Synthetic isoseismals of two Californian earthquakes

Abstract

Comparison between the observed and the synthesized isoseismals of the relatively small earthquake of Sierra Madre (1991) and of the big one in San Francisco (1906), California, suggests that sometimes the areal shapes of the territories damaged by earthquakes might be synthetically traced out with a simple kinematic function which, following the asymptotic approach, takes into account some gross features of the sources. The rather good fits presented herein may indicate the possibility of substituting in some regions the so-called empirical ‘attenuation relations’, which are currently used in regional seismic hazard studies, by new more source-dependent algorithms. Conversely, the technique could help in retrieving information about sources of earthquakes from the pre-instrumental era, (i) in areas where it could be proved that the effects due to the travel paths and to local site conditions are negligible, (ii) when the detailed modelling techniques nowadays available are inapplicable due to lack of data, or (iii) for saving time and money. It seems that the algorithm gives rather stable results.