Reprocessing and analysis of multi-channel seismic data from the northern Okinawa Trough and adjacent shelf

Abstract

The Okinawa Trough is the only modern example of an incipient continental back-arc basin, providing a unique opportunity to study the early processes of continental back-arc opening. Over 7,000 km of multi-channel seismic reflection data from the northern Okinawa Trough and adjacent shelf were reprocessed to interpret the structural characteristics of the area. F-K filtering, wave-equation multiple rejection, and radon filtering were applied to the data to attenuate noises. The sedimentary strata in the East China Sea shelf basin to the west of the Taiwan-Sinzi belt are severely compressed and cut by the Late Miocene unconformity. On the other hand, numerous normal faults cut the sedimentary strata in the western margin of the northern Okinawa Trough to the east of the Taiwan-Sinzi belt, indicating extension; here, the Late Miocene horizon forms a conformable surface. The Taiwan-Sinzi belt probably acted as a buttress against the compressional tectonism that caused uplift and folding in the northern East China Sea shelf basin. The normal faults along the western margin of the northern part of the northern Okinawa Trough dip northwest whereas those along the western margin of the southern part of the northern Okinawa Trough dip southeast. The abrupt along-strike change in the dip orientation of the normal faults may suggest the presence of a NNW-trending transfer fault. The sedimentary strata in the northern Okinawa Trough are older than the Late Miocene, constraining the timing of the onset of the opening of the northern Okinawa Trough probably to the Middle Miocene. The western boundary of the northern part of the northern Okinawa Trough is characterized by the gently deepening seafloor, whereas the western margin of the southern part of the northern Okinawa Trough is characterized by steep boundary faults, suggesting more rapid subsidence in the southern part of the northern Okinawa Trough. The bathymetry of the Okinawa Trough shows contrasting styles across the axial region: very smooth seafloor in the west and rugged seafloor in the east. The rugged seafloor may be due to more active volcanism near the Ryukyu Arc.