5:15 PM - 7:15 PM
[SCG50-P02] Improved sedimentary layer model including the accretionary prism in the fore-arc region of Ryukyu arc, Japan
Keywords:Ryukyu arc, 3D sedimentary layer model, Accretionary prism
An accurate sedimentary layer model including the accretionary prism in the fore-arc region is essential for high-resolution seismic motion prediction of earthquakes occurring in the vicinity of an oceanic trench. In the Ryukyu arc, Japan, recent seismic reflection profiles have clarified the existence of an accretionary prism with varying thickness along the trench. In this study, we combine the above recent seismic reflection profiles to construct a new seismic velocity structure model incorporating the accretionary prism. In constructing the new model, we refer to the zoning (ZONE1 to ZONE4 shown in Figure 1) identified by Okamura et al. (2017). The construction process consists of the following three steps:
First, we digitize either unconformities or VP 4 to 5 km/s lines as the seismic basement, whichever is more clearly identifiable. Second, each digitized thickness datum of sedimentary layer is combined to construct three-dimensional structure model through spatial interpolation. Finally, we supplement the external region of the newly constructed 3D sedimentary model using the J-SHIS model provided by NIED to complete the 3D velocity structure model in the entire Ryukyu arc.
The main features of our constructed model are as follows (Figure 1): In ZONE1, off Ishigaki-jima island, a thick sedimentary layer approximately 50 km wide extends from the Ryukyu trench. In ZONE2, off Miyako-jima island, thinner layer compared to other zones is found near the trench, with a thin sedimentary terrace covering the area behind it. In ZONE3, off Okinawa-jima island, sedimentary layer deepens as it approaches the trench. In ZONE4, off Tokara islands, deepest layer among all zones is identified. In this presentation, we will evaluate the effect of our new structure model on seismic motion simulation.
Acknowledgments: In this study, we applied waveform data observed in NIED and JMA, the 250-m mesh land model (Geospatial Information Authority of Japan), the JTOPO30v2 seafloor model, and the J-SHIS subsurface structure model. This study was supported by JSPS KAKENHI Grant Number JP23K22582, ERI JURP 2024-S-B102, provided by Earthquake Research Institute, the University of Tokyo, and "Joint Usage/Research Center for Interdisciplinary Large-scale Information Infrastructures (JHPCN)" in Japan (Project ID: jh240056).
First, we digitize either unconformities or VP 4 to 5 km/s lines as the seismic basement, whichever is more clearly identifiable. Second, each digitized thickness datum of sedimentary layer is combined to construct three-dimensional structure model through spatial interpolation. Finally, we supplement the external region of the newly constructed 3D sedimentary model using the J-SHIS model provided by NIED to complete the 3D velocity structure model in the entire Ryukyu arc.
The main features of our constructed model are as follows (Figure 1): In ZONE1, off Ishigaki-jima island, a thick sedimentary layer approximately 50 km wide extends from the Ryukyu trench. In ZONE2, off Miyako-jima island, thinner layer compared to other zones is found near the trench, with a thin sedimentary terrace covering the area behind it. In ZONE3, off Okinawa-jima island, sedimentary layer deepens as it approaches the trench. In ZONE4, off Tokara islands, deepest layer among all zones is identified. In this presentation, we will evaluate the effect of our new structure model on seismic motion simulation.
Acknowledgments: In this study, we applied waveform data observed in NIED and JMA, the 250-m mesh land model (Geospatial Information Authority of Japan), the JTOPO30v2 seafloor model, and the J-SHIS subsurface structure model. This study was supported by JSPS KAKENHI Grant Number JP23K22582, ERI JURP 2024-S-B102, provided by Earthquake Research Institute, the University of Tokyo, and "Joint Usage/Research Center for Interdisciplinary Large-scale Information Infrastructures (JHPCN)" in Japan (Project ID: jh240056).