Weekly earthquake information 2024.11.17 Aomori / Mutsu Bay earthquake reaches magnitude 4, largest in 48 years

At approximately 21:22 on Saturday the 16th, an earthquake estimated at magnitude 4.6 and a depth of approximately 10km occurred with its epicenter in Mutsu Bay, Aomori Prefecture. As a result of this earthquake, a maximum seismic intensity of 4 was observed in Hiranai City, Aomori Prefecture, and a seismic intensity of 3 was observed in Sotogahama City, Noheji City, Yokohama City, and Sai City.

It is the first earthquake of magnitude 4 or greater centered in Mutsu Bay since 1919, when detailed records are kept by the Japan Meteorological Agency, and the first earthquake of magnitude 4.5 or greater in the 48 years since November 29, 1976, when it was magnitude 4.9. The mechanism of the earthquake is being investigated as a type of reverse fault with a stress axis running in the north-east-south-west direction.

Sensible earthquakes occur in Mutsu Bay about once every few years, and in 2018 there were three earthquakes with a seismic intensity of 3. Most earthquakes occur on coast of the Shimokita Peninsula, and earthquake swarm activity continued for about a year in 1976.

Within Aomori Prefecture, the Aomori Bay West Coast Fault Zone and the Tsugaru Mountains West Edge Fault Zone are known, and for the former, the probability of a magnitude 7.3 earthquake is estimated to be within the Next 30 years 0.5 to 1%. (According to the Earthquake Research Promotion Headquarters)

The government’s Headquarters for the Promotion of Earthquake Research estimates that there is a 70-80% chance of an earthquake with a magnitude of around 7.1 occurring in the Hyuga-nada Sea within the next 30 years, and this earthquake seems to be identical with this.

An assessment review meeting was held because the epicenter was within the Nankai Trough mega-earthquake monitoring area and the magnitude was 6.8 or higher. As a result, it was determined that the probability of a large earthquake occurring in the Nankai Trough earthquake is relatively high compared to the normal times, and the Nankai Trough earthquake emergency information (main earthquake warning) to issue.

This is the first time this information has been announced since it started working in 2019. e

If you are already well prepared for an earthquake, please review your preparedness, and if you are not, now is the time to review your product disaster prevention, evacuation routes, hazard maps, etc.

At approximately 2:58 on the 16th (Saturday), an earthquake estimated at magnitude 5.1 and a depth of approximately 30 km occurred with its epicenter off the east coast of Chiba Prefecture. As a result of this earthquake, a maximum seismic intensity of 3 was observed in Choshi City, Asahi City, Chiba Prefecture, and Kamisu City, Ibaraki Prefecture, and a seismic intensity of 2 was observed in a wide area from east- northern Chiba Prefecture to southern Ibaraki. Prefecture.

This is the first earthquake with a seismic intensity of 3 or higher centered on the east coast of Chiba Prefecture in four months since July this year (magnitude 5.2, maximum seismic intensity 4). The mechanism of the earthquake is being investigated to be strike-slip.

Off the east coast of Chiba Prefecture, the Philippine Sea plate and the Pacific plate merge into the earth’s plate, creating a complex underground structure. Although the depth of this earthquake is close to the subduction boundary of the Philippine Sea plate, it is considered to be of a different type from earthquakes that occur at plate boundaries, since a study was conducted because it has a strike-slip mechanism.

At approximately 12:29 on Saturday the 10th, an earthquake estimated at magnitude 6.8 and a depth of approximately 490km occurred with its epicenter in the southern part of the Sea of ​​Okhotsk. As a result of this earthquake, a seismic intensity of 3 was observed in Hakodate City, Hokkaido, Hachinohe City, Mutsu City, Hashikami Town, and Hiranai Town, Aomori Prefecture, and Morioka City, Iwate Prefecture.

In this earthquake, there were few places where a seismic intensity of 1 or higher was observed on the Sea of ​​Okhotsk side of Hokkaido, which is near the epicenter, and a seismic intensity of 3 was observed on the Tohoku Pacific side, which is far from the center.

In the case of a large, deep earthquake, a distribution of seismic intensity called an “abnormal seismic region” can be seen, where strong shaking is transmitted far away. Although it is called an anomaly, it is a phenomenon that often occurs during deep earthquakes.

In deep earthquakes, strong shaking is transmitted along the subducting plate, and the shaking can be large away near the plate boundary. In this earthquake, it is thought that the shaking moved to the coast of the Pacific Ocean in Hokkaido and Tohoku on the Pacific Plate, where seismic waves can move easily.

Similar earthquakes have occurred in the Sea of ​​Okhotsk in the past, with a magnitude 7.3 earthquake in 2012 causing tremors that reached the Kanto region. Large, deep earthquakes can cause strong tremors far from the epicenter, so you need to be careful.

According to a study by the US Geological Survey, two earthquakes with a magnitude of 6 or higher have occurred. The largest earthquake occurred in southern Cuba with a magnitude of 6.8.

In the early hours of the 11th (Monday) Japan time, an earthquake occurred that was estimated at a magnitude of 6.8 and a depth of about 14 km with its epicenter in southern Cuba. The mechanism of the earthquake is being investigated to be strike-slip type.

The center of this earthquake was near the boundary between the North American and Caribbean plates. Transformation faults have formed in southern Cuba, and large earthquakes occur frequently.

A magnitude 7.7 earthquake occurred in 2020 just west of this epicenter, and other magnitude 7 earthquakes have also occurred as a result of the transformation of fault activity. However, given its size, large tsunamis are unlikely to occur.

On the night of the 5th (Friday, Japan time), an earthquake that was estimated to have a magnitude of 4.8 and a depth of about 5 km occurred with its epicenter in New Jersey, near New York. The earthquake mechanism is considered to be strike-slip.

This earthquake is believed to have caused shaking of magnitude IV on the revised Mercalli intensity scale, even in central New York. Although a precise comparison is not possible, the shaking corresponds to a seismic intensity level of 1 to 2 on the Japanese seismic intensity scale.

Earthquakes are rare in the northeastern United States, including the New York area, and only 40 earthquakes of magnitude 3 or higher have occurred within 250 km of the epicenter. -average recently since 1950. Among them, this magnitude 4.8 is the largest.

In addition, a magnitude 5.8 earthquake that occurred in Virginia in August 2011 is known as an earthquake that caused tremors in New York and other areas.