T. Yatimantoro¹ , J. Murjaya¹ , D. Karnawati¹ , S. Rohadi¹

¹National Seismological Center, Meterological and Geophysical Agency

Abstract:

On Friday, 28 September 2018 (10:02:45 UTC) a large, damaging earthquake occurred in Palu, Central Sulawesi, Indonesia. Based on BMKG analysis, the earthquake has a magnitude Mw 7.4, depth 11 km, and epicenter of 0.2˚S - 119.89˚E. This event caused destructive secondary effects such as a tsunami, landslides, liquefaction, and collapsed structures in many place in Palu city. Slip distribution and Source Time Function (STF) were determined to investigate the causes of the earthquake. The investigation used 37 teleseismic waveforms obtained through IRIS. The result of STF graphic modelling showed that 3 peaks of Moment Rate Function (MRF) appeared during 35 seconds. This MRF is consistent with 3 asperity zones in the fault plane, that consist of 2 asperities near the hypocenter and 1 shallow asperity located around 50 km south of the hypocenter. Those asperities were presumably cracked and became the new sources of shaking while movement of the strike-slip Palu earthquake Mw 7.4 was not yet finished. This phenomena was suspected to cause a submarine landslide that generated the tsunami after the earthquake of Mw 7.4.