Weekly earthquake data 2021.3.28 28 (Sunday) off the east coast of Hachijojima M5.8 Shaking sensation in Kanto area –Weathernews

Around 9:27 a.m. on Sunday the 28th, there was an earthquake with a magnitude of 5.8 and an estimated depth of about 50 km, with its epicenter off the east coast of Hachijojima. Due to this earthquake, tremors with a maximum seismic intensity of 3 were observed in Miyake Village, Hachijo City and Tateyama City, Chiba Prefecture, and a seismic intensity of 2 was observed in a wide area of ​​Tokyo, Kanagawa and Saitama. Prefectures.

According to the preliminary analysis of the National Research Institute for Earth Sciences and Disaster Prevention, it is a type of reverse fault with a pressure axis in a north-northwest-south-southeast direction, and it is a mechanism that contains a slight component slip.

Off the east coast of Hachijojima it is close to the boundary where the Pacific plate is subducting into the Philippine Sea plate, and large earthquakes often occur. Recently, there was a 6.0 magnitude earthquake in November 2017, slightly south of the epicenter. In 1972, a large earthquake with a magnitude of 7.2 occurred in a region relatively close to this time, and Hachijojima was hit by strong shaking with a seismic intensity of 6 (class at that time) and a wide range from southern Kanto such as Chiyoda . -ku, Tokyo …

At around 7:02 on Saturday the 27th, there was an earthquake with a magnitude of 6.2 and an estimated depth of about 150 km, which originated off the northwestern coast of Miyakojima. In this earthquake, a seismic intensity 2 was observed in a wide area of ​​the Nansei Islands, such as Naha City, Ishigaki City, and Miyakojima City.

Although the magnitude of the earthquake was as large as 6 or more, the maximum seismic intensity was only 2 because it was a so-called deep-focus earthquake with a depth of about 150 km. Earthquakes that occur off the northwest coast of Miyakojima include relatively shallow earthquakes that occur in the lowered area of ​​the seafloor called the “Okinawa Trough” and deep earthquakes that occur near the subduction of the Philippine Sea plate and the limits of the terrestrial plate. This time, it corresponds to the latter.

There are relatively many magnitude 5 class earthquakes, the most recent in July 2019, but the magnitude 6 class has decreased dramatically since the magnitude 6.2 earthquake in December 1961 with a depth of approximately 258 km.

Although the epicenter is deep and the shaking is difficult to transmit, there are cases where a 7.0 magnitude deep-focus earthquake occurred in 2011 off the northwest coast of the main island of Okinawa, slightly northeast of the epicenter, and the seismic intensity 4. was observed at many points. Yes, you cannot be alert.

In shallow earthquakes, areas with strong tremors are often concentrically distributed from the epicenter, but in deep-focus earthquakes, tremors are transmitted to distant areas along the Pacific plate where seismic waves are easily transmitted. It can be a distribution.

Similar deep-focus earthquakes often occur where the Pacific plate is deeply subducted, and earthquakes of magnitude 6 and above occur once every few years. On the other hand, it is also characterized by the fact that there are almost no aftershocks in a single earthquake.

The United States Geological Survey did not analyze earthquakes of magnitude 6 or greater. The largest is the earthquake on the northwest coast of Miyakojima. (Magnitude 5.9 in the USGS analysis)

The notable earthquake is an earthquake that occurred off the northeast coast of Guadeloupe in the Caribbean Sea. An earthquake with a magnitude of 5.8 and a depth of 19 km occurred on Friday the 26th Japan time. The mechanism is analyzed as a type of reverse fault with a pressure axis in the west-southwest-east-northeast direction.

The coastal waters of the eastern Caribbean Sea, such as Guadeloupe and Dominica, are close to the boundary between the Caribbean Plate, the North American Plate, and the South American Plate, and large earthquakes sometimes occur. There are shallow and deep epicenters. In 2007, a magnitude of 7.4 occurred at a depth of 156 km, and even a shallow type had a magnitude of 7.4 in 1974.

A volcanic eruption began in the early hours of Saturday, Japan time, on the Reykjanes Peninsula, Iceland, where seismic activity had been active since late February. The Icelandic Meteorological Office has raised the color code, which indicates the alert level for aircraft, to red, which requires maximum alert, but has reduced it by one range to orange because no volcanic ash or other eruptions have been seen. .

At this stage, the eruptive activity is focused on the lava flows and the output range is limited. Due to its remoteness from densely populated areas, it is not expected to have a significant impact immediately.

* Information on the epicenter and seismic intensity in Japan comes from the Japan Meteorological Agency, unless otherwise noted. Information on overseas epicenters comes from the United States Geological Survey (USGS) unless otherwise noted. The epicenter information may differ depending on the issuing organization.