By RYO SASAKI/ Staff Writer
November 15, 2022 at 18:03 JST
When a magnitude-6.1 earthquake struck on Nov. 14, all of the shaking occurred far from the focal center, while practically none was felt close to it.
The quake hit at 5:09 p.m. on Nov. 14 some 350 kilometers deep off the southeast coast of Mie Prefecture. But no seismic intensity was recorded in nearby areas, including Mie Prefecture, which is close to the epicenter in central Japan.
Yet the temblor registered a up to 4 on the Japanese seismic intensity scale of 7 in Ibaraki and Fuskushima prefectures.
The Mie prefectural capital of Tsu is about 300 km from Tokyo, 400 km from the Ibaraki prefectural capital of Mito, and approximately 500 km from Fukushima city.
According to a top seismologist, this all has to do with where exactly the quake struck underground.
Takashi Furumura, a professor at Tokyo University’s Earthquake Research Institute, said the Nov. 14 earthquake is classified as a “deep-focus earthquake” because its hypocenter was deep underground. It struck inside the Pacific Plate, which runs underneath near Japan.
The tremors were transmitted through the plate, he said, so shaking was recorded in places closer to where the plate starts to sink into the interior of the Earth, such as the Kanto and Tohoku regions.
But according to Furumura, the mantle directly above the hypocenter is soft, which makes it less likely for tremors to be transmitted through it.
A deep-focus earthquake is less likely to cause an aftershock compared to one that has a hypocenter at a shallow depth, Furumura explained.
“Even a deep-focus earthquake can cause a tremor of 5 or more on the Japanese seismic intensity scale if it reaches a bigger magnitude,” he said. “I want the (Nov. 14) earthquake to be an opportunity to encourage everyone to review their disaster preparations.”
When the shaking happens in areas far from the hypocenter rather than areas closer to it, experts call it an “abnormal intensity area.”
Furumura said earthquakes around this size occur off the southeast coast of Mie Prefecture every few years that come with abnormal intensity areas.
Japan creates new alert for risk of subsequent earthquakes
November 9, 2022
JMA quake early warning to cover shakes that affect high-rises
November 2, 2022
Big aftershock hits Ishikawa after quake that injured 6
June 20, 2022
Tokyo quake scenario warns of 4.5 million not able to go home
May 26, 2022
Latest estimate sees 6,200 deaths if megaquake strikes Tokyo
May 25, 2022
Water could be causing mystery quakes, land rise in Ishikawa
January 19, 2022
Stories about memories of cherry blossoms solicited from readers
Cooking experts, chefs and others involved in the field of food introduce their special recipes intertwined with their paths in life.
A series based on diplomatic documents declassified by Japan’s Foreign Ministry
A series on the death of a Japanese woman that sparked a debate about criminal justice policy in the United States
A series about Japanese-Americans and their memories of World War II
Here is a collection of first-hand accounts by “hibakusha” atomic bomb survivors.
