EGU General Assembly 2023  

It will probably come as no surprise to any geologist that earthquakes and tectonic faults are highly variable and complex phenomena. Active (and inactive) faults rarely occur in isolation and have variable geometries, kinematics, and slip rates. This fact, coupled with fault interaction, means that earthquakes are variably distributed in time and space over tectonically active regions. These complexities contribute to some of the challenges associated with probabilistic seismic hazard assessment. In this talk, I will mostly focus on the insights we can gain about normal faulting and earthquake behaviour from the central Apennines of Italy, and how our results can be used to inform potential variability and therefore uncertainties in other tectonically active regions.

Where there are good historical records of earthquakes available, interactions between individual earthquakes and/or faults can be studied by modelling Coulomb stress transfer and calculating how stress accumulates over time. Our results from modelling the ~700 year historical sequence in central Italy supports the hypothesis that past earthquakes affect the location of subsequent events, though the models are not enough to fully hindcast the historical record of damaging events. Furthermore, these models also indicate that variations in the geometry of individual faults and the regional fault network may affect earthquake occurrence.

The geometric complexity of normal faults is evident both via surface observations of faults scarps and from sub-surface techniques such as seismic reflection. Observations from normal faults in the central Italian Apennines indicates that the geometry of normal faults may affect the magnitude and patterns of both short-term (coseismic) and long-term (15 kyr) slip and throw. These geometric variations may also control the propagation and/or termination of earthquakes, as evident from recent earthquakes both in Italy and globally. Extending our observations into the sub-surface using seismic reflection datasets of both active and inactive faults gives us further insights into how fault geometry and slip rates evolve over much longer (million year) time scales than is possible from field studies alone.

These observations of variability are giving us insights into some of the physical mechanisms controlling fault behaviour over a range of timescales and earthquake occurrence. Knowing the variability helps us to understand the uncertainties of inputs into seismic hazard assessment and can also help us to think about other possible approaches to seismic hazard, such as time-dependent hazard.

How to cite: Mildon, Z.: Variability of earthquakes, faults, and the resulting seismic hazard, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17059, https://doi.org/10.5194/egusphere-egu23-17059, 2023.

Economies are critically dependent on the secure provision of raw materials. The EU commission currently lists 30 elements as critical, including base metals as well as high-tech metals. Projections indicate a significant increase in demand within the next decades, in parts due to the transformation of the energy sector and the digital revolution. Therefore, reuse of raw materials in the context of circular economies must be accompanied by the development of additional primary resources. Furthermore, to minimize dependencies from individual producing countries, the supply chains must be diversified, including the exploitation of domestic resources. Consequently, exploration activities - of which geophysics is a critical component - must be intensified today to increase the reserves for tomorrow.

New deposits are likely to be found under cover and at depths greater than has typically been exploited in the past. Both greenfield and brownfield environments, such as historic mining districts, have a potential for new discoveries. Recent developments in airborne geophysics aim at increasing the exploration depth and improving the imaging capabilities to detect targets that have previously remained hidden. In this lecture, I will discuss the challenges for airborne geophysical exploration, with a particular focus on semi-airborne electromagnetics, a hybrid approach that combines the benefits of powerful land-based transmitter deployments with the dense spatial coverage of overflights with passive airborne receivers. This concept has been implemented in the ongoing DESMEX project and has also received interest elsewhere. The hybrid approach can be shown to exhibit significantly increased penetration depth than classical airborne EM systems. Moreover, without the need to tow heavy transmitters airborne, the concept can be ideally transferred to unmanned platforms, reducing the costs significantly. Finally, three-dimensional inverse modelling becomes tractable with this setup; this is because the number of involved simulation steps per iteration scales with the number of transmitter installations (typically less than ten) instead of the number of measurement points with fixed transmitter-receiver geometries as in classical airborne measurements (typically several thousand). I will present case studies from demonstration measurements in Europe and beyond.

How to cite: Becken, M.: Resources for tomorrow – how airborne geophysics can contribute for the exploration of deep mineral deposits, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8765, https://doi.org/10.5194/egusphere-egu23-8765, 2023.