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Coulomb stress interactions among M≥5.9 earthquakes in the Gorda deformation zone and on the Mendocino Fracture Zone, Cascadia megathrust, and northern San Andreas fault

Journal of Geophysical Research B: Solid Earth

By:
and
DOI: 10.1029/2009JB007117

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Abstract

The Gorda deformation zone, a 50,000 km2 area of diffuse shear and rotation offshore northernmost California, has been the site of 20 M ≥ 5.9 earthquakes on four different fault orientations since 1976, including four M ≥ 7 shocks. This is the highest rate of large earthquakes in the contiguous United States. We calculate that the source faults of six recent M ≥ 5.9 earthquakes had experienced ≥0.6 bar Coulomb stress increases imparted by earthquakes that struck less than 9 months beforehand. Control tests indicate that ≥0.6 bar Coulomb stress interactions between M ≥ 5.9 earthquakes separated by <9 months are unlikely to occur by random chance, suggesting that the multiple short-term stress interactions observed among the recent Gorda zone earthquakes are not an apparent effect. In all well-constrained ≥0.2 bar Coulomb stress interactions between earthquakes that occurred within 4 years of each other, the second earthquake is promoted. On longer timescales, calculated stress changes imparted by the 1980 Mw = 7.3 Trinidad earthquake are consistent with the locations of M ≥ 5.9 earthquakes in the Gorda zone until at least 1995, as well as earthquakes on the Mendocino Fault Zone in 1994 and 2000. Coulomb stress changes imparted by the 1980 earthquake are also consistent with its distinct elbow-shaped aftershock pattern. From these observations, we derive generalized static stress interactions among right-lateral, left-lateral and thrust faults near triple junctions.

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Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Coulomb stress interactions among M≥5.9 earthquakes in the Gorda deformation zone and on the Mendocino Fracture Zone, Cascadia megathrust, and northern San Andreas fault
Series title:
Journal of Geophysical Research B: Solid Earth
DOI:
10.1029/2009JB007117
Volume
115
Year Published:
2010
Language:
English
Publisher:
American Geophysical Union
Publisher location:
Washington, D.C.
Contributing office(s):
Earthquake Science Center
Description:
19 p.; B12306
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Journal of Geophysical Research B: Solid Earth
Country:
United States
State:
California