Following the seismic microzonation of Basel, the project «Basel Erdbebenvorsorge» was funded by the canton Basel-Stadt. It aimed first at improving the seismic network in Basel and collecting data for the next generation of microzonation studies, and second at proposing earthquake scenarios and risk computations for all cantonal school buildings. This study sets the framework for studies including the whole city, supporting earthquake mitigation and crisis management.

In a first phase, 6 new modern strong-motion stations have been installed, complementing the installations from the SSMNet renewal project. The sites have been characterized through geophysical measurements. In addition, 5 temporary stations have been installed for the period of the project. In a second phase, a new amplification map was developed accounting for all information collected for the completed microzonation study and more recent data. The third phase was the development of a risk framework using the Openquake software. The company Resonance Ingénieurs-Conseils performed the assessment of the capacity curves of the school buildings, that were implemented through fragility curves. A particular focus of the project was put on the uncertainties of the risk-calculation process. Scenarios for typical events of the area were assessed, based on the historical seismicity and the de-aggregation of the regional seismic hazard. The effect of retrofitting of the school-building stock through the ongoing HARMOS project was quantified with a cost-benefit analysis.

The objective of this project is the microzonation of the Bucharest city (Romania).

For a better understanding of the geological structure under Bucharest, non-invasive methods are used, as: wavelet-polarization analysis at each station, H/V for ambient vibrations and earthquakes, and the three-components array analysis of ambient vibration recordings from URS experiment, in order to retrieve the characteristics of surface waves. Surface wave dispersion curves, their ellipticity and the data from boreholes (depth < 100m) are jointly inverted to estimate the velocity structure under the city.

The final 3D structure will be used for the numerical simulation of the seismic waves propagation from the Vrancea intermediate-depth source to the city in order to investigate the seismic hazard in the city.

Data used in this project are from: National Institute of Earth Physics, CRC461-Proiect URS – URban Seismology 2003-2004, BIGSEES ”BrIdging the Gap between Seismology and Earthquake Engineering: from the Seismicity of Romania towards a refined implementation of seismic action EN1998-1 in earthquake resistant design of buildings”

NERA was a project in the Seventh Framework Program (FP7) of the European Commission (EC) that integrated key research infrastructures in Europe to monitor earthquakes and assess their hazard and risk to improve and make a long-term impact on the assessment and the reduction of the vulnerability of constructions and citizens to earthquakes.

Our group was involved in the Work package JRA1, Waveform modelling and site coefficients for basin response and topography, and Workpackage NA5, Networking near-fault observatories.

The key objective of JRA1 was to establish some scientifically solid and practically acceptable propositions to incorporate basin and surface topography effects in seismic design (building codes, microzonation studies, critical facilities). We contributed with a systematic study of the topographic site effects with emphasis on reasonable characterization of the both topographic site structures and observed effects on ground motion. We gathered available earthquake and ambient vibration recordings from sites with pronounced topography (Europe, Japan) and performed joint analysis with digital elevation models.

The results and final recommendations have been published in a report. These conclusions contribute to the ongoing (light) revision of EC8.

The objective of NA5 was to collaborate in sharing of technological and scientific experience and know-how between the near-fault observatories. We shared our experience with the installation (including data gathering and data archiving) of various instruments in the Valais region. This workpackage represented an infrastructural support for workpackage 2 of the project REAKT.

COGEAR was an interdisciplinary natural hazards project investigating the hazard chain induced by earthquakes. It addressed tectonic processes and the related variability of seismicity in space and time, earthquake forecasting and short-term precursors, and strong ground motion as a result of source and complex path effects.

