10:45 AM - 12:15 PM
[SSS10-P18] Visualization of recent seismic activity in southwest Japan using eMAP(2)
Keywords:seismic activity, quiescence, southwest Japan, Nankai trough
Visualization of the spatio-temporal distribution of quiescence and activation of micro-seismicity will be effective for early and objective detection of seismic activity anomalies such as quiescence and doughnut patterns in the preparatory process of large-scale earthquakes. By applying eMAP (Hayashimoto and Aketagawa, 2010; Yoshikawa, Hayashimoto, Aketagawa, Katsumata, and Miyaoka, 2021) to micro-seismicity of southwest Japan in the last study (Yoshikawa, 2022), a major quiescence zone, where seismicity relatively becomes lower in the crust, was found in the Kinki and Chubu regions since around 2016, whereas several activation zones with relatively high seismic activity have emerged in the surrounding areas. The analysis of b-values indicates that the quiescent and active zones may have experienced a decrease and an increase in the stress field, respectively, during the same period. Since the trend has continued for more than five years and seismic activity seems to fluctuate within a short period of one to two years, the author is keeping the analysis.
One feature of eMAP is to compare the seismicity rate changes (SRCs) between the reference and evaluation periods for a small area centered on all hypocenters to be analyzed. Another feature of this method is that the time series of earthquakes in the reference period is assumed to be a Poisson process and the SRC in the evaluation period is expressed as a cumulative probability (0 to 1), so that the SRCs can be measured on the same scale regardless of their levels in different areas. The data used are from the unified hypocenter catalog of JMA (since October 1997), and the earthquakes of M2.0 or greater which were de-clustered for 10 km and less within 7 days.
According to the present study, a new activation zone has become apparent in the central Kinki region in the crust since the later 2021, and activation is also seen in the Chugoku region as if to cut off the dominant quiescence zone, which appeared around 2016 (Fig. A). Changes in the cumulative number of earthquakes in the quiescence zone (within the dashed bold line) indicates a quiescence around 2016 and an increase in activity after late 2021(Fig. B).
One feature of eMAP is to compare the seismicity rate changes (SRCs) between the reference and evaluation periods for a small area centered on all hypocenters to be analyzed. Another feature of this method is that the time series of earthquakes in the reference period is assumed to be a Poisson process and the SRC in the evaluation period is expressed as a cumulative probability (0 to 1), so that the SRCs can be measured on the same scale regardless of their levels in different areas. The data used are from the unified hypocenter catalog of JMA (since October 1997), and the earthquakes of M2.0 or greater which were de-clustered for 10 km and less within 7 days.
According to the present study, a new activation zone has become apparent in the central Kinki region in the crust since the later 2021, and activation is also seen in the Chugoku region as if to cut off the dominant quiescence zone, which appeared around 2016 (Fig. A). Changes in the cumulative number of earthquakes in the quiescence zone (within the dashed bold line) indicates a quiescence around 2016 and an increase in activity after late 2021(Fig. B).