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Volume 17th Swiss Geoscience Meeting Fribourg, 22nd + 23rd November 2019

This report illustrates the data collection, processing and elaborations carried out in the framework of strategy 1 (“An updated classification of empirical amplification functions”) of the project “Development of site-specific elastic design spectra for future building codes”. This strategy aims at reconstructing a set of site-specific uniform hazard spectra (UHS), based on seismic hazard inputs representative of the Swiss hazard scenario and comprehensive of local amplification effects. We consider site amplification for a variety of subsurface soil configurations. These site-specific UHSs are sorted according to the characteristics of the corresponding subsoil, and collated with the elastic design spectra from the present building codes. The input empirical data set is constituted by the recordings of the Japanese KiK-net strong motion network, including approximately 700 sites, each instrumented with a downhole reference seismometer (generally encased within the seismic bedrock) coupled with a receiver placed at the soil surface. This instrumental configuration is ideal for the study of site amplification phenomena. Earthquake waveforms from KiK-net stations were processed to derive Fourier amplification functions at each site of the network; these functions are then referred to a common seismic bedrock condition (the same as in the Swiss hazard maps) and finally translated to the response spectral domain, so to express the site amplification in terms of spectral acceleration. In this process, the relevance of non- linear soil behavior is also discussed. At the last processing step, the empirically derived response spectral amplification functions are finally superimposed to seismic hazard inputs characteristic for the Swiss hazard scenario, yielding site-specific UHSs, which are compared with elastic design spectra from the present building code. The obtained results have evidenced the need for an improved site-condition classification and changes in the definition of normative spectra that would take into consideration site-amplification effects, in particular resonances. Conservative and simplified solutions are proposed for the case when only indirect or poor information is available for the considered site; vice versa, in case of well-constrained site characterization, a more specific and complex approach should be preferred. --> This report illustrates the data collection, processing and elaborations carried out in the framework ofstrategy 1 (“An updated classification of empirical amplification functions”) of the project“Development of site-specific elastic design spectra for future building codes”.This strategy aims at reconstructing a set of site-specific uniform hazard spectra (UHS), based on seismichazard inputs representative of the Swiss hazard scenario and comprehensive of local amplificationeffects. We consider site amplification for a variety of subsurface soil configurations. These site-specificUHSs are sorted according to the characteristics of the corresponding subsoil, and collated with theelastic design spectra from the present building codes.The input empirical data set is constituted by the recordings of the Japanese KiK-net strong motionnetwork, including approximately 700 sites, each instrumented with a downhole reference seismometer(generally encased within the seismic bedrock) coupled with a receiver placed at the soil surface. Thisinstrumental configuration is ideal for the study of site amplification phenomena.Earthquake waveforms from KiK-net stations were processed to derive Fourier amplification functionsat each site of the network; these functions are then referred to a common seismic bedrock condition(the same as in the Swiss hazard maps) and finally translated to the response spectral domain, so toexpress the site amplification in terms of spectral acceleration. In this process, the relevance of non-linear soil behavior is also discussed.At the last processing step, the empirically derived response spectral amplification functions are finallysuperimposed to seismic hazard inputs characteristic for the Swiss hazard scenario, yielding site-specificUHSs, which are compared with elastic design spectra from the present building code.The obtained results have evidenced the need for an improved site-condition classification and changesin the definition of normative spectra that would take into consideration site-amplification effects, inparticular resonances. Conservative and simplified solutions are proposed for the case when onlyindirect or poor information is available for the considered site; vice versa, in case of well-constrainedsite characterization, a more specific and complex approach should be preferred., Technical Report

During 2014, 817 earthquakes and 180 quarry blasts were detected and located in the region under consideration. An additional 160 earthquakes with ML ≤ 1.0 were located using supplementary analysis techniques. The number of located earthquakes in 2014 was the largest since the installation of a seismic network in Switzerland in 1975. This unusually large number is mainly due to the occurrence of two vigorous earthquake sequences, and the local reduction of the earthquake detection thresholds of the Swiss seismic network. With a total of 22 earthquakes of ML ≥ 2.5, the seismic activity of larger and potentially felt events was close to the average of 23 earthquakes over the previous 39 years. The most noteworthy seismicity was the earthquake sequence near Diemtigen, west of Lake Thun, where more than 270 events were located between April and December. High-precision hypocenter relocation was applied to image the spatio-temporal evolution of this seismicity. The sequence culminated in an M L 3.2 event in October, which was felt in the region of Lake Thun and Bern. Other cases of earthquakes felt by the public include earthquakes in the region of Biel (ML 3.2), in Vallorcine (ML 3.2), and in Stalden (ML 3.0). Finally, a small but unusually deep earthquake was recorded beneath the Jura Mountains. Focal depth, apparent velocities, as well as waveform characteristics of this earthquake are consistent with a source in the uppermost mantle. This earthquake is the first reliable record of a sub-Moho event ever observed in Switzerland., Swiss Journal of Geosciences, 108 (2-3), ISSN:1661-8734, ISSN:1661-8726

Single-station sigma values for more than 600 stations have been computed using the same method for all records and datasets from different tectonic regions (California, Taiwan, Japan, Turkey, Mexico, Switzerland and France). This work has been driven by the need to develop better estimates of standard deviation for non-ergodic probabilistic seismic hazard assessment in Switzerland (PEGASOS Refinement Project), and for new ground motion models being developed for eastern North America (NGA-east) and western North America (NGA-west2). The results show that the average single-station standard deviations are lower than the ergodic values of standard deviation. Moreover, the single-station withinevent standard deviations appear to have little variability across different tectonic regions. However, there is significant variability between stations and, in some instances, values of single-station standard deviation are higher than their ergodic counterpart. This variability seems to be (on the first order) controlled by path effects, and it can be modelled by probability distribution functions. Our results also show that the Vs30 dependency is weak, while a reduction of the withinevent standard deviation is apparent with increasing distance (and magnitude). We finally amalgamate all within-event residuals from the different tectonic regions in order to propose and test several within-event single-station sigma models (constant, distance-dependent, distance and magnitude-dependent).