2022/08/21 10:18 Weather News
Seismic activity in northern Hokkaido continues, and land earthquakes are occurring in various places from Tohoku to Kanto and western Japan. Five earthquakes with a seismic intensity of 3 or higher occurred. (Tally from August 15th to 21st at 10:00)
Japan: M3.7 maximum seismic intensity 3 in central Tottori prefecture
This is the second time an earthquake centered in central Tottori Prefecture has occurred since May this year. According to the automatic analysis of the National Research Institute for Earth Science and Disaster Resilience, the mechanism of the earthquake is thought to be a strike-slip type.
Although there are no known active faults in central Tottori prefecture, on October 11, 2016, an earthquake with a magnitude of 6.6 and a maximum seismic intensity of lower 6 occurred. 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’s Earthquake Research Committee conducted an earthquake assessment, which found that the area, including central Tottori Prefecture, has few known active faults, but is relatively seismically active. did.
In Tottori Prefecture, large earthquakes that occur in shallow land areas are conspicuous, such as the 1943 Tottori Earthquake, the 2000 Western Tottori Earthquake, and the 2016 Central Tottori Earthquake. Daily vigilance is essential.
Japan: Seismic intensity 3 at eastern Kanagawa prefecture
The mechanism of the earthquake is analyzed as a reverse fault type with a pressure axis in the west-northwest-east-southeast direction. This is the first time an earthquake with a seismic intensity of 3 or more with an epicenter in eastern Kanagawa occurred in February this year. The February quake had an epicenter as deep as 100 km, which is the first since the February 2016 magnitude 4.6 earthquake with a depth of 26 km to be limited to a shallow type earthquake similar to this one.
At a depth of around 30 km in eastern Kanagawa Prefecture, earthquakes with a magnitude of around 5 occur occasionally. In November 1923, there was an earthquake of magnitude 6.3, which is thought to be an aftershock of the Great Kanto Earthquake or related activity.
The Cabinet Office’s assumption of an earthquake directly hitting the Tokyo metropolitan area includes an earthquake with an epicenter in Kanagawa Prefecture, so it is essential to take countermeasures on a daily basis.
Japan: In the Soya region of Hokkaido, seismic intensity 3 to 4 in quick succession
Also, just 20 minutes later, at around 1:59, there was a magnitude 3.5 earthquake, and nearly three hours later at around 4:28, a magnitude 2.9 earthquake occurred, both with a maximum seismic intensity of 3. The epicenters and depths are almost the same, and it seems to be a series of seismic activity. No felt earthquake has occurred since the earthquake at 7:09 on Friday, April 4.
An earthquake with a magnitude of 4.4 also occurred near the epicenter this time on June 20, and a maximum seismic intensity of 4 was observed.
Although the Soya region has relatively few earthquakes compared to other parts of Hokkaido, displacement that 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 Soya region. According to the government’s Headquarters for Earthquake Research Promotion, the probability of an earthquake of magnitude 7.6 or so occurring within the next 30 years is less than 4%. Although there have not been many major earthquakes in recent years, the area is not necessarily safe.
There have been earthquakes as large as M6.0 in the past.
Most of the earthquakes are concentrated at a depth of around 10 km even in the depth of the east-west cross section. There are few occurrences at depths of 20 km or more, but there are a few at depths of 100 km or more. These are earthquakes that occur near the boundary between the Pacific plate and the Eurasian plate or within the Pacific plate.
Most deep earthquakes are around magnitude 4, but in May 2014, a large earthquake with a magnitude of 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 in the wide area of the Kanto region, causing damage such as injuries.
World: Magnitude 6.4 earthquake near New Caledonia
Early in the morning of the 15th (Monday) Japan time, an earthquake with a magnitude of 6.4 and a depth of about 78 km occurred with an epicenter near the Loyalty Islands, east of New Caledonia. The earthquake mechanism is a normal fault type with a tension axis in the northwest-southeast direction, and includes a slight strike-slip 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 this year, a magnitude 7.0 earthquake occurred with a slightly shallower epicenter, and last year there was a magnitude 7.7 earthquake. Even before that, an earthquake of magnitude 7 class occurred once every few years.
The magnitude 7.7 earthquake in 2021 is a reverse fault type earthquake unlike this time, and the epicenter was shallow, so a tsunami was generated.
M5.5 near the Strait of Gibraltar
The Strait of Gibraltar is the strait that separates Europe and Africa, as well as the boundary between the Eurasian and African plates. Because it is not a subduction zone, many strike-slip earthquakes occur, and the magnitude 6.3 earthquake that occurred in 2016 and the magnitude 6.4 earthquake that occurred in 2004 have the same mechanism.
Since many earthquakes occur in shallow areas, if they occur close to land or on land, they will be strong near the epicenter.
Reference materials, etc.
*Information on earthquake sources and seismic intensity in Japan is from the Japan Meteorological Agency unless otherwise specified. Overseas epicenter information is from the United States Geological Survey (USGS) unless otherwise specified. There may be differences in hypocenter information depending on the publishing organization.