy Cartwright
In the vicinity of Ottawa, Ontario, Canada, we have recorded many multicomponent seismic data sets using an in-house multicomponent vibrator source named Microvibe and a landstreamer receiver array with 48 3-C 28-Hz geophones at 0.75-m intervals. The receiver spread length was 35.25 m, and the near-offset was 1.50 m. We used one, two or three source and three receiver orientations — vertical (V), inline-horizontal (H1), and transverse-horizontal (H2). We identified several reflection wave modes in the field records — PP, PS, SP, and SS, in addition to refracted waves, and Rayleigh-mode and Love-mode surface waves. We computed the semblance spectra of the selected shot records and ascertained the wave modes based on the semblance peaks. We then performed CMP stacking of each of the 9-C data sets using the PP and SS stacking velocities to compute PP and SS reflection profiles.
Despite the fact that any source type can generate any combination of wave modes — PP, PS, SP, and SS, partitioning of the source energy depends on the source orientation and VP/VS ratio. Our examples demonstrate that the most prominent PP reflection energy is recorded by the VV source-receiver orientation, whereas the most prominent SS reflection energy is recorded by the H2H2 source-receiver orientation with possibility to obtain decent shear wave near surface data in all other vibrating and receiving directions.
Pugin, Andre and Yilmaz, Öz, 2019. Optimum source-receiver orientations to capture PP, PS, SP, and SS reflected wave modes. The Leading Edge, vol. 38/1, p. 45-52. https://doi.org/10.1190/tle38010045.1
How to cite: Pugin, A., Dietiker, B., Brewer, K., and Cartwright, T.: Shear and compressive wave data acquisition using multicomponent vibrating source and landstreamer, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10170, https://doi.org/10.5194/egusphere-egu21-10170, 2021.
In the vicinity of Ottawa, Ontario, Canada, we have recorded many multicomponent seismic data sets using an in-house multicomponent vibrator source named Microvibe and a landstreamer receiver array with 48 3-C 28-Hz geophones at 0.75-m intervals. The receiver spread length was 35.25 m, and the near-offset was 1.50 m. We used one, two or three source and three receiver orientations — vertical (V), inline-horizontal (H1), and transverse-horizontal (H2). We identified several reflection wave modes in the field records — PP, PS, SP, and SS, in addition to refracted waves, and Rayleigh-mode and Love-mode surface waves. We computed the semblance spectra of the selected shot records and ascertained the wave modes based on the semblance peaks. We then performed CMP stacking of each of the 9-C data sets using the PP and SS stacking velocities to compute PP and SS reflection profiles.
Despite the fact that any source type can generate any combination of wave modes — PP, PS, SP, and SS, partitioning of the source energy depends on the source orientation and VP/VS ratio. Our examples demonstrate that the most prominent PP reflection energy is recorded by the VV source-receiver orientation, whereas the most prominent SS reflection energy is recorded by the H2H2 source-receiver orientation with possibility to obtain decent shear wave near surface data in all other vibrating and receiving directions.
Pugin, Andre and Yilmaz, Öz, 2019. Optimum source-receiver orientations to capture PP, PS, SP, and SS reflected wave modes. The Leading Edge, vol. 38/1, p. 45-52. https://doi.org/10.1190/tle38010045.1
How to cite: Pugin, A., Dietiker, B., Brewer, K., and Cartwright, T.: Shear and compressive wave data acquisition using multicomponent vibrating source and landstreamer, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10170, https://doi.org/10.5194/egusphere-egu21-10170, 2021.
EGU21-2916 | vPICO presentations | SM5.3
Shear-wave seismic reflection processing - the importance of velocity analysisBarbara Dietiker, André J.-M. Pugin, Matthew P. Griffiths, Kevin Brewer, and Timothy Cartwright
Based on our experience, one of the most important steps in processing shear-wave seismic reflection data is the velocity analysis. In unconsolidated materials a very fine velocity analysis is more essential for S-waves than for P-waves because shear-wave velocities vary over several orders of magnitude and can change very quickly laterally and with depth. Velocities between 100m/s in glaciolacustine/marine deposits (clay-sized silts) and 1200m/s in stiff diamicton (till) were encountered in recent surveys. Shear-wave velocities have the large advantage of not being changed by the phase of the pore content such as the groundwater table.
We present two fundamentally different methods for velocity determination: 1) velocity semblance analysis based on hyperbolic reflection move-out on common midpoint (cmp) gathers and 2) Local Phase – Local Shift (LPLS) method which automatically estimates the reflection slope (local static shift) in the time-frequency domain of cmp gathers. Published in 2020, the latter method can be used for automated processing and substantially saves processing time.
Processing steps in preparation for velocity analysis (independent of the chosen method) include frequency filtering, trace equalizing and muting. We show velocity semblance images from different geological settings (glacial, postglacial) and from different shear components and discuss differences. Information gained besides shear velocities include mapped reflectors and located diffractions. Using those examples, we demonstrate how combining all information using visualisation techniques enhances interpretation of such data sets.
How to cite: Dietiker, B., Pugin, A. J.-M., Griffiths, M. P., Brewer, K., and Cartwright, T.: Shear-wave seismic reflection processing - the importance of velocity analysis, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2916, https://doi.org/10.5194/egusphere-egu21-2916, 2021.
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Based on our experience, one of the most important steps in processing shear-wave seismic reflection data is the velocity analysis. In unconsolidated materials a very fine velocity analysis is more essential for S-waves than for P-waves because shear-wave velocities vary over several orders of magnitude and can change very quickly laterally and with depth. Velocities between 100m/s in glaciolacustine/marine deposits (clay-sized silts) and 1200m/s in stiff diamicton (till) were encountered in recent surveys. Shear-wave velocities have the large advantage of not being changed by the phase of the pore content such as the groundwater table.
We present two fundamentally different methods for velocity determination: 1) velocity semblance analysis based on hyperbolic reflection move-out on common midpoint (cmp) gathers and 2) Local Phase – Local Shift (LPLS) method which automatically estimates the reflection slope (local static shift) in the time-frequency domain of cmp gathers. Published in 2020, the latter method can be used for automated processing and substantially saves processing time.
Processing steps in preparation for velocity analysis (independent of the chosen method) include frequency filtering, trace equalizing and muting. We show velocity semblance images from different geological settings (glacial, postglacial) and from different shear components and discuss differences. Information gained besides shear velocities include mapped reflectors and located diffractions. Using those examples, we demonstrate how combining all information using visualisation techniques enhances interpretation of such data sets.
How to cite: Dietiker, B., Pugin, A. J.-M., Griffiths, M. P., Brewer, K., and Cartwright, T.: Shear-wave seismic reflection processing - the importance of velocity analysis, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2916, https://doi.org/10.5194/egusphere-egu21-2916, 2021.
EGU21-11685 | vPICO presentations | SM5.3
Reflection seismic imaging of buried shallow salt structures – examples from ongoing case studies in Northern GermanyUlrich Polom, Rebekka Mecking, Phillip Leineweber, and Andreas Omlin
In the North German Basin salt tectonics generated a wide range of evaporite structures since the Upper Triassic, resulting in e.g. extended salt walls, salt diapirs, and salt pillows in the depth range up to 8 km. Due to their trap and seal properties these structures were in the focus of hydrocarbon exploration over many decades, leading to an excellent mapping of their geometries below 300 m in depth. During salt rise Rotliegend formations were partly involved as a constituent. Some structures penetrated the salt table, some also the former surface. Dissolution (subrosion) and erosion of the salt cap rock by meteoric water took place, combined with several glacial and intraglacial overprints. Finally the salt structures were covered by pleistocene and holocene sediments. This situation partly resulted in proneness for ongoing karstification of the salt cap rock, leading to e.g. local subsidence and sinkhole occurrence at the surface. The geometry, structure and internal lithology of these shallow salt cap rocks are widely unknown. Expanding urban and industrial development, water resources management and increasing climate change effects enhance the demands for shallow mapping and characterization of these structures regarding save building grounds and sustainable water resources.
Results of shallow drilling investigations of the salt cap rock and the overburden show unexpectedly heterogenous subsurface conditions, yielding to limited success towards mapping and characterization. Thus, shallow high-resolution geophysical methods are in demand to close the gaps with preferred focus of applicability in urban and industrial environments. Method evaluations starting in 2010 geared towards shallow high-resolution reflection seismic to meet the requirements of both depth penetration and structure resolution. Since 2017 a combination of S-wave and P-wave seismic methods including depth calibrations by Vertical Seismic Profiling (VSP) enabled 2.5D subsurface imaging starting few meters below the surface up to several hundred meters depth in 0.5-5 m resolution range, respectively. The resulting profiles image strong variations along the boundaries and on top of the salt cap rock. Beside improved mapping capabilities, aim of research is the development of characteristic data features to differentiate save and non-save areas.
How to cite: Polom, U., Mecking, R., Leineweber, P., and Omlin, A.: Reflection seismic imaging of buried shallow salt structures – examples from ongoing case studies in Northern Germany, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11685, https://doi.org/10.5194/egusphere-egu21-11685, 2021.
In the North German Basin salt tectonics generated a wide range of evaporite structures since the Upper Triassic, resulting in e.g. extended salt walls, salt diapirs, and salt pillows in the depth range up to 8 km. Due to their trap and seal properties these structures were in the focus of hydrocarbon exploration over many decades, leading to an excellent mapping of their geometries below 300 m in depth. During salt rise Rotliegend formations were partly involved as a constituent. Some structures penetrated the salt table, some also the former surface. Dissolution (subrosion) and erosion of the salt cap rock by meteoric water took place, combined with several glacial and intraglacial overprints. Finally the salt structures were covered by pleistocene and holocene sediments. This situation partly resulted in proneness for ongoing karstification of the salt cap rock, leading to e.g. local subsidence and sinkhole occurrence at the surface. The geometry, structure and internal lithology of these shallow salt cap rocks are widely unknown. Expanding urban and industrial development, water resources management and increasing climate change effects enhance the demands for shallow mapping and characterization of these structures regarding save building grounds and sustainable water resources.
Results of shallow drilling investigations of the salt cap rock and the overburden show unexpectedly heterogenous subsurface conditions, yielding to limited success towards mapping and characterization. Thus, shallow high-resolution geophysical methods are in demand to close the gaps with preferred focus of applicability in urban and industrial environments. Method evaluations starting in 2010 geared towards shallow high-resolution reflection seismic to meet the requirements of both depth penetration and structure resolution. Since 2017 a combination of S-wave and P-wave seismic methods including depth calibrations by Vertical Seismic Profiling (VSP) enabled 2.5D subsurface imaging starting few meters below the surface up to several hundred meters depth in 0.5-5 m resolution range, respectively. The resulting profiles image strong variations along the boundaries and on top of the salt cap rock. Beside improved mapping capabilities, aim of research is the development of characteristic data features to differentiate save and non-save areas.
How to cite: Polom, U., Mecking, R., Leineweber, P., and Omlin, A.: Reflection seismic imaging of buried shallow salt structures – examples from ongoing case studies in Northern Germany, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11685, https://doi.org/10.5194/egusphere-egu21-11685, 2021.
EGU21-12202 | vPICO presentations | SM5.3
Physics of shear-waves propagating in saturated and unsaturated soils: new potential for monitoring soil dynamics and stabilityRanajit Ghose
Shear waves are uniquely informative because of their vector nature – with both polarization and propagation of shear waves being useful sources of information, their sensitivity to in-situ stress and grain-to-grain contact, and also because of the low velocity of shear waves in relatively soft formations - offering short wavelength and hence high resolution. Decimetre-scale resolution found in shear-wave reflection data in soft soil has resulted in new application possibilities. Medium anisotropy extracted from multi-component shear-wave data has provided information on natural symmetries in small-strain rigidity and/or stress in the shallow subsurface, which are caused by factors that are of great interest to the engineers. AVO response of shear waves at near-surface soil-layer boundaries has also proven to be useful for extracting local information in the subsoil.
In the present research we have looked at the sensitivity of shear-wave velocity and the underlying physics in both saturated and unsaturated near-surface soils, and if these can practically be used for monitoring soil dynamics and soil stability. Time-lapse changes in shear-wave velocity could be used to monitor changes in in-situ stress in the saturated sands. More recently, we have developed methodologies to invert time-lapse shear-wave velocity information together with geo-electrical information to obtain in-situ values of water saturation and suction in different partially saturated soil units. Incorporation of this information in a spatially varying sense is imperative in order to make assessment of stability of unsaturated soil slopes subjected to rainfall, modelling flooding and sediment flows due to increased surface runoff and erosion, sustainable agriculture through in-situ water moisture monitoring, and modelling pollutant transport through soils.
How to cite: Ghose, R.: Physics of shear-waves propagating in saturated and unsaturated soils: new potential for monitoring soil dynamics and stability, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12202, https://doi.org/10.5194/egusphere-egu21-12202, 2021.
Shear waves are uniquely informative because of their vector nature – with both polarization and propagation of shear waves being useful sources of information, their sensitivity to in-situ stress and grain-to-grain contact, and also because of the low velocity of shear waves in relatively soft formations - offering short wavelength and hence high resolution. Decimetre-scale resolution found in shear-wave reflection data in soft soil has resulted in new application possibilities. Medium anisotropy extracted from multi-component shear-wave data has provided information on natural symmetries in small-strain rigidity and/or stress in the shallow subsurface, which are caused by factors that are of great interest to the engineers. AVO response of shear waves at near-surface soil-layer boundaries has also proven to be useful for extracting local information in the subsoil.
In the present research we have looked at the sensitivity of shear-wave velocity and the underlying physics in both saturated and unsaturated near-surface soils, and if these can practically be used for monitoring soil dynamics and soil stability. Time-lapse changes in shear-wave velocity could be used to monitor changes in in-situ stress in the saturated sands. More recently, we have developed methodologies to invert time-lapse shear-wave velocity information together with geo-electrical information to obtain in-situ values of water saturation and suction in different partially saturated soil units. Incorporation of this information in a spatially varying sense is imperative in order to make assessment of stability of unsaturated soil slopes subjected to rainfall, modelling flooding and sediment flows due to increased surface runoff and erosion, sustainable agriculture through in-situ water moisture monitoring, and modelling pollutant transport through soils.
How to cite: Ghose, R.: Physics of shear-waves propagating in saturated and unsaturated soils: new potential for monitoring soil dynamics and stability, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12202, https://doi.org/10.5194/egusphere-egu21-12202, 2021.
EGU21-14727 | vPICO presentations | SM5.3
A shallow Vs model from full wave inversion for hydraulic fracturing siteGuoliang Li and Min Chen
EGU21-11287 | vPICO presentations | SM5.3
Delineation of S-wave velocity profiles across the Himalayan Frontal Thrust (HFT) using metaheuristic approaches.Prabhakar Kumar and Dibakar Ghosal
The continent-continent collision between the Indian and Asian Plate formed a series of major faults from north to south along the Himalayan belt. Among these Himalayan Frontal Thrust (HFT) is the southernmost and youngest one and is tectonically very active. Any information on the shear wave velocity distribution across the fault is therefore very important. In this study, we have used the Wide Angle Multichannel Analysis of Surface Wave (WAMASW) to estimate the subsurface shear wave velocity profiles across HFT at Pawalgarh in Uttarakhand, India, using widely used stochastic global search Particle Swarm Optimization (PSO) and Grey wolf Optimization (GWO) algorithms. To gain confidence on the accuracy of the inversion results, we first generated an elastic synthetic seismic shot gather with ground rolls by using the forward modelling scheme of SOFI2D for a two-layer velocity depth model overlying a half-space. The generated gather was then processed in MATLAB to generate the experimental dispersion curve using the Phase shift method. We then extracted the fundamental mode for the gather and inverted it using the standard PSO and GWO algorithms and estimated 1D shear wave velocity profile. After getting acceptable results for the synthetic dataset, we then applied the PSO algorithm to generate the 1D S-wave velocity (Vs) profile across the Himalayan Frontal Thrust (HFT). In the study area, the Rayleigh wave phase velocity for the first shot varies from 444 to 743 m/s. We then obtained the 1D shear wave velocity profiles and a jump in Vs is observed across the HFT indicating variation in the sediment stiffness across the fault.
Keywords: WAMASW, dispersion, Meta- Heuristic, PSO, GWO, 1D Shear wave velocity
How to cite: Kumar, P. and Ghosal, D.: Delineation of S-wave velocity profiles across the Himalayan Frontal Thrust (HFT) using metaheuristic approaches., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11287, https://doi.org/10.5194/egusphere-egu21-11287, 2021.
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The continent-continent collision between the Indian and Asian Plate formed a series of major faults from north to south along the Himalayan belt. Among these Himalayan Frontal Thrust (HFT) is the southernmost and youngest one and is tectonically very active. Any information on the shear wave velocity distribution across the fault is therefore very important. In this study, we have used the Wide Angle Multichannel Analysis of Surface Wave (WAMASW) to estimate the subsurface shear wave velocity profiles across HFT at Pawalgarh in Uttarakhand, India, using widely used stochastic global search Particle Swarm Optimization (PSO) and Grey wolf Optimization (GWO) algorithms. To gain confidence on the accuracy of the inversion results, we first generated an elastic synthetic seismic shot gather with ground rolls by using the forward modelling scheme of SOFI2D for a two-layer velocity depth model overlying a half-space. The generated gather was then processed in MATLAB to generate the experimental dispersion curve using the Phase shift method. We then extracted the fundamental mode for the gather and inverted it using the standard PSO and GWO algorithms and estimated 1D shear wave velocity profile. After getting acceptable results for the synthetic dataset, we then applied the PSO algorithm to generate the 1D S-wave velocity (Vs) profile across the Himalayan Frontal Thrust (HFT). In the study area, the Rayleigh wave phase velocity for the first shot varies from 444 to 743 m/s. We then obtained the 1D shear wave velocity profiles and a jump in Vs is observed across the HFT indicating variation in the sediment stiffness across the fault.
Keywords: WAMASW, dispersion, Meta- Heuristic, PSO, GWO, 1D Shear wave velocity
How to cite: Kumar, P. and Ghosal, D.: Delineation of S-wave velocity profiles across the Himalayan Frontal Thrust (HFT) using metaheuristic approaches., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11287, https://doi.org/10.5194/egusphere-egu21-11287, 2021.
EGU21-9243 | vPICO presentations | SM5.3
H/V spectral ratios at the InSight landing site using ambient noise and Marsquake recordsSebastián Carrasco, Brigitte Knapmeyer-Endrun, Ludovic Margerin, Cédric Schmelzbach, John Clinton, Simon Stähler, Domenico Giardini, Sharon Kedar, Matthias Grott, Matthew Golombek, Philippe Lognonné, and Don Banfield
The InSight mission landed on Mars on November 26th, 2018 and its seismometer, the Seismic Experiment for Interior Structure (SEIS), has recorded continuous Martian seismic data since February 2019, consisting of mainly ambient seismic noise but also hundreds of seismic events.
We used the SEIS data to study the horizontal-to-vertical spectral ratios from both the ambient seismic noise (nHV) and the seismic events (eHV), for frequencies above 0.6 Hz, in order to get further constraints on the first tens of meters at the Insight landing site. The nHV curve was obtained by using data segments of 50 s over more than 400 Sols. The preferred nHV curve is observed during the northern spring and summer at low wind levels and it is a mostly flat curve with a prominent trough around ~2.4 Hz. Outside of these time periods, the nHV curve is contaminated with artificial peaks likely related to lander modes. On the other hand, the eHV curve was created using 336 seismic events with quality either A, B or C, as defined by the Marsquake Service. For each seismic event, we computed the signal-to-noise ratio (SNR) at each frequency and only frequencies with SNR>3 were used to obtain the final eHV curve. In addition to the 2.4 Hz trough, the final eHV curve shows a strong peak around 8 Hz, which is not observed from the ambient noise data possibly due to a lack of seismic energy in this frequency band able to excite it.
A preliminary inversion of the eHV curve, considering the fundamental mode of the Rayleigh wave only, shows that the 2.4 Hz trough and the 8 Hz peak can be explained by a shear-wave velocity model increasing from the surface to a depth of 5-8 m (likely the boundary between the regolith and coarse ejecta), in good agreement with previous analysis based on compliance observations, hammering measurements and satellite images. At this depth, a discontinuity leading to a higher velocity layer is observed, which is followed by a deeper low-velocity layer about 20 m thick. The modeling assuming body waves only or a full diffuse seismic wavefield is currently under investigation.
How to cite: Carrasco, S., Knapmeyer-Endrun, B., Margerin, L., Schmelzbach, C., Clinton, J., Stähler, S., Giardini, D., Kedar, S., Grott, M., Golombek, M., Lognonné, P., and Banfield, D.: H/V spectral ratios at the InSight landing site using ambient noise and Marsquake records, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9243, https://doi.org/10.5194/egusphere-egu21-9243, 2021.
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The InSight mission landed on Mars on November 26th, 2018 and its seismometer, the Seismic Experiment for Interior Structure (SEIS), has recorded continuous Martian seismic data since February 2019, consisting of mainly ambient seismic noise but also hundreds of seismic events.
We used the SEIS data to study the horizontal-to-vertical spectral ratios from both the ambient seismic noise (nHV) and the seismic events (eHV), for frequencies above 0.6 Hz, in order to get further constraints on the first tens of meters at the Insight landing site. The nHV curve was obtained by using data segments of 50 s over more than 400 Sols. The preferred nHV curve is observed during the northern spring and summer at low wind levels and it is a mostly flat curve with a prominent trough around ~2.4 Hz. Outside of these time periods, the nHV curve is contaminated with artificial peaks likely related to lander modes. On the other hand, the eHV curve was created using 336 seismic events with quality either A, B or C, as defined by the Marsquake Service. For each seismic event, we computed the signal-to-noise ratio (SNR) at each frequency and only frequencies with SNR>3 were used to obtain the final eHV curve. In addition to the 2.4 Hz trough, the final eHV curve shows a strong peak around 8 Hz, which is not observed from the ambient noise data possibly due to a lack of seismic energy in this frequency band able to excite it.
A preliminary inversion of the eHV curve, considering the fundamental mode of the Rayleigh wave only, shows that the 2.4 Hz trough and the 8 Hz peak can be explained by a shear-wave velocity model increasing from the surface to a depth of 5-8 m (likely the boundary between the regolith and coarse ejecta), in good agreement with previous analysis based on compliance observations, hammering measurements and satellite images. At this depth, a discontinuity leading to a higher velocity layer is observed, which is followed by a deeper low-velocity layer about 20 m thick. The modeling assuming body waves only or a full diffuse seismic wavefield is currently under investigation.
How to cite: Carrasco, S., Knapmeyer-Endrun, B., Margerin, L., Schmelzbach, C., Clinton, J., Stähler, S., Giardini, D., Kedar, S., Grott, M., Golombek, M., Lognonné, P., and Banfield, D.: H/V spectral ratios at the InSight landing site using ambient noise and Marsquake records, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9243, https://doi.org/10.5194/egusphere-egu21-9243, 2021.
SM6.1 – Earthquake swarms and complex seismic sequences driven by transient forcing in tectonic and volcanic regions
EGU21-1073 | vPICO presentations | SM6.1
Dual seismic migration velocities reveal imbricated fluid diffusion and aseismic slip In a Corinth Gulf swarm (Greece)Louis De Barros, Pierre Dublanchet, Frédéric Cappa, and Anne Deschamps
Fluid induced earthquake sequences generally appear as expanding swarms activating a particular fault. Such swarms are generally interpreted as fluid diffusion, which ignores the possibility of static, dynamic or aseismic triggering, and the existence of rapid migration. Here, we study the temporal evolution of a seismic swarm that occurred over a 10-day period in October 2015 in the extensional rift of the Corinth Gulf (Greece) using high-resolution earthquakes relocations. The seismicity radially migrates on a normal fault at a fluid diffusion velocity (~125 m/day). However, this migration occurs intermittently, with periods of fast expansion (2-to-10 km/day) during short seismic bursts alternating with quiescent periods. Moreover, the growing phases of the swarm illuminate a high number of repeaters. Therefore, we propose a new model to explain the combination of multiple driving processes for such swarms. Fluid up flow in the fault may induce aseismic slip episodes, separated by phases of fluid pressure build-up. The stress perturbation due to aseismic slip may activate small asperities in the fault that produce bursts of seismicity during the most intense phase of the swarm. We then validated this model through hydro-mechanical modeling, where earthquakes consist in the failure of asperities on a creeping fault infiltrated by fluid. For that, we couple rate‐and‐state friction, non‐linear diffusivity and elasticity along a 1D interface. This model reproduces the dual migration speeds observed in real swarms. We show that migration speeds increase linearly with the mean pressurization, and are not dependent on the hydraulic diffusivity, as traditionally suggested.
How to cite: De Barros, L., Dublanchet, P., Cappa, F., and Deschamps, A.: Dual seismic migration velocities reveal imbricated fluid diffusion and aseismic slip In a Corinth Gulf swarm (Greece), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1073, https://doi.org/10.5194/egusphere-egu21-1073, 2021.
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Fluid induced earthquake sequences generally appear as expanding swarms activating a particular fault. Such swarms are generally interpreted as fluid diffusion, which ignores the possibility of static, dynamic or aseismic triggering, and the existence of rapid migration. Here, we study the temporal evolution of a seismic swarm that occurred over a 10-day period in October 2015 in the extensional rift of the Corinth Gulf (Greece) using high-resolution earthquakes relocations. The seismicity radially migrates on a normal fault at a fluid diffusion velocity (~125 m/day). However, this migration occurs intermittently, with periods of fast expansion (2-to-10 km/day) during short seismic bursts alternating with quiescent periods. Moreover, the growing phases of the swarm illuminate a high number of repeaters. Therefore, we propose a new model to explain the combination of multiple driving processes for such swarms. Fluid up flow in the fault may induce aseismic slip episodes, separated by phases of fluid pressure build-up. The stress perturbation due to aseismic slip may activate small asperities in the fault that produce bursts of seismicity during the most intense phase of the swarm. We then validated this model through hydro-mechanical modeling, where earthquakes consist in the failure of asperities on a creeping fault infiltrated by fluid. For that, we couple rate‐and‐state friction, non‐linear diffusivity and elasticity along a 1D interface. This model reproduces the dual migration speeds observed in real swarms. We show that migration speeds increase linearly with the mean pressurization, and are not dependent on the hydraulic diffusivity, as traditionally suggested.
How to cite: De Barros, L., Dublanchet, P., Cappa, F., and Deschamps, A.: Dual seismic migration velocities reveal imbricated fluid diffusion and aseismic slip In a Corinth Gulf swarm (Greece), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1073, https://doi.org/10.5194/egusphere-egu21-1073, 2021.
EGU21-2930 | vPICO presentations | SM6.1
What drives the growth of earthquake clusters?Tomáš Fischer, Sebastian Hainzl, Josef Vlček, and Ali Salama
Migration of hypocenters is a common attribute of induced injection seismicity and of earthquake swarms, which distinguishes them from aftershock sequences. Spreading of the triggering front is often examined by fitting the time dependence of hypocenter distances from the origin by the pore pressure diffusion model. The earthquake migration patterns however often exhibit not only spreading envelopes, but also fast-growing streaks embedded in the overall migration trends. We review the observed migration patterns and show that in the case of self-driven seismicity, where the new ruptures are triggered at the edge of previous ruptures, it is more suitable to examine the cluster growth as a function of the event index instead of time, which often discloses a continuous linear growth during time periods which appeared strongly discontinuous in the coordinate-time plots.
We propose a model that relates the speed of seismicity spreading to the average rupture area and the effective magnitude of the hypocenter cluster. Application of the model to selected linearly growing clusters of the 2008 West Bohemia swarm gives almost linear increase of the measured total rupture area with the event index, which fits the proposed model. This is confirmed by a self-similar scaling of the average rupture area with the effective magnitude for stress drops ranging from 0.1 to 1 MPa. The relatively small stress drop level indicates the presence of voids along the fault plane and a possible role of aseismic deformation. Further application of the model to seismic swarms from different areas confirms its validity and potential for distinguishing fluid-triggered seismicity.
How to cite: Fischer, T., Hainzl, S., Vlček, J., and Salama, A.: What drives the growth of earthquake clusters?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2930, https://doi.org/10.5194/egusphere-egu21-2930, 2021.
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Migration of hypocenters is a common attribute of induced injection seismicity and of earthquake swarms, which distinguishes them from aftershock sequences. Spreading of the triggering front is often examined by fitting the time dependence of hypocenter distances from the origin by the pore pressure diffusion model. The earthquake migration patterns however often exhibit not only spreading envelopes, but also fast-growing streaks embedded in the overall migration trends. We review the observed migration patterns and show that in the case of self-driven seismicity, where the new ruptures are triggered at the edge of previous ruptures, it is more suitable to examine the cluster growth as a function of the event index instead of time, which often discloses a continuous linear growth during time periods which appeared strongly discontinuous in the coordinate-time plots.
We propose a model that relates the speed of seismicity spreading to the average rupture area and the effective magnitude of the hypocenter cluster. Application of the model to selected linearly growing clusters of the 2008 West Bohemia swarm gives almost linear increase of the measured total rupture area with the event index, which fits the proposed model. This is confirmed by a self-similar scaling of the average rupture area with the effective magnitude for stress drops ranging from 0.1 to 1 MPa. The relatively small stress drop level indicates the presence of voids along the fault plane and a possible role of aseismic deformation. Further application of the model to seismic swarms from different areas confirms its validity and potential for distinguishing fluid-triggered seismicity.
How to cite: Fischer, T., Hainzl, S., Vlček, J., and Salama, A.: What drives the growth of earthquake clusters?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2930, https://doi.org/10.5194/egusphere-egu21-2930, 2021.
EGU21-15544 | vPICO presentations | SM6.1
Slowly migrating tectonic microearthquake swarms in the Icelandic Rift Zone: driven by pore-pressure or aseismic slip transients?Tom Winder and Robert S White
Intense swarms of microearthquakes have been detected in the rift zone of Central Iceland since the 1970s, but the cause of their clear swarm-like nature remains enigmatic. We use the QuakeMigrate earthquake detection and location software1 to produce a highly complete catalogue of microseismicity from 2007-2020, using data from a dense local seismic network. Automatic hypocentre locations have been refined using waveform cross-correlation and double-difference relocation, and tightly constrained focal mechanisms have been obtained by manual analysis of a subset of events.
The resulting high-resolution earthquake catalogue reveals a network of conjugate strike-slip faults, oriented to accommodate plate-boundary extension. Sharply defined fault planes imaged by the microearthquake hypocentres range from 1-10 km in length, and are found between 1 and 8 km b.s.l., with their orientations closely matching the fault plane geometry inferred from the fault plane solutions. Seismicity within individual swarms displays a systematic migration of hypocentres at velocities of ~ 1 km/day. In the majority of swarms we also observe clusters of identical repeating events, providing evidence for re-loading of brittle asperities.
For a selection of swarms our high resolution seismic observations are complemented by GPS and InSAR measurements, allowing us to place constraints on the amount of fault slip. Comparing this, and the area of the fault plane activated in the swarm, to the seismic moment release reveals a significant contribution of aseismic slip, or very low effective stress drop. Analysis of swarms within this fault network triggered by the 2014 Bárðarbunga-Holuhraun dike intrusion provides further constraint on the amplitude of the stress cycle.
We combine our observations with comparisons to numerical & laboratory modelling studies, observed swarm scaling properties and knowledge of the geological and permeability structure of the Icelandic crust to determine the nature of the transient forcing driving these exceptionally well-recorded tectonic earthquake swarms.
1: https://github.com/QuakeMigrate/QuakeMigrate Tom Winder, Conor Bacon, Jonathan D. Smith, Thomas S. Hudson, Julian Drew, & Robert S. White. (2021, January 15). QuakeMigrate v1.0.0 (Version v1.0.0). Zenodo. http://doi.org/10.5281/zenodo.4442749
How to cite: Winder, T. and White, R. S.: Slowly migrating tectonic microearthquake swarms in the Icelandic Rift Zone: driven by pore-pressure or aseismic slip transients?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15544, https://doi.org/10.5194/egusphere-egu21-15544, 2021.
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Intense swarms of microearthquakes have been detected in the rift zone of Central Iceland since the 1970s, but the cause of their clear swarm-like nature remains enigmatic. We use the QuakeMigrate earthquake detection and location software1 to produce a highly complete catalogue of microseismicity from 2007-2020, using data from a dense local seismic network. Automatic hypocentre locations have been refined using waveform cross-correlation and double-difference relocation, and tightly constrained focal mechanisms have been obtained by manual analysis of a subset of events.
The resulting high-resolution earthquake catalogue reveals a network of conjugate strike-slip faults, oriented to accommodate plate-boundary extension. Sharply defined fault planes imaged by the microearthquake hypocentres range from 1-10 km in length, and are found between 1 and 8 km b.s.l., with their orientations closely matching the fault plane geometry inferred from the fault plane solutions. Seismicity within individual swarms displays a systematic migration of hypocentres at velocities of ~ 1 km/day. In the majority of swarms we also observe clusters of identical repeating events, providing evidence for re-loading of brittle asperities.
For a selection of swarms our high resolution seismic observations are complemented by GPS and InSAR measurements, allowing us to place constraints on the amount of fault slip. Comparing this, and the area of the fault plane activated in the swarm, to the seismic moment release reveals a significant contribution of aseismic slip, or very low effective stress drop. Analysis of swarms within this fault network triggered by the 2014 Bárðarbunga-Holuhraun dike intrusion provides further constraint on the amplitude of the stress cycle.
We combine our observations with comparisons to numerical & laboratory modelling studies, observed swarm scaling properties and knowledge of the geological and permeability structure of the Icelandic crust to determine the nature of the transient forcing driving these exceptionally well-recorded tectonic earthquake swarms.
1: https://github.com/QuakeMigrate/QuakeMigrate Tom Winder, Conor Bacon, Jonathan D. Smith, Thomas S. Hudson, Julian Drew, & Robert S. White. (2021, January 15). QuakeMigrate v1.0.0 (Version v1.0.0). Zenodo. http://doi.org/10.5281/zenodo.4442749
How to cite: Winder, T. and White, R. S.: Slowly migrating tectonic microearthquake swarms in the Icelandic Rift Zone: driven by pore-pressure or aseismic slip transients?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15544, https://doi.org/10.5194/egusphere-egu21-15544, 2021.
EGU21-6421 | vPICO presentations | SM6.1 | Highlight
Latent seismicity driven by aseismic creep and enhanced pore-fluid pressure in NE British ColumbiaRebecca O. Salvage and David W. Eaton
The global pandemic of COVID-19 furnished an opportunity to study seismicity in the Kiskatinaw area of British Columbia, noted for hydraulic-fracturing induced seismicity, during a period of anthropogenic quiescence. A total of 389 events were detected from April to August 2020, encompassing a period with no hydraulic-fracturing operations during a government-imposed lockdown. During this time period, observed seismicity had a maximum magnitude of ML 1.2 and lacked temporal clustering that is often characteristic of hydraulic-fracturing induced sequences. Instead, seismicity was persistent over the lockdown period, similar to swarm-like seismicity with no apparent foreshock-aftershock type sequences. Hypocenters occurred within a corridor orientated NW-SE, just as seismicity had done in previous years in the area, with focal depths near the target Montney formation or shallower (<2.5 km). Based on the Gutenberg-Richter relationship, we estimate that a maximum of 21% of the detected events during lockdown may be attributable to natural seismicity, with a further 8% possibly due to dynamic triggering of seismicity from teleseismic events. The remaining ~70% cannot be attributed to direct pore pressure increases induced by fluid injection, and therefore is inferred to represent latent seismicity i.e. seismicity that occurs after an unusually long delay following primary activation processes, with no obvious triggering mechanism. We can exclude pore-pressure diffusion from the most recent fluid injection, as is there is no clear pattern of temporal or spatial seismicity migration. If elevated pore pressure from previous injections became trapped in the subsurface, this could explain the localization of seismicity within an operational corridor, but it does not explain the latency of seismicity on a timescale of months. However, aseismic creep on weak surfaces such as faults, in response to tectonic stresses, in addition to trapped elevation pore-pressure could play a role in stress re-loading to sustain the observed pattern of seismicity.
How to cite: Salvage, R. O. and Eaton, D. W.: Latent seismicity driven by aseismic creep and enhanced pore-fluid pressure in NE British Columbia, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6421, https://doi.org/10.5194/egusphere-egu21-6421, 2021.
The global pandemic of COVID-19 furnished an opportunity to study seismicity in the Kiskatinaw area of British Columbia, noted for hydraulic-fracturing induced seismicity, during a period of anthropogenic quiescence. A total of 389 events were detected from April to August 2020, encompassing a period with no hydraulic-fracturing operations during a government-imposed lockdown. During this time period, observed seismicity had a maximum magnitude of ML 1.2 and lacked temporal clustering that is often characteristic of hydraulic-fracturing induced sequences. Instead, seismicity was persistent over the lockdown period, similar to swarm-like seismicity with no apparent foreshock-aftershock type sequences. Hypocenters occurred within a corridor orientated NW-SE, just as seismicity had done in previous years in the area, with focal depths near the target Montney formation or shallower (<2.5 km). Based on the Gutenberg-Richter relationship, we estimate that a maximum of 21% of the detected events during lockdown may be attributable to natural seismicity, with a further 8% possibly due to dynamic triggering of seismicity from teleseismic events. The remaining ~70% cannot be attributed to direct pore pressure increases induced by fluid injection, and therefore is inferred to represent latent seismicity i.e. seismicity that occurs after an unusually long delay following primary activation processes, with no obvious triggering mechanism. We can exclude pore-pressure diffusion from the most recent fluid injection, as is there is no clear pattern of temporal or spatial seismicity migration. If elevated pore pressure from previous injections became trapped in the subsurface, this could explain the localization of seismicity within an operational corridor, but it does not explain the latency of seismicity on a timescale of months. However, aseismic creep on weak surfaces such as faults, in response to tectonic stresses, in addition to trapped elevation pore-pressure could play a role in stress re-loading to sustain the observed pattern of seismicity.
How to cite: Salvage, R. O. and Eaton, D. W.: Latent seismicity driven by aseismic creep and enhanced pore-fluid pressure in NE British Columbia, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6421, https://doi.org/10.5194/egusphere-egu21-6421, 2021.
EGU21-5282 | vPICO presentations | SM6.1
Variations of the earthquake diffusion rates in the Western Gulf of Corinth (Greece)Georgios Michas, Vasilis Kapetanidis, George Kaviris, and Filippos Vallianatos
Earthquake diffusion is frequently observed in the spatiotemporal evolution of seismic clusters and regional seismicity, a characteristic that is attributed to a triggering mechanism, such as fluid flow, aseismic creep and/or stress transfer effects. In this work, we study the earthquake diffusion properties in the Western Gulf of Corinth (central Greece), an area that presents high extension rates, moderate to large magnitude earthquakes, intense microseismicity and frequent seismic swarms. We focus on the period 2013–2014 that is characterized by intense background microseismic activity along with significant seismic sequences. More specifically, the latter include the 2013 Helike swarm, the 2014 seismic sequence between Nafpaktos and Psathopyrgos, which culminated with an Mw 4.9 event on 21 September 2014, as well as moderate magnitude events that were followed by aftershock sequences. In the herein analysis, we employ a relocated earthquake catalogue of ~9000 events which delineates the activated areas during the study period in high-resolution. We consider the most significant seismic sequences and calculate their respective spatial correlation histograms and the evolution of the mean squared distance of the hypocenters with time, in order to study the earthquake diffusion rates and possible variations that might be related to the triggering mechanisms of seismicity. Our results demonstrate a weak earthquake diffusion process, analogous to subdiffusion within a stochastic framework, for the seismic sequences under consideration, providing further evidence for slow earthquake diffusion in regional and global seismicity. In addition, the earthquake diffusion rates exhibit variations that can be associated with the triggering mechanism. In particular, seismic sequences which are related with pore-fluid pressure diffusion present considerably higher diffusion rates than mainshock/aftershock sequences or the background activity. Such results may provide novel constraints on the triggering mechanisms of clustered seismic activity based on the study of the earthquake diffusion rates.
