Weekly Earthquake Information 2022.12.25 M4.1 seismic intensity 3 or more in the sea near Niijima and Kozushima for the first time in about 2 years – Weather News

2022/12/25 11:06 Weather News

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

There were few earthquakes on the Pacific Ocean side of Hokkaido from Tohoku, and most of them occurred from the southern part of Kanto to the Izu Islands. In western Japan, earthquakes are occurring mainly in Kyushu. There were two earthquakes with a seismic intensity of 3 or higher. (Tally from 10:00 on December 19th to 25th)

Japan: There are many earthquakes related to volcanoes in the sea near Niijima and Kozushima.

Earthquake near Niijima and Kozushima

At around 4:56 on the 21st (Wednesday), an earthquake estimated to have a magnitude of 4.1 and a depth of 10 km occurred near Niijima and Kozushima. This earthquake recorded a maximum seismic intensity of 3 in Niijima Village and a seismic intensity of 2 in Toshima Village. This earthquake was preceded by two felt-earthquakes, and many other small earthquakes.

It is the first time in regarding two years since an earthquake with a seismic intensity of 3 or more with an epicenter in the sea near Niijima and Kozushima occurred on January 1, last year, with a magnitude of 4.7 and a maximum seismic intensity of 4. Two years ago, a swarm of earthquakes occurred in December.

Earthquake swarms often occur in the Izu Islands due to subsurface magma activity, and there have been several cases of large earthquakes of magnitude 6 or higher, such as in 2000 associated with volcanic activity on Miyakejima. Although there are no signs of activity for this earthquake so far, it is necessary to prepare on a daily basis.

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: Seismic intensity 4 earthquake in northeastern Chiba Prefecture

Earthquake in northeastern Chiba Prefecture

At around 00:02 on the 19th (Monday), an earthquake estimated to have a magnitude of 4.1 and a depth of 27 km occurred with an epicenter in the northeastern part of Chiba Prefecture. Due to this earthquake, a maximum seismic intensity of 4 was observed in Chonan Town, Chiba Prefecture, and a seismic intensity of 3 was observed in Mobara City, Oamishirasato City, Isumi City, etc.

It is the first time in two years and seven months since May 2020 that an earthquake centered in the northeastern part of Chiba Prefecture occurred. The mechanism of the earthquake is analyzed as a reverse fault type with a pressure axis in the northwest-southeast direction.

Relatively large earthquakes have occurred in the northeastern part of Chiba Prefecture, in the area close to Ibaraki Prefecture, and in the vicinity of this epicenter. In 2019, we observed a strong shaking with a maximum seismic intensity of lower 5 due to a magnitude 5.1 earthquake with an epicenter a little further inland than this time.

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: Damage caused by M6.4 strong tremors off the coast of Northern California, USA

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

There has been one earthquake with a magnitude of 6 or higher according to US Geological Survey analysis. The largest quake was a magnitude 6.4 off the coast of Northern California.

On the night of the 20th (Tuesday) Japan time, an earthquake estimated to have a magnitude of 6.4 and a depth of regarding 18 km occurred off the coast of Northern California, USA. The earthquake mechanism is analyzed as strike-slip type. Because it occurred relatively close to the land, it is thought that the coastal area experienced a tremor of VIII on the revised Mercalli seismic intensity scale.

In areas where the tremors were strong, there were cracks in bridges and roads, and power outages occurred.

The epicenter of this quake was near the boundary of three plates: the Pacific plate, the North American plate, and the Fandeca plate, an area where many strong earthquakes occur. Exactly one year ago, on December 20th, a magnitude of 6.2 occurred. In 2005, there was also an earthquake with a magnitude of 7.2, although the epicenter was a little further away.

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.