Global earthquake forecasts

Yan Y. Kagan, & David D. Jackson

Published 2010, SCEC Contribution #1453

We have constructed daily worldwide long- and short-term earthquake forecasts. These forecasts specify the earthquake rate per unit area, time, and magnitude on a 0.5 degree grid for a global zone region between 75N and 75S latitude (301 by 720 grid cells). We use both the CMT and PDE catalogs. Like our previous forecasts, the new forecasts are based largely on smoothed maps of past seismicity and assume spatial and temporal clustering. The forecast based on the CMT catalog, with the magnitude completeness threshold 5.8, includes an estimate of focal mechanisms of future earthquakes and of the mechanism uncertainty. The forecasted tensor focal mechanism makes it possible in principle to calculate an ensemble of seismograms for each point of interest on the Earth's surface. We also introduce a new approach that circumvents the need for focal mechanisms. This permits the use of the PDE catalog that reliably documents many smaller quakes with a higher location accuracy. The result is a forecast at a higher spatial resolution and down to a magnitude threshold below 5.0. Such new forecasts can be prospectively tested within a relatively short time, such as a few years, because smaller events occur with greater frequency. The forecast's efficiency can be measured by its average probability gains per earthquake compared to the spatially or temporally uniform Poisson distribution. For the short-term forecast the gain is about 2.0 for the CMT catalog and 3.7 for the PDE catalog relative to a temporally random but spatially localized null hypothesis. Preliminary tests indicate that for the long-term global spatial forecast the gain is of the order 20-25 compared to the uniform event distribution over the Earth surface. We can also prospectively test the long-term forecast to check whether it can be improved.

Citation
Kagan, Y. Y., & Jackson, D. D. (2010). Global earthquake forecasts. Geophysical Journal International, 184(2), 759-776. doi: 10.1111/j.1365-246X.2010.04857.x.