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Coseismic Throw Variation Across Along‐Strike Bends on Active Normal Faults: Implications for Displacement Versus Length Scaling of Earthquake Ruptures

iezzi, F; Mildon, Z; Faure Walker, JP; Roberts, G; huw, G; wilkinson, M; robertson, J; (2018) Coseismic Throw Variation Across Along‐Strike Bends on Active Normal Faults: Implications for Displacement Versus Length Scaling of Earthquake Ruptures. Journal of Geophysical Research: Solid Earth , 123 (11) pp. 9817-9841. 10.1029/2018JB016732. Green open access

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Abstract

Fault bends, and associated changes in fault dip, play a key role in explaining the scatter in maximum offset versus surface rupture length fault scaling relationships. Detailed field measurements of the fault geometry and magnitude of slip in the 2016–2017 Central Italy earthquake sequence, alongside three examples from large historical normal‐faulting earthquakes in different tectonic settings, provide multiple examples in which coseismic throw increases across bends in fault strike where dip also increases beyond what is necessary to accommodate a uniform slip vector. Coseismic surface ruptures produced by two mainshocks of the 2016–2017 Central Italy earthquake sequence (24 August 2016 Mw 6.0 and 30 October 2016 Mw 6.5) cross a ~0.83‐km amplitude along‐strike bend, and the coseismic throws for both earthquakes increase by a factor of 2–3, where the strike of the fault changes by ~28o and the dip increases by 20–25o. We present similar examples from historical normal faulting earthquakes (1887, Sonora earthquake, Mw 7.5; 1981, Corinth earthquakes, Mw 6.7–6.4; and 1983, Borah Peak earthquake, Mw 7.3). We demonstrate that it is possible to estimate the expected change in throw across a bend by applying equations that relate strike, dip, and slip vector to horizontal strain conservation along a nonplanar fault for a single earthquake rupture. The calculated slip enhancement in bends can explain much of the scatter in maximum displacement (Dmax) versus surface rupture length scaling relationships. If fault bends are unrecognized, they can introduce variation in Dmax that may lead to erroneous inferences of stress drop variability for earthquakes, and exaggerate maximum earthquake magnitudes derived from vertical offsets in paleoseismic data sets.

Type: Article
Title: Coseismic Throw Variation Across Along‐Strike Bends on Active Normal Faults: Implications for Displacement Versus Length Scaling of Earthquake Ruptures
Open access status: An open access version is available from UCL Discovery
DOI: 10.1029/2018JB016732
Publisher version: https://doi.org/10.1029/2018JB016732
Language: English
Additional information: This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Keywords: earthquake, coseismic surface ruptures, fault scaling relationships, fault geometry, seismic moment
UCL classification: UCL
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Earth Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Inst for Risk and Disaster Reduction
UCL > Provost and Vice Provost Offices > UCL SLASH
UCL > Provost and Vice Provost Offices > UCL SLASH > Faculty of S&HS
URI: https://discovery.ucl.ac.uk/id/eprint/10061293
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