INVESTIGATION OF SEDIMENT THICKNESS BENEATH THE MANDALIKA CIRCUIT AND ITS SURROUNDINGS BASED ON MICROTREMOR DATA

Abstract

The Mandalika Circuit, now one of the icons of Indonesian pride, is located on the south coast of Lombok Island. The south coast of Lombok Island is an area where the Indo-Australian plate subducts into the Eurasian plate, known as the subduction zone. Coastal areas dominated by sediment deposits (alluvial) and adjacent to subduction zones are disaster-prone areas, such as damage from earthquakes and liquefaction.  The objective of this research is centered on the analysis of the potential damage due to geological conditions and liquefaction caused by the earthquake. This microseismic method with a total of 51 measuring points scattered around the Mandalika circuit was employed in this research. The microseismic data were measured using a portable three-component seismograph and processed using the horizontal-to-vertical spectral ratio (HVSR) method. HVSR analysis results are presented in terms of natural frequency (f₀), amplification factor (A₀), seismic vulnerability index (K_g), shear wave velocity profile at 30m depth (Vs₃₀), and sediment thickness. Groundwater level data was used to support the potential liquefaction analysis. Based on the Vs₃₀ soil type classification, soft and medium soils dominate the Mandalika International Circuit. Estimates of sediment thickness range from 5 to 90 meters. The Mandalika Circuit and its surrounding area are vulnerable to earthquakes and liquefaction hazards that may potentially decrease to the north or away from the coastline.