Seismic Hazard Assessment of Switzerland, 2004

We present the results of a new generation of probabilistic seismic hazard assessment for Switzerland. This study replaces the previous intensity based generation of hazard maps of 1978. It is the first to systematically consider aleatoric and epistemic uncertainties and compute spectral hazard. Based on a revised moment-magnitude earthquake catalog for Switzerland and the surrounding regions, covering the period 1300–2003, sets of recurrence parameters ( a- and b -value, M max ) are estimated. Information an active faulting in Switzerland is too sparse to be used as source zones. We develop instead two models of areal sources. The first oriented more towards capturing historical and instrumental seismicity, the second guided largely by tectonic principles and expressing the alterative view that seismicity is less stationary and thus future activity may occur in previously quiet regions. We derive two distinct models of catalog completeness, in order to express the considerable uncertainty in rates stemming from the uncertainty in completeness. To estimate three alternative a - and b -value sets and their relative weighting, we introduce a novel approach based on the modified Akaike Information Criterion, which allows us to decide when the data in a zone deserves to be fitted with a zone-specific b -value. From these input parameters, we simulate synthetic earthquake catalogs of 1 million year duration down to magnitude 4.0, which also reflect the difference in depth distribution between the Alpine Foreland and the Alps. Using a new predictive spectral ground-motion attenuation and scaling model for Switzerland, we estimate expected ground-motions in units of the 5% damped acceleration response spectrum at frequencies of 0.5–10 Hz for all of Switzerland, referenced to rock sites with an estimated shear wave velocity of 1500 m/s 2 in the upper 30m. We present hazard curves and uniform hazard spectra for selected cities in Switzerland as well as hazard maps for return periods of 100, 475, 2500 and 10’000 years. Full results are available on the Internet (www.seismo.ethz.ch). The highest hazard is found in the Wallis, in the Basel region, in Graubünden and along the alpine front, with maximum ground accelerations at 5 Hz frequency reaching 150 cm/s 2 for a return period of 475 years, and 720 cm/s 2 for 10’000 years. identifying deformation structures; the development of calibration functions to map the seismic shaking with distance and magnitude on the basis of deformation structures recognized in lake sediments; the identification of the causative fault of the 1356, I o =IX Basel earthquake—the largest historical event in central-northern Europe; a multi-disciplinary approach combining an array of geological, geomorphological and geophysical techniques to the characterization of the surface expression of major seismogenic faults; the first comprehensive reconstruction of the complete sedimentation history of a large lake with the purpose of locating and characterizing all subaqueous slumping events; the development of innovative tools to map, date and characterize the fine structure of lacustrine sediments associated to subaqueous sliding; the characterization of the fine structure and deposition characteristics of subaqueous slumps; the definition of rigorous criteria to classify triggering mechanisms for subaqueous slumpings; the study of earthquake-triggered rockfalls and landslides; the investigation of secondary and tertiary hazards by modelling tsunami waves generated by the slumping triggered by earthquakes; the first joint investigation of historical and prehistorical earthquakes, integrating different paleoseismological techniques and results to identify and date prehistorical seismic events. results change understanding how