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Afterslip moment scaling and variability from a global compilation of estimates

Churchill, R. M., Werner, M. J., Biggs, J. and Fagereng, Å. ORCID: 2022. Afterslip moment scaling and variability from a global compilation of estimates. Journal of Geophysical Research. Solid Earth 127 (4) , e2021JB023897. 10.1029/2021JB023897

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Aseismic afterslip is postseismic fault sliding that may significantly redistribute crustal stresses and drive aftershock sequences. Afterslip is typically modeled through geodetic observations of surface deformation on a case-by-case basis, thus questions of how and why the afterslip moment varies between earthquakes remain largely unaddressed. We compile 148 afterslip studies following 53 Mw6.0–9.1 earthquakes, and formally analyze a subset of 88 well-constrained kinematic models. Afterslip and coseismic moments scale near-linearly, with a median Spearman's rank correlation coefficient (CC) of 0.91 after bootstrapping (95% range: 0.89–0.93). We infer that afterslip area and average slip scale with coseismic moment as urn:x-wiley:21699313:media:jgrb55593:jgrb55593-math-0001 and urn:x-wiley:21699313:media:jgrb55593:jgrb55593-math-0002, respectively. The ratio of afterslip to coseismic moment (Mrel) varies from <1% to >300% (interquartile range: 9%–32%). Mrel weakly correlates with Mo (CC: −0.21, attributed to a publication bias), rupture aspect ratio (CC: −0.31), and fault slip rate (CC: 0.26, treated as a proxy for fault maturity), indicating that these factors affect afterslip. Mrel does not correlate with mainshock dip, rake, or depth. Given the power-law decay of afterslip, we expected studies that started earlier and spanned longer timescales to capture more afterslip, but Mrel does not correlate with observation start time or duration. Because Mrel estimates for a single earthquake can vary by an order of magnitude, we propose that modeling uncertainty currently presents a challenge for systematic afterslip analysis. Standardizing modeling practices may improve model comparability, and eventually allow for predictive afterslip models that account for mainshock and fault zone factors to be incorporated into aftershock hazard models.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Earth and Environmental Sciences
Additional Information: This is an open access article under the terms of the Creative Commons Attribution License
Publisher: American Geophysical Union
ISSN: 2169-9313
Date of First Compliant Deposit: 4 August 2022
Date of Acceptance: 5 April 2022
Last Modified: 06 May 2023 17:29

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