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2020/11/22 11:01 Weather News
In the last week, the number of earthquakes observed in Japan has decreased as in the previous week. There have been no earthquakes with a seismic intensity of 3 or more. Since the total number of earthquakes is small, there are no discernible areas. (Added from November 16 to November 22 at 10:00)
This earthquake is a very deep earthquake with a depth of origin of approximately 394 km. While we have not observed tremors with a seismic intensity of 1 or more in Shizuoka and Mie prefectures, which are closer to the center of the earthquake, we are capturing tremors in Tokyo and Utsunomiya, which are further away. It is a distribution of seismic intensity called “abnormal seismic area” that is characteristic of deep earthquakes.
This earthquake appears to have occurred deep in the Philippine Sea plate, and is a different mechanism from the “Giant Nankai Canal Earthquake” that occurs at the edge of the plate.
Similar deep earthquakes often occur from the southeast coast of Mie prefecture to the southern coast of Tokaido and the sea near Torishima, and earthquakes of M6 or larger occur once every few years. On the other hand, it is also characterized by the fact that there are almost no after-effects from a single earthquake.
On January 1, 1984, an M7.0 earthquake occurred off the southeastern coast of Mie Prefecture, and seismic intensity 4 was observed in Chiyoda District, Tokyo, and Yokohama City. Although these earthquakes do not cause tsunamis, they can be accompanied by large tremors, so caution is required.
The depth of the source of this earthquake is estimated to be about 43 km. The shaking is not that great, and even near the source, it is considered to be V in the revised Mercari seismic intensity class (about 3 in the Japanese seismic intensity class), and no damage has been reported from this earthquake.
The eastern part of the island of Mindanao is the area where the Philippine Sea plate is submerged in the Eurasian plate, and many plate boundary-type earthquakes occur. The mechanism of this earthquake is analyzed as a type of reverse fault with a pressure axis in the east-west direction, and it is a pattern that is common in this area.
In the vicinity of this earthquake, there is a record of an earthquake with a magnitude of 7.6 in 1989 and an earthquake with a magnitude of 7.0 in 1991, and if the range is further widened, an earthquake of magnitude class 8. As in Japan, the risk of a large plate boundary earthquake is high and if a tsunami occurs, it will reach land in a relatively short time, so it can be said that it requires caution.
* Information on the source and intensity of seismic intensity in Japan comes from the Meteorological Agency, unless otherwise noted. Information on overseas earthquake sources comes from the US Geological Survey (USGS), unless otherwise noted. Source information may differ depending on the issuing organization.
