The 2 March 2016 Wharton Basin M_w 7.8 earthquake: High stress drop north‐south strike‐slip rupture in the diffuse oceanic deformation zone between the Indian and Australian Plates

Abstract

The diffuse deformation zone between the Indian and Australian plates has hosted numerous major and great earthquakes during the seismological record, including the 11 April 2012 Mw 8.6 event, the largest recorded intraplate earthquake. On 2 March 2016, an Mw 7.8 strike‐slip faulting earthquake occurred in the northwestern Wharton Basin, in a region bracketed by north‐south trending fracture zones with no previously recorded large event nearby. Despite the large magnitude, only minor source finiteness is evident in aftershock locations or resolvable from seismic wave processing including high‐frequency P wave backprojections and Love wave directivity analysis. Our analyses indicate that the event ruptured bilaterally on a north‐south trending fault over a length of up to 70 km, with rupture speed of ≤ 2 km/s, and a total duration of ~35 s. The estimated stress drop, ~20 MPa, is high, comparable to estimates for other large events in this broad intraplate oceanic deformation zone.

Rupture process of the 2016 Wharton Basin strike‐slip faulting earthquake estimated from joint inversion of teleseismic and tsunami waveforms

“…This rupture front speed estimate is consistent with that estimated by Lay et al [2016], although their fault plane is dipping eastward. The 2016 Wharton Basin earthquake is estimated to have a north-south striking westward dipping plane.…”

“…Results from joint inversions using various rupture front speeds indicate that the rupture model with a front speed of 2.0 km/s gives the best match to both teleseismic and tsunami waveforms. This rupture front speed estimate is consistent with that estimated by Lay et al [2016], although their fault plane is dipping eastward. The total seismic moment is estimated from the joint inversion as 7.69 × 10 20 Nm (M w 7.9).…”

“…The fault plane orientation of this earthquake is not obvious because of no prominent structure from the bathymetry at the epicenter, although nearby fracture zones have north-south orientation [Lay et al, 2016]. The fault plane orientation of this earthquake is not obvious because of no prominent structure from the bathymetry at the epicenter, although nearby fracture zones have north-south orientation [Lay et al, 2016].…”

“…The GCMT and WCMT solutions suggest that the fault is almost vertical and has four possibilities of dipping direction. Various seismic analyses including aftershock, backprojection, surface wave directivity analyses, and finite fault modeling for the 2016 event have been done in a previous study [Lay et al, 2016]. They estimated a rupture model for the earthquake with a strike of 5°, a dip of 79°, an average rake of 5.8°(NS striking and eastward dipping), and rupture speed of less than 2 km/s.…”

“…In this study, we use both teleseismic body waves and tsunami waveforms in a joint inversion to estimate the kinematic rupture process of the 2016 Wharton Basin strike-slip earthquake. The fault plane orientation of this earthquake is not obvious because of no prominent structure from the bathymetry at the epicenter, although nearby fracture zones have north-south orientation [Lay et al, 2016]. Therefore, we evaluate the four possible fault geometries from the GCMT and WCMT solutions by teleseismic inversion and tsunami simulation to first determine the fault geometry of the earthquake.…”