New predictive equations and site amplification estimates for the next-generation Swiss ShakeMaps

We present a comprehensive scientific and technical update of the Swiss customization of United States Geological Survey ShakeMap, in use at the Swiss Seismological Service since 2007. The new Swiss ShakeMaps are based on predictive equations for peak ground-motions and response spectra derived from stochastic simulations tailored to Swiss seismicity. Using synthetics allows overcoming the difficulties posed by: (i) the paucity of strong-motion data recordings in Switzerland; (ii) the regional dependence of shear wave energy attenuation and focal depth distribution in the Swiss Alps and foreland; (iii) the depth dependence of stress parameters suggested by macroseismic and instrumental observations. In the new Swiss ShakeMaps, VS, 30 is no longer used as proxy for site amplification at regional scale, and is replaced by macroseismic intensity increments for different soil classes, based on the recently revised earthquake catalogue of Switzerland (ECOS-09). The new implementation converts ground-motion levels into macroseismic intensity by means of ground-motion to intensity conversion equations based on the Italian strong-motion and intensity databanks and is therefore well constrained for intensities larger than VII. The new Swiss ShakeMaps show a satisfactory agreement with the macroseimic fields of both large historical events and recent well-recorded earthquakes of moderate magnitude. The new implementation is now fully consistent with the state-of-the-art in engineering seismology in Switzerland.