SM – Seismology

SM1.1 – General Contributions on Earthquakes, Earth Structure, Seismology

EGU22-4071 | Presentations | SM1.1

Which picker fits my data? A quantitative evaluation of deep learning based seismic pickers

Jannes Münchmeyer, Jack Woollam, Andreas Rietbrock, Frederik Tilmann, Dietrich Lange, Thomas Bornstein, Tobias Diehl, Carlo Giunchi, Florian Haslinger, Dario Jozinović, Alberto Michelini, Joachim Saul, and Hugo Soto

Seismic event detection and phase picking are the base of many seismological workflows. In recent years, several publications demonstrated that deep learning approaches significantly outperform classical approaches, achieving human-like performance under certain circumstances. However, as studies differ in the datasets and evaluation tasks, it is yet unclear how the different approaches compare to each other. Furthermore, there are no systematic studies about model performance in cross-domain scenarios, i.e., when applied to data with different characteristics.

Here, we present the results from a large-scale benchmark to address these questions. We compare six previously published deep learning models on eight datasets covering local to teleseismic distances and on three tasks: event detection, phase identification and onset time picking. Furthermore, we compare the results to a classical Baer-Kradolfer picker.

Overall, we observe the best performance for EQTransformer, GPD and PhaseNet, with a small advantage for EQTransformer on teleseismic data. Furthermore, we conduct a cross-domain study, analyzing model performance on datasets they were not trained on. We show that trained models can be transferred between regions with only mild performance degradation, but models trained on regional data do not transfer well to teleseismic data.

As deep learning for detection and picking is a rapidly evolving field, we ensured extensibility of our benchmark by building our code on standardized frameworks and making it openly accessible. This allows model developers to easily evaluate new models or performance on new datasets. Furthermore, we make all trained models available through the SeisBench framework, giving end-users an easy way to apply these models.

 

Published as Münchmeyer, J., Woollam, J., Tilmann, F., Rietbrock, A., Lange, D., Bornstein, T., Diehl, T., Giunchi, C., Haslinger, F., Jozinović, D., Michelini, A., Saul, J. & Soto, H. (2021). Which picker fits my data? A quantitative evaluation of deep learning based seismic pickers. Journal of Geophysical Research: Solid Earth. doi.org/10.1029/2021JB023499

How to cite: Münchmeyer, J., Woollam, J., Rietbrock, A., Tilmann, F., Lange, D., Bornstein, T., Diehl, T., Giunchi, C., Haslinger, F., Jozinović, D., Michelini, A., Saul, J., and Soto, H.: Which picker fits my data? A quantitative evaluation of deep learning based seismic pickers, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4071, https://doi.org/10.5194/egusphere-egu22-4071, 2022.

EGU22-12782 | Presentations | SM1.1

Integrated Seismic Program (ISP): A new Python GUI-based software for earthquake seismology and seismic signal processing 

Andrés Olivar-Castaño, Roberto Cabieces, Jesús Relinque, and Thiago C. Junqueira

EGU22-9027 | Presentations | SM1.1

The investigation of back projection location errors in  Commander Island

Yijun Zhang, Han Bao, and Yosuke Aoki

EGU22-9062 | Presentations | SM1.1

Investigating Vrancea intermediate depth seismic activity in Romania using automatic waveform processing methods

Natalia Poiata, Bogdan Grecu, Raluca Dinescu, Felix Borleanu, and Dragos Tataru

Seismic activity in Romania is dominated by the intermediate-depth earthquakes generated inside the seismogenic body of the Vrancea seismic zone extending to the depth of 180 km. This earthquakes represent the main source of seismic hazard for Romania and neighbouring countries, with the most recent largest events of M 7.7 and 7.4 in 1940 and 1977 that caused significant and widespread destruction. Space distribution of the intermediate-depth earthquakes from Vrancea is constrained to a compact volume (60-180 km in depth and 20x50 km areal extent) falling into the category of, so called, “seismic nests”, which have peculiar and not well understood seismogenic mechanisms.

We present first results obtained by applying the automated waveform analysis schemes to the detection, location and characterization of seismicity from the Vrancea zone to the continuous data recorded at seismic stations of the Romanian seismic network. We evaluate the performance of the methods like network-based full-waveform coherency earthquake detection and location and the template-based waveform similarity analysis for building a detailed view of seismic activity in space and time and to provide a fully automated workflow for continuous seismic data analysis. We use case-specific, for Vrancea seismic region, synthetic example to test the detection and location scheme setup and resolution. The real dataset of continuous seismic data focuses on the two month time period around the recent, moderate (M 5.6) December 27, 2016 earthquake.

The preliminary results of the automated detection and location analysis indicate reduced foreshock and aftershock activity for this event. According to the Romanian earthquake catalog, this appears to be a common pattern for moderate (M ~5.0-6.0) magnitude events. We also discuss the results of the template-based waveform similarity analysis for the detected and located events, as well as how the combination of the two methods can contribute to the enhanced seismic monitoring and hazard assessment.

How to cite: Poiata, N., Grecu, B., Dinescu, R., Borleanu, F., and Tataru, D.: Investigating Vrancea intermediate depth seismic activity in Romania using automatic waveform processing methods, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9062, https://doi.org/10.5194/egusphere-egu22-9062, 2022.

EGU22-9192 | Presentations | SM1.1

Recalculating the local magnitude of events in the Hungarian National Seismological Bulletin

Marietta Csatlós and Bálint Süle

Local magnitude is one of the oldest and widely used term for characterizing the size of seismic events. Mostly based on the maximum amplitude measured on the components of the seismograms associated with the seismic event. The events in the Hungarian National Seismological Bulletin were relocated by Bondar et al. (2018). Before 2015 the bulletin did not contain amplitudes therefore it was not possible to calculate new local magnitudes for the new hypocenters. Moreover, the magnitudes were calculated by different methodology before 2015.

In this study, all three components of all available waveforms were collected for the events occurred between 1996 and 2016, and the local magnitudes were recalculated. Thus, we present a consistent data set for the whole period. Magnitude values based on both horizontal and vertical components are presented.

Amplitudes were measured on all three components, thus it was possible to compare the maximum amplitudes of the horizontal and vertical components recorded at stations in different geological conditions. For stations located on sediment, generally higher amplitude values were obtained on the horizontal components. The horizontal amplitude was 2.5 or 3 times larger for the Great Hungarian Plain stations on thick sediments. The differences between stations on firm bed rock were smaller.

The collected waveforms and amplitude measurements provide the opportunity to perform the calibration of the local magnitude scale to the geological conditions of Hungary.

 

 

Bondár, I., Mónus, P., Czanik, Cs., Kiszely, M., Gráczer, Z., Wéber, Z., the AlpArrayWorking Group. 2018: Relocation of Seismicity in the Pannonian Basin Using a Global 3D Velocity Model. Seismological Research Letters. pp.2284-2293.

How to cite: Csatlós, M. and Süle, B.: Recalculating the local magnitude of events in the Hungarian National Seismological Bulletin, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9192, https://doi.org/10.5194/egusphere-egu22-9192, 2022.

EGU22-2839 | Presentations | SM1.1

A decade of short-period earthquake rupture histories from multi-array back-projection

Felipe Vera, Frederik Tilmann, and Joachim Saul

Teleseismic back-projection has emerged as a widely-used tool for understanding the rupture histories of large earthquakes. However, its application often suffers from artifacts related to the receiver array geometry, notably the `swimming' artifact. We present a teleseismic back-projection method with multiple arrays and combined P and pP waveforms. The method is suitable for defining arrays ad-hoc in order to achieve a good azimuthal distribution for most earthquakes.

We present a catalog of short-period rupture histories (0.5-2.0 Hz) containing 54 events from 2010 to 2021 (Mw  7.5), including recent and significant earthquake ruptures, e.g., 2021 Mw 8.3 South of Sandwich Islands, 2021 Mw 8.2 Chignik, 2021 Mw 8.1 Kermadec Islands, and 2020 Mw 7.8 Simeonof Island.

The method provides semi-automatic estimates of rupture length, directivity, speed, and aspect ratio, which are related to the complexity of large ruptures. We determined short-period rupture length scaling relations that are in good agreement with previously published relations based on estimates of total slip. Rupture speeds were consistently in the sub-Rayleigh regime for thrust and normal earthquakes, whereas strike-slip events propagated in the unstable supershear range. Many of the rupture histories exhibited complex behaviors such as rupture on conjugate faults (e.g., 2018 Mw 7.9 Gulf of Alaska), bilateral ruptures (e.g., 2017 Mw 7.8 Komandorsky Islands), and dynamic triggering by a P wave (e.g., 2016 Mw 7.9 Solomon Islands). For megathrust earthquakes, ruptures encircling asperities were frequently observed, with down-dip (e.g., 2021 Mw 8.1 Kermadec Islands), up-dip (e.g., 2016 Mw 7.8 Pedernales), double encircling (e.g., 2015 Mw 8.3 Illapel), and segmented (e.g., 2020 Mw 7.8 Simeonof Island) patterns. Although there is a preference for short-period emissions to emanate from central and down-dip parts of the megathrust, emissions up-dip of the main asperities are more frequent than suggested by earlier results.

How to cite: Vera, F., Tilmann, F., and Saul, J.: A decade of short-period earthquake rupture histories from multi-array back-projection, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2839, https://doi.org/10.5194/egusphere-egu22-2839, 2022.

EGU22-11974 | Presentations | SM1.1

Covariance Matrix Analysis and Classification of Low-Frequency Tectonic Seismic Activity in Shikoku, Japan

Andres Barajas, Cyril Journeau, and Nikolai Shapiro

Low-frequency seismic tremors and earthquakes play an important role in the understanding of the seismic processes occurring in seismogenic fault zones and volcanic systems. The covariance matrix, a method that analyses the spatial coherence of continuous seismic noise records on the surface, has proven to be an efficient tool to detect and localize seismovolcanic processes, allowing the classification between local earthquakes, tremors, and low-frequency earthquakes. We use this method in the analysis of tectonic seismic activity in the region of Shikoku, Japan, where a high rate of tremors and low-frequency earthquakes have been previously reported. The classification of the seismic activity over the spectral width and the network response function, shows distinct characteristic distributions from studies done in volcanic systems. We perform a series of synthetic tests that reproduce the classification patterns and spectral widths observed in volcanic and tectonic systems, allowing us to recognize fundamental differences in the duration, frequency and distribution patterns of volcanic and tectonic tremors and low-frequency earthquakes. 

How to cite: Barajas, A., Journeau, C., and Shapiro, N.: Covariance Matrix Analysis and Classification of Low-Frequency Tectonic Seismic Activity in Shikoku, Japan, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11974, https://doi.org/10.5194/egusphere-egu22-11974, 2022.

EGU22-8492 | Presentations | SM1.1

Boundary and elastic parameter sensitivity kernels for a receiver function waveform misfit in a global earth.

Janneke de Jong, Hanneke Paulssen, and Jeannot Trampert

The receiver function method is widely used in seismology to study the characteristics of Earth’s major discontinuities. Ray theory and an assumed planar incoming wave are often used to estimate which regions of the mantle, crust and discontinuity contribute to the receiver function. To test the validity of these simplifying assumptions, we derived the adjoint source of a receiver function waveform misfit and applied the adjoint method on synthetic teleseismic receiver functions to calculate their sensitivity kernels of both subsurface velocity parameters in the mantle and boundary topography on the discontinuity. Here we focused on the P660s-phase and the 660-discontinuity. We observe a strong sensitivity to the wavefield far away from the discontinuity, particularly for the Vp sensitivity kernel. It has a strong sensitivity to the Fresnel zone of the P660s-phase before conversion, but also to the scatterers of the direct P-wave and other phases that arrive within the considered time window. This implies that mapping the observations solely to the P660s ray paths and ray-theoretical conversion points might be too simplistic and lead to inaccuracies in the conclusions. In general, a receiver function has a strong dependance on the background velocity models everywhere in the mantle. The boundary topography kernels have a sensitivity predominantly to the area near the conversion point. The diameter of the high-sensitivity area is roughly 300 km for an event with a source halftime of 5 s. Relatively weak sensitivity to the source region and the scatterers of the direct P-wave are observed in the boundary kernels as well. Our results show that using the adjoint method on receiver function waveforms to invert for mantle structure and boundary topography is possible and advisable. It allows for an automatic consideration of all contributing phases and scatterers arriving within the chosen time window, which is important for correctly dealing with velocity perturbations. The boundary kernels demonstrate that the receiver functions’ sensitivity to topography is concentrated to the region around the ray theoretical conversion point.

How to cite: de Jong, J., Paulssen, H., and Trampert, J.: Boundary and elastic parameter sensitivity kernels for a receiver function waveform misfit in a global earth., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8492, https://doi.org/10.5194/egusphere-egu22-8492, 2022.

EGU22-10613 | Presentations | SM1.1

Meeting the challenging performance requirements of Global Seismic Observatory Networks with the new Trillium 360 GSN

Geoffrey Bainbridge, Bruce Townsend, Sarvesh Upadhyaya, and Valarie Hamilton

Nanometrics new Trillium 360 GSN seismometer embodies the culmination of many years of research and technology innovation as well as extensive collaboration with and input from the scientific community interested in very broadband seismometry.  Several generations of seismometers with 240 or 360 second corner frequency have demonstrated successive improvements in self-noise at both very low and high frequencies.  The most recent development has produced the lowest self-noise of any vault seismometer, and is the only seismometer currently being manufactured that meets the performance requirements of a primary seismometer for the Global Seismographic Network and Geoscope. 

Posthole, Borehole and Vault form factors are available and being manufactured and delivered to the GSN.  Performance testing of several units of each model type has been carried out at the facilities of GSN participating member institutions.  The results of the performance testing are reviewed and interpreted, and compared with other co-located instrument types including the venerable STS-1.  Field deployment is now proceeding, to upgrade networks with the Trillium 360 GSN seismometer.  We will show results from new deployments as available at the time of the 2022 SSA conference.  

We will also present the Trillium 360 roadmap, with a smaller low-power version for ocean bottom and portable land deployments in development for 2022, and early test results as available.  The goal of this next phase is to bring very broadband performance to any location and environment at reduced logistical cost.

How to cite: Bainbridge, G., Townsend, B., Upadhyaya, S., and Hamilton, V.: Meeting the challenging performance requirements of Global Seismic Observatory Networks with the new Trillium 360 GSN, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10613, https://doi.org/10.5194/egusphere-egu22-10613, 2022.

EGU22-4238 | Presentations | SM1.1

MERMAIDs in the South Pacific Ocean: Observations, Measurements, Modeling, Data Availability, and First Hints at Mantle Structure

Jessica Irving, Joel Simon, Sirawich Pipatprathanporn, Frederik Simons, and The EarthScope-Oceans Consortium


MERMAIDs (Mobile Earthquake Recording in Marine Areas by Independent Divers) are seismic instruments which record local, regional and teleseismic earthquakes, and other signals, in the oceans. In the Southern Pacific Ocean, some fifty MERMAIDs are collecting acoustic pressure time series as part of the South Pacific Plume Imaging and Modeling (SPPIM) project. Deployed in 2018 and 2019 by members of the EarthScope-Oceans consortium, these instruments record continuous time series data on a one-year buffer and autonomously report a wealth of waveforms, selectively triggered mostly by teleseismic events, suitable for mantle tomography. 

Listening for signals while roughly 1.5 km below the ocean surface, MERMAIDs' primary mission is to detect and deliver records of P-waves generated by distant earthquakes, and collectively they have returned many thousands of seismograms corresponding to such signals. We present highlights from our earthquake catalog and discuss the changing character and causes of the background noise. Whilst the South Pacific fleet is programmed to only send short seismic records, corresponding to confident identifications of teleseismic first arrivals, some records contain later-arriving phases. In addition to P-waves, we present a miscellany of observations of other signals, including core phases, converted S- and surface waves, and T-phases. Furthermore, we illustrate that we are able to obtain other recorded data segments through buffer requests via satellite. 

Data from the MERMAIDs owned by Geoazur and Princeton University that we report on here are being archived by IRIS—those from three instruments is available without embargo. We highlight MERMAID waveform availability and its utility to the scientific community via examples of their modeling and preliminary interpretations that can be made regarding wavespeed heterogeneity in the dynamic mantle below the Pacific Ocean. 

How to cite: Irving, J., Simon, J., Pipatprathanporn, S., Simons, F., and EarthScope-Oceans Consortium, T.: MERMAIDs in the South Pacific Ocean: Observations, Measurements, Modeling, Data Availability, and First Hints at Mantle Structure, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4238, https://doi.org/10.5194/egusphere-egu22-4238, 2022.

EGU22-8833 | Presentations | SM1.1

Searching for Mid-Mantle Water with Multitaper-Correlation SS Precursors

William Frazer and Jeffrey Park

Earth’s mantle transition zone (MTZ) is a possible global water reservoir and may be responsible for long-term (~100 Ma) ocean-mass regulation, driven by plate tectonics and mantle convection. Estimates of MTZ mineral water capacity exceed 1 wt%, far greater than that of rocks of either the upper- or lower-mantle. When water-rich material from the transition zone penetrates the upper or lower mantle, partial melting occurs due to the decrease in water capacity after phase transition, generating a reduction in seismic velocities. This process can add an additional low-velocity zone (LVZ) that can be imaged above(below) the 410(660)-km discontinuities, if melt is present. Depending on the melt fraction and wetting angle at mineral-grain boundaries, decreases in shear velocity of 0.5-2.6% can be generated. Seismic receiver functions have detected velocity reductions both above and below the MTZ, interpreted to be partial melting induced by high water content under the Alpine orogeny, in the deep Japan-slab subduction zone, and across the western United States. Since much of Earth lacks seismic stations, we apply SS precursors to conduct a global survey for such LVZs. The precursors to the SS phase reflect off interfaces near the source-receiver midpoint, so seismic stations are not required to be located above the target region. Detection and interpretation of LVZs surrounding sharp positive-velocity gradients, such as the 410- or 660-km discontinuity, is often complicated by side lobes, an artifact of common signal-processing routines. To address this challenge, we develop an SS precursor method based on the multitaper-correlation (MTC) technique. MTC allows for analysis at higher frequency, leading to finer depth resolution, and can increase the number of useful data records. We conduct MTC SS-precursor analysis for seismic waveforms recorded on the ~125 stations of the Global Seismographic Network to benchmark our new method and search for LVZs. Results will be compared to LVZs interpreted from previous seismic analysis.

How to cite: Frazer, W. and Park, J.: Searching for Mid-Mantle Water with Multitaper-Correlation SS Precursors, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8833, https://doi.org/10.5194/egusphere-egu22-8833, 2022.

EGU22-2498 | Presentations | SM1.1

Crustal structure and mantle anisotropy beneath Klyuchevskoy Volcano and surrounding regions in Kamchatka

Ayoub Kaviani, Georg Rümpker, Ivan Koulakov, Christoph Sens‐Schönfelder, and Nikolay Shapiro

We use seismological data collected from a recently deployed seismic network around the Klyuchevskoy Volcanic Group (KVG) in Kamchatka to study the crustal structure and mantle anisotropy beneath the region. In order to improve and extend the data coverage, we combined this data set with data from previous temporary deployments and permanent stations to reach a total number of 145 stations covering a region defined in the geographic coordinates 150°-167°E and 50°-61°N.

We use receiver function (RF) analysis to study the crustal structure beneath the study area. P-RFs are migrated to depth and stacked to image seismic interfaces beneath the network of seismic stations. We used a recently published three-D seismic tomography model to migrate the RFs from time to space domain. The RF amplitudes are stacked in the space domain using the Common Conversion Point (CCP) approach. The stacked RF amplitudes provide a 3-D image of seismic interfaces. The use of the 3-D velocity model helps migrate the RF amplitude to correct depths so that the depth and geometry of subsurface interfaces are constrained more correctly.  Furthermore, we are able to better compare the 3-D CCP images with the 3-D tomography model. In addition, at stations with a sufficient number of RFs, we also tried to calculate Moho depth and mean Vp/Vs ratio using the single-station H-k stacking approach. This analysis provides a way to better identify the interfaces beneath different locations and verify and adjust the depths obtained using the CCP stacking. We found a relatively complex crustal structure in the entire region of the KVG that laterally merges to a simpler structure to the west. Seismic tomography images provide better lateral resolution of velocity anomalies while RF analysis provides better vertical resolution of vertical velocity constants. Our RF-CCP images reveal two main interfaces beneath the active volcanic region. The shallow interfaces with a limited lateral extent have depths varying between 20 and 30 km. The deeper interface occurs at depths 50-60 km with an east-to-west dipping direction. In comparison with the seismic tomography model, we infer that the shallow interface is related to a velocity increase from <6 km/s to >7 km/s, implying the presence of a shallow low-velocity zone beneath the volcanic group. The deeper interface that correlates with a velocity increase from <7 km/s to around 8 km/s might be related to the top of the subducting plate. 

In addition to the RF analysis for the crustal structure, we also perform splitting analysis of core-refracted shear waves (SKS) to study mantle seismic anisotropy as a proxy for the pattern of the mantle flow field. Our SKS-splitting analysis indicates a trench-normal mantle flow beneath the eastern edge of the Kamchatka peninsula that converts to a more complex pattern beneath the KVG region. We argue that this pattern of fast polarization direction suggests the rotational mantle flow that may be related to a slab gap at the junction between the Kuril-Kamchatka and Aleutian arcs.

How to cite: Kaviani, A., Rümpker, G., Koulakov, I., Sens‐Schönfelder, C., and Shapiro, N.: Crustal structure and mantle anisotropy beneath Klyuchevskoy Volcano and surrounding regions in Kamchatka, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2498, https://doi.org/10.5194/egusphere-egu22-2498, 2022.

EGU22-3017 | Presentations | SM1.1

An Improved shear velocity model beneath the Iranian plateau using adjoint noise tomography

Abolfazl komeazi, Ayoub Kaviani, Farzam Yaminifard, and Georg Rümpker

We perform an adjoint waveform tomography using Rayleigh-wave empirical Green‘s functions (EGFs) at periods 10-50 s to improve a pre-existing 3-D velocity model of the crust and uppermost mantle beneath the Iranian plateau. The starting model was derived from a conventional surface-wave dispersion tomography based on high-frequency ray-theory assumption to invert of a quasi-3-D shear-wave velocity model. We use the EGFs from the same study that were derived from cross correlation of continuous seismic noise. Adjoint tomography refines the initial model by iteratively minimizing the frequency-dependent travel-time misfits between synthetic and observed EGFs measured in different period bands. Our new model covers the known tectonic units such as the Central Iranian Block, Zagros fold-and-thrust belt, Sanandaj-Sirjan metamorphic zone and Urumieh-Dokhtar magmatic arc.

Overall, the adjoint tomography provides images with better lateral resolution and depth sensitivity and more realistic absolute velocity values due to the inclusion of finite-frequency waveforms. The use the numerical spectral-element solver in adjoint tomography provides accurate structural sensitivity kernels, which helps to obtain more robust images rather than those generated by ray-theory tomography. The final model adjusts the shapes of velocity anomalies at crustal depth more specifically for the eastern Zagros. The final model significantly improves the initial model at the upper mantle depths and provides a higher resolution for the shape of velocity anomalies.

How to cite: komeazi, A., Kaviani, A., Yaminifard, F., and Rümpker, G.: An Improved shear velocity model beneath the Iranian plateau using adjoint noise tomography, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3017, https://doi.org/10.5194/egusphere-egu22-3017, 2022.

