Liquefaction Potential in Waterfront Area of Labuan Bajo Based on Earthquake Return Period

The assessment of liquefaction potential after an earthquake is important to understanding earthquake risks to coastal infrastructure, thereby making it a secondary impact of seismic events. Therefore, this research compared liquefaction potential in Labuan Bajo waterfront area using various parameters, with a focus on earthquake return period to gauge liquefaction conditions in different seismic scenarios. Three earthquake scenarios with return period of 50 years, 100 years, and 2500 years were analyzed and used to evaluate potential for liquefaction under varying seismic conditions. A semi-empirical procedure was used to evaluate liquefaction potential in ten boreholes situated along Labuan Bajo waterfront. This assessment considered factors such as the Cyclic Stress Ratio (CSR) and Cyclic Resistance Ratio (CRR). Peak Ground Acceleration (PGA) and moment magnitude values were derived from the seismic code provided by the Ministry of Public Works and Housing of Indonesia. Meanwhile, the moment magnitude used for frequent earthquake was determined based on historical earthquake data around Labuan Bajo using Zmap 7.1. The results showed that liquefaction occurred with an SPT (Standard Penetration Test) value of 8, 18 and 31 for 50, 100 and 2500-year return period. When comparing Liquefaction Potential Index (LPI) values for each location, it became evident that BH-03 and BH-04 exhibited high values of 38.69 and 39.86, respectively, in the 50-year return period scenario. By using three parameters, the locations with high liquefaction potential can be determined precisely and mitigation can be planned early.