Eight days have passed since the M7.6 earthquake with a maximum seismic intensity of 7 that occurred in the Noto region of Ishikawa Prefecture on January 1st (Reiwa 6 Noto Peninsula Earthquake), and the number of earthquakes is gradually decreasing.
However, today, the 9th (Tuesday) at around 5:59 pm, an M6.0 earthquake occurred near Sado, and a maximum seismic intensity of 5 lower was observed in Nagaoka City, Niigata Prefecture. This is the first earthquake of magnitude 6 or higher in eight days, and we need to be careful as strong earthquakes continue to occur sporadically.
This is a summary of the seismic activity status up to 7:00 pm on the 9th (Tuesday).
» Earthquake information list
The number of earthquakes is gradually decreasing
Number of earthquakes with a seismic intensity of 1 or higher per hour (Weather News tabulation)
The number of earthquakes with a seismic intensity of 1 or higher from 16:00 on the 1st (Monday) to 13:00 on the 8th (Monday) is 359 on the 1st, 414 on the 2nd, 176 on the 3rd, and 85 on the 4th. 81 times on the 5th, 55 times on the 6th, 35 times on the 7th, 31 times on the 8th, and 23 times on the 9th. The total number of earthquakes was 1257, of which 16 were earthquakes with a maximum seismic intensity of 5 or higher.
January 9th (Tuesday) around 17:59 M6.0 earthquake near Sado Seismic intensity distribution
MT diagram including earthquakes with a maximum seismic intensity of less than 1 Epicenter distribution including earthquakes with a maximum seismic intensity of less than 1
Although the number of earthquakes is decreasing day by day, one earthquake with a seismic intensity of lower than 5 occurred on the 9th (Tuesday), 8 days after the M7.6 earthquake. This is the first earthquake of magnitude 6 or higher since the magnitude 6.1 earthquake that occurred at 16:18 on January 1, and is the largest earthquake to occur near Sado in a series of seismic activities.
Looking at the epicenter distribution map at the beginning of the article, which includes earthquakes with a maximum seismic intensity of less than 1, it is believed that this earthquake near Sado also occurred near the northeastern end of the epicenter area of the January 1st earthquake. The epicenters of other earthquakes are generally distributed within a range of about 150 km from the west coast of Ishikawa Prefecture to the west of Sado Island, and no noticeable expansion has been observed so far.
Although the number of earthquakes is decreasing, strong earthquakes still occur sporadically, so we cannot let our guard down.
» Earthquake information list
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 case, 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.
The main shock tends to be an aftershock type, with some cases where the largest aftershock occurred a month later
Regarding the seismic activity that has been continuing since 2020 around the Noto Peninsula, the largest earthquake so far was an M6.5 earthquake with a maximum seismic intensity of 6+ on May 5, 2023, but this M7.6 earthquake is one of the 40th to 40th. That’s about 50 times more energy. Looking at the earthquakes that have occurred around Japan, excluding deep earthquakes, this is the largest earthquake since the Tohoku Pacific Coast Earthquake in March 2011.
Looking at the state of seismic activity, unlike the swarm type of seismic activity that has occurred around the Noto Peninsula over the past few years, there has been a tendency for mainshocks to be followed by aftershocks, which is commonly seen in other regions. It is thought that the number of earthquakes will gradually decrease in the future.
However, it is impossible to predict how long strong aftershocks will continue. Looking at past mainshock-aftershock type earthquakes, some M5-6 class aftershocks occurred several weeks or months later. Looking at cases similar in magnitude to this earthquake, the M7.7 Central Japan Sea Earthquake that occurred in 1983 and the M7.8 Hokkaido Nansei-Oki Earthquake that occurred in 1993 both reached their peak approximately one month after the main shock. Aftershocks are occurring.
As of the 8th (Monday), the Japan Meteorological Agency has calculated that the probability of an earthquake with a seismic intensity of 5 or higher has decreased to about 1/2 compared to when the main shock first occurred, but it is still very high compared to normal times. It is over 100 times more.
If the building has been damaged in the past, there is a risk that it may collapse due to aftershocks, so please continue to stay in a safe place.
» Earthquake information list
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Looking at the distribution of the series of earthquakes, we can see that the earthquakes are not limited to the area at the northeastern tip of the Noto Peninsula, where earthquake swarms have frequently occurred since December 2020, but have spread over an area of about 150 km from the west coast of the Noto Peninsula to near Sado Island. You can see that there are. However, the epicenter area has not expanded since the day after the major earthquake, and it appears that activity has increased within the same epicenter area.
The M7.6 earthquake that occurred at 4:10 p.m. on the 1st (Monday) was much larger than previous earthquakes, so it is thought that the destruction of the bedrock caused by fault activity was widespread. For some time to come, we will need to be careful about both the intense shaking caused by the earthquake directly beneath the Noto Peninsula and the possibility of tsunamis caused by offshore earthquakes.
In Shiga Town, which was hit by an earthquake with a magnitude of 7, there were reports of buildings collapsing and cracks appearing on roads. According to the fire department and police, five people have been confirmed dead in Ishikawa Prefecture as of 6:00 a.m. on the 2nd (Tuesday). It is said that there are still many people who have not been contacted, and it may take some time before the full extent of the damage is revealed.
Overview of the series of largest earthquakes
Epicenter: Noto region, Ishikawa prefecture
Scale (magnitude): M7.6
Depth of epicenter: 16km
Seismic intensity in various places (seismic intensity 6 lower or higher)
■Seismic intensity 7:
[Ishikawa Prefecture]Kano, Shiga Town
■Seismic intensity 6+:
[Ishikawa Prefecture]Kakiyoshi-cho, Nanao City, Mukoda-cho, Notojima, Nanao City, Houji-cho, Wajima City, Kawai-cho, Wajima City, Misaki-cho, Suzu City, Shoin-cho, Suzu City, Otani-cho, Suzu City, Omachi, Anamizu-cho
■Seismic intensity 6 lower:
[Niigata Prefecture]Nakanoshima, Nagaoka City
[Ishikawa Prefecture]Shiga Town, Togiryoke Town, Shiga Town, Sueyoshi Chifuru, Nanao City, Honfuchu Town, Nanao City, Sodegae Town, Nakanoto Town, Suesaka, Nakanoto Town, Noto Shita, Noto Town, Ushitsu
Due to this earthquake, a major tsunami warning was issued for Ishikawa Prefecture and a tsunami warning for the Hokuriku region and other areas, but both were canceled as the earthquake weakened over time.
The height of the observed tsunami at Wajima Port, the largest port, was announced to be “1.2 meters or more,” but the exact height of the tsunami around the Noto Peninsula is currently unknown.
This is the first time that a seismic intensity of 7 has been observed in Japan since the 2018 earthquake in the central-eastern Iburi region.Other earthquakes include the Kumamoto Earthquake, the Tohoku Pacific Coast Earthquake that caused the Great East Japan Earthquake, and the Niigata Prefecture Chuetsu Earthquake, all of which caused significant damage. It’s all about things. It was the first time since observations began that a seismic intensity of 7 was observed within Ishikawa Prefecture.
source
Epicenter distribution data: From the Japan Meteorological Agency website
Reference materials etc.
2024-01-09 10:50:00
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