Paleoseismology of the 2016 M_W 6.1 Petermann earthquake source: Implications for intraplate earthquake behaviour and the geomorphic longevity of bedrock fault scarps in a low strain‐rate cratonic region

Abstract

The 20 May 2016 MW 6.1 Petermann earthquake in central Australia generated a 21 km surface rupture with 0.1 to 1 m vertical displacements across a low‐relief landscape. No paleo‐scarps or potentially analogous topographic features are evident in pre‐earthquake Worldview‐1 and Worldview‐2 satellite data. Two excavations across the surface rupture expose near‐surface fault geometry and mixed aeolian‐sheetwash sediment faulted only in the 2016 earthquake. A 10.6 ± 0.4 ka optically stimulated luminescence (OSL) age of sheetwash sediment provides a minimum estimate for the period of quiescence prior to 2016 rupture. Seven cosmogenic beryllium‐10 (10Be) bedrock erosion rates are derived for samples < 5 km distance from the surface rupture on the hanging‐wall and foot‐wall, and three from samples 19 to 50 km from the surface rupture. No distinction is found between fault proximal rates (1.3 ± 0.1 to 2.6 ± 0.2 m Myr−1) and distal samples (1.4 ± 0.1 to 2.3 ± 0.2 m Myr−1). The thickness of rock fragments (2–5 cm) coseismically displaced in the Petermann earthquake perturbs the steady‐state bedrock erosion rate by only 1 to 3%, less than the erosion rate uncertainty estimated for each sample (7–12%). Using 10Be erosion rates and scarp height measurements we estimate approximately 0.5 to 1 Myr of differential erosion is required to return to pre‐earthquake topography. By inference any pre‐2016 fault‐related topography likely required a similar time for removal. We conclude that the Petermann earthquake was the first on this fault in the last ca. 0.5–1 Myr. Extrapolating single nuclide erosion rates across this timescale introduces large uncertainties, and we cannot resolve whether 2016 represents the first ever surface rupture on this fault, or a > 1 Myr interseismic period. Either option reinforces the importance of including distributed earthquake sources in fault displacement and seismic hazard analyses.

Exploring Australian hazard map exceedance using an Atlas of historical ShakeMaps

“…There is growing evidence to support the notion of “one-off” ruptures in cratonic regions of Australia (Clark et al, 2020; King et al, 2021). Therefore, we may expect that large infrequent earthquakes (possibly exceeding magnitude M W 7.0) could occur in an unanticipated location that is currently characterized by low seismicity and seismic hazard.…”

Reactivation of Non‐Optimally Orientated Faults Due to Glacially Induced Stresses

“…However, such type of reactivation would likely only be the case for faults with a more optimal orientation in the prevailing background stress field. On another note, Olesen, Olsen, et al (2021) and Olesen, Steffen, and Sutinen (2021) suggested that reactivations in Northern Europe that happened a few thousand years after the end of deglaciation could be related to ordinary intraplate seismicity as seen in other areas that were not loaded by an ice sheet in the recent past (e.g., Australia, T. R. King et al, 2021), or not solely be due to GIA. More research is needed to understand the occurrences of these earthquakes, for example, with a more realistic GIA model and consideration of GIF orientation parameters and defined background stress regime.…”

Not too old to rock: ESR and OSL dating methods reveal Quaternary activity of the Periadriatic Fault

“…Instrumental seismicity does not necessarily help to identify active faults, and geodetic monitoring may fail to recognize active fault segments in case of locked faults and low deformation rates. The problem may be exacerbated by long or unknown recurrence rates of large earthquakes in regions with low overall deformation rates such as the Alps and the Dinarides (Cheloni et al, 2014;Hintersberger et al, 2018;Grützner et al, 2021;Oswald et al, 2022), or intra-continental regions (e.g., 1811-1812 New Madrid earthquakes; Tuttle et al, 2002;2001 Gujarat earthquake; Rajendran et al, 2008Rajendran et al, 2016 Peterman Ranges Earthquake; King et al, 2021). To date, there is no single de nition for an "active fault".…”