Acknowledgements
We would like to thank the personnel of the Hellenic Unified Seismological Network (http://eida.gein.noa.gr/) and the Corinth Rift Laboratory Network (https://doi.org/10.15778/RESIF.CL) for the installation and operation of the stations used in the current article. The present research is co-financed by Greece and the European Union (European Social Fund- ESF) through the Operational Programme «Human Resources Development, Education and Lifelong Learning 2014-2020» in the context of the project “The role of fluids in the seismicity of the Western Gulf of Corinth (Greece)” (MIS 5048127).
How to cite: Michas, G., Kapetanidis, V., Kaviris, G., and Vallianatos, F.: Variations of the earthquake diffusion rates in the Western Gulf of Corinth (Greece), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5282, https://doi.org/10.5194/egusphere-egu21-5282, 2021.
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We are sorry, but presentations are only available for users who registered for the conference. Thank you.
Earthquake diffusion is frequently observed in the spatiotemporal evolution of seismic clusters and regional seismicity, a characteristic that is attributed to a triggering mechanism, such as fluid flow, aseismic creep and/or stress transfer effects. In this work, we study the earthquake diffusion properties in the Western Gulf of Corinth (central Greece), an area that presents high extension rates, moderate to large magnitude earthquakes, intense microseismicity and frequent seismic swarms. We focus on the period 2013–2014 that is characterized by intense background microseismic activity along with significant seismic sequences. More specifically, the latter include the 2013 Helike swarm, the 2014 seismic sequence between Nafpaktos and Psathopyrgos, which culminated with an Mw 4.9 event on 21 September 2014, as well as moderate magnitude events that were followed by aftershock sequences. In the herein analysis, we employ a relocated earthquake catalogue of ~9000 events which delineates the activated areas during the study period in high-resolution. We consider the most significant seismic sequences and calculate their respective spatial correlation histograms and the evolution of the mean squared distance of the hypocenters with time, in order to study the earthquake diffusion rates and possible variations that might be related to the triggering mechanisms of seismicity. Our results demonstrate a weak earthquake diffusion process, analogous to subdiffusion within a stochastic framework, for the seismic sequences under consideration, providing further evidence for slow earthquake diffusion in regional and global seismicity. In addition, the earthquake diffusion rates exhibit variations that can be associated with the triggering mechanism. In particular, seismic sequences which are related with pore-fluid pressure diffusion present considerably higher diffusion rates than mainshock/aftershock sequences or the background activity. Such results may provide novel constraints on the triggering mechanisms of clustered seismic activity based on the study of the earthquake diffusion rates.
Acknowledgements
We would like to thank the personnel of the Hellenic Unified Seismological Network (http://eida.gein.noa.gr/) and the Corinth Rift Laboratory Network (https://doi.org/10.15778/RESIF.CL) for the installation and operation of the stations used in the current article. The present research is co-financed by Greece and the European Union (European Social Fund- ESF) through the Operational Programme «Human Resources Development, Education and Lifelong Learning 2014-2020» in the context of the project “The role of fluids in the seismicity of the Western Gulf of Corinth (Greece)” (MIS 5048127).
How to cite: Michas, G., Kapetanidis, V., Kaviris, G., and Vallianatos, F.: Variations of the earthquake diffusion rates in the Western Gulf of Corinth (Greece), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5282, https://doi.org/10.5194/egusphere-egu21-5282, 2021.
EGU21-1119 | vPICO presentations | SM6.1
Seismic doublets and a complex seismic sequence controlled by the rotation of the Juan Fernández microplateSimone Cesca, Carla Valenzuela Malebrán, José Ángel López-Comino, Timothy Davis, Carlos Tassara, Onno Oncken, and Torsten Dahm
A complex seismic sequence took place in 2014 at the Juan Fernández microplate, a small microplate located between Pacific, Nazca and Antarctica plates. Despite the remoteness of the study region and the lack of local data, we were able to resolve earthquake source parameters and to reconstruct the complex seismic sequence, by using modern waveform-based seismological techniques. The sequence started with an exceptional Mw 7.1-6.7 thrust – strike slip earthquake doublet, the first subevent being the largest earthquake ever recorded in the region and one of the few rare thrust earthquakes in a region otherwise characterized by normal faulting and strike slip earthquakes. The joint analysis of seismicity and focal mechanisms suggest the activation of E-W and NE-SW faults or of an internal curved pseudofault, which is formed in response to the microplate rotation, with alternation of thrust and strike-slip earthquakes. Seismicity migrated Northward in its final phase, towards the microplate edge, where a second doublet with uneven focal mechanisms occurred. The sequence rupture kinematics is well explained by Coulomb stress changes imparted by the first subevent. Our analysis show that compressional stresses, which have been mapped at the northern boundary of the microplate, but never accompanied by large thrust earthquakes, can be accommodated by the rare occurrence of large, impulsive, shallow thrust earthquakes, with a considerable tsunamigenic potential.
How to cite: Cesca, S., Valenzuela Malebrán, C., López-Comino, J. Á., Davis, T., Tassara, C., Oncken, O., and Dahm, T.: Seismic doublets and a complex seismic sequence controlled by the rotation of the Juan Fernández microplate, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1119, https://doi.org/10.5194/egusphere-egu21-1119, 2021.
A complex seismic sequence took place in 2014 at the Juan Fernández microplate, a small microplate located between Pacific, Nazca and Antarctica plates. Despite the remoteness of the study region and the lack of local data, we were able to resolve earthquake source parameters and to reconstruct the complex seismic sequence, by using modern waveform-based seismological techniques. The sequence started with an exceptional Mw 7.1-6.7 thrust – strike slip earthquake doublet, the first subevent being the largest earthquake ever recorded in the region and one of the few rare thrust earthquakes in a region otherwise characterized by normal faulting and strike slip earthquakes. The joint analysis of seismicity and focal mechanisms suggest the activation of E-W and NE-SW faults or of an internal curved pseudofault, which is formed in response to the microplate rotation, with alternation of thrust and strike-slip earthquakes. Seismicity migrated Northward in its final phase, towards the microplate edge, where a second doublet with uneven focal mechanisms occurred. The sequence rupture kinematics is well explained by Coulomb stress changes imparted by the first subevent. Our analysis show that compressional stresses, which have been mapped at the northern boundary of the microplate, but never accompanied by large thrust earthquakes, can be accommodated by the rare occurrence of large, impulsive, shallow thrust earthquakes, with a considerable tsunamigenic potential.
How to cite: Cesca, S., Valenzuela Malebrán, C., López-Comino, J. Á., Davis, T., Tassara, C., Oncken, O., and Dahm, T.: Seismic doublets and a complex seismic sequence controlled by the rotation of the Juan Fernández microplate, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1119, https://doi.org/10.5194/egusphere-egu21-1119, 2021.
EGU21-5034 | vPICO presentations | SM6.1
Complex behaviour highlighted by earthquake aftershock and swarm sequences in Ubaye Region (French Western Alps).Marion Baques, Louis De Barros, Maxime Godano, Hervé Jomard, Clara Duverger, Francoise Courboulex, and Christophe Larroque
The Ubaye Region, where the city of Barcelonnette is settled, is the most seismically active region in the French Western Alps since at least two centuries. Seismicity in this area exhibits a dual behaviour, with mainshock-aftershock sequences alternating with abnormally high rate of seismicity associated with seismic swarms. Understanding processes triggering such a peculiar seismic behaviour is of primary importance in order to assess the seismic hazard in this region. The latest swarm activity started on February 26, 2012, with an earthquake of moment magnitude 4.2. It was followed two years later (on April 7, 2014) by a shock of magnitude Mw 4.8. From the first earthquake to the end of 2016, the seismic level has not returned to the background level and shares the same characteristics as a seismic swarm.
With the aim to discuss the seismogenic processes involved in the area, we focused on the two months following the 2014 mainshock (Mw=4.8). During this period, a dense temporary network (7 stations) was operating at a maximal distance of 10km from the epicentre area. We analysed this period starting with a double-difference relocation of ~ 6,000 earthquakes previously detected by template-matching. These hypocentres did not align on the fault plane of the 2014 mainshock, but on conjugated structures belonging to the 2-km wide damaged zone of the main fault plane and on remote structures with various orientations further away. We then computed 99 focal mechanisms from a joint inversion of P polarity and S/P ratio to clarify the geometry of the active structures. Many nodal planes are inconsistent with the structures deduced from the alignments of the earthquake locations. The stress-state orientation obtained from those focal mechanisms (σ1 trending N27°± 5°, plunging 50°± 9°, a σ2 trending N215°± 5°, plunging 40°± 9°, and a sub-horizontal σ3 trending N122°± 3°) is consistent with those previously calculated in the area (Fojtíková and Vavryčuk, 2018). Nevertheless, some structures are unfavourably oriented to slip within this stress-field, suggesting that additional processes are required to explain them. As the presence of fluids was highlighted for the 2003-2004 and the 2012-2015 crisis, we calculated the fluid pressure needed to trigger slip on the planes from the focal mechanisms using Cauchy's equation. We found that a median fluid-overpressure of ~20 MPa (range between 0 to 50 MPa) is needed to cause slip. Although the origin of fluids and how they are pressurized at depth remains open. The fluid processes seem to be the most favourable additional processes and were also proposed to explain the 2003-2004 crisis.
How to cite: Baques, M., De Barros, L., Godano, M., Jomard, H., Duverger, C., Courboulex, F., and Larroque, C.: Complex behaviour highlighted by earthquake aftershock and swarm sequences in Ubaye Region (French Western Alps). , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5034, https://doi.org/10.5194/egusphere-egu21-5034, 2021.
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The Ubaye Region, where the city of Barcelonnette is settled, is the most seismically active region in the French Western Alps since at least two centuries. Seismicity in this area exhibits a dual behaviour, with mainshock-aftershock sequences alternating with abnormally high rate of seismicity associated with seismic swarms. Understanding processes triggering such a peculiar seismic behaviour is of primary importance in order to assess the seismic hazard in this region. The latest swarm activity started on February 26, 2012, with an earthquake of moment magnitude 4.2. It was followed two years later (on April 7, 2014) by a shock of magnitude Mw 4.8. From the first earthquake to the end of 2016, the seismic level has not returned to the background level and shares the same characteristics as a seismic swarm.
With the aim to discuss the seismogenic processes involved in the area, we focused on the two months following the 2014 mainshock (Mw=4.8). During this period, a dense temporary network (7 stations) was operating at a maximal distance of 10km from the epicentre area. We analysed this period starting with a double-difference relocation of ~ 6,000 earthquakes previously detected by template-matching. These hypocentres did not align on the fault plane of the 2014 mainshock, but on conjugated structures belonging to the 2-km wide damaged zone of the main fault plane and on remote structures with various orientations further away. We then computed 99 focal mechanisms from a joint inversion of P polarity and S/P ratio to clarify the geometry of the active structures. Many nodal planes are inconsistent with the structures deduced from the alignments of the earthquake locations. The stress-state orientation obtained from those focal mechanisms (σ1 trending N27°± 5°, plunging 50°± 9°, a σ2 trending N215°± 5°, plunging 40°± 9°, and a sub-horizontal σ3 trending N122°± 3°) is consistent with those previously calculated in the area (Fojtíková and Vavryčuk, 2018). Nevertheless, some structures are unfavourably oriented to slip within this stress-field, suggesting that additional processes are required to explain them. As the presence of fluids was highlighted for the 2003-2004 and the 2012-2015 crisis, we calculated the fluid pressure needed to trigger slip on the planes from the focal mechanisms using Cauchy's equation. We found that a median fluid-overpressure of ~20 MPa (range between 0 to 50 MPa) is needed to cause slip. Although the origin of fluids and how they are pressurized at depth remains open. The fluid processes seem to be the most favourable additional processes and were also proposed to explain the 2003-2004 crisis.
How to cite: Baques, M., De Barros, L., Godano, M., Jomard, H., Duverger, C., Courboulex, F., and Larroque, C.: Complex behaviour highlighted by earthquake aftershock and swarm sequences in Ubaye Region (French Western Alps). , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5034, https://doi.org/10.5194/egusphere-egu21-5034, 2021.
EGU21-7463 | vPICO presentations | SM6.1
Spatial and temporal variations of seismicity during the Maurienne swarm (French Alps): short- and long-term migrations and b-value dependence with depthRiccardo Minetto, Agnès Hemlstetter, Philippe Guéguen, and Mickaël Langlais
We analyse the spatio-temporal variations of the seismicity recorded during the Maurienne swarm. The Maurienne swarm occurred between 2017 and 2018 in the French Alps in the central part of the external crystalline massif of Belledonne. This massif extends for more than 120km in N30 direction, it is bounded to the west by the wide topographic depression of the Isère valley and the Combe de Savoie, and it is crosscut by the Maurienne valley. The location and the 3D shape of the seismic swarm are consistent with an outcroping N80 vertical fault zone. The seismic activity is interpreted as a result of the reactivation of this inherited vertical fault system. The largest event had a magnitude of 3.5.
We used a catalog of 58000 events that were detected using template-matching and relocated with a double-difference method.
We show that the swarm is characterised by short-term (days) and long-term (months) migrations that may be related to the presence of fluids.
We also observe that the b-value decreases with depth and we discuss how this variation may due to shallow fault systems whose geometry differs from the one of the main fault system.
Part of the events occurred when only one station was active. This study shows that, by grouping earthquakes into groups of similar events (clusters), it is possible to study spatio-temporal variations in such conditions.
How to cite: Minetto, R., Hemlstetter, A., Guéguen, P., and Langlais, M.: Spatial and temporal variations of seismicity during the Maurienne swarm (French Alps): short- and long-term migrations and b-value dependence with depth, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7463, https://doi.org/10.5194/egusphere-egu21-7463, 2021.
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We analyse the spatio-temporal variations of the seismicity recorded during the Maurienne swarm. The Maurienne swarm occurred between 2017 and 2018 in the French Alps in the central part of the external crystalline massif of Belledonne. This massif extends for more than 120km in N30 direction, it is bounded to the west by the wide topographic depression of the Isère valley and the Combe de Savoie, and it is crosscut by the Maurienne valley. The location and the 3D shape of the seismic swarm are consistent with an outcroping N80 vertical fault zone. The seismic activity is interpreted as a result of the reactivation of this inherited vertical fault system. The largest event had a magnitude of 3.5.
We used a catalog of 58000 events that were detected using template-matching and relocated with a double-difference method.
We show that the swarm is characterised by short-term (days) and long-term (months) migrations that may be related to the presence of fluids.
We also observe that the b-value decreases with depth and we discuss how this variation may due to shallow fault systems whose geometry differs from the one of the main fault system.
Part of the events occurred when only one station was active. This study shows that, by grouping earthquakes into groups of similar events (clusters), it is possible to study spatio-temporal variations in such conditions.
How to cite: Minetto, R., Hemlstetter, A., Guéguen, P., and Langlais, M.: Spatial and temporal variations of seismicity during the Maurienne swarm (French Alps): short- and long-term migrations and b-value dependence with depth, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7463, https://doi.org/10.5194/egusphere-egu21-7463, 2021.
EGU21-9641 | vPICO presentations | SM6.1
Spatiotemporal evolution of deep seismicity beneath the central HimalayasKonstantinos Michailos, N. Seth Carpenter, and György Hetényi
The Himalayan orogen, formed by the continental collision between the Indian and Eurasian plates, is a unique geological structure that has been extensively studied over the past few decades. These previous studies highlighted the occurrence of earthquakes in the orogen's roots beneath the central Himalayas. However, the characterization of these deep earthquakes remains limited. Here, we compiled a detailed, long-duration catalog, which we use to investigate the spatiotemporal characteristics of seismicity beneath the Himalayan orogen.
To create this catalog, we collected all available continuous seismic data acquired during the last two decades in the central Himalayas region (i.e., 2001-2005). We applied a systematic, semi-automatic processing routine to obtain absolute earthquake locations using a 1-D velocity model. Using high-quality picks, ~8,000 preliminary earthquake locations have been determined, at least 1,000 of which have hypocentral depths >50 km. We plan to refine the preliminary locations and calculate local magnitudes for the intermediate-depth lithospheric earthquakes. Using this refined catalog, we will analyze the spatiotemporal evolution pattern and properties of the Himalayan deep seismicity. This analysis is expected to provide us with insights into the processes and mechanisms that control seismogenesis beneath the orogen. For example, is seismicity driven by earthquake stress transfer (mainshock-aftershock sequences), or is it caused by external processes like fluids or aseismic slip, or both?
How to cite: Michailos, K., Carpenter, N. S., and Hetényi, G.: Spatiotemporal evolution of deep seismicity beneath the central Himalayas, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9641, https://doi.org/10.5194/egusphere-egu21-9641, 2021.
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The Himalayan orogen, formed by the continental collision between the Indian and Eurasian plates, is a unique geological structure that has been extensively studied over the past few decades. These previous studies highlighted the occurrence of earthquakes in the orogen's roots beneath the central Himalayas. However, the characterization of these deep earthquakes remains limited. Here, we compiled a detailed, long-duration catalog, which we use to investigate the spatiotemporal characteristics of seismicity beneath the Himalayan orogen.
To create this catalog, we collected all available continuous seismic data acquired during the last two decades in the central Himalayas region (i.e., 2001-2005). We applied a systematic, semi-automatic processing routine to obtain absolute earthquake locations using a 1-D velocity model. Using high-quality picks, ~8,000 preliminary earthquake locations have been determined, at least 1,000 of which have hypocentral depths >50 km. We plan to refine the preliminary locations and calculate local magnitudes for the intermediate-depth lithospheric earthquakes. Using this refined catalog, we will analyze the spatiotemporal evolution pattern and properties of the Himalayan deep seismicity. This analysis is expected to provide us with insights into the processes and mechanisms that control seismogenesis beneath the orogen. For example, is seismicity driven by earthquake stress transfer (mainshock-aftershock sequences), or is it caused by external processes like fluids or aseismic slip, or both?
How to cite: Michailos, K., Carpenter, N. S., and Hetényi, G.: Spatiotemporal evolution of deep seismicity beneath the central Himalayas, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9641, https://doi.org/10.5194/egusphere-egu21-9641, 2021.
EGU21-1227 | vPICO presentations | SM6.1
Episodic earthquake swarms in the Mineral Mountains, Utah driven by the Roosevelt hydrothermal systemMaria Mesimeri, Kristine Pankow, Ben Baker, and J. Mark Hale
The Mineral Mountains are located in south-central Utah within the transition zone from the Basin and Range to Colorado Plateau physiographic provinces, near the Roosevelt Hot Springs. First evidence of swarm-like activity in the area was found in 1981, when a six-station temporary network detected a very energetic swarm of ~1,000 earthquakes. More recently, in mid-2016, a dense local broadband seismic network was installed around the Frontier Observatory for Research in Geothermal Energy (FORGE) in southcentral Utah, ~10 km west of the Mineral Mountains. Beginning in 2016, the University of Utah Seismograph Stations detected, located, and characterized 75 earthquakes beneath the Mineral Mountains. In this study, we build an enhanced earthquake catalog to confirm the episodic swarm-like nature of seismicity in the Mineral Mountains. We use the 75 cataloged earthquakes as templates and detect 1,000 earthquakes by applying a matched-filter technique. The augmented catalog reveals that seismicity in the Mineral Mountains occurs as short-lived earthquake swarms followed by periods of quiescence. Earthquake relocation of ~800 earthquakes shows that activity is concentrated in a <2 km long E-W striking narrow zone, ~4 km east of the Roosevelt hydrothermal system. Two fault orientations, both N-S and E-W parallel to the Opal Mound and Mag Lee faults, respectively, are observed after computing composite focal mechanisms of highly similar earthquakes. After examining the spatial and temporal patterns of the best recorded earthquake swarm in October 2019, we find that a complex mechanism of fluid diffusion and aseismic slip is responsible for the swarm evolution with migration velocities reaching 10 km/day. We hypothesize that these episodic swarms in the Mineral Mountains are primarily driven by migrating fluids that originate within the Roosevelt hydrothermal system.
How to cite: Mesimeri, M., Pankow, K., Baker, B., and Hale, J. M.: Episodic earthquake swarms in the Mineral Mountains, Utah driven by the Roosevelt hydrothermal system, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1227, https://doi.org/10.5194/egusphere-egu21-1227, 2021.
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The Mineral Mountains are located in south-central Utah within the transition zone from the Basin and Range to Colorado Plateau physiographic provinces, near the Roosevelt Hot Springs. First evidence of swarm-like activity in the area was found in 1981, when a six-station temporary network detected a very energetic swarm of ~1,000 earthquakes. More recently, in mid-2016, a dense local broadband seismic network was installed around the Frontier Observatory for Research in Geothermal Energy (FORGE) in southcentral Utah, ~10 km west of the Mineral Mountains. Beginning in 2016, the University of Utah Seismograph Stations detected, located, and characterized 75 earthquakes beneath the Mineral Mountains. In this study, we build an enhanced earthquake catalog to confirm the episodic swarm-like nature of seismicity in the Mineral Mountains. We use the 75 cataloged earthquakes as templates and detect 1,000 earthquakes by applying a matched-filter technique. The augmented catalog reveals that seismicity in the Mineral Mountains occurs as short-lived earthquake swarms followed by periods of quiescence. Earthquake relocation of ~800 earthquakes shows that activity is concentrated in a <2 km long E-W striking narrow zone, ~4 km east of the Roosevelt hydrothermal system. Two fault orientations, both N-S and E-W parallel to the Opal Mound and Mag Lee faults, respectively, are observed after computing composite focal mechanisms of highly similar earthquakes. After examining the spatial and temporal patterns of the best recorded earthquake swarm in October 2019, we find that a complex mechanism of fluid diffusion and aseismic slip is responsible for the swarm evolution with migration velocities reaching 10 km/day. We hypothesize that these episodic swarms in the Mineral Mountains are primarily driven by migrating fluids that originate within the Roosevelt hydrothermal system.
How to cite: Mesimeri, M., Pankow, K., Baker, B., and Hale, J. M.: Episodic earthquake swarms in the Mineral Mountains, Utah driven by the Roosevelt hydrothermal system, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1227, https://doi.org/10.5194/egusphere-egu21-1227, 2021.
EGU21-536 | vPICO presentations | SM6.1
The 2020 Haenam earthquake sequence: The first observation of a seismic front on the Korean Peninsula migrating in a manner similar to fluid diffusionMinkyung Son, Chang Soo Cho, Jin-Hyuck Choi, Jeong-Soo Jeon, and Yun Kyung Park
Low-magnitude earthquakes (maximum Mw: 3.2) were recorded from late April 2020 onward in the county of Haenam, southwestern South Korea. Moderate to strong earthquakes had not previously been documented in instrumental, historical, or geological records. We identified 226 hypocentres in this earthquake sequence from April 25 to May 11, 2020. The seismic front of this sequence migrated in a manner similar to a diffusing fluid, with a hydraulic diffusivity of 0.012 m2/s. This is the first observation of natural seismicity on the Korean Peninsula imitating fluid diffusion. We applied a cross-correlation approach to detect unrecorded events, and relocated the hypocentres of the 71 previously recorded and 155 newly detected events using data collected at permanent seismic stations; clear linearity was observed at the metre scale. Spatially, the hypocentres were distributed within a 0.3 km × 0.3 km fault plane at a depth of ~20 km, trending west-northwest–east-southeast with a dip of ~70° in the south-southwestern direction. The moment tensor solution of the largest event had a strike of 98°, dip of 65°, and rake of 7°, which correspond to the fault geometry of the relocated hypocentres. The hypocentres progressed toward the upper eastern edge of the lineament. The largest event occurred at a shallow region of the fault plane, in the direction of hypocentre migration. Together, these results showed that the migration sequence of the 2020 Haenam earthquake mimicked the flow of a diffusing fluid. The structural data indicate that a fault–fracture mesh geometry channelled fluid flow, supporting the concept of a “fluid-driven earthquake swarm” for the 2020 Haenam earthquake sequence. Regarding the final parts of the sequence, there appeared to be a second intrusion at the western end, and a permeability barrier at the eastern end, of the fault plane. The well-constrained hypocentre locations in our study provide essential data for future research, and our interpretations of hypocentre migration during this earthquake sequence may help to elucidate the mechanisms driving earthquake swarms under conditions of intraplate stress.
How to cite: Son, M., Cho, C. S., Choi, J.-H., Jeon, J.-S., and Park, Y. K.: The 2020 Haenam earthquake sequence: The first observation of a seismic front on the Korean Peninsula migrating in a manner similar to fluid diffusion, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-536, https://doi.org/10.5194/egusphere-egu21-536, 2021.
Please decide on your access
Please use the buttons below to download the presentation materials or to visit the external website where the presentation is linked. Regarding the external link, please note that Copernicus Meetings cannot accept any liability for the content and the website you will visit.
Forward to presentation link
You are going to open an external link to the presentation as indicated by the authors. Copernicus Meetings cannot accept any liability for the content and the website you will visit.
We are sorry, but presentations are only available for users who registered for the conference. Thank you.
Low-magnitude earthquakes (maximum Mw: 3.2) were recorded from late April 2020 onward in the county of Haenam, southwestern South Korea. Moderate to strong earthquakes had not previously been documented in instrumental, historical, or geological records. We identified 226 hypocentres in this earthquake sequence from April 25 to May 11, 2020. The seismic front of this sequence migrated in a manner similar to a diffusing fluid, with a hydraulic diffusivity of 0.012 m2/s. This is the first observation of natural seismicity on the Korean Peninsula imitating fluid diffusion. We applied a cross-correlation approach to detect unrecorded events, and relocated the hypocentres of the 71 previously recorded and 155 newly detected events using data collected at permanent seismic stations; clear linearity was observed at the metre scale. Spatially, the hypocentres were distributed within a 0.3 km × 0.3 km fault plane at a depth of ~20 km, trending west-northwest–east-southeast with a dip of ~70° in the south-southwestern direction. The moment tensor solution of the largest event had a strike of 98°, dip of 65°, and rake of 7°, which correspond to the fault geometry of the relocated hypocentres. The hypocentres progressed toward the upper eastern edge of the lineament. The largest event occurred at a shallow region of the fault plane, in the direction of hypocentre migration. Together, these results showed that the migration sequence of the 2020 Haenam earthquake mimicked the flow of a diffusing fluid. The structural data indicate that a fault–fracture mesh geometry channelled fluid flow, supporting the concept of a “fluid-driven earthquake swarm” for the 2020 Haenam earthquake sequence. Regarding the final parts of the sequence, there appeared to be a second intrusion at the western end, and a permeability barrier at the eastern end, of the fault plane. The well-constrained hypocentre locations in our study provide essential data for future research, and our interpretations of hypocentre migration during this earthquake sequence may help to elucidate the mechanisms driving earthquake swarms under conditions of intraplate stress.
How to cite: Son, M., Cho, C. S., Choi, J.-H., Jeon, J.-S., and Park, Y. K.: The 2020 Haenam earthquake sequence: The first observation of a seismic front on the Korean Peninsula migrating in a manner similar to fluid diffusion, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-536, https://doi.org/10.5194/egusphere-egu21-536, 2021.
EGU21-1682 | vPICO presentations | SM6.1
Elastic properties and fluid abundance in the source volume of the 2010-2014 Pollino seismic sequence from P and S wave tomographyFerdinando Napolitano, Ortensia Amoroso, Valeria Vitale, Anna Gervasi, Mario La Rocca, and Paolo Capuano
The 2010-2014 Pollino seismic sequence occurred in a well known seismic gap zone in Southern Italy. Although paleoseismological studies revealed the occurrence of at least two earthquakes of MW6.5-7 in the last 10,000 years, no earthquakes larger than M6 occurred in historical times. The sequence had a long duration and it was characterized by a variable seismic rate and by two mainshocks (ML4.3 and ML5.0) occurred in May and October 2012, two years after the beginning of the swarm. In the same area a slow slip event started three months before the ML5.0 earthquake and lasted for one year.
The aim of this work is the investigation of the elastic properties of the seismogenic volume and the presence of abundant fluids inferred from the study of attenuation. The role that fluids in highly fractured media play in triggering and driving the occurrence of earthquake swarms is believed very important, but yet to be understood clearly. In order to investigate the elastic properties of the medium, we performed a local P- and S-wave 3D tomographic image. We selected 870 earthquakes (ML1.8–5.0) occurred between 2010 and 2014 from the sequence and nearby within a volume of 100x120x25km3. We manually picked 9981 P and 6862 S arrivals recorded by 39 seismic stations. The picking consistency was estimated by modified Wadati diagram which also provided an estimate of VP/Vs equal to 1.786.
We applied a linearized, iterative delay-time inversion approach, which simultaneously inverts the first arrivals of direct waves for both velocity model parameters and earthquake locations. The dataset and the station distribution allow us to set a 5x5x1km3 grid for the inversion. We performed several numerical tests to estimate a reliable starting 1D P- and S-wave velocity model. A finer grid of 0.5x0.5x0.5km3 has been set to compute the theoretical arrival travel times at each station through a finite-difference solution of the eikonal equation. The model parameters have been inverted using LSQR method. The best regularization parameter of the inversion has been obtained from the trade-off curve between the model parameters and the data variances. The Derivative Weight Sum and the checkerboard tests have been performed to assess the resolved area of the map.
The preliminary results show a significant increase of VP and VS velocity at depth of about 6 km beneath Mt. Pollino. This interface likely corresponds to the top of the Apulian platform. A low VP, low VP/VS anomaly is found above the eastern cluster of seismicity, and a low VP, high VP/VS anomaly appear north and south-east of the sequence. The latter is spatially consistent with the fluid-rich volume suggested by the results of attenuation analysis. Further analyses will follow to provide more insights about this complex sequence and, in a broader view, about similar swarm-like sequences.
How to cite: Napolitano, F., Amoroso, O., Vitale, V., Gervasi, A., La Rocca, M., and Capuano, P.: Elastic properties and fluid abundance in the source volume of the 2010-2014 Pollino seismic sequence from P and S wave tomography, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1682, https://doi.org/10.5194/egusphere-egu21-1682, 2021.
The 2010-2014 Pollino seismic sequence occurred in a well known seismic gap zone in Southern Italy. Although paleoseismological studies revealed the occurrence of at least two earthquakes of MW6.5-7 in the last 10,000 years, no earthquakes larger than M6 occurred in historical times. The sequence had a long duration and it was characterized by a variable seismic rate and by two mainshocks (ML4.3 and ML5.0) occurred in May and October 2012, two years after the beginning of the swarm. In the same area a slow slip event started three months before the ML5.0 earthquake and lasted for one year.
The aim of this work is the investigation of the elastic properties of the seismogenic volume and the presence of abundant fluids inferred from the study of attenuation. The role that fluids in highly fractured media play in triggering and driving the occurrence of earthquake swarms is believed very important, but yet to be understood clearly. In order to investigate the elastic properties of the medium, we performed a local P- and S-wave 3D tomographic image. We selected 870 earthquakes (ML1.8–5.0) occurred between 2010 and 2014 from the sequence and nearby within a volume of 100x120x25km3. We manually picked 9981 P and 6862 S arrivals recorded by 39 seismic stations. The picking consistency was estimated by modified Wadati diagram which also provided an estimate of VP/Vs equal to 1.786.
We applied a linearized, iterative delay-time inversion approach, which simultaneously inverts the first arrivals of direct waves for both velocity model parameters and earthquake locations. The dataset and the station distribution allow us to set a 5x5x1km3 grid for the inversion. We performed several numerical tests to estimate a reliable starting 1D P- and S-wave velocity model. A finer grid of 0.5x0.5x0.5km3 has been set to compute the theoretical arrival travel times at each station through a finite-difference solution of the eikonal equation. The model parameters have been inverted using LSQR method. The best regularization parameter of the inversion has been obtained from the trade-off curve between the model parameters and the data variances. The Derivative Weight Sum and the checkerboard tests have been performed to assess the resolved area of the map.
The preliminary results show a significant increase of VP and VS velocity at depth of about 6 km beneath Mt. Pollino. This interface likely corresponds to the top of the Apulian platform. A low VP, low VP/VS anomaly is found above the eastern cluster of seismicity, and a low VP, high VP/VS anomaly appear north and south-east of the sequence. The latter is spatially consistent with the fluid-rich volume suggested by the results of attenuation analysis. Further analyses will follow to provide more insights about this complex sequence and, in a broader view, about similar swarm-like sequences.
How to cite: Napolitano, F., Amoroso, O., Vitale, V., Gervasi, A., La Rocca, M., and Capuano, P.: Elastic properties and fluid abundance in the source volume of the 2010-2014 Pollino seismic sequence from P and S wave tomography, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1682, https://doi.org/10.5194/egusphere-egu21-1682, 2021.
EGU21-4532 | vPICO presentations | SM6.1
Comparison of two low magnitude seismic swarms in Calabria (Italy)Giuseppe Davide Chiappetta, Anna Gervasi, and Mario La Rocca
We studied two seismic swarms occurred recently in Calabria, one in the Mesima-valley and one near Albi. Earthquakes were located by manually picking P and S waves. A search for clusters of events characterized by similar waveform was done, then the relative location was performed for any clusters. The focal mechanism was computed for as many events as possible, comparing the observed seismograms with synthetic signals for events of M>2.8, and considering the polarity of P and S waves for smaller events. For very small earthquakes we tried an estimation of the focal mechanism by comparison of the few clear signals with the recordings of stronger events. This analysis is aimed at investigating whether the many earthquakes of a swarm are produced by the same fault or by faults characterized by different orientation.
The Mesima valley area was affected by a seismic swarm that begun with a M3.6 earthquake on May 26, 2019. More than 140 events of smaller magnitude occurred in the same area during the following month. The relative location shows a hypocenter distribution with depth between 16 and 19 km and elongated for about 2 km in the NE-SW direction. The seismogenetic volume estimated from the relative location is of about 12 km3. The focal mechanisms computed for the 9 strongest events of the swarm are very similar among them, indicating a dip-slip normal kinematics. The comparative observation of P-wave polarity suggests that the most events of this swarm were likely generated by the same fault. In fact, even very small earthquakes (M<1.5) for which we can't give a reliable estimate of the focal mechanism, are characterized by P wave of the same polarity of stronger events at the stations around the epicenter.
Albi seismic swarm is one of the most interesting occurred in the central-eastern part of Calabria during the last 10 years. It begun on January 16, 2020, with a M3.8 earthquake, followed by more than 120 events in a month, and many others later. Detailed analyses were performed on as many earthquakes as possible, including absolute location, search for clusters of similar events and their relative location, and the estimation of focal mechanism. Results clearly indicate that this swarm was generated by a much greater seismogenetic volume if compared with the Mesima valley swarm. In fact hypocenters are much more spread, forming a cloud in the 6-12 km depth range, with a volume of at least 30-40 km3, and without any clear shape or direction. The search for clusters gave many families of similar events. Events of different clusters show waveforms quite different among them. Sometimes earthquakes located very near to each other have opposite P-wave polarity at the same station. Focal mechanisms confirm the heterogeneity of this swarm. The only common feature is the normal kinematics, while strike and dip cover wide ranges of values. Therefore we conclude that this swarm was generated by many small faults with different directions, activated by an extensional stress field.
How to cite: Chiappetta, G. D., Gervasi, A., and La Rocca, M.: Comparison of two low magnitude seismic swarms in Calabria (Italy), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4532, https://doi.org/10.5194/egusphere-egu21-4532, 2021.
We studied two seismic swarms occurred recently in Calabria, one in the Mesima-valley and one near Albi. Earthquakes were located by manually picking P and S waves. A search for clusters of events characterized by similar waveform was done, then the relative location was performed for any clusters. The focal mechanism was computed for as many events as possible, comparing the observed seismograms with synthetic signals for events of M>2.8, and considering the polarity of P and S waves for smaller events. For very small earthquakes we tried an estimation of the focal mechanism by comparison of the few clear signals with the recordings of stronger events. This analysis is aimed at investigating whether the many earthquakes of a swarm are produced by the same fault or by faults characterized by different orientation.
The Mesima valley area was affected by a seismic swarm that begun with a M3.6 earthquake on May 26, 2019. More than 140 events of smaller magnitude occurred in the same area during the following month. The relative location shows a hypocenter distribution with depth between 16 and 19 km and elongated for about 2 km in the NE-SW direction. The seismogenetic volume estimated from the relative location is of about 12 km3. The focal mechanisms computed for the 9 strongest events of the swarm are very similar among them, indicating a dip-slip normal kinematics. The comparative observation of P-wave polarity suggests that the most events of this swarm were likely generated by the same fault. In fact, even very small earthquakes (M<1.5) for which we can't give a reliable estimate of the focal mechanism, are characterized by P wave of the same polarity of stronger events at the stations around the epicenter.
Albi seismic swarm is one of the most interesting occurred in the central-eastern part of Calabria during the last 10 years. It begun on January 16, 2020, with a M3.8 earthquake, followed by more than 120 events in a month, and many others later. Detailed analyses were performed on as many earthquakes as possible, including absolute location, search for clusters of similar events and their relative location, and the estimation of focal mechanism. Results clearly indicate that this swarm was generated by a much greater seismogenetic volume if compared with the Mesima valley swarm. In fact hypocenters are much more spread, forming a cloud in the 6-12 km depth range, with a volume of at least 30-40 km3, and without any clear shape or direction. The search for clusters gave many families of similar events. Events of different clusters show waveforms quite different among them. Sometimes earthquakes located very near to each other have opposite P-wave polarity at the same station. Focal mechanisms confirm the heterogeneity of this swarm. The only common feature is the normal kinematics, while strike and dip cover wide ranges of values. Therefore we conclude that this swarm was generated by many small faults with different directions, activated by an extensional stress field.
How to cite: Chiappetta, G. D., Gervasi, A., and La Rocca, M.: Comparison of two low magnitude seismic swarms in Calabria (Italy), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4532, https://doi.org/10.5194/egusphere-egu21-4532, 2021.
EGU21-10143 | vPICO presentations | SM6.1
Insights into a tectonic swarm-like seismic Sequence related to a Low Angle Normal Fault system from a Seismic Catalog enhanced by Template MatchingDavid Essing, Piero Poli, and Glenn Cougoulat
The Alto Tiberina fault (ATF) system (Northern Apennines, Italy) is dominated by a low-angle normal fault with syn- and antithetic splay faults located in the hanging wall. Starting in August 2013 the hanging wall has been affected by a swarm-like sequence that lasted until the end of 2014. Within this period more than ~20k events are listed to have nucleated along the same fault segment with the largest events having magnitudes of ~Mw 3.9.
In this study we aim to constrain the physical forces driving the swarm-like sequence (e.g. pore pressure diffusion, transient slow slip) in this fault segment by combining a template matching approach with continuous seismic data from a borehole array deployed in the near field of the ATF. This array approach helps us to identify small events which are hidden in the background noise and usually undetected with conventional picking approaches.
We are able to extend the preexisting catalog by a factor > 5. The new detected events decrease the magnitude of completeness and the inter-event time resolution. We use the extended catalog to analyze the spatio-temporal evolution, scaling properties and statistical behavior to enhance insights on the physical forces driving this swarm like sequence.
How to cite: Essing, D., Poli, P., and Cougoulat, G.: Insights into a tectonic swarm-like seismic Sequence related to a Low Angle Normal Fault system from a Seismic Catalog enhanced by Template Matching, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10143, https://doi.org/10.5194/egusphere-egu21-10143, 2021.
Please decide on your access
Please use the buttons below to download the presentation materials or to visit the external website where the presentation is linked. Regarding the external link, please note that Copernicus Meetings cannot accept any liability for the content and the website you will visit.
Forward to presentation link
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We are sorry, but presentations are only available for users who registered for the conference. Thank you.
