Weekly Earthquake Information 2023.1.29 Earthquake off the coast of Fukushima Prefecture with a seismic intensity of 4, the first scale in three months since October last year – Weather News

2023/01/29 10:27 Weather News

The number of felt-earthquakes observed in Japan over the past week is at a lower level than the previous week.

Earthquakes were conspicuous in the Kanto region to the southern Tohoku region, and tended to be few in other regions. There was one earthquake with a seismic intensity of 3 or higher. (Tally from January 23rd to 29th at 10:00)

Domestic: M5.1 occurred off the coast of Fukushima Prefecture Last year and the year before last, M7 class occurred

Earthquake off the coast of Fukushima Prefecture

At around 10:01 on the 25th (Wednesday), an earthquake estimated to have a magnitude of 5.1 and a depth of 55 km occurred off the coast of Fukushima Prefecture. In this earthquake, a maximum seismic intensity of 4 was observed in Soma City and Namie Town, Fukushima Prefecture, and Ishinomaki City, Miyagi Prefecture, and a seismic intensity of 3 was observed over a wide area of ​​Fukushima Prefecture and Miyagi Prefecture.

This is the first time in regarding three months since the October 21, 2011 earthquake (maximum seismic intensity of 5 lower) that an earthquake with a seismic intensity of 4 or more occurred off the coast of Fukushima Prefecture. The mechanism of the earthquake is analyzed as a reverse fault type with a pressure axis in the northeast-southwest direction.

In recent years, there have been a series of large earthquakes off the coast of Fukushima Prefecture. Two years ago, on February 13, 2021, a magnitude 7.3 earthquake occurred, and on March 16, 2022, a magnitude 7.4 earthquake occurred.

I don’t know if a similar earthquake will occur this year, but it’s true that it happened two years in a row at a similar time, so it might be a good idea to reconfirm earthquake countermeasures.

Epicenters where anomalous seismic regions are likely to appear

Abnormal seismic regions often appear in deep earthquakes off the southeast coast of Mie prefecture. In many earthquakes, areas with strong shaking are distributed concentrically from the epicenter. On the other hand, in deep earthquakes, strong tremors are transmitted along the subducting plate, and a phenomenon in which the tremors become larger far from the epicenter can be seen, and this is called an “abnormal earthquake zone.”

Other than the southeastern offshore of Mie Prefecture, similar deep earthquakes often occur in the Sea of ​​Okhotsk, the Sea of ​​Japan, the southern offshore of Tokaido, and the sea near Torishima, and once every few years, an earthquake with a magnitude of 6 or more also occurs.

Even if the tremors were small near the epicenter, strong tremors were transmitted far away. Mie Prefecture, which is close to the epicenter, did not have any locations where felt earthquakes were observed, and the maximum seismic intensity of 4 was observed in Ibaraki and Fukushima prefectures. A large-scale earthquake may cause tremors exceeding seismic intensity 5 lower, so caution is required.

Japan: Deep earthquake abnormal seismic area seen off the west coast of the Ogasawara Islands

At around 13:50 on the 16th (Monday), an earthquake estimated to have a magnitude of 5.9 and a depth of 422 km occurred off the west coast of the Ogasawara Islands. In this earthquake, a maximum seismic intensity of 3 was observed in Ogasawara Village, and a seismic intensity of 1 was observed from the Kanto region to the southern Tohoku region.

Because it was a deep earthquake with a depth of 400 km, the epicenter distribution was in an abnormal seismic area. In many earthquakes, strong tremors are distributed concentrically from the epicenter, but in deep earthquakes, strong tremors are transmitted along the subducted plate, and a phenomenon in which the tremors become stronger in the distance near the plate boundary is observed. This is called an “abnormal seismic area”.

In this earthquake, it is thought that the shaking propagated to the Pacific coast of northern Japan and eastern Japan along the Pacific plate where seismic waves easily propagate.

Japan: A strong earthquake in January this year with a seismic intensity of 4 in Hyuga Nada

At around 3:06 on the 18th (Sunday), an earthquake estimated to have a magnitude of 5.4 and a depth of regarding 30 km occurred with an epicenter in Hyuga-nada. In this earthquake, a maximum seismic intensity of 4 was observed in Miyazaki City and Nichinan City, and a seismic intensity of 3 was observed in Miyakonojo City and Kobayashi City in Miyazaki Prefecture, Kirishima City and Kanoya City in Kagoshima Prefecture, and Kumamoto City in Kumamoto Prefecture.

This is the first earthquake with a seismic intensity of 4 or higher with its epicenter in Hyuga-nada since January 22, 2018. The mechanism of the earthquake was analyzed as a normal fault type with a tension axis in the east-west direction.

The epicenter is further south than the magnitude 6.6 earthquake that occurred in January, and the area is close to the magnitude 7.0 earthquake that occurred in 1961.

World: Another deep earthquake in Argentina, South America

Earthquakes of M4.5 or higher around the world (quoted from USGS website/processed by Weathernews)

There have been two earthquakes with a magnitude of 6 or higher according to US Geological Survey analysis. The largest earthquake was a magnitude 6.4 that occurred in Argentina, South America.

In the early hours of the 25th (Wednesday) Japan time, an earthquake with a magnitude of 6.4 and an estimated depth of regarding 596 km occurred with an epicenter in northern Argentina. The earthquake mechanism is analyzed as a normal fault type with a tension axis in the east-northeast-west-southwest direction.

Four days ago, on the 21st (Saturday), an earthquake with a magnitude of 6.8 occurred at almost the same epicenter. A sequence of actions is possible, as the mechanisms are also similar.

On the South American continent, the Nazca Plate is subducting into the South American Plate, and large earthquakes often occur in shallow areas along the Pacific coast such as Chile. The farther away from the sea, the deeper the epicenter becomes, and in northern Argentina near the epicenter this time, an earthquake occurs at a depth of 500 to 600 km.

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.