Identification of Magnetic Anomaly at Geothermal Subsurface Area PLTP Sarulla Unit I Pahae Jae, North Sumatera, Indonesia

This research was done entitled Identification of Magnetic Anomalies at Geothermal Subsurface Area at PLTP Sarulla Unit I Pahae Jae, North Tapanuli. This research was conducted to find out the dispersion pattern of earth magnetic anomaly based on its magnetism and to know the rock structure based on susceptibility value in the geothermal area. The measurements of Total magnetic field using Proton Precission Magnetometer (PPM) Elsec 770 type, Global Position System (GPS) for positioning and geological compass for north direction orientation. The data were collected randomly with the number of points obtained as much as 50 measuring point, then data analysis was done by using surfer 11 to get contour map and Mag2DCfor windows maps to get the magnetic anomaly cross section. The results showed that the magnetic anomaly value had the lowest value of 34,4358 nT and the highest value 144,789 nT moving from North toward East. While the results of quantitative interpretation of A'A model show sedimentary rock with k value (0.0035 x 103, 00059 x 103, 00061 x 103), and esite lava with k value (0.0277 x 103, 0.0241 x 103) and basalt with k value (0.2437 x 103).