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Earthquake Analysis

The Earthquake Analysis section covers the analysis and interpretation of recorded waveforms from seisms. Data recorded by the Swiss Seismological Service (SED) and its counterparts elsewhere form the basis for numerous research and service projects. For example, such data are essential for analysing the structure and composition of the Alps and their foothills, characterising fault properties, understanding intrinsic physics causing earthquakes and seismological statistics, improving earthquake predictability or for distinguishing natural from induced earthquakes, including those caused by nuclear explosions.

The Earthquake Analysis section is divided into four research groups that focus on specific domains, but often also study shared topics of interest. The section is headed by Professor Dr. Stefan Wiemer.

The Induced Seismicity group is currently led by Dr. Antonio P. Rinaldi and it primarily researches the monitoring, understanding and assessment of hazards associated with man-made earthquakes. The topic of induced earthquakes is increasingly under discussion around the world, since many different kinds of human activity can trigger earthquakes underground. In Switzerland, induced earthquakes are mainly associated with geothermal power projects. In 2006, the high-pressure injection of water into the subsoil caused an earthquake in Basel with a magnitude of 3.4. In 2013, a magnitude 3.5 earthquake occurred near St. Gallen.

But earthquakes are also triggered when the subsoil is breached for other reasons, such as the injection of CO2 or wastewater, for the conventional and unconventional extraction of crude oil and natural gas through fracking, or in mining and tunneling. Furthermore, man-made alterations to the Earth’s surface can also trigger earthquakes, for instance when reservoirs are filled with water for the first time.

Assisted by local seismic networks, the Induced Seismicity group has monitored numerous earthquake sequences (e.g. St Gallen, Basel, Iceland), sometimes working alongside the Swiss Federal Office of Energy (SFOE) and EnergieSchweiz (see GEOBEST-CH). Working in close collaboration with the Swiss Competence Centre for Energy Research-Supply of Electricity (SCCER-SoE), the group develops methods for estimating and minimising seismic hazards associated with geothermal power plants. In 2015, 2017, and 2019 the group organised an international workshop on induced seismicity for more than 150 participants on Schatzalp mountain in Davos.

The Statistical Seismology group is led by Professor Dr Stefan Wiemer and investigates how statistical methods can serve to enhance our understanding of earthquakes and improve the forecasting of seismic events. The members of this group endeavour to devise and systematically test earthquake prediction models, which attempt to reproduce spatiotemporal seismicity patterns as accurately as possible and use them to forecast seismic activity over the coming days, months or decades. Statistical analyses of earthquake catalogues provide inferences about seismotectonics, such as the origin of magma underneath volcanoes, stress distribution in the Earth's crust, the aftershock sequence decay rate or the spread of liquids in the underground. Another key component of the group's work entails verifying the quality and homogeneity of earthquake catalogues and constantly improving them.

The Laboratory Seismology group is led by Dr Paul Selvadurai and focuses on understanding fundamental questions surrounding physical processes that lead to earthquakes. While many people think an earthquake is the ground shaking they can feel, it is actually a by-product occurring when the subsurface suddenly breaks or ruptures. A rupture event is the earthquake and it is responsible for the felt shaking. The genesis of these events occurs on weaker sections in the Earth known as faults.

As a rupture breaks a fault, it quickly grows larger, sending out «shaking waves» – a behaviour that is controlled by frictional physics. However, friction is not entirely understood and requires careful laboratory experiments that study fundamental questions, such as: How do earthquakes prepare? Why is there suddenly an earthquake? What physics control how big it gets? And when does it stop? To answer these questions, we use state-of-the-art laboratory facilities (Rock Physics and Mechanics Lab and LabQuake) and ETH-developed sensors. With better understanding, we improve our ability to enhance earthquake forecasting of destructive natural earthquakes. Our research also extends to the usefulness and societal acceptance of geo-energy applications such as deep geothermal energy exploitation.

The Seismic Hazard and Risk Research Group aims at cutting edge research and knowledge in the field of earthquake related hazards. Its competence and core activities cover the development of seismic hazard and risk models, probabilistic seismic hazard and risk analysis, building key model components (i.e. earthquake catalogues, active faults, seismogenic source models, earthquake rate forecast, ground motion characteristic models, exposure, vulnerability of built environment, consequence models), uncertainties quantification, technical integration and software development.

This research group is engaged in various national and international research collaborations such as the 2022 Earthquake Risk Model of Switzerland and the European Seismic Hazard and Risk Model (www.sera-eu.org). The group has a strong collaboration with the GEM Foundation Pavia in contributing to the Global Earthquake Model and development of the OpenQuake software. At the regional scale, the research group is actively involved in the development and maintenance of the web-platform of the European Facilities for Earthquake Hazard and Risk (www.efehr.org). The platform provides information about earthquake hazard and risk models in Switzerland (i.e. SuiHaz15), Europe (i.e. ESHM13) and Middle East (i.e. EMME14). For further information of the research group please contact Dr. Laurentiu Danciu.

The Seismic Interferometry & Imaging group is led by Dr. Anne Obermann. The term seismic interferometry refers to the principle of reconstructing seismic responses associated with virtual sources by cross-correlating seismic wavefield records obtained at different receiver locations.

These responses are then used to obtain images of the velocity and scattering distribution of the subsurface. The direct waves are used for static imaging of the velocity structure of the subsurface (3D tomography). However, the sensitivity of the direct wave to small variations of physical properties is often limited. When we want to monitor the dynamic evolution of the subsurface, a large body of work focuses on the reconstructed seismic coda waves. Similar to the coda of earthquakes, these long-lasting tails in the correlograms result from the scattering of the wave energy at the heterogeneities of the Earth. The evolving targets – e.g. magma chambers, fault zones, reservoirs etc. – sometimes generate only tiny perturbations of stress or density of the propagating medium. Such perturbations can be detected in form of phase shifts or waveform changes with the very sensitive seismic coda waves.

Not only the temporal evolution of the changes is of interest, but also their spatial distribution within the medium. Retrieving the spatial distribution of the changes using coda waves is not a straightforward problem given the complexity of the multiply-scattered wave paths. The group developed 3D “probabilistic” sensitivity kernel to model the waveform perturbations induced by the medium changes.

At present, the group is transferring these methods to the scale of underground laboratories.