On secular spatial seismicity

Yosihiko Ogata

Published August 9, 2017, SCEC Contribution #7469, 2017 SCEC Annual Meeting Poster #006 (PDF)

It has been passed 15 years since the hierarchical (i.e., location-dependent) space-time ETAS (HIST-ETAS) models have been proposed (Ogata et al., 2003); and the short-term (daily) and intermediate-term (3-months and one year) earthquake forecasts in and around Japan using the HIST-ETAS model has been tested for 8 years by the Testing Center of the Collaborative Study of Earthquake Predictability (CSEP) (Ogata, 2011).

Some characteristic parameters of the HIST-ETAS model are represented by piecewise-linear surfaces whose value at any location is linearly interpolated by the values at the nearest three earthquake locations that consists a Delaunay triangle. The solutions of the coefficients of the parameter functions are obtained through the inversion of the log-likelihood function of the space-time earthquake data, with certain smoothness constraints. This is suited not only for high resolution inversion in the region of clustered earthquakes but also accurate space-time forecast in the active stage of seismicity.

Among the characteristic parameters of the HIST-ETAS models, we are primary interested in intensity of the background seismicity that subtracted the triggering effect of the HIST-ETAS model. This solution values vary regionally in the range of a few orders within a seismogenic zone, but are confirmed to always take the same pattern, independent of observed periods. In particular, in inland Japan, the spatial intensity is highly correlated with the spatial variation of shear stress accumulation rates or volumetric stressing rates calculated from the geodetic GPS data. Thus, we think the estimated background activity to be secular spontaneous seismicity. Hence, this is quite useful for the secular prediction of large earthquake locations, in conjunction with Gutenberg-Richter distribution where the b-value is also location dependent.

Key Words
Earthquake forecasting

Citation
Ogata, Y. (2017, 08). On secular spatial seismicity. Poster Presentation at 2017 SCEC Annual Meeting.

Related Projects & Working Groups
Earthquake Forecasting and Predictability (EFP)