The Alto Tiberina fault (ATF) system (Northern Apennines, Italy) is dominated by a low-angle normal fault with syn- and antithetic splay faults located in the hanging wall. Starting in August 2013 the hanging wall has been affected by a swarm-like sequence that lasted until the end of 2014. Within this period more than ~20k events are listed to have nucleated along the same fault segment with the largest events having magnitudes of ~Mw 3.9.
In this study we aim to constrain the physical forces driving the swarm-like sequence (e.g. pore pressure diffusion, transient slow slip) in this fault segment by combining a template matching approach with continuous seismic data from a borehole array deployed in the near field of the ATF. This array approach helps us to identify small events which are hidden in the background noise and usually undetected with conventional picking approaches.
We are able to extend the preexisting catalog by a factor > 5. The new detected events decrease the magnitude of completeness and the inter-event time resolution. We use the extended catalog to analyze the spatio-temporal evolution, scaling properties and statistical behavior to enhance insights on the physical forces driving this swarm like sequence.
How to cite: Essing, D., Poli, P., and Cougoulat, G.: Insights into a tectonic swarm-like seismic Sequence related to a Low Angle Normal Fault system from a Seismic Catalog enhanced by Template Matching, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10143, https://doi.org/10.5194/egusphere-egu21-10143, 2021.
EGU21-16045 | vPICO presentations | SM6.1
Enahancing the detail on low-level seismicity and swarms in central-southern Italy by template matchingLuca Carbone, Rita de Nardis, Giusy Lavecchia, Laura Peruzza, Enrico Priolo, Adelaide Romano, and Alessandro Vuan
During the seismic sequence which followed the devastating L’Aquila 2009 earthquake, on 27 May 2009 the OGS (Istituto Nazionale di Oceanografia e di Geofisica Sperimentale) and the GeosisLab (Laboratorio di Geodinamica e Sismogenesi, Chieti-Pescara University) installed a temporary seismometric network around the Sulmona Basin, a high seismic risk area of Central Italy located right at SE of the epicentral one. This area of the central Apennines is generally characterized by low level seismicity organized in low energy clusters, but it experienced destructive earthquakes both in historical and in early instrumental time (Fucino 1915 =XI MCS, Majella 1706 =X-XI MCS, Barrea 1984 =VIII MCS).
From the 27 May 2009 to 22 November 2011, the temporary network provided a huge amount of continuous seismic recordings, and a seismic catalogue covering the first seven months of network operation (-1.5≤ML≤3.7, with a completeness magnitude of 1.1) and a spatial area that stretches from the Sulmona Basin to Marsica-Sora area. Aiming to enhance the detection of microearthquakes reported in this catalogue, we applied the matched-filter technique (MFT) to continuous waveforms properly integrated with data from permanent stations belonging to the national seismic network. Specifically, we used the open-source seismological package PyMPA to detect microseismicity from the cross-correlation of continuous data and templates. As templates we used only the best relocated events of the available seismic catalogue. Starting from 366 well located earthquakes we obtain a new seismic catalogue of 6084 new events (-2<ML<4) lowering the completeness magnitude to 0.2. To these new seismic locations, we applied a declustering method to separate background seismicity from clustered seismicity in the area. All the seismicity shows a bimodal behaviour in term of distribution of the nearest-neighbor distance/time with the presence of two statistically distinct earthquake populations. We focused the attention on two of these clusters (C1 and C2) that numerically represent the 60% of the catalogue. They consist in 2619 and 995 events, respectively, with magnitude -2.0<ML<3.6 and -0.5<ML<3.2 occurred in Marsica-Sora area. C1 shows the typical characteristics of a seismic swarm, without a clear mainshock, but with 8 more energetic events (3.0≤ML≤3.5); the temporal evolution is very articulated with a total duration of one month with different bursts of seismicity and characteristic time extension of approximately one week. C2 instead has a different space-time evolution and consists of different swarm-like seismic sequences more discontinuous in comparison with C1. These swarms are described in greater detail to investigate the influence of overpressurized fluids and their space-time distribution.
How to cite: Carbone, L., de Nardis, R., Lavecchia, G., Peruzza, L., Priolo, E., Romano, A., and Vuan, A.: Enahancing the detail on low-level seismicity and swarms in central-southern Italy by template matching, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16045, https://doi.org/10.5194/egusphere-egu21-16045, 2021.
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During the seismic sequence which followed the devastating L’Aquila 2009 earthquake, on 27 May 2009 the OGS (Istituto Nazionale di Oceanografia e di Geofisica Sperimentale) and the GeosisLab (Laboratorio di Geodinamica e Sismogenesi, Chieti-Pescara University) installed a temporary seismometric network around the Sulmona Basin, a high seismic risk area of Central Italy located right at SE of the epicentral one. This area of the central Apennines is generally characterized by low level seismicity organized in low energy clusters, but it experienced destructive earthquakes both in historical and in early instrumental time (Fucino 1915 =XI MCS, Majella 1706 =X-XI MCS, Barrea 1984 =VIII MCS).
From the 27 May 2009 to 22 November 2011, the temporary network provided a huge amount of continuous seismic recordings, and a seismic catalogue covering the first seven months of network operation (-1.5≤ML≤3.7, with a completeness magnitude of 1.1) and a spatial area that stretches from the Sulmona Basin to Marsica-Sora area. Aiming to enhance the detection of microearthquakes reported in this catalogue, we applied the matched-filter technique (MFT) to continuous waveforms properly integrated with data from permanent stations belonging to the national seismic network. Specifically, we used the open-source seismological package PyMPA to detect microseismicity from the cross-correlation of continuous data and templates. As templates we used only the best relocated events of the available seismic catalogue. Starting from 366 well located earthquakes we obtain a new seismic catalogue of 6084 new events (-2<ML<4) lowering the completeness magnitude to 0.2. To these new seismic locations, we applied a declustering method to separate background seismicity from clustered seismicity in the area. All the seismicity shows a bimodal behaviour in term of distribution of the nearest-neighbor distance/time with the presence of two statistically distinct earthquake populations. We focused the attention on two of these clusters (C1 and C2) that numerically represent the 60% of the catalogue. They consist in 2619 and 995 events, respectively, with magnitude -2.0<ML<3.6 and -0.5<ML<3.2 occurred in Marsica-Sora area. C1 shows the typical characteristics of a seismic swarm, without a clear mainshock, but with 8 more energetic events (3.0≤ML≤3.5); the temporal evolution is very articulated with a total duration of one month with different bursts of seismicity and characteristic time extension of approximately one week. C2 instead has a different space-time evolution and consists of different swarm-like seismic sequences more discontinuous in comparison with C1. These swarms are described in greater detail to investigate the influence of overpressurized fluids and their space-time distribution.
How to cite: Carbone, L., de Nardis, R., Lavecchia, G., Peruzza, L., Priolo, E., Romano, A., and Vuan, A.: Enahancing the detail on low-level seismicity and swarms in central-southern Italy by template matching, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16045, https://doi.org/10.5194/egusphere-egu21-16045, 2021.
EGU21-9561 | vPICO presentations | SM6.1
High frequency array observations of December 2020 swarm at surface and borehole stations at ICDP Eger Rift site Landwüst (Vogtland)Katrin Hannemann, Matthias Ohrnberger, Nikolaus Lerbs, Dorina Domigall, Marius Isken, René Voigt, Daniel Vollmer, Ralf Bauz, Jakub Klicpera, Lutz Sonnabend, Michael Korn, Frank Krüger, Tomáš Fischer, and Torsten Dahm
Within the ICDP project “Drilling the Eger Rift”, we focus on the German-Czech border region West Bohemia/ Vogtland which is known for its earthquake swarms. These swarms are clusters of small magnitude (ML<4) earthquakes which are supposed to be linked to the rise of fluids with mainly mantle origin. We aim to improve the seismological observation of these small magnitude earthquakes and related processes especially at frequencies above 100 Hz by installing three dense small aperture 3D arrays. Each single 3D array will consist of a 400 m deep vertical array borehole installation and a small aperture (400 m) surface array.
The drill site S1 in Landwüst and its surroundings serve as pilot site for the first installation. The borehole chain consists of eight 3-component 10 Hz geophones and the continous recordings are sampled with 1000 Hz. In parallel, twelve surface stations are installed which are equiped with 4.5 Hz geophones. The data were recorded with 400 Hz sampling rate at most locations, but at some selected stations we additionally record data with 1000 Hz sampling rate being the desired sampling rate for the final array configuration. Due to the high sampling rates and the high frequency content of the recorded earthquake signals, local site conditions may lead to non-coherent recordings for different parts of the array which have a major influence on the overall array performance. However, preliminary results from broad band frequency wave number analysis (5-180 Hz) in a moving time window (0.2 s) with first test installation data also indicate that the coherency across the array site is still high enough to clearly identify P and S waves from local earthquakes.
In the period December 2020 – January 2021, an earthquake swarm took place with two activity clusters in Nový Kostel (Czech Republic) and Obertriebel/ Oelsnitz (Vogtland, Germany) about 20 km apart. This swarm was recorded by both borehole stations and surface stations in Landwüst. Preliminary results show that more than 14000 events can be identified at the borehole stations and that about 70-80% of these events are also observed at the surface stations. For small earthquakes, mainly the S wave can be identified, but also impulsive P waves are clearly visible at the surface stations. These high frequency waves (up to 230 Hz at the surface) show a good coherency across the surface array. At the borehole stations, we observe an even higher frequency content up to 300 Hz and more. We present recordings from selected events to analyse frequency content and coherency across the 3D array.
How to cite: Hannemann, K., Ohrnberger, M., Lerbs, N., Domigall, D., Isken, M., Voigt, R., Vollmer, D., Bauz, R., Klicpera, J., Sonnabend, L., Korn, M., Krüger, F., Fischer, T., and Dahm, T.: High frequency array observations of December 2020 swarm at surface and borehole stations at ICDP Eger Rift site Landwüst (Vogtland), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9561, https://doi.org/10.5194/egusphere-egu21-9561, 2021.
Within the ICDP project “Drilling the Eger Rift”, we focus on the German-Czech border region West Bohemia/ Vogtland which is known for its earthquake swarms. These swarms are clusters of small magnitude (ML<4) earthquakes which are supposed to be linked to the rise of fluids with mainly mantle origin. We aim to improve the seismological observation of these small magnitude earthquakes and related processes especially at frequencies above 100 Hz by installing three dense small aperture 3D arrays. Each single 3D array will consist of a 400 m deep vertical array borehole installation and a small aperture (400 m) surface array.
The drill site S1 in Landwüst and its surroundings serve as pilot site for the first installation. The borehole chain consists of eight 3-component 10 Hz geophones and the continous recordings are sampled with 1000 Hz. In parallel, twelve surface stations are installed which are equiped with 4.5 Hz geophones. The data were recorded with 400 Hz sampling rate at most locations, but at some selected stations we additionally record data with 1000 Hz sampling rate being the desired sampling rate for the final array configuration. Due to the high sampling rates and the high frequency content of the recorded earthquake signals, local site conditions may lead to non-coherent recordings for different parts of the array which have a major influence on the overall array performance. However, preliminary results from broad band frequency wave number analysis (5-180 Hz) in a moving time window (0.2 s) with first test installation data also indicate that the coherency across the array site is still high enough to clearly identify P and S waves from local earthquakes.
In the period December 2020 – January 2021, an earthquake swarm took place with two activity clusters in Nový Kostel (Czech Republic) and Obertriebel/ Oelsnitz (Vogtland, Germany) about 20 km apart. This swarm was recorded by both borehole stations and surface stations in Landwüst. Preliminary results show that more than 14000 events can be identified at the borehole stations and that about 70-80% of these events are also observed at the surface stations. For small earthquakes, mainly the S wave can be identified, but also impulsive P waves are clearly visible at the surface stations. These high frequency waves (up to 230 Hz at the surface) show a good coherency across the surface array. At the borehole stations, we observe an even higher frequency content up to 300 Hz and more. We present recordings from selected events to analyse frequency content and coherency across the 3D array.
How to cite: Hannemann, K., Ohrnberger, M., Lerbs, N., Domigall, D., Isken, M., Voigt, R., Vollmer, D., Bauz, R., Klicpera, J., Sonnabend, L., Korn, M., Krüger, F., Fischer, T., and Dahm, T.: High frequency array observations of December 2020 swarm at surface and borehole stations at ICDP Eger Rift site Landwüst (Vogtland), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9561, https://doi.org/10.5194/egusphere-egu21-9561, 2021.
EGU21-15429 | vPICO presentations | SM6.1
Improving the detection capability of the West Bohemian network by template matching approachAli Salama and Tomas Fischer
During the West-Bohemia/Vogtland earthquake swarms thousands of events are detected within short periods of few days, whose preliminary location is provided by an automated procedure. The manually verified high quality catalog is provided with some delay and is usually less complete than the automatic one.
We developed a template matching procedure combined with differential time measurement and double difference location whose application in real time will allow to provide precise hypocentre locations for much larger data set than provided by the manual processing. Among others, the template matching approach includes flexible setting of the time difference between P and S waves which allows for event detection in a wider distance to the template’s hypocentre. This makes the size of the template dataset small enough to allow for efficient detection process.
Our application of the template matching approach is aimed at identifying repeated activation of some patches during the swarms and weak background activity in the intermediate periods. Detecting and analyzing the repeating earthquakes will help revealing the continuing background activity and identifying fault areas that are active permanently. This will point to the possible sources of fluids or aseismic creep that are supposed to play significant role in swarm generation.
How to cite: Salama, A. and Fischer, T.: Improving the detection capability of the West Bohemian network by template matching approach , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15429, https://doi.org/10.5194/egusphere-egu21-15429, 2021.
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We are sorry, but presentations are only available for users who registered for the conference. Thank you.
During the West-Bohemia/Vogtland earthquake swarms thousands of events are detected within short periods of few days, whose preliminary location is provided by an automated procedure. The manually verified high quality catalog is provided with some delay and is usually less complete than the automatic one.
We developed a template matching procedure combined with differential time measurement and double difference location whose application in real time will allow to provide precise hypocentre locations for much larger data set than provided by the manual processing. Among others, the template matching approach includes flexible setting of the time difference between P and S waves which allows for event detection in a wider distance to the template’s hypocentre. This makes the size of the template dataset small enough to allow for efficient detection process.
Our application of the template matching approach is aimed at identifying repeated activation of some patches during the swarms and weak background activity in the intermediate periods. Detecting and analyzing the repeating earthquakes will help revealing the continuing background activity and identifying fault areas that are active permanently. This will point to the possible sources of fluids or aseismic creep that are supposed to play significant role in swarm generation.
How to cite: Salama, A. and Fischer, T.: Improving the detection capability of the West Bohemian network by template matching approach , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15429, https://doi.org/10.5194/egusphere-egu21-15429, 2021.
EGU21-14986 | vPICO presentations | SM6.1
Are the recurring earthquake swarms in West-Bohemia rain triggered?Josef Vlcek, Roman Beránek, and Tomáš Fischer
In past decades, a significant effort was spent to find the origin of recurring earthquake swarms in West-Bohemia/Vogtland. Widespread understanding accepts that crustal fluids migration along the fault zones is responsible for earthquake triggering in this area. Recently, a new model was suggested, which tests the hypothesis whether the diffusion of hydraulically induced pore pressure could be a valid trigger mechanism. In this approach the precipitation signal was transformed by diffusion equation to the hypocenter depth and statistically compared with the earthquake occurrence in time and concluded that at least 19% of the seismicity could have been triggered by rain.
In our study we apply a different approach to verify the validity of these results. We use two types of rain signal on the input which is compared with the time series of earthquake weekly rate for the past 25 years. To remove the strong episodic character of the swarm seismicity we use a declustered seismic catalog, which is characteristic by almost continuous seismic activity.
The rain signal is represented first by the precipitation data and second by the water level data in the Horka reservoir, which is located above the main focal zone of Nový Kostel. We test the possible relation to the earthquake swarm activity by cross correlating both the rain signal types and the seismicity rate. To amplify the possible seasonal periodicity of the data we stacked the explored time series data (precipitation, water level and seismic activity) according to their occurrence date in a single year. The results show that in any of the input data and seismicity do not correlate.
In the next step, we tested the possible (annual) periodicity of the data in question by the singular spectral analysis (SSA), which is a sensitive method to identify possible periodic signals in the presence of noise. While the water level data showed a striking peak for the period of 1 year, any indication of annual periodicity was never found in the seismicity data. Accordingly, we conclude that our analysis has shown no influence of the precipitation or the water level fluctuations in the Horka dam to the earthquake swarm activity in West Bohemia/Vogtland.
How to cite: Vlcek, J., Beránek, R., and Fischer, T.: Are the recurring earthquake swarms in West-Bohemia rain triggered?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14986, https://doi.org/10.5194/egusphere-egu21-14986, 2021.
Please decide on your access
Please use the buttons below to download the presentation materials or to visit the external website where the presentation is linked. Regarding the external link, please note that Copernicus Meetings cannot accept any liability for the content and the website you will visit.
Forward to presentation link
You are going to open an external link to the presentation as indicated by the authors. Copernicus Meetings cannot accept any liability for the content and the website you will visit.
We are sorry, but presentations are only available for users who registered for the conference. Thank you.
In past decades, a significant effort was spent to find the origin of recurring earthquake swarms in West-Bohemia/Vogtland. Widespread understanding accepts that crustal fluids migration along the fault zones is responsible for earthquake triggering in this area. Recently, a new model was suggested, which tests the hypothesis whether the diffusion of hydraulically induced pore pressure could be a valid trigger mechanism. In this approach the precipitation signal was transformed by diffusion equation to the hypocenter depth and statistically compared with the earthquake occurrence in time and concluded that at least 19% of the seismicity could have been triggered by rain.
In our study we apply a different approach to verify the validity of these results. We use two types of rain signal on the input which is compared with the time series of earthquake weekly rate for the past 25 years. To remove the strong episodic character of the swarm seismicity we use a declustered seismic catalog, which is characteristic by almost continuous seismic activity.
The rain signal is represented first by the precipitation data and second by the water level data in the Horka reservoir, which is located above the main focal zone of Nový Kostel. We test the possible relation to the earthquake swarm activity by cross correlating both the rain signal types and the seismicity rate. To amplify the possible seasonal periodicity of the data we stacked the explored time series data (precipitation, water level and seismic activity) according to their occurrence date in a single year. The results show that in any of the input data and seismicity do not correlate.
In the next step, we tested the possible (annual) periodicity of the data in question by the singular spectral analysis (SSA), which is a sensitive method to identify possible periodic signals in the presence of noise. While the water level data showed a striking peak for the period of 1 year, any indication of annual periodicity was never found in the seismicity data. Accordingly, we conclude that our analysis has shown no influence of the precipitation or the water level fluctuations in the Horka dam to the earthquake swarm activity in West Bohemia/Vogtland.
How to cite: Vlcek, J., Beránek, R., and Fischer, T.: Are the recurring earthquake swarms in West-Bohemia rain triggered?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14986, https://doi.org/10.5194/egusphere-egu21-14986, 2021.
EGU21-2654 | vPICO presentations | SM6.1
Investigating the relationship between seismic sequences and hydrological loading in the AzoresAna L. Lordi, Maria C. Neves, and Susana Custódio
Hydrological loads can be either surface loads induced by precipitation, changes in water levels at crater volcanic lakes, or subsurface loads created by seasonal changes in groundwater levels. These may contribute to strain and stress transients that trigger small earthquake swarms at faults that are already near failure. This work focusses on how annual and multi-annual stress changes of hydrological origin may affect the generation of seismic sequences on several tectonic settings, such as the New Madrid Seismic Zone and the Azores. The New Madrid seismic Zone is used as a benchmark test study region, while the Azores has been chosen for its intense seismic activity of both tectonic and volcanic origin. The magnitude of the hydrologically derived variations in stress is small compared with the long-term tectonic stresses, so we look for seasonal and inter-annual modulations of the earthquake occurrence rate. This requires the manipulation of seismic catalogues and the use of statistical methods to check if the seasonal and inter-annual variations are statistically significant, and not the result of extreme climatic events. The impact of hydrologic loads on faults is addressed using high-quality time series of seismic sequences, rainfall and other loads produced by variations in water levels, methods of decomposition and reconstruction of geophysical time series (SSA and wavelet transform) to identify modes of oscillation, and correlation analysis to recognize common patterns in seismicity and water loads. The results provide the first assessment of cyclic variations in seismicity and its relationship with atmospheric disturbances and hydrologically-driven load in the Azores region, and contributes to improve our understanding of the physics of earthquake triggering processes. The authors would like to acknowledge the financial support FCT through project UIDB/50019/2020 – IDL. This is a contribution to the RESTLESS project PTDC/CTA-GEF/6674/2020.
How to cite: Lordi, A. L., Neves, M. C., and Custódio, S.: Investigating the relationship between seismic sequences and hydrological loading in the Azores, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2654, https://doi.org/10.5194/egusphere-egu21-2654, 2021.
Hydrological loads can be either surface loads induced by precipitation, changes in water levels at crater volcanic lakes, or subsurface loads created by seasonal changes in groundwater levels. These may contribute to strain and stress transients that trigger small earthquake swarms at faults that are already near failure. This work focusses on how annual and multi-annual stress changes of hydrological origin may affect the generation of seismic sequences on several tectonic settings, such as the New Madrid Seismic Zone and the Azores. The New Madrid seismic Zone is used as a benchmark test study region, while the Azores has been chosen for its intense seismic activity of both tectonic and volcanic origin. The magnitude of the hydrologically derived variations in stress is small compared with the long-term tectonic stresses, so we look for seasonal and inter-annual modulations of the earthquake occurrence rate. This requires the manipulation of seismic catalogues and the use of statistical methods to check if the seasonal and inter-annual variations are statistically significant, and not the result of extreme climatic events. The impact of hydrologic loads on faults is addressed using high-quality time series of seismic sequences, rainfall and other loads produced by variations in water levels, methods of decomposition and reconstruction of geophysical time series (SSA and wavelet transform) to identify modes of oscillation, and correlation analysis to recognize common patterns in seismicity and water loads. The results provide the first assessment of cyclic variations in seismicity and its relationship with atmospheric disturbances and hydrologically-driven load in the Azores region, and contributes to improve our understanding of the physics of earthquake triggering processes. The authors would like to acknowledge the financial support FCT through project UIDB/50019/2020 – IDL. This is a contribution to the RESTLESS project PTDC/CTA-GEF/6674/2020.
How to cite: Lordi, A. L., Neves, M. C., and Custódio, S.: Investigating the relationship between seismic sequences and hydrological loading in the Azores, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2654, https://doi.org/10.5194/egusphere-egu21-2654, 2021.
EGU21-5131 | vPICO presentations | SM6.1
Hydroacoustic observations of Two Contrasted Seismic Swarms along the Southwest Indian Ridge in 2018Vaibhav Vijay Ingale, Sara Bazin, and Jean-Yves Royer
In 2018, two earthquake swarms occurred along segments of the ultra-slow Southwest Indian Ridge (spreading rate: 14-15 mm/a). The first swarm is located at the spreading-ridge intersection with the Atlantis Fracture Zone and comprises 9 Mw > 5.0 events (GCMT catalogue) and about 227 lower magnitude events (ISC catalogue), spanning over 9 days (July 10-18). The second crisis is more of a cluster of events focusing near a discontinuity, 220km away from the Indian Triple Junction and comprises 6 Mw > 5 events (GCMT) and 87 lower magnitude events (ISC catalogue), spanning over 30 days (September 28 to October 27). All focal mechanisms (GCMT) indicate normal faulting for both swarms. These two swarms are examined using hydroacoustic records from the OHASISBIO network with 7 to 9 autonomous hydrophones moored on either side of Southwest Indian Ridge.
The first swarm initiates with a Mw=4.9 event (July 10 2018, 03h55) which triggers numerous events with an average of ~250 events per day for the first three days (July 10to 12), propagating in the NE direction. After this, the seismic activity ceases down along with a sparse distribution of events until another burst of activity initiating after July 15, lasting for 3 days and comprising of several high intensity events. Overall, this swarm includes ~1100 hydroacoustic events spanning over 13 days.
The second swarm, further east, starts with two events, Mw=5.5 and 5.6 (Sept. 28 2018, 6h21 and 7h06), followed by a few discrete events. After 3 days, a dense cluster of events initiates with a Mw=5.4 event (October 1st, 18h16) and lasts for 7 days (~415 events per day) and decreases till the end of October. Two additional sub-swarms occur on October 1st and on October 6, both propagating towards the NE. Several other high intensity events occur October 10, after which seismic activity propagates towards the SE and fades away until October 27. Overall, this swarm includes ~5000 hydroacoustic events spanning over 33 days.
The number of events per day is thus larger for the second swarm than for the first one. Also, event source levels are in average smaller in the second crisis than in the first one. Further analyses of these characteristics, along with the different geographical and time distribution of the ~6000 acoustic events (vs ~300 events in the land-based catalogues), provide insights on the onset and on the tectonic or magmatic origin of these two contrasting swarms.
How to cite: Ingale, V. V., Bazin, S., and Royer, J.-Y.: Hydroacoustic observations of Two Contrasted Seismic Swarms along the Southwest Indian Ridge in 2018 , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5131, https://doi.org/10.5194/egusphere-egu21-5131, 2021.
In 2018, two earthquake swarms occurred along segments of the ultra-slow Southwest Indian Ridge (spreading rate: 14-15 mm/a). The first swarm is located at the spreading-ridge intersection with the Atlantis Fracture Zone and comprises 9 Mw > 5.0 events (GCMT catalogue) and about 227 lower magnitude events (ISC catalogue), spanning over 9 days (July 10-18). The second crisis is more of a cluster of events focusing near a discontinuity, 220km away from the Indian Triple Junction and comprises 6 Mw > 5 events (GCMT) and 87 lower magnitude events (ISC catalogue), spanning over 30 days (September 28 to October 27). All focal mechanisms (GCMT) indicate normal faulting for both swarms. These two swarms are examined using hydroacoustic records from the OHASISBIO network with 7 to 9 autonomous hydrophones moored on either side of Southwest Indian Ridge.
The first swarm initiates with a Mw=4.9 event (July 10 2018, 03h55) which triggers numerous events with an average of ~250 events per day for the first three days (July 10to 12), propagating in the NE direction. After this, the seismic activity ceases down along with a sparse distribution of events until another burst of activity initiating after July 15, lasting for 3 days and comprising of several high intensity events. Overall, this swarm includes ~1100 hydroacoustic events spanning over 13 days.
The second swarm, further east, starts with two events, Mw=5.5 and 5.6 (Sept. 28 2018, 6h21 and 7h06), followed by a few discrete events. After 3 days, a dense cluster of events initiates with a Mw=5.4 event (October 1st, 18h16) and lasts for 7 days (~415 events per day) and decreases till the end of October. Two additional sub-swarms occur on October 1st and on October 6, both propagating towards the NE. Several other high intensity events occur October 10, after which seismic activity propagates towards the SE and fades away until October 27. Overall, this swarm includes ~5000 hydroacoustic events spanning over 33 days.
The number of events per day is thus larger for the second swarm than for the first one. Also, event source levels are in average smaller in the second crisis than in the first one. Further analyses of these characteristics, along with the different geographical and time distribution of the ~6000 acoustic events (vs ~300 events in the land-based catalogues), provide insights on the onset and on the tectonic or magmatic origin of these two contrasting swarms.
How to cite: Ingale, V. V., Bazin, S., and Royer, J.-Y.: Hydroacoustic observations of Two Contrasted Seismic Swarms along the Southwest Indian Ridge in 2018 , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5131, https://doi.org/10.5194/egusphere-egu21-5131, 2021.
EGU21-16252 | vPICO presentations | SM6.1
Complex magmatic-tectonic interactions during the 2020 Makushin Volcano, Alaska, earthquake swarmDiana Roman, Federica Lanza, John Power, Cliff Thurber, and Thomas Hudson
We investigate the processes driving a significant earthquake swarm that occurred between June and December 2020 on Unalaska Island, Alaska, ~12 km southeast of the summit of Makushin Volcano. The swarm was energetic, with two M>4 events that were widely felt by the population in Dutch Harbor, ~ 15 km west of the epicenters. This is the strongest seismic activity ever recorded at Makushin since instrumental monitoring began in 1996. To date, no eruptive activity or other surface changes have been observed at the volcano in satellite views, webcam images, GPS or InSAR. Seismic swarms close to volcanoes are often associated with the onset of unrest that can lead to eruption. However, determining whether they reflect magmatic rather than tectonic stresses is challenging. Here, we integrate information from space-time patterns of the hypocenters of the swarm earthquakes with their double-couple fault-plane solutions (FPS). We relocate swarm events using double-difference relocation techniques and a 3D velocity model. We find that most of the events cluster into two perpendicular lineaments with NW-SE and SW-NE orientations, but no apparent migration in time towards a preferred fault. On the one hand, the lack of temporal migration (with both faults slipping concurrently), and FPS for M3+ events consistent with regional stresses, seem to indicate a tectonic driving process. On the other hand, FPS for the lower-magnitude earthquakes have 90°-rotated P-axes perpendicular to the regional principal stress orientation, providing strong evidence for dike inflation/magma intrusion. Coulomb stress modeling indicates that the rotated FPS are best explained by an inflating dike to the SW of the swarm epicenters, in a zone of long-term elevated seismicity. This complex overlapping of regional and magmatic stresses is also evident in the statistical analysis of the sequence, which started as a main-shock/aftershock sequence with the first event having the largest magnitude, and evolved into a swarm sequence indicative of a more pronounced role of magmatic processes.
How to cite: Roman, D., Lanza, F., Power, J., Thurber, C., and Hudson, T.: Complex magmatic-tectonic interactions during the 2020 Makushin Volcano, Alaska, earthquake swarm, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16252, https://doi.org/10.5194/egusphere-egu21-16252, 2021.
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We investigate the processes driving a significant earthquake swarm that occurred between June and December 2020 on Unalaska Island, Alaska, ~12 km southeast of the summit of Makushin Volcano. The swarm was energetic, with two M>4 events that were widely felt by the population in Dutch Harbor, ~ 15 km west of the epicenters. This is the strongest seismic activity ever recorded at Makushin since instrumental monitoring began in 1996. To date, no eruptive activity or other surface changes have been observed at the volcano in satellite views, webcam images, GPS or InSAR. Seismic swarms close to volcanoes are often associated with the onset of unrest that can lead to eruption. However, determining whether they reflect magmatic rather than tectonic stresses is challenging. Here, we integrate information from space-time patterns of the hypocenters of the swarm earthquakes with their double-couple fault-plane solutions (FPS). We relocate swarm events using double-difference relocation techniques and a 3D velocity model. We find that most of the events cluster into two perpendicular lineaments with NW-SE and SW-NE orientations, but no apparent migration in time towards a preferred fault. On the one hand, the lack of temporal migration (with both faults slipping concurrently), and FPS for M3+ events consistent with regional stresses, seem to indicate a tectonic driving process. On the other hand, FPS for the lower-magnitude earthquakes have 90°-rotated P-axes perpendicular to the regional principal stress orientation, providing strong evidence for dike inflation/magma intrusion. Coulomb stress modeling indicates that the rotated FPS are best explained by an inflating dike to the SW of the swarm epicenters, in a zone of long-term elevated seismicity. This complex overlapping of regional and magmatic stresses is also evident in the statistical analysis of the sequence, which started as a main-shock/aftershock sequence with the first event having the largest magnitude, and evolved into a swarm sequence indicative of a more pronounced role of magmatic processes.
How to cite: Roman, D., Lanza, F., Power, J., Thurber, C., and Hudson, T.: Complex magmatic-tectonic interactions during the 2020 Makushin Volcano, Alaska, earthquake swarm, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16252, https://doi.org/10.5194/egusphere-egu21-16252, 2021.
EGU21-495 | vPICO presentations | SM6.1
Triggering of the 2012 Ahar-Varzaghan earthquake doublet (Mw6.5&6.3) by the Sahand Volcano and North Tabriz fault (NW-Iran); Implications on the seismic hazard of Tabriz citySeyyedmaalek Momeni
How to cite: Momeni, S.: Triggering of the 2012 Ahar-Varzaghan earthquake doublet (Mw6.5&6.3) by the Sahand Volcano and North Tabriz fault (NW-Iran); Implications on the seismic hazard of Tabriz city, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-495, https://doi.org/10.5194/egusphere-egu21-495, 2021.
How to cite: Momeni, S.: Triggering of the 2012 Ahar-Varzaghan earthquake doublet (Mw6.5&6.3) by the Sahand Volcano and North Tabriz fault (NW-Iran); Implications on the seismic hazard of Tabriz city, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-495, https://doi.org/10.5194/egusphere-egu21-495, 2021.
EGU21-2124 | vPICO presentations | SM6.1
Clogging and un-clogging of the subduction plumbing system may generate tremor-like patternsGaspard Farge, Claude Jaupart, and Nikolaï Shapiro
Many subduction zones host intermittent, low-frequency, low-magnitude seismic activity emitted from the vicinity of the plates' interface. For instance, in Guerrero, Mexico, deep (30--50 km) low-frequency earthquakes (LFEs) occur in bursts, and migrate in cascades along the subduction interface. Those patterns are often attributed to episodic pulses of fluid pressure and slow slip that travel within the fault zone. However, the dynamic behavior of the permeable system in which fluid-pressure circulates remains a blindspot in most models of tremor generation, even as geological observations report pervasive imprint of strong, localized fluid pressure and permeability variations in its source region.
In order to analyze the role of such processes in generating tremor, we design a simple model of how fluid pressure and permeability can interact within the subduction interface, and generate realistic, tremor-like patterns. It is based on seismic source triggering and interaction in a permeable channel. The latter contains a number of low-permeability plugs acting as elementary fault-valves. In a mechanism akin to erosive burst documented in porous media, valve permeability abruptly opens and closes in response to the local fluid pressure. The brutal pressure transient and/or mechanical fracturing associated with valve opening acts as the seismic source of an LFE-like event. The strong fluid pressure transient that it triggers allows valves to interact constructively: as a valve breaks open, neighbor valves are more likely to break. This interaction therefore leads to cascades and migrations of synthetic seismicity along the model fault channel, that can synchronize into larger bursts of activity that migrate more slowly along the channel. In our model, valve activity draws patterns of that closely resemble tremor patterns in Guerrero and other subduction zones.
The input metamorphic fluid flux at the base of the channel exerts a key control on the occurence of and distribution of synthetic tremor in space and time. A weak input flux will not allow valves to open, conversely a strong flux will not allow them to close. In both cases, no activity will occur. However when the value of the fluid flux is intermediate, permanent regimes of sustained activity arise. Depending on its value, activity can be strongly time-clustered, quasi-periodic or random but constant in time.
Our model is based on a simple yet powerful and realistic description of the permeability and its dynamics in fault zones. It allows for new interpretations of low-frequency seismicity in terms of effective flux and fault-zone permeability, both for long-term regimes and finer scale, transient dynamics. Eventually, it could lead to deep enhancements of our understanding of fault-zone hydraulic processes and how they are coupled with fault-slip.
How to cite: Farge, G., Jaupart, C., and Shapiro, N.: Clogging and un-clogging of the subduction plumbing system may generate tremor-like patterns, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2124, https://doi.org/10.5194/egusphere-egu21-2124, 2021.
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Many subduction zones host intermittent, low-frequency, low-magnitude seismic activity emitted from the vicinity of the plates' interface. For instance, in Guerrero, Mexico, deep (30--50 km) low-frequency earthquakes (LFEs) occur in bursts, and migrate in cascades along the subduction interface. Those patterns are often attributed to episodic pulses of fluid pressure and slow slip that travel within the fault zone. However, the dynamic behavior of the permeable system in which fluid-pressure circulates remains a blindspot in most models of tremor generation, even as geological observations report pervasive imprint of strong, localized fluid pressure and permeability variations in its source region.
In order to analyze the role of such processes in generating tremor, we design a simple model of how fluid pressure and permeability can interact within the subduction interface, and generate realistic, tremor-like patterns. It is based on seismic source triggering and interaction in a permeable channel. The latter contains a number of low-permeability plugs acting as elementary fault-valves. In a mechanism akin to erosive burst documented in porous media, valve permeability abruptly opens and closes in response to the local fluid pressure. The brutal pressure transient and/or mechanical fracturing associated with valve opening acts as the seismic source of an LFE-like event. The strong fluid pressure transient that it triggers allows valves to interact constructively: as a valve breaks open, neighbor valves are more likely to break. This interaction therefore leads to cascades and migrations of synthetic seismicity along the model fault channel, that can synchronize into larger bursts of activity that migrate more slowly along the channel. In our model, valve activity draws patterns of that closely resemble tremor patterns in Guerrero and other subduction zones.
The input metamorphic fluid flux at the base of the channel exerts a key control on the occurence of and distribution of synthetic tremor in space and time. A weak input flux will not allow valves to open, conversely a strong flux will not allow them to close. In both cases, no activity will occur. However when the value of the fluid flux is intermediate, permanent regimes of sustained activity arise. Depending on its value, activity can be strongly time-clustered, quasi-periodic or random but constant in time.
Our model is based on a simple yet powerful and realistic description of the permeability and its dynamics in fault zones. It allows for new interpretations of low-frequency seismicity in terms of effective flux and fault-zone permeability, both for long-term regimes and finer scale, transient dynamics. Eventually, it could lead to deep enhancements of our understanding of fault-zone hydraulic processes and how they are coupled with fault-slip.
How to cite: Farge, G., Jaupart, C., and Shapiro, N.: Clogging and un-clogging of the subduction plumbing system may generate tremor-like patterns, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2124, https://doi.org/10.5194/egusphere-egu21-2124, 2021.
EGU21-14520 | vPICO presentations | SM6.1
Analyzing the tremor of the Holuhraun eruption 2014-2015 using tremor modellingThoralf Dietrich and Eva P.S. Eibl
The 2014-2015 Holuhraun eruption was the largest eruption in Iceland in the last 230 years. After magma ascended below the Bárðarbunga volcano’s icecap, an about 2 week long lateral migration of earthquakes was observed; later interpreted as dike formation in 4km to 6km depth. An eruption started on 29th and 31st of August 2014 at Holuhraun. During dike formation and eruption a long-lasting seismic signal called tremor was recorded by seismometers in the area. Eruptive tremor emerged with the onset of the eruptions on 29th and 31st of August . Tremor sources were located and interpreted in the context of the fissure and the lava flow field. However, a complete geophysical model to explain these is missing. Our starting point is the model on tremor generation based on conduit wall vibrations exited by laminar flow (B. Julian 1994) to replicate the observed tremor signals. We performed a grid search and compare it with other models. In the range of rock parameter tolerance, we present implied characteristics of frequency and amplitude of the signals, if the Julian model were used as explanation for the tremor signals.
How to cite: Dietrich, T. and Eibl, E. P. S.: Analyzing the tremor of the Holuhraun eruption 2014-2015 using tremor modelling, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14520, https://doi.org/10.5194/egusphere-egu21-14520, 2021.
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The 2014-2015 Holuhraun eruption was the largest eruption in Iceland in the last 230 years. After magma ascended below the Bárðarbunga volcano’s icecap, an about 2 week long lateral migration of earthquakes was observed; later interpreted as dike formation in 4km to 6km depth. An eruption started on 29th and 31st of August 2014 at Holuhraun. During dike formation and eruption a long-lasting seismic signal called tremor was recorded by seismometers in the area. Eruptive tremor emerged with the onset of the eruptions on 29th and 31st of August . Tremor sources were located and interpreted in the context of the fissure and the lava flow field. However, a complete geophysical model to explain these is missing. Our starting point is the model on tremor generation based on conduit wall vibrations exited by laminar flow (B. Julian 1994) to replicate the observed tremor signals. We performed a grid search and compare it with other models. In the range of rock parameter tolerance, we present implied characteristics of frequency and amplitude of the signals, if the Julian model were used as explanation for the tremor signals.
