Preliminary Assessment of Liquefaction Vulnerability using Microtremor Analysis in North Lombok

One of the disasters associated with the Mw 6.9 Lombok earthquake on August 5, 2018 was liquefaction. The liquefaction took the form of sand boil and lateral spreading, causing damage to buildings, docks, and wells in the North Lombok region. Therefore, liquefaction vulnerability assessment in this region is necessary to prevent future damage. This study presents an assessment of the liquefaction vulnerability in North Lombok using microtremor analysis. Single-station microtremor measurements were conducted at 37 sites, including around the liquefaction sites caused by the 2018 event. The soil susceptibility index (Kg) was estimated from these recordings using the horizontal-to-vertical spectral ratio (HVSR) and compared with geological conditions and liquefaction history. A comparison of the spatial distribution between Kg values and liquefaction sites shows that almost all liquefaction events occur at Kg values greater than 6. Our results also show that liquefaction events occur mostly in coastal areas, illustrating a strong influence of groundwater level on liquefaction potential. This research finds that microtremor analysis combined with groundwater level information can adequately illustrate the liquefaction potential of an area. Therefore, this study can also identify highly liquefiable zones in North Lombok.