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

Abstract

The 23rd March 2012 Mw 5.2 Pukatja earthquake produced an arcuate surface rupture 1.6 km long with a maximum vertical offset of 0.48 m. We reclassify its length to 1 km based on application of orientation and kinematic criteria used previously to measure other historic Australian surface ruptures. Epicentres are poorly constrained and inaccurate, located up to 17 km from the surface rupture with no reported uncertainties. Published interpretations of available seismological data do not provide constraints on rupture processes, hypocentre depth, and fault geometry. Sections of the surface rupture match the strike and dip of an intrusive contact as mapped in the field < 500 m from the rupture. This feature is evident as a linear magnetic anomaly co-located and parallel to the surface rupture, suggesting a strong bedrock control on the location and orientation of surface rupture. There is no topographic expression of prior rupture, and a shallow hand-dug trench shows evidence of only the historic rupture. However, erosion rates estimates suggest that residency time of any prior ruptures in the landscape may have been < 50 kyrs, and hence topographic evidence may have been removed prior to deposition of overlying sediments. Investigations of rock falls surrounding the historic rupture may provide estimates of strong ground motion recurrence in the absence of other paleoseismic data.

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

“…Detailed summaries of the geology, seismology, surface rupture and palaeoseismology for the eleven considered historical surface ruptures from 1968 to 2016 are available as seven EarthArXiv reports ( [120][121][122][123][124][125][126]). Figures and data in these reports include available geological maps, geophysical maps, borehole data, surface rupture maps, displacement data, and available palaeoseismic trench logs.…”

“…The Marryat Creek, Pukatja and Petermann events occurred within the Mesoproterozoic Musgrave Block (Figure 1) within 0-10 km of major terrane boundaries. The Tennant Creek ruptures extend across the boundary of the Proterozoic Warramunga Province and Neoproterozoic-Cambrian Wiso Basin (Figure 1) (summary of all regional geology in Table 3, comprehensive details in EarthArXiv reports [120][121][122][123][124][125][126]). Granitic gneiss, migmatite, mylonite, granulite, and/or amphibolite basement rock is observed in trenches or outcrop at <1 m depth at multiple locations along the Petermann (Figure 2), Pukatja, Marryat Creek (Figure 2), Cadoux and Meckering ruptures.…”

“…This may relate to dip measurement difficulties for heavily weathered bedrock. (Summary of basement/bedrock in Table 4, comprehensive details in EarthArXiv reports [120][121][122][123][124][125][126]).…”

“…Uncertainties listed in Table 5 include published uncertainties or an assigned value of ± 10 km where no uncertainties are available [102]. Epicenters with lower uncertainties are derived using a variety of relocation methods including extra analysis (e.g., InSAR slip distributions, joint hypocenter determination) or extra data (e.g., surface rupture location, aftershocks from temporary seismometer arrays) (comprehensive details in EarthArXiv reports [120][121][122][123][124][125][126]). The epistemic uncertainty relating to the quality of velocity models used to locate epicenters is unconstrainted but appears to be one of the major sources of inaccurate locations where instrumentation is particularly sparse.…”

“…3 Centroid moment tensor depth, preferred value from publication. 4 Earthquake within 6 months and 50 km of epicenter (affected by catalogue completeness for very remote events, see EarthArXiv reports ( [120][121][122][123][124][125][126]) for details). 5 Earthquakes (n > 5) within 10 years and 50 km of the epicenter (affected by catalogue completeness for very remote events, see EarthArXiv reports for details).…”