The connection of coloumb stresses and aftershock imparted by the 18 August 2012 Mw 6.3 Palu-Koro earthquake

Abstract

Palu-Koro fault is exist in Central Sulawesi fault system which consists of complex left-lateral strike-slip fault zones located within the triple junction area between the Pacific, Indo-Australian and Eurasian plates. Understanding the occurrence or characteristics of an earthquake can be done by the analysis of ’Butterfly Pattern’ which is one description of the relationship between Static Coulomb stress transfer and aftershock sequence of large earthquake. An earthquake was occurred at 18th August 2012 in Palu, Central Sulawesi Indonesia. With hypocenters position on the land and has a strike-slip mechanism, this Mw 6.3 earthquake caused several damage around Palu city. In this study, we examined the relationship between static coulomb stress and the distribution of Palu Koro earthquake aftershock on August 18, 2012. We do earthquake relocations with using double difference and waveform cross correlation together to provide a better, precisely and refined aftershocks distribution. To provided a better phase onset observation, P and S arrival times were manualy picked using SAC programs (Seismic Analysis Code) and we generated bandpass filtering 2-8 Hz previously to displayed the local seismic signal clearly. The predicted Static Coloumb stress were generated by Coloumb3.3 program. We succesfully relocated 86 events and constrained the RMS residual < 10 ms. Unexpected, we obtained a relative small correlation between relocated aftershock and Static Coloumb Stress generated by 18 August 2012 Mw 6.3 Palu-Koro earthquake. Seemingly, the increased stress field from the mainshock uncapable to raising aftershock significantly. In further, transfered only 0.5 bar of stress which is very small compared to local site stress and not too affected to background seismicity. To analizing the possible hazards and risks from the next earthquake sequence should be better examining another factor than predicted Static Coloumb stress alone.