The Eifel region is a large volcanic system in the middle of European continent. From the Eifel teleseismic tomography experiment (8 months in 1997-1998), a mantle plume beneath the volcanic fields (down to 400 km depth) has been identified and further confirmed by receiver function and teleseismic surface wave dispersion analyses. A study in 2020 using dense geodetic observations leads to the conclusion that the Eifel region experiences a pronounced uplift encompassing the neighbouring countries Netherlands, Belgium, Luxembourg and France, which is attributed to the same buoyant mantle plume.

A detailed focus on the uppermost 30 km above the Moho has been missing until recently. However, a noteworthy recent seismological investigation showed the evidence of a deep magmatic recharge beneath the Laacher See Volcano in East Eifel between 2013 and 2018. Located at depth roughly between 40 and 10 km, low-frequency seismic swarms, which are typical of volcanic environment, convey the presence of magma movements and potential storage zones in the crust.  

The present study aims to bring additional information on this shallow active magmatic system using an Ambient Noise Tomography (ANT). Thanks to theoretical and technical developments over the two last decades, this approach has been increasingly popular for imaging Earth structure worldwide at different scales. We use here ambient noise data from archives of the 1997-1998 Eifel experiment and more recent (2019-2020) continuous seismic record. The group velocity dispersion of Rayleigh waves are estimated between station pairs from Noise Cross-correlation Functions (NCF) covering the secondary microseismic frequency band, which allows to sample the uppermost 10-20 km of the crust. Our contribution includes a complete description of the ANT/NCF processing (e.g., directivity of the noise sources, sensitivity tests) in order to better constrain the velocity anomalies observed in the Eifel region and around.

How to cite: Barrière, J. and Oth, A.: Imaging the uppermost layers of the Eifel volcanic system (Germany) using ambient microseismic noise, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7268, https://doi.org/10.5194/egusphere-egu22-7268, 2022.

EGU22-5860 | Presentations | SM1.1

Seismicity analysis in southern Ghana- I: Detecting local earthquakes by Deep Learning

Hamzeh Mohammadigheymasi, Nasrin Tavakolizadeh, S. Mostafa Mousavi, Graça Silveira, and Rui Fernandes

A large volume of digital seismic data was recorded by six broadband seismic sensors equipped with GPS-clock timing in the Ghana Digital Seismic Network (GHDSN) between October 2012 and April 2014. For this period, no public seismicity catalog was reported by the global data centers, International Seismological Center (ISC), and United States Geological Survey (USGS) for southern Ghana. In this study, this database is processed to detect local earthquakes. To facilitate the challenging and time-consuming process of detecting the earthquakes and picking the arrival times of P and S phases, we utilize EQTransformer, a Deep Learning (DL) model deploying Hierarchical Attention Mechanism (HAM) for simultaneous earthquake detection and phase picking. This model utilizes global and local levels of attention mechanism for identifying earthquake and seismic phases deriving benefits from deep neural networks, including convolutional and recurrent neurons. The thresholding values of 0.2, 0.07, and 0.07 are set for earthquake detection, P-picking, and S-picking, respectively. As a result, a list of events for each station of the network with the associated time of detection, as well as P and S phase arrivals are obtained. Taking these arrival times into account, we have devised a so-called ”conservative strategy” to optimally extract all possible earthquakes in the data set, amenable to locate. Initially, a list of preliminary events recorded by at least two stations is created by comparing the earthquake occurrence and arrival times of the P and S phases for all stations regarding a 100 sec time threshold. The list in this step includes 317 events recorded by at least two stations. Eventually, an analyst controls the obtained waveforms in other stations assesses whether EQTranasformer misses the preliminary list of events in those stations. Consequently, a number of 533 picked phases (282 P and 251 S) recorded by a minimum of 3 stations are finalized. Incorporating these phases and removing the instrument response from the waveforms, the hypocentral parameters for 73 earthquakes with 2.5 ≤ M L ≤ 4.0 are estimated. The main concentration of events is on the intersection of the Akwapim fault zone and the coastal boundary fault, with some scattered seismicity along the Akwapim fault zone. The corresponding set of seismic phases is utilized to estimate an updated 1D crustal velocity model for the study area. This research contributes to the FCT-funded projects SHAZAM (Ref. PTDC/CTA-GEO/31475/2017), RESTLESS (Ref. PTDC/CTA-GEF/6674/2020), SIGHT (Ref. PTDC/CTA-GEF/30264/2017), and IDL (Ref. UIDB/50019/2020).

How to cite: Mohammadigheymasi, H., Tavakolizadeh, N., Mousavi, S. M., Silveira, G., and Fernandes, R.: Seismicity analysis in southern Ghana- I: Detecting local earthquakes by Deep Learning, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5860, https://doi.org/10.5194/egusphere-egu22-5860, 2022.

EGU22-5570 | Presentations | SM1.1

Seismicity analysis of Southern Ghana II: Updated crustal velocity model and hypocentral parameters

Susana Custódio, Hamzeh Mohammadigheymasi, Nasrin Tavakolizadeh, Luis Matias, and Graça Silveira

A small network of six broadband seismic sensors operated in southern Ghana between October 2012 and April 2014 (GHDSN). During this period, no seismicity was reported by the global data centers, however application of the Deep Learning algorithm EQTransformer resulted in the detection and subsequent location of 73 earthquakes. Preliminary constant crustal velocity models with  vp=5.55 km/s and vs=3.36 km/s have been utilized since 2002 to locate the local earthquakes in southern Ghana. Using this crude velocity model resulted in scattered seismicity, hinting into a likely inadequacy of these preliminary velocity parameters to represent the elastic properties of the area. In this study, we perform a joint-inversion for estimating an updated 1D crustal velocity model and the hypocentral parameters of the 73 recently detected local earthquakes. A grid search method is implemented and a 6-layer velocity model is defined, down to 45 km crustal depth. The space of velocity model parameters is searched by altering the upper depth of the layers (ud), P-wave velocity in each layer (vp), and the ratio of vp/vs. The optimized velocity model and hypocenteral parameters are evaluated by minimizing the RMS error function between the observed (533 picked phases consisting of 282 P and 251 S phases) and calculated arrival times. A two-step implementation is devised to increase the computational efficiency of the inversion process. Initially, the optimum  vp/vs is estimated by implementing a coarse grid search on vp and ud values. Then, incorporating the optimum vp/vs a fine grid search on vp and ud is applied.
The results yields layers with 1, 13, 8, 13 and 10 km thickness, with vp = 5.9, 6.1, 6.3, 6.5, 6.9 and 7.2 km/s, respectively. The updated velocities for the first and last layers are 6% and 26% percent higher than the previously reported constant velocity models. Furthermore, the updated vp/vs=1.70 is 0.03% higher than the corresponding value vp/vs=1.65 of the constant velocity model. The updated hypocentral locations of the 73 earthquakes with  2.5<ML<3.9 are concentrated on five major clusters. Two clusters are located on the AFZ, indicative of the active role of this structure in the seismicity of the region. Two other clusters, which have the highest rate of activity,  are positioned in the intersection between the AFZ and CBF. The last cluster consists of scattered earthquakes that coincide with mapped segments of the AFZ. Incorporating the updated velocity model for estimating the hypocentral parameters resulted in enhanced seismogenic source delineation in southern Ghana.  This research contributes to the FCT-funded projects SHAZAM (PTDC/CTA-GEO/31475/2017), RESTLESS (PTDC/CTA-GEF/6674/2020), SIGHT (PTDC/CTA-
GEF/30264/2017) and IDL (UIDB/50019/2020).

How to cite: Custódio, S., Mohammadigheymasi, H., Tavakolizadeh, N., Matias, L., and Silveira, G.: Seismicity analysis of Southern Ghana II: Updated crustal velocity model and hypocentral parameters, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5570, https://doi.org/10.5194/egusphere-egu22-5570, 2022.

EGU22-11076 | Presentations | SM1.1

Preliminary results of the two seismic sequences in the Vienna Basin in March and April 2021 

María del Puy Papí Isaba, Wolfgang Lenhardt, Rita Meurers, Maria Theresia Apoloner, Helmut Hausmann, Maurizio Mattesini, and Elisa Buforn

We present a preliminary analysis of two seismic sequences between March and April 2021, near Neunkirchen and Gloggnitz, about 50 km from Vienna, Austria, and around 15 km apart from each other. Despite the moderate magnitudes, the recent earthquakes in the epicentral region, in the southern part of the Vienna Basin, were felt in the epicentral region and up to a distance of 300 km away. 

The Neunkirchen sequence started on March 11th, 2021. According to the Austrian Seismological Service at ZAMG, the last recorded earthquake occurred on May 12th, 2021. Over 245 earthquakes, with local magnitudes ranging from 0.5 to 4.6, were recorded until mid of May 2021. Out of the 245 earthquakes, 21 were felt by the population (1.8 ≤ ML ≤ 4.6), and two of them (ML4.6 and ML4.4) caused minor damage in the epicentral region. According to the Austrian Seismological Service, the depths of this sequence ranged from 7 to 12 km. 

The Gloggnitz sequence started on April 1st, 2021, and continued until May 8th, 2021. The epicenters of 65 detected earthquakes were located. Four earthquakes were felt, from which two (ML3.6 on April 20th and ML3.8 on April 23rd) caused slight damage. The local magnitudes of this seismic sequence ranged from -0.3 to 3.8; depths varied between 4 and 7 km. 

The relocation of the earthquakes of both sequences was carried out using the NonLinLoc by Lomax et al. (2019). We obtained the ellipse error for all relocated earthquakes. The focal mechanisms of the largest earthquakes were calculated using Seismic Moment-Tensor-Inversion. For the remaining events, a joint fault-plane solution was investigated. Furthermore, we compiled and analyzed the macro-seismic questionnaires of all felt earthquakes in the series and produced intensity maps (EMS-98). We compared the intensity attenuation as a function of distance with the newly available data and derived an Intensity Prediction Equation (IPE) for the region.

How to cite: Papí Isaba, M. P., Lenhardt, W., Meurers, R., Apoloner, M. T., Hausmann, H., Mattesini, M., and Buforn, E.: Preliminary results of the two seismic sequences in the Vienna Basin in March and April 2021 , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11076, https://doi.org/10.5194/egusphere-egu22-11076, 2022.

EGU22-8652 | Presentations | SM1.1

Testing seismic velocity models with quarry blast data

Pierre Arroucau, Jessie Mayor, Marc Grunberg, Emmanuelle Nayman, and Guillaume Daniel

Seismic event locations are usually performed by means of iterative, linearized arrival time inversion considering 1D velocity models with fixed data errors. Both the use of inaccurate velocity structure or data error estimates may however affect the quality of event location and uncertainty evaluation. Here, we test a 3D P- and S-wave velocity model built in a previous work for Metropolitan France (the part of France located in Europe) and we compare it with the “Auvergne” 1D velocity model used by BCSF-RéNaSS (Bureau Central Sismologique Français - Réseau National de Surveillance Sismique) using quarry blast data. The reason for using quarry blast data is that, to some extent, their epicentral location and depth are known, which is not the case for earthquakes. We first identify potential active quarries over the territory of Metropolitan France by comparing catalog quarry blast locations with those from quarries visible from satellite images. Relocation is achieved by means of a Hierarchical Bayesian inversion procedure in which not only the hypocentral parameters (longitude, latitude, depth, origin time) are inverted for, but also P- and S-wave arrival time errors. The area of interest is a 1° by 1° zone located between 4°E and 5°E in longitude and 44°N and 45°N in latitude, the region where the Le Teil earthquake occurred (Mw 4.9, 2019/11/11). We first demonstrate the ability of the algorithm to properly determine hypocentral parameters and data noise using two simple synthetic experiments. Then we apply it to real data and relocate 147 quarry blasts that occurred in the region between 1980 and 2020 and that were located wit the “Auvergne” 1D velocity model. Relocations obtained with the 1D and 3D model are rather similar. Estimated data errors are larger, in both cases, than the amplitude of picking uncertainties, meaning that both models could be improved, by seismic arrival time tomography for instance. They are larger in the 3D case, suggesting that, from that point of view, the 1D model is in better agreement with the data. Distances between relocated hypocenters and the closest known quarry are comparable but relocations with the 3D model are characterized by shallower hypocenters than those obtained with the 1D model, so they appear more consistent with the fact that events are quarry blasts. In both cases, some events are quite far away from the closest quarry, suggesting that some of them might be natural events.

How to cite: Arroucau, P., Mayor, J., Grunberg, M., Nayman, E., and Daniel, G.: Testing seismic velocity models with quarry blast data, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8652, https://doi.org/10.5194/egusphere-egu22-8652, 2022.

EGU22-8496 | Presentations | SM1.1

Characteristic of Source and Seismic Hazard Analysis of Majene Earthquake Mw 6.2, January 15, 2021

Retno Agung Prasetyo, Supriyanto Rohadi, Rahmat Setyo Yuliatmoko, Aditya Rahman, Yusuf Hadi Perdana, Nelly Florida Riama, Suko Prayitno Adi, Dwikorita Karnawati, and Bambang Setiyo Prayitno

A major earthquakes struck the Majene Regency, in West Sulawesi province, Indonesia, on 15 January 2021 at 02.28 local time, the hypocenter is 2.97°S, 118.99°E, depth 38.0 km, with moment magnitude Mw 6.2 with an epicenter located about 6 km Northeast Majene, West Sulawesi. This large event causing extensive damage, great economic loss and casualties in the Majene city and surrounding region. The mainshock preceded by significant foreshock on 14 January 2021 at 14.35 local time, 3°S, 118.94°E, depth 10.0 km Mw 5.9, epicenter was located at about 4 km Northwest of Majene. The faulting orientation of the mainshock, and foreshock was strike = 330°, dip = 17°, and slip = 59°, and strike = 353°, dip = 29°, and slip = 61°, respectively, is possibly related to Mamuju-Majene thrust fault. Focal mechanism solutions for the earthquakes indicate rupture occurred thrust fault with low dip angle. The mainshock was followed by low aftershocks productivity may due to homogeneous faulting systems and relatively uniform stress state in that region. We use hypocenter relocation, stress drop, coulomb stress and seismic hazard (PSHA) to investigate the earthquake characteristics and seismic hazard analysis. The distribution of hypocenter relocations indicate aftershock ruptured northern extension of the mainshock. This result supports that the highest of acceleration is the north component of the three component recorded acceleration, this detect the components of directivity toward the north for the foreshock distribution.

How to cite: Prasetyo, R. A., Rohadi, S., Yuliatmoko, R. S., Rahman, A., Perdana, Y. H., Riama, N. F., Adi, S. P., Karnawati, D., and Prayitno, B. S.: Characteristic of Source and Seismic Hazard Analysis of Majene Earthquake Mw 6.2, January 15, 2021, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8496, https://doi.org/10.5194/egusphere-egu22-8496, 2022.

EGU22-8366 | Presentations | SM1.1

The 14 December 2021, Mw 7.4 Flores Earthquake: Review of the hypocenter relocation, slip distribution, coulomb stress, and seismic hazard

Supriyanto Rohadi, Tio Azhar Prakoso, Tatok Yatimantoro, Aditya Rahman, Bambang Sunardi, Agustya Adimarta, Nelly Florida Riama, Suko Prayitno Adi, Bagus Adi Wibowo, and Dwikorita Karnawati

A major earthquakes struck the north of Flores island, in Nusa Tenggara Timur, Indonesia, on 14  December 2021 at 10:20:22 local time, the hypocenter is 7.59°S, 122.26°E, depth 12.0 km, with moment magnitude Mw 7.4. The faulting orientation of the mainshock, fault plane was strike = 290°, dip = 89°, and rake = 177°, and the auxiliary plane was strike = 21°, dip = 87°, and rake = 1°, respectively, is possibly related to thrust fault in the sea. Focal mechanism solutions for the earthquakes indicate rupture occurred thrust fault with large dip angle. The mainshock was followed by low aftershocks productivity may due to homogeneous faulting systems and relatively uniform stress state in that region. We analyze aftershock hypocenter relocation and gravity anomaly, slip distribution, coulomb stress and seismic hazard (PSHA) to investigate the earthquake characteristics and seismic hazard analysis. The distribution of hypocenter relocations show that aftershock ruptured distribute between two block of high gravity anomaly, its indicate that it was not the new fault. The inversion of the source model shows several time periods of energy release with three main peaks. These temporal rupture suggest repetition of a large scale slip on the large asperity. The models of coulomb stress indicate that static stress transfer due to the Mw 7.4 earthquake is suitable with aftershock spatial distribution. We compute the probabilistic seismic hazard assessment in the Flores region for Earthquake mitigation

How to cite: Rohadi, S., Prakoso, T. A., Yatimantoro, T., Rahman, A., Sunardi, B., Adimarta, A., Riama, N. F., Adi, S. P., Adi Wibowo, B., and Karnawati, D.: The 14 December 2021, Mw 7.4 Flores Earthquake: Review of the hypocenter relocation, slip distribution, coulomb stress, and seismic hazard, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8366, https://doi.org/10.5194/egusphere-egu22-8366, 2022.

EGU22-3794 | Presentations | SM1.1

Preliminary results of investigation of “unidentified fault” associated with the Mw 7.3 Flores Sea earthquake

Pepen Supendi, Nicholas Rawlinson, Bambang Setiyo Prayitno, Sri Widiyantoro, Kadek Hendrawan Palgunadi, Andrean Simanjuntak, Andri Kurniawan, Gayatri Indah Marliyani, Andri Dian Nugraha, Daryono Daryono, Iman Fatchurochman, Muhammad Sadly, Suko Prayitno Adi, Dwikorita Karnawati, Mohammad Taufik Gunawan, and Abraham Arimuko

On December 14, 2021, the Mw 7.3 Flores Sea earthquake occurred approximately 100 km to the north of Flores Island, one of the most complex tectonic settings in Indonesia. The existence of the causative fault that generated this earthquake was not been previously known, therefore making further analysis crucial for assessing future seismic hazard in the region. In this study, we relocated the hypocenter of the mainshock and aftershocks using a double-difference method, determine focal mechanisms using waveform inversion, and then analyse stress changes to estimate the fault type and stress transfer caused by this earthquake. Our relocated hypocenters show that this earthquake sequence ruptured on at least three segments: the source mechanism of the mainshock exhibits dextral strike-slip motion (strike N288oW and dip 78o) that occurred on a West-East trending fault which we call the Kalaotoa Fault, while rupture of the other two segments located to the west and east of the mainshock (WSW-ESE directions, respectively) may have been triggered by this earthquake. The Coulomb stress change of the mainshock shows that areas to the northwest and southeast experienced an increase in stress, which is consistent with the observed aftershock pattern.

How to cite: Supendi, P., Rawlinson, N., Prayitno, B. S., Widiyantoro, S., Palgunadi, K. H., Simanjuntak, A., Kurniawan, A., Marliyani, G. I., Nugraha, A. D., Daryono, D., Fatchurochman, I., Sadly, M., Adi, S. P., Karnawati, D., Gunawan, M. T., and Arimuko, A.: Preliminary results of investigation of “unidentified fault” associated with the Mw 7.3 Flores Sea earthquake, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3794, https://doi.org/10.5194/egusphere-egu22-3794, 2022.

EGU22-8536 | Presentations | SM1.1

The DEnse mulTi-paramEtriC observations and 4D high resoluTion imaging (DETECT) experiment, a new paradigm for near-fault observations

Matteo Picozzi, Antonio Giovanni Iaccarino, Dino Bindi, Fabrice Cotton, Gaetano Festa, Angelo Strollo, Aldo Zollo, Tony Alfredo Stabile, Guido Maria Adinolfi, Claudio Martino, Ortensia Amoroso, Raffaella De Matteis, Vincenzo Convertito, and Daniele Spallarossa and the DETECT team

Near-fault observations can provide insights into the physical process interaction between fault slip activation, fluid presence/migration and seismicity production, processes acting at different timescales that generate large earthquakes.

The DETECT experiment aims at exploiting very dense seismic networks deployed across a segmented faults system to foster the development of scientific integrated methodologies for monitoring and imaging the faults behavior during the inter-seismic phase. Target of the monitoring is to: detect and track space-time trends of different source parameters that could be related to a preparation process leading to a larger earthquake; investigate the frictional and stress states of the fault segments to anticipate the characteristics of the future large earthquake (e.g., hypocenter but also future large seismic energy release locations); analyze the interactions between the different fault segments to model/anticipate potential cascade effects.

The DETECT experiment is carried out in the Irpinia area (southern Italy), one of the regions in Italy and Europe showing the highest seismic hazard. Since august 2021, a constellation of 20 seismic arrays, for a total of 200 seismic stations (20 broad-band sensors and 180 short-periods), has been installed over the fault segments responsible for the Ms 6.9, 1980 Irpinia earthquake, the strongest and most destructive seismic event of the last half-century in southern Italy.

DETECT results from a joint effort of local Universities, National and International Research Institutes. A novel and crucial aspect is that, differently from most studies concerning intra-plate earthquakes which are usually carried out after that large magnitude earthquakes have occurred, DETECT aims to put us in advantageous position and to unveil the preparatory process that generate large earthquakes and anticipate the role of the segmentation by studying at one time different fault segments, some of which are in rather late stage of their seismic cycle.

With this contribution, we aim to present the DETECT experiment, the preliminary results and foster additional cooperation including complementary expertise to further enrich the partnership.

How to cite: Picozzi, M., Iaccarino, A. G., Bindi, D., Cotton, F., Festa, G., Strollo, A., Zollo, A., Stabile, T. A., Adinolfi, G. M., Martino, C., Amoroso, O., De Matteis, R., Convertito, V., and Spallarossa, D. and the DETECT team: The DEnse mulTi-paramEtriC observations and 4D high resoluTion imaging (DETECT) experiment, a new paradigm for near-fault observations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8536, https://doi.org/10.5194/egusphere-egu22-8536, 2022.

EGU22-7994 | Presentations | SM1.1

The impact of the September 27, 2021, Mw=6.0 Arkalochori (Central Crete, Greece) earthquake on the natural environment and the building stock

Spyridon Mavroulis, Haralambos Kranis, Stylianos Lozios, Ioannis Argyropoulos, Emmanuel Vassilakis, Konstantinos Soukis, Emmanuel Skourtsos, Efthymis Lekkas, and Panayotis Carydis

On September 27, 2021, an Mw=6.0 earthquake struck the central part of Crete Island (southern Greece) and in particular the Heraklion Region. This event was preceded by an extended foreshock sequence started on early July 2021 and it was followed by an Mw=5.3 aftershock on the following day.

Taking into account the spatial distribution of foreshocks and aftershocks and the focal mechanism of mainshock as well as the active faults of the earthquake-affected area, it is evident that the seismic activity is strongly related to the NNE-SSW striking W-dipping faults of the Kasteli fault zone located along the eastern margin of the Neogene to Quaternary Heraklion Basin. The latter has been filled with Miocene to Holocene post-alpine deposits.

A field reconnaissance conducted by the authors in the earthquake-affected area shortly after the mainshock revealed that the earthquake-triggered effects comprised mainly rockfalls and slides, as well as ground cracks within or close to landslide zones. These effects were located within the hanging-wall of the KFZ. The affected sites are mainly composed of Miocene deposits and they are characterized by pre-existing instability conditions and high susceptibility to landslides. Far field effects were also observed south of the earthquake-affected area and in particular in the southern coastal part of Heraklion Region.

In regards to the spatial distribution of the earthquake-induced building damage, the vast majority was caused in villages and towns founded on Miocene and Holocene deposits of the hanging-wall. Damage was not reported in settlements located in the footwall, which is composed of alpine formations.

