Response of creepmeters on the San Andreas fault near Parkfield to the earthquake

Journal Article · Mon Jan 01 04:00:00 EST 1990 · United States Geological Survey, Professional Paper; (USA)

OSTI ID:5599636

Schulz, S S; Mavko, G M; Brown, B D

A total of 14 US Geological Survey creepmeters on the San Andreas fault in central California recorded coseismic steps coincident with the M = 6.7 May 2 earthquake. Creepmeters near Parkfield recorded the largest effects. Postearthquake creep rates slowed significantly, and creep at one station reversed to left lateral. About 4 months after the earthquake, decreased rates caused cumulative creep at four Parkfield stations to fall below long-term linear trends observed before May 2. At several stations, creep continued to be either left lateral or slower than normal for the rest of 1983. By January 31, 1984, all but two stations recorded resumption of right-lateral creep at reduced rates. As late as April 1, 1984, however, one station north of Parkfield continued to record left-lateral drift, and another station at the south end of the creeping section south of Parkfield recorded little or no movement. One interpretation of the creep slowdown after May 2 is that the Coalinga main shock released accumulated stress in the upper kilometer or so of the San Andreas fault near Parkfield, and several months elapsed before stress built up sufficiently to allow creep to resume. A multiple-linear-regression analysis of coseismic-step size as a function of distance from the creepmeter to an earthquake focus and (or) earthquake magnitude showed a linear correlation between step size and magnitude for the data from two stations. No correlation was found between step size and distance to focus for the data from any of the stations. Reduction in step sizes after May 2, despite numerous large aftershocks, suggests that stored local stress is the dominant factor in coseismic-step size.

• OSTI ID: 5599636
• Journal Information: United States Geological Survey, Professional Paper; (USA), Journal Name: United States Geological Survey, Professional Paper; (USA) Vol. 1487; ISSN XGPPA
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
AFTERSHOCKS
CALIFORNIA
CREEP
DEVELOPED COUNTRIES
EARTHQUAKE MAGNITUDE
EARTHQUAKES
FEDERAL REGION IX
FUNCTIONS
GEOLOGIC FAULTS
GEOLOGIC FRACTURES
GEOLOGIC STRUCTURES
GROUND MOTION
MATHEMATICS
MEASURING INSTRUMENTS
MECHANICAL PROPERTIES
MONITORING
MOTION
NORTH AMERICA
PERFORMANCE
REGRESSION ANALYSIS
RELAXATION
RESPONSE FUNCTIONS
SEISMIC EVENTS
STATISTICS
STRESS RELAXATION
TIME DEPENDENCE
USA