Weekly Earthquake Information 2023.1.15 Seismic intensity 3 earthquake in western Kanagawa Prefecture Area with many active faults – Weather News

2023/01/15 10:24 Weather news

The number of felt-earthquakes observed in Japan over the past week is at regarding the same level as the previous week.

While earthquakes are conspicuous from the Kanto region to northern Japan, there are fewer earthquakes in western Japan. There was one earthquake with a seismic intensity of 3 or higher. (Tally from January 9th to 15th at 10:00)

Japan: Shallow earthquake of magnitude 4.1 in western Kanagawa Prefecture

Western Kanagawa Earthquake

At around 12:19 on the 11th (Wednesday), an earthquake estimated to have a magnitude of 4.1 and a depth of 13 km occurred with an epicenter in western Kanagawa Prefecture. In this earthquake, a maximum seismic intensity of 3 was observed in Sagamihara City, Hadano City, Matsuda Town, etc. in Kanagawa Prefecture, and a seismic intensity of 1 or 2 was observed from Kanagawa Prefecture to Tokyo, Shizuoka Prefecture, and Yamanashi Prefecture.

It was the first time in regarding two months since November 17 last year that an earthquake with an epicenter in western Kanagawa Prefecture had a seismic intensity of 3 or higher. The earthquake mechanism is analyzed as strike-slip type.

Multiple active faults are distributed in the western part of Kanagawa Prefecture, including the Kozu-Matsuda fault zone, the Hirayama-Matsuda north fault zone, and the Shiozawa fault zone. The epicenter this time was near the Kurokura fault, which extends along the extension of the Shiozawa fault zone.

The government’s Headquarters for Earthquake Research Promotion is evaluating the activity of the Shiozawa fault zone, and the probability of a magnitude 6.8 earthquake occurring within the next 30 years is less than 4%. Among the active faults under evaluation, this group has a high probability of occurrence.

Even with a magnitude 6 earthquake, the epicenter is shallow on land, so there is a risk of strong tremors.

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 tremors become stronger far from the epicenter can be seen, and this is called an “abnormal seismic 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 in northeastern Chiba prefecture earthquake

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: Massive 7.6 earthquake in Banda Sea, Indonesia

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 earthquake was a magnitude 7.6 that occurred off the coast of Indonesia.

An earthquake estimated to have a magnitude of 7.6 and a depth of regarding 105 km occurred early in the morning of the 10th (Tuesday) Japan time, with an epicenter in the Banda Sea of ​​Indonesia. The mechanism of the earthquake is analyzed as a reverse fault type with a pressure axis in the northeast-southwest direction. It was the first time in regarding four months since the September 19th earthquake in Mexico last year that an earthquake of magnitude 7.5 or higher occurred.

Since the epicenter was far from the populated island, there were no reports of damage caused by the tremors. Also, because the epicenter was deep, there was no tsunami.

The Banda Sea is a region where the Eurasian plate, Australian plate, Pacific plate, Philippine Sea plate, etc. are all closely packed, and has a very complicated structure.

Many earthquakes in the latter half of the magnitude 7 class have occurred, and in 1963 a huge earthquake of magnitude 8.1 occurred in the immediate vicinity of this epicenter. In addition, shallow earthquakes with a depth of around 10 km often occur, making it one of the areas with many large earthquakes even in Indonesia, which is a seismic country.

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.