On the simulations of broad-band strong ground motions using a "k -2" kinematic source model: Applications to moderate earthquakes.

Baumont, D. (1), C. Berge-Thierry (1), P. Bernard (2), and A. Herrero (3) 12th symposium on earthquake engineering - Roorkee India - 16-18 décembre 2002

Simulating realistic near-source ground motion is of primary importance for assessing seismic hazard in the vicinity of the fault, however, it is a difficult task as it requires achieving calculations in a very broadband frequency range. Herrero et al. [1994] developed a kinematic source model based on "k-2" slip distribution to simulate in the far field approximation, "w2" accelerograms at frequencies up to few tens of Hz. Due to their working hypothesis of an instantaneous slipping, the apparent directivity was not modelled as Cd but as Cd2. Bernard et al. [1996], by considering a propagating pulse associated to a k-dependent source function, succeeded in modeling correctly the Cd directivity. A further evolution [Berge et al., 1999] includes a complete Green's function computation using the discrete wavenumber method [Bouchon and Aki, 1977] coupled to the reflection coefficient propagator technique [Kenett and Kerry, 1979]. Such approach being very time consuming, only few Green's functions are computed on the discretized fault, the others being interpolated. An alternative approach we envisaged in the future is to consider Empirical Green Functions. Within the framework of the European PRESAP project (Practical, Real-time Estimation of Spatial Aftershock Probabilities), we are presenting the results of the strong ground motion simulations for two moderate magnitude earthquakes : the 1999 Athens earthquake (Mw=5.9) and the 1997 Colfiorito earthquake (Mw=6.0). (1) Institut de Radioprotection et de Sûreté Nucléaire, Fontenay-Aux-Roses, France (2) Institut de Physique du Globe, Paris, France (3) Istituto Nazionale di Geofisica e Vulcanologia, Roma, Italy