We studied non-linear wave propagation phenomena, liquefaction and triggering of landslides in soils and rocks, as well as earthquake-induced snow avalanches. The Valais, and in particular parts of the Rhone, Visper and Matter valleys have been selected as study areas. Tasks included detailed field investigations, development and application of numerical modelling techniques, assessment of the susceptibility to seismically induced effects and installation of different monitoring systems to test and validate our models. These systems are for long-term operation and include a continuous GPS and seismic networks, a test installation for observing earthquake precursors, and a system to study site-effects and non-linear phenomena in two test areas (Visp, St. Niklaus-Randa). Risk-related aspects of impacts on buildings and lifelines were also considered.

COGEAR was supported by the Competence Center for Environment and Sustainability (CCES) of ETH Zurich.

For the city of Basel, a qualitative microzonation was performed in 1997. The zonation was mainly based mainly on the properties of the quaternary sediments. This triggered a study that provided a quantitative assessment of ground motion amplification in order to determine which levels of amplifications have to be taken into account a site-specific hazard assessment in the Basel area. It is the result of two large projects, the ETH project “Earthquake scenarios for Switzerland” (1997-2002) and the INTERREG project “Seismic Microzonation in the upper Rhine Graben area” (2003-2006) (Fäh end Huggenberger, 2006). Earthquakes in the Basel region triggered the strong motion network in Basel and provided a data set for comparison. Spectral ratios from recordings confirm the results of the microzonation study. Finally uniform hazard spectra were derived for each zone by combining the hazard on rock with the amplification functions. The microzonation is published on the Internet:

Basel Landschaft: http://geoview.bl.ch

Basel Stadt: www.geo.bs.ch/erdbebenmikrozonierung

The study of small earthquakes related to glacier flow, so-called icequakes, can reveal important insights into the dynamics and hydraulics of glaciers. Icequakes near the glacier bed are particularly interesting, because they may be a manifestation of microseismic stick-slip sliding. This phenomenon is not fully understood and has yet to be captured in ice flow models. At the same time, basal seismicity can be a manifestation of hydraulic fracturing as melt water opens up new water channels within and beneath the glacier, a process, which is analogous to the hydraulic stimulation within geothermal reservoirs.

This project focuses on the occurrence of sliding-related stick-slip icequakes beneath Aletschgletscher. Whereas these events have been confirmed beneath the polar ice sheets (e.g. Smith et al., 2015; Roeoesli et al., 2016), it is to date not clear if they also exist beneath relatively flat Alpine glaciers. To this end, the SED conducted a two-step seismometer deployment on the glacier tongue. In a first step, three shallow borehole seismometers were installed and maintained for 1.5 years (January 2015-July 2016). These data identified an icequake cluster at the glacier bed, which was monitored in near-real time with the help of state-of-the-art real-time data communication. In June 2016, an additional network with six seismometers was installed above the cluster to confirm that the recorded icequakes are indeed stick-slip events and to provide better hypocenter locations.

The seismic Aletschgletscher record is unique in that it contains stick-slip icequakes recorded at an unrivaled quality over more than a year. This will provide an unprecedented look at seismogenic stick-slip sliding and its changes over the course of a full year. As a result of harsh weather conditions in high-melt areas, on-ice seismometer installations are extremely difficult on Alpine glaciers. Consequently, the Aletschgletscher data set offers a first-of-its-kind view on how stick-slip seismicity changes as the glacier reacts to climatic changes.

Our project is embedded in cross-disciplinary collaborative research between the Glaciology division at the Laboratory of Hydraulics, Hydrology, and Glaciology (VAW) at ETH Zurich and the Exploration and Environmental Geophysics group at the Institute of Geophysics at ETH Zurich. In the past, these groups have collected milestone records in the field of glacier seismology (Podolskiy and Walter, 2016). The joint interpretation of the Aletschgletscher data will help to improve our understanding of glacier flow and its reaction to climate change and glacier retreat, also affecting the Swiss Alps.

