Understanding of flow liquefaction phenomena in Palu City from shear wave velocity profiles

Abstract

On 28 September 2018, a strong earthquake (Mw 7.5) struck Donggala Regency triggering flow liquefaction (locally termedNalodo) phenomena in two residential areas in Palu City. Mitigating such an earthquake collateral hazard requires understanding the geological condition controlling such liquefaction. This paper presents a geophysical study to clarify the geological condition controlling theNalodophenomena in Palu City. The objectives of this study were to estimate shear wave velocity (Vs) profiles in theNalodoand non-Nalodosites and evaluate liquefaction potential based on the shear wave velocity profiles. The study involved a series of array microtremor surveys in twoNalodosites and three non-Nalodosites in Palu City. The results show thatVsgenerally increases with depth but varies from one site to another. Based on theVsprofiles, a thick soil layer withVsof less than 175 m/s is present from the ground surface in the Balaroa and Petobo sites. Contrary, this soil layer is detected at a deeper depth in the non-Nalodosites. Based on the liquefaction potential analysis, the near-surface soil layers in the Balaroa and Petobo sites are clearly liquefiable for all the PGA values used in this study. Although deeper soil layers can also be liquefied, no liquefaction occurred in non-Nalodosites because a thick medium soil layer exists near the surface. Thus, a thick soil layer withVsof less than 175 m/s near the ground surface controls theNalodophenomena in Palu City. Further studies to clarify other factors controlling flow liquefaction are recommended.