Rupture directivity and fault plane determination from analysis of rupture duration using broadband P-waves of the September 2018 M _w 7.5 Palu, Indonesia earthquake

Abstract

The aim of this study is to determine earthquake rupture directivity and fault plane of the 28 September 2018 M w 7.5 event in Palu, Indonesia. The data used in the current study were all acquired from broadband seismograms recorded by a network of 56 seismic stations. The method included analysis of rupture duration, where T dur was calculated using the vertical component of P-waveforms downloaded from IRIS site at http://ds.iris.edu/wilber3/find_event. For all stations involved in the T dur calculations, the largest distance between the epicenter and the corresponding station was estimated to be 40° from the azimuth station. The direction of the rupture indicated fault plane geometry of the source. The rupture directivity was found to be at azimuth 179°, in good agreement with the Palu Koro Fault azimuth. The finding implies that the direction of the earthquake rupture passed below the sea surface of Palu Bay, which could be the main source of the tsunami.