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Group 1 – EFP | Poster Abstracts
reference model, we use the Pattern Informatics (PI) method (Tiampo et al., 2002) which identifies
areas of increase and decrease in the seismicity rate for days to months after the earthquake event.
Of particular increase are the areas of seismic quiescence, which are related to “stress shadows”
often calculated using Coulomb stress changes (Stein, 1992; Stein, 1999; Tiampo et al., 2006). We
will use slip models of the Landers earthquake to calculate the Coulomb stress changes (Lin and
Stein, 2004; Toda et al., 2005), and manipulate the constitutive parameters in order to recreate a
stress field comparable to that of the reference model. These parameters include the calculation
depth, the coefficient of friction, and most importantly the principal stress orientations. Currently,
we assume a uniform stress field, but further studies will introduce the complication of
heterogeneities which might improve the scale and detail of the resulting models. Determining the
stress field can improve earthquake modeling, and thus advance our understanding of the
principal mechanics involved with them.
1-101
QUANTIFYING LONG AND SHORT-RANGE EARTHQUAKE TRIGGERING AS A
FUNCTION OF DYNAMIC STRAIN van der Elst NJ, and Brodsky EE
Remote earthquake triggering by dynamic strain from seismic waves is a regularly observed
feature of earthquake interactions. However, the effectiveness of dynamic strains at triggering
earthquakes has not been well quantified. Do dynamically triggered earthquakes make up a large
proportion of earthquakes as a whole? Here we quantify the rate at which dynamic strains trigger
earthquakes at long distances, using the ANSS and JMA earthquake catalogs, and compare pre-and
post-trigger interevent time statistics. We find that the intensity of dynamic triggering scales
continuously as a function of peak dynamic strain, estimated from the seismic wave amplitude. We
compare these rates to aftershock triggering rates very near a mainshock, and find that dynamic
triggering can account for the majority of local aftershocks. Dynamic triggering also appears to be
ubiquitous -- not confined to geothermal and magmatic provinces. Some regions however, like
California, are more prone to triggering than others, like Japan. This result points the way to a new
methodology for earthquake forecasting based on the amplitude of the observed seismic waves.
1-102
EVIDENCE FOR MOGI DOUGHNUT BEHAVIOR IN SEISMICITY PRECEDING
SMALL EARTHQUAKES IN SOUTHERN CALIFORNIA Shearer PM, and Lin G
We examine the average space-time behavior of seismicity preceding M 2–5 earthquakes in
southern California from 1981 to 2007 using a high-resolution catalog and identify regions of
enhanced activity in a 1-day period preceding larger earthquakes at distances comparable to their
predicted source radii. The difference in precursory behavior between large and small earthquakes
is subtle but statistically significant when averaged over many earthquakes, and has similarities to
the “Mogi doughnut” seismicity pattern observed to occur prior to some M 6 and larger
earthquakes. These results indicate that many standard earthquake triggering models do not
account for all of the processes involved in earthquake occurrence.
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