The SED participated in building a state-of-the art seismic network in the Arctic. We built and now continue to operate 3 stations in the new international broadband seismic capability for Greenland, the GreenLand Ice Sheet monitoring Network (GLISN). This real-time sensor array enhances and upgrades performance of the very limited pre-existing Greenland seismic infrastructure for detecting and characterizing glacial earthquakes and other phenomena emitting seismic waves. The Greenland Ice Sheet is changing, and seismology has the means to “hear” and measure these changes. Continuous, long-term monitoring of the dynamics of the Greenland Ice Sheet and its relationship to global climate change is a fundamental observational enterprise which requires multi-sensing techniques. The development of GLISN brings the seismology component into focus for monitoring Greenland’s Ice Sheet.

Glacial earthquakes have been observed along the edges of Greenland with strong seasonality and increasing frequency since 2002 by continuously monitoring data from the Global Seismographic Network (GSN). These glacial earthquakes in the magnitude range 4.6-5.1 may be modeled as a large glacial ice mass sliding downhill several meters (e.g. 10 km3 by 10 m) on its basal surface over a duration of 30 to 60 seconds. Although the mechanics of sudden sliding motions at the glacial base are not known, seasonal and temporal patterns are consistent with a dynamic response to climate warming driven by an increase in surface melting and supply of meltwater to the glacial base, and suggest that the glacial earthquakes may serve as a marker of ice-sheet response to external forcing.

Before GLISN, the detection and characterization of smaller glacial earthquakes was limited by the propagation distance to globally distributed seismic stations. Now, glacial earthquakes can be identified only using the more than 30 GLISN seismic stations within and surrounding Greenland. Because of the long durations of sliding, these glacial earthquakes do not appear in standard earthquake catalogs, and are best detected by broadband seismometers, which accurately measure both fast (< second) and slow (> 100sec) vibrations. Such seismic monitoring of the Greenland Ice Sheet via glacial earthquakes will complement both surficial GPS monitoring and remote sensing from satellites, by providing sensitivity to the dynamics of the glaciers at basal depths. In addition, real-time detection of glacial earthquakes permits rapid response and focusing of other sensing techniques to the dynamic region of the Ice Sheet.

All the data from the GLISN is openly available to anyone in real-time, without restriction.

Chile has been struck by a number of very large earthquakes (magnitude 7.5 or greater) and tsunamis in the past. There is a clear need for building a system to provide rapid situational awareness, as well as earthquake and tsunami early warning. Since scientific instruments are expensive, we are exploring the use of dense networks of seismic and geodetic low-cost sensors. The Earthquake Science Center oft he U.S. Geological Survey (USGS) has recently started to deploy a prototype network of dedicated smartphone units along the Chilean coast (Brooks et al., 2016). Each sensor box contains a smartphone with integrated MEMS accelerometer, and an external consumer-quality GPS chip and antenna to determine real-time positioning data. The total cost of each box is on the order of a few hundred dollars, nearly two orders of magnitude lower than scientific-grade installations. A first subset of 9 smartphone-boxes has been installed in November 2015; another set of 200 units will be deployed by the end of 2016.

We will invert seismic and geodetic real-time data from the smartphone units to obtain finite-fault models of large earthquakes by joint application of the seismic FinDer algorithm developed at the Swiss Seismological Service (SED) (Böse et al., 2012, 2015) and the geodetic BEFORES algorithm developed by Minson et al. (2014).

The SED collaborates in this project closely with partners at the USGS, the University of Chile, Chilean National Seismological Center, University of Houston, and GISMatters Inc.

The objective of the ShakeAlert project is to implement a prototype Earthquake Early Warning (EEW) system for California and the pacific northwest of the United States. The system is currently sending warnings of imminent strong ground shaking to a selected group of test users. The project comprises algorithm development, EEW system design and implementation, and public outreach. The SED was involved in Phase I – III of the project, implementing and testing the Virtual Seismologist (VS) [Cua and Heaton, 2009], a Bayesian approach to EEW. In Phase III, the SED team also began to contribute to the development and implementation of FinDer, the first finite fault algorithm to be included in the prototype system. Currently about 300 scientists and engineers and several project partners from the public and private sector receive alerts from the ShakeAlert EEW system. The ShakeAlert project continues without formal ETH participation, though VS and FinDer continue to be core components in the development system.

