Short- and long-term earthquake forecasts for California and Nevada

Yan Y. Kagan, & David D. Jackson

Published 2010, SCEC Contribution #1246

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 California and
Nevada, based only on data from past earthquakes.
Our long-term forecast is not explicitly time-dependent, but
it can be updated at any time to incorporate information from
recent earthquakes. The present version, founded on several
decades worth of data, is suitable for testing without
updating over a five-year period as part of the experiment
conducted by the Collaboratory for Study of Earthquake
Predictability (CSEP).
The short-term forecast is meant to be updated daily and
tested against similar models by CSEP.
The short-term forecast includes a fraction of our long-term
one plus time-dependent contributions from all previous
Those contributions decrease with time according to the Omori
law: proportional to the reciprocal of the elapsed time.
Both forecasts estimate rate density using a radially
symmetric spatial smoothing kernel decreasing approximately as
the reciprocal of the square of epicentral distance,
weighted according to the magnitude of each past earthquake.
We made two versions of both the long- and short-term
forecasts, based on the Advanced National Seismic System
(ANSS) and Preliminary Determinations of Epicenters
(PDE) catalogs, respectively.
The two versions are quite consistent, but for testing
purposes we prefer those based on the ANSS catalog since it
covers a longer time interval, 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 assume a tapered Gutenberg-Richter magnitude
distribution extending to a lower threshold of 4.0.

Kagan, Y. Y., & Jackson, D. D. (2010). Short- and long-term earthquake forecasts for California and Nevada. Pure and Applied Geophysics, 167(6/7), 685-692. doi: 10.1007/s00024-010-0073-5.