Long‐period and broad‐band teleseismic body‐wave modeling of the October 18, 1989 Loma Prieta Earthquake

Inversion of long‐period, teleseismic body waves for the Loma Prieta earthquake yields a nearly double‐couple moment tensor corresponding to an oblique mechanism with strike 130°, dip 73° and rake 146°. The long‐period centroid depth of the source is 18 km, and the seismic moment is 2.8×10 19 Nm. The source time history consists of two pulses with a total duration of 8–9 sec. Preliminary forward modeling of broad‐band, teleseismic body waves indicates the occurrence of at least two sub‐sources. Constraining the fault orientation to the long‐period inversion result, the first source was located at 18 km depth, and the second source was located updip at about 14 km depth. The second source has a seismic moment 2.7 times that of the first, and occurred 2.0 sec after the first. The precise location of the second source will require further modeling.