Does a damaged fault zone mitigate the near-field landslide risk during supershear earthquakes?—Application to the 2018 magnitude 7.5 Palu earthquake

Elif Oral, Huihui Weng, & Jean-Paul Ampuero

Submitted July 24, 2019, SCEC Contribution #9253, 2019 SCEC Annual Meeting Poster #145 (PDF)

Poster Image: 
The 2018 Mw 7.5 Palu earthquake ruptured a strike-slip fault with a length of 150 km and struck the city of Palu severely by triggering many catastrophic phenomena in the proximity of the fault. Devastating tsunamis in the Palu Bay are triggered shortly after the earthquake, possibly by coseismic vertical displacements, resonance due to narrow bay geometry and submarine landslides. Coseismic landslides were also reported in the rupture direction. The rupture reached to an early steady state with a sustained velocity of 4.1 km/s, exceeding the S-wave velocity, Vs. Conventionally supershear ruptures propagate stably at speeds between Eshelby’s speed (sqrt(2)Vs) and the P-wave velocity ; the observed speed implies an unstable regime. Such a low rupture speed was interpreted possibly by the presence of a low-velocity damaged fault zone (LVFZ). In this study, first, we analyse the effect of LVFZ on rupture development by accounting for the seismogenic width and different initial conditions. Furthermore, we investigate the effects of rupture speed and the LVFZ on ground motion. The preliminary results confirm the possibility of a steady-state supershear rupture at the observed velocity due to the LVFZ; and, a slower rupture speed results in an expected attenuation of ground motion and a reduction in landslide risk. Moreover, only the LVFZ leads to amplification of near-field ground motion, particularly on the frequency band of (1 - 2) Hz, compared to a homogeneous fault medium with the same rupture speed. Our findings support the significance of rupture details (such as rupture velocity and LVFZ) on near-field ground motion and related landslide triggering.

Key Words
supershear ruptures, damaged-fault zones, near-field ground motion, dynamic rupture modelling

Citation
Oral, E., Weng, H., & Ampuero, J. (2019, 07). Does a damaged fault zone mitigate the near-field landslide risk during supershear earthquakes?—Application to the 2018 magnitude 7.5 Palu earthquake. Poster Presentation at 2019 SCEC Annual Meeting.


Related Projects & Working Groups
Fault and Rupture Mechanics (FARM)