February 13, 2021 Earthquake: Off Fukushima, Japan

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Tectonic Summary

The February 13, 2021, M 7.1 earthquake near the east coast of Honshu, Japan, occurred as the result of thrust faulting near the subduction zone interface plate boundary between the Pacific and North America plates. Moment tensor solutions indicate that slip occurred either on a moderately dipping fault striking to the south, or a moderately dipping fault striking to the north-northeast, consistent with the east-west oriented compression expected in this region. At the location of this earthquake, the Pacific plate moves approximately westward relative to the North America plate at a velocity of 70 mm/yr, subducting beneath Japan at the Japan Trench and dipping to the west beneath Japan. Note that some researchers divide this region into several microplates that together define the relative motions among the larger Pacific, North America, and Eurasia plates; these include the Okhotsk and Amur microplates local to this earthquake that are part of North America and Eurasia, respectively.

While commonly plotted as points on maps, earthquakes of this size are more appropriately described as slip over a larger fault area. Reverse (thrust) faulting events of the size of the February 13, 2021 earthquake are typically about 45 km long by 25 km wide in size.

The February 13 earthquake occurred in the vicinity of the rupture area of the March 11, 2011 M9.1 Tohoku earthquake. The March 2011 M9.1 earthquake was widely felt on the islands of Honshu and Hokkaido in Japan. Notably, that earthquake generated a significant tsunami that led to extensive destruction along the Japanese coast and propagated throughout the Pacific Ocean basin. Approximately 16,000 people perished as a result of the earthquake and subsequent tsunami. The February 13 earthquake epicenter was located ~75 km from the epicenter of the March 2011 earthquake. In the past century, 33 earthquakes of M7 or greater have occurred within 250 km of the February 13 earthquake, including 6 earthquakes >M7 since the March 2011 M9.1 earthquake.

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The quake damaged about 1,400 houses in Fukushima, according to the prefectural government. In Miyagi, 186 houses were partially destroyed, the internal affairs ministry said.

The powerful earthquake injured nearly 160 people, according to the ministry. The temblor also caused damage to school buildings in Fukushima and Miyagi prefectures, prompting a total of 82 schools to close on Monday.

A total of 324 cases of damage to school buildings had been discovered in four prefectures, including 121 in Miyagi and 192 in Fukushima, including cracked walls and floors, shattered windows, and burst water pipes, according to the education ministry.

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The Fire and Disaster Management Agency (FDMA) preliminary report on February 19 claimed that the earthquake caused injuries to at least 185 people across nine prefectures with 12 people suffering serious injuries. Reports indicate at least 100 people injured in Fukushima Prefecture and 63 in Miyagi Prefecture, with 30 in Sendai city. Reports indicate at least 2,649 residential structures damaged in Miyagi and Fukushima Prefectures with the majority of damage occurring in the towns of Shinchi and Kagamiishi.

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When it struck, this offshore quake left one person dead and injured more than 186, while causing significant structural damage across the Tohoku and Kanto regions of Japan. Japan’s Fire and Disaster Management Agency explained that over 9,137 buildings were damaged in the earthquake, many severely, which has driven an escalating insured loss total.

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Deaths 1; 186 injuries; 69 properties completely destroyed; 720 properties partially destroyed; 19,758 properties partially damaged

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Total damages USD 7.7 billion