HR: 0800h
AN: ED31B-1207    [Abstracts]
TI: Relations Between Microseismicity and Surface Creep Along Major Strike-Slip Faults of the San Francisco Bay Region (CA)
AU: * Mascorro, M T
EM: marina@mascorro.us
AF: San Francisco State University, Department of Geosciences 1600 Holloway Ave., San Francisco, CA 94132 United States
AU: Caskey, J
EM: caskey@sfsu.edu
AF: San Francisco State University, Department of Geosciences 1600 Holloway Ave., San Francisco, CA 94132 United States
AU: Lienkaemper, J J
EM: jlienk@usgs.gov
AF: United States Geological Survey MS977, 345 Middlefield Road, Menlo Park, CA 94025 United States
AB: Few studies have examined temporal relations between microseismicity and creep. Most strike-slip faults in the San Francisco Bay Area have sections that exhibit fault creep, with varying rates of 1-18 mm/yr. It is well known that creeping faults commonly show high microseismicity rates. It has also been shown that rates and character of creep respond to regional stress changes associated with large earthquakes (e.g., 1989, M7 Loma Prieta). Relations between creep behavior and microseismicity were examined using alinement array data acquired from the San Francisco State University Creep Monitoring project collected at 21 sites since 1979 and seismicity data from the Northern California Earthquake Data Catalog. Catalog completeness was tested using the Gutenberg-Richter relation and found to be complete for M ≥ 1 for the Bay Area since 1979. We conducted catalog searches within a 5 to 10 km radius of each creep monitoring site, finding that sites with higher creep rates generally show higher seismicity rates. Creep data and seismicity histogram plots were compared over identical time periods and examined for correlations between details of creep behavior and seismic events or temporal variations in seismicity. We largely focused on sites that show episodic creep behavior or significant variations in creep rates over time. Creep episodes sometimes occur at nearly regular time intervals. Many sites also exhibit temporal clusters of seismicity, also at nearly regular time intervals, but the apparent frequencies of these clusters are different than the frequency of creep episodes. These observations suggest little or no correspondence between seismicity patterns and creep behavior. One notable exception occurs at the north end of the creeping section of the San Andreas fault, where creep nearly stopped in 1997-98 and resumed to a rate of 11 mm/yr following a M4.4 earthquake and it's aftershocks. Finally, we determined that the cumulative moment from seismicity in the vicinity of creep sites is generally two orders of magnitude lower than the effective seismic moment represented by fault creep. Although fault creep and high seismicity rates are both a response to mechanical fault weaknesses, our analysis suggests that they generally respond independently to elastic strain build-up. Further work will focus on statistically quantifying relations between creep and microseismicity in the Bay Area and examining relations between creep behavior and seismicity depth distribution and possible implications for fault locking depths.
UR: http://virga.sfsu.edu/creep/
DE: 7223 Earthquake interaction, forecasting, and prediction (1217, 1242)
SC: Education and Human Resources [ED]
MN: Fall Meeting 2005