The dominant building types of the earthquake-affected area comprise: (i) buildings with load-bearing masonry walls made of stones and bricks with clay or lime mortar, mainly constructed without any anti-seismic provisions and (ii) buildings with reinforced-concrete frame and infill walls constructed according to the applicable seismic codes. The former suffered the most severe structural damage including partial or total collapse in many villages founded on post-alpine deposits of the hanging-wall of KFZ. The latter responded satisfactory during the mainshock and were less affected with only non-structural damage including cracking, detachment of infill walls from the surrounding reinforced concrete frame, peeling of concrete and short-column failures.

From the abovementioned, it is concluded that the impact of the 2021 Arkalochori earthquake was limited to the hanging-wall of the causative fault zone and in particular to residential areas founded on post-alpine deposits and to slopes highly susceptible to failure within the Heraklion Basin.

How to cite: Mavroulis, S., Kranis, H., Lozios, S., Argyropoulos, I., Vassilakis, E., Soukis, K., Skourtsos, E., Lekkas, E., and Carydis, P.: The impact of the September 27, 2021, Mw=6.0 Arkalochori (Central Crete, Greece) earthquake on the natural environment and the building stock, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7994, https://doi.org/10.5194/egusphere-egu22-7994, 2022.

EGU22-10192 | Presentations | SM1.1

Remote Reconnaissance Mission to the 14th August 2021 Haiti Earthquake; remote sensing and building damage assessments 

Michael Whitworth, Giorgia Giardina, Camilla Penney, Luigi Di Sarno, Keith Adams, Tracy Kijewski-Correa, Josh Macabuag, Fatemeh Foroughnia, Valentina Macchiarulo, Mobin Ojaghi, Alessandra Orfeo, Francesco Pugliese, Kökcan Dönmez, Jacob Black, and Yasemin d Aktas

Post-earthquake reconnaissance missions are critical to understand the event characteristics, identify building and infrastructure vulnerabilities, and improve future construction practice. However, in-field missions can present logistic and safety challenges that do not make them viable in every post-disaster scenario. Remote sensing technique can be used to rapidly collect a large amount information that can be used to enrich the post-event learning process. While the possibility to deploy teams in the field remain a valuable asset for an integrated understanding of technical and socio-economic factors, a mix of remote and in-field reconnaissance activities can be a way forward in post-disaster management.

This work presents the results of a hybrid mission mobilised by the Earthquake Engineering Field Investigation Team (EEFIT) after the 2021 Haiti earthquake. On 14 August 2021, a 7.2 magnitude earthquake struck the Tiburon Peninsula in the Caribbean nation of Haiti, approximately 150km east of the capital Port au Prince. The event was followed by numerous aftershocks up to magnitude 5.7, and tiggered over 1000 landslides. Over 2000 people lost their lives, with over 15,000 injured and over 137,000 houses damaged or destroyed. The estimated economic impact is of the order of US$1.6 billion. Due the complex political and security situation in Haiti, coupled with the global pandemic, a full in field mission was not considered feasible, so a hybrid mission was designed instead.

First, open-source information was collected and used to characterise the seismic event, analyse the strong ground motion and compare to established national and international earthquake codes and standard. Second, remote sensing techniques including Interferometric Synthetic Aperture Radar (InSAR) and Optical/Multispectral imagery were used to understand the earthquake mechanism, the ground displacement distribution and the possibility to detect landslide on a regional scale. The general applicability of remote sensing technique in the context of post disaster assessment was also evaluated. Finally, the earthquake impact on different building typologies in Haiti was investigated through the damage assessment of over 2000 buildings comprising schools, hospitals, churches and housing. This was done in collaboration with the Structural Extreme Events Reconnaissance (StEER) team, who mobilised a team of local non-experts to rapidly record building damage.

This talk summarises the mission setup and findings, and discusses the benefits of and difficulties encountered during this hybrid reconnaissance.

How to cite: Whitworth, M., Giardina, G., Penney, C., Di Sarno, L., Adams, K., Kijewski-Correa, T., Macabuag, J., Foroughnia, F., Macchiarulo, V., Ojaghi, M., Orfeo, A., Pugliese, F., Dönmez, K., Black, J., and d Aktas, Y.: Remote Reconnaissance Mission to the 14th August 2021 Haiti Earthquake; remote sensing and building damage assessments , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10192, https://doi.org/10.5194/egusphere-egu22-10192, 2022.

SM2.1 – Advances in fiber-optic sensing technologies for geophysical applications

EGU22-7153 | Presentations | SM2.1

MEGLIO: an experiment to record seismic waves on a commercial fiber optic cable through interferometry measures with an ultra stable laser.

Andre Herrero, Davide Calonico, Francesco Piccolo, Francesco Carpentieri, Aladino Govoni, Lucia Margheriti, Maurizio Vassallo, Rita di Giovambattista, Salvatore Stramondo, Cecilia Clivati, Roberto Concas, Simone Donadello, Fabio Simone Priuli, Filippo Orio, and Andrea Romualdi

The experiment MEGLIO follows the seminal work of Marra et al. (2018) where the authors demonstrate the possibility to observe seismic waves on fiber optic cables over large distances. The measure was based on an interferometric technique using an ultra stable laser. In theory, this active measurement technique is compatible with a commercial operation on a fiber, i.e. the fiber does not need to be dark. In 2019, Open Fiber, the largest optic fiber infrastructure provider in Italy, has decided to test this new technology on its own commercial network on land.

A team of experts in the different fields has been gathered to achieve this goal : besides Open Fiber, Metallurgica Bresciana; INRiM, which initially developed the technique, for their expertise on laser and sensors; Bain & Company for the analysis and the processing of the data; INGV for the expertise in the seismology field and for the validation of the observations.

The first year has been dedicated to developing the sensors. In the meantime, a buried optic cable has been chosen in function of its length and the seismicity nearby. The best candidate was the fiber connecting the towns of Ascoli Piceno (Marche, Italy) and Teramo (Abruzzo, Italy) for a length of around 30 km. Although  this technique allows using cable lengths larger than 5.000 km, for this first test we have decided to keep the length short. Actually the cable is mainly buried underneath a road with medium traffic, passes across different bridges and viaducts, starts in the middle of a town and loops in the middle of another town. Thus we expected a strong anthropic noise on the data.

The measurement on the field started in mid June 2020 and the system was operational in early July. We also installed a seismic station at one end of the cable. During these first six months, we have compared the observations on the fiber with the Italian national seismic catalog and the worldwide catalog for the major events. We consider the first results a success. We have detected so far nearly all the seismic activity with magnitude larger than 2.5 for epicentral distance lesser than 50 km. Moreover, we have recorded large events in Mediterranean region and teleseisms. Finally we have recorded new and interesting noise signals. Collecting additional events will be helpful for a better characterization of the technique, its performances and for a statistical analysis.

How to cite: Herrero, A., Calonico, D., Piccolo, F., Carpentieri, F., Govoni, A., Margheriti, L., Vassallo, M., di Giovambattista, R., Stramondo, S., Clivati, C., Concas, R., Donadello, S., Priuli, F. S., Orio, F., and Romualdi, A.: MEGLIO: an experiment to record seismic waves on a commercial fiber optic cable through interferometry measures with an ultra stable laser., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7153, https://doi.org/10.5194/egusphere-egu22-7153, 2022.

EGU22-5743 | Presentations | SM2.1

Making sense of urban DAS data with clustering of coherence-based array features

Julius Grimm and Piero Poli

Seismic noise monitoring in urban areas can yield valuable information about near-surface structures and noise sources like traffic activity. Distributed Acoustic Sensing (DAS) is ideal for this task due to its dense spatial resolution and the abundance of existing fiber-optic cables below cities.
A 15 km long dark fiber below the city of Grenoble was transformed into a dense seismic antenna by connecting it to a Febus A1-R interrogator unit. The DAS system acquired data continuosly for 11 days with a sampling frequency of 250 Hz and a channel spacing of 19.2 m, resulting in a total of 782 channels. The cable runs through the entirety of the city, crossing below streets, tram tracks and a river. Various noise sources are visible on the raw strain-rate data. A local earthquake (1.3 MLv) was also recorded during the acquisition period.
To characterize the wavefield, the data is divided into smaller sub-windows and coherence matrices at different frequency bands are computed for each sub-window. Clustering is then performed directly on the covariance matrices, with the goal of identifying repeating sub-structures in the covariance matrices (e.g. localized repeating noise sources). Finding underlying patterns in the complex dataset helps us to better understand the spatio-temporal distribution of the occurring signals.

How to cite: Grimm, J. and Poli, P.: Making sense of urban DAS data with clustering of coherence-based array features, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5743, https://doi.org/10.5194/egusphere-egu22-5743, 2022.

EGU22-11864 | Presentations | SM2.1

Distributed Acoustic Sensing in the Athens Metropolitan Area: Preliminary Results

Krystyna T. Smolinski, Daniel C. Bowden, Konstantinos Lentas, Nikolaos S. Melis, Christos Simos, Adonis Bogris, Iraklis Simos, Thomas Nikas, and Andreas Fichtner

Once a niche technology, Distributed Acoustic Sensing (DAS) has gained increasing popularity over the last decade, due to its versatility and ability to capture extremely dense seismic datasets in a wide range of challenging environments. While DAS has been utilised in some particularly remote locations, such as on glaciers and volcanoes, it also holds a great deal of potential closer to home; beneath our cities. As DAS is able to be used with existing telecommunication fibres, urban areas contain huge potential networks of strain or strain-rate sensors, right beneath our feet. This data enables us to monitor the local environment, recording events such as earthquakes, as well as characterising and monitoring the shallow subsurface. DAS experiments using dark fibres are unintrusive and highly repeatable, meaning that this method is ideal for long-term site monitoring.

In collaboration with the OTE Group (the largest telecommunications company in Greece), we have collected urban DAS data beneath North-East Athens, utilising existing, in-situ telecommunication fibres. This large dataset contains a wide range of anthropogenic signals, as well as many seismic events, ranging from small, local events, to an internationally reported Magnitude 6.4 earthquake in Crete.

We conduct a preliminary analysis of the dataset, identifying and assessing the earthquake signals recorded. This will be compared with the event catalogue of the local, regional network in Athens, to determine our sensitivity to events of different magnitudes, and in a range of locations. We hope to gain an understanding of how DAS could be combined with the existing network for seismic monitoring and earthquake detection.

Moving forward, we aim to also apply ambient noise methods to this dataset in order to extract dispersion measurements, and ultimately invert for a shallow velocity model of the suburbs of Athens.

How to cite: Smolinski, K. T., Bowden, D. C., Lentas, K., Melis, N. S., Simos, C., Bogris, A., Simos, I., Nikas, T., and Fichtner, A.: Distributed Acoustic Sensing in the Athens Metropolitan Area: Preliminary Results, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11864, https://doi.org/10.5194/egusphere-egu22-11864, 2022.

EGU22-5551 | Presentations | SM2.1

A showcase pilot of seismic campaign using Distributed Acoustic Sensing solutions

Camille Jestin, Christophe Maisons, Aurélien Chérubini, Laure Duboeuf, and Jean-Claude Puech

Distributed Acoustic Sensing (DAS) is a rapidly evolving technology that can turn a fibre optic cable into thousands of acoustic sensors. In this study, we propose to present a seismic survey conducted as a business showcase relying on a collaborative work supported by five partners: FEBUS Optics, RealTimeSeismic (RTS), Gallego Technic Geophysics (GTG), Petro LS and Well-SENSE. The project was carried out at a deep solution mining site developed for salt production, operated by KEMONE, and located nearby Montpellier (South of France).

The seismic campaign was based on two different cable deployments.

On the first hand, a Vertical Seismic Profile survey was conducted on borehole seismic measurements using two different fibre optic cables deployed in a 1800m deep vertical well. The first set of tests was performed along a Petro LS wireline cable including optical fibres. This deployment corresponds to a conventional wireline operation. The second set of data has been acquired along a FibreLine Intervention system (FLI) developed by WellSENSE. The deployment of the FLI system relies on the unspooling a bare optical fibre using a probe along a wellbore. This solution is single-use and sacrificial and can be left in the well at the end of the survey.

On another hand, a short 400m-surface 2D profile has been achieved along both a fibre optic cable and a set of STRYDE nodes deployed by GTG.

Fibre optic cables have been connected to FEBUS DAS interrogator to collect distributed acoustic measurements.  The seismic tests, performed in collaboration with GTG, have been achieved with basic “weight drops” (1T falling from 4m) for the checkshot surveys and with an "IVI Mark 4" 44,000-pound seismic vibrator for VSP shots at offset from wellhead reaching 865m. Acquired data have been analysed by RTS.

This work will describe the survey, present the results, and discuss the learnings in two ways:  the optimisation of acquisition setups and processing parameters to obtain the best exploitable results and seismic surveys perspectives and challenges using DAS technology.

How to cite: Jestin, C., Maisons, C., Chérubini, A., Duboeuf, L., and Puech, J.-C.: A showcase pilot of seismic campaign using Distributed Acoustic Sensing solutions, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5551, https://doi.org/10.5194/egusphere-egu22-5551, 2022.

EGU22-3728 | Presentations | SM2.1

Detecting earthen dam defects using seismic interferometry monitoring on Distributed Acoustic Sensing data

Aurelien Mordret, Anna Stork, Sam Johansson, Anais Lavoue, Sophie Beaupretre, Romeo Courbis, Ari David, and Richard Lynch

Earthen dams and embankments are prone to internal erosion, their most significant source of failure. Standard monitoring techniques often measure erosion effects when they appear at the surface, reducing the potential response time to address the problem before failure. Through their integrative sensitivity along their propagation, seismic signals are well suited to assess mechanical changes in the bulk of a dam. Moreover, seismic velocities are strongly sensitive to porosity, pore pressure, and water saturation, physical properties that vary the most for internal erosion. Here, we used fiber optics and a Distributed Acoustic Sensing (DAS) array installed on an experimental dam with built-in defects to record the ambient seismic wavefield for one month while the dam reservoir is gradually filled up. The position and nature of the dam defects are unknown to us, to allow an actual blind-detection experiment. We computed cross-correlations between equidistant channels along the dam every 15 minutes and monitored the relative seismic velocity changes at each location for the whole month. The results show a strong correlation of the velocity changes with the water level in the reservoir at all locations along the dam. We also observe systematic deviations from the average velocity change trend. We interpret these anomalies as the effects of the built-in defects placed at different positions in the bulk of the dam. The careful analysis of the residual velocity changes allows us to hypothesize on the position and nature of the defects. 

How to cite: Mordret, A., Stork, A., Johansson, S., Lavoue, A., Beaupretre, S., Courbis, R., David, A., and Lynch, R.: Detecting earthen dam defects using seismic interferometry monitoring on Distributed Acoustic Sensing data, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3728, https://doi.org/10.5194/egusphere-egu22-3728, 2022.

EGU22-2188 | Presentations | SM2.1

Locating Nearby Explosions in Fürstenfeldbruck, Germany, Combining 8 Rotational Sensors 

Gizem Izgi, Eva P.S. Eibl, Frank Krüger, and Felix Bernauer

The seismic wavefield can only be completely described by the combination of translation, rotation and strain. Direct measurement of rotational motions in combination with the translational motions allow observing the complete seismic ground motion. Portable blueSeis-3A (iXblue) sensors allow to measure 3 components of rotational motions. We co-located Nanometrics Horizon seismometers with blueSeis-3A sensors and measured the full wavefield.

An active source experiment was performed in Fürstenfeldbruck, Germany in November 2019, in order to further investigate the performance of multiple rotational instruments in combination with seismometers. Within the scope of the experiment 5 explosions took place. For the first two explosions, all 8 rotational sensors were located inside of a bunker while for the rest of explosions, 4 sensors each were located at 2 different sites of the field. One group was co-located with translational seismometers. This is the first time the recordings of 8 rotational sensors are combined for event analysis and location. We calculate and intersect the back azimuths and derive phase velocities of the five explosions.

We discuss the reliability of the data recorded by the rotational sensors for further investigations in other environments.

How to cite: Izgi, G., Eibl, E. P. S., Krüger, F., and Bernauer, F.: Locating Nearby Explosions in Fürstenfeldbruck, Germany, Combining 8 Rotational Sensors , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2188, https://doi.org/10.5194/egusphere-egu22-2188, 2022.

EGU22-6976 | Presentations | SM2.1

Comparison between Distributed Acoustic Sensing (DAS) and strain meter measurements at the Black Forest Observatory

Jérôme Azzola, Nasim Karamzadeh Toularoud, Emmanuel Gaucher, Thomas Forbriger, Rudolf Widmer-Schnidrig, Felix Bögelspacher, Michael Frietsch, and Andeas Rietbrock

We present an original DAS measurement station, equipped with the Febus A1-R interrogator, which has been deployed at the Black Forest Observatory (Schiltach, Germany). The objective of this deployment is twofold. The first is to test the deployed fibre optic cables and to better characterise the recorded signals. The second is to define standards for the processing of these DAS measurements, with a view to using the equipment for passive seismic monitoring in the INSIDE project (supported by the German Federal Ministry for Economic Affairs and Energy, BMWi).

Testing sensors involving new acquisition technologies, such as instruments based on Distributed Fiber Optic Sensing (DFOS), is part of the observatory's goals, in order to assess, to maintain and to improve signal quality. Interestingly, reference geophysical instruments are also deployed on a permanent basis in this low seismic-noise environment. Our analyses thus benefit from the records of the observatory's measuring instruments, in particular a set of three strain meters recording along various azimuths. This configuration enables a unique comparison between strain meter and DAS measurements. In addition, an STS-2 seismometer (part of German Regional Seismic Network, GRSN) allows for additional comparisons.

These instruments provide a basis for a comparative analysis between the DAS records and the measurements of well-calibrated sensing devices (STS-2 sensor, strain meter array). Such a comparison is indeed essential to physically understand the measurements provided by the Febus A1-R interrogator and to characterise the coupling between the ground and the fiber, in various deployment configurations.

We present the experiment where we investigate several Fiber Optic Cable layouts, with currently our most successful setup involving loading a dedicated fiber with sandbags. We discuss different processing approaches, resulting in a considerable improvement of the fit between DAS and strain array acquisitions. The presented comparative analysis is based on the recordings of different earthquakes, including regional and teleseismic events.

How to cite: Azzola, J., Toularoud, N. K., Gaucher, E., Forbriger, T., Widmer-Schnidrig, R., Bögelspacher, F., Frietsch, M., and Rietbrock, A.: Comparison between Distributed Acoustic Sensing (DAS) and strain meter measurements at the Black Forest Observatory, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6976, https://doi.org/10.5194/egusphere-egu22-6976, 2022.

EGU22-8787 | Presentations | SM2.1

PSD analysis and seismic event detectability of Distributed Acoustic Sensing (DAS) mesurements from several monitoring sites

Nasim Karamzadeh Toularoud, Jérôme Azzola, Emmanuel Gaucher, Thomas Forbriger, Rudolf Widmer-Schnidrig, Felix Bögelspacher, Michael Frietsch, and Andreas Rietbrock

High spatial and temporal resolution of distributed acoustic sensing (DAS) measurements makes them very attractive in different applications in seismology, such as seismic noise analysis (e.g. Bahavar et al 2020, Spica et al 2020) and seismic event detection (e.g. Ajo-Franklin et al 2019, Fernandez Ruiz 2020, Jousset 2020). The quantity measured by a DAS is strain or strain rate of an optic fiber cable, which is related to the spatial gradient of displacement and velocity that is usually measured by single point seismometers. The amplitude (and signal to noise ratio, SNR) and frequency resolutions of DAS recordings depend on spatial and temporal acquisition parameters, such as i.e. gauge-length (GL) and derivative time (DT), the latter being of importance only if the device records the strain rate.

In this study, our aims have been to investigate, experimentally, how to adapt the averaging parameters such as GL and DT to gain sensitivity in frequency bands of interests, and to investigate the seismic event detection capability of DAS data under specific set up. We recorded samples of DAS raw data, over a few hours at the German Black Forest Observatory (BFO) and in Sardinia, Italy.  We studied the spectral characteristics of strain and strain rate converted from DAS raw data, to analyze the sensitivity of DAS measurements to GL and DT. The power spectral densities are compared with the strain meter recordings at BFO site as a benchmark, which is recorded using the strain-meter arrays measuring horizontal strain in three different directions independently from the DAS (For details about the DAS measurement station at BFO see Azzola et al.  EGU 2022). We concluded about the lower limit of the DAS noise level that is achievable with employing different acquisition parameters. Accordingly, we applied suitable parameters for continuous strain-rate data acquisition at another experimental site in Georgia, which is related to the DAMAST (Dams and Seismicity) project.  

During the acquisition time periods at BFO and in Georgia, the visibility of local, regional and teleseismic events on the DAS data has been investigated. At both sites, a broadband seismometer is continuously operating, and can be considered as a reference to evaluate the event detection capability of the DAS recordings taking into account the monitoring set-up, i.e. cable types,  cable coupling to the ground, directional sensitivity and acquisition parameters. In addition, at BFO the DAS seismic event detection capability is evaluated comparing with the strain-meter array. Examples of detected seismic events by DAS are discussed, in terms of achievable SNR for each frequency content and comparison with the seismometers and strain-meter array.

How to cite: Karamzadeh Toularoud, N., Azzola, J., Gaucher, E., Forbriger, T., Widmer-Schnidrig, R., Bögelspacher, F., Frietsch, M., and Rietbrock, A.: PSD analysis and seismic event detectability of Distributed Acoustic Sensing (DAS) mesurements from several monitoring sites, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8787, https://doi.org/10.5194/egusphere-egu22-8787, 2022.

EGU22-6984 | Presentations | SM2.1

Array signal processing on distributed acoustic sensing data: directivity effects in slowness space

Sven Peter Näsholm, Kamran Iranpour, Andreas Wuestefeld, Ben Dando, Alan Baird, and Volker Oye

Distributed Acoustic Sensing (DAS) involves the transmission of laser pulses along a fiber-optic cable. These pulses are backscattered at fiber inhomogeneities and again detected by the same interrogator unit that emits the pulses. Elastic deformation along the fiber causes phase shifts in the backscattered laser pulses which are converted to spatially averaged strain measurements, typically at regular fiber intervals.

DAS systems provide the potential to employ array processing algorithms. However, there are certain differences between DAS and conventional sensors. The current paper is focused on taking these differences into account. While seismic sensors typically record the directional particle displacement, velocity, or acceleration, the DAS axial strain is inherently proportional to the spatial gradient of the axial cable displacement. DAS is therefore insensitive to broadside displacement, e.g., broadside P-waves. In classical delay-and-sum beamforming, the array response function is the far-field response on a horizontal slowness (or wavenumber) grid. However, for geometrically non-linear DAS layouts, the angle between wavefront and cable varies, requiring the analysis of a steered response that varies with the direction of arrival. This contrasts with the traditional array response function which is given in terms of slowness difference between arrival and steering.

This paper provides a framework for DAS steered response estimation accounting also for cable directivity and gauge-length averaging – hereby demonstrating the applicability of DAS in array seismology and to assess DAS design aspects. It bridges a gap between DAS and array theory frameworks and communities, facilitating increased employment of DAS as a seismic array.

How to cite: Näsholm, S. P., Iranpour, K., Wuestefeld, A., Dando, B., Baird, A., and Oye, V.: Array signal processing on distributed acoustic sensing data: directivity effects in slowness space, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6984, https://doi.org/10.5194/egusphere-egu22-6984, 2022.

