AGU Fall Meeting, San Francisco, USA, 14-18 December, 2009
A. Emolo, V. Convertito, R. De Matteis, M. Caccavale, A. Zollo
The rapid evaluation of strong ground shaking maps after a moderate to large earthquake is crucial to recognize the areas where the largest damages and losses are expected. These maps play a fundamental role for orienting first aid emergency rescues, for loss estimation and the planning of emergency actions. This is particularly important for areas having high seismic risk potential and where dense seismic networks are deployed. We present an upgraded version of GRSmap (Convertito et al., 2009) that consists in a two steps procedure for rapid computation of ground shaking maps after moderate to large earthquakes. Ground shaking maps are first generated by using a point source model and an optimized data gridding scheme accounting for azimuth and distance variations of the strong ground motion field associated with source effects, such as rupture directivity, geometrical spreading, radiation pattern. In order to improve the predictions of the peak ground motion for large earthquakes, in the second stage, the orientation and the extension of the fault rupture are estimated through a rapid inversion procedure of residual peak ground motions (PGA and PGV). A grid-search approach is adopted to constrain the fault direction by using the directivity function for a line source (Ben Menahem, 1961; Boatwright, 2007). Next, the best fit fault dimensions are estimated by minimizing the residuals between observed and predicted PGA and PGV. The obtained surface fault projection is then used in the ground motion predictive equations to estimate peak motion in those areas not covered by the seismic network. The whole procedure has been tested off-line and the results obtained using simulated and observed data from large earthquakes in different seismogenic areas and with different source mechanisms are presented.