Geometry Analysis of Penang Island Faults Based on Satellite Gravity Data

Abstract

Abstract The gravity method is commonly used in geophysics for fault mapping. This method provides an overview of the subsurface density distribution. When applied to fault areas, the density gradient contrast can be used to map the fault geometry structure. The research area for this study is Penang Island, Malaysia, which is predominantly composed of granite. The Penang Island granite formation was created during the Triassic period, approximately 209 to 22 million years ago (Kwan and Yap, 1986). It underwent uplift during the Oligocene-Miocene period, exposing the previously buried granite. The second formation is a quaternary sediment that is believed to have formed during the Pleistocene and Holocene (Kamaluddin, 1990). Penang Island has 14 faults scattered throughout, with 5 main faults in the middle (Ong, 1993). The study aimed to determine the fracture geometry using the gravity method. The analysis revealed two main rock types: granite with a density range of 2-2.8 gr/cm3 and quaternary sediment with a density of 1.85-2 gr/cm3. Fault geometry analysis was conducted using the SVD method on four passages in Penang Island to identify fault types. The results showed six normal faults and seven thrust faults. Faults No. 3, 4, 8, 9, 12, and 13 are predicted to be normal faults, while Faults No. 1, 2, 5, 7, 10, 11, and 14 are predicted to be thrust faults. The dominant direction of the fault is North-South. The fault geometry on North Pluton has an average depth of 250 m with an average dip angle of 68°, while the fault on South Pluton has a depth of over 400 m with an average dip angle of 65°.