How to cite: Dietrich, T. and Eibl, E. P. S.: Analyzing the tremor of the Holuhraun eruption 2014-2015 using tremor modelling, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14520, https://doi.org/10.5194/egusphere-egu21-14520, 2021.
EGU21-8629 | vPICO presentations | SM6.1
Earthquake Cluster Analysis with Nearest Neighbor Approach in TaiwanYu-Fang Hsu, Hsin-Hua Huang, and Ray Y. Chuang
Spatiotemporal evolution of earthquake clusters can give insights into fault geometry, triggering process, and potential interaction with fluid and heat. Taiwan is one of the most active orogenic belts with high deformation rate and complex crustal structures, so it is expected to observe seismicity driven by varying mechanisms among different geological processes. For investigating the tectonic complexity and the triggering processes of seismicity in Taiwan, a high-quality and robust catalog of earthquake clusters is critical. This study collected a long-term-effort earthquake catalog from the Central Weather Bureau from 1990/01 to 2018/06 and produced the earthquake cluster and background seismicity catalogs by four different declustering methods. Among which, the statistics-based nearest neighbor approach (NNA) performs most desirably for passing the Poisson process statistic tests while also remaining more events. We further classified the extracted earthquake clusters into the typical mainshock-aftershock (M-A) sequences and the swarms. Most of the M-A sequences are distributed near the Western Foothill. The asperity sizes, duration, and cluster event numbers all show positive correlations with mainshock magnitude. In contrast, the swarms are mainly distributed in the northern and southern Central Range and the northern Hualien regions. The lower correlation of the asperity sizes, duration, and swarm event numbers with the mainshock magnitude is showed in swarms. Moreover, we find that some of the swarm may be driven by fluid diffusion and spatial correlated with the high heat flow and spring regions.
How to cite: Hsu, Y.-F., Huang, H.-H., and Chuang, R. Y.: Earthquake Cluster Analysis with Nearest Neighbor Approach in Taiwan, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8629, https://doi.org/10.5194/egusphere-egu21-8629, 2021.
Spatiotemporal evolution of earthquake clusters can give insights into fault geometry, triggering process, and potential interaction with fluid and heat. Taiwan is one of the most active orogenic belts with high deformation rate and complex crustal structures, so it is expected to observe seismicity driven by varying mechanisms among different geological processes. For investigating the tectonic complexity and the triggering processes of seismicity in Taiwan, a high-quality and robust catalog of earthquake clusters is critical. This study collected a long-term-effort earthquake catalog from the Central Weather Bureau from 1990/01 to 2018/06 and produced the earthquake cluster and background seismicity catalogs by four different declustering methods. Among which, the statistics-based nearest neighbor approach (NNA) performs most desirably for passing the Poisson process statistic tests while also remaining more events. We further classified the extracted earthquake clusters into the typical mainshock-aftershock (M-A) sequences and the swarms. Most of the M-A sequences are distributed near the Western Foothill. The asperity sizes, duration, and cluster event numbers all show positive correlations with mainshock magnitude. In contrast, the swarms are mainly distributed in the northern and southern Central Range and the northern Hualien regions. The lower correlation of the asperity sizes, duration, and swarm event numbers with the mainshock magnitude is showed in swarms. Moreover, we find that some of the swarm may be driven by fluid diffusion and spatial correlated with the high heat flow and spring regions.
How to cite: Hsu, Y.-F., Huang, H.-H., and Chuang, R. Y.: Earthquake Cluster Analysis with Nearest Neighbor Approach in Taiwan, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8629, https://doi.org/10.5194/egusphere-egu21-8629, 2021.
SM7.1 – Advances in Earthquake Forecasting and Model Testing
EGU21-5172 | vPICO presentations | SM7.1 | Highlight
Is Coulomb Stress the Best Choice for Aftershock Forecasting?Shubham Sharma, Sebastian Hainzl, Gert Zöller, and Matthias Holschneider
The Coulomb failure stress (CFS) criterion is the most commonly used method for predicting spatial distributions of aftershocks following large earthquakes. However, large uncertainties are always associated with the calculation of Coulomb stress change. The uncertainties mainly arise due to nonunique slip inversions and unknown receiver faults; especially for the latter, results are highly dependent on the choice of the assumed receiver mechanism. Based on binary tests (aftershocks yes/no), recent studies suggest that alternative stress quantities, a distance‐slip probabilistic model as well as deep neural network (DNN) approaches, all are superior to CFS with predefined receiver mechanism. To challenge this conclusion, which might have large implications, we use 289 slip inversions from SRCMOD database to calculate more realistic CFS values for a layered half‐space and variable receiver mechanisms. We also analyze the effect of the magnitude cutoff, grid size variation, and aftershock duration to verify the use of receiver operating characteristic (ROC) analysis for the ranking of stress metrics. The observations suggest that introducing a layered half‐space does not improve the stress maps and ROC curves. However, results significantly improve for larger aftershocks and shorter time periods but without changing the ranking. We also go beyond binary testing and apply alternative statistics to test the ability to estimate aftershock numbers, which confirm that simple stress metrics perform better than the classic Coulomb failure stress calculations and are also better than the distance‐slip probabilistic model.
How to cite: Sharma, S., Hainzl, S., Zöller, G., and Holschneider, M.: Is Coulomb Stress the Best Choice for Aftershock Forecasting?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5172, https://doi.org/10.5194/egusphere-egu21-5172, 2021.
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The Coulomb failure stress (CFS) criterion is the most commonly used method for predicting spatial distributions of aftershocks following large earthquakes. However, large uncertainties are always associated with the calculation of Coulomb stress change. The uncertainties mainly arise due to nonunique slip inversions and unknown receiver faults; especially for the latter, results are highly dependent on the choice of the assumed receiver mechanism. Based on binary tests (aftershocks yes/no), recent studies suggest that alternative stress quantities, a distance‐slip probabilistic model as well as deep neural network (DNN) approaches, all are superior to CFS with predefined receiver mechanism. To challenge this conclusion, which might have large implications, we use 289 slip inversions from SRCMOD database to calculate more realistic CFS values for a layered half‐space and variable receiver mechanisms. We also analyze the effect of the magnitude cutoff, grid size variation, and aftershock duration to verify the use of receiver operating characteristic (ROC) analysis for the ranking of stress metrics. The observations suggest that introducing a layered half‐space does not improve the stress maps and ROC curves. However, results significantly improve for larger aftershocks and shorter time periods but without changing the ranking. We also go beyond binary testing and apply alternative statistics to test the ability to estimate aftershock numbers, which confirm that simple stress metrics perform better than the classic Coulomb failure stress calculations and are also better than the distance‐slip probabilistic model.
How to cite: Sharma, S., Hainzl, S., Zöller, G., and Holschneider, M.: Is Coulomb Stress the Best Choice for Aftershock Forecasting?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5172, https://doi.org/10.5194/egusphere-egu21-5172, 2021.
EGU21-8775 | vPICO presentations | SM7.1
Prospective Evaluation of Multiplicative Hybrid Earthquake Forecast Models for CaliforniaJose A. Bayona, William Savran, Maximilian Werner, and David A. Rhoades
Developing testable seismicity models is essential for robust seismic hazard assessments and to quantify the predictive skills of posited hypotheses about seismogenesis. On this premise, the Regional Earthquake Likelihood Models (RELM) group designed a joint forecasting experiment, with associated models, data and tests to evaluate earthquake predictability in California over a five-year period. Participating RELM forecast models were based on a range of geophysical datasets, including earthquake catalogs, interseismic strain rates, and geologic fault slip rates. After five years of prospective evaluation, the RELM experiment found that the smoothed seismicity (HKJ) model by Helmstetter et al. (2007) was the most informative. The diversity of competing forecast hypotheses in RELM was suitable for combining multiple models that could provide more informative earthquake forecasts than HKJ. Thus, Rhoades et al. (2014) created multiplicative hybrid models that involve the HKJ model as a baseline and one or more conjugate models. Particularly, the authors fitted two parameters for each conjugate model and an overall normalizing constant to optimize each hybrid model. Then, information gain scores per earthquake were computed using a corrected Akaike Information Criterion that penalized for the number of fitted parameters. According to retrospective analyses, some hybrid models showed significant information gains over the HKJ forecast, despite the penalty. Here, we assess in a prospective setting the predictive skills of 16 hybrids and 6 original RELM forecasts, using a suite of tests of the Collaboratory for the Study of Earthquake Predicitability (CSEP). The evaluation dataset contains 40 M≥4.95 events recorded within the California CSEP-testing region from 1 January 2011 to 31 December 2020, including the 2016 Mw 5.6, 5.6, and 5.5 Hawthorne earthquake swarm, and the Mw 6.4 foreshock and Mw 7.1 mainshock from the 2019 Ridgecrest sequence. We evaluate the consistency between the observed and the expected number, spatial, likelihood and magnitude distributions of earthquakes, and compare the performance of each forecast to that of HKJ. Our prospective test results show that none of the hybrid models are significantly more informative than the HKJ baseline forecast. These results are mainly due to the occurrence of the 2016 Hawthorne earthquake cluster, and four events from the 2019 Ridgecrest sequence in two forecast bins. These clusters of seismicity are exceptionally unlikely in all models, and insufficiently captured by the Poisson distribution that the likelihood functions of tests assume. Therefore, we are currently examining alternative likelihood functions that reduce the sensitivity of the evaluations to clustering, and that could be used to better understand whether the discrepancies between prospective and retrospective test results for multiplicative hybrid forecasts are due to limitations of the tests or the methods used to create the hybrid models.
How to cite: Bayona, J. A., Savran, W., Werner, M., and Rhoades, D. A.: Prospective Evaluation of Multiplicative Hybrid Earthquake Forecast Models for California, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8775, https://doi.org/10.5194/egusphere-egu21-8775, 2021.
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Please use the buttons below to download the presentation materials or to visit the external website where the presentation is linked. Regarding the external link, please note that Copernicus Meetings cannot accept any liability for the content and the website you will visit.
Forward to presentation link
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Developing testable seismicity models is essential for robust seismic hazard assessments and to quantify the predictive skills of posited hypotheses about seismogenesis. On this premise, the Regional Earthquake Likelihood Models (RELM) group designed a joint forecasting experiment, with associated models, data and tests to evaluate earthquake predictability in California over a five-year period. Participating RELM forecast models were based on a range of geophysical datasets, including earthquake catalogs, interseismic strain rates, and geologic fault slip rates. After five years of prospective evaluation, the RELM experiment found that the smoothed seismicity (HKJ) model by Helmstetter et al. (2007) was the most informative. The diversity of competing forecast hypotheses in RELM was suitable for combining multiple models that could provide more informative earthquake forecasts than HKJ. Thus, Rhoades et al. (2014) created multiplicative hybrid models that involve the HKJ model as a baseline and one or more conjugate models. Particularly, the authors fitted two parameters for each conjugate model and an overall normalizing constant to optimize each hybrid model. Then, information gain scores per earthquake were computed using a corrected Akaike Information Criterion that penalized for the number of fitted parameters. According to retrospective analyses, some hybrid models showed significant information gains over the HKJ forecast, despite the penalty. Here, we assess in a prospective setting the predictive skills of 16 hybrids and 6 original RELM forecasts, using a suite of tests of the Collaboratory for the Study of Earthquake Predicitability (CSEP). The evaluation dataset contains 40 M≥4.95 events recorded within the California CSEP-testing region from 1 January 2011 to 31 December 2020, including the 2016 Mw 5.6, 5.6, and 5.5 Hawthorne earthquake swarm, and the Mw 6.4 foreshock and Mw 7.1 mainshock from the 2019 Ridgecrest sequence. We evaluate the consistency between the observed and the expected number, spatial, likelihood and magnitude distributions of earthquakes, and compare the performance of each forecast to that of HKJ. Our prospective test results show that none of the hybrid models are significantly more informative than the HKJ baseline forecast. These results are mainly due to the occurrence of the 2016 Hawthorne earthquake cluster, and four events from the 2019 Ridgecrest sequence in two forecast bins. These clusters of seismicity are exceptionally unlikely in all models, and insufficiently captured by the Poisson distribution that the likelihood functions of tests assume. Therefore, we are currently examining alternative likelihood functions that reduce the sensitivity of the evaluations to clustering, and that could be used to better understand whether the discrepancies between prospective and retrospective test results for multiplicative hybrid forecasts are due to limitations of the tests or the methods used to create the hybrid models.
How to cite: Bayona, J. A., Savran, W., Werner, M., and Rhoades, D. A.: Prospective Evaluation of Multiplicative Hybrid Earthquake Forecast Models for California, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8775, https://doi.org/10.5194/egusphere-egu21-8775, 2021.
EGU21-4829 | vPICO presentations | SM7.1
Testing non-linear amplification factors used in ground motion modelsKarina Loviknes, Danijel Schorlemmer, Fabrice Cotton, and Sreeram Reddy Kotha
Non-linear site effects are mainly expected for strong ground motions and sites with soft soils and more recent ground-motion models (GMM) have started to include such effects. Observations in this range are, however, sparse, and most non-linear site amplification models are therefore partly or fully based on numerical simulations. We develop a framework for testing of non-linear site amplification models using data from the comprehensive Kiban-Kyoshin network in Japan. The test is reproducible, following the vision of the Collaboratory for the Study of Earthquake Predictability (CSEP), and takes advantage of new large datasets to evaluate whether or not non-linear site effects predicted by site-amplification models are supported by empirical data. The site amplification models are tested using residuals between the observations and predictions from a GMM based only on magnitude and distance. When the GMM is derived without any site term, the site-specific variability extracted from the residuals is expected to capture the site response of a site. The non-linear site amplification models are tested against a linear amplification model on individual well-recording stations. Finally, the result is compared to building codes where non-linearity is included. The test shows that for most of the sites selected as having sufficient records, the non-linear site-amplification models do not score better than the linear amplification model. This suggests that including non-linear site amplification in GMMs and building codes may not yet be justified, at least not in the range of ground motions considered in the test (peak ground acceleration < 0.2 g).
How to cite: Loviknes, K., Schorlemmer, D., Cotton, F., and Reddy Kotha, S.: Testing non-linear amplification factors used in ground motion models, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4829, https://doi.org/10.5194/egusphere-egu21-4829, 2021.
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Please use the buttons below to download the presentation materials or to visit the external website where the presentation is linked. Regarding the external link, please note that Copernicus Meetings cannot accept any liability for the content and the website you will visit.
Forward to presentation link
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Non-linear site effects are mainly expected for strong ground motions and sites with soft soils and more recent ground-motion models (GMM) have started to include such effects. Observations in this range are, however, sparse, and most non-linear site amplification models are therefore partly or fully based on numerical simulations. We develop a framework for testing of non-linear site amplification models using data from the comprehensive Kiban-Kyoshin network in Japan. The test is reproducible, following the vision of the Collaboratory for the Study of Earthquake Predictability (CSEP), and takes advantage of new large datasets to evaluate whether or not non-linear site effects predicted by site-amplification models are supported by empirical data. The site amplification models are tested using residuals between the observations and predictions from a GMM based only on magnitude and distance. When the GMM is derived without any site term, the site-specific variability extracted from the residuals is expected to capture the site response of a site. The non-linear site amplification models are tested against a linear amplification model on individual well-recording stations. Finally, the result is compared to building codes where non-linearity is included. The test shows that for most of the sites selected as having sufficient records, the non-linear site-amplification models do not score better than the linear amplification model. This suggests that including non-linear site amplification in GMMs and building codes may not yet be justified, at least not in the range of ground motions considered in the test (peak ground acceleration < 0.2 g).
How to cite: Loviknes, K., Schorlemmer, D., Cotton, F., and Reddy Kotha, S.: Testing non-linear amplification factors used in ground motion models, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4829, https://doi.org/10.5194/egusphere-egu21-4829, 2021.
EGU21-8691 | vPICO presentations | SM7.1
The prognostic value of foreshocks - a statistical reevaluationEster Manganiello, Marcus Herrmann, and Warner Marzocchi
The ability to forecast large earthquakes on short time scales is strongly limited by our understanding of the earthquake nucleation process. Foreshocks represent promising seismic signals that may improve earthquake forecasting as they precede many large earthquakes. However, foreshocks can currently only be identified as such after a large earthquake occurred. This inability is because it remains unclear whether foreshocks represent a different physical process than general seismicity (i.e., mainshocks and aftershocks). Several studies compared foreshock occurrence in real and synthetic catalogs, as simulated with a well-established earthquake triggering/forecasting model called Epidemic-Type Aftershock Sequence (ETAS) that does not discriminate between foreshocks, mainshocks, and aftershocks. Some of these studies show that the spatial distribution of foreshocks encodes information about the subsequent mainshock magnitude and that foreshock activity is significantly higher than predicted by the ETAS model. These findings attribute a unique underlying physical process to foreshocks, making them potentially useful for forecasting large earthquakes. We reinvestigate these scientific questions using high-quality earthquake catalogs and study carefully the influence of subjective parameter choices and catalog artifacts on the results. For instance, we use data from different regions, account for the short-term catalog incompleteness and its spatial variability, and explore different criteria for sequence selection and foreshock definition.
How to cite: Manganiello, E., Herrmann, M., and Marzocchi, W.: The prognostic value of foreshocks - a statistical reevaluation, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8691, https://doi.org/10.5194/egusphere-egu21-8691, 2021.
The ability to forecast large earthquakes on short time scales is strongly limited by our understanding of the earthquake nucleation process. Foreshocks represent promising seismic signals that may improve earthquake forecasting as they precede many large earthquakes. However, foreshocks can currently only be identified as such after a large earthquake occurred. This inability is because it remains unclear whether foreshocks represent a different physical process than general seismicity (i.e., mainshocks and aftershocks). Several studies compared foreshock occurrence in real and synthetic catalogs, as simulated with a well-established earthquake triggering/forecasting model called Epidemic-Type Aftershock Sequence (ETAS) that does not discriminate between foreshocks, mainshocks, and aftershocks. Some of these studies show that the spatial distribution of foreshocks encodes information about the subsequent mainshock magnitude and that foreshock activity is significantly higher than predicted by the ETAS model. These findings attribute a unique underlying physical process to foreshocks, making them potentially useful for forecasting large earthquakes. We reinvestigate these scientific questions using high-quality earthquake catalogs and study carefully the influence of subjective parameter choices and catalog artifacts on the results. For instance, we use data from different regions, account for the short-term catalog incompleteness and its spatial variability, and explore different criteria for sequence selection and foreshock definition.
How to cite: Manganiello, E., Herrmann, M., and Marzocchi, W.: The prognostic value of foreshocks - a statistical reevaluation, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8691, https://doi.org/10.5194/egusphere-egu21-8691, 2021.
EGU21-7418 | vPICO presentations | SM7.1
Ranking earthquake forecasts: On the use of proper scoring rules to discriminate forecastsFrancesco Serafini, Mark Naylor, Finn Lindgren, and Maximilian Werner
Recent years have seen a growth in the diversity of probabilistic earthquake forecasts as well as the advent of them being applied operationally. The growth of their use demands a deeper look at our ability to rank their performance within a transparent and unified framework. Programs such as the Collaboratory Study for Earthquake Predictability (CSEP) have been at the forefront of this effort. Scores are quantitative measures of how well a dataset can be explained by a candidate forecast and allow forecasts to be ranked. A positively oriented score is said to be proper when, on average, the highest score is achieved by the closest model to the data generating one. Different meanings of closest lead to different proper scoring rules. Here, we prove that the Parimutuel Gambling score, used to evaluate the results of the 2009 Italy CSEP experiment, is generally not proper, and even for the special case where it is proper, it can still be used improperly. We show in detail the possible consequences of using this score for forecast evaluation. Moreover, we show that other well-established scores can be applied to existing studies to calculate new rankings with no requirement for extra information. We extend the analysis to show how much data are required, in principle, to distinguish candidate forecasts and therefore how likely it is to express a preference towards a forecast. This introduces the possibility of survey design with regard to the duration and spatial discretisation of earthquake forecasts. Our findings may contribute to more rigorous statements about the ability to distinguish between the predictive skills of candidate forecasts in addition to simple rankings.
How to cite: Serafini, F., Naylor, M., Lindgren, F., and Werner, M.: Ranking earthquake forecasts: On the use of proper scoring rules to discriminate forecasts, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7418, https://doi.org/10.5194/egusphere-egu21-7418, 2021.
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Recent years have seen a growth in the diversity of probabilistic earthquake forecasts as well as the advent of them being applied operationally. The growth of their use demands a deeper look at our ability to rank their performance within a transparent and unified framework. Programs such as the Collaboratory Study for Earthquake Predictability (CSEP) have been at the forefront of this effort. Scores are quantitative measures of how well a dataset can be explained by a candidate forecast and allow forecasts to be ranked. A positively oriented score is said to be proper when, on average, the highest score is achieved by the closest model to the data generating one. Different meanings of closest lead to different proper scoring rules. Here, we prove that the Parimutuel Gambling score, used to evaluate the results of the 2009 Italy CSEP experiment, is generally not proper, and even for the special case where it is proper, it can still be used improperly. We show in detail the possible consequences of using this score for forecast evaluation. Moreover, we show that other well-established scores can be applied to existing studies to calculate new rankings with no requirement for extra information. We extend the analysis to show how much data are required, in principle, to distinguish candidate forecasts and therefore how likely it is to express a preference towards a forecast. This introduces the possibility of survey design with regard to the duration and spatial discretisation of earthquake forecasts. Our findings may contribute to more rigorous statements about the ability to distinguish between the predictive skills of candidate forecasts in addition to simple rankings.
How to cite: Serafini, F., Naylor, M., Lindgren, F., and Werner, M.: Ranking earthquake forecasts: On the use of proper scoring rules to discriminate forecasts, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7418, https://doi.org/10.5194/egusphere-egu21-7418, 2021.
EGU21-1019 | vPICO presentations | SM7.1
Extreme value statistics of interval maximum amplitudes due to aftershocks and its application for early forecastKaoru Sawazaki
Waveforms from many aftershocks occurring immediately after a large earthquake tend to overlap in a seismogram, which makes it difficult to pick their P- and S-wave phases. Accordingly, to determine hypocenter and magnitude of the aftershocks becomes difficult and thereby causes deterioration of earthquake catalog. Using such deteriorated catalog may cause misevaluation of ongoing aftershock activity. Since aftershock activity is usually most intense in the early period after a large earthquake, requirement of early aftershock forecast and deterioration of the aftershock catalog are impatient.
Several methods for aftershock forecast, using deteriorated automatic earthquake catalog (Omi et al., 2016, 2019) or continuous seismic envelopes (Lippiello et al., 2016), have been proposed to overcome such a situation. In this study, I propose another method that evaluates excess probability of maximum amplitude (EPMA) due to aftershocks using a continuous seismogram. The proposed method is based on the extreme value statistics, which provides probability distribution of maximum amplitudes within constant time intervals. From the Gutenberg-Richter and the Omori-Utsu laws and a conventional ground motion prediction equation (GMPE), I derived this interval maximum amplitude (IMA) follows the Frechet distribution (or type Ⅱ extreme-value distribution). Using the Monte-Carlo based approach, I certified that this distribution is well applicable to IMAs and available for forecasting maximum amplitudes even if many seismograms are overlapped.
Applying the Frechet distribution to the first 3 hour-long seismograms of the 2008 Iwate-Miyagi Nairiku earthquake (MW 6.9), Japan, I computed the EPMAs for 4 days at 4 stations. The maximum amplitudes due to experienced aftershocks proceeded following mostly within the 10 % to 90 % EPMA curves. This performance may be acceptable for a practical use.
Differently from the catalog-based method, the proposed method is almost unaffected by overlap of seismograms even in early lapse times. Since it is based on a single station processing, even seismic “network” is not required, and can be easily deployed at locations of poor seismic network coverage. So far, this method is correctly applicable for typical mainshock-aftershock (Omori-Utsu-like) sequence only. However, potentially, it could be extended to multiple sequences including secondary aftershocks and remotely triggered earthquakes.
How to cite: Sawazaki, K.: Extreme value statistics of interval maximum amplitudes due to aftershocks and its application for early forecast, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1019, https://doi.org/10.5194/egusphere-egu21-1019, 2021.
Waveforms from many aftershocks occurring immediately after a large earthquake tend to overlap in a seismogram, which makes it difficult to pick their P- and S-wave phases. Accordingly, to determine hypocenter and magnitude of the aftershocks becomes difficult and thereby causes deterioration of earthquake catalog. Using such deteriorated catalog may cause misevaluation of ongoing aftershock activity. Since aftershock activity is usually most intense in the early period after a large earthquake, requirement of early aftershock forecast and deterioration of the aftershock catalog are impatient.
Several methods for aftershock forecast, using deteriorated automatic earthquake catalog (Omi et al., 2016, 2019) or continuous seismic envelopes (Lippiello et al., 2016), have been proposed to overcome such a situation. In this study, I propose another method that evaluates excess probability of maximum amplitude (EPMA) due to aftershocks using a continuous seismogram. The proposed method is based on the extreme value statistics, which provides probability distribution of maximum amplitudes within constant time intervals. From the Gutenberg-Richter and the Omori-Utsu laws and a conventional ground motion prediction equation (GMPE), I derived this interval maximum amplitude (IMA) follows the Frechet distribution (or type Ⅱ extreme-value distribution). Using the Monte-Carlo based approach, I certified that this distribution is well applicable to IMAs and available for forecasting maximum amplitudes even if many seismograms are overlapped.
Applying the Frechet distribution to the first 3 hour-long seismograms of the 2008 Iwate-Miyagi Nairiku earthquake (MW 6.9), Japan, I computed the EPMAs for 4 days at 4 stations. The maximum amplitudes due to experienced aftershocks proceeded following mostly within the 10 % to 90 % EPMA curves. This performance may be acceptable for a practical use.
Differently from the catalog-based method, the proposed method is almost unaffected by overlap of seismograms even in early lapse times. Since it is based on a single station processing, even seismic “network” is not required, and can be easily deployed at locations of poor seismic network coverage. So far, this method is correctly applicable for typical mainshock-aftershock (Omori-Utsu-like) sequence only. However, potentially, it could be extended to multiple sequences including secondary aftershocks and remotely triggered earthquakes.
How to cite: Sawazaki, K.: Extreme value statistics of interval maximum amplitudes due to aftershocks and its application for early forecast, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1019, https://doi.org/10.5194/egusphere-egu21-1019, 2021.
EGU21-15824 | vPICO presentations | SM7.1
Operational Aftershock Forecasting for 2017-2018 Seismic Sequence in Western IranFatemeh Jalayer and Hossein Ebrahimian
On Sunday November 12, 2017, at 18:18:16 UTC, (21:48:16 local time), a strong earthquake with Mw7.3 occurred in western Iran in the border region between Iran and Iraq in vicinity of the Sarpol-e Zahab town. Unfortunately, this catastrophic seismic event caused 572 causalities, thousands of injured and vast amounts of damage to the buildings, houses and infrastructures in the epicentral area. The mainshock of this seismic sequence was felt in the entire western and central provinces of Iran and surrounding areas. The main event was preceded by a foreshock with magnitude 4.5 about 43 minutes before the mainshock that warned the local residence to leave their home and possibly reduced the number of human casualties. More than 2500 aftershocks with magnitude greater than 2.5 have been reported up to January 2019 with the largest registered aftershock of Mw6.4. A novel and fully-probabilistic procedure is adopted for providing spatio-temporal predictions of aftershock occurrence in a prescribed forecasting time interval (in the order of hours or days). The procedure aims at exploiting the information provided by the ongoing seismic sequence in quasi-real time. The versatility of the Bayesian inference is exploited to adaptively update the forecasts based on the incoming information as it becomes available. The aftershock clustering in space and time is modelled based on an Epidemic Type Aftershock Sequence (ETAS). One of the main novelties of the proposed procedure is that it considers the uncertainties in the aftershock occurrence model and its model parameters. This is done by moving within a framework of robust reliability assessment which enables the treatment of uncertainties in an integrated manner. Pairing up the Bayesian robust reliability framework and the suitable simulation schemes (Markov Chain Monte Carlo Simulation) provides the possibility of performing the whole forecasting procedure with minimum (or no) need of human interference. The fully simulation-based procedure is examined for both Bayesian model updating of ETAS spatio-temporal model and robust operational forecasting of the number of events of interest expected to happen in various time intervals after main events within the sequence. The seismicity is predicted within a confidence interval from the mean estimate.
How to cite: Jalayer, F. and Ebrahimian, H.: Operational Aftershock Forecasting for 2017-2018 Seismic Sequence in Western Iran, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15824, https://doi.org/10.5194/egusphere-egu21-15824, 2021.
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On Sunday November 12, 2017, at 18:18:16 UTC, (21:48:16 local time), a strong earthquake with Mw7.3 occurred in western Iran in the border region between Iran and Iraq in vicinity of the Sarpol-e Zahab town. Unfortunately, this catastrophic seismic event caused 572 causalities, thousands of injured and vast amounts of damage to the buildings, houses and infrastructures in the epicentral area. The mainshock of this seismic sequence was felt in the entire western and central provinces of Iran and surrounding areas. The main event was preceded by a foreshock with magnitude 4.5 about 43 minutes before the mainshock that warned the local residence to leave their home and possibly reduced the number of human casualties. More than 2500 aftershocks with magnitude greater than 2.5 have been reported up to January 2019 with the largest registered aftershock of Mw6.4. A novel and fully-probabilistic procedure is adopted for providing spatio-temporal predictions of aftershock occurrence in a prescribed forecasting time interval (in the order of hours or days). The procedure aims at exploiting the information provided by the ongoing seismic sequence in quasi-real time. The versatility of the Bayesian inference is exploited to adaptively update the forecasts based on the incoming information as it becomes available. The aftershock clustering in space and time is modelled based on an Epidemic Type Aftershock Sequence (ETAS). One of the main novelties of the proposed procedure is that it considers the uncertainties in the aftershock occurrence model and its model parameters. This is done by moving within a framework of robust reliability assessment which enables the treatment of uncertainties in an integrated manner. Pairing up the Bayesian robust reliability framework and the suitable simulation schemes (Markov Chain Monte Carlo Simulation) provides the possibility of performing the whole forecasting procedure with minimum (or no) need of human interference. The fully simulation-based procedure is examined for both Bayesian model updating of ETAS spatio-temporal model and robust operational forecasting of the number of events of interest expected to happen in various time intervals after main events within the sequence. The seismicity is predicted within a confidence interval from the mean estimate.
How to cite: Jalayer, F. and Ebrahimian, H.: Operational Aftershock Forecasting for 2017-2018 Seismic Sequence in Western Iran, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15824, https://doi.org/10.5194/egusphere-egu21-15824, 2021.
EGU21-14716 | vPICO presentations | SM7.1
Do Enhanced Seismicity Catalogs Improve Aftershock Forecasts? A Test on the 2016-2017 Central Italy Earthquake CascadeSimone Mancini, Margarita Segou, and Maximilian J. Werner
Artificial intelligence methods are revolutionizing modern seismology by offering unprecedentedly rich seismic catalogs. Recent developments in short-term aftershock forecasting show that Coulomb rate-and-state (CRS) models hold the potential to achieve operational skills comparable to standard statistical Epidemic-Type Aftershock Sequence (ETAS) models, but only when the near real-time data quality allows to incorporate a more detailed representation of sources and receiver fault populations. In this framework, the high-resolution reconstructions of the seismicity patterns introduced by machine-learning-derived earthquake catalogs represent a unique opportunity to test whether they can be exploited to improve the predictive power of aftershock forecasts.
Here, we present a retrospective forecast experiment on the first year of the 2016-2017 Central Italy seismic cascade, where seven M5.4+ earthquakes occurred between a few hours and five months after the initial Mw 6.0 event, migrating over a 60-km long normal fault system. As target dataset, we employ the best available high-density machine learning catalog recently released for the sequence, which reports ~1 million events in total (~22,000 with M ≥ 2).
First, we develop a CRS model featuring (1) rate-and-state variables optimized on 30 years of pre-sequence regional seismicity, (2) finite fault slip models for the seven mainshocks of the sequence, (3) spatially heterogeneous receivers informed by pre-existing faults, and (4) updating receiver fault populations using focal planes gradually revealed by aftershocks. We then test the effect of considering stress perturbations from the M2+ events. Using the same high-precision catalog, we produce a standard ETAS model to benchmark the stress-based counterparts. All models are developed on a 3D spatial grid with 2 km spacing; they are updated daily and seek to forecast the space-time occurrence of M2+ seismicity for a total forecast horizon of one year. We formally rank the forecasts with the statistical scoring metrics introduced by the Collaboratory for the Study of Earthquake Predictability and compare their performance to a generation of CRS and ETAS models previously published for the same sequence by Mancini et al. (2019), who used solely real-time data and a minimum triggering magnitude of M=3.
We find that considering secondary triggering effects from events down to M=2 slightly improves model performance. While this result highlights the importance of better seismic catalogs to model local triggering mechanisms, it also suggests that to appreciate their full potential future modelling efforts will likely have to incorporate also fine-scale rupture characterizations (e.g., smaller source fault geometries retrieved from enhanced focal mechanism catalogs) and introduce denser spatial model discretizations.
How to cite: Mancini, S., Segou, M., and Werner, M. J.: Do Enhanced Seismicity Catalogs Improve Aftershock Forecasts? A Test on the 2016-2017 Central Italy Earthquake Cascade, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14716, https://doi.org/10.5194/egusphere-egu21-14716, 2021.
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Forward to presentation link
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We are sorry, but presentations are only available for users who registered for the conference. Thank you.
Artificial intelligence methods are revolutionizing modern seismology by offering unprecedentedly rich seismic catalogs. Recent developments in short-term aftershock forecasting show that Coulomb rate-and-state (CRS) models hold the potential to achieve operational skills comparable to standard statistical Epidemic-Type Aftershock Sequence (ETAS) models, but only when the near real-time data quality allows to incorporate a more detailed representation of sources and receiver fault populations. In this framework, the high-resolution reconstructions of the seismicity patterns introduced by machine-learning-derived earthquake catalogs represent a unique opportunity to test whether they can be exploited to improve the predictive power of aftershock forecasts.
Here, we present a retrospective forecast experiment on the first year of the 2016-2017 Central Italy seismic cascade, where seven M5.4+ earthquakes occurred between a few hours and five months after the initial Mw 6.0 event, migrating over a 60-km long normal fault system. As target dataset, we employ the best available high-density machine learning catalog recently released for the sequence, which reports ~1 million events in total (~22,000 with M ≥ 2).
First, we develop a CRS model featuring (1) rate-and-state variables optimized on 30 years of pre-sequence regional seismicity, (2) finite fault slip models for the seven mainshocks of the sequence, (3) spatially heterogeneous receivers informed by pre-existing faults, and (4) updating receiver fault populations using focal planes gradually revealed by aftershocks. We then test the effect of considering stress perturbations from the M2+ events. Using the same high-precision catalog, we produce a standard ETAS model to benchmark the stress-based counterparts. All models are developed on a 3D spatial grid with 2 km spacing; they are updated daily and seek to forecast the space-time occurrence of M2+ seismicity for a total forecast horizon of one year. We formally rank the forecasts with the statistical scoring metrics introduced by the Collaboratory for the Study of Earthquake Predictability and compare their performance to a generation of CRS and ETAS models previously published for the same sequence by Mancini et al. (2019), who used solely real-time data and a minimum triggering magnitude of M=3.
We find that considering secondary triggering effects from events down to M=2 slightly improves model performance. While this result highlights the importance of better seismic catalogs to model local triggering mechanisms, it also suggests that to appreciate their full potential future modelling efforts will likely have to incorporate also fine-scale rupture characterizations (e.g., smaller source fault geometries retrieved from enhanced focal mechanism catalogs) and introduce denser spatial model discretizations.
How to cite: Mancini, S., Segou, M., and Werner, M. J.: Do Enhanced Seismicity Catalogs Improve Aftershock Forecasts? A Test on the 2016-2017 Central Italy Earthquake Cascade, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14716, https://doi.org/10.5194/egusphere-egu21-14716, 2021.
EGU21-5157 | vPICO presentations | SM7.1
Testing physics and statics based hybrid ETAS modelsShubham Sharma, Shyam Nandan, and Sebastian Hainzl
Currently, the Epidemic Type Aftershock Sequence (ETAS) model is state-of-the-art for forecasting aftershocks. However, the under-performance of ETAS in forecasting the spatial distribution of aftershocks following a large earthquake make us adopt alternative approaches for the modelling of the spatial ETAS-kernel. Here we develop a hybrid physics and statics based forecasting model. The model uses stress changes, calculated from inverted slip models of large earthquakes, as the basis of the spatial kernel in the ETAS model in order to get more reliable estimates of spatiotemporal distribution of aftershocks. We evaluate six alternative approaches of stress-based ETAS-kernels and rank their performance against the base ETAS model. In all cases, an expectation maximization (EM) algorithm is used to estimate the ETAS parameters. The model approach has been tested on synthetic data to check if the known parameters can be inverted successfully. We apply the proposed method to forecast aftershocks of mainshocks available in SRCMOD database, which includes 192 mainshocks with magnitudes in the range between 4.1 and 9.2 occurred from 1906 to 2020. The probabilistic earthquake forecasts generated by the hybrid model have been tested using established CSEP test metrics and procedures. We show that the additional stress information, provided to estimate the spatial probability distribution, leads to more reliable spatiotemporal ETAS-forecasts of aftershocks as compared to the base ETAS model.
How to cite: Sharma, S., Nandan, S., and Hainzl, S.: Testing physics and statics based hybrid ETAS models, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5157, https://doi.org/10.5194/egusphere-egu21-5157, 2021.
Please decide on your access
Please use the buttons below to download the presentation materials or to visit the external website where the presentation is linked. Regarding the external link, please note that Copernicus Meetings cannot accept any liability for the content and the website you will visit.
Forward to presentation link
You are going to open an external link to the presentation as indicated by the authors. Copernicus Meetings cannot accept any liability for the content and the website you will visit.
We are sorry, but presentations are only available for users who registered for the conference. Thank you.
Currently, the Epidemic Type Aftershock Sequence (ETAS) model is state-of-the-art for forecasting aftershocks. However, the under-performance of ETAS in forecasting the spatial distribution of aftershocks following a large earthquake make us adopt alternative approaches for the modelling of the spatial ETAS-kernel. Here we develop a hybrid physics and statics based forecasting model. The model uses stress changes, calculated from inverted slip models of large earthquakes, as the basis of the spatial kernel in the ETAS model in order to get more reliable estimates of spatiotemporal distribution of aftershocks. We evaluate six alternative approaches of stress-based ETAS-kernels and rank their performance against the base ETAS model. In all cases, an expectation maximization (EM) algorithm is used to estimate the ETAS parameters. The model approach has been tested on synthetic data to check if the known parameters can be inverted successfully. We apply the proposed method to forecast aftershocks of mainshocks available in SRCMOD database, which includes 192 mainshocks with magnitudes in the range between 4.1 and 9.2 occurred from 1906 to 2020. The probabilistic earthquake forecasts generated by the hybrid model have been tested using established CSEP test metrics and procedures. We show that the additional stress information, provided to estimate the spatial probability distribution, leads to more reliable spatiotemporal ETAS-forecasts of aftershocks as compared to the base ETAS model.
How to cite: Sharma, S., Nandan, S., and Hainzl, S.: Testing physics and statics based hybrid ETAS models, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5157, https://doi.org/10.5194/egusphere-egu21-5157, 2021.
