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2020/12/06 10:46 Weather news
Last week, the number of earthquakes observed in Japan has been roughly the same as the week before. Once an earthquake has occurred with a seismic intensity of 3 or more. Although the total number of times is not that great, earthquakes are conspicuous in the Pacific region from Kanto to Hokkaido. Also, seismic activity is active in the sea near Miyakejima. (Added from November 30 to December 6 at 10:00)
The seismic intensity distribution of the “abnormal seismic area”, which is often observed in the case of an earthquake with a deep seismic source, appears on the Pacific side of the northern part of Tohoku, such as the Sanpachi-Kamikita region in Aomori prefecture, which is a little further from Hokkaido, which is close to the seismic source.
In the Sea of Okhotsk, where the Pacific Plate is deeply submerged, many of these deep earthquakes have occurred in the past, with recent earthquakes of magnitude 6.1 in 2018 and magnitude 8.3 in 2013.
There are few occurrences off the western coast of Sakhalin like this time, and deep earthquakes with a magnitude of 6 or greater have occurred since April 1939.
This earthquake is believed to have occurred in the deep part of the Pacific Plate, which sinks northwest of the Chishima Trench.
Similar deep earthquakes often occur where the Pacific plate is deeply subducted, and earthquakes of magnitude 6 and above 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.
In the 2013 magnitude 8.3 earthquake that occurred in the Okhotsk Sea, the maximum seismic intensity was only 3, but the earthquake with a seismic intensity of 1 or more reached Kyushu. Even in a deep earthquake, if the scale becomes large, the effects of the shaking will appear, so you cannot be alert.
This time, we focus on the 6.3 magnitude earthquake that occurred in northwestern Argentina on Tuesday. Argentina is less likely to experience earthquakes than its neighbor Chile, which is an earthquake-prone country. Earthquakes with a magnitude greater than 6 occur only near the border with Chile, including this source, and in deep earthquakes in Santiago del Estero. There are few major earthquakes in areas near the Atlantic Ocean, such as Buenos Aires.
Although the magnitude of the earthquake on day 1 (Tuesday) was quite large, the depth reached 189 km and there were no strong shaking around the center of the earthquake. The mechanism is analyzed as a normal failure type with an east-west axis of tension, and the inside of the plate is thought to be destroyed.
* Information on the source and intensity of seismic intensity in Japan comes from the Meteorological Agency, unless otherwise noted. Unless otherwise noted, overseas seismic source information comes from the American Geological Survey (USGS). Source information may differ depending on the issuing organization.
