[S13-4] Earthquake source mechanics IV

[S13-4-04] Intraplate events off Sumatra – 3-D evolution

^○Brian Kennett¹, Alexei Gorbatov², Stewart Fishwick³ (1.The Australian National University, Canberra, Australia, 2.Geoscience Australia, Canberra, Australia, 3.University of Leicester, Leicester, U.K.)

The dominantly strike-slip Mw 7.8 event on 2016 March 2 occurred in the northwestern Wharton Basin in an area with no previously recorded large earthquake. Analysis of the higher-frequency energy radiation (> 0.25 Hz) as a function of time using a suite of global stations, with good azimuthal control, indicates that the event initiated on a nearly east-west fault and then the main energy release was on a conjugate north-south fault. High frequency radiation is emitted through the full thickness of the lithosphere in the main part of the event. Late energy emission comes from depth over a broader area suggesting minor failures at the base of the lithosphere.
A similar behaviour is seen for the 2000 June 18 much further away from the subduction zone. In each case the events occur in a region with slightly lower shear wavespeed than their surroundings, perhaps indicating weakness in the full lithosphere.