Back-projection results for the M_w7.5, 28 September 2018 Palu earthquake-tsunami

Abstract

A back-projection technique allows seismologists to analyse rupture properties once seismic signals from a dense array of seismic networks are available. The observed waveforms are then traced back in space and time to the source region of an earthquake under investigation. In this study, the method utilised the back-projection image of the recorded high-frequency P-seismic waveforms filtered at 0.25-1.0 Hz by Multiple Signal Classification (MUSIC) processing to estimate the extent and the spread of earthquake rupture propagation of the M w 7.5 Palu event on 28 September 2018, generating a severe tsunami. This study aims to estimate rupture duration, its extent (the distance over which rupture propagates) and the corresponding speed, and rupture directivity (where most of the seismic energy propagates). The results revealed that the front of rupture propagates slightly offset southward at about 2.9 km/s over a distance of ~140 km away from the epicentre for about 49 s before slowing down at much smaller amplitudes after reaching the south end of Palu Bay. This finding is consistent with an NNW-SSE orientation of the active Palu-Koro Fault lying along the bay, suggesting that the strong ground motion is associated with the fault activities. This study has therefore substantial implications for enhanced earthquake and tsunami early warnings, helping the government and local authority build community resilience by warning people at risk from future possible earthquake and tsunami hazards.

Continual Advance in Earth Physics Research Group at Physics Study Program, Unesa: What’s new and the next step

“…Other projects for both the EPRG members and final year students include kinematic examination of earthquake rupture processes using the so-called multiple signal classification of back-projection imaging (MUSIC BPI) [19,20], referred to seismic signal processing with high resolution that relies on the signal coherence from P-seismic waveforms recorded by a dense seismic array and filtered at high frequency of 0.25-1.0 Hz. Applied to the case of the 2018 Palu-Donggala earthquake that in turn generated a locally propagating tsunami inside Palu Bay, this technique was successful to demonstrate a NNW-SSE trend in the aftershock data of the event [21]. Similarity found in the rupture direction to the lineament of the strike-slip Palu-Koro fault suggested that the 2018 Palu tsunami-earthquake event is partly associated with the active fault, consistent with previous work [22,23].…”