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Triggered reverse fault and earthquake due to crustal unloading, northwest Transverse Ranges, California.

Geology

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Abstract

A reverse-right-oblique surface rupture, associated with a ML 2.5 earthquake, formed in a diatomite quarry near Lompoc, California, in the northwesternmost Transverse Ranges on April 7, 1981. The 575-m-long narrow zone of ruptures formed in clay interbeds in diatomite and diatomaceous shale of the Neogene Monterey Formation. The ruptures parallel bedding, dip 39o-59oS, and trend about N84oE on the north limb of an open symmetrical syncline. Maximum net slip was 25 cm; maximum reverse dip slip was 23 cm, maximum right-lateral strike slip was about 9 cm, and average net slip was about 12 cm. The seismic moment of the earthquake is estimated at 1 to 2 X 1018 dyne/cm and the static stress drop at about 3 bar. The removal of an average of about 44 m of diatomite resulted in an average load reduction of about 5 bar, which decreased the normal stress by about 3.5 bar and increased the shear stress on the tilted bedding plane by about 2 bar. The April 7, 1981, event was a very shallow bedding-plane rupture, apparently triggered by crustal unloading. -Authors

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Triggered reverse fault and earthquake due to crustal unloading, northwest Transverse Ranges, California.
Series title:
Geology
Volume
11
Issue:
5
Year Published:
1983
Language:
English
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
First page:
287
Last page:
291
Number of Pages:
5