EGU21-6836 | vPICO presentations | SM7.1
Ensemble Kalman Filter estimates shear stress and seismic slip rates in synthetic laboratory experimentHamed Ali Diab-Montero, Meng Li, Ylona van Dinther, and Femke C Vossepoel
Our ability to forecast earthquake events is hampered by limited information of the state of stress and strength of faults and their governing parameters. Ensemble data assimilation methods provide a means to estimate these variables by combining physics-based models and observations taking into account their uncertainties. In this study, we estimate earthquake occurrences in synthetic experiments representing a meter-scale laboratory setup of a straight-fault governed by rate-and-state friction. We test an Ensemble Kalman Filter implemented in the Parallel Data Assimilation Framework, which is connected with a 1D forward model using the numerical library GARNET. A perfect-model test shows that the filter can estimate shear stresses, slip rates and state θ acting on the fault even when simulating slip rates up to m/s and can thus be used for estimating earthquake occurrences. We assimilate shear stress and slip-rate observations, representing measurements obtained from shear strain gauges and piezoelectric transducers sensors, and their uncertainties acquired at a small distance to the fault in the homogeneous elastic medium. In this study we evaluate how the Ensemble Kalman filter estimates the state and strength of the faults using these observations, and assess the relative influence of assimilating various observations. The results suggest that the data assimilation improves the estimated timing of the earthquake occurrences. The assimilation of the shear stress observed in the medium improves in particular the estimates of the state θ and the shear stress on the fault, while assimilating observations of velocity in the medium improves the slip-rate estimation.
How to cite: Diab-Montero, H. A., Li, M., van Dinther, Y., and Vossepoel, F. C.: Ensemble Kalman Filter estimates shear stress and seismic slip rates in synthetic laboratory experiment, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6836, https://doi.org/10.5194/egusphere-egu21-6836, 2021.
Our ability to forecast earthquake events is hampered by limited information of the state of stress and strength of faults and their governing parameters. Ensemble data assimilation methods provide a means to estimate these variables by combining physics-based models and observations taking into account their uncertainties. In this study, we estimate earthquake occurrences in synthetic experiments representing a meter-scale laboratory setup of a straight-fault governed by rate-and-state friction. We test an Ensemble Kalman Filter implemented in the Parallel Data Assimilation Framework, which is connected with a 1D forward model using the numerical library GARNET. A perfect-model test shows that the filter can estimate shear stresses, slip rates and state θ acting on the fault even when simulating slip rates up to m/s and can thus be used for estimating earthquake occurrences. We assimilate shear stress and slip-rate observations, representing measurements obtained from shear strain gauges and piezoelectric transducers sensors, and their uncertainties acquired at a small distance to the fault in the homogeneous elastic medium. In this study we evaluate how the Ensemble Kalman filter estimates the state and strength of the faults using these observations, and assess the relative influence of assimilating various observations. The results suggest that the data assimilation improves the estimated timing of the earthquake occurrences. The assimilation of the shear stress observed in the medium improves in particular the estimates of the state θ and the shear stress on the fault, while assimilating observations of velocity in the medium improves the slip-rate estimation.
How to cite: Diab-Montero, H. A., Li, M., van Dinther, Y., and Vossepoel, F. C.: Ensemble Kalman Filter estimates shear stress and seismic slip rates in synthetic laboratory experiment, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6836, https://doi.org/10.5194/egusphere-egu21-6836, 2021.
EGU21-5379 | vPICO presentations | SM7.1
Determination of site amplifications and moment magnitudes of East-Alpine earthquakesStefan Weginger
The Seismological Service of earthquakes Austria located at the Zentralanstalt für Meteorologie und Geodynamik (ZAMG; http://www.zamg.ac.at) is the federal agency for monitoring and seismic hazard assessments in Austria. The ZAMG seismological network currently consists of approximately 60 Stations (28 broadband and ~30 strong motion). The increasing number of earthquake records during the past 20 years - from the local seismic network with addition of surrounded stations from the EIDA archive - are used to determinate the local attenuation of seismic shear wave energies and the site amplifications.
The propagation path of the released seismic energy through the uppermost crust has a considerable influence on the ground movement recorded at the surface. This contribution follows the known method of combining a physical modeling and a statistical approach by separating the source, path and site effects by means of inversion. A geometrical spreading model defines the frequency-independent decay of energy while the frequency dependent decay is parameterized by the parameters Q and Kappa. The moment magnitudes and stress drops of small earthquakes were determined, and a scaling-relationship of local to moment magnitudes could be established.
Taking these site-effects into consideration reduces the uncertainties in the determination of empirical ground motion prediction equations (GMPE) and increases the accuracy of seismic hazard assessments, ShakeMaps and On-Site systems.
How to cite: Weginger, S.: Determination of site amplifications and moment magnitudes of East-Alpine earthquakes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5379, https://doi.org/10.5194/egusphere-egu21-5379, 2021.
The Seismological Service of earthquakes Austria located at the Zentralanstalt für Meteorologie und Geodynamik (ZAMG; http://www.zamg.ac.at) is the federal agency for monitoring and seismic hazard assessments in Austria. The ZAMG seismological network currently consists of approximately 60 Stations (28 broadband and ~30 strong motion). The increasing number of earthquake records during the past 20 years - from the local seismic network with addition of surrounded stations from the EIDA archive - are used to determinate the local attenuation of seismic shear wave energies and the site amplifications.
The propagation path of the released seismic energy through the uppermost crust has a considerable influence on the ground movement recorded at the surface. This contribution follows the known method of combining a physical modeling and a statistical approach by separating the source, path and site effects by means of inversion. A geometrical spreading model defines the frequency-independent decay of energy while the frequency dependent decay is parameterized by the parameters Q and Kappa. The moment magnitudes and stress drops of small earthquakes were determined, and a scaling-relationship of local to moment magnitudes could be established.
Taking these site-effects into consideration reduces the uncertainties in the determination of empirical ground motion prediction equations (GMPE) and increases the accuracy of seismic hazard assessments, ShakeMaps and On-Site systems.
How to cite: Weginger, S.: Determination of site amplifications and moment magnitudes of East-Alpine earthquakes, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5379, https://doi.org/10.5194/egusphere-egu21-5379, 2021.
EGU21-5995 | vPICO presentations | SM7.1
Source Parameter Sensitivity of Earthquake Simulations assisted by Machine LearningMarisol Monterrubio-Velasco, J. Carlos Carrasco-Jimenez, Otilio Rojas, Juan E. Rodriguez, David Modesto, and Josep de la Puente
After large magnitude earthquakes have been recorded, a crucial task for hazard assessment is to quickly estimate Ground Shaking (GS) intensities at the affected region. Urgent physics-based earthquake simulations using High-Performance Computing (HPC) facilities may allow fast GS intensity analyses but are very sensitive to source parameter values. When using fast estimates of source parameters such as magnitude, location, fault dimensions, and/or Centroid Moment Tensor (CMT), simulations are prone to errors in their computed GS. Although the approaches to estimate earthquake location and magnitude are consolidated, depth location estimates are largely uncertain. Moreover, automatic CMT solutions are not always provided by seismological agencies, or such solutions are available at later times after waveform inversions allow the determination of moment tensor components. The uncertainty on these parameters, especially a few minutes after the earthquake has been registered, strongly affects GS maps resulting from simulations.
In this work, we present a workflow prototype to produce an uncertainty quantification method as a function of the source parameters. The core of this workflow is based on Machine Learning (ML) techniques. As a study case, we consider a domain of 110x80 km centered in 63.9ºN-20.6ºW in Southern Iceland, where the 17 best-mapped faults have hosted the historical events of the largest magnitude. We generate synthetic GS intensity maps using the AWP-ODC finite-difference code for earthquake simulation and a one-dimensional velocity model, with 40 recording surface stations. By varying a few source parameters (e.g. event magnitude, CMT, and hypocenter location), we finally model tens of thousands of hypothetical earthquakes. Our ML analog will then be able to relate GS intensity maps to source parameters, thus simplifying sensitivity studies.
Additionally, the results of this workflow prototype will allow us to obtain ML-based intensity maps a few seconds after an earthquake occurs exploiting the predictive power of ML techniques. We will evaluate the accuracy of these maps as standalone complements to GMPEs and simulations.
How to cite: Monterrubio-Velasco, M., Carrasco-Jimenez, J. C., Rojas, O., Rodriguez, J. E., Modesto, D., and de la Puente, J.: Source Parameter Sensitivity of Earthquake Simulations assisted by Machine Learning , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5995, https://doi.org/10.5194/egusphere-egu21-5995, 2021.
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After large magnitude earthquakes have been recorded, a crucial task for hazard assessment is to quickly estimate Ground Shaking (GS) intensities at the affected region. Urgent physics-based earthquake simulations using High-Performance Computing (HPC) facilities may allow fast GS intensity analyses but are very sensitive to source parameter values. When using fast estimates of source parameters such as magnitude, location, fault dimensions, and/or Centroid Moment Tensor (CMT), simulations are prone to errors in their computed GS. Although the approaches to estimate earthquake location and magnitude are consolidated, depth location estimates are largely uncertain. Moreover, automatic CMT solutions are not always provided by seismological agencies, or such solutions are available at later times after waveform inversions allow the determination of moment tensor components. The uncertainty on these parameters, especially a few minutes after the earthquake has been registered, strongly affects GS maps resulting from simulations.
In this work, we present a workflow prototype to produce an uncertainty quantification method as a function of the source parameters. The core of this workflow is based on Machine Learning (ML) techniques. As a study case, we consider a domain of 110x80 km centered in 63.9ºN-20.6ºW in Southern Iceland, where the 17 best-mapped faults have hosted the historical events of the largest magnitude. We generate synthetic GS intensity maps using the AWP-ODC finite-difference code for earthquake simulation and a one-dimensional velocity model, with 40 recording surface stations. By varying a few source parameters (e.g. event magnitude, CMT, and hypocenter location), we finally model tens of thousands of hypothetical earthquakes. Our ML analog will then be able to relate GS intensity maps to source parameters, thus simplifying sensitivity studies.
Additionally, the results of this workflow prototype will allow us to obtain ML-based intensity maps a few seconds after an earthquake occurs exploiting the predictive power of ML techniques. We will evaluate the accuracy of these maps as standalone complements to GMPEs and simulations.
How to cite: Monterrubio-Velasco, M., Carrasco-Jimenez, J. C., Rojas, O., Rodriguez, J. E., Modesto, D., and de la Puente, J.: Source Parameter Sensitivity of Earthquake Simulations assisted by Machine Learning , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-5995, https://doi.org/10.5194/egusphere-egu21-5995, 2021.
SM8.1 – Advances in theoretical seismology and computational inverse problems
EGU21-12015 | vPICO presentations | SM8.1
Toward a full 4D seismic tomography: a case study of an active mineNicola Piana Agostinetti, Christina Dahnér-Lindkvist, and Savka Dineva
Rock elasticity in the subsurface can change in response to natural phenomena (e.g. massive precipitation, magmatic processes) and human activities (e.g. water injection in geothermal wells, ore-body exploitation). However, understanding and monitoring the evolution of physical properties of the crust is a challenging due to the limited possibility of reaching such depths and making direct measurements of the state of the rocks. Indirect measurements, like seismic tomography, can give some insights, but are generally biased by the un-even distribution (in space and time) of the information collected from seismic observations (travel-times and/or waveforms). Here we apply a Bayesian approach to overcome such limitations, so that data uncertainties and data distribution are fully accounted in the reconstruction of the posterior probability distribution of the rock elasticity We compute a full 4D local earthquake tomography based on trans-dimensional Markov chain Monte Carlo sampling of 4D elastic models, where the resolution in space and time is fully data-driven. To test our workflow, we make use of a “controlled laboratory”: we record seismic data during one month of mining activities across a 800x700x600 m volume of Kiruna mine (LKAB, Sweden). During such period, we obtain about 260 000 P-wave and 240 000 S-wave travel-times coming from about 36000 seismic events. We operate a preliminary selection of the well-located events, using a Monte Carlo search. Arrival-times of about 19 000 best-located events (location errors less than 20m) are used as input to the tomography workflow. Preliminary results indicate that: (1) short-term (few hours) evolutions of the elastic field are mainly driven by seismic activation, i.e. the occurrence of a seismic swarm, close to the mine ore-passes. Such phenomena partially mask the effects of explosions; (2) long-term (2-3 days) evolutions of the elastic field closely match the local measurements of the stress field at a colocated stress cell.
How to cite: Piana Agostinetti, N., Dahnér-Lindkvist, C., and Dineva, S.: Toward a full 4D seismic tomography: a case study of an active mine, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12015, https://doi.org/10.5194/egusphere-egu21-12015, 2021.
Rock elasticity in the subsurface can change in response to natural phenomena (e.g. massive precipitation, magmatic processes) and human activities (e.g. water injection in geothermal wells, ore-body exploitation). However, understanding and monitoring the evolution of physical properties of the crust is a challenging due to the limited possibility of reaching such depths and making direct measurements of the state of the rocks. Indirect measurements, like seismic tomography, can give some insights, but are generally biased by the un-even distribution (in space and time) of the information collected from seismic observations (travel-times and/or waveforms). Here we apply a Bayesian approach to overcome such limitations, so that data uncertainties and data distribution are fully accounted in the reconstruction of the posterior probability distribution of the rock elasticity We compute a full 4D local earthquake tomography based on trans-dimensional Markov chain Monte Carlo sampling of 4D elastic models, where the resolution in space and time is fully data-driven. To test our workflow, we make use of a “controlled laboratory”: we record seismic data during one month of mining activities across a 800x700x600 m volume of Kiruna mine (LKAB, Sweden). During such period, we obtain about 260 000 P-wave and 240 000 S-wave travel-times coming from about 36000 seismic events. We operate a preliminary selection of the well-located events, using a Monte Carlo search. Arrival-times of about 19 000 best-located events (location errors less than 20m) are used as input to the tomography workflow. Preliminary results indicate that: (1) short-term (few hours) evolutions of the elastic field are mainly driven by seismic activation, i.e. the occurrence of a seismic swarm, close to the mine ore-passes. Such phenomena partially mask the effects of explosions; (2) long-term (2-3 days) evolutions of the elastic field closely match the local measurements of the stress field at a colocated stress cell.
How to cite: Piana Agostinetti, N., Dahnér-Lindkvist, C., and Dineva, S.: Toward a full 4D seismic tomography: a case study of an active mine, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12015, https://doi.org/10.5194/egusphere-egu21-12015, 2021.
EGU21-10146 | vPICO presentations | SM8.1
The structure of signal space: a case study of direct mapping between seismic waveforms and event distributionDavid Harris and Douglas Dodge
Under special circumstances, waveform observations of seismic events related by a common, spatially-distributed source process exhibit a geometric architecture that is a distorted image of event distribution in the source region. We describe a prescription for visualizing this signal space image and use a machine-learning algorithm, Isomap, and an algorithm due to Menke to invert collections of waveforms directly for relative event location. We illustrate concepts and methods with well-characterized induced seismicity at a coal mine in the U.S. state of Utah observed by two local seismic instruments, and with synthetics. We anticipate application of these methods to repetitive volcanic seismicity, icequakes and induced seismicity.
This is Lawrence Livermore National Laboratory contribution LLNL-ABS-818445.
How to cite: Harris, D. and Dodge, D.: The structure of signal space: a case study of direct mapping between seismic waveforms and event distribution, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10146, https://doi.org/10.5194/egusphere-egu21-10146, 2021.
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Under special circumstances, waveform observations of seismic events related by a common, spatially-distributed source process exhibit a geometric architecture that is a distorted image of event distribution in the source region. We describe a prescription for visualizing this signal space image and use a machine-learning algorithm, Isomap, and an algorithm due to Menke to invert collections of waveforms directly for relative event location. We illustrate concepts and methods with well-characterized induced seismicity at a coal mine in the U.S. state of Utah observed by two local seismic instruments, and with synthetics. We anticipate application of these methods to repetitive volcanic seismicity, icequakes and induced seismicity.
This is Lawrence Livermore National Laboratory contribution LLNL-ABS-818445.
How to cite: Harris, D. and Dodge, D.: The structure of signal space: a case study of direct mapping between seismic waveforms and event distribution, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10146, https://doi.org/10.5194/egusphere-egu21-10146, 2021.
A model that explains the anomalies in the Love wave dispersion in the earth is presented. Conventionally, welded contact between the crust and the upper mantle is assumed, leading to Love wave generation when the earth is excited. However, the observations of SH wave dispersion at seismic frequencies is at variance with this model, at least for some crustal plates (Ekström, 2011). When frictional slip occurs at the crust-upper mantle interface, a new type of interfacial elastic wave called the antiplane slip wave can occur (Ranjith, 2017). It is shown that the antiplane slip waves can explain the observed anomalies in the Love wave dispersion.
How to cite: Kunnath, R.: Love wave or slip wave?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-273, https://doi.org/10.5194/egusphere-egu21-273, 2021.
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A model that explains the anomalies in the Love wave dispersion in the earth is presented. Conventionally, welded contact between the crust and the upper mantle is assumed, leading to Love wave generation when the earth is excited. However, the observations of SH wave dispersion at seismic frequencies is at variance with this model, at least for some crustal plates (Ekström, 2011). When frictional slip occurs at the crust-upper mantle interface, a new type of interfacial elastic wave called the antiplane slip wave can occur (Ranjith, 2017). It is shown that the antiplane slip waves can explain the observed anomalies in the Love wave dispersion.
How to cite: Kunnath, R.: Love wave or slip wave?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-273, https://doi.org/10.5194/egusphere-egu21-273, 2021.
EGU21-15267 | vPICO presentations | SM8.1
Eigenvalue decomposition polarization analysis: A regularized sparsity-based approachEduardo Almeida, Hamzeh Mohammadigheymasi, Maryam Fathi, Paul Crocker, and Graça Silveira
Polarization analysis is a signal processing tool for decomposing multi-component seismic signals to a set of rectilinearly or elliptically polarized elements. Theoretically, time-frequency polarization methods are the most compatible tool to analyze the intrinsically non-stationary seismic signals. They decompose the signal to a superposition of well-defined polarized elements, localized in the time and frequency domains. However, in practice, they suffer from instability and limited resolution for discriminating between interfering seismic phases in time and frequency, as the time-frequency decomposition methods are generally an underdetermined mapping from the time to the time-frequency domain. Our contribution is threefold: Firstly we obtain the frequency-dependent polarization properties in terms of the eigenvalue decomposition of the Fourier spectra of three-components of the signal. Secondly, by extending from the frequency to the time-frequency domain and using the regularized sparsity-based time-frequency decomposition (Portniaguine and Castagna, 2004) we are able to increase resolution and reduce instability in the presence of noise. Finally, by combining directivity, rectilineary, and amplitude attributes in the time-frequency domain, we extend the time-frequency polarization analysis to extract and filter different seismic phases. By applying this method on synthetic and real seismograms we demonstrate the efficacy of the method in discriminating between the interfering seismic phases in time and frequency, including the body, Rayleigh, Love, and coda waves. This research contributes to the FCT-funded SHAZAM (Ref. PTDC/CTA-GEO/31475/2017) project.
REFERENCES
Portniaguine, O., and J. Castagna, 2004, Inverse spectral decomposition, in SEG Technical Program Expanded Abstracts 2004: Society of Exploration Geophysicists, 1786–1789.
How to cite: Almeida, E., Mohammadigheymasi, H., Fathi, M., Crocker, P., and Silveira, G.: Eigenvalue decomposition polarization analysis: A regularized sparsity-based approach, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15267, https://doi.org/10.5194/egusphere-egu21-15267, 2021.
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Polarization analysis is a signal processing tool for decomposing multi-component seismic signals to a set of rectilinearly or elliptically polarized elements. Theoretically, time-frequency polarization methods are the most compatible tool to analyze the intrinsically non-stationary seismic signals. They decompose the signal to a superposition of well-defined polarized elements, localized in the time and frequency domains. However, in practice, they suffer from instability and limited resolution for discriminating between interfering seismic phases in time and frequency, as the time-frequency decomposition methods are generally an underdetermined mapping from the time to the time-frequency domain. Our contribution is threefold: Firstly we obtain the frequency-dependent polarization properties in terms of the eigenvalue decomposition of the Fourier spectra of three-components of the signal. Secondly, by extending from the frequency to the time-frequency domain and using the regularized sparsity-based time-frequency decomposition (Portniaguine and Castagna, 2004) we are able to increase resolution and reduce instability in the presence of noise. Finally, by combining directivity, rectilineary, and amplitude attributes in the time-frequency domain, we extend the time-frequency polarization analysis to extract and filter different seismic phases. By applying this method on synthetic and real seismograms we demonstrate the efficacy of the method in discriminating between the interfering seismic phases in time and frequency, including the body, Rayleigh, Love, and coda waves. This research contributes to the FCT-funded SHAZAM (Ref. PTDC/CTA-GEO/31475/2017) project.
REFERENCES
Portniaguine, O., and J. Castagna, 2004, Inverse spectral decomposition, in SEG Technical Program Expanded Abstracts 2004: Society of Exploration Geophysicists, 1786–1789.
How to cite: Almeida, E., Mohammadigheymasi, H., Fathi, M., Crocker, P., and Silveira, G.: Eigenvalue decomposition polarization analysis: A regularized sparsity-based approach, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15267, https://doi.org/10.5194/egusphere-egu21-15267, 2021.
EGU21-779 | vPICO presentations | SM8.1
Errors Introduced in Estimation of Surface Wave Phase and Group Velocities Due to Wrong Assumptions: An Assessment Using a Simple Model For Love WaveAkash Kharita and Sagarika Mukhopadhyay
The surface wave phase and group velocities are estimated by dividing the epicentral distance by phase and group travel times respectively in all the available methods, this is based on the assumptions that (1) surface waves originate at the epicentre and (2) the travel time of the particular group or phase of the surface wave is equal to its arrival time to the station minus the origin time of the causative earthquake; However, both assumptions are wrong since surface waves generate at some horizontal distance away from the epicentre. We calculated the actual horizontal distance from the focus at which they generate and assessed the errors caused in the estimation of group and phase velocities by the aforementioned assumptions in a simple isotropic single layered homogeneous half space crustal model using the example of the fundamental mode Love wave. We took the receiver locations in the epicentral distance range of 100-1000 km, as used in the regional surface wave analysis, varied the source depth from 0 to 35 Km with a step size of 5 km and did the forward modelling to calculate the arrival time of Love wave phases at each receiver location. The phase and group velocities are then estimated using the above assumptions and are compared with the actual values of the velocities given by Love wave dispersion equation. We observed that the velocities are underestimated and the errors are found to be; decreasing linearly with focal depth, decreasing inversely with the epicentral distance and increasing parabolically with the time period. We also derived empirical formulas using MATLAB curve fitting toolbox that will give percentage errors for any realistic combination of epicentral distance, time period and depths of earthquake and thickness of layer in this model. The errors are found to be more than 5% for all epicentral distances lesser than 500 km, for all focal depths and time periods indicating that it is not safe to do regional surface wave analysis for epicentral distances lesser than 500 km without incurring significant errors. To the best of our knowledge, the study is first of its kind in assessing such errors.
How to cite: Kharita, A. and Mukhopadhyay, S.: Errors Introduced in Estimation of Surface Wave Phase and Group Velocities Due to Wrong Assumptions: An Assessment Using a Simple Model For Love Wave, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-779, https://doi.org/10.5194/egusphere-egu21-779, 2021.
The surface wave phase and group velocities are estimated by dividing the epicentral distance by phase and group travel times respectively in all the available methods, this is based on the assumptions that (1) surface waves originate at the epicentre and (2) the travel time of the particular group or phase of the surface wave is equal to its arrival time to the station minus the origin time of the causative earthquake; However, both assumptions are wrong since surface waves generate at some horizontal distance away from the epicentre. We calculated the actual horizontal distance from the focus at which they generate and assessed the errors caused in the estimation of group and phase velocities by the aforementioned assumptions in a simple isotropic single layered homogeneous half space crustal model using the example of the fundamental mode Love wave. We took the receiver locations in the epicentral distance range of 100-1000 km, as used in the regional surface wave analysis, varied the source depth from 0 to 35 Km with a step size of 5 km and did the forward modelling to calculate the arrival time of Love wave phases at each receiver location. The phase and group velocities are then estimated using the above assumptions and are compared with the actual values of the velocities given by Love wave dispersion equation. We observed that the velocities are underestimated and the errors are found to be; decreasing linearly with focal depth, decreasing inversely with the epicentral distance and increasing parabolically with the time period. We also derived empirical formulas using MATLAB curve fitting toolbox that will give percentage errors for any realistic combination of epicentral distance, time period and depths of earthquake and thickness of layer in this model. The errors are found to be more than 5% for all epicentral distances lesser than 500 km, for all focal depths and time periods indicating that it is not safe to do regional surface wave analysis for epicentral distances lesser than 500 km without incurring significant errors. To the best of our knowledge, the study is first of its kind in assessing such errors.
How to cite: Kharita, A. and Mukhopadhyay, S.: Errors Introduced in Estimation of Surface Wave Phase and Group Velocities Due to Wrong Assumptions: An Assessment Using a Simple Model For Love Wave, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-779, https://doi.org/10.5194/egusphere-egu21-779, 2021.
EGU21-4214 | vPICO presentations | SM8.1
Improved interpretation of SAGEEP 2011 blind refraction data using Frequency-Dependent Traveltime TomographySiegfried Rohdewald
We demonstrate improved resolution in P-wave velocity tomograms obtained by inversion of the synthetic SAGEEP 2011 refraction traveltime data (Zelt 2010) using Wavepath-Eikonal Traveltime Inversion (WET; Schuster 1993) and Wavelength-Dependent Velocity Smoothing (WDVS; Zelt and Chen 2016). We use a multiscale inversion approach and a Conjugate-Gradient based search method. Our default starting model is a 1D-gradient model obtained directly from the traveltime first arrivals assuming diving waves (Sheehan, 2005). As a second approach, we map the first breaks to assumed refractors and obtain a layered starting model using the Plus-Minus refraction method (Hagedoorn, 1959). We compare tomograms obtained using WDVS to smooth the current velocity model grid before forward modeling traveltimes vs. tomograms obtained without WDVS. Results show that WET images velocity layer boundaries more sharply when engaging WDVS. We determine the optimum WDVS frequency iteratively by trial-and-error. We observe that the lower the used WDVS frequency, the stronger the imaged velocity contrast at the top-of-basement. Using a WDVS frequency that is too low makes WDVS based WET inversion unstable exhibiting increasing RMS error, too high modeled velocity contrast and too shallow imaged top-of-basement. To speed up WDVS, we regard each nth node only when scanning the velocity along straight scan lines radiating from the current velocity grid node. Scanned velocities are weighted with a Cosine-Squared function as described by (Zelt and Chen, 2016). We observe that activating WDVS allows decreasing WET regularization (smoothing and damping) to a higher degree than without WDVS.
References:
Hagedoorn, J.G., 1959, The Plus-Minus method of interpreting seismic refraction sections, Geophysical Prospecting, Volume 7, 158-182.
Rohdewald, S.R.C., 2021, SAGEEP11 data interpretation, https://rayfract.com/tutorials/sageep11_16.pdf.
Schuster, G.T., Quintus-Bosz, A., 1993, Wavepath eikonal traveltime inversion: Theory. Geophysics, Volume 58, 1314-1323.
Sheehan, J.R., Doll, W.E., Mandell, W., 2005, An evaluation of methods and available software for seismic refraction tomography analysis, JEEG, Volume 10(1), 21-34.
Shewchuk, J.R., 1994, An Introduction to the Conjugate Gradient Method Without the Agonizing Pain, http://www.cs.cmu.edu/~quake-papers/painless-conjugate-gradient.pdf.
Zelt, C.A., 2010, Seismic refraction shootout: blind test of methods for obtaining velocity models from first-arrival travel times, http://terra.rice.edu/department/faculty/zelt/sageep2011.
Zelt, C.A., Haines, S., Powers, M.H. et al. 2013, Blind Test of Methods for Obtaining 2-D Near-Surface Seismic Velocity Models from First-Arrival Traveltimes, JEEG, Volume 18(3), 183-194.
Zelt, C.A., Chen, J., 2016, Frequency-dependent traveltime tomography for near-surface seismic refraction data, Geophys. J. Int., Volume 207, 72-88.
How to cite: Rohdewald, S.: Improved interpretation of SAGEEP 2011 blind refraction data using Frequency-Dependent Traveltime Tomography, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4214, https://doi.org/10.5194/egusphere-egu21-4214, 2021.
Please decide on your access
Please use the buttons below to download the presentation materials or to visit the external website where the presentation is linked. Regarding the external link, please note that Copernicus Meetings cannot accept any liability for the content and the website you will visit.
Forward to presentation link
You are going to open an external link to the presentation as indicated by the authors. Copernicus Meetings cannot accept any liability for the content and the website you will visit.
We are sorry, but presentations are only available for users who registered for the conference. Thank you.
We demonstrate improved resolution in P-wave velocity tomograms obtained by inversion of the synthetic SAGEEP 2011 refraction traveltime data (Zelt 2010) using Wavepath-Eikonal Traveltime Inversion (WET; Schuster 1993) and Wavelength-Dependent Velocity Smoothing (WDVS; Zelt and Chen 2016). We use a multiscale inversion approach and a Conjugate-Gradient based search method. Our default starting model is a 1D-gradient model obtained directly from the traveltime first arrivals assuming diving waves (Sheehan, 2005). As a second approach, we map the first breaks to assumed refractors and obtain a layered starting model using the Plus-Minus refraction method (Hagedoorn, 1959). We compare tomograms obtained using WDVS to smooth the current velocity model grid before forward modeling traveltimes vs. tomograms obtained without WDVS. Results show that WET images velocity layer boundaries more sharply when engaging WDVS. We determine the optimum WDVS frequency iteratively by trial-and-error. We observe that the lower the used WDVS frequency, the stronger the imaged velocity contrast at the top-of-basement. Using a WDVS frequency that is too low makes WDVS based WET inversion unstable exhibiting increasing RMS error, too high modeled velocity contrast and too shallow imaged top-of-basement. To speed up WDVS, we regard each nth node only when scanning the velocity along straight scan lines radiating from the current velocity grid node. Scanned velocities are weighted with a Cosine-Squared function as described by (Zelt and Chen, 2016). We observe that activating WDVS allows decreasing WET regularization (smoothing and damping) to a higher degree than without WDVS.
References:
Hagedoorn, J.G., 1959, The Plus-Minus method of interpreting seismic refraction sections, Geophysical Prospecting, Volume 7, 158-182.
Rohdewald, S.R.C., 2021, SAGEEP11 data interpretation, https://rayfract.com/tutorials/sageep11_16.pdf.
Schuster, G.T., Quintus-Bosz, A., 1993, Wavepath eikonal traveltime inversion: Theory. Geophysics, Volume 58, 1314-1323.
Sheehan, J.R., Doll, W.E., Mandell, W., 2005, An evaluation of methods and available software for seismic refraction tomography analysis, JEEG, Volume 10(1), 21-34.
Shewchuk, J.R., 1994, An Introduction to the Conjugate Gradient Method Without the Agonizing Pain, http://www.cs.cmu.edu/~quake-papers/painless-conjugate-gradient.pdf.
Zelt, C.A., 2010, Seismic refraction shootout: blind test of methods for obtaining velocity models from first-arrival travel times, http://terra.rice.edu/department/faculty/zelt/sageep2011.
Zelt, C.A., Haines, S., Powers, M.H. et al. 2013, Blind Test of Methods for Obtaining 2-D Near-Surface Seismic Velocity Models from First-Arrival Traveltimes, JEEG, Volume 18(3), 183-194.
Zelt, C.A., Chen, J., 2016, Frequency-dependent traveltime tomography for near-surface seismic refraction data, Geophys. J. Int., Volume 207, 72-88.
How to cite: Rohdewald, S.: Improved interpretation of SAGEEP 2011 blind refraction data using Frequency-Dependent Traveltime Tomography, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4214, https://doi.org/10.5194/egusphere-egu21-4214, 2021.
EGU21-13094 | vPICO presentations | SM8.1
Seismic waveform modelling and inversion with velocity-deviatoric stress-isotropic pressure formulationYi Zhang, Luca de Siena, and Alexey Stovas
In waveform inversion, most of the existing adjoint-state methods are based on the second-order elastic wave equations subject to displacement. The implementation of the acoustic-elastic coupling problem and free-surface in this formulation is not explicit, especially for arbitrary boundaries. The formulation of velocity-deviatoric stress-isotropic pressure can tackle the above issue. We firstly review the difference between velocity stress equations and velocity-deviatoric stress-isotropic pressure equations. Then the adjoint state of the velocity-stress equations are derived, decomposing stresses into their deviatoric and isotropic parts. To simulate the unbounded wavefield, perfectly matched layers (PML) are embedded into the system of equations. It is modified for cheap computation, which avoids PML-related memory variables by applying complex coordinate stretch to three Cartesian axes in parallel.
A 3D velocity-deviatoric stress-isotropic stress formulation is implemented with the staggered finite-difference method for several synthetic models (including anisotropic models). And inversions are then performed to reconstruct the model parameters, which is followed by a sensitivity analysis.
This method has the potential to be used with real data, both for active and passive seismics. However, in its current form, since it does not treat fluid/anisotropic solid interfaces correctly, it is limited to fluid or isotropic solid problems.
How to cite: Zhang, Y., de Siena, L., and Stovas, A.: Seismic waveform modelling and inversion with velocity-deviatoric stress-isotropic pressure formulation, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13094, https://doi.org/10.5194/egusphere-egu21-13094, 2021.
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In waveform inversion, most of the existing adjoint-state methods are based on the second-order elastic wave equations subject to displacement. The implementation of the acoustic-elastic coupling problem and free-surface in this formulation is not explicit, especially for arbitrary boundaries. The formulation of velocity-deviatoric stress-isotropic pressure can tackle the above issue. We firstly review the difference between velocity stress equations and velocity-deviatoric stress-isotropic pressure equations. Then the adjoint state of the velocity-stress equations are derived, decomposing stresses into their deviatoric and isotropic parts. To simulate the unbounded wavefield, perfectly matched layers (PML) are embedded into the system of equations. It is modified for cheap computation, which avoids PML-related memory variables by applying complex coordinate stretch to three Cartesian axes in parallel.
A 3D velocity-deviatoric stress-isotropic stress formulation is implemented with the staggered finite-difference method for several synthetic models (including anisotropic models). And inversions are then performed to reconstruct the model parameters, which is followed by a sensitivity analysis.
This method has the potential to be used with real data, both for active and passive seismics. However, in its current form, since it does not treat fluid/anisotropic solid interfaces correctly, it is limited to fluid or isotropic solid problems.
How to cite: Zhang, Y., de Siena, L., and Stovas, A.: Seismic waveform modelling and inversion with velocity-deviatoric stress-isotropic pressure formulation, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13094, https://doi.org/10.5194/egusphere-egu21-13094, 2021.
EGU21-9868 | vPICO presentations | SM8.1
Numerical tools to model seismic waves in unconsolidated and partially saturated granular mediaKassem Asfour, Roland Martin, Ludovic Bodet, Didier El Baz, Bastien Plazolles, and Javier Abreu-Torres
How to cite: Asfour, K., Martin, R., Bodet, L., El Baz, D., Plazolles, B., and Abreu-Torres, J.: Numerical tools to model seismic waves in unconsolidated and partially saturated granular media, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9868, https://doi.org/10.5194/egusphere-egu21-9868, 2021.
How to cite: Asfour, K., Martin, R., Bodet, L., El Baz, D., Plazolles, B., and Abreu-Torres, J.: Numerical tools to model seismic waves in unconsolidated and partially saturated granular media, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9868, https://doi.org/10.5194/egusphere-egu21-9868, 2021.
EGU21-14565 | vPICO presentations | SM8.1
A hybrid method to calculate teleseismic body waves in a regional 3D model using GEMINI and SPECFEM.Thomas Möller and Wolfgang Friederich
Modeling waveforms of teleseismic body waves requires the solution of the seismic wave equation in the entire Earth. Since fully-numerical 3D simulations on a global scale with periods of a few seconds are far too computationally expensive, we resort to a hybrid approach in which fully-numerical 3D simulations are performed only within the target region and wave propagation through the rest of the Earth is modeled using methods that are much faster but apply only to spherically symmetric Earth models.
We present a hybrid method that uses GEMINI to compute wave fields for a spherically symmetric Earth model up to the boundaries of a regional box. The wavefield is injected at the boundaries, where wave propagation is continued using SPECFEM-Cartesian. Inside the box, local heterogeneities in the velocity distribution are allowed, which can cause scattered and reflected waves. To prevent these waves from reflecting off the edges of the box absorbing boundary conditions are specifically applied to these parts of the wavefields. They are identified as the difference between the wavefield calculated with SPECFEM at the edges and the incident wavefield.
The hybrid method is applied to a target region in and around the Alps as a test case. The region covers an area of 1800 by 1350 km centered at 46.2°N and 10.87°E and includes crust and mantle to a depth of 600 km. We compare seismograms with a period of up to ten seconds calculated with the hybrid method to those calculated using GEMINI only for identical 1D earth models. The comparison of the seismograms shows only very small differences and thus validates the hybrid method. In addition, we demonstrate the potential of the method by calculating seismograms where the 1D velocity model inside the box is replaced by a velocity model generated using P-wave traveltime tomography.
How to cite: Möller, T. and Friederich, W.: A hybrid method to calculate teleseismic body waves in a regional 3D model using GEMINI and SPECFEM., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14565, https://doi.org/10.5194/egusphere-egu21-14565, 2021.
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Modeling waveforms of teleseismic body waves requires the solution of the seismic wave equation in the entire Earth. Since fully-numerical 3D simulations on a global scale with periods of a few seconds are far too computationally expensive, we resort to a hybrid approach in which fully-numerical 3D simulations are performed only within the target region and wave propagation through the rest of the Earth is modeled using methods that are much faster but apply only to spherically symmetric Earth models.
We present a hybrid method that uses GEMINI to compute wave fields for a spherically symmetric Earth model up to the boundaries of a regional box. The wavefield is injected at the boundaries, where wave propagation is continued using SPECFEM-Cartesian. Inside the box, local heterogeneities in the velocity distribution are allowed, which can cause scattered and reflected waves. To prevent these waves from reflecting off the edges of the box absorbing boundary conditions are specifically applied to these parts of the wavefields. They are identified as the difference between the wavefield calculated with SPECFEM at the edges and the incident wavefield.
The hybrid method is applied to a target region in and around the Alps as a test case. The region covers an area of 1800 by 1350 km centered at 46.2°N and 10.87°E and includes crust and mantle to a depth of 600 km. We compare seismograms with a period of up to ten seconds calculated with the hybrid method to those calculated using GEMINI only for identical 1D earth models. The comparison of the seismograms shows only very small differences and thus validates the hybrid method. In addition, we demonstrate the potential of the method by calculating seismograms where the 1D velocity model inside the box is replaced by a velocity model generated using P-wave traveltime tomography.
How to cite: Möller, T. and Friederich, W.: A hybrid method to calculate teleseismic body waves in a regional 3D model using GEMINI and SPECFEM., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14565, https://doi.org/10.5194/egusphere-egu21-14565, 2021.
EGU21-9439 | vPICO presentations | SM8.1
On the modelling of self-gravitation for full 3D global seismic wave propagationMartin van Driel, Johannes Kemper, Christian Boehm, and Amir Khan
The last decade has witnessed an unprecedented increase in high quality long period seismic data. This is because of the occurrence of several very large Earthquakes that were recorded on an exponentially growing number of broadband seismic stations that are installed in very dense networks such as the USarray. While for surface and body waves, tomography based on full waveform observables and 3D numerical simulations has become a standard tool in seismology, this is not the case for the normal modes. The main reason for this discrepancy is the fact that there is no established method to model the full physics of long period seismology in 3D and compute gradients with respect to material properties at reasonable computational cost.
Here, we present a new approach to the inclusion of the full gravitational response to spectral element wave propagation solvers. We leverage the Salvus meshing software to include the external domain using adaptive mesh refinement and high order shape mapping. Together with Neumann boundary conditions based on a multipole expansion of the right hand side this minimizes the number of additional elements needed. Initial conditions for the iterative solution of the Poisson equation based on temporal extrapolation from previous time steps together with a polynomial multigrid method reduce the number of iterations needed for convergence. In summary this approach reduces the extra cost for simulating full gravity to a similar order as the elastic forces.
