Earthquake ground surface ruptures provide insights into faulting mechanics and inform seismic hazard analyses. We analyze surface ruptures for 11 historical (1968−2018) moment magnitude (Mw) 4.7−6.6 reverse earthquakes in Australia using statistical techniques and compare their characteristics with magnetic, gravity, and stress trajectory data sets. Of the total combined (summative) length of all surface ruptures (∼148 km), 133 km (90%) to 145 km (98%) align with the geophysical structure in the host basement rocks. Surface rupture length (SRL), maximum displacement (MD), and probability of surface rupture at a specified Mw are high compared with equivalent Mw earthquakes globally. This is attributed to (1) a steep cratonic crustal strength gradient at shallow depths, promoting shallow hypocenters (∼1−6 km) and limiting downdip rupture widths (∼1−8.5 km), and (2) favorably aligned crustal anisotropies (e.g., bedrock foliations, faults, fault intersections) that enhanced lateral rupture propagation and/or surface displacements. Combined (modeled and observed) MDs are in the middle third of the SRL with 68% probability and either the ≤33rd or ≥66th percentiles of SRL with 16% probability. MD occurrs proximate to or directly within zones of enhanced fault geometric complexity (as evidenced from surface ruptures) in 8 of 11 earthquakes (73%). MD is approximated by 3.3 ± 1.6 (1σ) × AD (average displacement). S-transform analyses indicates that high-frequency slip maxima also coincide with fault geometric complexities, consistent with stress amplifications and enhanced slip variability due to geometric and kinematic interactions with neighboring faults. Rupture slip taper angles exhibite large variations (−90% to +380% with respect to the mean value) toward rupture termini and are steepest where ruptures terminate at obliquely oriented magnetic lineaments and/or lithology changes. Incremental slip approximates AD between the 10th and 90th percentiles of the SRL. The average static stress drop of the studied earthquakes is 4.8 ± 2.8 MPa. A surface rupture classification scheme for cratonic stable regions is presented to describe the prevailing characteristics of intraplate earthquakes across diverse crustal structural-geophysical settings. New scaling relationships and suggestions for logic tree weights are provided to enhance probabilistic fault displacement hazard analyses for bedrock-dominated intraplate continental regions.
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Research Article|
January 13, 2021
Surface slip distributions and geometric complexity of intraplate reverse-faulting earthquakes
Haibin Yang;
Haibin Yang
1
School of Earth Sciences, University of Melbourne, Parkville, Victoria 3053, Australia
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Mark Quigley;
Mark Quigley
1
School of Earth Sciences, University of Melbourne, Parkville, Victoria 3053, Australia
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Tamarah King
Tamarah King
1
School of Earth Sciences, University of Melbourne, Parkville, Victoria 3053, Australia2
Centre for Observation and Modelling of Earthquakes, Volcanoes, and Tectonics (COMET), Department of Earth Sciences, University of Oxford, Oxford OX1 3AN, UK
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GSA Bulletin (2021)
Article history
received:
30 Jun 2020
rev-recd:
28 Oct 2020
accepted:
17 Nov 2020
first online:
13 Jan 2021
Citation
Haibin Yang, Mark Quigley, Tamarah King; Surface slip distributions and geometric complexity of intraplate reverse-faulting earthquakes. GSA Bulletin 2021; doi: https://doi.org/10.1130/B35809.1
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