Seismic Moments of the Larger Earthquakes of the Southern California Region

Abstract

The seismic moment (M_0) of an earthquake is a more consistent and more physical measure of source strength than magnitude (M) or strain release (see pdf for formula), and this measure of source strength is determined for 47 of the larger earthquakes occurring in the Southern California region since 1857. Most of the seismic moments are obtained by conventional seismological means, but a relationship between M_0 and the areal distribution of Intensity VI (A_(VI)) is developed and scaled to estimate M_0 when intensity data are available but instrumental data are not. This relationship is log M_0 = 1.97 log A_(VI) − 2.55. For the region as a whole, earthquakes at the threshold of M_0 ≥ 10^(25), ≥10^(26), and ≥10^(27) dyne-cm have occurred once every 3, 8, and 25 yr, respectively. The spatial occurrence of the five largest earthquakes (M_0 ≥ 1 × 10^(27) dyne-cm) is not limited to a particular geologic province, mode of tectonic accommodation, or geographic locality. It is unlikely that this data set can reliably predict long-term spatial and temporal patterns of the M_0 ≥ 10^(25) dyne-cm seismicity of the Southern California region.