The general objective of this EC-FP7 funded joint project was to improve the efficiency of real time earthquake risk mitigation methods and its capability of protecting structures, infrastructures and people. REAKT aimed at establishing the best practice on how to use jointly all the information coming from earthquake forecast, early warning and real time vulnerability assessment. All this information needs to be combined in a fully probabilistic framework, including realistic uncertainties estimations, to be used for decision making in real time.

REAKT used a system-level earthquake science approach that required that the various temporal scales of relevance for hazard and risk mitigation in the various WPs are integrated through common tools, databases and methods. 

Our group was involved in the Work Package 2: Physics of short term seismic changes and its use for large earthquakes predictability. The key objective was to improve short-term forecasting of large earthquakes through the monitoring of the seismic and strain activity within specific fault systems. We contributed with the monitoring system, which has been installed in the Valais region including dense seismic network, GPS, geochemical and geomagnetic sensors. Special attention was paid to the analysis of seismic swarms.

The Eastern, "straight" part of the Alps is home to a number of open questions. The most widespreadly known question is about lithospheric slab hanging beneath the Eastern Alps. Is it Adriatic (Lippitsch et al. 2003)? Is it European (Mitterbauer et al. 2011)? What is its extent and the related velocity anomaly?

Beyond carrying out tomographic calculations, one can also characterize the fabric of the lower crust with receiver functions. In the India-Asia collision zone this has helped to point out that the main lithosphere boundary is located at a very different place than the surface boundary of deformation. Anisotropic receiver function calculations are therefore one of the first tools to be applied on EASI data, with the main question of determining the role of the lower crust in shaping the orogen.

A recent Moho map compilation reveals another interesting features beneath the Eastern Alps and between the Europe and Adria plates: a Moho "gap" or "hole" (Spada et al. 2013). Near 47°N latitude and between 12° and 15.5°E longitude the crust-mantle boundary is not defined, or at least it does not appear as a sharp discontinuity. Mapping the extent of this hole, and characterizing the velocity gradient from crustal to mantle conditions is an interesting goal to tackle.

The relationship of the Alpine orogen to the adjacent foreland basin and the lithospheric blocks of the Bohemian Massif, with their own characteristic seismic signatures, is a structural target of EASI.

Our research methods include tomography, ambient noise analysis and receiver functions, with anisotropy included in all three types of investigations. The depth range of investigations encompasses the crust and the mantle lithosphere, down to the LAB.

Bhutan, a kingdom in the Eastern Himalayas, is living in self-imposed isolation: in order to preserve local culture, traditions and the environment, foreigners can enter in groups and in limited number only. Consequently, our geoscientific knowledge is very limited compared to other parts of the orogen. The first geological map was compiled in 1983 by the famous Swiss geologist Augusto Gansser. From a geophysical perspective, Bhutan is almost a blank spot: only very limited information exists on seismicity which shows a lower level of earthquake activity compared to other parts of the Himalayas; there is knowledge neither of the structure nor of the physical properties of the crust and the lithosphere. Illuminating the deep structure of Bhutan and comparing it with the much better known Central Himalayas of Nepal is highly relevant both for evaluating the earthquake hazard and for improving our geodynamic picture of the orogen.

We conducted a temporary seismic experiment in Bhutan. Two densely spaced profiles across the orogen allow us to produce the first images of the structure of the lithosphere in the Eastern Himalayas, as well as give an insight into lateral variations along the mountain belt. Our network provides reliable information on seismicity in Bhutan and establishes the first seismic velocity model of the crust. Furthermore, we will apply ambient noise tomography to map the physical properties of the lithosphere. The results will be interpreted jointly with gravity data to build physical models of the Eastern Himalayas as well as to draw conclusions on its geodynamics. Especially, seismotectonic studies that we plan to conduct by comparing different segments of the Himalayas may shed light on the origin of the apparent seismic gap in Bhutan.

