2024-03-24 01:30:00
2024/03/24 13:11 Weather News
The number of felt earthquakes observed in Japan over the past week is at a lower level compared to the previous week.
Earthquakes with epicenters around the Noto Peninsula and on land in the Kanto region were noticeable. Earthquakes with a seismic intensity of 3 or higher have occurred three times across the country, and on the 21st (Thursday), an earthquake with a seismic intensity of lower 5 occurred, following on from the previous week. (Tally from March 18th to 24th at 10am)
Domestic: M5.3 seismic intensity of lower 5 or higher in southern Ibaraki Prefecture for the first time in a year and a half
Earthquake in southern Ibaraki Prefecture
This earthquake had a maximum seismic intensity of lower 5 in Shimotsuke City, Tochigi Prefecture and Kazo City, Saitama Prefecture, Kasama City, Tsuchiura City, Chikusei City, Bando City, Ibaraki Prefecture, Utsunomiya City, Tochigi Prefecture, Tochigi City, Sano City, Tatebayashi City, Gunma Prefecture, and Saitama Prefecture. Seismic intensity 4 tremors have been observed across a wide area in the Kanto region, including Saitama City, Kasukabe City, Kawaguchi City, Noda City in Chiba Prefecture, and Kamagaya City.
This is the first time in about a year and a half since November 2022 that an earthquake with a seismic intensity of lower 5 or higher occurred in the southern part of Ibaraki Prefecture, and the mechanism of the earthquake is analyzed to be a reverse fault type with a pressure axis running from north-northwest to south-southeast.
The southern part of Ibaraki Prefecture is at the boundary where the Philippine Sea Plate subducts into the land plate, and is an area that can be called an “earthquake nest”, with many earthquakes in the Kanto region. This time’s earthquake appears to be of the same type as previous earthquakes, based on its mechanism and depth.
In addition to magnitude 5 class earthquakes like this one, earthquakes of magnitude 6 or higher can also occur. In 1985, an earthquake with a magnitude of 6.0 occurred, and a seismic intensity of 5 (class at the time) was observed in Otemachi, Tokyo. There is an old record of a magnitude 7.2 event occurring in 1895.
Earthquakes with a seismic intensity of 5 lower or 5 higher can occur at any time in this region, so if you are affected by this earthquake, such as things collapsing, please reconsider your countermeasures.
Domestic: Maximum seismic intensity 4 in Gifu Prefecture, epicenter near the Nobi fault zone
Earthquake in the Midwest of Mino, Gifu Prefecture
This is the first time in four years since June 2020 that an earthquake with a seismic intensity of 4 or higher occurred in the central western part of Mino, Gifu Prefecture, and the earthquake mechanism is analyzed to be strike-slip.
The epicenter of this earthquake was near the Nobi fault zone, which is distributed in western Gifu Prefecture. The Nobi fault zone is a fault zone that is thought to have been partially activated during the 1891 Nobi earthquake. The government’s Headquarters for Earthquake Research Promotion has estimated that there is a probability that an earthquake of magnitude 7.3 to 7.4 will occur within the next 30 years in the main part of the Nobi fault zone, which is believed to have been active during the Nobi earthquake, as well as the Neodani and Umehara fault zones. is almost 0%.
Be careful of shaking with a seismic intensity of less than 5
When slow slips occurred in the past, seismic activity increased, although there were slight differences from year to year. In 2007 and 2018, the number of earthquakes was particularly high, and land-based earthquakes were also noticeable. Strong shaking with a maximum seismic intensity of just under 5 was observed during the magnitude 4.8 earthquake on August 18, 2007.
The government’s Headquarters for Earthquake Research Promotion conducted an evaluation of a series of seismic activities and concluded that the earthquake was caused by slow slip off the coast of the Boso Peninsula.
As in the past, the activity is expected to continue for a week to several months, and depending on the scale of the earthquake and the location of the epicenter, it is thought that it may be accompanied by shaking with a seismic intensity of lower 5. Caution should be taken against strong shaking in areas close to the activity area.
The southern Kanto region, including the Boso Peninsula, experiences many magnitude 7 class earthquakes due to plate subduction. Even if there is no major earthquake during this activity, the area is at high risk, so it would be a good idea to double check to see if earthquake countermeasures are in place.
Domestic: M4.5 seismic intensity 3 observed off the coast of Urakawa
At around 14:18 on the 9th (Saturday), an earthquake estimated to have a magnitude of 4.5 and a depth of approximately 70 km occurred with its epicenter off the coast of Urakawa, Hokkaido. As a result of this earthquake, a maximum seismic intensity of 3 was observed in Atsuma, Abira, and Mukawa towns in Hokkaido, and a seismic intensity of 2 was observed in Sapporo, Chitose, Iwamizawa, Hakodate, Mutsu, Aomori, and other areas.
This is the second earthquake this year with a seismic intensity of 3 or higher that occurred off the coast of Urakawa on the 28th of last month. The mechanism of the earthquake is analyzed to be a reverse fault type with a pressure axis running northwest-southeast.
In this region, the Pacific plate is subducting under the land plate, and large earthquakes often occur. Recently, in 2016, an earthquake with a magnitude of 6.7 and a maximum seismic intensity of just under 5 occurred, and in 1982, an earthquake with a magnitude of 7.1 and a maximum seismic intensity of 6 (class at the time) occurred.
World: M6.4 off the coast of Indonesia
Earthquakes of M4.5 or higher around the world (USGS homepage quote/Weather News processing)
The earthquake we will be talking about this time is one that occurred in Indonesia. On the evening of the 22nd (Friday) Japan time, an earthquake with a magnitude of 6.4 and a depth of approximately 9 km occurred with its epicenter in the Java Sea north of Java Island, Indonesia. The mechanism of the earthquake is analyzed to be strike-slip type.
Bawean Island, which is close to the epicenter, is believed to have experienced a strong tremor of VII on the revised Mercari seismic intensity scale, and according to the Indonesian National Disaster Management Agency, there were some buildings damaged and minor injuries.
Huge earthquakes often occur in Indonesia due to the subduction of the Indo-Australian plate into the Eurasian plate. This earthquake appears to have occurred within a land plate rather than at a plate boundary. Most of the large earthquakes in the Java Sea are deep earthquakes at a depth of around 500 km, and there are not many earthquakes with shallow epicenters like this one that exceed magnitude 6.
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 the shaking was equivalent to V on the revised Mercalli seismic intensity scale, or 4 on Japan’s seismic intensity scale, although a strict comparison is not possible. 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.
Reference materials etc.
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