A Strike-Slip Fault System Trending NE in and Around the Northwestern Corner of the West Philippine Basin

Abstract

The nature of the plate boundary between the Eurasian and PhilippineSea Plates changes from subduction to collision along the northern extension of the Manila Trench,north of 21°N,offshore southwest Taiwan.Todetermine whether the collision-formed deformation front passes throughthe Tainan Basin,a region of petroleum interest,seismic profiles that crossa proposed”deformation front”are interpreted.However,only a majornormal fault,that is a growth fault that forms the northwestern side of atilted horst structure can be positively identified.The nature of this normal faulting is also supported by the modeling of gravity and magnetic data.The observation of only tensional faults in the Tainan Basin suggeststhat the deformation front is located to the southeast,near Kaohsiung oreven further to the south.The economic basement in the Tainan Basin region,defined as pre-Tertiary rocks that underlie the thick Tertiary sequences along the seismiclines we examined,maintains a depth of 3 to 5 km in a tilted horst-like zone,known as the Central Uplift,and deepens in either direction away from it.The thick Tertiary deposits provide excellent potential for source rock andseal.Petroleum exploration in this area should be directed toward generating prospects related to normal faulting if structural closures can be identified.