EGU22-11599 | Presentations | SM2.1

Comparing two fiber-optic sensing systems: Distributed Acoustic Sensing and Direct Transmission

Daniel Bowden, Andreas Fichtner, Thomas Nikas, Adonis Bogris, Konstantinos Lentas, Christos Simos, Krystyna Smolinski, Iraklis Simos, and Nikolaos Melis

Distributed Acoustic Sensing (DAS) systems have gained popularity in recent years due to the dense spatial coverage of strain observations; with one fiber and one interrogator researchers can have access to thousands of strain or strain-rate observations over a region. DAS systems have a limited range, however, with usual experiments being on the order of 10’s of kilometers, owing to their reliance on weakly backscattered light. In contrast, systems that transmit light through a fiber and measure signals on the other end (or looped back) can traverse significantly longer distances (e.g., Marra et. al 2018, Zhan et. al 2021, Bogris et. al 2021), and have the added advantages of being potentially cheaper and potentially operating in parallel with active telecommunications purposes. The disadvantage of such transmission systems is that only a single measurement of strain along the entire distance is given.

During September - October 2021, we operated examples of both systems side-by-side using telecommunications fibers underneath North Athens, Greece, in collaboration with the OTE telecommunications provider. Several earthquakes were detected by both systems, and we compare observations from both. The DAS system is a Silixa iDAS Interrogator measuring strain-rate. The newly designed transmission system relies on interferometric use of microwave frequency dissemination; signals sent along the fiber and back in a closed loop are compared to what was sent to measure phase differences (Bogris et. al 2021). We find that both systems are successful in sensing earthquakes and agree remarkably well when DAS signals are integrated over the length of the cable to properly mimic the transmission observations.

The direct transmission system, however, may not be as intuitive to interpret as an integral of displacement ground motions along the fiber. We discuss both theoretical and data-driven examples of how the observed phases depend on the curvature of a given length of fiber, and describe how asymmetries in the fiber’s index of refraction play a role in producing observed signals. Such an understanding is crucial if one is to properly interpret the signals from such a system (e.g., especially very long trans-oceanic cables). Given a full theoretical framework, we also discuss a strategy for seismic tomography given such a system: with a very long fiber, the spatial sensitivity should evolve over time as seismic signals reach different sections.

How to cite: Bowden, D., Fichtner, A., Nikas, T., Bogris, A., Lentas, K., Simos, C., Smolinski, K., Simos, I., and Melis, N.: Comparing two fiber-optic sensing systems: Distributed Acoustic Sensing and Direct Transmission, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11599, https://doi.org/10.5194/egusphere-egu22-11599, 2022.

EGU22-7311 | Presentations | SM2.1

Calibration and repositioning of an optical fibre cable from acoustic noise obtained by DAS technology

Lucas Papotto, Benoit DeCacqueray, and Diane Rivet

DAS (Distributed Acoustic Sensing) turns fibre optic cables used for telecommunications into multi-sensor antenna arrays. This technology makes it possible to detect an acoustic signal from a natural source such as cetacean or micro-earthquakes, or a man-made source by measuring the deformation of the cable. At sea, the coupling between the optical fibre and the ground on which it rests, as well as the calibration of the cable, is a critical point when the configuration of the cable is unknown. Is the fibre buried or suspended? What is the depth of the sensor being studied? What impact do these parameters have on the signal? The answers to these questions have an impact on the quality of the results obtained, the location of sources - seismic or acoustic - and the characterisation of the amplitude of signals are examples of this. Here, a first approach to study this calibration is proposed. Acoustic noise generated by passing ships in the vicinity of a 42km long optical fibre off Toulon, south-east France, is used to obtain signals for which the position and the signal of the source are known. Then, the synthetic and theoretical signal representing the ship's passage is modelled (3D model, AIS Long/Lat coordinates and depth, propagation speed in water c₀ = 1530m/s). This simulation allows us to compare the real and synthetic signals, in order to make assumptions about the actual cable configuration. We compare the signals through beamforming, f-k diagram and time-frequency diagram in particular. The grid search approach allowed us to determine the new position or orientation of a portion of the antenna. This new position is then evaluated from the signals of different vessels.

How to cite: Papotto, L., DeCacqueray, B., and Rivet, D.: Calibration and repositioning of an optical fibre cable from acoustic noise obtained by DAS technology, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7311, https://doi.org/10.5194/egusphere-egu22-7311, 2022.

EGU22-4963 | Presentations | SM2.1

A real-time classification method for pipeline monitoring combining Distributed Acoustic Sensing and Distributed Temperature and Strain Sensing

Camille Huynh, Camille Jestin, Clément Hibert, Jean-Philippe Malet, Vincent Lanticq, and Pierre Clément

Distributed Fiber Optic Systems (DFOSs) refer to an ensemble of innovative technology that turns an optical fiber into a vast network of hundreds to thousands equally spaced sensors. According to the nature of the sensor, one can be sensitive to acoustic vibration (Distributed Acoustic Sensing, DAS) or to strain and temperature variation (Distributed Temperature and Strain Sensing, DTSS). DAS systems are well suited to detect short-term events in contrast to DTSS systems, which are intended to prevent long-term events. A combination of these two systems appears to be a good way to prevent against most possible events that can appear along an infrastructure. Furthermore, DFOS systems allow the interrogation of long profiles with very dense spatial and temporal sampling. Handling such amounts of data then appears as a challenge when trying to identify a threat along the structure. Machine learning solutions then proves their relevance for robust, fast and efficient acoustical event classification.

The goal of our study is to develop a method to handle, in real time, acquired data from these two DFOSs, classify them according to the nature of their origin and trigger an alarm if required. We mainly focus on major threats that jeopardize the integrity of pipelines. Our database contains leaks, landslides, and third-party intrusion (footsteps, excavations, drillings, etc.) simulated and measured at FEBUS Optics test bench in South-West France. Water and air leaks were simulated using electrovalves of several diameters (1mm, 3mm and 5mm), and landslides with a plate whose inclination was controlled by 4 cylinders. These data were acquired under controlled conditions in a small-scale model of pipeline (around 20m long) along different fiber optic cables installed along the structure.

Our method relies on several tools. A Machine Learning algorithm called Random Forest is used to pre-classify the DAS signal. Our implementation of this algorithm works in flow for a real time event identification. For DTSS signal, a simple threshold is used to detect if a strain or temperature variation occurs. Both results are then gathered and analyzed using a decisional table to return a classification result. According to the potential threat represented by its identified class, the event is considered as dangerous or not. Using this method, we obtain good results with a good classification rate (threat/non-threat) of 93%, compared to 87% if the DAS is used without the DTSS. We have noticed that the combination of both devices enables a better classification, especially for landslides hard to detect with the DAS. This combination enables to dramatically reduce the part of undetected threats from 16% to 4%.

How to cite: Huynh, C., Jestin, C., Hibert, C., Malet, J.-P., Lanticq, V., and Clément, P.: A real-time classification method for pipeline monitoring combining Distributed Acoustic Sensing and Distributed Temperature and Strain Sensing, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4963, https://doi.org/10.5194/egusphere-egu22-4963, 2022.

EGU22-4583 | Presentations | SM2.1

Dynamic weakening in carbonate-built seismic faults: insights from laboratory experiments with fast and ultra-localized temperature measurements 

Stefano Aretusini, Arantzazu Nuñez Cascajero, Chiara Cornelio, Xabier Barrero Echevarria, Elena Spagnuolo, Alberto Tapetado, Carmen Vazquez, Massimo Cocco, and Giulio Di Toro

During earthquakes, seismic slip along faults is localized in < 1 cm-thick principal slipping zones. In such thin slipping zones, frictional heating induces a temperature increase which activates deformation processes and chemical reactions resulting in dramatic decrease of the fault strength (i.e., enhanced dynamic weakening) and, in a negative feedback loop, in the decrease of the frictional heating itself.

In the laboratory, temperature measurements in slipping zones are extremely challenging, especially at the fast slip rates and large slip displacements typical of natural earthquakes. Recently, we measured the temperature evolution in the slipping zone of simulated earthquakes at high acquisition rates (∼ kHz) and spatial resolutions (<< 1 mm2). To this end, we used optical fibres, which convey IR radiation from the hot rubbing surfaces to a two color pyrometer, equipped with photodetectors which convert the radiation into electric signals. The measured signals were calibrated into temperature and then synchronized with the mechanical data (e.g., slip rate, friction coefficient, shear stress) to relate the dynamic fault strength to the temperature evolution and eventually constrain the deformation processes and associated chemical reactions activated during seismic slip.

Here, we reproduce earthquake slip via rotary shear experiments performed on solid cylinders (= bare rock surfaces) and on gouge layers both made of 99.9% calcite. The applied effective normal stress is 20 MPa. Bare rock surfaces are slid for 20 m with a trapezoidal velocity function with a target slip rate of 6 m/s. Instead, the gouge layers are sheared imposing a trapezoidal (1 m/s target slip rate for 1 m displacement) and Yoffe (3.5 m/s peak slip rate, and 1.5 m displacement) velocity function. The temperature measured within the slipping zone, which in some experiments increases up to 1000 °C after few milliseconds from slip initiation, allow us to investigate the deformation mechanisms responsible for fault dynamic weakening over temporal (milliseconds) and spatial (contact areas << 1 mm2) scales which are impossible to detect with traditional techniques (i.e., thermocouples or thermal cameras).

Importantly, thanks to FE numerical simulations, these in-situ temperature measurements allow us to quantify the partitioning of the dissipated energy and power between frictional heating (temperature increase) and wear processes (e.g., grain comminution), to probe the effectiveness of other energy sinks (e.g., endothermic reactions, phase changes) that would buffer the temperature increase, and to determine the role of strain localization in controlling the temperature increase. The generalization of our experimental data and observations will contribute to shed light on the mechanics of carbonate-hosted earthquakes, a main hazard in the Mediterranean and other areas worldwide.

How to cite: Aretusini, S., Nuñez Cascajero, A., Cornelio, C., Barrero Echevarria, X., Spagnuolo, E., Tapetado, A., Vazquez, C., Cocco, M., and Di Toro, G.: Dynamic weakening in carbonate-built seismic faults: insights from laboratory experiments with fast and ultra-localized temperature measurements , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4583, https://doi.org/10.5194/egusphere-egu22-4583, 2022.

EGU22-2563 | Presentations | SM2.1

On the Multi-component Information of DAS for Near-Surface Seismic: A Pilot Field Experiment in the Groningen Area

Musab Al Hasani, Guy Drijkoningen, and Kees Wapenaar

In a surface-seismic setting, Distributed Acoustic Sensing (DAS) is still not a widely adopted method for near-surface characterisation, especially for reflection seismic imaging, despite the dense spatial sampling it provides over long distances. This is mainly due to the decreased broadside sensitivity that DAS suffers from when buried horizontally in the ground (that is when the upgoing wavefield (e.g. reflected wavefield) is perpendicular to the optical fibre). This is unlike borehole settings (e.g. zero-offset Vertical Seismic Profiling), where DAS has been widely adopted for many monitoring applications. Advancements in the field, like shaping the fibre to a helix, commonly known as helically wound fibre, allow better sensitivity for the reflections.

The promise of spatially dense seismic data over long distances is an attractive prospect for retrieving the local variations of near-surface properties. This is particularly valuable for areas impacted by induced seismicity, as is the case in the Groningen Province in the north of The Netherlands,  where near-surface properties, mostly composed of clays and peats, play an essential role on the amount of damage on the very near-surface and the structures built on it. Installing fibre-optic cables for passive and active measurements is valuable in this situation. We installed multiple cables containing different fibre configurations of straight and helically wound fibres, buried in a 2-m deep trench. The combination of the different fibre configurations allows us to obtain multi-component information. We observe differences in the amplitude and phase information, suggesting that these differences can be used for separating the different components of the wave motion. We also see that using enhanced backscatter fibres, reflection images can be obtained for the helically wound fibre as well as the straight fibre, despite the decreased broadside sensitivity for the latter.

How to cite: Al Hasani, M., Drijkoningen, G., and Wapenaar, K.: On the Multi-component Information of DAS for Near-Surface Seismic: A Pilot Field Experiment in the Groningen Area, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2563, https://doi.org/10.5194/egusphere-egu22-2563, 2022.

EGU22-8414 | Presentations | SM2.1

Towards microseismic moment tensor inversion in boreholes with DAS

Katinka Tuinstra, Federica Lanza, Andreas Fichtner, Andrea Zunino, Francesco Grigoli, Antonio Pio Rinaldi, and Stefan Wiemer

We present preliminary results on a moment tensor inversion workflow for Distributed Acoustic Sensing (DAS). It makes use of a fast-marching Eikonal solver and synthetically modeled data. The study specifically focuses on borehole settings for geothermal sites. Distributed Acoustic Sensing measures the wavefield with high spatial and temporal resolution. In borehole settings, individual DAS traces generally prove to be noisier than co-located geophones, whereas the densely spaced DAS shot-gathers show features that would have otherwise been missed by the commonly more sparsely distributed geophone chains. For example, the coherency in the DAS records shows the polarity reversals of the arriving wavefield in great detail, which can help constrain the moment tensor of the seismic source. The synthetic tests encompass different source types and source positions relative to the deployed fiber to assess moment tensor resolvability. Further tests include the addition of a three-component seismometer at different positions to investigate an optimal network configuration, as well as various noise conditions to mimic real data. The synthetic tests are tailored to prepare for the data from future microseismicity monitoring with DAS in the conditions of the Utah FORGE geothermal test site, Utah, USA. The proposed method aims at improving amplitude-based moment tensor inversion for DAS deployed in downhole or underground lab contexts.

How to cite: Tuinstra, K., Lanza, F., Fichtner, A., Zunino, A., Grigoli, F., Rinaldi, A. P., and Wiemer, S.: Towards microseismic moment tensor inversion in boreholes with DAS, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8414, https://doi.org/10.5194/egusphere-egu22-8414, 2022.

EGU22-7203 | Presentations | SM2.1

Multiphase observations of a meteoroid in Iceland recorded over 40 km of telecommunications cables and a large-N network

Ismael Vera Rodriguez, Torsten Dahm, Marius P. Isken, Toni Kraft, Oliver D. Lamb, Sin-Mei Wu, Sebastian Heimann, Pilar Sanchez-Pastor, Christopher Wollin, Alan F. Baird, Andreas Wüstefeld, Sigríður Kristjánsdóttir, Kristín Jónsdóttir, Eva P. S. Eibl, Bettina P. Goertz-Allmann, Philippe Jousset, Volker Oye, and Anne Obermann

On July 2, 2021, around 22:44 CET, a meteoroid was observed crossing the sky near Lake Thingvallavatn east of Reykjavik in Iceland. During this event, a large-N seismic network consisting of 500, 3-component geophones was monitoring local seismicity associated with the Hengill geothermal field southwest of the lake.  In addition to the large-N network, two fiber optic telecommunication cables, covering a total length of more than 40 km, were connected to distributed acoustic sensing (DAS) interrogation units. The systems were deployed under the frame of the DEEPEN collaboration project between the Eidgenössische Technische Hochschule Zürich (ETHZ), the German Research Centre for Geosciences (GFZ), NORSAR, and Iceland Geo-survey (ISOR). Both the large-N and the DAS recordings display multiple trains of infrasound arrivals from the meteoroid that coupled to the surface of the earth at the locations of the sensors. In particular, three strong phases and multiple other weaker arrivals can be identified in the DAS data.

Fitting each of the strong phases assuming point sources (i.e., fragmentations) generates travel time residuals on the order of several seconds, resulting in an unsatisfactory explanation of the observations. On the other hand, inverting the arrival times for three independent hypersonic-trajectories generating Mach cone waves reduces travel time residuals to well under 0.5 s for each arrival. However, whereas the 1st arrival is well constrained by more than 900 travel times from the large-N, DAS and additional seismic stations distributed over the Reykjanes peninsula, the 2nd and 3rd arrivals are mainly constrained by DAS observations near Lake Thingvallavatn. The less well-constrained, latter trajectories show a weak agreement with the trajectory of the first arrival. Currently, neither the multi-Mach-cone model nor the multi-fragmentation model explain all our observations satisfactorily. Thus, traditional models for interpreting meteoroid observations appear unsuitable to explain the combination of phase arrivals in the large-N network and DAS data consistently.

How to cite: Vera Rodriguez, I., Dahm, T., Isken, M. P., Kraft, T., Lamb, O. D., Wu, S.-M., Heimann, S., Sanchez-Pastor, P., Wollin, C., Baird, A. F., Wüstefeld, A., Kristjánsdóttir, S., Jónsdóttir, K., Eibl, E. P. S., Goertz-Allmann, B. P., Jousset, P., Oye, V., and Obermann, A.: Multiphase observations of a meteoroid in Iceland recorded over 40 km of telecommunications cables and a large-N network, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7203, https://doi.org/10.5194/egusphere-egu22-7203, 2022.

EGU22-4014 | Presentations | SM2.1

Near-field observations of snow-avalanches propagating over a fiber-optic array

Patrick Paitz, Pascal Edme, Andreas Fichtner, Nadja Lindner, Betty Sovilla, and Fabian Walter

We present and evaluate array processing techniques and algorithms for the characterization of snow avalanche signals recorded with Distributed Acoustic Sensing (DAS).

Avalanche observations rely on comprehensive measurements of sudden and rapid snow mass movement that is hard to predict. Conventional avalanche sensors are limited to observations on or above the surface. Recently, seismic sensors have increased in their popularity for avalanche monitoring and characterization due to their avalanche detection and characterization capabilities. To date, however, seismic instrumentation in avalanche terrain is sparse, thereby limiting the spatial resolution significantly.

As an addition to conventional seismic instrumentation, we propose DAS to measure avalanche-induced ground motion. DAS is a technology using backscattered light along a fiber-optic cable to measure strain (-rate) along the fiber with unprecedented spatial and temporal resolution - in our example with 2 m spatial sampling and a sampling rate of 1kHz.

We analyze DAS data recorded during winter 2020/2021 at the Valleé de la Sionne avalanche test site in the Swiss Alps, utilizing an existing 700 m long fiber-optic cable. Our observations include avalanches propagating on top of the buried cable, delivering near-field observations of avalanche-ground interactions. After analyzing the properties of near-field avalanche DAS recordings, we discuss and evaluate algorithms for (1) automatic avalanche detection, (2) avalanche surge propagation speed evaluation and (3) subsurface property estimation.

Our analysis highlights the complexity of near-field DAS data, as well as the suitability of DAS-based monitoring of avalanches and other hazardous granular flows. Moreover, the clear detectability of avalanche signals using existing fiber-optic infrastructure of telecommunication networks opens the opportunity for unrivalled warning capabilities in Alpine environments.

How to cite: Paitz, P., Edme, P., Fichtner, A., Lindner, N., Sovilla, B., and Walter, F.: Near-field observations of snow-avalanches propagating over a fiber-optic array, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4014, https://doi.org/10.5194/egusphere-egu22-4014, 2022.

EGU22-3404 | Presentations | SM2.1 | Highlight

Fibre-optic observation of volcanic tremor through floating ice sheet resonance

Andreas Fichtner, Sara Klaasen, Sölvi Thrastarson, Yesim Cubuk-Sabuncu, Patrick Paitz, and Kristin Jonsdottir

We report on the indirect observation of low-frequency tremor at Grimsvötn, Iceland, via resonance of an ice sheet, floating atop a volcanically heated subglacial lake.

Entirely covered by Europe’s largest glacier, Vatnajökull, Grimsvötn is among Iceland’s largest and most active volcanoes. In addition to flood hazards, ash clouds pose a threat to settlements and air traffic, as direct interactions between magma and meltwater cause Grímsvötn to erupt explosively. To study the seismicity and structure of Grimsvötn in detail, we deployed a 12.5 km long fibre-optic cable around and inside the caldera, which we used for Distributed Acoustic Sensing (DAS) measurements in May 2021.

The experiment revealed a previously unknown level of seismicity, with nearly 2’000 earthquake detections in less than one month. Furthermore, the cable segment within the caldera recorded continuous and nearly monochromatic oscillations at 0.23 Hz. This corresponds to the expected fundamental-mode resonance frequency of flexural waves within the floating ice sheet, which effectively acts as a damped harmonic oscillator with Q around 15.

In spite of the ice sheet being affected by ambient noise at slightly lower frequencies, the resonance amplitude does not generally correlate with the level of ambient noise throughout southern Iceland. It follows that an additional and spatially localised forcing term is required to explain the observations. A linear inversion reveals that the forcing acts continuously, with periods of higher or lower activity alternating over time scales of a few days.

A plausible explanation for the additional resonance forcing is volcanic tremor, most likely related to geothermal activity, that shows surface expressions in the form of cauldrons and fumaroles along the caldera rim. Being largely below the instrument noise at channels outside the caldera, the ice sheet resonance acts as a magnifying glass that increases tremor amplitudes to an observable level, thereby providing a new and unconventional form of seismic volcano monitoring.

How to cite: Fichtner, A., Klaasen, S., Thrastarson, S., Cubuk-Sabuncu, Y., Paitz, P., and Jonsdottir, K.: Fibre-optic observation of volcanic tremor through floating ice sheet resonance, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3404, https://doi.org/10.5194/egusphere-egu22-3404, 2022.

EGU22-5327 | Presentations | SM2.1

HDAS (High-Fidelity Distributed Acoustic Sensing) as a monitoring tool during 2021 Cumbre Vieja eruption

José Barrancos, Luca D'Auria, Germán Padilla, Javier Preciado-Garbayo, and Nemesio M. Pérez

La Palma is the second youngest and westernmost among Canary Island. Cumbre Vieja volcano formed in the last stage of the geological evolution of the island and had suffered eight volcanic eruptions over the previous 500 years. In 2017, two remarkable seismic swarms interrupted a seismic silence from the last eruption (Teneguía, 1971). Since then, nine additional seismic swarms have occurred at Cumbre Vieja volcano. On September 11th, 2021, seismic activity began to increase, and the depths of the earthquakes showed an upward migration. Finally, on September 19th, the eruption started after just a week of precursors.

During recent years, the seismic activity has been recorded by Red Sísmica Canaria (C7), composed of 6 seismic broadband stations, which was reinforced during the eruption by five additional broadband stations, three accelerometers and a seismic array consisting of 10 broadband stations.

Furthermore, as a result of a collaboration between INVOLCAN, ITER, CANALINK and Aragón Photonics Labs, it was possible to install, on October 19th, an HDAS (High-fidelity Distributed Acoustic Sensor). The HDAS was installed about 10 km from the eruptive vent and was connected to a submarine fibre optic cable directed toward Tenerife Island. Since then, the HDAS has been recording seismic with a temporal sampling rate of 100 Hz and a spatial sampling rate of 10m for a total length of 50 km using Raman Amplification. For more than two months, in addition to the intense volcanic tremor, the HDAS recorded thousands of earthquakes as well as regional and teleseismic events. On December 13th, 2021, after an intense paroxysmal phase with an eruptive column that reached 8 km in height, the volcanic tremor quickly decreased, and the eruption suddenly stopped. Only a weak volcano-tectonic seismicity and small amplitude long-period events were recorded in the next month.

This valuable dataset will provide a milestone for the development of techniques aimed at using DAS as a real-time volcano monitoring tool and studying the internal structure of active volcanoes.

How to cite: Barrancos, J., D'Auria, L., Padilla, G., Preciado-Garbayo, J., and Pérez, N. M.: HDAS (High-Fidelity Distributed Acoustic Sensing) as a monitoring tool during 2021 Cumbre Vieja eruption, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5327, https://doi.org/10.5194/egusphere-egu22-5327, 2022.

