17:15 〜 18:45
[SSS09-P04] Seismic imaging and pore-fluid pressure estimation along the Southern Kuril Trench subduction zone off Tokachi of Hokkaido, Japan
キーワード：地殻構造、千島海溝、反射法地震探査
The Southern Kuril Trench subduction zone offshore the Tokachi region of Hokkaido, Japan, is marked by large megathrust earthquakes and tsunamis. The tectonic and physical characteristics of this subduction zone offer valuable insights into plate dynamics and seismic hazard assessment. In the study area, some large megathrust earthquakes have occurred, such as the 2003 Tokachi-Oki Earthquake (Mw 8.3) in the Tokachi region and the 17th-century Kuril Earthquake (Mw 8.8) in the Nemuro-Tokachi region. The primary objective of this study is to figure out the detailed crustal structures of the Southern Kuril Trench subduction zone offshore the Tokachi region of Hokkaido and estimate the pore-fluid pressures of the megathrust fault, potentially generating large earthquakes and tsunamis.
We performed conventional data processing using multi-channel seismic (MCS) reflection data on survey line KT093, which was acquired by JAMSTEC during the KM20-E02 survey. For deep-penetration seismic imaging, a large-volume (~174 liters) airgun array was used as the controlled seismic source. The MCS data was recorded for 18 seconds at each shot point using a 444-channel streamer cable with 12.5 m group spacing. Conventional MCS data processing techniques were applied to the MCS data, including swell noise removal, amplitude correction, time-variant band-pass filtering, bubble suppression, deghosting, predictive deconvolution, multiple suppressions by surface-related multiple attenuation (SRMA) and parabolic radon transform (PRT), common midpoint (CMP) sort, normal moveout (NMO) correction, CMP stack, and Kirchhoff post-stack time migration (PoTM). On the current PoTM profile, the megathrust fault of the subducting Pacific Plate can be traced up to ~50 km landward from the trench, but it is quite ambiguous in some region. It may be caused by dehydration of subducting sediment to seafloor through splay faults. Near the Kuril Trench axis, horst-graben structures are imaged, which consist of reactivated abyssal-hill faults.
We are going to build an interval velocity model for pre-stack depth migration using the pre-conditioned CMP gather data and estimate the pore-fluid pressures of the megathrust fault. Then, we will compare the pore-fluid pressures of the study area with those of other areas, such as the 2011 Tohoku (Mw 9.0) coseismic rupture area, to understand the shallow megathrust fault behavior generating large tsunamis.
We performed conventional data processing using multi-channel seismic (MCS) reflection data on survey line KT093, which was acquired by JAMSTEC during the KM20-E02 survey. For deep-penetration seismic imaging, a large-volume (~174 liters) airgun array was used as the controlled seismic source. The MCS data was recorded for 18 seconds at each shot point using a 444-channel streamer cable with 12.5 m group spacing. Conventional MCS data processing techniques were applied to the MCS data, including swell noise removal, amplitude correction, time-variant band-pass filtering, bubble suppression, deghosting, predictive deconvolution, multiple suppressions by surface-related multiple attenuation (SRMA) and parabolic radon transform (PRT), common midpoint (CMP) sort, normal moveout (NMO) correction, CMP stack, and Kirchhoff post-stack time migration (PoTM). On the current PoTM profile, the megathrust fault of the subducting Pacific Plate can be traced up to ~50 km landward from the trench, but it is quite ambiguous in some region. It may be caused by dehydration of subducting sediment to seafloor through splay faults. Near the Kuril Trench axis, horst-graben structures are imaged, which consist of reactivated abyssal-hill faults.
We are going to build an interval velocity model for pre-stack depth migration using the pre-conditioned CMP gather data and estimate the pore-fluid pressures of the megathrust fault. Then, we will compare the pore-fluid pressures of the study area with those of other areas, such as the 2011 Tohoku (Mw 9.0) coseismic rupture area, to understand the shallow megathrust fault behavior generating large tsunamis.