GEAR1: a Global Earthquake Activity Rate model constructed from geodetic strain rates and smoothed seismicity

Peter Bird, David D. Jackson, Yan Y. Kagan, Cornelis W. Kreemer, & Ross S. Stein

Published October 1, 2015, SCEC Contribution #2075

GEAR1 estimates the rate of shallow earthquakes with magnitudes 6 through 9 everywhere on Earth. It was constructed through a reproducible algorithmic process to make testable earthquake forecasts. Our preferred hybrid forecast is a log-linear blend of the Global CMT catalog (smoothing 4602 m ≥ 5.767 shallow earthquakes during 1977-2004) and the Global Strain Rate Map version 2.1 (smoothing 22415 GPS velocities), optimized to best forecast the 2005-2012 GCMT catalog. Strain rate is a proxy for fault stress accumulation, and earthquakes indicate stress release, so a multiplicative blend is intrinsically desirable, capturing the strengths of both approaches. This preferred hybrid forecast outperforms its tectonic and seismicity parents; the chance that this improvement stems from random seismicity fluctuations is less than 1%. The preferred hybrid is also retrospectively tested against the independent ISC-GEM catalog (m ≥ 6.8 during 1918-1976) with similar success. To build parametric catastrophe bonds from GEAR1, one could calculate the magnitude for which there is a 1% (or any) annual probability of occurrence in local regions. Comparing the California portion of GEAR1 to the Uniform California Earthquake Rupture Forecast version 3 (UCERF3), net earthquake rates agree within 4% at m ≥ 5.8 and at m ≥ 7.0. The spatial distribution of UCERF3 forecast earthquake rates most resembles GEAR1 when UCERF3 is smoothed with a 30-km kernel. As UCERF3 is widely believed to derive useful information from fault geometry, slip rates, paleoseismic data, and enhanced seismic catalogs (not used in our model), this comparison is encouraging.

Bird, P., Jackson, D. D., Kagan, Y. Y., Kreemer, C. W., & Stein, R. S. (2015). GEAR1: a Global Earthquake Activity Rate model constructed from geodetic strain rates and smoothed seismicity. Bulletin of the Seismological Society of America, 105(5), 2538-2554. doi: 10.1785/0120150058.

Related Projects & Working Groups
Collaboratory for the Study of Earthquake Predictability