The Renewal Project of the Swiss Strong Motion Network (Ssmnet)

Abstract eng:
In an ongoing project, the Swiss Seismological Service (SED) is renewing and expanding its strong motion network. The goals of this enlargement are a better spatial coverage of recordings from earthquake-prone regions, a better assessment of ground motion variability and site effects, and ultimately the verification and improvement of seismic hazard models. During the first phase of the project, 30 new stations have been installed between 2009 and 2013, both replacing existing dial-up strong motion stations and installing new stations. In the framework of the ongoing second phase of the project, 70 more stations are planned to be installed by 2019. All stations of the new network are free-field and the majority are installed in densely populated urban areas of high seismic risk, though a few are located in more rural areas where significant earthquakes happened in the past. The process of the station installation takes several steps. Once a suitable target (usually a town) is identified, a first overview of the expected local site effects is obtained by performing an H/V survey and analyzing geological information. Suitable important public buildings like hospitals, schools or fire departments, which could house a free-field station in the vicinity, are then searched for. In these places, test stations are installed for several days in order to evaluate the local noise level. Using all available information, the final station location is selected. After the installation of the station, the site is characterized using passive and active seismic methods. Using one or several passive seismic arrays of variable sizes, we measure the Love and Rayleigh wave dispersion curves as well as the Rayleigh wave ellipticity curves using different analysis methods. In some locations with difficult site conditions, we also perform active measurements using MASW. All results from the measurements are combined to determine by inversion the shear-wave velocity profile underneath the strong motion station. Using this sub-surface profile, the amplification of the structure can be calculated and compared to the observed empirical amplification, identifying particular site-specific phenomena such as edge-generated surface waves or resonances. CPT measurements are scheduled for sites where non-linear site response and liquefaction are expected during strong ground shaking. We will present the status of the ongoing station installation, show results of the station characterization measurements, and relate them to observed ground motion.

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