2024/01/28 10:05 Weather News
The number of felt earthquakes observed in Japan over the past week is at a lower level compared to the previous week.
The Noto Peninsula earthquake activity continues, and many felt earthquakes have occurred. There were six earthquakes with a seismic intensity of 3 or higher around the Noto Peninsula, and two in other areas. (Tally from January 22nd to 28th at 10am)
Domestic: Earthquake in Tokyo Bay Seismic intensity 4 in Tokyo’s 23 wards
Earthquake in Tokyo Bay
This is the first time that shaking with a seismic intensity of 4 or higher has been observed in Tokyo’s 23 wards since the earthquake with its epicenter in southern Chiba Prefecture on May 11, 2023. In addition, if we limit ourselves to earthquakes in Tokyo with a magnitude of 4 or higher and with an epicenter in Tokyo Bay, this is the first earthquake in 6 years since the magnitude 4.7 earthquake on January 6, 2018, which occurred in almost the same area as the current epicenter.
The area where this earthquake occurred appears to be part of the northwestern part of Chiba Prefecture, which has been prone to earthquakes. The epicenter of the earthquake was concentrated at a depth of 70 to 80 km, and preliminary estimates indicate that the depth was approximately 80 km.
Domestic: Areas where huge earthquakes are expected along the Kuril Trench
Earthquake off the southeast coast of Nemuro Peninsula
At around 1:29 p.m. on the 25th (Thursday), an earthquake estimated to have a magnitude of 4.8 and a depth of 46 km occurred with its epicenter off the southeast coast of the Nemuro Peninsula. As a result of this earthquake, tremors with a maximum seismic intensity of 3 were observed in Nemuro City, Hokkaido, and tremors of intensity 2 were observed in Hamanaka Town, Shibecha Town, Rausu Town, Betsukai Town, and other areas.This is the first time in three years since February 2021 that an earthquake with a seismic intensity of 3 or higher occurred off the southeast coast of the Nemuro Peninsula. The mechanism of the earthquake is analyzed to be a reverse fault type with a pressure axis in the northwest-southeast direction.
Off the coast of Nemuro, the Pacific plate is subducting into the land plate, and the boundary is 40 to 50 km deep. This earthquake appears to have occurred close to the boundary due to its mechanism and depth.
The government’s Earthquake Research Promotion Headquarters assesses that giant interplate earthquakes off the coast of Nemuro occurred in 1843, 1894, and 1973. It is estimated that there is an 80% probability that an earthquake with a magnitude of 7.8 to 8.5 will occur within the next 30 years.
Aftershocks of the Noto Peninsula Earthquake had a seismic intensity of 3 or higher six times.
Regarding the aftershock activity of the Noto Peninsula Earthquake, the number of felt earthquakes remained at around 10 per day, and earthquakes with a seismic intensity of 3 or higher occurred 6 times in one week.
The largest earthquake occurred on Friday the 26th, with a magnitude of 4.4 and an estimated depth of 13 km, with a maximum seismic intensity of 4 observed in Shiga Town, Ishikawa Prefecture. This is the first time in a week since the 19th (Friday) that a seismic intensity of 4 or higher was observed due to a series of activities.
Domestic: Earthquake with maximum seismic intensity 4 in eastern Hokkaido
At around 3:56 p.m. on Saturday the 13th, an earthquake estimated to have a magnitude of 3.9 and a depth of approximately 10 km occurred with its epicenter in the northern Kushiro region.
This earthquake was observed in Teshikaga Town, Hokkaido, with a maximum seismic intensity of 4. The last earthquake with a seismic intensity of 4 or higher centered in the northern Kushiro region was in 1967, before the current observation network was built.
Although there are no known active faults in the Akan/Teshikaga region where this earthquake occurred, it is a highly active area. The aforementioned 1967 earthquake had a magnitude of 6.5, a depth of 12 km, and a seismic intensity of 4 was observed in Kushiro City and Abashiri City, which are far from the epicenter.
In addition, earthquakes of the magnitude 6 class have occurred frequently, and in 1959, earthquakes of magnitude 6.3 and 6.1 occurred one after another within a two-hour period, causing damage.
World: M7.0 human casualties also occur in Uighur Autonomous Region
Earthquakes of M4.5 or higher around the world (USGS homepage quote/Weather News processing)
According to an analysis by the U.S. Geological Survey, there have been three earthquakes with a magnitude of 6 or higher. The largest earthquake was a magnitude 7.0 earthquake that occurred in the Uighur Autonomous Region of China.In the early hours of the 23rd (Tuesday) Japan time, an earthquake estimated to have a magnitude of 7.0 and a depth of approximately 13 km occurred with its epicenter in the Uyghur Autonomous Region. The mechanism of the earthquake is a reverse fault type with a pressure axis in the north-south direction, and it has been analyzed that there is a slight strike-slip component.
The magnitude of the earthquake was large, and the epicenter was shallow, so the surrounding area experienced strong shaking of IX on the revised Mercalli seismic intensity scale (although a simple comparison cannot be made, it is about 6 lower on the Japanese seismic intensity scale). Many buildings were damaged and some people died.
Strong earthquakes with shallow epicenters often occur in the region from the Uyghur Autonomous Region to Kyrgyzstan, and there is an old record of a magnitude 8.0 earthquake in Kyrgyzstan in 1911.
World: Tsunami of up to 40cm in Izu Islands and Hachijojima
The earthquake was large and the epicenter was relatively shallow, causing a tsunami. In the Philippines, a tidal level change of 8cm was observed in Davao, Mindanao. Because Davao is located deep in a narrow bay, it is possible that a larger tsunami could have reached coastal areas closer to the epicenter.
The tsunami reached Japan in the early hours of the 3rd (Sunday), with a maximum height of 40 cm on the Izu Islands and Hachijo Island, and 10 to 20 cm on the Pacific coast from Kanto to Kyushu and Amami. The Japan Meteorological Agency issued a tsunami advisory shortly after the earthquake occurred, and all advisories were lifted at 9:00 a.m. on the 3rd (Sunday).
Large earthquakes frequently occur around the Philippines due to the subduction of the Philippine Sea plate into the Eurasian plate. On the 17th of last month, there was a magnitude 6.7 earthquake in the south of Mindanao. Even if we restrict ourselves to areas near the epicenter of this earthquake, there were earthquakes of magnitude 7.0 in 1991 and magnitude 7.6 in 1989.
M5.5 earthquake in Bangladesh
In addition, around noon on the 2nd (Saturday) Japan time, an earthquake estimated to have a magnitude of 5.5 and a depth of approximately 39 km occurred with its epicenter in the southern part of Bangladesh. The mechanism of the earthquake is analyzed to be strike-slip type.
Because the epicenter was on land, the shaking was somewhat strong near the epicenter, and it is believed that the shaking was equivalent to V on the revised Mercalli seismic intensity scale, or 4 on Japan’s seismic intensity scale, although it is not possible to make a strict comparison. Although the epicenter was not far from the capital Dhaka, the area affected by the strong shaking was small and no major damage was reported.
Bangladesh is located near the boundary between the Indian plate and the Eurasian plate. Earthquakes with a magnitude of 6 or more occur from time to time, and the most recent one was a magnitude 6.0 earthquake in 1997. There is a very old record of a magnitude 7.1 event occurring in 1918.
Source/Reference
*Information on the epicenter and intensity in Japan is from the Japan Meteorological Agency unless otherwise specified. Information on overseas epicenters is from the United States Geological Survey (USGS) unless otherwise noted. There may be differences in the epicenter information depending on the publishing organization.