10:45 AM - 12:15 PM
[SSS13-P13] High-resolution seismic reflection survey at Suo-nada Sea, western Japan
Keywords:offshore active fault survey, Suo-nada Sea, Quaternary, high-resolution multi-channnel sesimic reflection survey, South-off Ube fault, Ogori fault
We conducted high-resolution seismic reflection surveys as a part of offshore active fault survey at Suo-nada Sea, western Japan. According to “Regional evaluation of active faults” by the Headquarters for Earthquake Research Promotion, there are four active faults (Southern part of Kikugawa faults, South-off Ube fault, Offshore part of Ogori fault, and Suo-nada fault zone) at Suo-nada Sea. Among them, three faults (Southern part of Kikugawa faults, South-off Ube fault, and Offshore part of Ogori fault) are closely placing at coastal area of Ube city, Yamaguchi prefecture. Owing to development of the Ube submarine coal field, many researchers have investigated geological structure and stratigraphy of the coal-bearing Paleogene. However, few have carried out Neogene and Quaternary studies at this area. Therefore, obtaining accurate and high-resolution geological information of the Quaternary is necessary to determine the extent of the faults and evaluate their activities precisely.
The survey employed three different equipment to figure out both of deep (~500 m bsf) and detailed shallow (~ 150 m bsf) structures. Specifications of the surveys are followings. We used a mini GI-gun as a seismic source for multi-channel seismic (MCS) survey with a 24 ch streamer cable (receiver interval: 6.25 m) to obtain deep profile. Total length of the survey line of the GI-gun MCS is ~60 km long. We used a boomer as a seismic source for MCS survey with 12 ch streamer cable (receiver interval: 2.5 m) to obtain shallow profile. Total length of the survey line of the boomer MCS is ~210 km long. We also used CHIRP sonar to obtain sub-bottom seismic reflection image during MCS surveys. The survey period was 2022/11/07 to 2022/11/27.
Acoustic stratigraphy of the study area is investigated by compiling newly obtained seismic sections and previous works. Sections of the GI-gun MCS survey clearly illustrate the basement of the Neogene to Quaternary succession. The thickness of the succession is ~150 m at offshore area. We investigated detailed structure of upper part of the succession based on the boomer MCS survey sections. Active faults are deforming the succession. South-off Ube fault is thrusting and developing a fault-related fold. Offshore part of Ogori fault is a high-angle fault and deforming the Pleistocene cumulatively and developing a flexure zone.
The survey employed three different equipment to figure out both of deep (~500 m bsf) and detailed shallow (~ 150 m bsf) structures. Specifications of the surveys are followings. We used a mini GI-gun as a seismic source for multi-channel seismic (MCS) survey with a 24 ch streamer cable (receiver interval: 6.25 m) to obtain deep profile. Total length of the survey line of the GI-gun MCS is ~60 km long. We used a boomer as a seismic source for MCS survey with 12 ch streamer cable (receiver interval: 2.5 m) to obtain shallow profile. Total length of the survey line of the boomer MCS is ~210 km long. We also used CHIRP sonar to obtain sub-bottom seismic reflection image during MCS surveys. The survey period was 2022/11/07 to 2022/11/27.
Acoustic stratigraphy of the study area is investigated by compiling newly obtained seismic sections and previous works. Sections of the GI-gun MCS survey clearly illustrate the basement of the Neogene to Quaternary succession. The thickness of the succession is ~150 m at offshore area. We investigated detailed structure of upper part of the succession based on the boomer MCS survey sections. Active faults are deforming the succession. South-off Ube fault is thrusting and developing a fault-related fold. Offshore part of Ogori fault is a high-angle fault and deforming the Pleistocene cumulatively and developing a flexure zone.