EGU22-4478 | Presentations | SM2.1

Non-linear ground response triggered by volcanic explosions at Etna Volcano, Italy

Philippe Jousset, Lucile Costes, Gilda Currenti, Benjamin Schwarz, Rosalba Napoli, Sergio Diaz, and Charlotte Krawczyk

Volcanic explosions produce energy that propagates both in the subsurface as seismic waves and in the atmosphere as acoustic waves. We analyse thousands of explosions which occurred at different craters at Etna volcano (Italy) in 2018 and 2019. We recorded signals from infrasound sensors, geophones (GPH), broadband seismometers (BB) and Distributed Acoustic Sensing (DAS) with fibre optic cable. The instruments were deployed at Piano delle Concazze at about 2 to 2.5 km from the active craters, within (or onto) a ~300,000 m2 scoria layer deposited by recent volcanic eruptions. The DAS interrogator was setup inside the Pizzi Deneri Volcanic Observatory (~2800 m elevation). Infrasonic explosion records span over a large range of pressure amplitudes with the largest one reaching 130 Pa (peak to peak), with an energy of ca. 2.5x1011 J. In the DAS and the BB records, we find a 4-s long seismic “low frequency” signal (1-2 Hz) corresponding to the seismic waves, followed by a 2-s long “high-frequency” signal (16-21 Hz), induced by the infrasound pressure pulse. The infrasound sensors contain a 1-2 Hz infrasound pulse, but surprisingly no high frequency signal. At locations where the scoria layer is very thin or even non-existent, this high frequency signal is absent from both DAS strain-rate records and BB/GPH velocity seismograms. These observations suggest that the scoria layer is excited by the infrasound pressure pulse, leading to the resonance of lose material above more competent substratum. We relate the high frequency resonance to the layer thickness. Multichannel Analysis of Surface Wave from jumps performed along the fibre optic cable provide the structure of the subsurface, and confirm thicknesses derived from the explosion analysis. As not all captured explosions led to the observation of these high frequency resonance, we systematically analyze the amplitudes of the incident pressure wave versus the recorded strain and find a non-linear relationship between the two. This non-linear behaviour is likely to be found at other explosive volcanoes. Furthermore, our observations suggest it might also be triggered by other atmospheric pressure sources, like thunderstorms. This analysis can lead to a better understanding of acoustic-to-seismic ground coupling and near-surface rock response from natural, but also anthropogenic sources, such as fireworks and gas explosions.

How to cite: Jousset, P., Costes, L., Currenti, G., Schwarz, B., Napoli, R., Diaz, S., and Krawczyk, C.: Non-linear ground response triggered by volcanic explosions at Etna Volcano, Italy, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4478, https://doi.org/10.5194/egusphere-egu22-4478, 2022.

EGU22-5952 | Presentations | SM2.1

Strombolian seismic activity characterisation using fibre-optic cable and distributed acoustic sensing

Jean-Philippe Metaxian, Francesco Biagioli, Maurizio Ripepe, Eléonore Stutzmann, Pascal Bernard, Roberto Longo, Marie-Paule Bouin, and Corentin Caudron

Stromboli is an open-conduit volcano characterized by mild intermittent explosive activity that produces jets of gas and incandescent blocks. Explosions occur at a typical rate of 3-10 events per hour, VLP signals have dominant periods between 2 and 30 seconds. Seismic activity is also characterized by less energy short-period volcanic tremor related to the continuous out-bursting of small gas bubbles in the upper part of the magmatic column. The high rate of activity as well as the broadband frequency contents of emitted signals make Stromboli volcano an ideal site for testing new techniques of fibre-optic sensing.

In September 2020, approximately 1 km of fiber-optic cable was deployed on the Northeast flank of Stromboli volcano, together with several seismometers, to record the seismic signals radiated by the persistent Strombolian activity via both DAS and inertial-seismometers, and to compare their records.

The cable was buried manually about 30 cm deep over a relatively linear path at first and in a triangle-shaped array with 30-meters-long sides in the highest part of the deployment. The strain rate was recorded using a DAS interrogator Febus A1-R with a sampling frequency of 2000 Hz, a spatial interval of 2.4 m and a gauge length of 5m. Data were re-sampled at 200 Hz. A network of 22 nodes SmartSolo IGU-16HR 3C geophones (5 Hz) has been distributed over the fibre path. A Guralp digitizer equipped with a CMG CMG-40T 30 sec seismometer and an infrasound sensor were placed in the upper part of the path. The geolocation of the cable was obtained by performing kinematic GPS measurements with 2 Leica GR25 receivers. All equipment recorded simultaneously several hundreds of explosion quakes between September 20 and 23.

Data analysis provided the following main results:

  • DAS interrogator clearly recorded the numerous explosion-quakes which occurred during the experiment, as well as lower amplitude tremor and LP events.
  • DAS spectrum exhibits a lower resolution at long periods with a cut-off frequency of approximately 3 Hz.
  • VLP seismic events generated by Strombolian activity are identified only at a few DAS channels belonging to a specific portion of the path, which seems affected by local amplification. At these channels, they display waveforms similar to those sensed by the Güralp CMG-40T.
  • Comparison of DAS strain waveform to particle velocity recorded by co-located seismometers shows a perfect match in phase and a good agreement in amplitude.
  • Beamforming methods have been applied to nodes data located on the upper triangle and to strain rate data, both in the 3-5 Hz frequency band. Slightly different back-azimuths were obtained, values estimated via DAS point more to the southwest with respect to the crater area. Apparent velocities obtained with DAS recordings have lower values compared to those obtained with nodes.

How to cite: Metaxian, J.-P., Biagioli, F., Ripepe, M., Stutzmann, E., Bernard, P., Longo, R., Bouin, M.-P., and Caudron, C.: Strombolian seismic activity characterisation using fibre-optic cable and distributed acoustic sensing, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5952, https://doi.org/10.5194/egusphere-egu22-5952, 2022.

EGU22-8664 | Presentations | SM2.1

Seismic Exploration and monitoring of geothermal reservoirs usiNg distributed fibre optic Sensing - the joint project SENSE

CharLotte Krawczyk, Leila Ehsaniezhad, Christopher Wollin, Johannes Hart, and Martin Lipus

For a successful operation of energy or resources use in the subsurface, exploration for potential reservoir or storage horizons, monitoring of structural health and control of induced seismic unrest are essential both from a technical and a socio-economic perspective.  Furthermore, large-scale seismic surveys in densely populated areas are difficult to carry out due to the effort required to install sources and receivers and are associated with high financial and logistical costs.  Within the joint project SENSE*, a seismic exploration and monitoring approach is tested, which is based on fibre-optic sensing in urban areas.

Besides the further development of sensing devices, the monitoring of borehole operations as well as the development of processing workflows form central parts of the joint activities. In addition, the seismic wave field was recorded and the localisation of the cables was tested along existing telecommunication cables in Berlin. Further testing of measuring conditions in an urban environment was also conducted along an optic fibre separately laid out in an accessible heating tunnel.

We suggest a workflow for virtual shot gather extraction (e.g., band pass filtering, tapering, whitening, removal of poor traces before and after cross-correlation, stacking), that is finally including a coherence-based approach.  The picking of dispersion curves in the 1-7 Hz frequency range and inversion yield a shear wave velocity model for the subsurface down to a. 300 m depth.  Several velocity interfaces are evident, and a densely staggered zone appears between 220-270 m depth.  From lab measurements a distributed backscatter measurement in OTDR mode shows that high reflections and moderate loss at connectors can be achieved in a several hundred m distance.  Depending on drilling campaign progress, we will also present first results gained during the borehole experiment running until February 2022.

* The SENSE Research Group includes in addition to the authors of this abstract Andre Kloth and Sascha Liehr (DiGOS), Katerina Krebber and Masoud Zabihi (BAM), Bernd Weber (gempa), and Thomas Reinsch (IEG).

How to cite: Krawczyk, C., Ehsaniezhad, L., Wollin, C., Hart, J., and Lipus, M.: Seismic Exploration and monitoring of geothermal reservoirs usiNg distributed fibre optic Sensing - the joint project SENSE, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8664, https://doi.org/10.5194/egusphere-egu22-8664, 2022.

EGU22-8113 | Presentations | SM2.1

Exploration of Distributed Acoustic Sensing (DAS) data-space using a trans-dimensional algorithm, for locating geothermal induced microseismicity

Nicola Piana Agostinetti, Emanuele Bozzi, Alberto Villa, and Gilberto Saccorotti

Distributed Acoustic sensing (DAS) data have been widely recognised as the next generation of  seismic data for applied geophysics, given the ultra-high spatial resolution achieved. DAS data are recorded along a fiber optic cable at pre-defined distances (called “channels”, generally with 1-10 meters spacing). DAS data have been benchmarked to standard seismic data (e.g. geophones) for tasks related to both exploration and monitoring of georesources.

The analysis of DAS data has to face two key-issues: the amount of data available and their “directionality”. First, the huge amount of data recorded, e.g. in monitoring activities related to georesources exploitation, can not be easily handled with standard seismic workflow, given the spatial and temporal sampling (for example, manual picking of P-wave arrivals for 10 000 channels is not feasible). Moreover, standard seismic workflow have been generally developed for “sparse" network of sensors, i.e. for punctual measurements, without considering the possibility of recording the quasi-continuous seismic wavefield along a km-long cable. With the term “directionality" we mean the ability of the DAS data to record horizontal strain-rate only in the direction of the fiber optic cable. This can be seen as a measure of a single horizontal component in a standard seismometer. Obviously, standard seismic workflow have not been developed to work correctly for a network of seismometers with a unique horizontal component, oriented with variable azimuth from one seismometer to the other. More important, “directionality” can easily bias the recognition of the seismic phase arriving at the channel, which could be, based on the cable azimuth and the seismic noise level, a P-wave or an S-wave. 

We developed a novel application for exploring DAS data-space in a way that: (1) data are automatically down weighted with the distance from the event source; (2) recorded phases are associated to P- or S- waves with a probabilistic approach, without pre-defined phase identification; and (3) the presence of outliers is also statistically considered, each phase being potentially a converted/refracted wave to be discarded. Our methodology makes use of a trans-dimensional algorithm, for selecting relevant weights with distance. Thus, all inferences in the data-space are fully data-driven, without imposing additional constrains from the seismologist.

How to cite: Piana Agostinetti, N., Bozzi, E., Villa, A., and Saccorotti, G.: Exploration of Distributed Acoustic Sensing (DAS) data-space using a trans-dimensional algorithm, for locating geothermal induced microseismicity, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8113, https://doi.org/10.5194/egusphere-egu22-8113, 2022.

EGU22-11311 | Presentations | SM2.1

Overcoming limitations of seismic monitoring using fibre-optic distributed acoustic sensing

Regina Maaß, Sven Schippkus, Céline Hadziioannou, Benjamin Schwarz, Charlotte Krawczyk, and Philippe Jousset

Seismic monitoring refers to the measurement of time-lapse changes of seismic wave velocities and is a frequently used technique to detect dynamic changes in the Earth‘s crust. Its applications include a broad range of topics, such as natural hazard assessment and structural health monitoring. To obtain reliable measurements, results are usually stacked over time. Thereby, temporal resolution is lost, which makes the measurement less sensitive to short-term environmental processes. Another problem is that conventional datasets often lack spatial density and velocity changes can only be attributed to large areas. Recently, distributed acoustic sensing (DAS) has gained a lot of attention as a way to achieve high spatial resolution at low cost. DAS is based on Rayleigh-scattering of photons within an optical fibre. Because measurements can be taken every few meters along the cable, the fibre is turned into a large seismic array that provides information about the Earth’s crust at unprecedented resolution.

In our study, we explore the potential of DAS for monitoring studies. Specifically, we investigate how spatial stacking of DAS traces affects the measurements of velocity variations. We use data recorded by a 21-km-long dark fibre located on Reykjanes Pensinsula, Iceland. The cable is sampled with a channel spacing of 4 meters. We analyze the energy of the oceans microseism continuously recorded between March and September 2020. At first, we stack adjacent traces on the fibre in space. We then cross correlate the stacks to obtain approximations of the Green’s functions between different DAS-channels. By measuring changes in the coda waveform of the extracted seismograms, velocity variations can be inferred. Our analysis shows that spatial stacking improves the reliability of our measurements considerably. Because of that, less temporal stacking is required and the time resolution of our measurements can be increased. In addition, the enhancement of the data quality helps resolve velocity variations in space, allowing us to observe variations propagating along the cable over time. These velocity changes are likely linked to magmatic intrusions associated with a series of repeated uplifts on the Peninsula. Our results highlight the potential of DAS for improving the localization capabilities and accuracy of seismic monitoring studies.

How to cite: Maaß, R., Schippkus, S., Hadziioannou, C., Schwarz, B., Krawczyk, C., and Jousset, P.: Overcoming limitations of seismic monitoring using fibre-optic distributed acoustic sensing, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11311, https://doi.org/10.5194/egusphere-egu22-11311, 2022.

EGU22-10322 | Presentations | SM2.1

Strain accumulation along a 21km long optic fibre during a seismic crisis in Iceland, 2020

Christopher Wollin, Philippe Jousset, Thomas Reinsch, Martin Lipus, and Charlotte Krawczyk

Slow slip plays an important role in accommodating plate motion along plate boundaries throughout the world. Further understanding of the interplay between aseismic and seismic slip has gained particular attention as it is crucial for the assessment of seismic risk. A wide range of instruments and acquisition techniques exist to quantify tectonic deformation which spans multiple orders of magnitude in duration as well as spatial extend. For example, seismometers acquire dense temporal data, however are sparsely deployed, leading to spatial aliasing. As opposite, remote sensing techniques have wide aperture but rather crude temporal resolution and accuracy (mm-range). In selected areas, strain is continuously measured with laser or borehole strainmeters.
In this contribution, we investigate the distribution of permanent strain along a telecommunication optic fibre on the Reykjanes Peninsula, South West Iceland. Continuous strain-rate was recorded via DAS (Distributed Acoustic Sensing) over a period of six months during the recent unrest of the Svartsengi volcano which began in January 2020. The interrogated fibre connects the town of Gridavik with the Svartsengi geothermal power plant and was patched to a second fibre leading to the western most tip of the Reykjanes Peninsula. It is approximately between 10 and 20km west of the active volcanic area which produced abundant local seismicity as well as surface uplift and subsidence in areas crossed with the optical fiber. The fibre was installed in a trench at less than one meter depth and consists of two roughly straight segments of 7 and 14km length. Whereas the longer segment trends WSW parallel to the strike of the Mid-Atlantic Ridge at this geographic height, the shorter segment trends NEN and thus almost coincides with the maximum compressive stress axis of the region.
Inspection of the spatio-temporal strain-rate records after the occurrence of local earthquakes indicates the accumulation of compressive as well as extensive strain in short fibre sections of a few dozen meters which could correlate with local geologic features like faults or dykes. This holds for events of M~2.5 and fibre segments in epicentral distances of more than 20km. Preliminary results regarding the total deformation of the fibre as response to an individual seismic event show a distinct behaviour for differently oriented fibre segments correlating with the overall stress regime, i.e. shortening in the order of some dozen nanometers in the direction of SHmax. Unfortunately, recordings of the two largest intermediate M>=4.8 events indicate saturation of the recording system or loss of ground coupling thus preventing a meaningful interpretation of their effect on permanent surface motion. 
Perspectively, our efforts aim at investigating the feasibility of distributed optical strain-rate measurements along telecommunication infrastructure to track locally accumulated strain.

How to cite: Wollin, C., Jousset, P., Reinsch, T., Lipus, M., and Krawczyk, C.: Strain accumulation along a 21km long optic fibre during a seismic crisis in Iceland, 2020, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10322, https://doi.org/10.5194/egusphere-egu22-10322, 2022.

EGU22-11508 | Presentations | SM2.1 | Highlight

Building a new type of seafloor observatory on submarine telecom fiber optic cables in Chile

Diane Rivet, Sergio Barrientos, Rodrigo Sánchez-Olavarría, Jean-Paul Ampuero, Itzhak Lior, Jose-Antonio Bustamente Prado, and German-Alberto Villarroel Opazo

In most subduction zones, a great portion of seismicity is located offshore, away from permanent onland seismic networks. Chile is not the exception; since the upgraded seismic observation system began operating in 2013, 35% of the ~7000 earthquakes with M≥3 recorded yearly were located offshore. Most importantly, the epicenters of the largest earthquakes (M>7.5) from 2014 to 2016 were located offshore as well.

The Chilean national seismic network is mainly composed of coastal and inland stations, except for two stations located on oceanic islands, Rapa Nui (Easter Island) and Juan Fernandez archipelago. This station configuration makes it difficult to observe in sufficient detail the lower-magnitude seismicity at the nucleation points of large events. Moreover, the lack of seafloor stations limits the efficiency of earthquake early warning systems during offshore events. These challenges could be overcome by permanently instrumenting existing submarine telecom cables with Distributed Acoustic Sensing (DAS).

Thanks to GTD, a private telecommunications company that owns a 3500-km-long network of marine fiber optic cables with twelve landing points in Chile (Prat project), from Arica (~ 18⁰S) to Puerto Montt (~ 41⁰S), we conducted the POST (Submarine Earthquake Observation Project in Spanish) DAS experiment on the northern leg of the Concón landing site of the Prat cable. This experiment, one of the first to be conducted on a commercial undersea infrastructure in a very seismically active region, was carried out from October 28 to December 3, 2021. Based on the longitudinal strain-rate data measured along 150 km of cable with a spatial resolution of 4 meters and a temporal sampling of 125 Hz, we present preliminary results of analyses to assess the possibility of building a new type of permanent, real-time and distributed seafloor observatory for continuous monitoring of active faults and earthquake early warning systems.

How to cite: Rivet, D., Barrientos, S., Sánchez-Olavarría, R., Ampuero, J.-P., Lior, I., Bustamente Prado, J.-A., and Villarroel Opazo, G.-A.: Building a new type of seafloor observatory on submarine telecom fiber optic cables in Chile, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11508, https://doi.org/10.5194/egusphere-egu22-11508, 2022.

EGU22-6580 | Presentations | SM2.1

Quantifying microseismic noise generation from coastal reflection of gravity waves using DAS

Gauthier Guerin, Diane Rivet, Martijn van den Ende, Eléonore Stutzmann, Anthony Sladen, and Jean-Paul Ampuero

Secondary microseisms are the most energetic noise in continuous seismometer recordings, and they are generated by interactions between ocean waves. Coastal reflections of ocean waves leading to coastal microseismic sources are hard to estimate in various global numerical wave models, and independent quantification of these coastal sources through direct measurements can therefore greatly improve these models. Here, we exploit a 40 km long submarine optical fiber cable located offshore Toulon, France using Distributed Acoustic Sensing (DAS). We record both the amplitude and frequency of ocean gravity waves, as well as secondary microseisms caused by the interaction of gravity waves incident and reflected from the coast. By leveraging the spatially distributed nature of DAS measurements, additional fundamental information are recovered such as the velocity and azimuth of the waves. On average, 30\% of the gravity waves are reflected at the shore and lead to the generation of local secondary microseisms that manifest as Scholte waves. These local sources can give way to other sources depending on the characteristics of the swell, such as its azimuth or its strength. These sources represent the most energetic contribution to the secondary microseism recorded along the optical fiber, as well as on an onshore broadband station. Furthermore, we estimate the coastal reflection coefficient R$^2$ to be constant at around 0.07 for our 5-day time series. The use of DAS in an underwater environment provides a wealth of information on coastal reflection sources, reflection of gravity waves and new constraints for numerical models of microseismic noise.

How to cite: Guerin, G., Rivet, D., van den Ende, M., Stutzmann, E., Sladen, A., and Ampuero, J.-P.: Quantifying microseismic noise generation from coastal reflection of gravity waves using DAS, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6580, https://doi.org/10.5194/egusphere-egu22-6580, 2022.

EGU22-7182 | Presentations | SM2.1 | Highlight

Monitoring a submarine strike-slip fault, using a fiber optic strain cable

Marc-Andre Gutscher, Jean-Yves Royer, David Graindorge, Shane Murphy, Frauke Klingelhoefer, Arnaud Gaillot, Chastity Aiken, Antonio Cattaneo, Giovanni Barreca, Lionel Quetel, Giorgio Riccobene, Salvatore Aurnia, Lucia Margheriti, Milena Moretti, Sebastian Krastel, Florian Petersen, Morelia Urlaub, Heidrun Kopp, Gilda Currenti, and Philippe Jousset

The goal of the ERC (European Research Council) funded project - FOCUS is to apply laser reflectometry on submarine fiber optic cables to detect deformation at the seafloor in real time using BOTDR (Brillouin Optical Time Domain Reflectometry). This technique is commonly used monitoring large-scale engineering infrastructures (e.g. - bridges, dams, pipelines, etc.) and can measure very small strains (<< 1 mm/m) at very large distances (10 - 200 km), but until now has never been used to study tectonic faults and deformation on the seafloor.

Here, we report that BOTDR measurements detected movement at the seafloor consistent with ≥1 cm dextral strike-slip on the North Alfeo fault, 25 km offshore Catania, Sicily over the past 10 months. In Oct. 2020 a dedicated 6-km long fiber-optic strain cable was connected to the INFN-LNS (Catania physics institute) cabled seafloor observatory at 2060 m depth and deployed across this submarine fault, thus providing continuous monitoring of seafloor deformation at a spatial resolution of 2 m. The laser observations indicate significant elongation (20 - 40 microstrain) at two fault crossings, with most of the movement occurring between 19 and 21 Nov. 2020. A network of 8 seafloor geodetic stations for direct path measurements was also deployed in Oct. 2020, on both sides of the fault to provide an independent measure of relative seafloor movements. These positioning data are being downloaded during ongoing oceanographic expeditions to the working area (Aug. 2021 R/V Tethys; Jan. 2022 R/V PourquoiPas) using an acoustic modem to communicate with the stations on the seafloor. An additional experiment was performed in Sept. 2021 using an ROV on the Fugro vessel Handin Tide, by weighing down unburied portions of the submarine cable with pellet bags and sandbags (~25kg each) spaced every 5m. The response was observed simultaneously by DAS (Distributed Acoustic Sensing) recordings using two DAS interrogators (a Febus and a Silixa). The strain caused by the bag deployments was observed using BOTDR and typically produced a 50 - 100 microstrain signal across the 120 meter-long segments which were weighed down. In Jan. 2022 during the FocusX2 marine expedition, 21 ocean bottom seismometers were deployed for 12-14 months, which together with 15 temporary land-stations as well as the existing network of permanent stations (both operated by INGV) will allow us to perform a regional land-sea passive seismological monitoring experiment.

How to cite: Gutscher, M.-A., Royer, J.-Y., Graindorge, D., Murphy, S., Klingelhoefer, F., Gaillot, A., Aiken, C., Cattaneo, A., Barreca, G., Quetel, L., Riccobene, G., Aurnia, S., Margheriti, L., Moretti, M., Krastel, S., Petersen, F., Urlaub, M., Kopp, H., Currenti, G., and Jousset, P.: Monitoring a submarine strike-slip fault, using a fiber optic strain cable, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7182, https://doi.org/10.5194/egusphere-egu22-7182, 2022.

