Fault Structure Interpretation on the Western Part of East Java Using Second Vertical Derivative

The National Earthquake Center (PusGeN) in 2017 stated that East Java was traversed by several active faults that extended towards Bali and Flores. The gravity research was carried out to map the fault structure in the western part of East Java. Gravity method is applied to identify subsurface geological structures by utilizing variations in Earth's gravity caused by differences in density of subsurface rocks. The processed data is satellite gravity data (TOPEX) as many as 110 data spread in Lamongan, Gresik, and Surabaya City. Gravity Topex is a Geodesy satellite altimeter launched by NASA to measure the altitude of the satellite above the closest sea surface point to a very high precision. Gravity data that collected from Topex/Poseidon satellite are already processed into free air anomaly, further, it is performed Bouguer Correction and Terrain Correction, resulting in Bouguer Anomaly data which is then filtered using Second Vertical Derivative (SVD). The results of SVD 2-D modeling have a high level of accuracy because the faults are well identified and highly correlated with the PuSGeN faults map (2017). The curve of the slice profiling results on the Surabaya Fault shows that the maximum value of SVD is 0.1 mGal/m² and the minimum value is 0.2 mGal/m² which is identified as a reverse fault. The curve of the slice profiling results on the Waru Fault shows that the maximum value of SVD is 0.2 mGal/m² and the minimum value is 0.3 mGal/m² which is identified as a reverse fault.