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[MIS10-04] Seismic quiescence before the October 7, 2021 earthquake that observed a seismic intensity of upper 5 in Tokyo for the first time after the Tohoku devastating earthquake
Keywords:seismic quiescence, aging of infrastructure
The advantage of seismic activity research is that the basic observations have been made by the JMA and NIED after the 1995 Kobe Earthquake (Hi-net). Now Japan has the world's highest level seismic observation network.
Although time accuracy of several months may be achievable by seismic activity research. However, it is very difficult at the present stage to forecast the occurrence of an earthquake with an accuracy of several days by using only seismicity changes.
On October 7, 2021, we had an earthquake in Tokyo that observed a seismic intensity of upper 5, the fourth-highest level on the Japanese seismic intensity scale of 7, in JMA for the first time in 10 years. This was the first time after the Tohoku devastating earthquake. The epicenter was in northern Chiba Prefecture, and the magnitude was 5.9.
In the Kanto region, earthquakes of this magnitude range have sometimes occurred, but the characteristic of this earthquake is that the seismic intensity of 5+ caused a lot of damage to infrastructure such as water services. In fact, in 2005, there was an earthquake of almost the same magnitude at the same epicenter, but at that time there was no damage to infrastructure including water supply. It was an event that made us feel that the social infrastructure was aging in Japan.
Before this earthquake, from the summer of 2020, clear seismic quiescence phenomena had been observed, which can be said to be the first time since the 2011 Tohoku earthquake, which was observed mainly in the southern part of the Kanto region. The peak of quiescence was around February 2021. It was found that this quiescence disappeared at the beginning of October. It is not clear at this time whether this quiescence corresponded only to this single earthquake.
This is because, on December 2 and 3, magnitude 5 class earthquakes occurred in the vicinity of the observed seismic quiescence area.
Furthermore, in the Miura Peninsula in the Kanto region, after the summer of 2020, there were many incidents in which "nasty smell troubles" occurred repeatedly and the relationship with the earthquake became a hot topic. Of course, the relationship between these smells and earthquakes is not clear yet.
In the future, it will be essential to consider not only seismic activity research and electromagnetic precursory phenomenon research but also such anomalous phenomena as a comprehensive seismic precursory process to improve short-term forecast accuracy.
Although time accuracy of several months may be achievable by seismic activity research. However, it is very difficult at the present stage to forecast the occurrence of an earthquake with an accuracy of several days by using only seismicity changes.
On October 7, 2021, we had an earthquake in Tokyo that observed a seismic intensity of upper 5, the fourth-highest level on the Japanese seismic intensity scale of 7, in JMA for the first time in 10 years. This was the first time after the Tohoku devastating earthquake. The epicenter was in northern Chiba Prefecture, and the magnitude was 5.9.
In the Kanto region, earthquakes of this magnitude range have sometimes occurred, but the characteristic of this earthquake is that the seismic intensity of 5+ caused a lot of damage to infrastructure such as water services. In fact, in 2005, there was an earthquake of almost the same magnitude at the same epicenter, but at that time there was no damage to infrastructure including water supply. It was an event that made us feel that the social infrastructure was aging in Japan.
Before this earthquake, from the summer of 2020, clear seismic quiescence phenomena had been observed, which can be said to be the first time since the 2011 Tohoku earthquake, which was observed mainly in the southern part of the Kanto region. The peak of quiescence was around February 2021. It was found that this quiescence disappeared at the beginning of October. It is not clear at this time whether this quiescence corresponded only to this single earthquake.
This is because, on December 2 and 3, magnitude 5 class earthquakes occurred in the vicinity of the observed seismic quiescence area.
Furthermore, in the Miura Peninsula in the Kanto region, after the summer of 2020, there were many incidents in which "nasty smell troubles" occurred repeatedly and the relationship with the earthquake became a hot topic. Of course, the relationship between these smells and earthquakes is not clear yet.
In the future, it will be essential to consider not only seismic activity research and electromagnetic precursory phenomenon research but also such anomalous phenomena as a comprehensive seismic precursory process to improve short-term forecast accuracy.