Estimating maximum expectable magnitude of earthquakes from fault dimensions

Abstract

The evaluation of seismic risk at locations where sensitive man-made structures are planned depends critically on a correct estimate of the maximum expectable earthquake magnitude, M</em>_max, in that region. By assuming that the longest fault (or fault unit) with length L</em>_max could break in a single earthquake, one estimates M</em>_max from L</em>_max on the basis of a magnitude versus source-length relation, which is derived empirically. The maximum expectable ground accelerations are then estimated from M</em>_max. I propose that a more accurate estimate of M</em>_max can be obtained by determining the maximum expected rupture area, A</em>_max, and using the magnitude-area relation M</em> = log A</em> + 4.15 (valid for M</em> > 5.6). A</em>_max can be obtained from the product of L</em>_max times the expected fault width. The latter can probably be estimated more accurately than L</em>_max on the basis of tectonic analysis and microearthquakes studies. The M</em>_max estimates derived from rupture area</em> give more accurate results than the estimates based on rupture length</em> alone, because narrow faults produce less powerful earthquakes than do wide faults of the same length.