A gravity survey of the Tuban Karst Area was established to map subsurface structures that control groundwater flow. However, the research is still limited to the surface area. To complete the research of the area, gravity data were collected at 70 stations using the Scintrex CG-5 gravimeter. Data processing uses a Gaussian Low-pass filter and forward modeling. To show correlation between gravity method and geological studies, a sample test of 18 rock samples from representative formations have an average rock density value of 2.61 g/cm3. Interpretation of the residual anomaly map has a value of -9.5 to 6.7 mGal. The low anomaly zone is -9.5 to -2.5 mGal which is Ngrayonng Formation. Medium anomaly zone is -2.5 to 1.4 mGal which is Paciran and Bulu Formation. High anomaly zone is 1.9 to 6.7 mGal which is Wonocolo, Mundu, Ledok, and Lidah Formations. This study shows that the dominant orientation of lineament in the NW-SE direction, which is indicated by anomaly contrasts in the Paciran and Bulu Formations. The orientation of lineament is assumed to control Krawak groundwater flow. The forward modeling has been applied to the gravity data and provides information about the subsurface of geological formations. The order of formation layers from oldest to youngest is Tawun, Ngrayong, Bulu, Wonocolo, and Paciran respectively. There is a dip-slip fault with a slope close to 90o. This study provides new information for better understanding of the subsurface structures that control groundwater flow using gravity data of the Tuban Karst Area.

Topics
Gravimeter, Gravitation, Geophysical techniques, Linear filters, Data processing, Java
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