Weekly earthquake information 2024.11.3 Maximum seismic intensity 3 off the coast of Ibaraki Prefecture South of the middle of last week

At approximately 23:16 on Friday, November 1, an earthquake estimated at magnitude 4.6 and a depth of 40 km occurred with its epicenter off the coast of Ibaraki Prefecture.

As a result of this earthquake, shaking with a maximum seismic intensity of 3 was felt in Kashima City, Ibaraki Prefecture, Kamisu City, and Asahi City, Chiba Prefecture, while a tremor with a seismic intensity of 2 was felt in most some in Ibaraki Prefecture and Chiba Prefecture. This is the first earthquake with a maximum seismic intensity of 3 centered on the coast of Ibaraki Prefecture since October 27 (Sunday). The mechanism of the earthquake is studied as a type of reverse fault with a stress axis running from west-northwest to south-east.

Earthquakes with a seismic intensity of 3 or higher occur off the coast of Ibaraki Prefecture an average of 5 to 10 times a year, and this year marks the 5th. The center of this earthquake was in an area to the south compared to October 27, close to the earthquake that happened in May this year.

Off the coast of Ibaraki Prefecture, the Pacific plate is intruding into the Earth’s plate, and the boundary is thought to be about 40 to 50 km deep. Based on the depth and mechanism, it appears that the earthquake occurred near a plate boundary.

In the past, earthquakes with a magnitude of 6 or more that occurred off the coast of Ibaraki Prefecture tended to be located somewhat far from land. However, a magnitude 6.0 earthquake occurred in 1946 near the epicenter of this earthquake, which is relatively close to land. The highest seismic intensity was 3, but this was because there were not many observation points at that time.

Since October, the number of earthquakes in southern Ibaraki Prefecture has increased slightly. Let’s revisit earthquake countermeasures.

The government’s Headquarters for the Promotion of Earthquake Research estimates that there is a 70-80% chance that an earthquake with a magnitude of around 7.1 will occur 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 15:19 on the 21st (Monday), an earthquake estimated at a magnitude of 3.8 and a depth of 17 km occurred with its epicenter in the central west of Mino, Gifu Prefecture.

As a result of this earthquake, a maximum seismic intensity of 3 was observed in Ichinomiya City, Aichi Prefecture, and a seismic intensity of 2 was observed in the western part of Aichi Prefecture and the Mino area of ​​Gifu Prefecture. This is the first earthquake with a seismic intensity of 3 or higher in the central and western Mino region of Gifu Prefecture since March this year.

Gifu Prefecture has many active faults. The Yoro-Kuwana-Yokkaichi fault zone extends to the southwest of the prefecture, but the epicenter of this earthquake was slightly away from the fault zone.

At approximately 12:29 on Saturday the 10th, an earthquake estimated at magnitude 6.8 and a depth of approximately 490 km 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 was a magnitude 6.0 earthquake that occurred off the west coast of the United States and near Papua New Guinea.

This time we will focus on earthquakes in the United States. Early in the morning on October 31 (Thursday) Japan time, an earthquake estimated at magnitude 6.0 and a depth of about 10 km occurred with its epicenter off the west coast of Oregon, USA. The mechanism of the earthquake is being investigated to be strike-slip type.

In this region, a relatively small plate called the “Juan de Fuca Plate” is sandwiched between the North American Plate and the Pacific Plate. The area where the Juan de Fuca plate moves under the North American plate is known as the Cascade subduction zone, and it is believed that very large earthquakes have occurred in the past.

However, the epicenter of this earthquake appears to be near the transform fault at the boundary with the Pacific Plate, an area where the potential for a large earthquake to cause a low tsunami is high.

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.