Augusto Gansser, "Geology Father of the Himalayas" and first geological mapmaker of Bhutan, has passed away earlier this year (2012), at the age of 101. We would like to dedicate this experiment to his memory.

Outreach

• Article on the project results in Kuensel, Bhutan's most read newspaper: part I, part II (2015.05.09. and 16.)
• Interview in ETH Life [en] [de] (2013.02.12.)
• Article in the Newsletter of the Society Switzerland-Bhutan (2013.06.)

GEOTHERM-2 conducts cross-disciplinary research towards the development of Enhanced Geothermal Systems (EGS). EGS is a technology that will allow the heat resources residing at several kilometers depths to be exploited for electricity and heat production. At present, EGS technology is not mature; two of the key challenges are the difficulty of (1) engineering a lasting heat exchanger with appropriate properties within deep, hot, low-porosity rocks, and (2) the risk of inducing felt and potentially hazardous seismic events during the development and operation of the heat exchanger.

GEOTHERM-2 continues the work initiate in the GEOTHERM-1 project (2009-2012). The project was conceived in order to provide a bridge to a major nationwide project in geothermal energy, the Swiss Competence Center Energy Research-Supply of Energy (SCCER-SoE), that was in its planning phase when GEOTHERM-2 was proposed, and has begun in the meantime.

In total thirty eight co-workers from various Departments and Institutes in ETH and in EPFL, and of the Paul Scherrer Institute contribute to the project.

The main strength of GEOTHERM-2 is to adopt a cross-disciplinary approach to the challenges mentioned above. The contributions of GEOTHERM-2 in terms of scientific results, capacity building and knowledge transfer are a therefore critical intermediate step towards successful future Pilot and Demonstration projects, and complement the activities conducted in SCCER-SoE.

The research activities in GEOTHERM-2 are organized in six Modules or work packages, which are designed to:

• Develop and test novel observational tools for the geomechanics of reservoir creation;
• Assess and mitigate the risks associated with noticeable induced seismicity;
• Assess potential accidental risks leading to health and environmental impacts as well as public perceptions of risks associated with geothermal energy development;
• Expand a multi-scale – multi-process modeling code for simulating the process of reservoir generation as well as the longer-term evolution of the reservoir during production;
• Investigate the effects of chemical reaction between fluid and rock on long-term permeability evolution and heat extraction from the reservoir;
• Design a decision-support tool for optimizing the use of geothermal energy in cities, by quantifying all interacting factors including geological and economic parameters, conversion efficiency and temporal heat storage, complementary energy sources and societal acceptance.

To a large part, the seismicity of Switzerland is characterized by swarm-like earthquake sequences of natural, and to a minor extent of man-made origin. Many of these sequences have been studied using relative location techniques, which often allowed to constrain the active fault plane of the larger events in a sequence and shed light on the tectonic processes that drive the seismicity. Yet, in the majority of cases the number of located earthquakes was too small to infer the details of the space-time evolution of the sequences, and their statistical parameters (e.g. magnitude-frequency distribution, Omori parameters). Therefore, it has been largely impossible to resolve clear patterns in the seismicity of individual earthquake sequences that are needed to improve our understanding of the mechanisms behind, and the differences between natural and induced earthquake sequences.

In this project we aim to significantly improve the completeness of detected and located earthquakes in the Swiss catalog. We plan to develop techniques that take advantage of the waveform similarity in natural and induced earthquake sequences to detect seismic events several orders of magnitude below the detection threshold of classical signal energy based detectors. Waveform similarity will than further be exploited to derive accurate and consistent magnitudes and locations for even the smallest events of the sequences.

