Abstract
Remote earthquake triggering is a well-established phenomenon. Triggering is commonly identified from statistically significant increases in earthquake rate coincident with the passage of seismic energy. In establishing rate changes, short duration earthquake catalogs are commonly used, and triggered sequences are not typically analyzed within the context of background seismic activity. Using 500 mainshocks and four western USA 33-yearlong earthquake catalogs, we compare the ability of three different statistical methods to identify remote earthquake triggering. Counter to many prior studies, we find remote dynamic triggering is rare (conservatively, <2% of the time). For the mainshocks associated with remote rate increases, the spatial and temporal signatures of triggering differ. We find that a rate increase coincident in time with mainshock energy alone is insufficient to conclude that dynamic triggering occurred. To classify dynamically triggered sequences, we suggest moving away from strict statistical measurements and instead use a compatibility assessment that includes multiple factors, like spatial and temporal indicators.
Highlights
Clear examples of remote dynamic triggering include increases in local earthquake rates over large areal extents as observed following the Mw 7.3 1992 Landers, California, earthquake[1]; the Mw 7.9 2002 Denali Fault, Alaska earthquake[2,3,4,5]; and the Mw7.4 1999 Izmit, Turkey, earthquake[6]
The difference between the obvious remote triggering following the Landers, Denali Fault, and Izmit earthquakes, and the subtler instances of triggering and instances of delayed dynamic triggering leads to the question: what are the indicators for dynamic triggering and do different indicators imply differences in the physical mechanisms generating the triggered earthquakes? Here, we step back and first ask whether statistically significant changes in rate are sufficient to be the sole indicator for dynamic triggering
We examine statistical significance in context of the spatial characteristics of the triggered events and the temporal behavior of the rate changes
Summary
Remote earthquake triggering is a well-established phenomenon. Triggering is commonly identified from statistically significant increases in earthquake rate coincident with the passage of seismic energy. Applying the DFM method using the short, 5-hour, pre-event time window identifies the most instances of rate increases coincident with the arrival of the seismic waves, 38 and 24, at the 95% and 99% confidence levels, respectively. All three statistical methods, identify previously documented cases of remote triggering in Utah and Yellowstone following the 2002 Mw 7.9 Denali Fault, Alaska, earthquake[2,3,4,5], triggering in Utah following the 1992 Mw 7.3 Landers, California earthquake[1], and in Anza following the 2010 Mw 7.2 El Mayor Cucapah earthquake[47], (Fig. 2 and Supplementary Data Files 2 and 3). For the triggered earthquakes in Utah following the 2002 Denali Fault earthquake, what was unique was the widespread distribution of events over a short-time window (not just the rate increase) and that the widespread seismicity tended to form clusters[4]. The burst cycle initiates with the (a) Anza 95% (N=10) 8.5
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