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Group 1 – EFP | Poster Abstracts
1-089
A FIVE-YEAR FORECAST OF EARTHQUAKE LARGER THAN 5 IN CALIFORNIA
BASED ON SMOOTHED SEISMICITY Wang Q, Jackson DD, and Kagan YY
A forecast method based on smoothed seismicity was presented by Kagan and Jackson (1994) and
has been widely used since then. It is based on earthquake occurrences, and it assumes the
earthquake rate density is constant in time and the rate density is proportional to a smoothed
version of past seismicity. Kagan and Jackson (2007) have presented a five-year forecast of southern
California earthquake with magnitude larger than 5. At present, we extend the forecast region from
southern California to all of California using the new California earthquake catalog. This catalog
covers all known earthquakes larger than 4.7 in California from 1800 to 2007. All earthquake
magnitudes are converted to moment magnitude in this catalog. Earthquakes less then magnitude
6.5 are treated as point sources. Some earthquakes larger than 6.5 are replaced by ensembles of
smaller events with equivalent total moment, distributed along the rupture surface. This forecast
model differs from others like it because it includes historical as well as instrumented earthquakes,
and because larger events are represented by multiple point sources.
1-090
SHORT- AND LONG-TERM EARTHQUAKE FORECASTS FOR CALIFORNIA AND
NEVADA Kagan YY, and Jackson DD
We present estimates of future earthquake rate density (probability per unit area, time, and
magnitude) on a 0.1 degree grid for a region including most of California and Nevada. Our longterm
forecast is inherently independent of time and it is suitable for testing over a five-year period
as part of the experiment conducted by the Collaboratory for Study of Earthquake Predictability
(CSEP). In the short-term forecast the earthquake rate decreases following each past earthquake by
an Omori-type temporal decay. The short-term forecast is meant to be updated daily and tested
against similar models by CSEP. The full forecast includes a fraction of our long-term forecast plus
contributions from the short-term forecast. Both forecasts estimate rate density using a radially
symmetric spatial smoothing kernel decreasing approximately as in the reciprocal of the square of
epicentral distance, weighted according to the magnitude of each past earthquake. Both forecasts
are based on cataloged earthquakes only, with no dependence on mapped faults or geodetic strain
rates. We made two versions of both the long- and short-term forecasts, based on the ANSS and
PDE catalogs, respectively. The two versions are quite consistent, and for testing purposes we
prefer those based on the ANSS catalog as it is complete to a lower magnitude threshold and has
more precise locations. Both forecasts apply to shallow earthquakes only (depth 25 km or less) and
they assume a modified Gutenberg-Richter magnitude distribution extending to a lower threshold
of 4.0.
1-091
EARTHQUAKE PATTERNS IN DIVERSE TECTONIC ZONES OF THE GLOBE Kagan
YY, Bird P, and Jackson DD
We extend existing branching models for earthquake occurrence by allowing their parameters to
vary by tectonic zone. We partition Earth’s surface into five zones: Trenches (including subduction
zones, oceanic convergent boundaries, and earthquakes in the outer rise or overriding plate), Fast
spreading ridges and oceanic transforms, Slow spreading ridges and transforms, Active continents,
and Plate interiors (everything else). Our purpose is to specialize the models to give them the
greatest possible predictive power for use in earthquake forecasts. We expected the parameters of
the branching models to be different in the various tectonic zones, because earlier studies [Bird &
Kagan, 2004] found that magnitude limits and other parameters differed by plate boundary class.
2008 SCEC Annual Meeting | 117