We demonstrate the efficacy of the proposed method using the displacement from an elastic global wave propagation simulation at 200s period as the right hand side in the Poisson equation.
How to cite: van Driel, M., Kemper, J., Boehm, C., and Khan, A.: On the modelling of self-gravitation for full 3D global seismic wave propagation, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9439, https://doi.org/10.5194/egusphere-egu21-9439, 2021.
The last decade has witnessed an unprecedented increase in high quality long period seismic data. This is because of the occurrence of several very large Earthquakes that were recorded on an exponentially growing number of broadband seismic stations that are installed in very dense networks such as the USarray. While for surface and body waves, tomography based on full waveform observables and 3D numerical simulations has become a standard tool in seismology, this is not the case for the normal modes. The main reason for this discrepancy is the fact that there is no established method to model the full physics of long period seismology in 3D and compute gradients with respect to material properties at reasonable computational cost.
Here, we present a new approach to the inclusion of the full gravitational response to spectral element wave propagation solvers. We leverage the Salvus meshing software to include the external domain using adaptive mesh refinement and high order shape mapping. Together with Neumann boundary conditions based on a multipole expansion of the right hand side this minimizes the number of additional elements needed. Initial conditions for the iterative solution of the Poisson equation based on temporal extrapolation from previous time steps together with a polynomial multigrid method reduce the number of iterations needed for convergence. In summary this approach reduces the extra cost for simulating full gravity to a similar order as the elastic forces.
We demonstrate the efficacy of the proposed method using the displacement from an elastic global wave propagation simulation at 200s period as the right hand side in the Poisson equation.
How to cite: van Driel, M., Kemper, J., Boehm, C., and Khan, A.: On the modelling of self-gravitation for full 3D global seismic wave propagation, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9439, https://doi.org/10.5194/egusphere-egu21-9439, 2021.
EGU21-704 | vPICO presentations | SM8.1
Downscaling seismic tomography modelsNavid Hedjazian, Thomas Bodin, and Yann Capdeville
Seismic imaging techniques such as elastic full waveform inversion (FWI) have their spatial resolution limited by the maximum frequency present in the observed waveforms. Scales smaller than a fraction of the minimum wavelength cannot be resolved, only a smoothed version of the true underlying medium can be recovered. Application of FWI to media containing small and strong heterogeneities therefore remains problematic. This smooth tomographic image is related to the effective elastic properties, which can be exposed with the homogenization theory of wave propagation. We study how this theory can be used in the FWI context. The seismic imaging problem is broken down in a two-stage multiscale approach. In the first step, called homogenized full waveform inversion (HFWI), observed waveforms are inverted for a macro-scale, fully anisotropic effective medium, smooth at the scale of the shortest wavelength present in the wavefield. The solution being an effective medium, it is difficult to directly interpret it. It requires a second step, called downscaling, where the macro-scale image is used as data, and the goal is to recover micro-scale parameters. All the information contained in the waveforms is extracted in the HFWI step. The solution of the downscaling step is highly non-unique as many fine-scale models may share the same long wavelength effective properties. We therefore rely on the introduction of external a priori information. In this step, the forward theory is the homogenization itself. It is computationally cheap, allowing to consider geological models with more complexity.
In a first approach to downscaling, the ensemble of potential fine-scale models is described with an object-based parametrization, and explored with a MCMC algorithm. We illustrate the method with a synthetic cavity detection problem. In a second approach, the prior information is introduced by the means of a training image, and the fine-scale model is recovered with a multi-point statistics algorithm. We apply this method on a subsurface synthetic problem, where the goal is to recover geological facies.
How to cite: Hedjazian, N., Bodin, T., and Capdeville, Y.: Downscaling seismic tomography models, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-704, https://doi.org/10.5194/egusphere-egu21-704, 2021.
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We are sorry, but presentations are only available for users who registered for the conference. Thank you.
Seismic imaging techniques such as elastic full waveform inversion (FWI) have their spatial resolution limited by the maximum frequency present in the observed waveforms. Scales smaller than a fraction of the minimum wavelength cannot be resolved, only a smoothed version of the true underlying medium can be recovered. Application of FWI to media containing small and strong heterogeneities therefore remains problematic. This smooth tomographic image is related to the effective elastic properties, which can be exposed with the homogenization theory of wave propagation. We study how this theory can be used in the FWI context. The seismic imaging problem is broken down in a two-stage multiscale approach. In the first step, called homogenized full waveform inversion (HFWI), observed waveforms are inverted for a macro-scale, fully anisotropic effective medium, smooth at the scale of the shortest wavelength present in the wavefield. The solution being an effective medium, it is difficult to directly interpret it. It requires a second step, called downscaling, where the macro-scale image is used as data, and the goal is to recover micro-scale parameters. All the information contained in the waveforms is extracted in the HFWI step. The solution of the downscaling step is highly non-unique as many fine-scale models may share the same long wavelength effective properties. We therefore rely on the introduction of external a priori information. In this step, the forward theory is the homogenization itself. It is computationally cheap, allowing to consider geological models with more complexity.
In a first approach to downscaling, the ensemble of potential fine-scale models is described with an object-based parametrization, and explored with a MCMC algorithm. We illustrate the method with a synthetic cavity detection problem. In a second approach, the prior information is introduced by the means of a training image, and the fine-scale model is recovered with a multi-point statistics algorithm. We apply this method on a subsurface synthetic problem, where the goal is to recover geological facies.
How to cite: Hedjazian, N., Bodin, T., and Capdeville, Y.: Downscaling seismic tomography models, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-704, https://doi.org/10.5194/egusphere-egu21-704, 2021.
EGU21-14954 | vPICO presentations | SM8.1
Targeted stacking of weak seismic phases for improving mantle discontinuity imaging using full-waveform inversionMaria Koroni and Andreas Fichtner
This study is a continuation of our efforts to connect adjoint methods and full-waveform inversion to common beamforming techniques, widely used and developed for signal enhancement. Our approach is focusing on seismic waves traveling in the Earth's mantle, which are phases commonly used to image internal boundaries, being however quite difficult to observe in real data. The main goal is to accentuate precursor waves arriving in well-known times before some major phase. These waves generate from interactions with global discontinuities in the mantle, thus being the most sensitive seismic phases and therefore most suitable for better understanding of discontinuity seismic structure.
Our work is based on spectral-element wave propagation which allows us to compute exact synthetic waveforms and adjoint methods for the calculation of sensitivity kernels. These tools are the core of full-waveform inversion and by our efforts we aim to incorporate more parts of the waveform in such inversion schemes. We have shown that targeted stacking of good quality waveforms arriving from various directions highlights the weak precursor waves. It additionally makes their traveltime finite frequency sensitivity prominent. This shows that we can benefit from using these techniques and exploit rather difficult parts of the seismogram. It was also shown that wave interference is not easily avoided, but coherent phases arriving before the main phase also stack well and show on the sensitivity kernels. This does not hamper the evaluation of waveforms, as in a misfit measurement process one can exploit more phases on the body wave parts of seismograms.
In this study, we go a step forward and present recent developments of the approach relating to the effects of noise and a real data experiment. Realistic noise is added to synthetic waveforms in order to assess the methodology in a more pragmatic scenario. The addition of noise shows that stacking of coherent seismic phases is still possible and the sensitivity kernels of their traveltimes are not largely distorted, the precursor waves contribute sufficiently to their traveltime finite-frequency sensitivity kernels.
Using a well-located seismic array, we apply the method to real data and try to examine the possibilities of using non-ideal waveforms to perform imaging of the mantle discontinuity structure on the specific areas. In order to make the most out of the dense array configuration, we try subgroups of receivers for the targeted stacking and by moving along the array we aim at creating a cluster of stacks. The main idea is to use the subgroups as single receivers and create an evaluation of seismic discontinuity structure using information from each stack belonging to a subgroup.
Ideally, we aim at improving the tomographic images of discontinuities of selected regions by exploiting weaker seismic waves, which are nonetheless very informative.
How to cite: Koroni, M. and Fichtner, A.: Targeted stacking of weak seismic phases for improving mantle discontinuity imaging using full-waveform inversion, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14954, https://doi.org/10.5194/egusphere-egu21-14954, 2021.
This study is a continuation of our efforts to connect adjoint methods and full-waveform inversion to common beamforming techniques, widely used and developed for signal enhancement. Our approach is focusing on seismic waves traveling in the Earth's mantle, which are phases commonly used to image internal boundaries, being however quite difficult to observe in real data. The main goal is to accentuate precursor waves arriving in well-known times before some major phase. These waves generate from interactions with global discontinuities in the mantle, thus being the most sensitive seismic phases and therefore most suitable for better understanding of discontinuity seismic structure.
Our work is based on spectral-element wave propagation which allows us to compute exact synthetic waveforms and adjoint methods for the calculation of sensitivity kernels. These tools are the core of full-waveform inversion and by our efforts we aim to incorporate more parts of the waveform in such inversion schemes. We have shown that targeted stacking of good quality waveforms arriving from various directions highlights the weak precursor waves. It additionally makes their traveltime finite frequency sensitivity prominent. This shows that we can benefit from using these techniques and exploit rather difficult parts of the seismogram. It was also shown that wave interference is not easily avoided, but coherent phases arriving before the main phase also stack well and show on the sensitivity kernels. This does not hamper the evaluation of waveforms, as in a misfit measurement process one can exploit more phases on the body wave parts of seismograms.
In this study, we go a step forward and present recent developments of the approach relating to the effects of noise and a real data experiment. Realistic noise is added to synthetic waveforms in order to assess the methodology in a more pragmatic scenario. The addition of noise shows that stacking of coherent seismic phases is still possible and the sensitivity kernels of their traveltimes are not largely distorted, the precursor waves contribute sufficiently to their traveltime finite-frequency sensitivity kernels.
Using a well-located seismic array, we apply the method to real data and try to examine the possibilities of using non-ideal waveforms to perform imaging of the mantle discontinuity structure on the specific areas. In order to make the most out of the dense array configuration, we try subgroups of receivers for the targeted stacking and by moving along the array we aim at creating a cluster of stacks. The main idea is to use the subgroups as single receivers and create an evaluation of seismic discontinuity structure using information from each stack belonging to a subgroup.
Ideally, we aim at improving the tomographic images of discontinuities of selected regions by exploiting weaker seismic waves, which are nonetheless very informative.
How to cite: Koroni, M. and Fichtner, A.: Targeted stacking of weak seismic phases for improving mantle discontinuity imaging using full-waveform inversion, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14954, https://doi.org/10.5194/egusphere-egu21-14954, 2021.
EGU21-12899 | vPICO presentations | SM8.1
Full-waveform inversion of the African PlateDirk-Philip van Herwaarden, Michael Afanasiev, Sölvi Thrastarson, and Andreas Fichtner
We present a full-waveform inversion (FWI) of the African plate. Starting from the Collaborative Seismic Earth Model, we invert seismograms that are filtered to 35 s and compute gradients using the adjoint state method. This FWI uses a novel approach that we introduced earlier with the name Evolutionary FWI.
In contrast to conventional waveform inversion, our approach uses dynamically changing mini-batches (subsets of the full dataset) that approximate the gradient of the larger dataset at each iteration. This has three major advantages, (1) We exploit redundancies within the dataset, which results in a reduced computational cost for model updates, (2) The size of the complete dataset does not directly impact the computational cost of an iteration, thereby enabling us to work with larger datasets, and (3) The nature of the algorithm makes it trivial to assimilate new data, as the new data can simply be added to the complete dataset from which the mini-batches are sampled.
The aforementioned advantages enable us to extend the boundaries of what was previously possible for a given computational budget. We perform more than 80 mini-batch iterations and invert waveforms from over 400 unique earthquakes. This has the same cost as 8 iterations with all data. Our latest model clearly images tectonic features such as the Afar triple junction as well as slow zones below areas with dynamic topography, such as the Tibesti and Hoggar mountain ranges.
How to cite: van Herwaarden, D.-P., Afanasiev, M., Thrastarson, S., and Fichtner, A.: Full-waveform inversion of the African Plate, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12899, https://doi.org/10.5194/egusphere-egu21-12899, 2021.
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We are sorry, but presentations are only available for users who registered for the conference. Thank you.
We present a full-waveform inversion (FWI) of the African plate. Starting from the Collaborative Seismic Earth Model, we invert seismograms that are filtered to 35 s and compute gradients using the adjoint state method. This FWI uses a novel approach that we introduced earlier with the name Evolutionary FWI.
In contrast to conventional waveform inversion, our approach uses dynamically changing mini-batches (subsets of the full dataset) that approximate the gradient of the larger dataset at each iteration. This has three major advantages, (1) We exploit redundancies within the dataset, which results in a reduced computational cost for model updates, (2) The size of the complete dataset does not directly impact the computational cost of an iteration, thereby enabling us to work with larger datasets, and (3) The nature of the algorithm makes it trivial to assimilate new data, as the new data can simply be added to the complete dataset from which the mini-batches are sampled.
The aforementioned advantages enable us to extend the boundaries of what was previously possible for a given computational budget. We perform more than 80 mini-batch iterations and invert waveforms from over 400 unique earthquakes. This has the same cost as 8 iterations with all data. Our latest model clearly images tectonic features such as the Afar triple junction as well as slow zones below areas with dynamic topography, such as the Tibesti and Hoggar mountain ranges.
How to cite: van Herwaarden, D.-P., Afanasiev, M., Thrastarson, S., and Fichtner, A.: Full-waveform inversion of the African Plate, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12899, https://doi.org/10.5194/egusphere-egu21-12899, 2021.
EGU21-12687 | vPICO presentations | SM8.1
Long-Wavelength Earth Model via Accelerated Full-Waveform InversionSolvi Thrastarson, Dirk-Philip van Herwaarden, Lion Krischer, Martin van Driel, Christian Boehm, and Andreas Fichtner
As the volume of available seismic waveform data increases, the responsibility to use the data in an effective way emerges. This requires computational efficiency as well as maximizing the exploitation of the information associated with the data.
In this contribution, we present a long-wavelength Earth model, created by using the data recorded from over a thousand earthquakes, starting from a simple one-dimensional background (PREM). The model is constructed with an accelerated full-waveform inversion (FWI) method which can seamlessly include large data volumes with a significantly reduced computational overhead. Although we present a long-wavelength model, the approach has the potential to go to much higher frequencies, while maintaining a reasonable cost.
Our approach combines two novel FWI variants. (1) The dynamic mini-batch approach which uses adaptively defined subsets of the full dataset in each iteration, detaching the direct scaling of inversion cost from the number of earthquakes included. (2) Wavefield-adapted meshes which utilize the azimuthal smoothness of the wavefield to design meshes optimized for each individual source location. Using wavefield adapted meshes can drastically reduce the cost of both forward and adjoint simulations as well as it makes the scaling of the computing cost to modelled frequencies more favourable.
How to cite: Thrastarson, S., van Herwaarden, D.-P., Krischer, L., van Driel, M., Boehm, C., and Fichtner, A.: Long-Wavelength Earth Model via Accelerated Full-Waveform Inversion, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12687, https://doi.org/10.5194/egusphere-egu21-12687, 2021.
As the volume of available seismic waveform data increases, the responsibility to use the data in an effective way emerges. This requires computational efficiency as well as maximizing the exploitation of the information associated with the data.
In this contribution, we present a long-wavelength Earth model, created by using the data recorded from over a thousand earthquakes, starting from a simple one-dimensional background (PREM). The model is constructed with an accelerated full-waveform inversion (FWI) method which can seamlessly include large data volumes with a significantly reduced computational overhead. Although we present a long-wavelength model, the approach has the potential to go to much higher frequencies, while maintaining a reasonable cost.
Our approach combines two novel FWI variants. (1) The dynamic mini-batch approach which uses adaptively defined subsets of the full dataset in each iteration, detaching the direct scaling of inversion cost from the number of earthquakes included. (2) Wavefield-adapted meshes which utilize the azimuthal smoothness of the wavefield to design meshes optimized for each individual source location. Using wavefield adapted meshes can drastically reduce the cost of both forward and adjoint simulations as well as it makes the scaling of the computing cost to modelled frequencies more favourable.
How to cite: Thrastarson, S., van Herwaarden, D.-P., Krischer, L., van Driel, M., Boehm, C., and Fichtner, A.: Long-Wavelength Earth Model via Accelerated Full-Waveform Inversion, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12687, https://doi.org/10.5194/egusphere-egu21-12687, 2021.
EGU21-1334 | vPICO presentations | SM8.1
Interrogating Tomographic Uncertainties for Subsurface Structural InformationAndrew Curtis, Xuebin Zhao, and Xin Zhang
The ultimate goal of a geophysical investigation is usually to find answers to scientific (often low-dimensional) questions: how large is a subsurface body? How deeply does lithosphere subduct? Does a certain subsurface feature exist? Background research reviews existing information, an experiment is designed and performed to acquire new data, and the most likely answer is estimated. Typically the answer is interpreted from geophysical inversions, but is usually biased because only one particular forward function (model-data relationship) is considered, one inversion method is used, and because human interpretation is a biased process. Interrogation theory provides a systematic way to answer specific questions. Answers balance information from multiple forward models, inverse methods and model parametrizations probabilistically, and optimal answers are found using decision theory.
Two examples illustrate interrogation of the Earth’s subsurface. In a synthetic test, we estimate the cross-sectional area of a subsurface low velocity anomaly by interrogating Bayesian probabilistic tomographic maps. By combining the results of four different nonlinear inversion algorithms, the optimal answer is very close to the true answer. In a field data application, we evaluate the extent of the Irish Sea Sedimentary Basin based on the uncertainties in velocity structure derived from Love wave tomography. This example shows that the computational expense of estimating uncertainties adds explicit value to answers.
This study demonstrates that interrogation theory answers realistic questions about the Earth’s subsurface. The same theory can be used to solve different types of scientific problem - experimental design, interpreting models, expert elicitation and risk estimation - and can be applied in any field of science. One of its most important contributions is to show that fully nonlinear estimates of uncertainty are critical for decision-making in real-world geoscientific problems, potentially justifying their computational expense.
How to cite: Curtis, A., Zhao, X., and Zhang, X.: Interrogating Tomographic Uncertainties for Subsurface Structural Information, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1334, https://doi.org/10.5194/egusphere-egu21-1334, 2021.
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Please use the buttons below to download the presentation materials or to visit the external website where the presentation is linked. Regarding the external link, please note that Copernicus Meetings cannot accept any liability for the content and the website you will visit.
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The ultimate goal of a geophysical investigation is usually to find answers to scientific (often low-dimensional) questions: how large is a subsurface body? How deeply does lithosphere subduct? Does a certain subsurface feature exist? Background research reviews existing information, an experiment is designed and performed to acquire new data, and the most likely answer is estimated. Typically the answer is interpreted from geophysical inversions, but is usually biased because only one particular forward function (model-data relationship) is considered, one inversion method is used, and because human interpretation is a biased process. Interrogation theory provides a systematic way to answer specific questions. Answers balance information from multiple forward models, inverse methods and model parametrizations probabilistically, and optimal answers are found using decision theory.
Two examples illustrate interrogation of the Earth’s subsurface. In a synthetic test, we estimate the cross-sectional area of a subsurface low velocity anomaly by interrogating Bayesian probabilistic tomographic maps. By combining the results of four different nonlinear inversion algorithms, the optimal answer is very close to the true answer. In a field data application, we evaluate the extent of the Irish Sea Sedimentary Basin based on the uncertainties in velocity structure derived from Love wave tomography. This example shows that the computational expense of estimating uncertainties adds explicit value to answers.
This study demonstrates that interrogation theory answers realistic questions about the Earth’s subsurface. The same theory can be used to solve different types of scientific problem - experimental design, interpreting models, expert elicitation and risk estimation - and can be applied in any field of science. One of its most important contributions is to show that fully nonlinear estimates of uncertainty are critical for decision-making in real-world geoscientific problems, potentially justifying their computational expense.
How to cite: Curtis, A., Zhao, X., and Zhang, X.: Interrogating Tomographic Uncertainties for Subsurface Structural Information, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1334, https://doi.org/10.5194/egusphere-egu21-1334, 2021.
EGU21-9615 | vPICO presentations | SM8.1
Hamiltonian Monte Carlo inversion of seismic reflection data in the acoustic approximationAndrea Zunino, Klaus Mosegaard, Christian Boehm, Lars Gebraad, and Andreas Fichtner
The Hamiltonian Monte Carlo method (HMC) is gaining popularity in the geophysical community to fully address nonlinear inverse problems and related uncertainty quantification. We present here an application of HMC to invert seismic data in the acoustic approximation in the context of reflection seismology. We address a 2-D problem, in the form of a vertical cross section where both source and receivers are located near the surface of the model. To solve the forward problem we utilise the finite-difference method with PML absorbing boundary conditions. The observed data are represented by a set of shotgathers.
The crucial aspect for a successful application of the HMC lies in the capability of performing gradient computations in an efficient manner. To this end, we use the adjont state method to compute the gradient of the misfit functional, which has a computational cost of only about twice that of the forward computation, a very efficient strategy. From the collection of samples characterising the posterior distribution obtained with the HMC, we can derive quantities of interest using statistical analysis and assess uncertainties.
We illustrate an application of this methodology on a synthetic test mimicking the setup encountered in exploration problems.
How to cite: Zunino, A., Mosegaard, K., Boehm, C., Gebraad, L., and Fichtner, A.: Hamiltonian Monte Carlo inversion of seismic reflection data in the acoustic approximation, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9615, https://doi.org/10.5194/egusphere-egu21-9615, 2021.
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The Hamiltonian Monte Carlo method (HMC) is gaining popularity in the geophysical community to fully address nonlinear inverse problems and related uncertainty quantification. We present here an application of HMC to invert seismic data in the acoustic approximation in the context of reflection seismology. We address a 2-D problem, in the form of a vertical cross section where both source and receivers are located near the surface of the model. To solve the forward problem we utilise the finite-difference method with PML absorbing boundary conditions. The observed data are represented by a set of shotgathers.
The crucial aspect for a successful application of the HMC lies in the capability of performing gradient computations in an efficient manner. To this end, we use the adjont state method to compute the gradient of the misfit functional, which has a computational cost of only about twice that of the forward computation, a very efficient strategy. From the collection of samples characterising the posterior distribution obtained with the HMC, we can derive quantities of interest using statistical analysis and assess uncertainties.
We illustrate an application of this methodology on a synthetic test mimicking the setup encountered in exploration problems.
How to cite: Zunino, A., Mosegaard, K., Boehm, C., Gebraad, L., and Fichtner, A.: Hamiltonian Monte Carlo inversion of seismic reflection data in the acoustic approximation, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9615, https://doi.org/10.5194/egusphere-egu21-9615, 2021.
EGU21-1330 | vPICO presentations | SM8.1
Bayesian Full-waveform Inversion with Weak PriorsXin Zhang and Andrew Curtis
Seismic full waveform inversion (FWI) produces high resolution images of the subsurface directly from seismic waveforms, and has been applied at global, regional and industrial spatial scales. FWI is traditionally solved using optimization methods, by iteratively updating a model of the subsurface so as to minimize the misfit between observed waveforms and those predicted by linearised (approximate) physics. Due to the nonlinearity of the physical relation between model parameters and seismic waveforms, a good starting model (derived from other methods) and hence strong prior information is required in order that the linearised physical relationships are reasonable in the vicinity of the true solution. Such linearised methods cannot provide accurate estimates of uncertainties, which are required if we are to understand and interpret the results appropriately.
To estimate uncertainties more accurately, nonlinear Bayesian methods have been deployed to solve the FWI problem. Monte Carlo sampling is one such algorithm but it is computationally expensive, and all Markov chain Monte Carlo-based methods are difficult to parallelise fully. Variational inference provides an efficient, fully parallelisable alternative methodology. This is a class of methods that optimize an approximation to a probability distribution describing post-inversion parameter uncertainties. Both Monte Carlo and variational full waveform inversion (VFWI) have been applied previously to solve FWI problems, but only with strong prior information about the velocity structure to limit the space of possible models. Unfortunately such strong information is almost never available in practice. In addition, VFWI has only been applied to wavefield transmission problems in which seismic data are recorded on a receiver array that lies above the structure to be imaged, given known, double-couple (earthquake-like) sources located underneath the same structure. In practice, knowledge of such sources is never definitive, and usually depends circularly on the unknown structure itself. In this study, we present the first application of VFWI to seismic reflection data acquired from known (deliberately fired) near-surface sources. We also apply variational inference (specifically, Stein variational gradient descent) to solve FWI problems with realistic prior information. We perform multiple inversions using data from different frequency ranges, and show that VFWI produces high resolution mean and uncertainty models using both low and high frequency data, and given only weak prior information. This is usually impossible using traditional linearised methods. We conclude that VFWI may be a useful method to produce high resolution images and reliable uncertainties, at least in smaller FWI problems.
How to cite: Zhang, X. and Curtis, A.: Bayesian Full-waveform Inversion with Weak Priors, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1330, https://doi.org/10.5194/egusphere-egu21-1330, 2021.
Seismic full waveform inversion (FWI) produces high resolution images of the subsurface directly from seismic waveforms, and has been applied at global, regional and industrial spatial scales. FWI is traditionally solved using optimization methods, by iteratively updating a model of the subsurface so as to minimize the misfit between observed waveforms and those predicted by linearised (approximate) physics. Due to the nonlinearity of the physical relation between model parameters and seismic waveforms, a good starting model (derived from other methods) and hence strong prior information is required in order that the linearised physical relationships are reasonable in the vicinity of the true solution. Such linearised methods cannot provide accurate estimates of uncertainties, which are required if we are to understand and interpret the results appropriately.
To estimate uncertainties more accurately, nonlinear Bayesian methods have been deployed to solve the FWI problem. Monte Carlo sampling is one such algorithm but it is computationally expensive, and all Markov chain Monte Carlo-based methods are difficult to parallelise fully. Variational inference provides an efficient, fully parallelisable alternative methodology. This is a class of methods that optimize an approximation to a probability distribution describing post-inversion parameter uncertainties. Both Monte Carlo and variational full waveform inversion (VFWI) have been applied previously to solve FWI problems, but only with strong prior information about the velocity structure to limit the space of possible models. Unfortunately such strong information is almost never available in practice. In addition, VFWI has only been applied to wavefield transmission problems in which seismic data are recorded on a receiver array that lies above the structure to be imaged, given known, double-couple (earthquake-like) sources located underneath the same structure. In practice, knowledge of such sources is never definitive, and usually depends circularly on the unknown structure itself. In this study, we present the first application of VFWI to seismic reflection data acquired from known (deliberately fired) near-surface sources. We also apply variational inference (specifically, Stein variational gradient descent) to solve FWI problems with realistic prior information. We perform multiple inversions using data from different frequency ranges, and show that VFWI produces high resolution mean and uncertainty models using both low and high frequency data, and given only weak prior information. This is usually impossible using traditional linearised methods. We conclude that VFWI may be a useful method to produce high resolution images and reliable uncertainties, at least in smaller FWI problems.
How to cite: Zhang, X. and Curtis, A.: Bayesian Full-waveform Inversion with Weak Priors, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1330, https://doi.org/10.5194/egusphere-egu21-1330, 2021.
EGU21-1455 | vPICO presentations | SM8.1
Bayesian Variational Seismic Tomography using Normalizing FlowsXuebin Zhao, Andrew Curtis, and Xin Zhang
Seismic travel time tomography is used widely to image the Earth's interior structure and to infer subsurface properties. Tomography is an inverse problem, and computationally expensive nonlinear inverse methods are often deployed in order to understand uncertainties in the tomographic results. Monte Carlo sampling methods estimate the posterior probability distribution which describes the solution to Bayesian tomographic problems, but they are computationally expensive and often intractable for high dimensional model spaces and large data sets due to the curse of dimensionality. We therefore introduce a new method of variational inference to solve Bayesian seismic tomography problems using optimization methods, while still providing fully nonlinear, probabilistic results. The new method, known as normalizing flows, warps a simple and known distribution (for example a Uniform or Gaussian distribution) into an optimal approximation to the posterior distribution through a chain of invertible transforms. These transforms are selected from a library of suitable functions, some of which invoke neural networks internally. We test the method using both synthetic and field data. The results show that normalizing flows can produce similar mean and uncertainty maps to those obtained from both Monte Carlo and another variational method (Stein varational gradient descent), at significantly decreased computational cost. In our tomographic tests, normalizing flows improves both accuracy and efficiency, producing maps of UK surface wave speeds and their uncertainties at the finest resolution and the lowest computational cost to-date, allowing results to be interrogated efficiently and quantitatively for subsurface structure.
How to cite: Zhao, X., Curtis, A., and Zhang, X.: Bayesian Variational Seismic Tomography using Normalizing Flows, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1455, https://doi.org/10.5194/egusphere-egu21-1455, 2021.
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Seismic travel time tomography is used widely to image the Earth's interior structure and to infer subsurface properties. Tomography is an inverse problem, and computationally expensive nonlinear inverse methods are often deployed in order to understand uncertainties in the tomographic results. Monte Carlo sampling methods estimate the posterior probability distribution which describes the solution to Bayesian tomographic problems, but they are computationally expensive and often intractable for high dimensional model spaces and large data sets due to the curse of dimensionality. We therefore introduce a new method of variational inference to solve Bayesian seismic tomography problems using optimization methods, while still providing fully nonlinear, probabilistic results. The new method, known as normalizing flows, warps a simple and known distribution (for example a Uniform or Gaussian distribution) into an optimal approximation to the posterior distribution through a chain of invertible transforms. These transforms are selected from a library of suitable functions, some of which invoke neural networks internally. We test the method using both synthetic and field data. The results show that normalizing flows can produce similar mean and uncertainty maps to those obtained from both Monte Carlo and another variational method (Stein varational gradient descent), at significantly decreased computational cost. In our tomographic tests, normalizing flows improves both accuracy and efficiency, producing maps of UK surface wave speeds and their uncertainties at the finest resolution and the lowest computational cost to-date, allowing results to be interrogated efficiently and quantitatively for subsurface structure.
How to cite: Zhao, X., Curtis, A., and Zhang, X.: Bayesian Variational Seismic Tomography using Normalizing Flows, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1455, https://doi.org/10.5194/egusphere-egu21-1455, 2021.
EGU21-16089 | vPICO presentations | SM8.1
Accelerating inverse problems in seismology using adjoint-based machine learningLars Gebraad, Sölvi Thrastarson, Andrea Zunino, and Andreas Fichtner
Uncertainty quantification is an essential part of many studies in Earth science. It allows us, for example, to assess the quality of tomographic reconstructions, quantify hypotheses and make physics-based risk assessments. In recent years there has been a surge in applications of uncertainty quantification in seismological inverse problems. This is mainly due to increasing computational power and the ‘discovery’ of optimal use cases for many algorithms (e.g., gradient-based Markov Chain Monte Carlo (MCMC). Performing Bayesian inference using these methods allows seismologists to perform advanced uncertainty quantification. However, oftentimes, Bayesian inference is still prohibitively expensive due to large parameter spaces and computationally expensive physics.
Simultaneously, machine learning has found its way into parameter estimation in geosciences. Recent works show that machine learning both allows one to accelerate repetitive inferences [e.g. Shahraeeni & Curtis 2011, Cao et al. 2020] as well as speed up single-instance Monte Carlo algorithms using surrogate networks [Aleardi 2020]. These advances allow seismologists to use machine learning as a tool to bring accurate inference on the subsurface to scale.
In this work, we propose the novel inclusion of adjoint modelling in machine learning accelerated inverse problems. The aforementioned references train machine learning models on observations of the misfit function. This is done with the aim of creating surrogate but accelerated models for the misfit computations, which in turn allows one to compute this function and its gradients much faster. This approach ignores that many physical models have an adjoint state, allowing one to compute gradients using only one additional simulation.
The inclusion of this information within gradient-based sampling creates performance gains in both training the surrogate and the sampling of the true posterior. We show how machine learning models that approximate misfits and gradients specifically trained using adjoint methods accelerate various types of inversions and bring Bayesian inference to scale. Practically, the proposed method simply allows us to utilize information from previous MCMC samples in the algorithm proposal step.
The application of the proposed machinery is in settings where models are extensively and repetitively run. Markov chain Monte Carlo algorithms, which may require millions of evaluations of the forward modelling equations, can be accelerated by off-loading these simulations to neural nets. This approach is also promising for tomographic monitoring, where experiments are repeatedly performed. Lastly, the efficiently trained neural nets can be used to learn a likelihood for a given dataset, to which subsequently different priors can be efficiently applied. We show examples of all these use cases.
Lars Gebraad, Christian Boehm and Andreas Fichtner, 2020: Bayesian Elastic Full‐Waveform Inversion Using Hamiltonian Monte Carlo.
Ruikun Cao, Stephanie Earp, Sjoerd A. L. de Ridder, Andrew Curtis, and Erica Galetti, 2020: Near-real-time near-surface 3D seismic velocity and uncertainty models by wavefield gradiometry and neural network inversion of ambient seismic noise.
Mohammad S. Shahraeeni and Andrew Curtis, 2011: Fast probabilistic nonlinear petrophysical inversion.
Mattia Aleardi, 2020: Combining discrete cosine transform and convolutional neural networks to speed up the Hamiltonian Monte Carlo inversion of pre‐stack seismic data.
How to cite: Gebraad, L., Thrastarson, S., Zunino, A., and Fichtner, A.: Accelerating inverse problems in seismology using adjoint-based machine learning, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16089, https://doi.org/10.5194/egusphere-egu21-16089, 2021.
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Uncertainty quantification is an essential part of many studies in Earth science. It allows us, for example, to assess the quality of tomographic reconstructions, quantify hypotheses and make physics-based risk assessments. In recent years there has been a surge in applications of uncertainty quantification in seismological inverse problems. This is mainly due to increasing computational power and the ‘discovery’ of optimal use cases for many algorithms (e.g., gradient-based Markov Chain Monte Carlo (MCMC). Performing Bayesian inference using these methods allows seismologists to perform advanced uncertainty quantification. However, oftentimes, Bayesian inference is still prohibitively expensive due to large parameter spaces and computationally expensive physics.
Simultaneously, machine learning has found its way into parameter estimation in geosciences. Recent works show that machine learning both allows one to accelerate repetitive inferences [e.g. Shahraeeni & Curtis 2011, Cao et al. 2020] as well as speed up single-instance Monte Carlo algorithms using surrogate networks [Aleardi 2020]. These advances allow seismologists to use machine learning as a tool to bring accurate inference on the subsurface to scale.
In this work, we propose the novel inclusion of adjoint modelling in machine learning accelerated inverse problems. The aforementioned references train machine learning models on observations of the misfit function. This is done with the aim of creating surrogate but accelerated models for the misfit computations, which in turn allows one to compute this function and its gradients much faster. This approach ignores that many physical models have an adjoint state, allowing one to compute gradients using only one additional simulation.
The inclusion of this information within gradient-based sampling creates performance gains in both training the surrogate and the sampling of the true posterior. We show how machine learning models that approximate misfits and gradients specifically trained using adjoint methods accelerate various types of inversions and bring Bayesian inference to scale. Practically, the proposed method simply allows us to utilize information from previous MCMC samples in the algorithm proposal step.
The application of the proposed machinery is in settings where models are extensively and repetitively run. Markov chain Monte Carlo algorithms, which may require millions of evaluations of the forward modelling equations, can be accelerated by off-loading these simulations to neural nets. This approach is also promising for tomographic monitoring, where experiments are repeatedly performed. Lastly, the efficiently trained neural nets can be used to learn a likelihood for a given dataset, to which subsequently different priors can be efficiently applied. We show examples of all these use cases.
Lars Gebraad, Christian Boehm and Andreas Fichtner, 2020: Bayesian Elastic Full‐Waveform Inversion Using Hamiltonian Monte Carlo.
Ruikun Cao, Stephanie Earp, Sjoerd A. L. de Ridder, Andrew Curtis, and Erica Galetti, 2020: Near-real-time near-surface 3D seismic velocity and uncertainty models by wavefield gradiometry and neural network inversion of ambient seismic noise.
Mohammad S. Shahraeeni and Andrew Curtis, 2011: Fast probabilistic nonlinear petrophysical inversion.
Mattia Aleardi, 2020: Combining discrete cosine transform and convolutional neural networks to speed up the Hamiltonian Monte Carlo inversion of pre‐stack seismic data.
How to cite: Gebraad, L., Thrastarson, S., Zunino, A., and Fichtner, A.: Accelerating inverse problems in seismology using adjoint-based machine learning, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16089, https://doi.org/10.5194/egusphere-egu21-16089, 2021.
EGU21-3371 | vPICO presentations | SM8.1
HypoSVI: Hypocenter inversion with Stein Variational Inference and Physics Informed Neural NetworksJonathan Smith, Zachary Ross, Kamyar Azizzadenesheli, and Jack Muir
High resolution earthquake hypocentral locations are of critical importance for understanding the regional context driving seismicity. We introduce a scheme to reliably approximate a hypocenter posterior in a continuous domain that relies on recent advances in deep learning.
Our method relies on a differentiable forward model in the form of a deep neural network, which is trained to solve the Eikonal equation (EikoNet). EikoNet can rapidly determine the travel-time between any source-receiver pair for a non-gridded solution. We demonstrate the robustness of these travel-time solutions are for a series of complex velocity models.
For the inverse problem, we utilize Stein Variational Inference, which is a recent approximate inference procedure that iteratively updates a configuration of particles to approximate a target posterior by minimizing the so-called Stein discrepancy. The gradients of this objective function can be rapidly calculated due to the differentiability of the EikoNet. The particle locations are updated until convergence, after which we utilize clustering techniques and kernel density methods to determine the optimal hypocenter and its uncertainty.
The inversion procedure outlined in this work is validated using a series of synthetic tests to determine the parameter optimisation and the validity for large observational datasets, which can locate earthquakes in 439s per event for 2039 observations. In addition, we apply this technique to a case study of seismicity in the Southern California region for earthquakes from 2019.
How to cite: Smith, J., Ross, Z., Azizzadenesheli, K., and Muir, J.: HypoSVI: Hypocenter inversion with Stein Variational Inference and Physics Informed Neural Networks, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3371, https://doi.org/10.5194/egusphere-egu21-3371, 2021.
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We are sorry, but presentations are only available for users who registered for the conference. Thank you.
High resolution earthquake hypocentral locations are of critical importance for understanding the regional context driving seismicity. We introduce a scheme to reliably approximate a hypocenter posterior in a continuous domain that relies on recent advances in deep learning.
Our method relies on a differentiable forward model in the form of a deep neural network, which is trained to solve the Eikonal equation (EikoNet). EikoNet can rapidly determine the travel-time between any source-receiver pair for a non-gridded solution. We demonstrate the robustness of these travel-time solutions are for a series of complex velocity models.
For the inverse problem, we utilize Stein Variational Inference, which is a recent approximate inference procedure that iteratively updates a configuration of particles to approximate a target posterior by minimizing the so-called Stein discrepancy. The gradients of this objective function can be rapidly calculated due to the differentiability of the EikoNet. The particle locations are updated until convergence, after which we utilize clustering techniques and kernel density methods to determine the optimal hypocenter and its uncertainty.
The inversion procedure outlined in this work is validated using a series of synthetic tests to determine the parameter optimisation and the validity for large observational datasets, which can locate earthquakes in 439s per event for 2039 observations. In addition, we apply this technique to a case study of seismicity in the Southern California region for earthquakes from 2019.
How to cite: Smith, J., Ross, Z., Azizzadenesheli, K., and Muir, J.: HypoSVI: Hypocenter inversion with Stein Variational Inference and Physics Informed Neural Networks, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3371, https://doi.org/10.5194/egusphere-egu21-3371, 2021.
