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[SSS11-P02] Visualization of recent seismic activity in southwest Japan using eMAP
Keywords:Southwest Japan, Nankai Trough, Seismic activity
In the epicenter and its surrounding area before a major earthquake occurs, there have long been reports of significant spatio-temporal changes in seismic activity, such as seismic gaps, seismic quiescence, foreshock activity, and donut patterns. ZMAP (Wiemer and Wyss, 1994) has been developed to detect changes in seismic activity over a medium to long period of time, ranging from a few months to a decade, by visualizing seismic activity rather than the source distribution itself. There are more than 100 cases of anomalous seismic activity before major earthquakes detected by this method. Matsumura's method (Matsumura, 2002) and eMAP (JMA, et al., 2011) have also been developed for the same purpose. The essential difference between these methods is that the other methods reflect the change of seismic activity linearly, while eMAP represents it nonlinearly, and the contrast is emphasized according to the degree of activation and quiescence (Yoshikawa et al., 2021). Here we analyzed the recent changes in seismic activity in southwest Japan based on the unified seismic catalog of JMA by this method.
Although there are some fluctuations in the spatio-temporal distribution of the quieting and active areas, we can find the influence of the 2011 Tohoku Earthquake and the 2016 Kumamoto Earthquake in some areas, and we can see the whole seismic activity history in southwest Japan. Especially the following characteristics and trends are found in the quieting and activation status: 1) Active regions are observed around the plate subduction zone in the Tokai region, the central Kyushu region, and the Kii Channel. 2) Quieting regions in the crust and plate appear from the Kinki to the Chubu areas. An earthquake of magnitude 6.6 occurred in the pacific coast of Kyushu region on January 22, 2022, after the evaluation period, which is considered to reflect the active seismic activity in this region.
The figure shows an example of the results, visualizing the vertical and planar distribution of crustal and intraplate seismic activity in the land area of southwest Japan. The intra-plate map shows the distribution of the sea area, but the accuracy of activity and source determination is not very high. It should be noted that the aftershock activity of the 2004 off the southeast coast of Kii Peninsula events.
Although there are some fluctuations in the spatio-temporal distribution of the quieting and active areas, we can find the influence of the 2011 Tohoku Earthquake and the 2016 Kumamoto Earthquake in some areas, and we can see the whole seismic activity history in southwest Japan. Especially the following characteristics and trends are found in the quieting and activation status: 1) Active regions are observed around the plate subduction zone in the Tokai region, the central Kyushu region, and the Kii Channel. 2) Quieting regions in the crust and plate appear from the Kinki to the Chubu areas. An earthquake of magnitude 6.6 occurred in the pacific coast of Kyushu region on January 22, 2022, after the evaluation period, which is considered to reflect the active seismic activity in this region.
The figure shows an example of the results, visualizing the vertical and planar distribution of crustal and intraplate seismic activity in the land area of southwest Japan. The intra-plate map shows the distribution of the sea area, but the accuracy of activity and source determination is not very high. It should be noted that the aftershock activity of the 2004 off the southeast coast of Kii Peninsula events.