Changes in Groundwater Level Possibly Encourage Shallow Earthquakes in Central Australia: The 2016 Petermann Ranges Earthquake

Abstract

The mechanisms of unusual shallow intraplate earthquakes that occasionally occur in stable cratons remain poorly understood. Here we analyze coseismic and postseismic displacement fields associated with the 2016 Petermann Ranges earthquake in central Australia using interferometric synthetic aperture radar data. The earthquake ruptured a previously unmapped fault and was dominated by thrust slip motion of up to 95 cm within the top 3 km of the crust. Postseismic deformation analysis suggests that a combination of poroelastic rebound and afterslip are responsible for the observed signals. The inferred afterslip overlapping spatially with the coseismic rupture highlights that the postseismic slip is coupled with the pore fluid flow around the fault zones. Analysis of historic groundwater‐level changes suggests that shallow seismicity around the Petermann Ranges may have been triggered by environmental stress perturbations due to the fluctuations of groundwater level; however, it is not easy to document statistical significance of this correlation.

Surface Rupture and Distributed Deformation Revealed by Optical Satellite Imagery: The Intraplate 2016 Mw 6.0 Petermann Ranges Earthquake, Australia

“…We generated a coseismic interferogram from the JAXA ALOS‐2 PALSAR L‐band instrument (15 December 2015 to 14 June 2016, ascending orbit). This analysis largely reproduces previously published results (Polcari et al, ; Wang et al, ). Details on data processing are provided in the electronic supplement.…”

“…Deformation is asymmetric, with more deformation in the hanging wall and less in the footwall. This signal was previously recognized in the residuals from a slip model derived from InSAR (Wang et al, 2019). The ICP analysis in our investigation quantifies the near-fault signal and shows that the deformation cannot be explained solely by elastic deformation and displacement corresponding with fault scarps.…”

“…The epicenter was located ~120 km west‐southwest of Yulara (Uluru) in the sparsely populated southwest corner of the Northern Territory, Australia (Figure ). InSAR modeling suggests that the source fault dips 22–39° to the northeast and that the earthquake produced largely reverse motion with a minor left‐lateral component of slip (Polcari et al, ; Wang et al, ). Maximum slip derived from InSAR modeling was ~1 m and occurred at shallow depths, <3–4 km (Polcari et al, ; Wang et al ).…”

“…InSAR modeling suggests that the source fault dips 22-39°to the northeast and that the earthquake produced largely reverse motion with a minor left-lateral component of slip (Polcari et al, 2018;Wang et al, 2019). Maximum slip derived from InSAR modeling was~1 m and occurred at shallow depths, <3-4 km (Polcari et al, 2018;Wang et al 2019). Polcari et al (2018) conclude that the causative fault is a back thrust that soles into the NW-striking, SW dipping Woodroffe thrust fault, a structure associated with the late Proterozoic to Cambrian Petermann orogeny (Camacho et al, 1995;Edgoose et al, 2004).…”

“…However, postseismic afterslip typically composes only a small percentage of overall coseismic surface displacement (e.g., Kaneko & Fialko, 2011). In this case, Wang et al (2019) document a maximum of 10 cm of postseismic afterslip, which is approximately 10-15% of the total.…”