9:15 AM - 9:30 AM
[SSS06-02] Statistical analysis and its characteristics of the earthquake activity near the border of Nagano, Gifu and Fukui prefectures
Keywords:Earthquake swarm, background seismicity, nonstationary modeling
An earthquake swarm activity has occurred in April 2020 near the border between Nagano and Gifu prefectures. In the same region another event had started in August 1998. These two events have comparable sizes, similar period of activities and similar transitions in time. We analyzed these events with statistical models, ETAS model and its variations to capture the characteristics of the earthquakes in the focal region.
These earthquake swarms have many strike-slip fault types with the northwest-southeast direction as the compression axis, reflecting the stress field. Since it occurred near the volcanic area, it may be related to the movement of hot water and magma fluid and the diffusion of pore pressure.
The proportion of non-double couple components (% CLVD) in the CMT solution in the focal region shows a relatively high value. Comparing to the surrounding area, other high values appear only near Mt. Ontake; many are low in the Itoigawa-Shizuoka Tectonic Line and other major active fault areas.
For the spatiotemporal patterns, there earthquake swarms both started in the southernmost region the moved northward. Earthquakes with high % CLVD occur in relatively deep locations.
The background seismic activity in 1998, which is estimated by the non-stationary ETAS model, reached dozens to hundreds of times larger than the normal level in 50 days from the beginning. This active area is concentrated in the southernmost region. In 2020, three similar peaks with similar sizes are estimated. There was another increased activity from the end of 2020, but it is settling down; the background seismic activity is dropping down to the normal level. High % CLVD values are connected with these high values in the background.
These earthquake swarms have many strike-slip fault types with the northwest-southeast direction as the compression axis, reflecting the stress field. Since it occurred near the volcanic area, it may be related to the movement of hot water and magma fluid and the diffusion of pore pressure.
The proportion of non-double couple components (% CLVD) in the CMT solution in the focal region shows a relatively high value. Comparing to the surrounding area, other high values appear only near Mt. Ontake; many are low in the Itoigawa-Shizuoka Tectonic Line and other major active fault areas.
For the spatiotemporal patterns, there earthquake swarms both started in the southernmost region the moved northward. Earthquakes with high % CLVD occur in relatively deep locations.
The background seismic activity in 1998, which is estimated by the non-stationary ETAS model, reached dozens to hundreds of times larger than the normal level in 50 days from the beginning. This active area is concentrated in the southernmost region. In 2020, three similar peaks with similar sizes are estimated. There was another increased activity from the end of 2020, but it is settling down; the background seismic activity is dropping down to the normal level. High % CLVD values are connected with these high values in the background.