Analysis and Interpretation of High-Resolution Geophysical Data: Offshore Sarawak, South China Sea

摘要

Pockmarks and related subsurface features are mapped and interpreted in offshore Sarawak, South China Sea. Data was collected using sidescan sonar, sub-bottom profiler, 2D high-resolution seismic and core samples. Pockmark distributions are interpreted and defined on the basis of these high-resolution geophysical data in three zones: near shore with -20-30 m water depth, offshore shallow water with 80-90 m water depth, and offshore deep water with -150-500 m water depth. We propose that pockmark formation is controlled by overpressured layers, faults and fractures, shallow gas accumulation in shallow sand layers, and sediment deposition rates. Of the three zones the offshore deep water zone is characterized by relatively higher overpressure, distinct seafloor faults, and a low sediment deposition rate; it has the densest pockmark concentration of the three zones. Although shallow gas and shallow sand layers are interpreted in the near shore zone, it is characterized by lower overpressure, an absence of well defined seafloor faulting, and relative higher sediment deposition rate. No obvious pockmarks are visible in the near shore zone. Understanding pockmark distribution and formation mechanisms will help in assessing potential geohazards and defining strategies for efficient identification of oil and gas seeps in seep-hunting project.