EVALUATION OF POST-EARTHQUAKE WITH MAGNITUDE OF MW 7.5 IN PALU CITY USING THE PETROGRAPHY, ERT AND CPT

Abstract

A critical element in addressing disaster events is conducting a comprehensive study of the phenomenon caused by the disaster (earthquake). Therefore, a comprehensive study of the material from the disaster site, post-disaster handling, and disaster mitigation is needed to understand the phenomenon that occurs. This report presents preliminary results of field monitoring and surveys from several locations affected by the earthquake in Palu on September 28th, 2018, particularly in the Balaroa area and Anutapura Hospital. The purpose of this study is to evaluate the liquefaction potential of earthquake-affected areas using Electrical Resistivity Tomography (ERT) and Cone Penetration Test (CPT). The specific aspect investigated was the condition of the subsoil after the earthquake tested by ERT and CPT. The ERT test result on Trajectories in Balaroa shows the occurrence of a broken aquifer phenomenon, which causes an increase in the water content in the subsoil above it. Smear slides for petrographic investigation were created after the separation of grain sizes. Quartz, biotite, orthoclase, hornblende, plagioclase, and opaque minerals were among the minerals found. The collapse of the Anutapura Hospital building was possibly caused by the presence of local liquefaction phenomena that occurred in some areas of the hospital, which was proven by overlay between CPT and ERT results. Moreover, site investigation by CPT in the disaster area exhibits that soil in particular depth did not reach a non-liquefiable state after an earthquake, indicated by the value of safety factor, and possibly reliquefied for the next earthquake event.