A New Method For Rapid Computation Of Earthquake Ground Shaking Maps

Strong ground-shaking mapping soon after a moderate-to-large earthquake is crucial to recognize the areas which suffered for largest damages and losses. These maps play a fundamental role for directing first-aid emergency rescues, for loss estimation and the planning of emergency actions. The most critical issue in strong ground-shaking map computation, are the assumed correlation between one or more selected ground motion parameters (e.g., Pga, Pgv, Sa(T)) and damage and reliability of ground motion predictions in areas not covered by the seismic network. We propose a new technique for rapid computation of ground-shaking maps after moderate-to-large earthquakes based on an optimal data gridding. The gridding technique uses a triangulation where recording stations are the vertices of the triangles and ground motion measurements are used to correct predicted data at the barycentres of each triangle. This scheme allows to account for bidimensional characteristics of the ground-shaking with respect to the predictions obtained by using empirical ground motion models which depend only on magnitude and distance. As a consequence, the computed map accounts for earthquake specific features, such as rupture extension, radiation pattern and directivity to which larger part of damages can be correlated. The method is tested off-line on a set of worldwide M > 6.5 earthquakes with different fault characteristics and located in different tectonic environments. The resulting maps, which refer to rock site conditions, are compared with those obtained by using the software ShakeMap®. The comparison is devoted to outline the main differences in the interpolation and gridding schemes adopted by the two techniques and the capability to display some features of the selected earthquake by looking at the ground motion parameters distribution. However, due to the main goal of the ground-shaking maps, more remarkable is the comparison between predicted and observed instrumental intensities field when available.