Seismicity prior to the July 2019 M7.1 Ridgecrest earthquake
Abstract
We studied seismicity during the time period from the M6.4 Searles Valley earthquake to the M7.1 Ridgecrest earthquake. The primary purpose is to investigate if any sign indicative of the M7.1 quake could be found in the space-time changes in seismicity after the M6.4 quake.
We used the b-value of the Gutenberg-Richter frequency-magnitude law, known to be inversely dependent on differential stresses. In this context, the b-value is considered to be a proxy of stress which could help designate highly stressed patches where future ruptures are likely to occur in California, Japan, and others [e.g., Schorlemmer and Wiemer, 2005; Nanjo et al., 2012, 2016]. We also used the phi -value to quantify the seismicity concentration/diffusion [Lippiello et al., 2012]. The phi -value is defined phi = R-1/Rb-1 where R-1 is the inverse distance averaged over the last n events before given time t, and Rb-1 is the same as R-1 but the average is taken over the (n+1)-th to 2n-th events before t. phi > 1 represents seismicity concentration while phi < 1 indicates seismicity diffusion. Lippiello et al. [2012] showed phi > 1 before all M > 6 mainshocks in southern California since 1980's. A three-dimensional (3D) view that shows data from the earthquake catalog from the southern California Earthquake Data Center reveals a patch of low b-values (b ~ 0.7) near the eventual hypocenter of the M7.1 quake. Another 3D analysis of phi -values pinpointed an area of seismicity concentration (phi ~ 1.5) immediately before the M7.1 quake, again near the eventual hypocenter. We also found that the location of low b-values remarkably coincides with that of high phi -values. The nucleation of the M7.1 quake rupture might correlate with the area of high stress and seismicity concentration.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.S31F0479N
- Keywords:
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- 7299 General or miscellaneous;
- SEISMOLOGY