2022/08/21 18:11 Meteorological news
Seismic activity in northern Hokkaido continues and earthquakes are occurring in various places from Tohoku to Kanto and western Japan. There were five earthquakes with seismic intensity equal to or greater than 3. (Tally from 15 to 21 August at 10:00)
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Japan: M3.7 maximum seismic intensity 3 in central Tottori prefecture
This is the second time since May of this year an earthquake centered in the central Tottori Prefecture. According to the automatic analysis of the National Research Institute for Earth Science and Disaster Resilience, the mechanism of the earthquake is believed to be of the strike-slip type.
Six years ago, on 21 October 2016, an earthquake with a magnitude of 6.6 and maximum seismic intensity of less than 6 occurred in the central Tottori Prefecture, although no active faults are known. The active area is distributed from north-northwest to south-southeast and the epicenter of this event is included in that area. The mechanism of the 2016 earthquake and the current one are similar, so related activity is possible.
After the 2016 earthquake, the Government Committee for Earthquake Research conducted a seismic assessment, which showed that the area, including the central Tottori Prefecture, has few known active faults, but is relatively seismically active.
In Tottori prefecture, large earthquakes occurring in shallow areas of land are evident, such as the 1943 Tottori earthquake, the western 2000 Tottori earthquake and the 2016 central Tottori earthquake. Daily vigilance is essential.
– The earthquake mechanism is analyzed as a type of reverse fault with a pressure axis in the west-northwest-east-southeast direction. This is the first time that an earthquake with a seismic intensity of 3 or more with its epicenter in eastern Kanagawa has occurred in February of this year. The February earthquake had an epicenter up to 100 km deep, which is the first since the 4.6 magnitude earthquake in February 2016 with a depth of 26 km to be limited to a similar shallow-type earthquake. At a depth of about 30 km in eastern Kanagawa prefecture, earthquakes with a magnitude of around 5 occasionally occur. In November 1923 there was a magnitude 6.3 earthquake, thought to be an aftershock of the Great Kanto earthquake or related activity. The Cabinet Office hypothesis of an earthquake affecting the Tokyo metropolitan area directly includes an earthquake with its epicenter in Kanagawa prefecture, so it is essential to take countermeasures on a daily basis. – Also, just 20 minutes later, around 1:59, there was a 3.5 magnitude earthquake and nearly three hours later, around 4:28, a 2.9 magnitude earthquake, both with an intensity maximum seismic of 3. The epicenters and depths are almost the same and it appears to be a series of seismic activity. No earthquake felt has occurred since the quake at 7:09 am on Friday April 4th. A magnitude 4.4 earthquake occurred on June 20 near the epicenter and a maximum seismic intensity of 4 was observed. Although the Soy region has relatively few earthquakes compared to other parts of Hokkaido, the displacement which appears to be a fault has been confirmed slightly north of the epicenter. In addition, the Sarobetsu fault zone is known along the coast of the Sea of Japan in the Soy region. According to the government headquarters for promoting earthquake research, the likelihood of an earthquake measuring approximately 7.6 magnitude within the next 30 years is less than 4%. While there haven’t been many major earthquakes in recent years, the area isn’t necessarily safe. – Most earthquakes are concentrated at a depth of about 10 km even in the depth of the east-west section. There are few events at depths of 20km or more, but there are some at depths of 100km or more. Earthquakes that occur near the boundary between the Pacific Plate and the Eurasian Plate or within the Pacific Plate. Most of the deep earthquakes are of magnitude 4, but in May 2014 a large earthquake of magnitude 6.0 occurred. In this earthquake, a maximum seismic intensity of 5 lower was observed in Chiyoda Ward, Tokyo, and a seismic intensity of 3 to 4 was observed over a large area of the Kanto region, causing damage such as injuries. – In the early morning of 15 (Monday) Japan time, an earthquake with a magnitude of 6.4 and a depth of about 78 km occurred with its epicenter near the Loyalty Islands, east of New Caledonia. The seismic mechanism is a type of normal fault with a tension axis in the north-west-south-east direction, and includes a slight passing component. There are no islands near the epicenter, so there was no impact from the tremors. The epicenter of this earthquake was near the boundary between the Pacific Plate and the Australian Plate, and many earthquakes have occurred in the past. In March of this year there was a 7.0 magnitude earthquake with a slightly shallow epicenter and last year a 7.7 magnitude earthquake occurred. Even earlier, once every few years, a class 7 earthquake of magnitude occurred. The 7.7 magnitude earthquake in 2021 is a reverse fault type earthquake unlike this time and the epicenter was shallow, so a tsunami was generated. – The Strait of Gibraltar is the strait that separates Europe and Africa, as well as the border between the Eurasian and African plates. Since it is not a subduction zone, many transcurrent earthquakes occur and the 6.3 magnitude earthquake that occurred in 2016 and the 6.4 magnitude earthquake that occurred in 2004 have the same mechanism. Since many earthquakes occur in shallow areas, if they occur near the mainland or on land, they will be strong near the epicenter. – * Information on earthquake sources and seismic intensity in Japan comes from the Japanese Meteorological Agency, unless otherwise specified. Information about the overseas epicenter comes from the United States Geological Survey (USGS), unless otherwise noted. There may be differences in the hypocenter information depending on the publishing organization. – –
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Japan: seismic intensity 3 in eastern Kanagawa prefecture
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Japan: in the Hokkaido Soy region, seismic intensity from 3 to 4 in rapid succession
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There have been earthquakes as large as M6.0 in the past.
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World: 6.4 magnitude earthquake near New Caledonia
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M5.5 near the Strait of Gibraltar
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Reference materials, etc.
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