The number of felt earthquakes observed in Japan in the past week is at an extremely high level due to the occurrence of the 2020 Noto Peninsula Earthquake. Earthquakes with a seismic intensity of 3 or higher have occurred approximately 180 times.
On the other hand, seismic activity outside the Noto Peninsula area was low. (Tally from January 1st to 7th at 10am)
Domestic: M7.6 tsunami also occurs in the Noto region of Ishikawa Prefecture
Earthquake in Noto region, Ishikawa Prefecture
At around 16:10 on Monday, January 1st, an earthquake estimated to have a magnitude of 7.6 and a depth of 16 km occurred with its epicenter on the Noto Peninsula in Ishikawa Prefecture.As a result of this earthquake, a maximum seismic intensity of 7 was observed in Shiga Town, Ishikawa Prefecture, a seismic intensity 6 upper was observed in Nanao City, Wajima City, Suzu City, and Anamizu Town, Ishikawa Prefecture, and a seismic intensity 6 lower was observed in Nakanoto Town, Noto Town, Ishikawa Prefecture, and Nagaoka City, Niigata Prefecture. Tremors with a seismic intensity of 1 or higher were felt across a wide area from Hokkaido to Kyushu. The Japan Meteorological Agency has named this earthquake the “Reiwa 6 Noto Peninsula Earthquake.”
This is the first shallow earthquake near Japan with a magnitude of 7.5 or higher since the 2011 series of events that caused the Great East Japan Earthquake. This is the seventh earthquake in Japan with a seismic intensity of 7, and the first since the 2018 Hokkaido Eastern Iburi Earthquake in 2018. The mechanism of the earthquake is analyzed to be a reverse fault type with a pressure axis running northwest-southeast.
A tsunami occurred because the epicenter was a shallow earthquake that included ocean waters, and the Japan Meteorological Agency issued a major tsunami warning. Tide gauges observed a tsunami of over 1.2 meters high, and the interpretation of aerial photographs by the Geospatial Information Authority of Japan indicates that a wide area centered on Suzu City was inundated by the tsunami.
In addition, due to crustal deformation caused by the earthquake, the Geospatial Information Authority of Japan has observed uplifts of up to 1 meter or more, and even more in some places. It is also known that the tsunami observation point set up by the Japan Meteorological Agency in Suzu City has become unobservable due to the uplift.
Areas where seismic activity has continued for more than 3 years
Seismic activity has been increasing in the Noto region of Ishikawa Prefecture since December 2020. On May 5th of last year, the largest earthquake to date occurred with a magnitude of 6.5 and a seismic intensity of 6+.
This earthquake includes the area of activity up until last year, but the area is much larger. While the activity from 2020 to 2023 was within an area of approximately 30km square, this time it is over a wide area of more than 150km in the northeast to southwest direction.
Even when comparing the energy of an earthquake, a magnitude 7.6 is more than 40 times that of a magnitude 6.5, indicating that much more destruction occurred.
Several active faults have been identified near the north coast of the Noto Peninsula that have not been evaluated by the government’s Headquarters for Earthquake Research Promotion. It is thought that these faults were activated all at once, causing a large earthquake.
Damage to houses is widespread
Damage situation to houses etc.
Many houses collapsed in the northern part of the Noto Peninsula, which was hit by intense shaking with a seismic intensity of 7 to over 6. An emergency survey conducted by Weather News for its members revealed that damage to homes and other areas was widespread, although no responses were received from the severely damaged areas.Damage to houses was most noticeable in areas that experienced earthquakes of magnitude 5 or higher, such as throughout Ishikawa Prefecture and eastern Toyama Prefecture. Additionally, there was a lot of damage in the Echigo Plain, including Niigata City, which is a little far from the epicenter. Liquefaction occurred in many places in Niigata City, and it is thought that this had an impact on houses.
Houses that have been damaged by an earthquake may have new parts damaged by aftershocks or future snowfall, so care must be taken.
Weather News has also set up a special website to support disaster-stricken areas. We are currently updating real-time feedback from the local community.
Seismic activity continues to be active
Nearly a week has passed since the magnitude 7.6 earthquake occurred, and activity continues to be high. Although the number has decreased compared to immediately after the earthquake occurred, the number of felt earthquakes with a seismic intensity of 1 or higher still exceeded 50 on the 6th (Saturday).
Earthquakes with a magnitude of 4 to 5 occur sporadically, and if such an earthquake were to occur on land, it would be accompanied by shaking with a seismic intensity of 5 lower to 5 higher.
In past cases, earthquakes exceeding magnitude 5 have often occurred long after the main shock.
The 2016 Kumamoto Earthquake (M7.3) occurred twice five days later, the 2004 Niigata Prefecture Chuetsu Earthquake (M6.8), which had a large number of aftershocks, occurred 18 days later, and the 1948 Fukui Earthquake ( M7.1) occurs after 12 days.
Although it is difficult to make general statements about the occurrence of aftershocks as they differ from earthquake to earthquake, this time’s magnitude was 7.6, which is larger than the previous cases, so it would not be surprising if the activity lasted for a long time. It is thought that we will need to be on guard against strong shaking for a while.
World: No major earthquakes worldwide
Earthquakes of M4.5 or higher around the world (USGS homepage quote/Weather News processing)
According to analysis by the U.S. Geological Survey, two earthquakes with a magnitude of 6 or higher have occurred. All of these earthquakes were due to activity on the Noto Peninsula, and there were no earthquakes exceeding magnitude 6 outside of Japan.Looking at the world as a whole, earthquake activity is not very active, and even the strongest earthquakes are around magnitude 5.5. Even from Indonesia to the South Pacific, where many earthquakes occur, most earthquakes are small.
Looking at the past week, we can see that the seismic activity in the Noto Peninsula is remarkable even on a global scale.
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.
2024-01-07 01:00:00
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