16:15 〜 16:30
[SCG50-10] The New Ryukyu Area CMT (RACMT) Catalog: Implications for Ryukyu Subduction Zone Rupture Behavior
★Invited Papers
Seismic hazard evaluation relies on comprehensive geodetic observations and seismic catalogs. Seismicity and focal mechanisms reveal seismogenic structures and tectonic stress conditions. The spatial variation of focal mechanisms represents local seismogenic heterogeneity. Furthermore, the temporal evolution of focal mechanisms may indicate interactions between tremors, slow-slip events, or major earthquakes. These insights depend on a comprehensive focal mechanism catalog.
However, the Ryukyu region's seismic database for small to large earthquakes is incomplete due to limited seismic network coverage. In this study, we apply the AutoBATS CMT algorithm using data from joint seismic networks: BATS (Broadband Array in Taiwan for Seismology), F-net from NIED, and the FJ-network (Fujian Earthquake Agency) to analyze earthquakes (M≧4) from 2002 to 2022. The new Ryukyu Area Centroid Moment Tensor (RACMT) catalog reveals significant along-trench variations in deformation across the entire Ryukyu subduction system.
The updated centroid depth in the RACMT catalog clarifies that most shallow, small earthquakes result from Ryukyu arc deformation. Therefore, the apparent deficiency of interplate thrusting earthquakes is not due to catalog incompleteness. Forearc ruptures are dominated by strike-slip earthquakes with compression axes parallel to the trench. Along the trench, a series of normal faulting earthquakes exhibit extension axes perpendicular to the trench. The northwestward oblique subduction of the Philippine Sea Plate (PSP) is likely the key factor controlling the transition from normal faulting in the east to strike-slip faulting in the west. A similar transition is also observed in PSP intraplate ruptures.
These preliminary observations highlight the necessity of a complete regional CMT catalog. Further stress inversion analysis will provide a more detailed depiction of stress distribution across different tectonic elements and their transitions.
However, the Ryukyu region's seismic database for small to large earthquakes is incomplete due to limited seismic network coverage. In this study, we apply the AutoBATS CMT algorithm using data from joint seismic networks: BATS (Broadband Array in Taiwan for Seismology), F-net from NIED, and the FJ-network (Fujian Earthquake Agency) to analyze earthquakes (M≧4) from 2002 to 2022. The new Ryukyu Area Centroid Moment Tensor (RACMT) catalog reveals significant along-trench variations in deformation across the entire Ryukyu subduction system.
The updated centroid depth in the RACMT catalog clarifies that most shallow, small earthquakes result from Ryukyu arc deformation. Therefore, the apparent deficiency of interplate thrusting earthquakes is not due to catalog incompleteness. Forearc ruptures are dominated by strike-slip earthquakes with compression axes parallel to the trench. Along the trench, a series of normal faulting earthquakes exhibit extension axes perpendicular to the trench. The northwestward oblique subduction of the Philippine Sea Plate (PSP) is likely the key factor controlling the transition from normal faulting in the east to strike-slip faulting in the west. A similar transition is also observed in PSP intraplate ruptures.
These preliminary observations highlight the necessity of a complete regional CMT catalog. Further stress inversion analysis will provide a more detailed depiction of stress distribution across different tectonic elements and their transitions.