Simulation of Mw = 6.0 earthquakes in the Upper Rhinegraben using empirical Green functions

Abstract

In low seismicity areas such as southwestern Germany, quantitative statements on strong ground, motion suffer from the lack of instrumental strong motion data although the historic catalogue indicates that events of moment magnitudes up to Mw = 6 are conceivable. This is the situation in the Upper Rhinegraben area were moderate earthquakes with low probability but high impact caused by the significant aggregation of population, infrastructure and industrial facilities are expected to happen. We have developed scenarios of crustal earthquakes with moment magnitudes Mw = 6.0 for a source region southeast of Basel (Switzerland), itself being struck by a strong earthquake in 1356 with an intensity of up to IX (EMS98 intensity). In order to synthesize strong ground motion seismograms, we are using an empirical Green's function (EGF) approach. We utilize records in the frequency range of 0.5-25 Hz of permanent stations in the Rhinegraben and the adjacent Black Forest in southwestern Germany as EGFs. To be consistent with the local seismicity, we model earthquakes with a left-lateral strike slip focal mechanism. The applied EGF approach allows one to define independently a variety of rupture scenarios on the fault plane by varying the hypocentre location, rupture velocity, fault plane geometry, slip distribution and rise time. Therefore, we can create worst-case scenarios for the chosen sites. We compare peak horizontal acceleration (PHA) and response spectra in terms of spectral accelerations and PHAs with attenuation laws proposed for Europe. Our results encourage the application of the EGF approach as a supplementary tool for site-specific strong ground motion prediction in low-seismicity regions such as the Upper Rhinegraben area.