Building on the data from this analysis we plan to study the processes and physics behind natural and induced microseismicity, e.g.:

• understanding why natural earthquakes occur in swarm-like sequences
• identifying triggering mechanisms of natural and induced earthquake sequences
• understanding the differences and similarities of natural and induced earthquake sequences
• detect and study repeated earthquakes

The processes and conditions underpinning induced seismicity associated with deep geothermal operations are still not sufficiently well understood to make useful predictions as to the likely seismic response to reservoir development and exploitation. The empirical data include only a handful of well-monitored EGS experiments; models are consequently poorly constrained. Unfortunately, datasets of well-monitored deep hydrothermal experiments are missing and empirical constraints of induced seismicity models for these cases do not exist. Given that the majority of the projects underway or planned in Europe are of the hydrothermal type, there is hope that this deficit can be remedied in the near future through a close cooperation of geothermal industry, science and public authorities.

This is where the GeoBest project comes to play. By supporting selected pilot project for a limited time, SED facilitates the dialog with geothermal industry. Besides of the unique opportunity to collect high quality seismic data and being able to access relevant project data, gaining first hand practical experience in this field is of paramour importance for the development of significant best practice guidlines.

In cooperation with the National Cooperative for the Disposal of Radioactive Waste (Nagra), the Swiss Seismological Service has recently completed the installation of ten new seismological observation stations, three of them including a co-located borehole sensor. The ultimate goal of the project is to densify the existing Swiss Digital Seismic Network (SDSNet) in Northern Switzerland, in order to increase the sensitivity to very-low magnitude events and to improve the accuracy of future location solutions. This is strategic for unbiased monitoring of micro-seismicity at the places of proposed nuclear waste repositories.

At each site, to further improve the quality and usability of the recordings, a full seismic characterization of the area surrounding the installation area was performed. The investigation consisted of a preliminary geological and geotechnical study, followed by an accurate seismic site response analysis by means of state-of-art geophysical techniques. For the borehole stations, in particular, the characterization was performed by combining different types of active seismic methods (refraction tomography, surface wave analysis, Vertical Seismic Profiling, VSP) with ambient vibration based approaches (wavelet decomposition, H/V spectral ratio, polarization analysis, three component f-k analysis).

Results converged to the definition a unique summary velocity profile for the site, later used for the computation of the analytical SH-wave amplification function

Hydrocarbon-bearing geological structures might cause characteristic modifications of the ambient vibration background noise. This question is addressed in a project supported by the Commission for Technology and Innovation (CTI) together with the company SpectraSeis. The link between observations and geological structure can only be made by understanding the wavefield that is recorded. This requires the simultaneous recording and analysis of ambient vibration wave-fields on arrays. Such methods have been developed in the past, and they have been applied to study soft-sediment surface deposits for seismic hazard analysis.

The analysis of all three components of ground motion is addressed. Analysis of such recordings targets to distinguish between standing waves (global resonances) and propagating surface waves (Love- and Rayleigh-waves) as well as body waves (SH and PSV). By adapting array configurations during the measurements in the field, the identification of the wave-types with the corresponding propagation velocity and direction is optimized and allows to determine the source region of the waves and their possible origin. From the wave characteristics, structural information can be inverted that allows to improve structural models. The development of a real-time system for array measurements is part of the project.

The project includes the work of two PhD candidates, addressing practical problems related to source characterization (Falko Bethmann) and site-effect assessment (Valerio Poggi). In the first part of this PhD project, scaling relations between small and large earthquakes are developed and the potential impact of such relations on estimating maximum near-fault ground motions is studied. In the second part of the project, new techniques for site characterization and site response analysis are implemented. First, a new method to analyze three component array recordings of ambient vibration is developed that allows retrieving the ellipticity functions of the different Rayleigh-wave modes. Subsequently, a procedure to combine passive (ambient vibration) and active-source techniques is proposed, with the goal to improve resolution of array measurements on shallow layers from high frequency component of the wave-field. Finally, generic amplification functions are developed for a common reference condition in Switzerland that serve as input for site-specific seismic hazard assessment.