17:15 〜 18:45
[SCG40-P17] Structural description and interpretation of the seismic reflection image along subducting seamount in Hyuga-nada
キーワード：Slow earthquake、Hyuga-nada、Seamount subduction、Seismic reflection image
The development of seismic observation network in recent years has led to the discovery of diverse seismic activities including slow earthquakes. Slow earthquakes have been studied by seismological observations, however, the geological feature of slow earthquakes has not yet revealed how and where they actually occur. Slow earthquakes are also frequent along the Nankai Trough, occurring off the Kii Peninsula, Muroto Peninsula, and off Hyuga-nada Sea at depths different from those of regular earthquakes. Especially off Hyuga-nada, slow earthquakes have been observed in the area where the Kyushu-Palau Ridge is subducted. The purpose of this study is to clarify the relationship between the slow earthquake generation off Hyuga-nada and the structure of the subducting seamounts in order to shed light on the geological feature of the slow earthquake-genic zone.
In this study, we used reflection seismic profiles of the Hyuga-nada seamount subducting region obtained by multi-channel reflection seismic surveys. The HYG-1 cross section is parallel to the direction of plate subduction, and the HYG-2T and HYG-2S are parallel to the trench axis. Seamounts were identified as elevations of the oceanic crust in HYG-1 and HYG-2S. The subducting sediments were identified in the vicinity of the seamount. The number of faults is higher in the frontal accretionary wedge near trench and its formation is not seems to be related to the seamount subduction. On the other hand, a major fault extends from the top of the seamount to seafloor, dipping to landward.
Comparing the distribution of slow earthquakes with the structure found in this study, slow earthquakes occur mostly in the vicinity of the seamount and not in the trench-side area where the number of faults is larger. The number of slow earthquakes was also small on the landward side of the seamounts nor sedimentary basins are developed.
In this study, we were able to clarify to some extent where the slow earthquakes occurred. The detailed mechanism between faulting and slow earthquake occurrence, however, could not be resolved, and further research are needed such as investigate the relationship between the distribution of elastic wave velocity, heat flow, and stress distribution to clarify the role of seamount subduction on slow earthquake activity.
In this study, we used reflection seismic profiles of the Hyuga-nada seamount subducting region obtained by multi-channel reflection seismic surveys. The HYG-1 cross section is parallel to the direction of plate subduction, and the HYG-2T and HYG-2S are parallel to the trench axis. Seamounts were identified as elevations of the oceanic crust in HYG-1 and HYG-2S. The subducting sediments were identified in the vicinity of the seamount. The number of faults is higher in the frontal accretionary wedge near trench and its formation is not seems to be related to the seamount subduction. On the other hand, a major fault extends from the top of the seamount to seafloor, dipping to landward.
Comparing the distribution of slow earthquakes with the structure found in this study, slow earthquakes occur mostly in the vicinity of the seamount and not in the trench-side area where the number of faults is larger. The number of slow earthquakes was also small on the landward side of the seamounts nor sedimentary basins are developed.
In this study, we were able to clarify to some extent where the slow earthquakes occurred. The detailed mechanism between faulting and slow earthquake occurrence, however, could not be resolved, and further research are needed such as investigate the relationship between the distribution of elastic wave velocity, heat flow, and stress distribution to clarify the role of seamount subduction on slow earthquake activity.