17:15 〜 19:15
[SIT19-P03] Seismic Reflection Imaging and Refraction Tomographic Velocity Refinement of the 2024 NotoEarthquake (M7.6) Rupture Area
キーワード：能登半島地震、活断層、キルヒホッフ重合前深度マイグレーション、屈折トモグラフィ、P波速度構造
The 2024 M7.6 Noto earthquake was a reverse fault event with a northwest-southeast oriented compressional axis. Aftershock distribution revealed a ~150 km-long fault extending from the Noto Peninsula's western coast to the northeastern seabed. The tsunami induced by the earthquake has been elucidated through tide gauge records and seafloor inversion analyses, which indicate that the combined effects of fault slip and associated coastal uplift generated tsunami waves reaching several meters in height. Despite its hazard potential, the detailed geometry and physical properties of the tsunamigenic faults remain poorly constrained, necessitating high-resolution subsurface imaging to elucidate its role in co-seismic deformation and tsunami generation.
During the R/V Hakuho-maru cruise (KH-24-E1) on March 2024, we conducted a high-resolution multi-channel seismic (MCS) reflection survey for tsunamigenic fault imaging using two GI guns with a total volume of 710 cubic inches (355 cubic inches each) and a shot spacing of 18.75 meters. Data acquisition employed a 48-channel streamer cable with a group interval of 25 meters, resulting in a total streamer length of 1200 meters. The recording length was set to 6 seconds with a sampling rate of 2 milliseconds.
Pre-processing included deghosting and demultiple to enhance signal-to-noise ratios. Normal moveout (NMO) velocity analysis and Post-stack time migration (PoTM) were then applied to produce time-migrated sections. Grid-based tomography further refined the P-wave velocity model, enabling the production of high-resolution Kirchhoff pre-stack depth migration (KPSDM) images that delineate fault geometry and overlying sediment-basement interfaces. The KPSDM section clearly reveals the NT2 fault, which potentially triggered the Noto earthquake and tsunamis, as well as deformation of the basement.
In the seismic reflection imaging method we used above, the velocities of acoustic basement and across the fault zone are hard to determine, while using refraction tomography could help improve the velocity model. So, we implemented refraction tomography using travel-time tomography module on RadExPro software to optimize the velocity structure. The workflow includes: (1) Pick the first break travel time, (2) Load the travel time curves in the module, (3) Edit the travel time curves manually, if necessary, (4) Create the initial model, or import the model under improvement, (5) Configure the inversion parameters and run inversion, and (6) Iteration and Adjustment. Refraction tomography reduces velocity uncertainties in basement, constraining P-wave velocities across the fault zone. With the updated velocity model, we can do better geologic interpretation and estimate physical properties of the fault zone. These results are expected to provide critical constraints on fault mechanics and rupture propagation, advancing our understanding of tsunamigenic potential in the submarine active fault system.
During the R/V Hakuho-maru cruise (KH-24-E1) on March 2024, we conducted a high-resolution multi-channel seismic (MCS) reflection survey for tsunamigenic fault imaging using two GI guns with a total volume of 710 cubic inches (355 cubic inches each) and a shot spacing of 18.75 meters. Data acquisition employed a 48-channel streamer cable with a group interval of 25 meters, resulting in a total streamer length of 1200 meters. The recording length was set to 6 seconds with a sampling rate of 2 milliseconds.
Pre-processing included deghosting and demultiple to enhance signal-to-noise ratios. Normal moveout (NMO) velocity analysis and Post-stack time migration (PoTM) were then applied to produce time-migrated sections. Grid-based tomography further refined the P-wave velocity model, enabling the production of high-resolution Kirchhoff pre-stack depth migration (KPSDM) images that delineate fault geometry and overlying sediment-basement interfaces. The KPSDM section clearly reveals the NT2 fault, which potentially triggered the Noto earthquake and tsunamis, as well as deformation of the basement.
In the seismic reflection imaging method we used above, the velocities of acoustic basement and across the fault zone are hard to determine, while using refraction tomography could help improve the velocity model. So, we implemented refraction tomography using travel-time tomography module on RadExPro software to optimize the velocity structure. The workflow includes: (1) Pick the first break travel time, (2) Load the travel time curves in the module, (3) Edit the travel time curves manually, if necessary, (4) Create the initial model, or import the model under improvement, (5) Configure the inversion parameters and run inversion, and (6) Iteration and Adjustment. Refraction tomography reduces velocity uncertainties in basement, constraining P-wave velocities across the fault zone. With the updated velocity model, we can do better geologic interpretation and estimate physical properties of the fault zone. These results are expected to provide critical constraints on fault mechanics and rupture propagation, advancing our understanding of tsunamigenic potential in the submarine active fault system.