5:15 PM - 6:45 PM
[SCG55-P03] Characteristics of Stress and strain rate field around the Hinagu Fault Zone, Kyushu, Japan
Keywords:Kumamoto, Hinagu Fault Zone, Stress field, Strain rate field
The 2016 Kumamoto earthquake sequence, which occurred at western part of Kyushu Island, caused large ruptures in the northern part of the Hinagu Fault Zone and the Futagawa Fault Zone due to the largest foreshock (M6.5) and mainshock (M7.3). On the other hand, the southern part of the Hinagu Fault Zone has not been large ruptured by the sequence and could have the potential to occur a large earthquake in the future. The purpose of this study is to investigate the current stress and crustal strain states in and around the southern part of the Hinagu Fault Zone. The data used in this study are the seismic data obtained from the dense seismic observation network around the target area. The network is composed by over hundred temporary deployed stations by Kyushu University and stationary observation sites. Data for strain rate field estimation is GNSS data from GEONET(GNSS Earth Observation NETwork System) installed by the Geospatial Information Authority of Japan (GSI). The interval of seismic stations is approximately 5 km, and the interval of GNSS stations is approximately 25 km. From the seismic data, we obtained the hypocenters and the focal mechanisms, and the seismic moment tensors derived from focal mechanism. The area was divided into blocks with 0.05 degrees longitude and latitude intervals, and the major fault planes (Hinagu and Midorikawa faults) were used as the block boundaries. We estimated the stress field in the seismogenic zone by adding up the seismic moment tensors within each block. In addition, the strain rate field around the Hinagu Fault Zone was calculated from the steady displacement velocities at GNSS sites.
By comparing the principal axes of the two fields, we obtained the both principal directions tend to be in north-south extension and east-west compression on the west side of the Hinagu Fault Zone. On the other hand, significant difference in the direction of the principal axes were found at the east side of the Hinagu Fault Zone, around the Midorikawa Fault. In addition, GNSS data also confirmed that crustal deformation with a tendency of horizontal extension around the Uto Peninsula, which is located west of the coseismic fault of the 2016 Kumamoto earthquake, has been observed since occurrence of the earthquake and continues to this day.
It has been reported that the target area has a complex tectonic field bounded the Beppu-Shimabara graben in the north and shear zone across the Kyushu Island in the south. It is a future issue to consider how tectonic activities in and around the Kyushu Island affect the stress and deformation state around the Hinagu Fault Zone.
By comparing the principal axes of the two fields, we obtained the both principal directions tend to be in north-south extension and east-west compression on the west side of the Hinagu Fault Zone. On the other hand, significant difference in the direction of the principal axes were found at the east side of the Hinagu Fault Zone, around the Midorikawa Fault. In addition, GNSS data also confirmed that crustal deformation with a tendency of horizontal extension around the Uto Peninsula, which is located west of the coseismic fault of the 2016 Kumamoto earthquake, has been observed since occurrence of the earthquake and continues to this day.
It has been reported that the target area has a complex tectonic field bounded the Beppu-Shimabara graben in the north and shear zone across the Kyushu Island in the south. It is a future issue to consider how tectonic activities in and around the Kyushu Island affect the stress and deformation state around the Hinagu Fault Zone.