EGU22-3729 | Presentations | SM2.1

The Potential of DAS on Underwater Suspended Cables for Oceanic Current Monitoring and Failure Assessment of Fiber Optic Cables

Daniel Mata, Jean-Paul Ampuero, Diego Mercerat, Diane Rivet, and Anthony Sladen

Distributed Acoustic Sensing (DAS) enables the use of existing underwater telecommunication cables as multi-sensor arrays. The great majority of underwater telecommunication cables are deployed from the water surface and the coupling between the cable and the seafloor is not fully controlled. This implies that there exists many poorly coupled cable segments less useful for seismological research. In particular, underwater cables include segments that are suspended in the water column across seafloor valleys or other bathymetry irregularities. However, it might be possible to use DAS along the suspended sections of underwater telecommunication cables for other purposes. A first one investigated here is the ability to monitor deep-ocean currents. It is common to observe that some particular sections of a cable oscillate with great amplitudes. These oscillations are commonly interpreted as due to vortex shedding induced by the currents. We investigate this hypothesis by estimating the oceanic current speeds from vortex frequencies measured in two underwater fiber optic cables located at Methoni, Greece, and another in Toulon, France. Our results in Greece are in agreement with in-situ historical measurements of seafloor currents while our estimations in Toulon are compatible with synchronous measurements of a nearby current meter. These different measurements therefore point to the possibility to exploit DAS measurements as a tool to monitor the activity of seafloor currents. A second possible application of DAS is to estimate how the cable is coupled to the seafloor, even in the absence of the strong oscillations associated to vortex shedding. For that, we have analyzed the spectral signature of the different cables. Some sections feature fundamental frequencies as expected from a theoretical model of in-plane vibration of hanging cables. By analyzing how the fundamental frequencies change along the cable, we are potentially inferring the contact points of the cable with the seafloor, which will promote fatigue of the cable and potential failure. This mapping of the coupling characteristics of the cable with the seafloor could also be useful to better interpret other DAS signals.

How to cite: Mata, D., Ampuero, J.-P., Mercerat, D., Rivet, D., and Sladen, A.: The Potential of DAS on Underwater Suspended Cables for Oceanic Current Monitoring and Failure Assessment of Fiber Optic Cables, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3729, https://doi.org/10.5194/egusphere-egu22-3729, 2022.

EGU22-10574 | Presentations | SM2.1

Innovative high resolution optical geophysical instruments at the termination of long fibers: first results from the Les Saintes optical ocean bottom seismometer, and from the Stromboli optical strainmeter

Pascal Bernard, Guy Plantier, Philippe Ménard, Yann Hello, Guillaume Savaton, Jean-Philippe Metaxian, Maurizio Ripepe, Marie-Paule Bouin, Frederick Boudin, Romain Feron, Sébastien Deroussi, and Roberto Moretti and the optic-OBS-strain-2022 team

In June 2022, in the frame of the PREST interreg Caraïbe project, we installed an optical OBS offshore the Les Saintes archipelago (Guadeloupe, Lesser Antilles), at the termination of a 5.5 km long optic cable buried in the sea floor and landing in Terre-de-Bas island (FIBROSAINTES campaign: Antea vessel from the FOF, plow from GEOAZUR). This innovative seismometer, developped in the last decade by ESEO, is based on Fabry-Perot (FP) interferometry, tracking at high resolution (rms 30 pm) the displacement of the mobile mass of a 10 Hz, 3 component, purely mechanical geophone (no electronics nor feed-back). This optically cabled OBS is the marine version of the optical seismometer installed at the top of La Soufrière volcano of Guadeloupe, in 2019, at the termination of a 1.5 km long fiber (HIPERSIS ANR project). Both seismometers are telemetered in real-time to the Guadeloupe Observatory (IPGP/OVSG). The optical seismometer, located at a water depth of 43 m near the edge of the immersed reef, is aimed at improving the location of the swarm-like seismicity which still persists after the Les Saintes 2004, M6.3 normal fault earthquake. The considerable advantage of such a purely optical submarine sensor over commercial, electric ones is that its robustness, due to the absence of electrical component, guarantees a very low probability of failure, and thus significantly reduces the costs of maintenance. In May 2022, an optical pressiometer and an optical hydrostatic tiltmeter designed and constructed by ENS shoud be installed offshore and connected to the long fiber, next to the optical OBS.

Based on the same FP interrogator, ESEO and IPGP recently developped a high resolution fiber strainmeter, the sensing part being a 5 m long fiber, to be buried or cemented to the ground. A prototype has been installed mid-September 2021 on the Stromboli volcano, in the frame of the MONIDAS (ANR) and LOFIGH (Labex Univearth, Univ. Paris) projects. The interrogator was located in the old volcanological observatory, downslope, and the optical sensors, at 500 m altitude, were plugged at the end of a 3 km optic cable. They consist of three fibers, 5 m long each, buried 50 cm into the ground. Their different orientation allowed to retrieve the complete local strain field. The four weeks of continuous operation clearly recorded the dynamic strain from the frequent ordinary summital explosion ( several per hour), and, most importantly, the major explosion of the 6th of October (only a few per year). The records show a clear precursory signal, starting 120s before this explosion, corresponding to a transient compression, oriented in the crater azimuth, peaking at 0.9 microstrain  10 s before the explosion.

These two successfull installations of optical instruments open promising perspectives for the seismic and strain real-time monitoring in many sites, offshore, on volcanoes, and more generally in any site, natural or industrial, presenting harsh environmental conditions, where commercial, electrical sensors are difficult and/or costly to install and to maintain, or simply cannot be operated.

How to cite: Bernard, P., Plantier, G., Ménard, P., Hello, Y., Savaton, G., Metaxian, J.-P., Ripepe, M., Bouin, M.-P., Boudin, F., Feron, R., Deroussi, S., and Moretti, R. and the optic-OBS-strain-2022 team: Innovative high resolution optical geophysical instruments at the termination of long fibers: first results from the Les Saintes optical ocean bottom seismometer, and from the Stromboli optical strainmeter, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10574, https://doi.org/10.5194/egusphere-egu22-10574, 2022.

EGU22-7742 | Presentations | SM2.1

Strain evolution on a submarine cable during the 2020-2021 Etna eruption

Shane Murphy, Pierre Garreau, Mimmo Palano, Stephan Ker, Lionel Quetel, Philippe Jousset, Giorgio Riccobene, Salvatore Aurnia, Gilda Currenti, and Marc-Andre Gutscher

On the 13th December 2020, a Strombolian eruption occurred on Mount Etna. We present a study of the temporal and spatial variation of strain measured at the underwater base of volcano during this event. 

As part of the FOCUS project, a BOTDR (Brillouin Optical Time Domain Reflectometry) interrogator has been connected to the INFN-LNS ( Istituto Nazionale di Fisica Nucleare - Laboratori Nazionali del Sud) fibre optic cable that extends from the port of Catania 25km offshore to TTS (Test Site South) in a water depth of 2km. This interrogator has been continuously recording the relative strain changes at 2m spacing along the length of the cable every 2 hrs since May 2020. 

On preliminary analysis, a change in strain is observed at the around the time of the eruption, however this variation occurs close to the shore where seasonal variations in water temperatures are in the order of 5°C. As Brillouin frequency shifts are caused by both temperature and strain variations, it is necessary to remove this effect. To do so, numerical simulations of seasonal sea temperature specific to offshore Catania have used to estimate the change in temperature along the cable. This temperature change is then converted to a Brillouin frequency shift and removed from the frequency shift recorded by the interrogator before being converted to relative strain measurements. This processing produces a strain signature that is consistent with deformation observed by nearby geodetic stations on land.

How to cite: Murphy, S., Garreau, P., Palano, M., Ker, S., Quetel, L., Jousset, P., Riccobene, G., Aurnia, S., Currenti, G., and Gutscher, M.-A.: Strain evolution on a submarine cable during the 2020-2021 Etna eruption, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7742, https://doi.org/10.5194/egusphere-egu22-7742, 2022.

EGU22-8294 | Presentations | SM2.1 | Highlight

Real-Time Magnitude Determination and Ground Motion Prediction using Optical Fiber Distributed Acoustic Sensing for Earthquake Early Warning

Itzhak Lior, Diane Rivet, Anthony Sladen, Diego Mercerat, and Jean-Paul Ampuero

Distributed Acoustic Sensing (DAS) is ideally suited for the challenges of Earthquake Early Warning (EEW). These distributed measurements allow for robust discrimination between earthquakes and noise, and remote recordings at hard to reach places, such as offshore, close to the hypocenters of most of the largest earthquakes on Earth. In this study, we propose the first application of DAS for EEW. We present a framework for real-time strain-rate to ground accelerations conversion, magnitude estimation and ground shaking prediction. The conversion is applied using the local slant-stack transform, adapted for real-time applications. Since currently, DAS earthquake datasets are limited to low-to-medium magnitudes, an empirical magnitude estimation approach is not feasible. To estimate the magnitude, we derive an Omega-squared-model based theoretical description for acceleration root-mean-squares (rms), a measure that can be calculated in the time-domain. Finally, peak ground motions are predicted via ground motion prediction equation that are derived using the same theoretical model, thus constituting a self-consistent EEW scheme. The method is validated using a composite dataset of earthquakes from different tectonic settings up to a magnitude of 5.7. Being theoretical, the presented approach is readily applicable to any DAS array in any seismic region and allows for continuous updating of magnitude and ground shaking predictions with time. Applying this method to optical fibers deployed near on-land and underwater faults could be decisive in the performance of EEW systems, significantly improving earthquake warning times and allowing for better preparedness for intense shaking.

How to cite: Lior, I., Rivet, D., Sladen, A., Mercerat, D., and Ampuero, J.-P.: Real-Time Magnitude Determination and Ground Motion Prediction using Optical Fiber Distributed Acoustic Sensing for Earthquake Early Warning, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8294, https://doi.org/10.5194/egusphere-egu22-8294, 2022.

EGU22-2455 | Presentations | SM2.1

Understanding surface-wave modal content for high-resolution imaging with ocean-bottom distributed acoustic sensing

Zack Spica, Loïc Viens, Mathieu Perton, Kiwamu Nishida, Takeshi Akuhara, Masanao Shinohara, and Tomoaki Yamada

Ocean Bottom Distributed Acoustic Sensing (OBDAS) is emerging as a new measurement method providing dense, high-fidelity, and broadband seismic observations from fiber-optic cables. Here, we use ~40 km of a telecommunication cable located offshore the Sanriku region, Japan, and apply ambient seismic field interferometry to obtain an extended 2-D high-resolution shear-wave velocity model. In some regions of the array, we observe and invert more than 20 higher modes and show that the accuracy of the retrieval of some modes strongly depends on the processing steps applied to the data. In addition, numerical simulations suggest that the number of modes that can be retrieved is proportional to the local velocity gradient under the cable. Regions with shallow low-velocity layers tend to contain more modes than those located in steep bathymetry areas, where sediments accumulate less. Finally, we can resolve sharp horizontal velocity contrasts under the cable suggesting the presence of faults and other sedimentary features. Our results provide new constraints on the shallow submarine structure in the area and further demonstrate the potential of OBDAS for offshore geophysical prospecting.

How to cite: Spica, Z., Viens, L., Perton, M., Nishida, K., Akuhara, T., Shinohara, M., and Yamada, T.: Understanding surface-wave modal content for high-resolution imaging with ocean-bottom distributed acoustic sensing, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2455, https://doi.org/10.5194/egusphere-egu22-2455, 2022.

EGU22-11869 | Presentations | SM2.1

Long range distributed acoustic sensing technology for subsea geophysical applications

Erlend Rønnekleiv, Ole Henrik Waagaard, Jan Petter Morten, and Jan Kristoffer Brenne

Recent advances in range and performance of distributed acoustic sensing (DAS) enable new geophysical applications by measuring fiber strain in existing telecom cables and subsea power cables that incorporate optical fibers. We will  present new field data showing the usability of DAS for environmental and geophysical applications, focusing especially on seabed surface waves and the sub-Hz domain. These examples show that highly sensitive DAS technology can be a valuable tool within seismology and oceanography.

The sensitive range along the fiber for DAS was previously limited to about 50 km. We will demonstrate a newly developed system (named OptoDAS) that allows for launching several orders of more optical power into the fiber, and thereby significantly improving the range beyond 150 km.

This new interrogation approach allows for high degree of flexibility optimizing the interrogation parameters to optimize the noise floor, spatial and temporal resolution according to the application. The gauge length (spatial resolution) can be set from 2 to 40 m. For interrogation of 10 km fiber, we achieve a record low noise floor of 1.4 pε/√Hz with 10 m spatial resolution. For interrogation of fibers beyond 150 km, we achieve a noise floor below 50 pε/√Hz up to 100 km. Above 100 km, the noise is limited by the level of reflected optical power, and the noise increases by ~0.3-0.4 dB/km, corresponding to the dual path optical loss in the fiber.

A modern instrument control interface allows for automatic optimalization of interrogation parameters based on application parameters in a few minutes. The instrument computer provides a flexible platform for different applications. The high-capacity storage system can store recorded time-series of several weeks to support e.g., geophysical investigations where extensive post-processing is required. The computational capacity can also be used for real-time visualization and advanced signal processing, for example for event detection and direct reporting of estimated parameters.

The OptoDAS system can convert a submarine cable into a 100 km+ densely sampled array.  From the recordings on a telecom cable in the North Sea, we will show examples of propagating Rayleigh and Love acoustical modes bounded to the seafloor surface. These modes can be excited by acoustic sources on or above the seafloor, such as trawls and anchors. The dense spatial sampling allows for accurate estimates of the location of these sources. The system also allows for applications in seismology and earthquake monitoring. When attached to a cable with non-straight geometry, the measurements have substantial information to determine the location of seismic events. This will be demonstrated using field data from the North Sea telecom cable.

From recordings on a submarine cable between Norway and Denmark, we present the DAS response in the frequency range 0.1 mHz-10Hz across a cable span of 120 km. The response in this frequency range will be a combination of temperature changes, ocean swells and tides. We show that increasing the gauge length in post-processing allows for improving the sensitivity for detecting ultra-low frequency signals.

How to cite: Rønnekleiv, E., Waagaard, O. H., Morten, J. P., and Brenne, J. K.: Long range distributed acoustic sensing technology for subsea geophysical applications, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11869, https://doi.org/10.5194/egusphere-egu22-11869, 2022.

SM2.2 – Direct observation of seismic wavefield gradients – a new approach to seismic experiments

EGU22-13511 | Presentations | SM2.2

Quartz Rotation Sensor

Krishna Venkateswara, Jerome Paros, Paul Bodin, William Wilcock, and Harold J. Tobin

A new high-precision ground- or platform-rotation sensor called the Quartz Rotation Sensor (QRS) has been developed and tested. The QRS is a mechanical angular accelerometer that senses rotational torque with an inherently digital, load-sensitive resonant quartz crystal. It is a portable broadband sensor with a noise floor measured to be ∼45 pico-radian/root (Hz) near 1 Hz, and a resonant period of ~10 s. The noise floor of the sensor near 0.1 Hz is more than two orders of magnitude lower than other similarly sized instruments enabling a dramatic improvement in ability to measure rotational teleseismic signals and tilt contamination in horizontal seismometers. We will present details of the sensor and measurements of rotational components of teleseismic waves recorded with the sensor at a vault. The QRS is useful for rotational seismology and for improving low-frequency seismic isolation in demanding applications such as the Laser Interferometer Gravitational-Wave Observatories.

How to cite: Venkateswara, K., Paros, J., Bodin, P., Wilcock, W., and Tobin, H. J.: Quartz Rotation Sensor, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13511, https://doi.org/10.5194/egusphere-egu22-13511, 2022.

EGU22-9352 | Presentations | SM2.2

A highly sensitive instrument for direct and long-term observations of seismic and natural-mode rotational movements

Leszek Jaroszewicz, Anna Kurzych, and Michał Dudek

Over the last decade, the interest of rotational ground movements has become significant in the field of seismological research, especially in seismic engineering. Being able to reliably detect and record rotational motions is a key point in rotational seismology to better understand the origin of earthquakes and in particular to relate them to the geological context. The area of rotational seismology includes seismology, earthquake engineering, seismotectonic, geodesy as well as gravitation waves. Generally, in classical approach, seismic events are monitored by underground and surface seismic stations based on translational vibration sensors (seismometers, geophones, accelerometers). However, a full description of wave motion requires information about both displacements along the three perpendicular axes X, Y, and Z as well the rotation around these axes. The lack of a possibility of complete wave motion measurements results mainly due to technical difficulties in providing the appropriate sensors meeting all technical requirements of rotational seismology.

In this paper we present the laboratory analysis and field records of the fibre-optic seismograph (FOS) that utilizes the Sagnac effect based on a minimum optical configuration designed for a huge fibre-optic gyroscope with special attention to angular motion detection. Presented FOS utilizes a closed-loop configuration, which is based on the compensatory phase measurement method as well as specific electronic system. The experimental results showed that described FOS is characterized by a wide measuring range, it detects signals with amplitudes ranging from several dozen nrad/s up to even few rad/s and frequencies from 0.01 Hz to 100 Hz. The determined angle random walk was equal to 3∙10−8 rad/s and bias instability was equal to 2∙10−8 rad/s. Moreover,  besides the laboratory verification of FOS’s proper operation, the field observation results are also presented. Aforementioned device is constantly registering rotational motions in the seismological observatory located in the basement of the Książ Castle near Wałbrzych, Poland. We present the rotational events induced by the exploitation of the copper ore deposit in this area as well as long-term measurements, showing results confirming positive detection of small differences in Earth’s rotation rate – mainly diurnal and semi-diurnal. The presented data give broad view of the potential FOS’s application in the area of rotational seismology, including seismic monitoring in observatories, buildings, mines, chimneys and even on glaciers and in their vicinity.

How to cite: Jaroszewicz, L., Kurzych, A., and Dudek, M.: A highly sensitive instrument for direct and long-term observations of seismic and natural-mode rotational movements, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9352, https://doi.org/10.5194/egusphere-egu22-9352, 2022.

EGU22-6357 | Presentations | SM2.2

blueSeis-1C Fiber Optical Gyroscope for enhanced and versatile ground rotation measurements

Frédéric Guattari, Guillaume Lenogue, Kevin Gautier, Hugo Anthonioz, and André Couderette

EGU22-3158 | Presentations | SM2.2

Advancing the Analysis of Volcano-seismic Signals on Etna using Rotational Sensor Data

Eva P. S. Eibl, Martina Rosskopf, Mariangela Sciotto, Giuseppe Di Grazia, Gilda Currenti, Philippe Jousset, Frank Krüger, and Michael Weber

Etna volcano in Italy is one of the most active volcanoes in Europe. We recorded the volcanic activity including degassing and vigorous strombolian activity using a seismometer and a rotational sensor in August to September 2019. We test the newly developed rotational sensor in the field in comparison to the broadband seismometer and seismic-network-based locations using the INGV network. We demonstrate that a single rotational sensor co-located with a seismometer can be used to identify specific seismic wave types, to estimate the back azimuth of wave arrivals and the local seismic phase velocities.

Using the rotational sensor, we easily detected the dominant SH-type waves composing volcanic tremor during weak volcanic activity and the recorded VLP/ LP events. Changes in the composition of the tremor wavefield caused by the onset of vigorous volcanic activity are obvious and can be detected in near real-time if data is streamed. We discuss the changes in the wavefield composition from SH-type waves to a mixed wavefield in the context of the volcanic activity, the back azimuth of the signals and associated phase velocities. Our findings are consistent with observations by INGV and hence the rotational sensor reliably enlarges our sensor portfolio in volcanic environments. In fact, wavefield and ground properties can be derived using just one sensor instead of a sensor network, which makes experiments in remote areas cheaper and easier to maintain. In addition, you can observe phenomena that otherwise go unnoticed, like near vent block rotation.

How to cite: Eibl, E. P. S., Rosskopf, M., Sciotto, M., Di Grazia, G., Currenti, G., Jousset, P., Krüger, F., and Weber, M.: Advancing the Analysis of Volcano-seismic Signals on Etna using Rotational Sensor Data, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3158, https://doi.org/10.5194/egusphere-egu22-3158, 2022.

EGU22-13447 | Presentations | SM2.2

Tilt removal on 6-axis ground motion measurements: experiments at iXblue

Guillaume Lenogue, Baptiste Pinot, Frederic Guattari, and David Mimoun

EGU22-6577 | Presentations | SM2.2

Wave Gradiometry and Continuous Wavelet Transform Thresholding

Oluwaseyi Bolarinwa and Charles Langston

A gradiometer array was deployed as part of the wavefields community experiment conducted by IRIS in the summer of 2016 near Enid, Oklahoma, USA. The gradiometer consisted of 7 levels of concentric square rings with each ring being four times the area of the immediate smaller ring; the largest ring spanned an 800X800 km2 area. Each ring was made up of 16 three-component, 4.5 Hz nodal instruments. In a bid to appraise the effectiveness of the gradiometer in characterizing seismic waves, we computed seismic wave attributes in the form of apparent slowness and signal azimuth from gradiometer records of a magnitude 4.2 event that occurred during the wavefields experiment and compared these attributes with those computed from a coincidental, 3-km aperture phased array by means of a new array analysis method based on the continuous wavelet transform (CWT). Just as in gradiometry, the phased array technique provides wave attributes for all time points, which allows a point-for-point comparison of the gradiometry attributes with those for the phased array method. Prior to analysis, we extracted body wave phases from the gradiometer and phased array data by means of scale-time gating in the CWT space. This step was necessary to reduce the effect of seismic phase interference that can negatively impact gradiometry results. Gradiometry analysis of the vertical component data revealed a P wave horizontal phase velocity of 6.17+-0.04 km/s, which only deviates by 0.03 km/s from the phase array result obtained over an identical time window. The corresponding azimuth computed using gradiometry is 2.2 degrees off the great circle path between the event’s epicenter and the gradiometer center. If the smallest gradiometer ring is labelled 1 and the rest progressively labelled based on their sizes up to 7, this optimal result was obtained using the gradiometer subarray that combines rings 1,3 and 5. Thus, the gradiometer with its relative portability may be preferred over a traditional phased array deployment in some geophysical campaigns.  Using CWT thresholding techniques finds those areas of the wavelet transform plane that contain high SNR for useful processing using beam forming or gradiometry.

How to cite: Bolarinwa, O. and Langston, C.: Wave Gradiometry and Continuous Wavelet Transform Thresholding, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6577, https://doi.org/10.5194/egusphere-egu22-6577, 2022.

EGU22-11072 | Presentations | SM2.2

Array-derived peak ground rotation rate vs. peak ground acceleration: scaling relations from seismicity induced by the Espoo/Helsinki geothermal stimulation

Gregor Hillers, Amir Sadeghi-Bagherabadi, Tommi A.T. Vuorinen, and George Taylor

Observations of ground motion in the near-field of induced earthquakes are important to assess ground shaking limits and design pumping protocols for geothermal stimulation projects, in particular near densely popluated urban areas where such zero-emission geo-energy systems can supply heat and electricity close to the consumer. Diverse seismic networks around the 2018 and 2020 geothermal stimulations in the Otaniemi district in the Espoo/Helsinki area, southern Finland, recorded the ground motions of 6-km-deep induced events at epicentral distances in the 2 to 20 km range. Key features of the seismic networks are seismic arrays consisting of 3 to 25 three-component 4.5 Hz geophones recording at 400 Hz, with interstation distances in the 50 m range. From the array seismograms of translational motion it is possible to compute rotational motion for some 200 events with local magnitudes between 0 and 1.8. The data allow the rare assessment of ground motion patterns at small distances in the cratonic low-attenuation environment of the Fennoscandian shield. Here wo focus on a systematic evaluation of the scaling relations between array-derived peak ground rotation rate (PRR) and peak ground acceleration (PGA) that have been shown to be linearly related. Array-derived motion around all three axes is computed using the ObsPy community tool implementation of Spudich and Fletcher’s seismogeodetic approach. The array and subarray size controls the frequency range for which the rotational motion can be reliably estimated, hence we focus on the robustness and accuracy of the obtained PRR values. We explore the array shape dependent frequency range by a combined analysis of the quality of the PRR estimates, the quality of the linear relationship between PRR and PGA, and the wavelength-to-array-size ratio. The target frequency range is 2 – 15 Hz. We further test if the bandlimited PRR-PGA scaling differs from PGA-scaling obtained from the full bandwidth records. For narrow-band signals the proportionality factor or slope of the PRR-PGA scaling is the local slowness, which opens intriguing opportunities to probe the local velocity structure. From our data we can analyze the scaling relations and therefore consistency between the nine different component pairs of PRR and PGA motion. These results based on ratios of single peak values in a 2 s long seismogram—the S minus P time is about 1 s—are compared to local phase speed estimates from a previous analysis based on optimizing translational acceleration and vertical rotation of the full S-waveform. Data from the many small arrays are used to explore the attenuation of PRR with distance from the source. The deployment of broadband rotational sensors and DAS systems for wavefield gradiometry analyses is anticipated to become more common in future networks; this study contributes to bridging the waiting time by providing low-tech observations of band-limited array-derived rotational motion estimates from induced seismicity for seismic engineering studies.

