The number of felt-earthquakes observed in Japan over the past week is at a lower level than the previous week. There was no particular concentration of seismic activity.
There have been two earthquakes with a seismic intensity of 3 or higher. (Tally from June 26th to July 2nd at 10:00)
Japan: Deep earthquake of M6.3 in the Sea of Japan
Earthquake in northern Japan Sea
At around 8:38 on June 28 (Wednesday), an earthquake estimated to have a magnitude of 6.3 and a depth of 518 km occurred with an epicenter in the northern part of the Sea of Japan. In this earthquake, a maximum seismic intensity of 3 was observed in Urahoro Town, Hokkaido, and a seismic intensity of 1 to 2 was observed on the Pacific Ocean side from Hokkaido to Tohoku.It was the first time in about 10 years since September 2013 that a deep earthquake with an epicenter in the northern part of the Sea of Japan had a seismic intensity of 3.
In this earthquake, there were few places where shaking with a seismic intensity of 1 or more was observed on the Sea of Japan side, which is close to the epicenter, and a seismic intensity distribution of the so-called “abnormal seismic zone” appeared, where the shaking was larger on the Pacific side.
What is an anomalous seismic area?
Mechanism of anomalous seismic regions
This earthquake is thought to be a deep earthquake that occurred on the Pacific plate, which has subducted very deep underground.In shallow earthquakes, areas with strong shaking are distributed concentrically from the epicenter, but in deep earthquakes, strong shaking is transmitted along the subducted plate, and a phenomenon is observed in which the shaking becomes stronger in the distant region near the plate boundary. This is called an “abnormal seismic area”. Even if the tremor is small near the epicenter, strong tremors may be transmitted to distant places, so caution is required.
The possibility of a tsunami is small in a deep-focused earthquake, and in general, it is thought that there is almost no risk of a tsunami in an earthquake whose epicenter is deeper than 100 km.
In the Sea of Japan, a deep earthquake of magnitude 6 class similar to this one occurs at a rate of about once every few years. Recently, in September 2021, an earthquake of magnitude 6.1 occurred. Compared to this time, it occurred closer to Honshu, so a seismic intensity of 3 was observed over a wide area on the Pacific side from Hokkaido to Kanto.
Japan: An earthquake with a maximum seismic intensity of 3 occurred in the southern Tokachi region of Hokkaido
At around 13:50 on the 19th (Monday), an earthquake estimated to have a magnitude of 5.0 and a depth of 59 km occurred with an epicenter in the southern part of the Tokachi region of Hokkaido. A maximum seismic intensity of 3 was observed in Urakawa-cho, Makubetsu-cho, Urahoro-cho, and Hiroo-cho in Hokkaido.
It was the first time in nine months since September 24, 2018 that an earthquake with a seismic intensity of 3 or higher centered in the southern part of the Tokachi region. The mechanism of the earthquake is analyzed as a reverse fault type with a pressure axis in the northwest-southeast direction.
Although there are no known active faults in the area near the Hidaka Mountains, where this earthquake occurred, large-scale earthquakes often occur. In 2012, an earthquake with a magnitude of 6.1 occurred a little further south, causing strong shaking with a maximum seismic intensity of lower 5.
In addition, the Tokachi region has the Tokachi Plain Fault Zone, which is distributed in the plains, and the government’s Earthquake Research Promotion Headquarters says that if the entire fault zone were to move, there is a possibility of a large-scale earthquake with a magnitude of about 8.0. increase.
Japan: A strong earthquake in January this year with a seismic intensity of 4 in Hyuga Nada
World: M5.8 earthquake in Indian Ocean
Earthquakes of M4.5 or higher around the world (quoted from USGS website/processed by Weathernews)
There was one earthquake with a magnitude of 6 or higher according to US Geological Survey analysis. The largest one is the magnitude 6.0 that occurred in the South Pacific Ocean near Tonga.An earthquake estimated to have a magnitude of 5.8 and a depth of about 10 km occurred in the Indian Ocean on the evening of Saturday, July 1, Japan time. Since the earthquake occurred far from land, there was no impact from the shaking.
The epicenter of this earthquake is far from the plate boundary, and it is considered to have occurred within the Indo-Australian plate. Similar types of earthquakes occur from time to time, and in 2014 there was a magnitude 6.5 earthquake with an epicenter further south than this one.
World: Rare damaging earthquake in western France
An earthquake estimated to have a magnitude of 4.8 and a depth of about 5 km occurred early in the morning of Saturday, 17th Japan time, with an epicenter in western France. Although the scale of the earthquake was small, it was a shallow earthquake, so it was hit by strong shaking in the vicinity of the epicenter, and it is believed that buildings and other buildings were damaged.
There are few earthquakes in France, and even earthquakes with magnitudes in the upper 4s like this one don’t happen often. It is the first time in a year and three months since March last year that an earthquake of magnitude 4.5 or higher occurred.
The area around the epicenter of this earthquake is relatively prone to earthquakes in France, and in 2005 there was an earthquake with a magnitude of 5.2.
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.
2023-07-02 01:06:00
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