SM8.2 – Physics-based earthquake modeling and engineering
EGU21-14875 | vPICO presentations | SM8.2
Complex rupture dynamics of the 2020 Mw 6.8 Elazığ (Sivrice) earthquake, TurkeyFrantišek Gallovič, Jiří Zahradník, Vladimír Plicka, Efthimios Sokos, Christos Evangelidis, Ioannis Fountoulakis, and Fatih Turhan
The 2020 Mw 6.8 Elazığ (Sivrice) earthquake occurred on the Pütürge segment of the East Anatolian Fault zone. This strike-slip segment is situated between strong earthquakes that happened 100–150 years ago, and, since that time, the segment remained with eight Mw5-6 events, but with no Mw 6+. We relocate the mainshock and aftershock sequence and infer basic characteristics of the event using the ISOLA multiple point source approach and backpropagation of S-waveforms from local strong-motion recordings. Together with clear secondary P wave onsets identified in the recordings, the results suggest complex rupture propagation with reversal of the rupture propagation. We apply a recently developed Bayesian dynamic source inversion with slip-weakening friction and spatially inhomogeneous stress and friction parameters to gain better insight into the rupture process. Using high-quality near field recordings in the low-frequency range (<0.3Hz), we obtain a complex dynamic rupture model explaining the weak rupture initiation followed by a cascade of at least three rupture episodes, including the rupture reversal. The dynamic model explains significant features of the recordings even in a broader frequency range interesting for seismic engineering applications (<2.5Hz), e.g., a directivity pulse associated with rupturing the event’s strongest asperity with 4 m of slip and local stress drop of 40 MPa. We show that by reducing the initial stress in the top 10 km by 10%, the rupture fails to develop into the larger event, finishing as an Mw 5.8 earthquake. Considering the latter experiment corresponds to an earlier state of the fault in the seismic cycle, we hypothesize that the interseismic M5+ events on the Pütürge segment were undeveloped rudiments of potentially large events. Thus, the fault seems to have been ready for the Mw6.8 earthquake only by the time of the earthquake occurrence in 2020. This suggests that at the time of the Elazığ earthquake initiation, the final Mw6.8 magnitude was not determined, making it a treacherous case for early warning systems.
How to cite: Gallovič, F., Zahradník, J., Plicka, V., Sokos, E., Evangelidis, C., Fountoulakis, I., and Turhan, F.: Complex rupture dynamics of the 2020 Mw 6.8 Elazığ (Sivrice) earthquake, Turkey, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14875, https://doi.org/10.5194/egusphere-egu21-14875, 2021.
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Please use the buttons below to download the presentation materials or to visit the external website where the presentation is linked. Regarding the external link, please note that Copernicus Meetings cannot accept any liability for the content and the website you will visit.
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The 2020 Mw 6.8 Elazığ (Sivrice) earthquake occurred on the Pütürge segment of the East Anatolian Fault zone. This strike-slip segment is situated between strong earthquakes that happened 100–150 years ago, and, since that time, the segment remained with eight Mw5-6 events, but with no Mw 6+. We relocate the mainshock and aftershock sequence and infer basic characteristics of the event using the ISOLA multiple point source approach and backpropagation of S-waveforms from local strong-motion recordings. Together with clear secondary P wave onsets identified in the recordings, the results suggest complex rupture propagation with reversal of the rupture propagation. We apply a recently developed Bayesian dynamic source inversion with slip-weakening friction and spatially inhomogeneous stress and friction parameters to gain better insight into the rupture process. Using high-quality near field recordings in the low-frequency range (<0.3Hz), we obtain a complex dynamic rupture model explaining the weak rupture initiation followed by a cascade of at least three rupture episodes, including the rupture reversal. The dynamic model explains significant features of the recordings even in a broader frequency range interesting for seismic engineering applications (<2.5Hz), e.g., a directivity pulse associated with rupturing the event’s strongest asperity with 4 m of slip and local stress drop of 40 MPa. We show that by reducing the initial stress in the top 10 km by 10%, the rupture fails to develop into the larger event, finishing as an Mw 5.8 earthquake. Considering the latter experiment corresponds to an earlier state of the fault in the seismic cycle, we hypothesize that the interseismic M5+ events on the Pütürge segment were undeveloped rudiments of potentially large events. Thus, the fault seems to have been ready for the Mw6.8 earthquake only by the time of the earthquake occurrence in 2020. This suggests that at the time of the Elazığ earthquake initiation, the final Mw6.8 magnitude was not determined, making it a treacherous case for early warning systems.
How to cite: Gallovič, F., Zahradník, J., Plicka, V., Sokos, E., Evangelidis, C., Fountoulakis, I., and Turhan, F.: Complex rupture dynamics of the 2020 Mw 6.8 Elazığ (Sivrice) earthquake, Turkey, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14875, https://doi.org/10.5194/egusphere-egu21-14875, 2021.
EGU21-8882 | vPICO presentations | SM8.2
Embedding Spectral Decomposition Results in Broadband Simulation: Application to Rhine Graben AreaHoby Razafindrakoto, Fabrice Cotton, Dino Bindi, Marco Pilz, and Robert Graves
Over the past decade, there is growing consensus that physics-based simulations can be utilized in engineering applications. However, for the simulations to be accepted, they need to be calibrated and validated. This study presents the results of ground motion simulation calibration and validation using earthquakes that occurred in the Upper Rhine Graben with a modified version of the Graves-Pitarka (GP) hybrid ground-motion simulation methodology implemented on the Southern California Earthquake Center Broadband Platform, which uses an improved high-frequency computation. To calibrate the HF simulation, we take advantage of the growth of seismological data (including weak motions) in the region and the ability to evaluate critical seismic parameters such as anelastic attenuation, stress drop, and site effects through spectral decomposition methods (separate site-source-propagation from the datasets). Hence in the simulation, the adopted anelastic attenuation and stress parameter are defined based on the spectral decomposition results. The additional modification of the standard GP method is the incorporation of compressional wave in the HF motion.
Results are compared with observations and simulations from the unmodified GP approach; we also use a range of ground motion intensity measures as summary statistics. We found that in general, the modification in the HF part (e.g., incorporation of compressional waves) was necessary to improve the fit with observations. Our findings also validate the fact that parameters from the spectral decomposition are giving well-calibrated time-histories (in terms of frequency and amplitude) when used as input parameters of the broadband simulations. The findings in this study support the incorporation of scenario-based ground motion simulations for use in the characterization of seismic hazard and other engineering applications. For simulation of future earthquakes, instead of using event-specific stress-drops, we use the average stress-drops taken from the distribution of the stress drops derived from spectral decomposition.
How to cite: Razafindrakoto, H., Cotton, F., Bindi, D., Pilz, M., and Graves, R.: Embedding Spectral Decomposition Results in Broadband Simulation: Application to Rhine Graben Area, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8882, https://doi.org/10.5194/egusphere-egu21-8882, 2021.
Over the past decade, there is growing consensus that physics-based simulations can be utilized in engineering applications. However, for the simulations to be accepted, they need to be calibrated and validated. This study presents the results of ground motion simulation calibration and validation using earthquakes that occurred in the Upper Rhine Graben with a modified version of the Graves-Pitarka (GP) hybrid ground-motion simulation methodology implemented on the Southern California Earthquake Center Broadband Platform, which uses an improved high-frequency computation. To calibrate the HF simulation, we take advantage of the growth of seismological data (including weak motions) in the region and the ability to evaluate critical seismic parameters such as anelastic attenuation, stress drop, and site effects through spectral decomposition methods (separate site-source-propagation from the datasets). Hence in the simulation, the adopted anelastic attenuation and stress parameter are defined based on the spectral decomposition results. The additional modification of the standard GP method is the incorporation of compressional wave in the HF motion.
Results are compared with observations and simulations from the unmodified GP approach; we also use a range of ground motion intensity measures as summary statistics. We found that in general, the modification in the HF part (e.g., incorporation of compressional waves) was necessary to improve the fit with observations. Our findings also validate the fact that parameters from the spectral decomposition are giving well-calibrated time-histories (in terms of frequency and amplitude) when used as input parameters of the broadband simulations. The findings in this study support the incorporation of scenario-based ground motion simulations for use in the characterization of seismic hazard and other engineering applications. For simulation of future earthquakes, instead of using event-specific stress-drops, we use the average stress-drops taken from the distribution of the stress drops derived from spectral decomposition.
How to cite: Razafindrakoto, H., Cotton, F., Bindi, D., Pilz, M., and Graves, R.: Embedding Spectral Decomposition Results in Broadband Simulation: Application to Rhine Graben Area, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8882, https://doi.org/10.5194/egusphere-egu21-8882, 2021.
EGU21-9463 | vPICO presentations | SM8.2
Spatial Variability of Near-field Ground Motions from Pseudo-Dynamic Rupture SimulationsJayalakshmi Sivasubramonian and Paul Martin Mai
We analyze the effect of earthquake source parameters on ground-motion variability based on near-field wavefield simulations for large earthquakes. We quantify residuals in simulated ground motion intensities with respect to observed records, the associated variabilities are then quantified with respect to source-to-site distance and azimuth. Additionally, we compute the variabilities due to complexities in rupture models by considering variations in hypocenter location and slip distribution that are implemented a new Pseudo-Dynamic (PD) source parameterization.
In this study, we consider two past events – the Mw 6.9 Iwate Miyagi Earthquake (2008), Japan, and the Mw 6.5 Imperial Valley Earthquake, California (1979). Assuming for each case a 1D velocity structure, we first generate ensembles of rupture models using the pseudo-dynamic approach of Guatteri et.al (2004), by assuming different hypocenter and asperities locations (Mai and Beroza, 2002, Mai et al., 2005; Thingbaijam and Mai, 2016). In order to efficiently include variations in high-frequency radiation, we adopt a PD parameterization for rupture velocity and rise time distribution in our rupture model generator. Overall, we generate a database of rupture models with 50 scenarios for each source parameterization. Synthetic near-field waveforms (0.1-2.5Hz) are computed out to Joyner-Boore distances Rjb ~ 150km using a discrete-wavenumber finite-element method (Olson et al., 1984). Our results show that ground-motion variability is most sensitive to hypocenter locations on the fault plane. We also find that locations of asperities do not alter waveforms significantly for a given hypocenter, rupture velocity and rise time distribution. We compare the scenario-event simulated ground motions with simulations that use the rupture models from the SRCMOD database (Mai and Thingbaijam, 2014), and find that the PD method is capable of reducing the ground motion variability at high frequencies. The PD models are calibrated by comparing the mean residuals with the residuals from SRCMOD models. We present the variability due to each source parameterization as a function of Joyner-Boore distance and azimuth at different natural period.
How to cite: Sivasubramonian, J. and Mai, P. M.: Spatial Variability of Near-field Ground Motions from Pseudo-Dynamic Rupture Simulations, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9463, https://doi.org/10.5194/egusphere-egu21-9463, 2021.
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We analyze the effect of earthquake source parameters on ground-motion variability based on near-field wavefield simulations for large earthquakes. We quantify residuals in simulated ground motion intensities with respect to observed records, the associated variabilities are then quantified with respect to source-to-site distance and azimuth. Additionally, we compute the variabilities due to complexities in rupture models by considering variations in hypocenter location and slip distribution that are implemented a new Pseudo-Dynamic (PD) source parameterization.
In this study, we consider two past events – the Mw 6.9 Iwate Miyagi Earthquake (2008), Japan, and the Mw 6.5 Imperial Valley Earthquake, California (1979). Assuming for each case a 1D velocity structure, we first generate ensembles of rupture models using the pseudo-dynamic approach of Guatteri et.al (2004), by assuming different hypocenter and asperities locations (Mai and Beroza, 2002, Mai et al., 2005; Thingbaijam and Mai, 2016). In order to efficiently include variations in high-frequency radiation, we adopt a PD parameterization for rupture velocity and rise time distribution in our rupture model generator. Overall, we generate a database of rupture models with 50 scenarios for each source parameterization. Synthetic near-field waveforms (0.1-2.5Hz) are computed out to Joyner-Boore distances Rjb ~ 150km using a discrete-wavenumber finite-element method (Olson et al., 1984). Our results show that ground-motion variability is most sensitive to hypocenter locations on the fault plane. We also find that locations of asperities do not alter waveforms significantly for a given hypocenter, rupture velocity and rise time distribution. We compare the scenario-event simulated ground motions with simulations that use the rupture models from the SRCMOD database (Mai and Thingbaijam, 2014), and find that the PD method is capable of reducing the ground motion variability at high frequencies. The PD models are calibrated by comparing the mean residuals with the residuals from SRCMOD models. We present the variability due to each source parameterization as a function of Joyner-Boore distance and azimuth at different natural period.
How to cite: Sivasubramonian, J. and Mai, P. M.: Spatial Variability of Near-field Ground Motions from Pseudo-Dynamic Rupture Simulations, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9463, https://doi.org/10.5194/egusphere-egu21-9463, 2021.
EGU21-11998 | vPICO presentations | SM8.2
High-frequency ground-motion variability for rough-fault rupturesJagdish Chandra Vyas, Martin Galis, and Paul Martin Mai
Geological observations show variations in fault-surface topography not only at large scale (segmentation) but also at small scale (roughness). These geometrical complexities strongly affect the stress distribution and frictional strength of the fault, and therefore control the earthquake rupture process and resulting ground-shaking. Previous studies examined fault-segmentation effects on ground-shaking, but our understanding of fault-roughness effects on seismic wavefield radiation and earthquake ground-motion is still limited.
In this study we examine the effects of fault roughness on ground-shaking variability as a function of distance based on 3D dynamic rupture simulations. We consider linear slip-weakening friction, variations of fault-roughness parametrizations, and alternative nucleation positions (unilateral and bilateral ruptures). We use generalized finite difference method to compute synthetic waveforms (max. resolved frequency 5.75 Hz) at numerous surface sites to carry out statistical analysis.
Our simulations reveal that ground-motion variability from unilateral ruptures is almost independent of distance from the fault, with comparable or higher values than estimates from ground-motion prediction equations (e.g., Boore and Atkinson, 2008; Campbell and Bozornia, 2008). However, ground-motion variability from bilateral ruptures decreases with increasing distance, in contrast to previous studies (e.g., Imtiaz et. al., 2015) who observe an increasing trend with distance. Ground-shaking variability from unilateral ruptures is higher than for bilateral ruptures, a feature due to intricate seismic radiation patterns related to fault roughness and hypocenter location. Moreover, ground-shaking variability for rougher faults is lower than for smoother faults. As fault roughness increases the difference in ground-shaking variabilities between unilateral and bilateral ruptures increases. In summary, our simulations help develop a fundamental understanding of ground-motion variability at high frequencies (~ 6 Hz) due small-scale geometrical fault-surface variations.
How to cite: Vyas, J. C., Galis, M., and Mai, P. M.: High-frequency ground-motion variability for rough-fault ruptures , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11998, https://doi.org/10.5194/egusphere-egu21-11998, 2021.
Geological observations show variations in fault-surface topography not only at large scale (segmentation) but also at small scale (roughness). These geometrical complexities strongly affect the stress distribution and frictional strength of the fault, and therefore control the earthquake rupture process and resulting ground-shaking. Previous studies examined fault-segmentation effects on ground-shaking, but our understanding of fault-roughness effects on seismic wavefield radiation and earthquake ground-motion is still limited.
In this study we examine the effects of fault roughness on ground-shaking variability as a function of distance based on 3D dynamic rupture simulations. We consider linear slip-weakening friction, variations of fault-roughness parametrizations, and alternative nucleation positions (unilateral and bilateral ruptures). We use generalized finite difference method to compute synthetic waveforms (max. resolved frequency 5.75 Hz) at numerous surface sites to carry out statistical analysis.
Our simulations reveal that ground-motion variability from unilateral ruptures is almost independent of distance from the fault, with comparable or higher values than estimates from ground-motion prediction equations (e.g., Boore and Atkinson, 2008; Campbell and Bozornia, 2008). However, ground-motion variability from bilateral ruptures decreases with increasing distance, in contrast to previous studies (e.g., Imtiaz et. al., 2015) who observe an increasing trend with distance. Ground-shaking variability from unilateral ruptures is higher than for bilateral ruptures, a feature due to intricate seismic radiation patterns related to fault roughness and hypocenter location. Moreover, ground-shaking variability for rougher faults is lower than for smoother faults. As fault roughness increases the difference in ground-shaking variabilities between unilateral and bilateral ruptures increases. In summary, our simulations help develop a fundamental understanding of ground-motion variability at high frequencies (~ 6 Hz) due small-scale geometrical fault-surface variations.
How to cite: Vyas, J. C., Galis, M., and Mai, P. M.: High-frequency ground-motion variability for rough-fault ruptures , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11998, https://doi.org/10.5194/egusphere-egu21-11998, 2021.
EGU21-16183 | vPICO presentations | SM8.2
10 July 1894 Istanbul Earthquake: Comparing Damages and Ground Motion SimulationsNesrin Yenihayat, Eser Çaktı, and Karin Şeşetyan
One of the major earthquakes that resulted in intense damages in Istanbul and its neighborhoods took place on 10 July 1894. The 1894 earthquake resulted in 474 losses of life and 482 injuries. Around 21,000 dwellings were damaged, which is a number that corresponds to 1/7 of the total dwellings of the city at that time. Without any doubt, the exact loss of life was higher. Because of the censorship, the exact loss numbers remained unknown. There is still no consensus about its magnitude, epicentral location, and rupture of length. Even though the hardness of studying with historical records due to their uncertainties and discrepancies, researchers should enlighten the source parameters of the historical earthquakes to minimize the effect of future disasters especially for the cities located close to the most active fault lines as Istanbul. The main target of this study is to enlighten possible source properties of the 1894 earthquake with the help of observed damage distribution and stochastic ground motion simulations. In this paper, stochastic based ground motion scenarios will be performed for the 10 July 1894 Istanbul earthquake, using a finite fault simulation approach with a dynamic corner frequency and the results will be compared with our intensity map obtained from observed damage distributions. To do this, in the first step, obtained damage information from various sources has been presented, evaluated, and interpreted. Secondly, we prepared an intensity map associated with the 1894 earthquake based on macro-seismic information, and damage analysis and classification. For generating ground motions with a stochastic finite fault simulation approach, the EXSIM 2012 software has been used. Using EXSIM, several scenarios are modeled with different source, path, and site parameters. Initial source properties have been obtained from findings of our previous study on the simulation of the 26 September 2019 Silivri (Istanbul) earthquake with Mw 5.8. With the comparison of spatial distributions of the ground motion intensity parameters to the obtained damage and intensity maps, we estimate the optimum location and source parameters of the 1894 Earthquake.
How to cite: Yenihayat, N., Çaktı, E., and Şeşetyan, K.: 10 July 1894 Istanbul Earthquake: Comparing Damages and Ground Motion Simulations, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16183, https://doi.org/10.5194/egusphere-egu21-16183, 2021.
One of the major earthquakes that resulted in intense damages in Istanbul and its neighborhoods took place on 10 July 1894. The 1894 earthquake resulted in 474 losses of life and 482 injuries. Around 21,000 dwellings were damaged, which is a number that corresponds to 1/7 of the total dwellings of the city at that time. Without any doubt, the exact loss of life was higher. Because of the censorship, the exact loss numbers remained unknown. There is still no consensus about its magnitude, epicentral location, and rupture of length. Even though the hardness of studying with historical records due to their uncertainties and discrepancies, researchers should enlighten the source parameters of the historical earthquakes to minimize the effect of future disasters especially for the cities located close to the most active fault lines as Istanbul. The main target of this study is to enlighten possible source properties of the 1894 earthquake with the help of observed damage distribution and stochastic ground motion simulations. In this paper, stochastic based ground motion scenarios will be performed for the 10 July 1894 Istanbul earthquake, using a finite fault simulation approach with a dynamic corner frequency and the results will be compared with our intensity map obtained from observed damage distributions. To do this, in the first step, obtained damage information from various sources has been presented, evaluated, and interpreted. Secondly, we prepared an intensity map associated with the 1894 earthquake based on macro-seismic information, and damage analysis and classification. For generating ground motions with a stochastic finite fault simulation approach, the EXSIM 2012 software has been used. Using EXSIM, several scenarios are modeled with different source, path, and site parameters. Initial source properties have been obtained from findings of our previous study on the simulation of the 26 September 2019 Silivri (Istanbul) earthquake with Mw 5.8. With the comparison of spatial distributions of the ground motion intensity parameters to the obtained damage and intensity maps, we estimate the optimum location and source parameters of the 1894 Earthquake.
How to cite: Yenihayat, N., Çaktı, E., and Şeşetyan, K.: 10 July 1894 Istanbul Earthquake: Comparing Damages and Ground Motion Simulations, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16183, https://doi.org/10.5194/egusphere-egu21-16183, 2021.
EGU21-597 | vPICO presentations | SM8.2
Can Machine Learning help us in [re]assessing historical earthquakes?María del Puy Papí Isaba, Christa Hammerl, Maurizio Mattesini, and Vicenta María Elisa Buforn Peiró
Tyrol is one of the provinces with the highest seismicity in Austria. Most of the stronger historical earthquakes occurred around Innsbruck and Hall in Tirol (1572, 1670, 1689).
Within the framework of the project[1] “Historical and recent earthquake activity in Tyrol - sources, data, seismological analysis”, a study was carried out from 2014-2020, which mainly deals with historical earthquakes in Tyrol up to 1900 but also in detail with damaging earthquakes in Tyrol in the 20th century. The project’s purpose was to create a new earthquake catalog for Tyrol, which for the first time also includes Macroseismic/Intensity Data Points (M/IDPs).
An essential aspect of this study is that the sources and literature references used for all Tyrolean earthquakes up to 1900 are largely documented. Furthermore, selected damaging earthquakes of the 20th century are reported in detail. Numerous Tyrolean archives, such as the Tyrolean Provincial Archives, and the City Archives of Hall in Tyrol, were searched for contemporary earthquake sources. Likewise, the seismic archive of the Austrian Seismological Service at ZAMG (Zentralanstalt für Meteorologie und Geodynamik) contains a wealth of valuable recent information, such as the questionnaires on earthquakes of the entire 20th century.
The very time-consuming research and documentation are followed by the conversion of the written information into earthquake parameters. Briefly outlined, this comprises the following working steps: Interpretation of the sources, assignment of geographical coordinates to the pieces of evidence, evaluation of the intensity according to the European Macroseismic Scale (EMS-98), (re)calculation of the focal parameters of all damaging earthquakes and numerous newly found earthquakes.
The latter is the content of this presentation, namely to (re-)evaluate the focal parameters for historical and recent earthquakes in Tyrol for the first time using the intensity prediction equations (IPE) with the Grid Search (GS) technique. GS has been widely used in many Machine Learning types of research when it comes to hyperparameter optimization, which in this study corresponds to the earthquake focal parameters.
We used IDPs whose intensities were mostly assessed from contemporary historical sources, such as annals, chronicles, questionnaires, newspapers, etc.
A total of 1750 M/IDPs for 35 damaging earthquakes from the Austrian Earthquake Catalogue (AEC2020) could be determined based on the historical sources. The focal parameters for these earthquakes were reevaluated by means of the IPE and GS.
Likewise, 726 new M/IDPs from a total of 154 non-damaging earthquakes not yet included in the AEC2020 were determined. For 38 of them, it was possible to calculate new sets of focal parameters.
Problems encountered, accuracy, and error of the results will be introduced in the presentation.
How to cite: Papí Isaba, M. P., Hammerl, C., Mattesini, M., and Buforn Peiró, V. M. E.: Can Machine Learning help us in [re]assessing historical earthquakes?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-597, https://doi.org/10.5194/egusphere-egu21-597, 2021.
Tyrol is one of the provinces with the highest seismicity in Austria. Most of the stronger historical earthquakes occurred around Innsbruck and Hall in Tirol (1572, 1670, 1689).
Within the framework of the project[1] “Historical and recent earthquake activity in Tyrol - sources, data, seismological analysis”, a study was carried out from 2014-2020, which mainly deals with historical earthquakes in Tyrol up to 1900 but also in detail with damaging earthquakes in Tyrol in the 20th century. The project’s purpose was to create a new earthquake catalog for Tyrol, which for the first time also includes Macroseismic/Intensity Data Points (M/IDPs).
An essential aspect of this study is that the sources and literature references used for all Tyrolean earthquakes up to 1900 are largely documented. Furthermore, selected damaging earthquakes of the 20th century are reported in detail. Numerous Tyrolean archives, such as the Tyrolean Provincial Archives, and the City Archives of Hall in Tyrol, were searched for contemporary earthquake sources. Likewise, the seismic archive of the Austrian Seismological Service at ZAMG (Zentralanstalt für Meteorologie und Geodynamik) contains a wealth of valuable recent information, such as the questionnaires on earthquakes of the entire 20th century.
The very time-consuming research and documentation are followed by the conversion of the written information into earthquake parameters. Briefly outlined, this comprises the following working steps: Interpretation of the sources, assignment of geographical coordinates to the pieces of evidence, evaluation of the intensity according to the European Macroseismic Scale (EMS-98), (re)calculation of the focal parameters of all damaging earthquakes and numerous newly found earthquakes.
The latter is the content of this presentation, namely to (re-)evaluate the focal parameters for historical and recent earthquakes in Tyrol for the first time using the intensity prediction equations (IPE) with the Grid Search (GS) technique. GS has been widely used in many Machine Learning types of research when it comes to hyperparameter optimization, which in this study corresponds to the earthquake focal parameters.
We used IDPs whose intensities were mostly assessed from contemporary historical sources, such as annals, chronicles, questionnaires, newspapers, etc.
A total of 1750 M/IDPs for 35 damaging earthquakes from the Austrian Earthquake Catalogue (AEC2020) could be determined based on the historical sources. The focal parameters for these earthquakes were reevaluated by means of the IPE and GS.
Likewise, 726 new M/IDPs from a total of 154 non-damaging earthquakes not yet included in the AEC2020 were determined. For 38 of them, it was possible to calculate new sets of focal parameters.
Problems encountered, accuracy, and error of the results will be introduced in the presentation.
How to cite: Papí Isaba, M. P., Hammerl, C., Mattesini, M., and Buforn Peiró, V. M. E.: Can Machine Learning help us in [re]assessing historical earthquakes?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-597, https://doi.org/10.5194/egusphere-egu21-597, 2021.
EGU21-2573 | vPICO presentations | SM8.2
Can plasticity explain microseismic source mechanisms?Viktoriya Yarushina and Alexander Minakov
The microseismic events can often be characterized by a complex non-double couple source mechanism. Recent laboratory studies recording the acoustic emission during rock deformation help connecting the components of the seismic moment tensor with the failure process. In this complementary contribution, we offer a mathematical model which can clarify these connections. We derive the seismic moment tensor based on classical continuum mechanics and plasticity theory. The moment tensor density can be represented by the product of elastic stiffness tensor and the plastic strain tensor. This representation of seismic sources has several useful properties: i) it accounts for incipient faulting as a microseismicity source mechanism, ii) it does not require a pre-defined fracture geometry, iii) it accounts for both shear and volumetric source mechanisms, iv) it is valid for general heterogeneous and anisotropic rocks, and v) it is consistent with elasto-plastic geomechanical simulators. We illustrate the new approach using 2D numerical examples of seismicity associated with cylindrical openings, analogous to wellbore, tunnel or fluid-rich conduit, and provide a simple analytic expression of the moment density tensor. We compare our simulation results with previously published data from laboratory and field experiments. We consider three special cases corresponding to "dry" isotropic rocks, "dry" transversely isotropic rocks and "wet" isotropic rocks. The model highlights theoretical links between stress state, geomechanical parameters and conventional representations of the moment tensor such as Hudson source type parameters.
How to cite: Yarushina, V. and Minakov, A.: Can plasticity explain microseismic source mechanisms?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2573, https://doi.org/10.5194/egusphere-egu21-2573, 2021.
Please decide on your access
Please use the buttons below to download the presentation materials or to visit the external website where the presentation is linked. Regarding the external link, please note that Copernicus Meetings cannot accept any liability for the content and the website you will visit.
Forward to presentation link
You are going to open an external link to the presentation as indicated by the authors. Copernicus Meetings cannot accept any liability for the content and the website you will visit.
We are sorry, but presentations are only available for users who registered for the conference. Thank you.
The microseismic events can often be characterized by a complex non-double couple source mechanism. Recent laboratory studies recording the acoustic emission during rock deformation help connecting the components of the seismic moment tensor with the failure process. In this complementary contribution, we offer a mathematical model which can clarify these connections. We derive the seismic moment tensor based on classical continuum mechanics and plasticity theory. The moment tensor density can be represented by the product of elastic stiffness tensor and the plastic strain tensor. This representation of seismic sources has several useful properties: i) it accounts for incipient faulting as a microseismicity source mechanism, ii) it does not require a pre-defined fracture geometry, iii) it accounts for both shear and volumetric source mechanisms, iv) it is valid for general heterogeneous and anisotropic rocks, and v) it is consistent with elasto-plastic geomechanical simulators. We illustrate the new approach using 2D numerical examples of seismicity associated with cylindrical openings, analogous to wellbore, tunnel or fluid-rich conduit, and provide a simple analytic expression of the moment density tensor. We compare our simulation results with previously published data from laboratory and field experiments. We consider three special cases corresponding to "dry" isotropic rocks, "dry" transversely isotropic rocks and "wet" isotropic rocks. The model highlights theoretical links between stress state, geomechanical parameters and conventional representations of the moment tensor such as Hudson source type parameters.
How to cite: Yarushina, V. and Minakov, A.: Can plasticity explain microseismic source mechanisms?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2573, https://doi.org/10.5194/egusphere-egu21-2573, 2021.
EGU21-6144 | vPICO presentations | SM8.2 | Highlight
Physics-Based Estimates of the Maximum Magnitude of Induced Earthquakes in the Groningen Gas FieldHuihui Weng, Jean-Paul Ampuero, and Loes Buijze
The induced seismicity in the Groningen gas field, The Netherlands, has led to intense public concerns and comprehensive investigations. One of the main challenges for assessing future seismic hazard in the Groningen gas field is to estimate the maximum possible earthquake magnitude (Mmax) that could be induced by gas extraction. Previous methods are strongly rooted in empirical and statistical approaches that are inherently limited by the scarcity of data. Here, we combine a physics-based dynamic rupture model based on the 3D theory of fracture mechanics with field-based and lab-based constraints to estimate Mmax in the Groningen gas field. If earthquakes in the reservoir have a rupture depth extension constrained by the reservoir thickness, the largest earthquakes should develop a large aspect ratio (longer horizontally than vertically). The model is thus an extension of the 3D theoretical rupture model on long faults with uniform stress and strength developed by Weng & Ampuero (2019), in which we have incorporated spatial heterogeneities, such as along-strike variable fault width, depth-dependent initial stresses and friction properties. The essential parameters that control rupture propagation and earthquake magnitude are the stored elastic energy and the fracture energy. Our method requires estimates of the stored elastic energy on reservoir faults as a result of the stresses induced by differential reservoir compaction during depletion. The fracture energy is constrained by laboratory experiments and theoretical frictional models. Coupling physics-based rupture models with field and lab observations provides an estimate of Mmax in the Groningen gas field and serves as a practical step toward physics-based seismic hazard assessment for other gas fields in the world.
Citation:
Weng, H. and J. P. Ampuero (2019). "The Dynamics of Elongated Earthquake Ruptures." Journal of Geophysical Research: Solid Earth.
How to cite: Weng, H., Ampuero, J.-P., and Buijze, L.: Physics-Based Estimates of the Maximum Magnitude of Induced Earthquakes in the Groningen Gas Field, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6144, https://doi.org/10.5194/egusphere-egu21-6144, 2021.
Please decide on your access
Please use the buttons below to download the presentation materials or to visit the external website where the presentation is linked. Regarding the external link, please note that Copernicus Meetings cannot accept any liability for the content and the website you will visit.
Forward to presentation link
You are going to open an external link to the presentation as indicated by the authors. Copernicus Meetings cannot accept any liability for the content and the website you will visit.
We are sorry, but presentations are only available for users who registered for the conference. Thank you.
The induced seismicity in the Groningen gas field, The Netherlands, has led to intense public concerns and comprehensive investigations. One of the main challenges for assessing future seismic hazard in the Groningen gas field is to estimate the maximum possible earthquake magnitude (Mmax) that could be induced by gas extraction. Previous methods are strongly rooted in empirical and statistical approaches that are inherently limited by the scarcity of data. Here, we combine a physics-based dynamic rupture model based on the 3D theory of fracture mechanics with field-based and lab-based constraints to estimate Mmax in the Groningen gas field. If earthquakes in the reservoir have a rupture depth extension constrained by the reservoir thickness, the largest earthquakes should develop a large aspect ratio (longer horizontally than vertically). The model is thus an extension of the 3D theoretical rupture model on long faults with uniform stress and strength developed by Weng & Ampuero (2019), in which we have incorporated spatial heterogeneities, such as along-strike variable fault width, depth-dependent initial stresses and friction properties. The essential parameters that control rupture propagation and earthquake magnitude are the stored elastic energy and the fracture energy. Our method requires estimates of the stored elastic energy on reservoir faults as a result of the stresses induced by differential reservoir compaction during depletion. The fracture energy is constrained by laboratory experiments and theoretical frictional models. Coupling physics-based rupture models with field and lab observations provides an estimate of Mmax in the Groningen gas field and serves as a practical step toward physics-based seismic hazard assessment for other gas fields in the world.
Citation:
Weng, H. and J. P. Ampuero (2019). "The Dynamics of Elongated Earthquake Ruptures." Journal of Geophysical Research: Solid Earth.
How to cite: Weng, H., Ampuero, J.-P., and Buijze, L.: Physics-Based Estimates of the Maximum Magnitude of Induced Earthquakes in the Groningen Gas Field, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6144, https://doi.org/10.5194/egusphere-egu21-6144, 2021.
EGU21-9064 | vPICO presentations | SM8.2
Numerical Modelling of Injection-induced Seismicity at Campi Flegrei Caldera, Southern ItalyWaheed Gbenga Akande, Quan Gan, David G. Cornwell, and Luca De Siena
Modelling volcanic processes at active volcanoes often requires a multidisciplinary approach, which adequately describes the complex and ever-dynamic nature of volcanic unrests. Campi Flegrei caldera (southern Italy) is an ideal laboratory where numerical modelling of injection-induced seismicity could be tested to match the observed seismicity. In the current study, thermal-hydraulic-mechanical (THM) effects of hot-water (fluid) injections were investigated to ascertain whether the observed seismicity (past and ongoing seismic swarms) could be quantitatively reproduced and modelled in isothermal or non-isothermal approximations. Fluid-flow modelling was carried out using a coupled TOUGHREACT-FLAC3D approach to simulate THM effects of fluid injections in a capped reservoir, where the sealing formation serves as a geological interface between supercritical reservoir and fractured shallow layers of the caldera. Results from previous seismic, deformation, tomographic and rock physics studies were used to constrain the model for realistic volcano modelling. The results indicated that fluid injections generated overpressure beneath the caprock and subjected it to different stress regimes at its top and bottom, and this prompted deformation. Thus, caprock deformation, triggered by injection-induced basal compressional forces and top extensional fractures, is a critical factor determining the required timing for pressure build-up and fault reactivation, and magnitudes of seismicity. Higher fluid injection rates and temperature contrasts, heterogeneity due to fault and its contrast with the host rock, and caprock hydraulic properties were among the identified secondary factors modulating fault reactivation and seismicity. Simulation results revealed that seismicity can be better modelled in isothermal (HM) approximations. A comparative study of the THM-modelled seismicity and 4-month-long (August 5th to December 5th, 2019) seismic monitoring data recorded at the Osservatorio Vesuviano showed that our model reproduced the magnitudes and depths (~2.5 Ms within 2 km) at the onset of the ongoing unrests on October 5th, 2019. However, the model could not adequately reproduce the highest magnitude (3.3 Ms at 2.57 km) seismicity on April 26th, 2020 observed since 1984 major unrests.
How to cite: Akande, W. G., Gan, Q., Cornwell, D. G., and De Siena, L.: Numerical Modelling of Injection-induced Seismicity at Campi Flegrei Caldera, Southern Italy, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9064, https://doi.org/10.5194/egusphere-egu21-9064, 2021.
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Modelling volcanic processes at active volcanoes often requires a multidisciplinary approach, which adequately describes the complex and ever-dynamic nature of volcanic unrests. Campi Flegrei caldera (southern Italy) is an ideal laboratory where numerical modelling of injection-induced seismicity could be tested to match the observed seismicity. In the current study, thermal-hydraulic-mechanical (THM) effects of hot-water (fluid) injections were investigated to ascertain whether the observed seismicity (past and ongoing seismic swarms) could be quantitatively reproduced and modelled in isothermal or non-isothermal approximations. Fluid-flow modelling was carried out using a coupled TOUGHREACT-FLAC3D approach to simulate THM effects of fluid injections in a capped reservoir, where the sealing formation serves as a geological interface between supercritical reservoir and fractured shallow layers of the caldera. Results from previous seismic, deformation, tomographic and rock physics studies were used to constrain the model for realistic volcano modelling. The results indicated that fluid injections generated overpressure beneath the caprock and subjected it to different stress regimes at its top and bottom, and this prompted deformation. Thus, caprock deformation, triggered by injection-induced basal compressional forces and top extensional fractures, is a critical factor determining the required timing for pressure build-up and fault reactivation, and magnitudes of seismicity. Higher fluid injection rates and temperature contrasts, heterogeneity due to fault and its contrast with the host rock, and caprock hydraulic properties were among the identified secondary factors modulating fault reactivation and seismicity. Simulation results revealed that seismicity can be better modelled in isothermal (HM) approximations. A comparative study of the THM-modelled seismicity and 4-month-long (August 5th to December 5th, 2019) seismic monitoring data recorded at the Osservatorio Vesuviano showed that our model reproduced the magnitudes and depths (~2.5 Ms within 2 km) at the onset of the ongoing unrests on October 5th, 2019. However, the model could not adequately reproduce the highest magnitude (3.3 Ms at 2.57 km) seismicity on April 26th, 2020 observed since 1984 major unrests.
How to cite: Akande, W. G., Gan, Q., Cornwell, D. G., and De Siena, L.: Numerical Modelling of Injection-induced Seismicity at Campi Flegrei Caldera, Southern Italy, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9064, https://doi.org/10.5194/egusphere-egu21-9064, 2021.
EGU21-6324 | vPICO presentations | SM8.2
Modeling the Interaction between Slow Slip Events and Earthquake Ruptures in the Nicoya Peninsula, Costa Rica.Lise Alalouf and Yajing Liu
Subduction zones are where the largest earthquakes occur. In the past few decades, scientists have also discovered the presence of episodic aseismic slip, including slow slip events (SSEs), along most of the subduction zones. However, it is still unclear how these SSEs can influence megathrust earthquake ruptures. The Costa Rica subduction zone is a particularly interesting area because a SSE was recorded 6 months before the 2012 Mw7.6 earthquake in the Nicoya Peninsula, suggesting a potential stress transfer from the SSE to the earthquake slip zone. SSEs beneath the Nicoya Peninsula were also recorded both updip and downdip the seismogenic zone, making it a unique area to study the complex interaction between SSEs and earthquakes.
As most of the shallow SSEs were recorded around the Nicoya Peninsula, we chose to start using a 1D planar fault embedded in a homogeneous elastic half-space, with different dipping angles following several geometric profiles of the subduction fault beneath the Nicoya Peninsula section of the Costa Rica margin. This 1D modelling study allows us to better investigate the interaction between shallow and deep SSEs and megathrust earthquakes with high numerical resolution and relatively short computation time. The model provides information on the long-term seismic history by reproducing the different stages of the seismic cycle (interseismic slip, shallow and deep episodic slow slip, and coseismic slip).
We study the influence of the variation of numerical parameters and frictional properties on the recurrence interval, maximum slip velocity and cumulative slip of SSEs (both shallow and deep) and earthquakes and their interaction with each other. We then compare our results with GPS and seismic observations (i.e. cumulative slip, characteristic duration, moment rate, depth and size of the rupture, equivalent magnitude) to identify an optimal set of model parameters to understand the interaction between various modes of subduction fault deformation.
