NEHRP Clearinghouse
- Title
- The Horse Canyon Earthquake of August 2, 1975-Two Stage Stress Release Process in a Strike-Slip Earthquake.
- File
- PB80157589.pdf
- Author(s)
- Hartzell, S.; Brune, J. N.
- Source
- National Science Foundation, Washington, DC. Engineering and Applied Science., January 1979, 31 p.
- Abstract
- The Horse Canyon earthquake which occurred on August 2, 1975 affords an opportunity to study the source mechanism of an earthquake in a relatively simple geologic setting. The earthquake was fairly well instrumented thereby providing considerable data from which to construct a model. Analysis of main shock and aftershock data suggest that stress release occurred in two stages: (1) faulting over a relatively small source area with a rapid dislocation rate; and (2) faulting during which the rupture grew at a smaller rate to a larger final source radius. The model explains the larger moment estimate based on 20 second surface waves compared to shorter period body wave estimates, and also the apparent increase in source dimension with time. It allows for large stress drops over small dimensions. Rupture of the asperity and the stress drops were characterized. Observations noted in this study together with those for other earthquakes with a wide range of magnitudes, suggest that a two-stage rupture mechanism may be a fairly common occurrence in shallow faulting and may reflect possible large variations in stress over a length scale of kilometers within the crust.
- Keywords
- Horse Canyon Earthquake; Surface waves; Seismic waves; California; Geologic structures; Seismic epicenter; Earthquake engineering; Secondary waves; Earthquakes; Geological faults