Weekly Earthquake Information 2022.10.2 M5.9 off the east coast of the Osumi Peninsula, 13 times this year with a seismic intensity of 5 or more – Weather News

2022/10/02 10:09 Weather News

The number of felt-earthquakes observed in Japan over the past week is at about the same level as the previous week.

Earthquakes with epicenters in inland Hokkaido are somewhat conspicuous. There are many earthquakes as usual from the Kanto region to the southern Tohoku region. There were four earthquakes with a seismic intensity of 3 or higher. (September 26th to October 2nd at 10:00)

Japan: Seismic intensity 5 lower in Miyazaki Prefecture Widespread tremors in western Japan

Earthquake off the east coast of the Osumi Peninsula

At around 00:02 on Sunday, October 2, an earthquake with an epicenter off the east coast of the Osumi Peninsula in Kagoshima Prefecture with a magnitude of 5.9 and an estimated depth of 29km occurred. This earthquake recorded a maximum seismic intensity of 5 lower in Nichinan City, Miyazaki Prefecture, a seismic intensity of 4 in Miyazaki City, Kushima City, Miyakonojo City, etc., and a seismic intensity of 3 in a wide area of ​​Kyushu and part of Shikoku.

This is the first time that a seismic intensity of 5-lower or higher has been observed in Miyazaki Prefecture since the Hyuga-nada earthquake on January 22nd (magnitude 6.6, maximum seismic intensity 5-upper). The mechanism of the earthquake is analyzed as a reverse fault type with a pressure axis in the northwest-southeast direction.

This is the 13th earthquake with a seismic intensity of 5 lower or more that has occurred in Japan this year.

Occurs near plate boundaries?

Epicenter distribution off the east coast of Osumi Peninsula

Similar to Hyuga-nada, the area near the epicenter of this earthquake is where the Philippine Sea plate is subducting into the Eurasian plate. Although it is out of the hypothetical focal region of the so-called Nankai Trough megathrust earthquake, the same mechanism is used to generate earthquakes.

This is the first time since 1919, when the Japan Meteorological Agency has detailed statistics, that an earthquake with an epicenter off the east coast of the Osumi Peninsula recorded a seismic intensity of 5 Lower or higher. However, due to the fact that there were few observation points in the past, earthquakes with a magnitude of 6 or more, which are larger than this time, often occur.

In 1948, an earthquake with a magnitude of 6.4 occurred near this epicenter, and a seismic intensity of 4 was observed in Miyazaki City and Kumamoto City.

Looking at the distribution of past hypocenters, in this region, earthquakes were concentrated at depths of 20 to 30 km, which corresponded to the plate boundaries, and deeper.

Japan: Earthquake in the Abashiri region with a seismic intensity of 3

Earthquakes in the Abashiri region

At around 5:02 on September 27 (Tuesday), an earthquake estimated to have a magnitude of 3.4 and a depth of 12 km occurred with its epicenter in the Abashiri region of Hokkaido. This earthquake recorded a maximum seismic intensity of 3 in Tsubetsu, Hokkaido, and a seismic intensity of 2 in Bihoro and Kitami.

This is the first time since April last year that an earthquake with a seismic intensity of 3 or higher centered in the Abashiri region. There are not many strong earthquakes with epicenters on land in the Abashiri region, except for an earthquake with a magnitude of 5.0 and a maximum seismic intensity of lower 5 in 2015 along the mountains near Lake Akan, south of this epicenter.

There have been earthquakes as large as M6.0 in the past.

Shallow earthquakes associated with volcanic activity are well known when it comes to earthquakes in the Izu Islands, such as Izu Oshima and Miyakejima. Looking at the hypocenter distribution of the earthquakes that actually occurred around the Izu Islands, most of them occurred in the area from the northwest of Izu Oshima to the Izu Peninsula, and in the area from Miyakejima to Kozushima.

Most of the earthquakes are concentrated at a depth of around 10 km even in the depth of the east-west cross section. There are few occurrences at depths of 20 km or more, but there are a few at depths of 100 km or more. Earthquakes that occur near the boundary between the Pacific plate and the Eurasian plate or within the Pacific plate.

Most deep earthquakes are around magnitude 4, but in May 2014, a large earthquake with a magnitude of 6.0 occurred. In this earthquake, a maximum seismic intensity of 5 lower was observed in Chiyoda Ward, Tokyo, and a seismic intensity of 3 to 4 was observed in a wide area of ​​the Kanto region, causing damage such as injuries.

World: Earthquakes frequently occur at the Reykjanes Ridge in the Atlantic Ocean

Earthquakes of M4.5 or higher around the world (quoted from USGS website/processed by Weathernews)

There have been two earthquakes with a magnitude of 6 or higher according to US Geological Survey analysis. The largest quake was a magnitude 6.5 near the South Sandwich Islands.

On the morning of Saturday, October 1, Japan time, an earthquake estimated to have a magnitude of 6.0 and a depth of about 10 km occurred near the Reykjanes Ridge in the Atlantic Ocean. The mechanism of the earthquake is analyzed as a reverse fault type with a pressure axis in the east-west direction.

Earthquakes have been occurring frequently around the epicenter since around September 26 (Monday). It is a situation where a rather strong earthquake such as magnitude 5.7 is occurring.

The Reykjanes Ridge is part of the Mid-Atlantic Ridge, which runs through the Atlantic from north to south, and is the boundary between the Eurasian and North American continents. The epicenters are distributed east and west across the ridge, and not only reverse-fault earthquakes but also normal-fault earthquakes have occurred.

Most of the large earthquakes that occur at the ridge are of the strike-slip type around the transform fault that develops in the surrounding area, and in 2015 an earthquake of magnitude 7.1 occurred. There are no records of earthquakes exceeding magnitude 6 in the vicinity of this epicenter, so future activity is attracting attention.

Magnitude 6.5 earthquake hits southern Taiwan

An earthquake estimated to have a magnitude of 6.5 and a depth of about 10 km occurred with an epicenter in southern Taiwan on the night of Saturday, 17th Japan time. According to the Taiwan Meteorological Bureau, the earthquake had a maximum seismic intensity of upper 6. (Taiwan’s seismic intensity scale is almost the same as Japan’s)

The earthquake mechanism is analyzed as strike-slip type.

Aftershocks followed one after another, and an earthquake of magnitude 5.5 occurred about an hour after the first one. There are concerns about damage due to strong tremors around the epicenter.

Reference materials, etc.

*Information on earthquake sources and seismic intensity in Japan is from the Japan Meteorological Agency unless otherwise specified. Overseas epicenter information is from the United States Geological Survey (USGS) unless otherwise specified. There may be differences in hypocenter information depending on the publishing organization.