2023-07-09 01:11:00
2023/07/09 10:11 Weather News
The number of felt-earthquakes observed in Japan over the past week is at a lower level than the previous week. Earthquakes with epicenters on land were relatively conspicuous.
There was one earthquake with a seismic intensity of 3 or higher. (Tally from July 3rd to 9th at 10:00)
Japan: M4.0 earthquake in Noto region, Ishikawa Prefecture
Earthquake in the Noto region of Ishikawa Prefecture
At around 21:36 on the 8th (Sat), an earthquake estimated to have a magnitude of 4.0 and a depth of regarding 10 km occurred with an epicenter in the Noto region of Ishikawa Prefecture. This earthquake recorded a maximum seismic intensity of 3 in Suzu City, Ishikawa Prefecture.This is the first time in regarding a month since June 9 that an earthquake with a seismic intensity of 3 or higher has been observed in the Noto earthquake that has continued for several years. The mechanism of the earthquake is a reverse fault type with a pressure axis in the northwest-southeast direction, which is the same type as previous activities.
After the 6.5-magnitude earthquake, the largest in a series of activities, occurred on May 5, Noto remained active for some time. Although it has calmed down since the beginning of June, felt earthquakes still occur several times a week.
What is an anomalous seismic area?
This earthquake is thought to be a deep earthquake that occurred on the Pacific plate, which has subducted very deep underground.
In shallow earthquakes, areas with strong shaking are distributed concentrically from the epicenter, but in deep earthquakes, strong shaking is transmitted along the subducted plate, and a phenomenon is observed in which the shaking becomes stronger in the distant region near the plate boundary. This is called an “abnormal seismic area”. Even if the tremor is small near the epicenter, strong tremors may be transmitted to distant places, so caution is required.
The possibility of a tsunami is small in a deep-focused earthquake, and in general, it is thought that there is almost no risk of a tsunami in an earthquake whose epicenter is deeper than 100 km.
In the Sea of Japan, a deep earthquake of magnitude 6 class similar to this one occurs at a rate of regarding once every few years. Recently, in September 2021, an earthquake of magnitude 6.1 occurred. Compared to this time, it occurred closer to Honshu, so a seismic intensity of 3 was observed over a wide area on the Pacific side from Hokkaido to Kanto.
Japan: Two felt-earthquakes in the Kumamoto region of Kumamoto Prefecture on Monday, March 3
At around 3:09 on the 3rd (Monday), an earthquake estimated to have a magnitude of 3.1 and a depth of 9 km occurred with an epicenter in the Kumamoto region of Kumamoto Prefecture, and a seismic intensity of 1 was observed in Yatsushiro City, Kumamoto Prefecture.
Also, at around 15:22, an earthquake estimated to have a magnitude of 2.5 and a depth of 10 km occurred with an epicenter in the Kumamoto region of Kumamoto Prefecture, and a seismic intensity of 1 was observed in Izumi Town, Kumamoto Prefecture and Omuta City, Fukuoka Prefecture.
The former earthquake occurred in the focal region of the 2016 Kumamoto earthquake, and the latter earthquake occurred in January 2019 in the focal region with a maximum seismic intensity of lower 6.
Although some time has passed since each earthquake occurred, the activity itself is still ongoing. No signs of activation have been seen.
Japan: A strong earthquake in January this year with a seismic intensity of 4 in Hyuga Nada
World: Deep M5.8 earthquake in Chile, South America
Earthquakes of M4.5 or higher around the world (quoted from USGS website/processed by Weathernews)
There have been no earthquakes of magnitude 6 or higher according to analysis by the United States Geological Survey. The largest earthquakes were magnitude 5.9 in the Antarctic Ocean and near the South Sandwich Islands.On the morning of the 6th (Thursday) Japan time, an earthquake estimated to have a magnitude of 5.9 and a depth of regarding 132 km occurred with an epicenter in Chile in South America. The earthquake mechanism is analyzed as a normal fault type with a tension axis in the northeast-southwest direction.
Since the epicenter was a deep earthquake, the tremors near the ground surface were not so large and there was no impact.
Near Chile, the Nazca plate is subducting under the South American plate, and many earthquakes occur. The subducting boundary of the plate is shallow off the coast of Chile, and deepens as it enters the land area.
A 6.8-magnitude earthquake occurred in 2020 near the epicenter of this earthquake, and there is an old record of a 8.2-magnitude earthquake in 1950.
World: Rare damaging earthquake in western France
An earthquake estimated to have a magnitude of 4.8 and a depth of regarding 5 km occurred early in the morning of Saturday, 17th Japan time, with an epicenter in western France. Although the scale of the earthquake was small, it was shallow, so it was hit by strong shaking in the vicinity of the epicenter, and it is believed that buildings and other structures were damaged.
There are few earthquakes in France, and even earthquakes with magnitudes in the upper 4s like this one don’t happen often. It is the first time in a year and three months since March last year that an earthquake of magnitude 4.5 or higher occurred.
The area around the epicenter of this earthquake is relatively prone to earthquakes in France, and in 2005 there was an earthquake with a magnitude of 5.2.
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.
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