11:30 AM - 11:45 AM
[SSS11-09] Detailed fault structure and Holocene activity of Hinagu Fault Zone at Yatsushiro Sea, Kyusyu, Japan
Keywords:Hinagu Fault Zone, dextral strike-slip fault, fault stepover, offshore boring survey, 3D seismic survey
Offshore active fault survey was executed on the offshore extension of Hinagu Fault Zone at Yatsushiro Sea, Kyusyu, Japan. The Hinagu Fault Zone is a dextral strike-slip fault lying NE-SW, which relatively downthrows the NW block. To evaluate the activity of the offshore fault, we obtained 2 sedimentary cores at both side of the fault. These cores penetrate the latest Pleistocene to Holocene marine succession. By means of high-resolution multi-channel seismic reflection surveys, we obtained 3D seismic data at a rectangle area of 1 km by 2 km.
Based on analysis of offshore sedimentary cores, we clarified that the marine succession consists of bay-floor or prodelta mud and has developed during transgressive (10 ka - 8 ka) and highstand (8 ka - present) stage. The age-depth curves of the cores indicate that sedimentation at the bay floor have continued regularly since 10 ka. 2D seismic-profile shows that vertical displacements of the fault are accumulated in the marine succession and indicates that at least 4 faulting events have occured during the Holocene.
Seismic time-slices generated from the 3D seismic data enable us to map plan distribution of offshore fault system in detail. The target fault lies NE-SW and steps to the right by ca. 300 m. At the stepping area, we recognize at least 2 faults (lying W-E) accompanying a “Sag” zone. The plan distribution of faults above should represent the extensional duplex structure associated with right stepover of dextral strike-slip fault system.
Based on analysis of offshore sedimentary cores, we clarified that the marine succession consists of bay-floor or prodelta mud and has developed during transgressive (10 ka - 8 ka) and highstand (8 ka - present) stage. The age-depth curves of the cores indicate that sedimentation at the bay floor have continued regularly since 10 ka. 2D seismic-profile shows that vertical displacements of the fault are accumulated in the marine succession and indicates that at least 4 faulting events have occured during the Holocene.
Seismic time-slices generated from the 3D seismic data enable us to map plan distribution of offshore fault system in detail. The target fault lies NE-SW and steps to the right by ca. 300 m. At the stepping area, we recognize at least 2 faults (lying W-E) accompanying a “Sag” zone. The plan distribution of faults above should represent the extensional duplex structure associated with right stepover of dextral strike-slip fault system.