LASEM FAULT MODELING IN PATI REMBANG AREA USING GRAVITY METHOD BASED ON TOPEX SATELLITE DATA

Abstract. Research on Lasem fault modeling has been carried out to analyze the location of the Lasem fault indication. The Lasem fault is indicated in 3 zones, namely the Rembang zone, Randublatung depression zone and Semarang-Rembang depression zone. Lasem fault is a fault located in the Pati-Rembang area which is an active fault and is close to the Semarang area. This research uses the gravity method as a basic understanding. The data uses obtained through the TOPEX/POSEIDON website. The data obtained were 154 measurement points at coordinates 111000' BT (E) 111013' BT (E) and 6040' LS (S) 6050' LS (S). The results obtained on TOPEX/POSEIDON are data of latitude and longitude coordinates, elevation and free air anomaly correction values. After that, further correction is made in the form of bouguer correction and terrain correction so that the complete bouguer anomaly value is obtained. The complete bouguer anomaly data is analyzed by spectrum with the results of depth estimation for the anomaly. Then an upward continuation is carried out to separate regional anomalies and residual anomalies. After that the gradient analysis filter, eulerdeconvolution, 3D and 2D modeling are done. Gradient analysis filter in the form of first horizontal gradient with the results in the form of fault indications and second vertical derivatives to determine the type of fault that is strike-slip fault. Euler deconvolution is used to determine the estimated subsurface depth with yields of up to 5000 m below sea level. 3D modeling is carried out to see fault indications which result that faults can be seen from depths of 1200 m to 4000 m. 2D modeling results show the types of rocks in the form of claystone, sandstone, limestone, and andesite, respectively the rocks have a density of 2.21 gr/cm 3 , 2.35 gr/cm 3 , 2.55 gr/cm 3 and 2.6 gr/cm 3 . Keywords—Lasem fault, gravity method, gradient analysis, euler analysis, 3D and 2D modeling..