SYNTHETIC ISOSEISMALS OF 2 CALIFORNIAN EARTHQUAKES

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 area l shapes of the territories damaged by earthquakes might be synthetica lly traced out with a simple kinematic function which, following the a symptotic approach, takes into account some gross features of the sour ces. The rather good fits presented herein may indicate the possibilit y of substituting in some regions the so-called empirical 'attenuation relations', which are currently used in regional seismic hazard studi es, by new more source-dependent algorithms. Conversely, the technique could help in retrieving information about sources of earthquakes fro m 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 avail able are inapplicable due to lack of data, or (iii) for saving time an d money. It seems that the algorithm gives rather stable results.