How to cite: Hillers, G., Sadeghi-Bagherabadi, A., Vuorinen, T. A. T., and Taylor, G.: Array-derived peak ground rotation rate vs. peak ground acceleration: scaling relations from seismicity induced by the Espoo/Helsinki geothermal stimulation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11072, https://doi.org/10.5194/egusphere-egu22-11072, 2022.

EGU22-13355 | Presentations | SM2.2

Analytical developments on 6C computation inspired by navigation algorithms

Baptiste Pinot, Frederic Guattari, Joachin Honthaas, and David Mimoun

The deployment of portable broadband rotational ground motion sensors in the field marks the beginning of 6 degrees of freedom simultaneous and co-located measurements in seismology, after decades of ground motion instrumentation measuring only translations. Regarding the computation of this new kind of data-set, there are obviously some analysis technics to inherit from navigation.

Hence, now seismology has also to solve the 6 equations system with 6 unknowns of dynamic motion. In a navigation system, it is computed real-time in onboard electronics, taking into account centrifugal forces, non-commutativity of rotations, and compensation of projection of gravity in accelerometers frame and Earth rotation rate in gyroscopes frame. For the moment, attempts at handling the merging of 6 components in seismology has remained mostly empirical, using cross-correlation maximization and other optimization methods.

In this study, we developed the analytical framework for seismological 6-C computation methods, derived from navigation-inspired methods to establish a stronger link between these algorithm expertises.

How to cite: Pinot, B., Guattari, F., Honthaas, J., and Mimoun, D.: Analytical developments on 6C computation inspired by navigation algorithms, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13355, https://doi.org/10.5194/egusphere-egu22-13355, 2022.

The seismic waves responsible for shaking 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 wavefield and amplify the ground rotations, thereby increasing the seismic hazard. However, due to paucity of direct recordings of rotational motions, little research has been done towards characterizing the amplifications of ground rotations in the presence of subsurface heterogeneities. This study aims to quantify these amplifications in the case of a 2-D heterogeneous elastic half-space excited by plane SH waves. A semi-analytical method based on the perturbation theory is developed to obtain the translational and rotational motions in the spectral domain. In this method, the problem of simulating motion in a heterogeneous medium is reduced to calculating the response of a homogeneous medium subjected to body forces representing the heterogeneities. Since the dynamic response of a homogeneous half-space subject to body forces is easier to synthesize, the proposed method is convenient to implement. The method is tested for accuracy by comparing its solution with that of a spectral finite element-based solver. Furthermore, the method is shown to be stable at high frequencies (up to 10 Hz) as well as when the subsurface heterogeneities are strong (~20%). The method is applied to an example 2-D heterogeneous medium to ascertain the amplifications in the ground rotations.

How to cite: Singla, V. and Lokmer, I.: Semi-Analytical Method for Simulating Rotational Ground Motion in Two-Dimensional Heterogeneous Elastic Half-Space, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5651, https://doi.org/10.5194/egusphere-egu22-5651, 2022.

EGU22-3112 | Presentations | SM2.2

A Low Noise Model for Rotational Ground Motions

Heiner Igel, Andreas Brotzer, Eleonore Stutzmann, Jean-Paul Montagner, Chin-Jen Lin, Celine Hadziioannou, Joachim Wassermann, and Ulrich Schreiber

The quantitative low/high noise models (L/HNM) for translational ground motions (e.g., Petersen 1993) based on many observations of acceleration power-spectral densities has been extremely successful for the evaluation of site quality, as well as the development of seismic sensors for passive experiments on Earth. No such L/HNM exists for rotational ground motions, primarily because 1) there are close to no direct sensors that measure below the Earth’s smallest rotational motions (large ring laser are currently the most sensitive instruments), and 2) small-scale seismic arrays can be used to derive rotational motions, but are limited in frequency range. A (even approximate) rotational L/HNM would be useful in particular for the development of new rotation sensors considering the numerous possible applications of 6 degree-of-freedom observations in terrestrial and planetary seismology as well as ocean bottom observations. As the terrestrial low-noise motion is primarily dominated by surface waves, the well-known connection between plane surface waves and rotational motions can be used to estimate rotational motions from classic seismometer records using local velocity information. We propose a methodology to derive a rotational L/HNM and support the model by ring laser and seismic array observations.

How to cite: Igel, H., Brotzer, A., Stutzmann, E., Montagner, J.-P., Lin, C.-J., Hadziioannou, C., Wassermann, J., and Schreiber, U.: A Low Noise Model for Rotational Ground Motions, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3112, https://doi.org/10.5194/egusphere-egu22-3112, 2022.

SM2.3 – Enhancing seismic network operations from site scouting to waveform services and products

EGU22-3954 | Presentations | SM2.3

Coordinating Access to Seismic Waveform Data in Europe: Overview of ORFEUS Activities, Services and Products

Carlo Cauzzi, Jarek Bieńkowski, Wayne Crawford, Susana Custódio, Sebastiano D'Amico, Christos Evangelidis, Philippe Guéguen, Christian Haberland, Florian Haslinger, Giovanni Lanzano, Lars Ottemöller, Stéphane Rondenay, Reinoud Sleeman, and Angelo Strollo

ORFEUS (Observatories and Research Facilities for European Seismology, http://orfeus-eu.org/) is a non-profit organization founded in 1986 with the chief goal to promote seismology in the Euro-Mediterranean area through the collection, archival and distribution of seismic waveform data, metadata, and closely related services and products. ORFEUS also supports the coordination and implementation of large scale community initiatives and experiments in observational seismology, and provides community support through software and travel grants, editorial initiatives and training activities. ORFEUS data and services are collected or developed at national level by more than 60 contributing Institutions (see https://orfeus-eu.org/organization/corporate_founders/ and https://orfeus-eu.org/organization/participation/) in the greater European region, and further developed, integrated, standardized, homogenized and promoted through ORFEUS. Within EPOS, ORFEUS represents the seismological waveform services as one of three sub-domains of EPOS Seismology. ORFEUS data and services are open, FAIR, and accompanied by clear policies and licensing information. Two Service Management Committees (SMCs) are established within ORFEUS, devoted to managing, operating and developing (with the support of one or more Infrastructure Development Groups): (i) the European Integrated waveform 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/). A new SMC is being formed to represent the community of European mobile instrument pools, including also amphibian instrumentation. Products and services for computational seismologists are also possible candidates for integration in the ORFEUS domain. Overall, ORFEUS services currently provide access to waveforms acquired by ~ 16,000 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 web services that allow automated user access to data gathered and/or distributed by the various ORFEUS institutions (see ​​https://orfeus-eu.org/data/eida/webservices/ and https://esm-db.eu/#/data_and_services/web_services). Particular attention is paid to acknowledging the crucial role played by data providers, who are part of the ORFEUS community. ORFEUS strongly encourages the use of international network codes, seismic network digital object identifiers, and full network citations. All ORFEUS services are developed in coordination with EPOS and are largely integrated in the EPOS Data Access Portal (https://www.ics-c.epos-eu.org/). Documentation on ORFEUS data and services is provided on the ORFEUS website and is complemented by a large archive of ORFEUS community workshops and seminars / webinars  (https://orfeus-eu.org/other/workshops/). ORFEUS data and services are assessed and improved with the help of technical and scientific feedback from a User Advisory Group (UAG), which comprises European Earth scientists with expertise on a broad range of observational seismology topics. ORFEUS is a key participant in EC-funded projects and collaborates with global and international organizations with similar scope, like the FDSN (https://fdsn.org/), IRIS (https://www.iris.edu/), and COSMOS (https://strongmotion.org/).

How to cite: Cauzzi, C., Bieńkowski, J., Crawford, W., Custódio, S., D'Amico, S., Evangelidis, C., Guéguen, P., Haberland, C., Haslinger, F., Lanzano, G., Ottemöller, L., Rondenay, S., Sleeman, R., and Strollo, A.: Coordinating Access to Seismic Waveform Data in Europe: Overview of ORFEUS Activities, Services and Products, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3954, https://doi.org/10.5194/egusphere-egu22-3954, 2022.

EGU22-6733 | Presentations | SM2.3

Enabling the Future Capabilities of the Global Seismographic Network (GSN)

Katrin Hafner, Stephen Arrowsmith, Jim Davis, Gabi Laske, Artie Rodgers, Robert Busby, and Robert Mellors

EGU22-12245 | Presentations | SM2.3

Expansion of the Irish National Seismic Network – Planning, Site-Testing and Installation of Real-Time Seismic Stations

James Grannell, Martin Mollhoff, David Craig, Louise Collins, Clare Horan, Philippe Grange, and Christopher Bean

EGU22-4410 | Presentations | SM2.3

Review of earthquake location quality since 2020 for Austria

Maria-Theresia Apoloner, Niko Horn, and Helmut Hausmann

When monitoring seismicity, detection thresholds for magnitude and location accuracy for epicentres are basic quality factors used. However, these factors can be estimated in numerous ways, depending on available data, the tasks the network is built for and customer/legal guidelines.

In this work, we focus on location quality. We analyse location quality for the area of Austria and a smaller project within. For this purpose, we calculate location errors with NLLoc (Lomax, et al. 2009) for Austria and compare them with location errors automatically computed for each earthquake located by the Austrian Seismological Servicewithin the last 2 years. Additionally, we use the quality parameters given in Bondar, et al. (2004) for further analysis.

How to cite: Apoloner, M.-T., Horn, N., and Hausmann, H.: Review of earthquake location quality since 2020 for Austria, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4410, https://doi.org/10.5194/egusphere-egu22-4410, 2022.

EGU22-2468 | Presentations | SM2.3

Deployment of a local seismic network around the northern Guadiana Menor River (Betic Cordillera, Spain)

Jesús Garrido, José A. Peláez, Jesús Henares, and Carlos Marín

The Guadiana Menor River, included in the Guadalquivir foreland basin, at the northern border of the Betic Cordillera, has suffered in the last decade some low to moderate magnitude seismic series. For instance, the so called 2012-2013 Sabiote-Torreperogil seismic sequence, 1 to 5 km deep, being the biggest recorded event a mbLg 3.9 earthquake, and the so called 2016-2018 Jódar-Peal de Becerro seismic series, less than 2 km and 9 to 13 km deep, 20 km southeast of the previous one, being a mbLg 4.1 event the greatest recorded magnitude. In both cases, seismic series show focal mechanism solutions mostly with strike-slip and some dip-slip and NW-SE compression with no clear tectonic features at surface, due to the sedimentary infill. The Spanish Instituto Geográfico Nacional (IGN) national seismic network recorded in the last years, mainly in the region of the 2016-2018 seismic sequence, some low magnitude earthquakes, showing that the fault that hosted these events continues to be active.

This was the main reason to develop a little local seismic network in the region, designed with the aim to study this persistent seismicity in terms of locations and focal mechanism solutions when there could be available data. It is equipped with six triaxial broadband sensors specifically deployed for this purpose, and also sharing data coming from a near IGN seismic station in the region. The seven seismic stations present as uniform azimuthal distribution as possible around the seismicity, being the nearest station less than 5 km from the seismicity area, and the farthest about 30 km away. Anyway, the seismic network spatial distribution has been conditioned for the fact that they are not permanent housing stations, requiring electric power. Most of the seismic stations are recording data from September 2021.

Real-time records are shared with the Spanish IGN seismic network in order to improve regional locations. Until now, several low magnitude earthquakes, below the perceptibility level of the national seismic network, have been located. In addition, focal mechanisms have been computed for some low magnitude events (~ mbLg 2.0), congruent with strike-slip solutions.

How to cite: Garrido, J., Peláez, J. A., Henares, J., and Marín, C.: Deployment of a local seismic network around the northern Guadiana Menor River (Betic Cordillera, Spain), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2468, https://doi.org/10.5194/egusphere-egu22-2468, 2022.

EGU22-13025 | Presentations | SM2.3

A volcano seismic monitoring network in the Caribbean Netherlands

Reinoud Sleeman and Elske de Zeeuw-van Dalfsen

The Lesser Antilles volcanic arc on the eastern boundary of the Caribbean Plate is part of the Caribbean subduction zone. The subduction process is responsible for the formation of 16 volcanoes in this arc, forming islands like Saba and St. Eustatius in the Caribbean Netherlands. KNMI deploys a monitoring network on these islands consisting of seismometers and GNSS stations. The seismic network is built with broadband seismometers to monitor seismic signals from (regional) earthquakes and from volcano related processes at Saba and St. Eustatius. We use local infrastructure as well as stand-alone VSAT technology to transmit seismic data in near real-time to KNMI. Data are forwarded in real-time to the Pacific Tsunami Warning Center (PWTC). Waveforms are openly available to the research community through ORFEUS/EIDA, and through EPOS-NL, a Dutch national research infrastructure for solid Earth science that integrates large-scale geophysical facilities in the Netherlands.

Volcanoes Mt. Scenery (Saba) and The Quill (St. Eustatius) are active but quiescent. Volcanic earthquakes may occur at different depths and are caused by various processes in a volcano. Each type of volcanic earthquake exposes differences in features in the waveform data, like frequency content, waveform envelope, duration, statistical parameters and type of onset. We are building a monitoring system based on various tools and techniques, like a) SeisComP3 for detecting and locating regional tectonic earthquakes, b) a coincidence trigger to detect small, local (volcanic) earthquakes, c) covariance matrix analysis to identify coherent signals across the network, d) seismic interferometry to monitor seismic velocity changes in the subsurface of the volcanoes and e) data quality monitoring  to ensure high quality of data.

We provide an overview of the seismic network, the infrastructure, the availability of data through EPOS-NL and the implementation of the various monitoring techniques.

How to cite: Sleeman, R. and de Zeeuw-van Dalfsen, E.: A volcano seismic monitoring network in the Caribbean Netherlands, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13025, https://doi.org/10.5194/egusphere-egu22-13025, 2022.

EGU22-8418 | Presentations | SM2.3

Two years of permanent deployment of seismic station LIVV, Antarctica

Liliya Dimitrova, Gergana Georgieva, Dragomir Dragomirov, and Valentin Buchekchiev

Livingston Island is one of the eleven islands of the South Shetland Archipelago which is separated from the Antarctic Peninsula by Bransfield Strait and from South America by the Drake Passage. In 1988 in the eastern part of the Island, the Bulgarian Antarctic Base “St. Kliment Ohridski” (BAB) was established. The Base works during the austral summers and accommodates scientists from different branches of the science. The first Bulgarian Polar Seismic Station LIVV was set in operation in 2014 as a seasonal station operating during the regular Antarctic expeditions. In 2019, the station was rebuilt on a new site one kilometer far from BAB. The seismological equipment was installed on a bedrock outcrop at the base of a hill. The equipment consists of broadband seismometer Guralp CMG40T with 30 s to 50 Hz flat velocity response and one short period 4.5 Hz Geophone. Thermo-insulation covers are mounted over the both sensors to ensure stable environment. The digitizer Reftek DAS-130/6 and the solar panel controller are installed close to the sensors in a thermo insulated box. The station is powered by a battery and solar panel. A GPS receiver ensures time synchronization. At the end of the XXVIII Bulgarian Antarctic expedition in March of 2020, the seismic station LIVV was set as permanent year-round operational Antarctic station. Using the recorded state of the health information and the registered seismic data, we analyzed the performance of the station LIVV. For the two years of permanent deployment, the seismic equipment works stable. The battery has retained its working capacity despite low temperatures and high humidity. There are interruptions in the recording when the sunlight is not high enough to charge the battery above 12V. After restoring the power supply, the equipment immediately is switched on in the normal registration mode. The temperature inside of the thermal box hasn’t dropped below 6⁰ C and the electronic components have worked in an optimal environment. The cycle operational mode of the GPS receiver is suitable set to ensure high accuracy time. The analysis of the recorded seismic data shows that the mode value of the ambient seismic noise, for longer periods greater than 1s, is 10-20dB below High Noise Model and for the shorter periods below 1 s it falls to -140dB. The noise level suggests good recording capabilities of the station especially in the short periods. This is proven by the large number of recorded earthquakes and events in the ice cover of the Livingston Island during the two years exploitation period. The analysis of the performance of the seismic station LIVV shows that the station is built on a stable foundation (bedrock), and the provided thermal insulation creates an optimal mode of operation of the seismic equipment. With an uninterruptible power supply, the seismic station will operate reliably and without interruption throughout the year, and the quality of the recorded data will be high enough to analyze the seismicity in the region and the behavior of the ice sheet of the Island.

How to cite: Dimitrova, L., Georgieva, G., Dragomirov, D., and Buchekchiev, V.: Two years of permanent deployment of seismic station LIVV, Antarctica, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8418, https://doi.org/10.5194/egusphere-egu22-8418, 2022.

EGU22-9762 | Presentations | SM2.3

SeisPPSD: an interactive web front-end and scalable HPC back-end for probabilistic power-spectral-density calculations

Vincent van der Heiden, Michael Frietsch, and Andreas Rietbrock

Offering a web-interface alongside a back-end for the calculation of probabilistic power-spectral-densities (PPSD) is the main goal of this project. No simple out-of-the-box open-source solution is available so far. Moreover, researchers should get access to the information needed in a straightforward way.

The project was initiated to process data routinely acquired at the KIT GPI seismological data center in order to enhance the quality control of the acquired data and station metadata. Furthermore, the PPSD gallery should develop into a starting point for further scientific research.

Here we present SeisPPSD, a comprehensive solution for the calculation and inspection of PPSDs building on existing ObsPy codes. Next to an intuitive gallery and archive which offers a fine granularity in time, the user can create PPSDs interactively, e.g. comparing the day and night noise levels. As well, plots with noise levels for distinct frequencies over time can be visualized.

The web front-end is mainly written in HTML but using Python and Javascript for the interactive parts. The back-end is implemented in Python and is distributing the PPSD calculation in a scalable fashion to the HPC environment.

Apart from an easy to use web-interface, the researcher has access to an archive with the data derived product. This creates the opportunity for the researchers to customize plots with the already (pre-)calculated PPSD files. Furthermore, those files are relatively small and therefore uncomplicated to share with researchers outside. The PPSD-files can be used with the standard ObsPy module opening the possibility for further collaboration.

How to cite: van der Heiden, V., Frietsch, M., and Rietbrock, A.: SeisPPSD: an interactive web front-end and scalable HPC back-end for probabilistic power-spectral-density calculations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9762, https://doi.org/10.5194/egusphere-egu22-9762, 2022.

Güralp’s smart seismic range of seismic instrumentation (incorporating Certimus, Fortimus, Minimus, Radian and Aquarius) prioritizes technical features like low-latency, communication, and computational processes, as well as practical features like compatibility and modular design for easy adaptation and integration with existing networks. 

The Güralp Data Centre interface offers ‘one click’ tools to configure seismic instruments to stream data to a central (typically cloud based) server. From here the data is saved in miniSEED form in configurable folder structures. This application is particularly important for operators dealing with large volumes of seismic waveform data from regional and national networks. The GDC proves to be particularly effective when coupled with low-latency transmission protocols, where data is streamed from seismic stations to the GDC and then efficiently forwarded to the desired location and in the most appropriate format, reducing the overall latency of the system.   

Additionally, the data can be streamed on to downstream processors such as Earthworm or SeisComP to build more advanced large-scale seismic monitoring and data analysis systems. Industry standard protocols are employed throughout whilst offering a simple interface to set up and monitor the operation of the network, meaning that the GDC can be easily implemented into existing systems and networks with minimal configuration.

Long term latency monitoring, network outages and bandwidth usage are all captured and displayed in a number of applets that make the maintenance of large networks straight forward. The Güralp Data Centre includes the Discovery software dashboard which allows network managers to monitor key SOH parameters in Realtime and to also configure system on mass.

Trigger events from instruments can be recorded and displayed on a map as part of a range of features dedicated to EEW implementations. This information is conveyed using the open Common Alert Protocol (CAP). The CAP messages are created as a result of individual station or sub-network triggers and will contain important parameters such the on-site recorded PGA, PGV and PGD. This method provides the lowest possible latency for simple network early warning.

 

How to cite: Lindsey, J., Barbara, R., Reis, W., Mohr, S., Cilia, M., Watkiss, N., and Hill, P.: The Güralp smart seismic range of instruments benefit from enhanced networking functionality with the new Güralp Data Centre (GDC) software package for easy mass data acquisition and station metadata observing, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7818, https://doi.org/10.5194/egusphere-egu22-7818, 2022.

EGU22-10500 | Presentations | SM2.3

Cascadia 120 Slim Posthole: A Combined Strong and Weak Motion Sensor for Early Warning and Regional Networks

Valarie Hamilton, Tim Parker, Geoffrey Bainbridge, and Daniela Wuthrich

Existing regional and EEW networks can be improved in data quality, providing more stations with unclipped continuous waveform observations and a uniform magnitude of completeness (Mc).  This is possible using upgraded deeper sensor emplacements and new instrumentation, based on a current understanding of system noise and updated equipment available today.  Station density is increasing with the EEW buildout, with a focus on minimizing latency, which also presents an opportunity to improve data quality for weak motion.  Mc and signal-to-noise ratio across the seismic and geodetic spectrum will be important for future OEF challenges and for hazard and science efforts such as 4D studies and the high resolution geophysical imaging of deep Earth structure.  Recent development of network Mc simulation code (Wilson et al., 2021) can be used to plan new networks, or infill stations to economically upgrade existing networks to these new best practices.  

An instrument system that provides high-gain weak motion data in precise alignment with strong motion data allows combined processing to create a seamless data set with maximum dynamic range.  The Nanometrics Cascadia 120 Slim Posthole has been designed to meet these requirements. Both weak and strong motion sensors are integrated in a single case which enables lowest system noise, unclipped observations, and precise coherence of signals between the weak and strong motion channels.  Cascadia 120 Slim and Cascadia Compact are deployed in networks now and we will present data showing the noise floor for weak motion, a seamless transition to strong motion, and high coherence between the two sensors for mid-sized events.

Authors: Valarie Hamilton, Geoffrey Bainbridge, Tim Parker, Daniela Wuthrich

How to cite: Hamilton, V., Parker, T., Bainbridge, G., and Wuthrich, D.: Cascadia 120 Slim Posthole: A Combined Strong and Weak Motion Sensor for Early Warning and Regional Networks, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10500, https://doi.org/10.5194/egusphere-egu22-10500, 2022.

An important consideration in selecting instrumentation to support the undertaking of portable seismic campaigns has been the costs associated with physical attributes, namely Size, Weight, and Power.  A more holistic approach would be to examine the overall campaign lifecycle and the phases which have the greatest impact on science outcomes. In this regard, some of the key success factors are the decisions made during the deployment planning phase that includes network size, station geolocation, instrumentation and sensor choices. Often overlooked is the data management problem associated with ensuring that the most up-to-date information associated with the plan is communicated to everyone who needs it. Further, another often overlooked aspect is the accurate tracking and reporting of what actually is deployed in the field relative to the plan, since such deviations inevitably occur.

