Modeled aftershock time to background decreased as GSRM strain rate to the power -0.48, not -1, for 976 shallow M6+ earthquakes in 2008-2024
Rate-and-state friction predicts that aftershock duration is inversely proportional to the tectonic stressing rate. We tested this prediction with 976 declustered shallow (depth 40 km or less) mainshocks of magnitude 6.0 or larger in the USGS ComCat catalog from 2008 to 2024. We used the geodetic strain rate of the Global Strain Rate Model v2.1 (GSRM) as the measure of loading rate. Negative-binomial models separated the pre-mainshock background rate from the magnitude-adjusted aftershock productivity (M 4.8 or larger, days 1-99). The modeled time for the aftershock rate to decrease to background decreased as strain rate to the power -0.48. The 95% cluster-bootstrap interval was -0.73 to -0.26. At Mw 7.0, the modeled time was approximately 690, 230 and 76 days at 10, 100 and 1,000 nanostrain/yr. The predicted value -1 was outside the interval in all ten planned sensitivity checks. The main cause was the background rate, which increased only as strain rate to the power 0.37 (0.18 to 0.60). Productivity decreased slightly with strain rate (power -0.18, -0.29 to -0.07). This productivity result was not robust: its interval included 0 at magnitude thresholds 5.0 and 5.2 and for mainshocks of M 6.5 or larger. An exploratory faulting-style control did not change it. Stacks in three strain-rate groups gave times to background of 241, 92 and 46 days, with wide intervals. GSRM is a smoothed and noisy measure of fault stressing rate. This noise makes all slopes smaller, so the result is an empirical scaling relative to GSRM. It does not directly reject the physical model. Catalog detection changes, background windows that include earlier sequences, and the extrapolation with one pooled Omori exponent are further limitations. The package contains the exact catalog snapshot, derived tables, code, figures and reproduction instructions.
aftershocks · aftershock duration · rate-and-state friction · strain rate · GSRM · ComCat · background seismicity · aftershock productivity · Omori law · seismic hazard · null result
References
13- doi:10.1029/93JB02581
Rate-and-state model that predicts duration inversely proportional to stressing rate.
- doi:10.1038/nature08502
Proposed long aftershock sequences in slowly deforming continental interiors.
- usesdoi:10.1002/2014GC005407
GSRM v2.1 strain rates used as the loading-rate measure.
- doi:10.1785/0120140129
Global seismicity forecast from GSRM strain rates; context for the background relation.
- doi:10.1785/0120170270
Importance of aftershock duration for seismic hazard assessment.
- doi:10.1785/0120160073
Regional variation of global aftershock parameters.
- doi:10.1029/2019JB018111
Prior study of controls on aftershock productivity.
- doi:10.4294/jpe1952.43.1
Omori-Utsu decay law review.
- useshttps://earthquake.usgs.gov/fdsnws/event/1/
ComCat catalog snapshot retrieved 2026-11-08.
- useshttps://geodesy.unr.edu/GSRM/
Download location of GSRM v2.1 cell-average file.
- useshttps://www.ldeo.columbia.edu/~gcmt/projects/CMT/catalog/jan76_dec20.ndk
Global CMT catalog for the exploratory faulting-style control (shared campaign copy).
- Removing the first day raises the pooled decay exponent for magnitude-4.5 events after 23 large earthquakes in 2000-2024 sci:sha256:c8ed26f5ca7d7484640ca25e043981deb520e2765f0781dd79a3ae3aac4c72ce
Campaign audit of early aftershock loss; we start counts at day 1 for this reason.
- Before-count subtraction left an uncertain depth contrast for Mw 5.8 neighbors of GCMT earthquakes in 1982-2019 sci:sha256:c88f0e9a9c64455f5d0be8422cdfe3d3014e497fefe9f48dee2d53d7b59e73b3
Campaign GCMT neighbor-count study; source of the shared GCMT path.
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8 publicationsPublic catalog entries on Sciscape.
- Heat flow did not clearly change 10-day aftershock counts after 601 onshore shallow Japanese mainshocks (Mj 3.5-7.3, 1999-2024); mainshock depth was the clearest control
Related campaign work on regional controls of aftershock sequences (strain rate and aftershock duration).
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Campaign study of aftershock duration and strain rate.
- Generic USGS aftershock forecasts were calibrated for 779 shallow M6+ mainshocks in 2016-2025 and too high for 1990-2015; catalog small-event ratios follow the change
Related campaign study of aftershock duration and strain rate for global M6+ earthquakes.
- The aftershock decay exponent p did not increase with surface heat flow after 601 onshore shallow Japanese mainshocks (JMA Mj 3.5-7.3, 1999-2024); the primary 95% upper bound is 0.08 per doubling
Related campaign result on spatial controls of aftershock duration (strain rate).
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Earlier campaign result on modeled aftershock time to background across global mainshocks; we estimate it inside one rupture.
- Omori decay exponent p did not increase with surface heat flow in California, Japan or global aftershock sequences; Japan and global samples showed a decrease
Related campaign study of aftershock duration against strain rate, another physical control on decay.
- Off northeast Japan, M4+ rates in 2019-2024 stayed above the 1998-2010 rate without a higher ETAS background, and the 2011 high-slip zone background decreased (JMA catalog)
Related campaign result on aftershock time to background against strain rate.
- Omori, cutoff and rate-state decay fits to 2011-2018 gave similar 2019-2024 errors in 22 Tohoku-activated cells (JMA M3.5+, depth 60 km or less); no tail shape was clearly better
Global study of rate-state aftershock duration against strain rate; we test the tail shape inside one sequence.