Surface-Rupturing Historical Earthquakes in Australia and Their Environmental Effects: New Insights from Re-Analyses of Observational Data

Abstract

We digitize surface rupture maps and compile observational data from 67 publications on ten of eleven historical, surface-rupturing earthquakes in Australia in order to analyze the prevailing characteristics of surface ruptures and other environmental effects in this crystalline basement-dominated intraplate environment. The studied earthquakes occurred between 1968 and 2018, and range in moment magnitude (Mw) from 4.7 to 6.6. All earthquakes involved co-seismic reverse faulting (with varying amounts of strike-slip) on single or multiple (1–6) discrete faults of ≥ 1 km length that are distinguished by orientation and kinematic criteria. Nine of ten earthquakes have surface-rupturing fault orientations that align with prevailing linear anomalies in geophysical (gravity and magnetic) data and bedrock structure (foliations and/or quartz veins and/or intrusive boundaries and/or pre-existing faults), indicating strong control of inherited crustal structure on contemporary faulting. Rupture kinematics are consistent with horizontal shortening driven by regional trajectories of horizontal compressive stress. The lack of precision in seismological data prohibits the assessment of whether surface ruptures project to hypocentral locations via contiguous, planar principal slip zones or whether rupture segmentation occurs between seismogenic depths and the surface. Rupture centroids of 1–4 km in depth indicate predominantly shallow seismic moment release. No studied earthquakes have unambiguous geological evidence for preceding surface-rupturing earthquakes on the same faults and five earthquakes contain evidence of absence of preceding ruptures since the late Pleistocene, collectively highlighting the challenge of using mapped active faults to predict future seismic hazards. Estimated maximum fault slip rates are 0.2–9.1 m Myr-1 with at least one order of uncertainty. New estimates for rupture length, fault dip, and coseismic net slip can be used to improve future iterations of earthquake magnitude—source size—displacement scaling equations. Observed environmental effects include primary surface rupture, secondary fracture/cracks, fissures, rock falls, ground-water anomalies, vegetation damage, sand-blows / liquefaction, displaced rock fragments, and holes from collapsible soil failure, at maximum estimated epicentral distances ranging from 0 to ~250 km. ESI-07 intensity-scale estimates range by ± 3 classes in each earthquake, depending on the effect considered. Comparing Mw-ESI relationships across geologically diverse environments is a fruitful avenue for future research.

Surface rupture and shallow fault reactivation during the 2019 Mw 4.9 Le Teil earthquake, France

“…Similar events have been described in normal and strike-slip environments as well, for instance in Peru (1986 M w 5. 24,31 . The LRF was not previously identified as potentially active 5 given that it does not display noticeable instrumental seismicity or geomorphologic expression that would suggest measurable tectonic activity since the Oligocene.…”

“…ref. 39 ), putting forward the possible one-off character of such earthquakes (such as in Australia 24 ). Genti et al 40 suggest that the present local stress field could be related to the uplift of the Massif Central and the Alps induced by erosional and/or post-glacial rebound processes (see also refs.…”

“…The preliminary InSAR analysis (see Fig. 3) was crucial to guide surface rupture investigations as has been demonstrated in similar studies [22][23][24] . Given the high density of vegetation that covers a large part of the area, we first focused on roads and paths crossing the InSAR discontinuity and found spot evidences of surface rupture.…”

Review paper: The 23rd March 2012 Mw 5.2 Pukatja surface rupturing earthquake, Australia

“…A review of all historic Australian surface rupturing earthquakes (King et al, 2019) (in review), found most published lengths for historic ruptures were derived from a simplification of rupture lengths rather than a direct measure of the mapped surface rupture trace. Conversely, the published length of the Pukatja rupture by Clark et al (2014) is derived from a near exact measure of the visible surface rupture without any simplification (Figure 6a,b), making it anomalous within the literature.…”

Use of Macroseismic Intensity Data to Validate a Regionally Adjustable Ground Motion Prediction Model

“…The basic idea of the ESI is to make use of traces of geological and/or geomorphological nature that have been left behind by primary and secondary surface ruptures and mass movements, so generated by large magnitude earthquakes to post-estimate the intensity of the hazard and the magnitude of the event [71]. Example applications of the ESI scale can be found in references [71][72][73][74][75]. Results reported in reference [73] indicate that incorporating ESI data into probabilistic/deterministic seismic hazard analysis can result in significant changes to the modelled PGA values.…”