The importance of gravity data for estimating and identifying the sediment thickness of subsurface structure around Majene Sulawesi Barat

Gravity method is one of the geophysical methods based on a gravity anomaly that arises due to a mass tight variation of the earth’s subsurface material constituents. Research with power spectral analysis of gravity anomaly data has been widely done for sediment thickness estimation. When the Mw 6.2 Majene earthquake occurred on January 15 2021, we want to know the estimation of sediment depth as well as the identification of subsurface structures in the region. The data used in this study is GGMPlus gravitational data and processed by transforming data from distance domains into wave number domains utilizing fourier transformation. 3D modeling is carried out using Grav3D software to determine subsurface structures in the region. The results of the study using fourier transformation showed that the estimated thickness of sediment amounted to 610.7 meters. Based on the east-west and north-south cross sections, the average estimated thickness of sediment is 557.4 meters and 664 meters, respectively. In short, the deeper sediment thickness of the sediment layer, will cause the amplification factor, that’s make strengthening of the seismic waves so that the vibrations on the surface are getting stronger and make severe damage. Then, 3D model shows us that the subsurface structure is dominated by clay stone because the value of rock density distribution ranges from 1.6 gr/cm3 to 2.4 gr/cm3 with a density contrast value of -0.98 gr/cm3 to 1.9 gr/cm3.