The number of felt earthquakes observed in Japan over the past week has been slightly lower than the previous week.
Aftershocks from the Noto Peninsula earthquake continue to be active, and earthquakes on the Pacific side of the Kanto and Tohoku regions are also noticeable. There were four earthquakes with a seismic intensity of 3 or higher around the Noto Peninsula, and three in other areas. (Tally from February 12th to 18th at 10am)
Domestic: M4.4 earthquake in southern Kyoto Prefecture
Earthquake in southern Kyoto Prefecture
At around 15:29 on Wednesday the 14th, an earthquake estimated to have a magnitude of 4.4 and a depth of 12 km occurred with its epicenter in southern Kyoto Prefecture. As a result of this earthquake, a maximum seismic intensity of 4 was observed in Fushimi Ward, Kyoto City, and a seismic intensity 3 was observed in a wide area including Kamigyo Ward, Kyoto City, Kameoka City, Nantan City, Takatsuki City, Osaka Prefecture, and Sanda City, Hyogo Prefecture.This is the first time in two years since May 2022 that an earthquake with a seismic intensity of 4 or higher occurred in southern Kyoto Prefecture. The mechanism of the earthquake is analyzed to be strike-slip type. In 2022, there were many earthquakes from March to May in almost the same area as this earthquake, with two earthquakes measuring intensity 4 and two earthquakes measuring intensity 3.
The Kyoto Nishiyama fault zone extends near the epicenter of this earthquake. The Kyoto Nishiyama Fault Zone is a fault zone that runs from Kyotanba Town in Kyoto Prefecture to Shimahon Town in Osaka Prefecture, passing through the west side of the Kyoto Basin. The government’s Earthquake Research Promotion Headquarters puts the probability of an earthquake of magnitude 7.5 occurring within 30 years at approximately 0-0.8%.
Domestic: Deep earthquake and abnormal seismic area seen off the eastern coast of the Izu Peninsula
At around 17:42 on Friday the 9th, an earthquake estimated to have a magnitude of 4.9 and a depth of 172 km occurred with its epicenter off the eastern coast of the Izu Peninsula. As a result of this earthquake, seismic intensity 2 was observed in a wide area centered on the Kanto region, including Chiyoda Ward and Nerima Ward in Tokyo, Yokohama City in Kanagawa Prefecture, Kawasaki City, Ichikawa City in Chiba Prefecture, Kisarazu City, and Utsunomiya City in Tochigi Prefecture.
In an earthquake with a shallow epicenter, areas with strong shaking are distributed concentrically from the epicenter, but in deep earthquakes, strong shaking is transmitted along the subducting plate, and the shaking becomes stronger in the distance near the plate boundary. This is called an “abnormal seismic area.” Even if the shaking is small near the epicenter, strong shaking can be transmitted far away, so caution is required.
Deep earthquakes often occur off the coast of the Tokai region. In 2022, a magnitude 6.4 earthquake occurred off the southeast coast of Mie Prefecture, and in 2014, a magnitude 6.0 earthquake occurred near Izu Oshima near this time, and a maximum seismic intensity of just under 5 was observed in Chiyoda Ward, Tokyo.
Earthquake with a seismic intensity of 3 to 4 around the Noto Peninsula
Epicenter distribution around Noto Peninsula
At around 10:32 on Wednesday the 14th, an earthquake estimated to have a magnitude of 4.5 and a depth of 11 km occurred with its epicenter in the Noto region of Ishikawa Prefecture. As a result of this earthquake, a maximum seismic intensity of 4 was observed in Anamizu Town, Ishikawa Prefecture, and a seismic intensity of 3 was observed in Nanao City, Wajima City, and Shiga Town.On the 15th (Thursday), there were two earthquakes with an intensity of 3. The number of rather strong aftershocks has increased over the past week, with one seismic intensity 3 on the 17th (Saturday). However, the number of felt earthquakes was almost unchanged from the previous week, so it is thought that there was no increase in activity.
The Japan Meteorological Agency announced on Friday the 16th that the probability of an earthquake with a maximum seismic intensity of lower 5 or higher continues to be about 40 times higher than normal, and urged people to continue to be on guard against strong shaking.
Domestic: Earthquake with maximum seismic intensity 4 in eastern Hokkaido
At around 15:56 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 seismic intensity 4 was observed in Kushiro City and Abashiri City, which are far from the epicenter.
In addition, earthquakes of magnitude 6 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: M6.1 deep earthquake south of Iwo Jima
Earthquakes of M4.5 or higher around the world (USGS homepage quote/Weather News processing)
There were two earthquakes with a magnitude of 6 or higher, according to analysis by the U.S. Geological Survey. The largest earthquake was a magnitude 6.1 earthquake that occurred in the waters south of the Ogasawara Islands.On the night of the 12th (Monday) Japan time, an earthquake estimated to have a magnitude of 6.1 and a depth of approximately 250 km occurred with its epicenter south of Iwo Jima in the Ogasawara Islands. The mechanism of the earthquake is analyzed to be a reverse fault type with a pressure axis running north-south.
Because the epicenter was deep and far from the island, there was no impact from the shaking.
The epicenter of this earthquake was near the boundary between the Philippine Sea plate and the Pacific plate. In addition to deep earthquakes with a magnitude of 6, shallow earthquakes often occur.
In 2016, a large earthquake with a magnitude of 7.7 and a depth of approximately 196 km occurred a little south of this time, and the largest earthquake in Japan was observed to be 2. Because it was a deep earthquake, the shaking is thought to have reached far along the Pacific Plate, where seismic waves can easily propagate.
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.
Reference materials etc.
2024-02-18 01:03:00
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