11:45 AM - 12:00 PM
[SCG50-11] Source-rupture process of the intraplate earthquake; its diversity related to the fault geometry and damaged fault zone
Keywords:Intraplate earthquake, Waveform inversion, Fault geometry, Supershear rupture, source rupture process
Here we present a kinematic rupture model for the intraplate, Mw 7.5 2018 Palu, Indonesia, earthquake. The 2018 Palu earthquake occurred along the strike-slip Palu-Koro fault zone, which is located around the triple junction of the Australia, Eurasia, and Philippines sea plates. The trace of the surface rupture of the 2018 Palu earthquake, mapped by the Interferometric Synthetic Aperture Rader (InSAR), shows the geometric complexity around the epicenter and south of the Palu bay. We inverted the teleseismic waveforms to resolve both the spatiotemporal evolution of shear slip and the variation of fault geometry by representing slip with five-basis potency-density tensors, without forcing a shear plane to be consistent with a pre-fixed model plane. A possibility of supershear rupture was taken into account by resolving slip in a wide parametric-model space with longer duration of slip-rate function and faster maximum rupture velocity.
The resultant model showed that a rupture front persistently propagated at a high speed (~5 km/s) that exceeds the local shear wave velocity throughout 200-km long within 40 s, but also showed the transient deceleration and acceleration of slip migration, which can be seen as an inchworm walking. The transient deceleration and acceleration of the slip migration was resolved in the area where the strike angle was rotated from the reference-model strike (358°), which also coincides with the geometric discontinuity of the surface rupture resolved by the InSAR analyses. We will then discuss possible roles of geometric discontinuity that develops inchworm-like slip evolution and damaged fault zone that enables long-lived supershear rupture propagation, which may be characteristic factors that control diverse rupture process of the intraplate earthquake.