Reflection seismology in the Southern Ayu Trough, a slow-spreading divergent boundary

Abstract

A multichannel seismic survey was conducted in the southern Ayu Trough which is the only spreading boundary between the Philippine Sea and Caroline plates. The seismic system used in this study comprises of 2.46-l sleeve gun and a 12-channel streamer with a group interval of 6.25 m. Migration technique was used to analyze seismic velocity, and poststack depth migration was applied to the stacked data. The sediment thickness obtained from the depth section tends to increase with distance from the spreading axis. Sedimentation rates are poorly constrained in the study area. The apparent half-spreading rates estimated from the sediment thickness and sedimentation rate from DSDP hole on the caroline plate are 4.7 mm/yr and 7.9 mm/yr at 1°24'N and 0°42'N, respectively, which are faster than previously suggested. On the basis of new oblique spreading geometry, the recalculated spreading rates are 5.4 mm/yr and 9.1 mm/yr at 1°24'N and 0°42'N, respectively. Seismic sections show that the topography is asymmetric across the Ayu Trough and the acoustic basement is rough. These features are consistent with the earlier suggestion that the Ayu Trough is a slow-spreading divergent boundary. A detailed examination of seismic profiles away from the axis shows that sediments can be divided into two layers which implies a possible change in the spreading rate and/or sedimentation condition during the formation of the trough.