3:30 PM - 4:30 PM
[J05-P-12] Depth dependence of stress field investigated from microseismicity in northwestern Kii Peninsula, southwestern Japan
The heterogeneous structure of the upper crust is one of the important factors controlling the earthquake occurrence. Therefore, understanding the influence of the heterogeneous structure of the upper crust on seismic activity leads to elucidating the process of the inland earthquake occurrence. To understand the above, we investigated the relationship between seismic activity and heterogeneous structure accommodating faults and fluids. In order to investigate the relationship between heterogeneous structure and seismic activity, the best study area is a region with high seismic activity. Thus, we selected the northwestern Kii Peninsula as the study area because of its high seismicity.
In this study, we focused on the seismic activity of the upper crust, and we investigated focal mechanism solutions of the microearthquakes and stress field in detail.
The focal mechanisms determined in this study are categorized into three groups and the predominant depths for the respective groups are different: 1) N-S tensional normal-fault type events mainly occur in the shallower part, 2) E-W compressional reverse-fault type at middle depths, and 3) N-S tensional and E-W compressional strike-slip-fault type in the deeper part. We carried out stress tensor inversions and the results also indicate that the stress field varies with depth: the shallower part is characterized by the strike-slip-fault type stress field of with N-S tension and E-W compression while the deeper part is the reverse-fault type with E-W compression.
The complicated distributions of focal mechanisms and stress mentioned above can be explained by thermal stress caused by a heat source in the lower crust and vertical weak planes related to the geological structure.
In this study, we focused on the seismic activity of the upper crust, and we investigated focal mechanism solutions of the microearthquakes and stress field in detail.
The focal mechanisms determined in this study are categorized into three groups and the predominant depths for the respective groups are different: 1) N-S tensional normal-fault type events mainly occur in the shallower part, 2) E-W compressional reverse-fault type at middle depths, and 3) N-S tensional and E-W compressional strike-slip-fault type in the deeper part. We carried out stress tensor inversions and the results also indicate that the stress field varies with depth: the shallower part is characterized by the strike-slip-fault type stress field of with N-S tension and E-W compression while the deeper part is the reverse-fault type with E-W compression.
The complicated distributions of focal mechanisms and stress mentioned above can be explained by thermal stress caused by a heat source in the lower crust and vertical weak planes related to the geological structure.