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Geometry and earthquake potential of the shoreline fault, central California

Bulletin of the Seismological Society of America

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DOI: 10.1785/0120120175

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Abstract

The Shoreline fault is a vertical strike‐slip fault running along the coastline near San Luis Obispo, California. Much is unknown about the Shoreline fault, including its slip rate and the details of its geometry. Here, I study the geometry of the Shoreline fault at seismogenic depth, as well as the adjacent section of the offshore Hosgri fault, using seismicity relocations and earthquake focal mechanisms. The Optimal Anisotropic Dynamic Clustering (OADC) algorithm (Ouillon et al., 2008) is used to objectively identify the simplest planar fault geometry that fits all of the earthquakes to within their location uncertainty. The OADC results show that the Shoreline fault is a single continuous structure that connects to the Hosgri fault. Discontinuities smaller than about 1 km may be undetected, but would be too small to be barriers to earthquake rupture. The Hosgri fault dips steeply to the east, while the Shoreline fault is essentially vertical, so the Hosgri fault dips towards and under the Shoreline fault as the two faults approach their intersection. The focal mechanisms generally agree with pure right‐lateral strike‐slip on the OADC planes, but suggest a non‐planar Hosgri fault or another structure underlying the northern Shoreline fault. The Shoreline fault most likely transfers strike‐slip motion between the Hosgri fault and other faults of the Pacific–North America plate boundary system to the east. A hypothetical earthquake rupturing the entire known length of the Shoreline fault would have a moment magnitude of 6.4–6.8. A hypothetical earthquake rupturing the Shoreline fault and the section of the Hosgri fault north of the Hosgri–Shoreline junction would have a moment magnitude of 7.2–7.5.

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Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Geometry and earthquake potential of the shoreline fault, central California
Series title:
Bulletin of the Seismological Society of America
DOI:
10.1785/0120120175
Volume
103
Issue:
1
Year Published:
2013
Language:
English
Publisher:
Seismological Society of America
Contributing office(s):
Earthquake Hazards Program
Description:
16 p.
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
First page:
447
Last page:
462
Country:
United States
State:
California