Near surface geophysics

[NS-05] High-resolution 3D marine seismic acquisition and imaging in shallow waters: Application to shallow fault detection, Beppu-Bay, Japan

*Yosuke Teranishi¹, Fumitoshi Murakami¹, Shinji Kawasaki¹, Motonori Higashinaka¹, Kei Konno¹, Hitoshi Tsukahara¹, Takeshi Kozawa¹, Shigeru Ino¹, Susumu Abe¹, Keiji Takemura², Shinji Ohsawa² (1. JGI (Japan), 2. Kyoto Univ (Japan))

A high-resolution 3D (HR3D) seismic survey was conducted to clearly reveal and map faults and fractures in a shallow-water region of Beppu-Bay, Japan, where is a pull-apart-basin developed with right-lateral strike-slip fault activities. The HR3D seismic survey was conducted using a dense array of 6-short streamers combined with a single GI-gun (150 cu.in.). The system configuration can provide excellent illumination of geological features, even in shallow waters which is hard to image accurately with traditional methods. This system realizes high cost-efficient acquisition, which is light in weight, easy to deploy and retrieve cables from a small vessel. It is also capable of acquiring high-resolution data.

In the HR3D seismic processing sequence, pre-stack noise attenuation, de-ghost, de-multiple, and acquisition footprints removal played an essential role to enhance seismic imaging quality. Then, the seismic data were processed into a post-stack time-migrated 3D volume. Compared to existing 2D seismic sections, the resolution achieved with the HR3D seismic was much higher. Furthermore, the HR3D migrated volume allowed to delineate highly detailed features of seafloor and subsurface.
Following the seismic processing sequence, similarity and thinned fault likelihood (TFL) attribute workflows were used to detect and visualize faults and fractures within the HR3D migrated volume. The workflows revealed a network of broadly distributed faults and fractures along an active fault system in Beppu-Bay.