Equivalent Offset Migration of Vertical Cable Seismic Data to Estimate the Velocity Model in Hydrothermal Deposits

Abstract

Vertical Cable Seismic (VCS) is a reflection seismic survey method, which uses hydrophone arrays vertically moored from the seafloor to record acoustic waves generated by seismic sources. It is useful for obtaining a high fidelity image over shallow, narrowly bounded areas, such as potential hydrothermal deposits. However, the irregular geometry including variation in receiver depth, and large differences in depth between sources and receivers presents challenges in processing VCS data. We have successfully utilized a modified Equivalent Offset Migration (EOM) technique to overcome these challenges. In 2011, we carried out a VCS survey using a GI gun in the Izena Hole, which is one of the most promising hydrothermal deposit areas around Japan. It had previously been explored through drilling, however no seismic survey had been carried out, as the efficiency of seismic survey methods in hydrothermal sulfide ore deposit exploration is unproven. The collected VCS data have been processed with EOM. We obtained a high-resolution image and a velocity model, which gives detailed structural information of the submarine hydrothermal system. We can recognize reflections related to hydrothermal deposits. These survey results gave useful information to geologists and we can conclude VCS is a promising survey tool for seafloor hydrothermal deposits exploration.