Determination of total strain from faulting using slip measurements

Abstract

IN the past twenty years it has become commonplace in seismology to sum seismic moments for large earthquakes to determine the contemporary fault slip rate¹ or regional strain rate produced by earthquakes². The method has several drawbacks: it often greatly underestimates deformation rates predicted from plate tectonics, either because the seismic history is of insufficient length or a substantial amount of fault slip is aseismic. Also, it can be used to calculate only current deformation rates, and cannot be applied to earlier geological eras or to estimate total strain. These problems can be overcome by applying the same methods to geological measures of fault displacement. Complete fault data sets, however, are generally not available. Here we show that faults obey general scaling laws in their size frequency distribution and in the relation between displacement and fault length. Combining these scaling relations, we demonstrate that the calculation of strain can be successfully applied to sparse geological data sets, because most strain is produced by the largest faults so that the data set need not be complete for small fault sizes.