1. 5/29/2015 Relations Between Microseismicity and Surface Creep Along Major Strike­Slip Faul
http://adsabs.harvard.edu/abs/2005AGUFMED31B1207M 1/2
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Title: Relations Between Microseismicity and Surface Creep Along Major Strike­Slip
Faults of the San Francisco Bay Region (CA)
Authors: Mascorro, M. T.; Caskey, J.; Lienkaemper, J. J.
Affiliation: AA(San Francisco State University, Department of Geosciences 1600 Holloway
Ave., San Francisco, CA 94132 United States marina@mascorro.us), AB(San
Francisco State University, Department of Geosciences 1600 Holloway Ave.,
San Francisco, CA 94132 United States caskey@sfsu.edu), AC(United States
Geological Survey MS977, 345 Middlefield Road, Menlo Park, CA 94025
United States jlienk@usgs.gov)
Publication: American Geophysical Union, Fall Meeting 2005, abstract #ED31B­1207
Publication Date: 12/2005
Origin: AGU
Keywords: 7223 Earthquake interaction, forecasting, and prediction (1217, 1242)
Bibliographic Code: 2005AGUFMED31B1207M
Abstract
Few studies have examined temporal relations between microseismicity and creep. Most strike­slip faults
in the San Francisco Bay Area have sections that exhibit fault creep, with varying rates of 1­18 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 Gutenberg­Richter 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 1997­98 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

2. 5/29/2015 Relations Between Microseismicity and Surface Creep Along Major Strike­Slip Faul
http://adsabs.harvard.edu/abs/2005AGUFMED31B1207M 2/2
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 build­up. 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.
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