Detailed Imaging of Deepwater Hydrate Geology With Horizontal Arrays of Seafloor Sensors

This paper describes new procedures for processing data acquired with 4C seismic sensors distributed as horizontal arrays on the seafloor and seismic sources positioned either at the sea surface or on the seafloor. Two types of images can be produced from 4C seismic data: a P-P image and a P-SV (converted-shear) image. For P-P imaging, the large elevation difference between deep-water seafloor sensors and air-gun sources at the sea surface allows P-P data to be processed with algorithms similar to those used to process vertical seismic profile (VSP) data. This novel VSP-type approach to processing deep-water seafloor sensor data provides optimal resolution of near-seafloor geology and does not appear to be documented in the literature. For P-SV imaging, low S-wave velocities in near-seafloor strata result in submeter wavelengths, even though signal energy from a surface-based air gun does not exceed 100 Hz. As a result, P-SV data image seafloor layering as thin as 1 m over subseafloor depths of several tens of meters. Combining high-resolution P-P and PSV images produced along horizontal seafloor arrays allows improved understanding of deep-water gas hydrate geology.