How to cite: Alalouf, L. and Liu, Y.: Modeling the Interaction between Slow Slip Events and Earthquake Ruptures in the Nicoya Peninsula, Costa Rica. , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6324, https://doi.org/10.5194/egusphere-egu21-6324, 2021.
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Subduction zones are where the largest earthquakes occur. In the past few decades, scientists have also discovered the presence of episodic aseismic slip, including slow slip events (SSEs), along most of the subduction zones. However, it is still unclear how these SSEs can influence megathrust earthquake ruptures. The Costa Rica subduction zone is a particularly interesting area because a SSE was recorded 6 months before the 2012 Mw7.6 earthquake in the Nicoya Peninsula, suggesting a potential stress transfer from the SSE to the earthquake slip zone. SSEs beneath the Nicoya Peninsula were also recorded both updip and downdip the seismogenic zone, making it a unique area to study the complex interaction between SSEs and earthquakes.
As most of the shallow SSEs were recorded around the Nicoya Peninsula, we chose to start using a 1D planar fault embedded in a homogeneous elastic half-space, with different dipping angles following several geometric profiles of the subduction fault beneath the Nicoya Peninsula section of the Costa Rica margin. This 1D modelling study allows us to better investigate the interaction between shallow and deep SSEs and megathrust earthquakes with high numerical resolution and relatively short computation time. The model provides information on the long-term seismic history by reproducing the different stages of the seismic cycle (interseismic slip, shallow and deep episodic slow slip, and coseismic slip).
We study the influence of the variation of numerical parameters and frictional properties on the recurrence interval, maximum slip velocity and cumulative slip of SSEs (both shallow and deep) and earthquakes and their interaction with each other. We then compare our results with GPS and seismic observations (i.e. cumulative slip, characteristic duration, moment rate, depth and size of the rupture, equivalent magnitude) to identify an optimal set of model parameters to understand the interaction between various modes of subduction fault deformation.
How to cite: Alalouf, L. and Liu, Y.: Modeling the Interaction between Slow Slip Events and Earthquake Ruptures in the Nicoya Peninsula, Costa Rica. , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6324, https://doi.org/10.5194/egusphere-egu21-6324, 2021.
EGU21-8682 | vPICO presentations | SM8.2
On the depth-dependent stress accumulation for earthquake generation processHideo Aochi and Kenichi Tsuda
Dynamic rupture simulation of an earthquake mostly aims at a characteristic event, which may rupture the entire seismogenic zone of a fault system, perhaps reaching the ground surface. However, hazardous earthquakes sometimes occur along a part of the depths of a fault. Many questions arise why only this particular depth does rupture and whether the surrounding part remains hazardous. Previously, Aochi (GJI, 2018) has considered a depth-dependent stress accumulation for emphasizing the difference of reverse and normal faults under the hypothesis that stress is sufficiently and uniformly charged at all depths. We probably need to revise this hypothesis and the partially charged fault along depth would be more suitable for explaining the given question. By developing the previous simulations by Aochi (GJI, 2018), we carry out numerical simulations for demonstrating the importance of the depth-dependent stress accumulation.
How to cite: Aochi, H. and Tsuda, K.: On the depth-dependent stress accumulation for earthquake generation process, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8682, https://doi.org/10.5194/egusphere-egu21-8682, 2021.
Dynamic rupture simulation of an earthquake mostly aims at a characteristic event, which may rupture the entire seismogenic zone of a fault system, perhaps reaching the ground surface. However, hazardous earthquakes sometimes occur along a part of the depths of a fault. Many questions arise why only this particular depth does rupture and whether the surrounding part remains hazardous. Previously, Aochi (GJI, 2018) has considered a depth-dependent stress accumulation for emphasizing the difference of reverse and normal faults under the hypothesis that stress is sufficiently and uniformly charged at all depths. We probably need to revise this hypothesis and the partially charged fault along depth would be more suitable for explaining the given question. By developing the previous simulations by Aochi (GJI, 2018), we carry out numerical simulations for demonstrating the importance of the depth-dependent stress accumulation.
How to cite: Aochi, H. and Tsuda, K.: On the depth-dependent stress accumulation for earthquake generation process, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8682, https://doi.org/10.5194/egusphere-egu21-8682, 2021.
EGU21-7496 | vPICO presentations | SM8.2
Exploring the dynamics of the Dead-Sea Transform fault using data-integrated numerical modelsThomas Ulrich, Alice-Agnes Gabriel, Yann Klinger, Jean-Paul Ampuero, Percy Galvez, and Bo Li
The Dead-Sea Transform fault system, a 1200 km-long strike-slip fault forming the tectonic boundary between the African Plate and the Arabian Plate, poses a major seismic hazard to the eastern Mediterranean region. The Gulf of Aqaba, which terminates the Dead Sea fault system to the South, results from a succession of pull-apart basins along the Dead-Sea Transform fault system. The complexity of the fault system in the Gulf has been recently evidenced by Ribot et al. (2020), who compiled a detailed map of its fault traces, based on a new multibeam bathymetric survey of the Gulf. Part of the Gulf of Aqaba was ruptured by an Mw 7.3 earthquake in 1995. Teleseismic data analysis suggests that it may have been a multi-segment rupture (Klinger et al., 1999). This event occurred offshore, in a poorly instrumented region, and therefore the exact sequence of faults that ruptured is not precisely known. The detailed fault mapping of Ribot et al. (2020) offers a fresh view of this earthquake. In particular, it identifies many oblique faults between the major strike-slip faults, which may have linked these segments.
Relying on this new dataset, on a new back-projection study, and on 3D dynamic rupture modeling with SeisSol (https://github.com/SeisSol/SeisSol), we revisit the 1995 Aqaba earthquake. Using back projection, we identify 2 strong radiators, which we associate with 2 step-overs. Using 3D dynamic rupture modeling, we propose scenarios of the 1995 earthquake, compatible with the various dataset available. Our modeling allows constraining the regional state of stress in the region, acknowledging transtension, offers constraints on the nucleation location and confirms the role of the oblique faults in propagating the rupture to the North. It offers new constraints on the regional seismic hazard, in particular on the expected maximum moment magnitude.
Finally, we explore the dynamics of the Gulf of Aqaba fault system using earthquake cycle modeling. For that purpose, we rely on QDYN (https://github.com/ydluo/qdyn), a boundary element software, which simulates earthquake cycles under the quasi-dynamic approximation on faults governed by rate-and-state friction and embedded in elastic media. We inform our parameterization of the earthquake cycle modeling using the previously described datasets and modeling results. Recently Galvez et al. (2020) demonstrated the capability of the method to model the dynamics of complex fault system in 3D. Here new code developments are required to adapt the method to the Gulf of Aqaba fault system, e.g. to allow accounting for normal stress changes and for variations in the fault rake.
Overall, we aim to better understand how large earthquakes may nucleate, propagate, and interact across a complex transform fault network. Our findings, e.g. on fault segmentation or the conditions that promote larger earthquakes, will have important implications for other large strike-slip fault systems worldwide.
How to cite: Ulrich, T., Gabriel, A.-A., Klinger, Y., Ampuero, J.-P., Galvez, P., and Li, B.: Exploring the dynamics of the Dead-Sea Transform fault using data-integrated numerical models, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7496, https://doi.org/10.5194/egusphere-egu21-7496, 2021.
The Dead-Sea Transform fault system, a 1200 km-long strike-slip fault forming the tectonic boundary between the African Plate and the Arabian Plate, poses a major seismic hazard to the eastern Mediterranean region. The Gulf of Aqaba, which terminates the Dead Sea fault system to the South, results from a succession of pull-apart basins along the Dead-Sea Transform fault system. The complexity of the fault system in the Gulf has been recently evidenced by Ribot et al. (2020), who compiled a detailed map of its fault traces, based on a new multibeam bathymetric survey of the Gulf. Part of the Gulf of Aqaba was ruptured by an Mw 7.3 earthquake in 1995. Teleseismic data analysis suggests that it may have been a multi-segment rupture (Klinger et al., 1999). This event occurred offshore, in a poorly instrumented region, and therefore the exact sequence of faults that ruptured is not precisely known. The detailed fault mapping of Ribot et al. (2020) offers a fresh view of this earthquake. In particular, it identifies many oblique faults between the major strike-slip faults, which may have linked these segments.
Relying on this new dataset, on a new back-projection study, and on 3D dynamic rupture modeling with SeisSol (https://github.com/SeisSol/SeisSol), we revisit the 1995 Aqaba earthquake. Using back projection, we identify 2 strong radiators, which we associate with 2 step-overs. Using 3D dynamic rupture modeling, we propose scenarios of the 1995 earthquake, compatible with the various dataset available. Our modeling allows constraining the regional state of stress in the region, acknowledging transtension, offers constraints on the nucleation location and confirms the role of the oblique faults in propagating the rupture to the North. It offers new constraints on the regional seismic hazard, in particular on the expected maximum moment magnitude.
Finally, we explore the dynamics of the Gulf of Aqaba fault system using earthquake cycle modeling. For that purpose, we rely on QDYN (https://github.com/ydluo/qdyn), a boundary element software, which simulates earthquake cycles under the quasi-dynamic approximation on faults governed by rate-and-state friction and embedded in elastic media. We inform our parameterization of the earthquake cycle modeling using the previously described datasets and modeling results. Recently Galvez et al. (2020) demonstrated the capability of the method to model the dynamics of complex fault system in 3D. Here new code developments are required to adapt the method to the Gulf of Aqaba fault system, e.g. to allow accounting for normal stress changes and for variations in the fault rake.
Overall, we aim to better understand how large earthquakes may nucleate, propagate, and interact across a complex transform fault network. Our findings, e.g. on fault segmentation or the conditions that promote larger earthquakes, will have important implications for other large strike-slip fault systems worldwide.
How to cite: Ulrich, T., Gabriel, A.-A., Klinger, Y., Ampuero, J.-P., Galvez, P., and Li, B.: Exploring the dynamics of the Dead-Sea Transform fault using data-integrated numerical models, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7496, https://doi.org/10.5194/egusphere-egu21-7496, 2021.
EGU21-8833 | vPICO presentations | SM8.2
Characteristics of earthquake sequences: comparison from 0D to 3DMeng Li, Casper Pranger, and Ylona van Dinther
Numerical models are well-suited to overcome limited spatial-temporal observations to understand earthquake sequences, which is fundamental to ultimately better assess seismic hazard. However, high-resolution numerical models in 3D are computationally time and memory consuming. This is not optimal if the aspects of lateral or depth variations within the results are not needed to answer a particular objective. In this study we quantify and summarize the limitations and advantages for simulating earthquake sequences in all spatial dimensions.
We simulate earthquake sequences on a strike-slip fault with rate-and-state friction from 0D to 3D using both quasi-dynamic and fully dynamic approaches. This cross-dimensional comparison is facilitated by our newly developed, flexible code library Garnet, which adopts a finite difference method with a fully staggered grid. We have validated our models using problems BP1-QD & FD and BP4-QD & FD of the SEAS (Sequences of Earthquakes and Aseismic Slip) benchmarks from the Southern California Earthquake Center.
Our results demonstrate that lower-dimensional/quasi-dynamic models are qualitatively similar in terms of earthquake cycle characteristics to their higher-dimensional/fully-dynamic counterparts, while they could be hundreds to millions times faster at the same time. Quantitatively, we observe that certain earthquake parameters, such as stress drop and fracture energy release, can be accurately reproduced in each of these simpler models as well. However, higher dimensional models generally produce lower maximum slip velocities and hence longer coseismic durations. This is mainly due to lower rupture speeds, which result from increased energy consumption along added rupture front directions. In the long term, higher dimensional models produce shorter recurrence interval and hence smaller total slip, which is mainly caused by the higher interseismic stress loading rate inside the nucleation zone. The same trend is also observed when comparing quasi-dynamic models to fully dynamic ones. We extend a theoretical calculation that to first order approximates the aforementioned physical observables in 3D to all other dimensions. These theoretical considerations confirm the same trend as what is observed for stress drop, recurrence interval and total slip across dimensions. These findings on similarities and differences of different dimensional models and a corresponding quantification of computational efficiency can guide model design and facilitate result interpretation in future studies.
How to cite: Li, M., Pranger, C., and van Dinther, Y.: Characteristics of earthquake sequences: comparison from 0D to 3D, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8833, https://doi.org/10.5194/egusphere-egu21-8833, 2021.
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Please use the buttons below to download the presentation materials or to visit the external website where the presentation is linked. Regarding the external link, please note that Copernicus Meetings cannot accept any liability for the content and the website you will visit.
Forward to presentation link
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We are sorry, but presentations are only available for users who registered for the conference. Thank you.
Numerical models are well-suited to overcome limited spatial-temporal observations to understand earthquake sequences, which is fundamental to ultimately better assess seismic hazard. However, high-resolution numerical models in 3D are computationally time and memory consuming. This is not optimal if the aspects of lateral or depth variations within the results are not needed to answer a particular objective. In this study we quantify and summarize the limitations and advantages for simulating earthquake sequences in all spatial dimensions.
We simulate earthquake sequences on a strike-slip fault with rate-and-state friction from 0D to 3D using both quasi-dynamic and fully dynamic approaches. This cross-dimensional comparison is facilitated by our newly developed, flexible code library Garnet, which adopts a finite difference method with a fully staggered grid. We have validated our models using problems BP1-QD & FD and BP4-QD & FD of the SEAS (Sequences of Earthquakes and Aseismic Slip) benchmarks from the Southern California Earthquake Center.
Our results demonstrate that lower-dimensional/quasi-dynamic models are qualitatively similar in terms of earthquake cycle characteristics to their higher-dimensional/fully-dynamic counterparts, while they could be hundreds to millions times faster at the same time. Quantitatively, we observe that certain earthquake parameters, such as stress drop and fracture energy release, can be accurately reproduced in each of these simpler models as well. However, higher dimensional models generally produce lower maximum slip velocities and hence longer coseismic durations. This is mainly due to lower rupture speeds, which result from increased energy consumption along added rupture front directions. In the long term, higher dimensional models produce shorter recurrence interval and hence smaller total slip, which is mainly caused by the higher interseismic stress loading rate inside the nucleation zone. The same trend is also observed when comparing quasi-dynamic models to fully dynamic ones. We extend a theoretical calculation that to first order approximates the aforementioned physical observables in 3D to all other dimensions. These theoretical considerations confirm the same trend as what is observed for stress drop, recurrence interval and total slip across dimensions. These findings on similarities and differences of different dimensional models and a corresponding quantification of computational efficiency can guide model design and facilitate result interpretation in future studies.
How to cite: Li, M., Pranger, C., and van Dinther, Y.: Characteristics of earthquake sequences: comparison from 0D to 3D, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8833, https://doi.org/10.5194/egusphere-egu21-8833, 2021.
EGU21-13090 | vPICO presentations | SM8.2
Simulation of Instant and Delayed Seismic Triggering Observed After the 30 October 2020 Samos Earthquake at Nearby FaultsEyup Sopaci and Atilla Arda Özacar
The 30 October 2020 Samos Earthquake (Mw=7.0) ruptured a north-dipping offshore normal fault, north of the Samos Island with an extensional mechanism. Aftershocks mainly occurred at the western and eastern ends of the rupture plane in agreement with the Coulomb static stress changes. Mechanism of aftershocks located west of the rupture area supported activation of the neighboring strike-slip fault almost instantly. In addition, a seismic cluster including events with magnitudes reaching close to 4 has emerged fifty hours later at the SE side of Samos Island. This off-plane cluster displays a clear example of delayed seismic triggering that produced small magnitude earthquakes at nearby active faults. In this study, numerical simulations are conducted using rate-and-state friction dependent quasi-static&full-dynamic spring slider model with shear-normal stress coupling to mimic the instant and delayed seismic triggering observed after this event. Coulomb static stress changes and seismic waveforms recorded at nearby strong-motion stations are used as static and dynamic triggers during simulations. According to our results, earthquakes with Mw<3.5 can be triggered almost instantly at the rupture edge and failure time of earthquakes with Mw>3.5 advances for both strike-slip and normal faults which may explain the delayed triggering observed SE of Samos Island. Moreover, simulations revealed that the shear-normal stress coupling increases the triggering potential.
How to cite: Sopaci, E. and Özacar, A. A.: Simulation of Instant and Delayed Seismic Triggering Observed After the 30 October 2020 Samos Earthquake at Nearby Faults, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13090, https://doi.org/10.5194/egusphere-egu21-13090, 2021.
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The 30 October 2020 Samos Earthquake (Mw=7.0) ruptured a north-dipping offshore normal fault, north of the Samos Island with an extensional mechanism. Aftershocks mainly occurred at the western and eastern ends of the rupture plane in agreement with the Coulomb static stress changes. Mechanism of aftershocks located west of the rupture area supported activation of the neighboring strike-slip fault almost instantly. In addition, a seismic cluster including events with magnitudes reaching close to 4 has emerged fifty hours later at the SE side of Samos Island. This off-plane cluster displays a clear example of delayed seismic triggering that produced small magnitude earthquakes at nearby active faults. In this study, numerical simulations are conducted using rate-and-state friction dependent quasi-static&full-dynamic spring slider model with shear-normal stress coupling to mimic the instant and delayed seismic triggering observed after this event. Coulomb static stress changes and seismic waveforms recorded at nearby strong-motion stations are used as static and dynamic triggers during simulations. According to our results, earthquakes with Mw<3.5 can be triggered almost instantly at the rupture edge and failure time of earthquakes with Mw>3.5 advances for both strike-slip and normal faults which may explain the delayed triggering observed SE of Samos Island. Moreover, simulations revealed that the shear-normal stress coupling increases the triggering potential.
How to cite: Sopaci, E. and Özacar, A. A.: Simulation of Instant and Delayed Seismic Triggering Observed After the 30 October 2020 Samos Earthquake at Nearby Faults, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13090, https://doi.org/10.5194/egusphere-egu21-13090, 2021.
EGU21-13830 | vPICO presentations | SM8.2 | Highlight
Dynamic Rupture Scenarios of Large Earthquakes on the Rodgers Creek-Hayward-Calaveras-Northern Calaveras Fault System, CaliforniaRuth Harris, Michael Barall, David Ponce, Diane Moore, Russell Graymer, David Lockner, Carolyn Morrow, Gareth Funning, Christos Kyriakopoulos, and Donna Eberhart-Phillips
The Rodgers Creek-Hayward-Calaveras-Northern Calaveras fault system in California dominates the hazard posed by active faults in the San Francisco Bay Area. Given that this fault system runs through a densely populated area, a large earthquake in this region is likely to affect millions of people. This study produced scenarios of large earthquakes in this fault system, using spontaneous (dynamic) rupture simulations. These types of physics-based computational simulations require information about the 3D fault geometry, physical rock properties, fault friction, and initial stress conditions. In terms of fault geometry, the well-connected multi-fault system includes the Hayward fault, at its southern end the Central and Northern Calaveras faults, and at its northern end the Rodgers Creek fault. Geodetic investigations of the fault system’s slip-rate pattern provide images of where the fault surfaces at depth are creeping or locked interseismically, and this helped us choose appropriate initial stress conditions for our simulations. A 3D geologic model of the fault system provides the 3D rock units and fault structure at depth, while field samples from rocks collected at Earth’s surface provide frictional parameters. We used this suite of information to investigate the behavior of large earthquake ruptures nucleating at various positions along this partially creeping fault system. We found that large earthquakes starting on the Hayward fault or on the Rodgers Creek fault may be slowed, stopped, or unaffected in their progress, depending on how much energy is released by the creeping regions of the Hayward and Central Calaveras faults during the time between large earthquakes. Large earthquakes starting on either the Hayward fault or the Rodgers Creek faults will likely not rupture the Northern Calaveras fault, and large earthquakes starting on either the Northern Calaveras fault or the Central Calaveras fault will likely remain confined to those fault segments.
How to cite: Harris, R., Barall, M., Ponce, D., Moore, D., Graymer, R., Lockner, D., Morrow, C., Funning, G., Kyriakopoulos, C., and Eberhart-Phillips, D.: Dynamic Rupture Scenarios of Large Earthquakes on the Rodgers Creek-Hayward-Calaveras-Northern Calaveras Fault System, California, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13830, https://doi.org/10.5194/egusphere-egu21-13830, 2021.
The Rodgers Creek-Hayward-Calaveras-Northern Calaveras fault system in California dominates the hazard posed by active faults in the San Francisco Bay Area. Given that this fault system runs through a densely populated area, a large earthquake in this region is likely to affect millions of people. This study produced scenarios of large earthquakes in this fault system, using spontaneous (dynamic) rupture simulations. These types of physics-based computational simulations require information about the 3D fault geometry, physical rock properties, fault friction, and initial stress conditions. In terms of fault geometry, the well-connected multi-fault system includes the Hayward fault, at its southern end the Central and Northern Calaveras faults, and at its northern end the Rodgers Creek fault. Geodetic investigations of the fault system’s slip-rate pattern provide images of where the fault surfaces at depth are creeping or locked interseismically, and this helped us choose appropriate initial stress conditions for our simulations. A 3D geologic model of the fault system provides the 3D rock units and fault structure at depth, while field samples from rocks collected at Earth’s surface provide frictional parameters. We used this suite of information to investigate the behavior of large earthquake ruptures nucleating at various positions along this partially creeping fault system. We found that large earthquakes starting on the Hayward fault or on the Rodgers Creek fault may be slowed, stopped, or unaffected in their progress, depending on how much energy is released by the creeping regions of the Hayward and Central Calaveras faults during the time between large earthquakes. Large earthquakes starting on either the Hayward fault or the Rodgers Creek faults will likely not rupture the Northern Calaveras fault, and large earthquakes starting on either the Northern Calaveras fault or the Central Calaveras fault will likely remain confined to those fault segments.
How to cite: Harris, R., Barall, M., Ponce, D., Moore, D., Graymer, R., Lockner, D., Morrow, C., Funning, G., Kyriakopoulos, C., and Eberhart-Phillips, D.: Dynamic Rupture Scenarios of Large Earthquakes on the Rodgers Creek-Hayward-Calaveras-Northern Calaveras Fault System, California, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13830, https://doi.org/10.5194/egusphere-egu21-13830, 2021.
EGU21-15202 | vPICO presentations | SM8.2
Earthquake rupture properties in presence of thermal -pressurization of pore fluidsP. Martin Mai, Jagdish Vyas, Alice-Agnes Gabriel, and Thomas Ulrich
Frictional heat generated in the fault core during earthquake rupture can raise the fluid pressure in the slip zone. Such increase of fluid pressure decreases the effective normal stress and thereby lowers the frictional strength of the fault. Therefore, thermal pressurization (TP) of pore fluid affects earthquake rupture processes including nucleation, propagation, and arrest. While the effects of pore pressure and fluid flow rate on dynamic weakening of faults are qualitatively understood, a detailed analysis of how TP affects earthquake rupture parameters is needed to further deepen our understanding.
In this study, we investigate the role of two key TP parameters -- hydraulic diffusivity and shear-zone half-width -- earthquake dynamics and kinematic source properties (slip, peak slip-rate, rupture speed and rise time). We conduct a suite of 3D dynamic rupture simulations applying a rate-and-state dependent friction law (with strong velocity weakening) coupled with thermal-pressurization of pore fluids. Simulations are carried out with the open source software SeisSol (www.seissol.org). The temporal evolution of rupture parameters over ~1’000 randomly distributed on-fault receivers is statistically analyzed in terms of mean variations of rupture parameters and correlations among rupture parameters.
Our simulations reveal that mean slip decreases with increasing hydraulic diffusivity, whereas mean peak slip-rate and rupture speed remain nearly constant. On the other hand, we observe only a slight decrease of mean slip with increasing shear-zone half-width, whereas mean peak slip-rate and rupture speed show clear decrease. The faster diffusion of pore pressure as hydraulic diffusivity increases promotes faster increase of the effective normal stress (and fault strength) behind the main rupture front, reducing the rise time and, therefore also affecting mean slip. An increase in shear-zone half- width represents a heat source distributed over larger fault normal distance causing a second-order effect on mean slip. Additionally, our simulations reveal correlations among rupture parameters: 1) slip has weak negative correlation with peak slip-rate and negligible correlation with rupture speed, but a positive correlation with rise time, 2) peak slip-rate has a strong positive correlation with rupture speed, but a strong negative correlation with rise time, 3) rupture speed has strong negative correlation with rise time. We observe little or negligible effects of variations of hydraulic diffusivity and shear-zone half- width on the correlations between rupture parameters. Overall, our study builds a fundamental understanding on how thermal pressurization of pore fluids affects dynamic and thereby kinematic earthquake rupture properties. Our findings are thus important for the earthquake source modeling community, and particularly, for assessing seismic hazard due to induced events in geo-reservoirs.
How to cite: Mai, P. M., Vyas, J., Gabriel, A.-A., and Ulrich, T.: Earthquake rupture properties in presence of thermal -pressurization of pore fluids, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15202, https://doi.org/10.5194/egusphere-egu21-15202, 2021.
Frictional heat generated in the fault core during earthquake rupture can raise the fluid pressure in the slip zone. Such increase of fluid pressure decreases the effective normal stress and thereby lowers the frictional strength of the fault. Therefore, thermal pressurization (TP) of pore fluid affects earthquake rupture processes including nucleation, propagation, and arrest. While the effects of pore pressure and fluid flow rate on dynamic weakening of faults are qualitatively understood, a detailed analysis of how TP affects earthquake rupture parameters is needed to further deepen our understanding.
In this study, we investigate the role of two key TP parameters -- hydraulic diffusivity and shear-zone half-width -- earthquake dynamics and kinematic source properties (slip, peak slip-rate, rupture speed and rise time). We conduct a suite of 3D dynamic rupture simulations applying a rate-and-state dependent friction law (with strong velocity weakening) coupled with thermal-pressurization of pore fluids. Simulations are carried out with the open source software SeisSol (www.seissol.org). The temporal evolution of rupture parameters over ~1’000 randomly distributed on-fault receivers is statistically analyzed in terms of mean variations of rupture parameters and correlations among rupture parameters.
Our simulations reveal that mean slip decreases with increasing hydraulic diffusivity, whereas mean peak slip-rate and rupture speed remain nearly constant. On the other hand, we observe only a slight decrease of mean slip with increasing shear-zone half-width, whereas mean peak slip-rate and rupture speed show clear decrease. The faster diffusion of pore pressure as hydraulic diffusivity increases promotes faster increase of the effective normal stress (and fault strength) behind the main rupture front, reducing the rise time and, therefore also affecting mean slip. An increase in shear-zone half- width represents a heat source distributed over larger fault normal distance causing a second-order effect on mean slip. Additionally, our simulations reveal correlations among rupture parameters: 1) slip has weak negative correlation with peak slip-rate and negligible correlation with rupture speed, but a positive correlation with rise time, 2) peak slip-rate has a strong positive correlation with rupture speed, but a strong negative correlation with rise time, 3) rupture speed has strong negative correlation with rise time. We observe little or negligible effects of variations of hydraulic diffusivity and shear-zone half- width on the correlations between rupture parameters. Overall, our study builds a fundamental understanding on how thermal pressurization of pore fluids affects dynamic and thereby kinematic earthquake rupture properties. Our findings are thus important for the earthquake source modeling community, and particularly, for assessing seismic hazard due to induced events in geo-reservoirs.
How to cite: Mai, P. M., Vyas, J., Gabriel, A.-A., and Ulrich, T.: Earthquake rupture properties in presence of thermal -pressurization of pore fluids, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15202, https://doi.org/10.5194/egusphere-egu21-15202, 2021.
EGU21-15686 | vPICO presentations | SM8.2
Non-planar dynamic rupture modelling across diffuse, deforming fault zones using a spectral finite element method with a non-mesh aligned embedded diffuse discontinuityJorge Nicolas Hayek Valencia, Dave A. May, and Alice-Agnes Gabriel
Faults in earthquake rupture dynamic simulations are typically treated as infinitesimally thin planes with distinct on- versus off-fault rheologies. These faults are prescribed and can be explicitly accounted for with hexahedral or unstructured tetrahedral meshing approaches.
We present a diffuse interface alternative to dynamic rupture modelling on non-mesh aligned faults and, by design, permits modelling of non-planar faults and time-dependent fault geometries. We use se2dr, a spectral finite element (continuous Galerkin) method with a non-mesh aligned embedded diffuse discontinuity for dynamic rupture simulations.
Natural fault systems are characterised by fault zone complexity, e.g. the frictional strength and spatio-temporal slip localisation may change drastically from the outer damage zone to the fault core. Complex volumetric failure patterns are observed in well-recorded large complex earthquakes (e.g., the 2016 Mw7.8 Kaikōura event, Klinger et al. 2018), small events (e.g., in the San Jacinto Fault Zone, Cheng et al. 2018), and laboratory-scale experiments (e.g., in high-velocity friction experiments, Passelègue et al., 2016).
We develop a diffuse description of fault slip to better understand complex volumetric failure patterns and the mechanics of slip in diffuse fault zones. The fault is defined via a signed distance function (s(x)), which is in turn used to define a fault indicator function with compact support H. If s(x) > H the material behaves as a pure elastic solid - otherwise the tangential stress is governed by a frictional sliding law.
Our approach is implemented on a structured hexahedral mesh using a spectral finite element (continuous Galerkin) method for wave propagation using PETSc. Our diffuse fault SEM method is inspired by the stress-glut method of Andrews, 1999. A non-mesh aligned embedded diffusive discontinuity allows for complex dynamic rupture simulations. We present 2D numerical experiments of kinematically driven rupture and spontaneous dynamic rupture on non-planar and non-mesh aligned complex fault geometries. The method can be used to model earthquake rupture dynamics on specifically complex and evolving fault faults such as the San Jacinto, CA, fault, or shallowly dipping megathrusts and splay faulting structures in subduction zones.
How to cite: Hayek Valencia, J. N., May, D. A., and Gabriel, A.-A.: Non-planar dynamic rupture modelling across diffuse, deforming fault zones using a spectral finite element method with a non-mesh aligned embedded diffuse discontinuity, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15686, https://doi.org/10.5194/egusphere-egu21-15686, 2021.
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Faults in earthquake rupture dynamic simulations are typically treated as infinitesimally thin planes with distinct on- versus off-fault rheologies. These faults are prescribed and can be explicitly accounted for with hexahedral or unstructured tetrahedral meshing approaches.
We present a diffuse interface alternative to dynamic rupture modelling on non-mesh aligned faults and, by design, permits modelling of non-planar faults and time-dependent fault geometries. We use se2dr, a spectral finite element (continuous Galerkin) method with a non-mesh aligned embedded diffuse discontinuity for dynamic rupture simulations.
Natural fault systems are characterised by fault zone complexity, e.g. the frictional strength and spatio-temporal slip localisation may change drastically from the outer damage zone to the fault core. Complex volumetric failure patterns are observed in well-recorded large complex earthquakes (e.g., the 2016 Mw7.8 Kaikōura event, Klinger et al. 2018), small events (e.g., in the San Jacinto Fault Zone, Cheng et al. 2018), and laboratory-scale experiments (e.g., in high-velocity friction experiments, Passelègue et al., 2016).
We develop a diffuse description of fault slip to better understand complex volumetric failure patterns and the mechanics of slip in diffuse fault zones. The fault is defined via a signed distance function (s(x)), which is in turn used to define a fault indicator function with compact support H. If s(x) > H the material behaves as a pure elastic solid - otherwise the tangential stress is governed by a frictional sliding law.
Our approach is implemented on a structured hexahedral mesh using a spectral finite element (continuous Galerkin) method for wave propagation using PETSc. Our diffuse fault SEM method is inspired by the stress-glut method of Andrews, 1999. A non-mesh aligned embedded diffusive discontinuity allows for complex dynamic rupture simulations. We present 2D numerical experiments of kinematically driven rupture and spontaneous dynamic rupture on non-planar and non-mesh aligned complex fault geometries. The method can be used to model earthquake rupture dynamics on specifically complex and evolving fault faults such as the San Jacinto, CA, fault, or shallowly dipping megathrusts and splay faulting structures in subduction zones.
How to cite: Hayek Valencia, J. N., May, D. A., and Gabriel, A.-A.: Non-planar dynamic rupture modelling across diffuse, deforming fault zones using a spectral finite element method with a non-mesh aligned embedded diffuse discontinuity, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15686, https://doi.org/10.5194/egusphere-egu21-15686, 2021.
EGU21-16028 | vPICO presentations | SM8.2
Synthetic seismic modeling and inversion for the Oldoinyo Lengai volcanic complex.Abolfazl komeazi, Yi Zhang, Luca de Siena, Georg rümpker, Boris Kaus, Miriam Reiss, César Castro, Arne Spang, Philip Hering, Andreas Junge, and Tobias Baumann
What is the effect of crustal melt accumulation on the seismic wavefield? Can we reproduce the dispersion, scattering and associated stress-anisotropy with modeling tools? By performing numerical experiments of seismic wave propagation in a synthetic and geodynamically-consistent volcanic system we can test our ability to model the seismic wavefield and to reconstruct the target “magma chamber”.
We built a synthetic volcano based on recent seismic observations at the Oldoinyo Lengai volcanic complex. The velocity model is based on a geodynamic model that provides shear modulus, Poisson's ratio, and density. The isotropic P- and S-wave velocities can be computed directly from these parameters. To test a more realistic depth dependence, we introduced a reference 1D velocity model for Northern Tanzania and expanded this to 3D. Then, we inserted variations in the rock parameters mimicking a magma chamber and resolved it using the Fast Marching Travel Time tomography code.
To further our understanding, we also added 3D anisotropy and random velocity fluctuations to the system, acting both as synthetic input for future applications and testing of seismic techniques (e.g., shear wave splitting analysis) and as noise for the travel time tomography. For the waveform modeling we used the velocity-deviatoric stress-isotropic pressure equations together with perfectly matched layers. Also, we encoded the boundary condition between solid and air in this formulation. The 25 receivers with their real geographic locations were placed for inversion sensitivity analysis. In particular, the ability to reconstruct the magma chamber and the effect of anisotropy and velocity fluctuations at frequencies up to 5 Hz are evaluated. The results are compared with a parallel forward modeling and inversion of synthetic MT data. To confirm our results and as an additional test, we also employ adjoint tomography based on spectral element method to implement a forward waveform modeling and inversion using the tools provided in the SPECFEM3D_Cartesian package.
The results present a better idea of how to construct a realistic synthetic volcano in the future. By combining multiple seismic forward models and inversion approaches, this study yields insights into the sensitivity of the seismic wavefield to geodynamically-consistent volcanic structures.
How to cite: komeazi, A., Zhang, Y., de Siena, L., rümpker, G., Kaus, B., Reiss, M., Castro, C., Spang, A., Hering, P., Junge, A., and Baumann, T.: Synthetic seismic modeling and inversion for the Oldoinyo Lengai volcanic complex., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16028, https://doi.org/10.5194/egusphere-egu21-16028, 2021.
Please decide on your access
Please use the buttons below to download the presentation materials or to visit the external website where the presentation is linked. Regarding the external link, please note that Copernicus Meetings cannot accept any liability for the content and the website you will visit.
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We are sorry, but presentations are only available for users who registered for the conference. Thank you.
What is the effect of crustal melt accumulation on the seismic wavefield? Can we reproduce the dispersion, scattering and associated stress-anisotropy with modeling tools? By performing numerical experiments of seismic wave propagation in a synthetic and geodynamically-consistent volcanic system we can test our ability to model the seismic wavefield and to reconstruct the target “magma chamber”.
We built a synthetic volcano based on recent seismic observations at the Oldoinyo Lengai volcanic complex. The velocity model is based on a geodynamic model that provides shear modulus, Poisson's ratio, and density. The isotropic P- and S-wave velocities can be computed directly from these parameters. To test a more realistic depth dependence, we introduced a reference 1D velocity model for Northern Tanzania and expanded this to 3D. Then, we inserted variations in the rock parameters mimicking a magma chamber and resolved it using the Fast Marching Travel Time tomography code.
To further our understanding, we also added 3D anisotropy and random velocity fluctuations to the system, acting both as synthetic input for future applications and testing of seismic techniques (e.g., shear wave splitting analysis) and as noise for the travel time tomography. For the waveform modeling we used the velocity-deviatoric stress-isotropic pressure equations together with perfectly matched layers. Also, we encoded the boundary condition between solid and air in this formulation. The 25 receivers with their real geographic locations were placed for inversion sensitivity analysis. In particular, the ability to reconstruct the magma chamber and the effect of anisotropy and velocity fluctuations at frequencies up to 5 Hz are evaluated. The results are compared with a parallel forward modeling and inversion of synthetic MT data. To confirm our results and as an additional test, we also employ adjoint tomography based on spectral element method to implement a forward waveform modeling and inversion using the tools provided in the SPECFEM3D_Cartesian package.
The results present a better idea of how to construct a realistic synthetic volcano in the future. By combining multiple seismic forward models and inversion approaches, this study yields insights into the sensitivity of the seismic wavefield to geodynamically-consistent volcanic structures.
How to cite: komeazi, A., Zhang, Y., de Siena, L., rümpker, G., Kaus, B., Reiss, M., Castro, C., Spang, A., Hering, P., Junge, A., and Baumann, T.: Synthetic seismic modeling and inversion for the Oldoinyo Lengai volcanic complex., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16028, https://doi.org/10.5194/egusphere-egu21-16028, 2021.
EGU21-16502 | vPICO presentations | SM8.2
State evolution laws and earthquake nucleationRobert Viesca
In models of faults as elastic continua with a frictional interface, earthquake nucleation is the initiation of a propagating dynamic fault rupture nucleated by a localized slip instability. A mechanism capturing both the weakening process leading to nucleation as well as fault healing between events, is a slip rate- and state-dependent friction, with so-called direct effect and evolution effects [Dieterich, JGR 1979; Ruina, JGR 1983]. While the constitutive representation of the direct effect is theoretically supported [e.g., Nakatani, JGR 2001; Rice et al., JMPS 2001], that of the evolution effect remains empirical and a number of state-evolution laws have been proposed to fit lab rock friction data [Ruina, JGR 1983; Kato and Tullis, GRL 2001; Bar-Sinai et al., GRL 2012; Nagata et al., JGR 2012]. These laws may share a common linearization about steady-state, such that a linear stability analysis of steady, uniform sliding yields a single critical wavelength for unstable growth of perturbations [Rice and Ruina, JAM 1983]. However, the laws’ differences are apparent at later, non-linear stages of instability development.
How to cite: Viesca, R.: State evolution laws and earthquake nucleation, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16502, https://doi.org/10.5194/egusphere-egu21-16502, 2021.
In models of faults as elastic continua with a frictional interface, earthquake nucleation is the initiation of a propagating dynamic fault rupture nucleated by a localized slip instability. A mechanism capturing both the weakening process leading to nucleation as well as fault healing between events, is a slip rate- and state-dependent friction, with so-called direct effect and evolution effects [Dieterich, JGR 1979; Ruina, JGR 1983]. While the constitutive representation of the direct effect is theoretically supported [e.g., Nakatani, JGR 2001; Rice et al., JMPS 2001], that of the evolution effect remains empirical and a number of state-evolution laws have been proposed to fit lab rock friction data [Ruina, JGR 1983; Kato and Tullis, GRL 2001; Bar-Sinai et al., GRL 2012; Nagata et al., JGR 2012]. These laws may share a common linearization about steady-state, such that a linear stability analysis of steady, uniform sliding yields a single critical wavelength for unstable growth of perturbations [Rice and Ruina, JAM 1983]. However, the laws’ differences are apparent at later, non-linear stages of instability development.
How to cite: Viesca, R.: State evolution laws and earthquake nucleation, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16502, https://doi.org/10.5194/egusphere-egu21-16502, 2021.