The Pegasus Data Acquisition System is an ecosystem of hardware and software components for portable seismic monitoring that fundamentally transforms how seismic campaigns are conducted. This integrated ecosystem-based approach to seismic data acquisition ensures that campaigns are easy to plan, execute and achieve superb outcome certainty and cost-efficiency. A range of Pegasus models have been designed specifically to support Portable, Polar and OBS campaigns. Seamlessly integrated workflows address all aspects of the campaign lifecycle from pre-planning to pre-configured deployments, harvesting ready-to-use complete data sets, configuration distribution to field technicians and automatically generated metadata.

Authors: David Easton, Michael Perlin, Sylvain Pigeon, Tim Parker, Valarie Hamilton

How to cite: Easton, D.: Transforming Portable Seismic Data Acquisition: From Experiment Design to Publishing, an Ecosystem Approach, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10561, https://doi.org/10.5194/egusphere-egu22-10561, 2022.

The densification of offshore observatories is the next important challenge for scientists as described in the New Advances of Geophysics’ (NAG) meeting in November 2018 in Edinburgh. 

Nanometrics is combining our latest land based technology with our proven OBS technologies to enable the next steps in offshore observation.  Specifically, we are building both 360 second and 120 second corner observatory class seismometers with the same performance specifications as land based instruments, but in a form factor allowing deployments to 6000m.   

 

These seismometers come in a form factor unique to the OBS community allowing exceptional advances in SWaP (size, weight and power), critical to reducing the expensive logistics of OBS work, and are suitable for autonomous stations and cabled stations.  Power usage and volume are reduced 60-70% versus previous generation options.

These new instruments expand Nanometrics' range of products enabling new ocean bottom science, reducing integration risk and time to deploy, while improving outcome certainty.  

Authors: Michael Perlin, Geoffrey Bainbridge, Bruce Townsend, Valarie Hamilton, Tim Parker

How to cite: Perlin, M.: A New Generation of Turnkey Broadband Solutions to Support Ocean Bottom Research, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10594, https://doi.org/10.5194/egusphere-egu22-10594, 2022.

EGU22-10623 | Presentations | SM2.3

Real Time Data Acquisition for Mission-Critical Seismic Networks

Michael Laporte

Ensuring the reliable acquisition of real time seismic data from remote monitoring stations is an inherently challenging task. Stations are often in isolated locations with little to no supporting infrastructure, creating limitations on power and communications systems which demand design tradeoffs. When the data is driving mission-critical public safety systems, such as Earthquake Early Warning (EEW) and future work for Operational Earthquake Forecasting (OEF), real time acquisition performance is of critical importance. 

In particular for EEW, acquisition performance must be measured not only in real time data availability, but also data latency and bandwidth utilization.  Beyond these key performance metrics, it is critical that the system is robust, with layers of redundancy to ensure continued operation in the event of a damaging earthquake. A comprehensive system test and acceptance program is needed to ensure performance requirements are met and to have confidence the system will function as intended at the critical moment.

 

This study examines the objectives, the factors considered and the approaches taken in the design and implementation of a real time acquisition systems for mission-critical networks.

Authors 

Michael Laporte, Michael Perlin, Ben Tatham, Valarie Hamilton, Bruce Townsend

How to cite: Laporte, M.: Real Time Data Acquisition for Mission-Critical Seismic Networks, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10623, https://doi.org/10.5194/egusphere-egu22-10623, 2022.

SM3.1 – Ambient Seismic Noise & Seismic Interferometry

Coda wave interferometry is an important tool to gain insights into the dynamic evolution of the Earth. A limitation of the majority of current studies employing this technique, is the neglect of variations in scattering strength in the lithosphere. Geological observations indicate that scattering properties can strongly vary laterally, especially in complex geological settings, e.g. in the vicinity of active tectonic or volcanic areas.

In presented work we explore the implications of non-uniform distribution of scattering strength on the spatio-temporal sensitivity of coda waves. In the first part, we numerically derive 2-D coda wave sensitivity kernels based on Monte Carlo simulations of the radiative transfer process, considering lateral heterogeneity of the crust. The kernels are calculated for three different observables, namely travel-time, decorrelation and intensity. Our results illustrate that laterally varying scattering properties can have a profound impact on the sensitivities of coda waves.

In a second part, we validate the kernels. Firstly, synthetic lapse-time based travel-time changes are calculated using the kernels for non-uniform media. Using these synthetic observations, we conduct damped least-squares inversions to localise changes in space for both a fault zone and volcanic setting. We compare the accuracy of localisation of the medium changes between inversions carried out with kernels for uniform and non-uniform media. Our results demonstrate that superior localisation of the seismic anomaly is obtained when considering local scattering information by employing kernels for non-uniform media. This holds for the fault zone as well as the volcanic setting. The stability of the results is verified by conducting inversions where 10dB white noise is added to the synthetic time-shift observations.

How to cite: van Dinther, C., Wang, Q., Margerin, L., and Campillo, M.: The impact of laterally varying scattering properties on subsurface monitoring using coda wave sensitivity kernels: Application to fault zone and volcanic areas, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11414, https://doi.org/10.5194/egusphere-egu22-11414, 2022.

EGU22-12941 | Presentations | SM3.1

The stationary phase approximation in seismic interferometry: Error quantification and the effects of source correlations.

Daniella Ayala-Garcia, Michal Branicki, and Andrew Curtis

Seismic interferometry is a powerful and well-established technique that relies on cross-correlating seismic observations at different receiver locations to yield new seismic responses that, under certain conditions, provide a useful estimate of the Green's function between the given receiver locations, as if there was a source at one of these locations. The inter-receiver signals thus estimated allow us to monitor and remotely illuminate near-surface crustal structures.

Underpinning seismic interferometry is the principle of stationary phase, which states that non-trivial contributions to highly oscillatory integrals, such as those found in interferometry, arise from stationary points of the phase of these cross-correlations. This principle is widely invoked to make approximations in interferometry, both in theory, to derive and simplify interferometric formulations, as well as in practical applications, to justify the use of non-ideal source or receiver distributions. Further, it has been established that spatial variations in the source intensity must be smooth in order to apply this approximation.

While there have been some empirical explorations of the uncertainty introduced by this approximation, the errors have not yet been quantified analytically, and neither the effects of non-smooth variations in the sources, nor of statistical correlations between sources, have been formally considered. In this work, we apply a mathematical framework to seismic interferometry in two dimensions. This analysis yields an exact expression for the error in the interferometric estimate of the inter-receiver Green’s function. Moreover, we extend this approach to a scenario of inhomogeneous, statistically correlated sources, and illustrate the effects of source correlation and roughness on the phase and amplitude of the stationary-phase interferometric estimate. We provide statistical conditions to ensure that the stationary phase estimate is unbiased, and give an explicit bound for the error in the estimated spectrum. These error quantities are given in terms of parameters that are either known (such as the inter-receiver distance), or can be estimated from empirical data. Therefore, we expect these results to be applicable in practical interferometric studies that make use of the stationary phase approximation, as a tool to quantify error and uncertainty in empirical results.

How to cite: Ayala-Garcia, D., Branicki, M., and Curtis, A.: The stationary phase approximation in seismic interferometry: Error quantification and the effects of source correlations., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12941, https://doi.org/10.5194/egusphere-egu22-12941, 2022.

Ambient noise tomography (ANT) based on empirical Green’s functions (EGFs) retrieved from cross-correlation functions (CCFs) of ambient noise is widely used to construct shear-wave velocity structures. EGFs from ambient noise can be treated as virtual seismograms with one station working as a virtual source and the other station working as a receiver. We propose a method named two-station C2 method(Rao et al., 2021), using one single station as a virtual source to obtain surface waves between a pair of asynchronous stations. This method can significantly improve ray path coverages and enhance the resolution in ANT for areas between asynchronous seismic arrays.

In our method, we select three stations, called a station triplet, which share the same great-circle path. We take one long-term station as a virtual source rather than using a number of stations as sources in the C3 method(Stehly et al., 2008; Ma and Beroza, 2012; Spica et al., 2016; Zhang et al., 2019). We use data from the USArray to demonstrate the feasibility of our method in retrieving surface waves from asynchronous stations.

Due to the harsh environment and inaccessibility of most of parts of the plateau, it is nearly impossible to deploy a large-scale synchronous seismic array across Tibet. In the past few decades, several isolated arrays have been deployed in Tibet at different periods of time. ANT has been applied to Tibet to generate phase velocity maps using these seismic arrays (e.g., Yang et al.,2012;Xie et al.,2013; Shen et al., 2016). However, due to the fact that these seismic arrays were not deployed synchronously, inter-array paths between asynchronous arrays cannot be obtained from the traditional C1 method, resulting in low resolution in the gaps of these seismic arrays.

We applied our method to the two seismic arrays (Z4 and X4) deployed in NE Tibet. The Z4 array was deployed from July 2007 to July 2008 and X4 from September 2008 to September 2009. For these two arrays, if we follow the C1 method, we can get at most 153 paths for Z4 array and 300 paths for X4 array. But no crossing-array paths can be obtained. Fortunately, there is a permanent Chinese National Seismic Network (Zheng et al., 2010) deployed across China. We can take the permanent stations from the Chinese National Seismic Network as source stations and obtain C2 functions following our method. Here, to illustrate the application of our C2 method for these two arrays, we select 153 permanent stations from the Chinese National Network as virtual sources. And, using these stations and our C2 method for these two arrays, we can retrieve 413 C2 functions with the source stations located within 5 degrees of the great-circle paths of receiver station pairs. The path coverage is improved by over 91%. Combining C1 and C2 paths, we can much better image the structures between these two arrays.

How to cite: Rao, H. and Luo, Y.: Extracting surface wave dispersion curves from asynchronous seismic stations in NE Tibet: A two-station C2 method, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6752, https://doi.org/10.5194/egusphere-egu22-6752, 2022.

EGU22-8290 | Presentations | SM3.1

Historical earthquake simulation using ambient seismic noise in Vrancea (Romania): preliminary results

Anica Otilia Placinta, Laura Petrescu, Felix Borleanu, and Mircea Radulian

The Vrancea Seismic Zone (VSZ), located in Romania, at the sharp bend of the southeastern Carpathians, is an anomalous intraplate seismic region releasing the largest strain in continental Europe. The seismicity is concentrated in a high-velocity focal volume down to 200 km, challenging classic earthquake mechanism theories due to its remote location and deep hypocenters in an expectedly ductile lithosphere. The last significant earthquake in Vrancea occurred in 1977 causing destruction to Romanian cities and long-term economic damage to an already struggling developing country. The seismic infrastructure was underdeveloped in Romania at that time and the earthquake was not well-recorded locally. The recent increase in seismic station coverage in Romania now provides the opportunity to systematically study seismogenic processes and apply the most novel processing methods.

We apply the recently developed algorithm of Virtual Earthquake Approach (VEA, Denolle et al., 2013) to reconstruct realistic ground motion records as if the stations operating today recorded historical earthquakes, such as the 1977 event. Predicting accurate ground motion is critical for earthquake hazard analysis, particularly in situations where sedimentary basins trap and amplify seismic waves. We gathered one year of three-component ambient noise data from 44 broadband seismic stations around the VSZ. We then construct the ambient noise Green’s tensor between pairs of stations and add the signatures of a realistic earthquake: double couple mechanism, buried source and a realistic earth model in the epicentral area.

Using the Romanian earthquake catalog (Romplus, www.infp.ro), we selected the last Mw>6.0 earthquakes since 1940 from the area and extracted the moment tensor solutions. Subsequently, we simulate the ground motion generated by these earthquakes recorded by modern seismometers decades after their occurrence. Our new results demonstrate the viability of this innovative method and provide a unique opportunity for more accurate seismic hazard analysis.

Keywords: ambient noise, historical earthquake, virtual earthquake approach.

Reference:

  • A. Denolle, E. M. Dunham, G. A. Prieto, G. C. Beroza, Ground motion prediction of realistic earthquake sources using the ambient seismic field, Journal of Geophysical Research: Solid Earth, Vol. 118, 2102–2118, doi:10.1029/2012JB009603, 2013.

 

How to cite: Placinta, A. O., Petrescu, L., Borleanu, F., and Radulian, M.: Historical earthquake simulation using ambient seismic noise in Vrancea (Romania): preliminary results, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8290, https://doi.org/10.5194/egusphere-egu22-8290, 2022.

EGU22-3956 | Presentations | SM3.1

Mitigating array-induced bias in ambient noise beamforming

Katrin Löer and Claudia Finger

We show that the geometry of a seismic array affects estimates of velocity and propagation direction of ambient seismic noise wavefields measured with beamforming techniques. We demonstrate how this results in apparent anisotropy estimates and present first approaches to mitigate the effect.

Beamforming is an array technique originating from earthquake seismology that has become increasingly popular to analyse the ambient noise wavefield with the goal to characterise ambient noise sources (e.g., regions of origin of Love and Rayleigh waves) as well as subsurface structures (shear-velocity profiles, fracture orientation). Beamforming techniques estimate the dominant velocity, direction of propagation, and (in case of three-component data) the polarisation of a wavefield recorded within a limited time window at a seismic array. An important parameter in beamforming is the array response function, which shows the response of an array to a wave that is arriving directly from below. It can be thought of as the fingerprint of the array and depends on the array geometry, i.e., number of stations, station spacing, and orientation of station pairs. A biased array can lead to oversampling of certain directions and, thus, prioritising them in the beamform heatmap.

The first attempt to mitigate the influence of the array focuses on analysing the orientation of station pairs in an array and applying a weighting matrix in order to enhance contributions from orientations that are underrepresented. This approach leads to a modified array response function, that looks more regular and has the fingerprint of the array partly removed. Using synthetic data and different array geometries we demonstrate the effect on the estimated anisotropy.

The second approach is based on simulating synthetic, isotropic wavefield recordings at an array of choice and measuring their dominant velocities and propagation directions using beamforming. Comparing expected and observed values shows that the effect of the array can be significant, in particular when multiple sources act simultaneously (as is often the case for ambient noise): both measured velocities and propagation directions are affected by the design of the array, leading to erroneous anisotropy estimates. Once we have an estimate of array-induced anisotropy, however, we can subtract it from the anisotropy measured in real data and thereby reduce the effect. Examples for different array geometries are presented and compared.

How to cite: Löer, K. and Finger, C.: Mitigating array-induced bias in ambient noise beamforming, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3956, https://doi.org/10.5194/egusphere-egu22-3956, 2022.

EGU22-3479 | Presentations | SM3.1 | Highlight

SANS: Publicly available daily seismic ambient noise source maps on a regional to global scale

Jonas Igel, Daniel Bowden, and Andreas Fichtner

To improve methods in full-waveform ambient noise tomography and monitoring it is important to have knowledge of the spatio-temporal variations of the noise source distribution. Without this knowledge, an uneven distribution of sources may bias observations, and a changing source distribution may be falsely interpreted as subsurface velocity changes. By combining two methods to locate noise sources and decreasing the computational cost, we are able to invert for the global noise source distribution of the secondary microseisms on a daily basis. Additionally, we present a web framework where the Seismic Ambient Noise Source (SANS) maps are made available to the public. 

Many different methods to locate ambient noise sources have been developed. Bowden et al. (2021) show how a more data-driven Matched-Field Processing (MFP) approach and a more rigorous finite-frequency sensitivity kernel method can be derived from one another.  Igel at al. (2021) implement spatially variable grids and pre-computed wavefields to make the finite-frequency inversion more efficient. This has made daily inversions on a regional to global scale feasible for secondary microseismic noise sources in a frequency range from 0.1 to 0.2 Hz. Since the inversion approach allows for prior information to be implemented, we use the more efficient MFP method to create an initial model and steer the inversion in the right direction. 

In collaboration with the Swiss National Supercomputing Centre (CSCS) we are able to run this workflow on a daily basis. The resulting noise source maps are subsequently made available to the public through our web framework SANS. A user can look through all iterations of the inversions, download all model and inversion files, and implement them in their own methods. Additionally, code is provided to help the user create plots and simplify the implementation in other studies. We are looking for collaboration with ambient noise tomography studies to investigate how the implementation of noise source maps could potentially improve the resulting structure models.

How to cite: Igel, J., Bowden, D., and Fichtner, A.: SANS: Publicly available daily seismic ambient noise source maps on a regional to global scale, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3479, https://doi.org/10.5194/egusphere-egu22-3479, 2022.

EGU22-252 | Presentations | SM3.1

Matched Field processing for complex Earth structure

Sven Schippkus and Céline Hadziioannou

Matched Field Processing (MFP) is a technique to locate the source of a recorded wave field. It is the generalisation of beamforming, allowing for curved wavefronts. In the standard approach to MFP, simple analytical Green's functions are used as synthetic wave fields that the recorded wave fields are matched against. We introduce an advancement of MFP by utilising Green's functions computed numerically for real Earth structure as synthetic wave fields. This allows in principle to incorporate the full complexity of elastic wave propagation, and through that provide more precise estimates of the recorded wave field's origin. This approach also further emphasises the deep connection between MFP and the recently introduced interferometry-based source localisation strategy for the ambient seismic field. We explore this connection further by demonstrating that both approaches are based on the same idea: both are measuring the (mis-)match of correlation wave fields. To demonstrate the applicability and potential of our approach, we present two real data examples, one for an earthquake in Southern California, and one for secondary microseism activity in the Northeastern Atlantic and Mediterranean Sea. We provide an accompanying simple code example to illustrate the method on github.

How to cite: Schippkus, S. and Hadziioannou, C.: Matched Field processing for complex Earth structure, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-252, https://doi.org/10.5194/egusphere-egu22-252, 2022.

Seismic noise above 2 Hz band would interfere with the lower frequency output from 3rd generation gravitational wave interferometers.
Sos Enattos, Sardinia, is a potential site for the future Einstein Telescope, which will be built hundreds of meters underground. To characterise one aspect of the seismic field at this potential site, I examined trends in wind speed, direction, and seismic noise. Elevated seismic energy across a broad range of frequencies occurs when wind speeds are higher. At frequencies below 1 Hz, sources appear to be regional (ocean generated microseisms). At 1-50Hz, local sources dominate. Deeper, the effects of local wind-generated noise are reduced and masked by other noise sources.

How to cite: Ensing, J.: Wind generates seismic noise at Sos Enattos, Sardinia, potential site for the Einstein Telescope., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4434, https://doi.org/10.5194/egusphere-egu22-4434, 2022.

EGU22-7881 | Presentations | SM3.1

Spatio-temporal Analysis of the Southern Ocean Storms Using the Australian Seismic Arrays

Abhay Pandey and Hrvoje Tkalčić

The mantle transition zone is delineated by seismic discontinuities at approximately 410-km and 660-km depth. The lateral variations in reflectivity and depth of the two seismic discontinuities reflect changes in mineralogy composition, thermal state, and water content, that is key to understanding the Earth’s dynamics. Traditional imaging methods based on the analysis of earthquake signals, such as seismic tomography and receiver function analysis, are often limited by earthquake occurrence and uncertainties related to the earthquake source parameters. Recent studies demonstrated the feasibility of recovering body waves from noise correlations, providing new prospects for imaging deep Earth [e.g., Poli et al., 2012; Boué et al., 2013]. 

In this study, we map the 410-km and 660-km discontinuities beneath the European Alps using reflected body waves recovered from noise correlations. To that end, we compute noise correlations using four years of continuous recordings from ∼1200 broadband stations in the greater Alpine region. To enhance the signal-to-noise ratio of the body-wave reflection phases, for each station pair, we stack daily noise correlations in selected time spans with a high level of near vertical-incident body waves and less dominant surface waves [Lu et al., 2021]. We further stack noise correlations of station pairs with common/nearby reflection points to obtain local zero-offset reflection waveforms. The retrieved P410P and P660P reflection phases clearly reveal lateral variations of both reflectivity and depth of the two discontinuities in the studied region, providing new constraints in addition to existing results from earthquake tomography and receiver function analysis. Besides, this study also sheds light on the strategies to recover deep reflection phases from noise correlations.

[1] Boué, P., Poli, P., Campillo, M., Pedersen, H., Briand, X., & Roux, P., 2013. Teleseismic correlations of ambient seismic noise for deep global imaging of the Earth, Geophys. J. Int., 194(2), 844-848.

[2] Lu, Y., Pedersen, H.A., Stehly, L., and AlpArray Working Group, 2022. Mapping the seismic noise field in Europe: spatio-temporal variations in wavefield composition and noise source contributions, Geophys. J. Int., 228(1), 171-192.

[3] Poli, P., Campillo, M., Pedersen, H., and L. W. Grp, 2012. Body-wave imaging of Earth’s mantle discontinuities from ambient seismic noise, Science, 338(6110), 1063-1065.

How to cite: Lu, Y. and Bokelmann, G.: Mapping the 410-km and 660-km discontinuities across the European Alps using noise correlations , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4747, https://doi.org/10.5194/egusphere-egu22-4747, 2022.

EGU22-9440 | Presentations | SM3.1

Focal spot imaging on USArray records

Christina Tsarsitalidou, Pierre Boué, Gregor Hillers, Bruno Giammarinaro, Laurent Stehly, and Michel Campillo

The spatial zero-lag amplitude distribution of correlations obtained from vertical component dense array records of diffuse seismic wave fields is characterized by a large-amplitude feature around the origin referred to as focal spot. In the context of time-reversed surface waves it can be understood as the collapse of a converging wavefront. The analogy to the SPAC method implies that the nine-component solutions that describe the spectral features can readily be applied to the time-domain focal spot shape to estimate local phase velocity, which connects this method to established elastographic medical imaging. In contrast to sparse SPAC arrays, modern dense arrays allow a properly resolved focal spot at near-field distances for an inversion-free sensor-by-sensor image compilation, with intriguing implications for vertical and lateral resolution enhancement. We demonstrate the applicability of this method on the basis of Rayleigh wave focal spots in the 60 s to 200 s period range that are obtained from ambient field correlations using USArray data between -125 and -90 degrees west. The 1000 s long noise correlations are computed using standard techniques, Gaussian filtered around the central target frequency, and the spatial zero-lag distribution fitted with the SPAC Bessel functions model to distances of 1.2 wavelengths. The effectiveness and accuracy of this approach is demonstrated by the impressive similarity between the obtained “instantaneous image” at 60 s and surface wave tomography results from the literature. The stark velocity contrast between the western and central U.S. is clearly resolved, but the similarity extends to well resolved details including the Sierra Nevada, the Snake River Plain feature, the circular low-velocity rim around the Colorado Plateau, and part of the Mississippi Embayment. Based on this benchmark result obtained with vertical-component data we explore the internal consistency of the obtained maps towards longer periods and the associated extension of dispersion measurements; we probe the limits of the near-field approach by systematically lowering the fitting distance to sub-wavelength scales; and we quantify the similarity of vertical-radial results. The zero-lag amplitude distributions in the wavenumber domain show signatures of near-vertically incident energy associated with global body wave reverberations. We mute this energy by neglecting time windows from the correlation data after global large earthquakes. Systematic tests of the window length, and again the comparison to the benchmark observations, inform about the efficiency of this approach. We conclude that time-domain dense array near-field imaging yields accurate distributions of the velocity structure. We emphasize the disadvantageous low randomization of the long period ambient field, and the sub-array shapes resulting from the rolling USArray deployment. Imaging on smaller scales should therefore work better.

How to cite: Tsarsitalidou, C., Boué, P., Hillers, G., Giammarinaro, B., Stehly, L., and Campillo, M.: Focal spot imaging on USArray records, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9440, https://doi.org/10.5194/egusphere-egu22-9440, 2022.