ESTIMATION OF RUPTURE DIRECTIVITY, CMT AND EARTHQUAKE TSUNAMI PARAMETERS AND THEIR CORRELATION WITH THE MAIN SOURCE OF THE FIRST TSUNAMI WAVE, SEPTEMBER 28, 2018

he purpose of this study is to analyze the main source of the Palu-Indonesia tsunami based on the direction of rupture, Centroid Moment Tensor (CMT), the tsunami parameters, including the rupture duration (Tdur), the 50 Seconds Exceed Duration (T50ex) and the dominant period (Td) of the earthquake that occurred on September 28, 2018. The method employed in this study involves fitting the rupture duration versus seismic station azimuth graph to estimate the direction of the rupture, the full waveforms inversion method for determining the CMT and the direct procedure method for estimating tsunami parameters. The estimated direction of the earthquake rupture is azimuth 179°, which almost coincides with the Palu Koro Fault (PKF) azimuth. The direction of the earthquake rupture passed below the surface of the seawater in Palu Bay, which could possibly be the main source of the tsunami. The strike and dip of the nodal plane generated by the earthquake are 350° and 64°, respectively, which shows that a vertical displacement pushed seawater vertically in Palu Bay and caused the tsunami. All tsunami parameters from the earthquake exceeded the threshold; therefore, it is very likely that the earthquake was the main source of the first tsunami wave. The estimation results of the rupture directivity, Centroid Moment Tensor, and tsunami parameters are confirmed by inundation data that are qualitatively comparable with the observations.