Surface deformation relating to the 2018 Lake Muir earthquake sequence, southwest Western Australia: New insight into stable continental region earthquakes

Dan J. Clark, Sarah Brennand, Gregory Brenn, Matthew C. Garthwaite, Jesse Dimech, Trevor I. Allen, Sean Standen

Research output: Contribution to journalArticlepeer-review

15 Citations (Scopus)

Abstract

A shallow Mw 5.3 earthquake near Lake Muir in the stable continental region (SCR) crust of southwest Western Australia on the 16 September 2018 was followed on the 8 November by a proximal Mw 5.2 event. Focal mechanisms produced for the events suggest reverse and strikeslip rupture, respectively. Field mapping, guided by Sentinel-1 InSAR data, reveals that the first event produced an approximately 3 km long and up to 0.4-0.6 m high west-facing surface rupture, consistent with reverse slip on a moderately east-dipping fault. The InSAR data also show that the surface scarp relates to a subsurface rupture &tild; 5 km long, bound at its northern and southern extremities by bedrock structures. The November event produced a surface deformation envelope that is spatially coincident with that of the September event but did not result in discrete surface rupture. Almost 900 aftershocks were recorded by a temporary seismometer deployment. Hypocentre locations correlate poorly with the rupture plane of their respective mainshocks but correlate well with regions of increased Coulomb stress. The spatial and temporal relationships between the Mw > 5:0 events and their aftershocks reveals dependencies with implications for how other less well-documented SCR earthquake sequences could be interpreted. Furthermore, the September Mw 5.3 Lake Muir earthquake was the ninth event documented to have produced surface rupture in Australia in historical times. These nine ruptures are located exclusively in the Precambrian non-extended SCR rocks of central and western Australia, and none could have been identified and mapped using topographic signature prior to the historical event. Consistent, though fragmentary, evidence exists from analogous regions worldwide. Our analysis of the Lake Muir earthquake sequence therefore provides constraint on models describing mechanisms for strain accumulation and localized release as earthquakes in non-extended SRC crust.

Original languageEnglish
Pages (from-to)691-717
Number of pages27
JournalSolid Earth
Volume11
Issue number2
DOIs
Publication statusPublished - 30 Apr 2020

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