Strong ground motion and source mechanism studies for earthquakes in the northern Baja California/southern California region
Earthquake data sets collected from arrays of digital seismic event recorders and strong motion instruments operated in the northern Baja California/southern California region are analyzed. Complementing these near-source data sets with data from more distant seismic stations it was possible to begin to separate and understand the effects of stress drop, source size, sediment amplification, and physical attenuation on the variation of ground motion with distance. Surprisingly large ground accelerations, over 0.5g, were recorded for some relatively small (M/sub L/ < 5) earthquakes in the Victoria, Baja California earthquake swarm of March 1978. It was concluded that this is a result of relatively high stress drops (approx. 1 kilobar) and a relatively high sediment amplification factor of about 3.4. The ground motion from these earthquakes was relatively high frequency, which was somewhat surprising since the well-established depth of the events is about 10-12 km and the energy thus passed through the 5 km thick column of sediments of the Imperial and Mexicali Valleys, which might have been expected to produce severe attenuation. The primary factors which influence the results of studies with distant station data are geologic complexities, especially the boundary region between the Imperial Valley and the granitic batholith of the Peninsular Ranges.
- OSTI ID:
- 5750393
- Resource Relation:
- Other Information: Thesis (Ph. D.)
- Country of Publication:
- United States
- Language:
- English
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