HASAKI, Japan — A magnitude 5.7 earthquake struck offshore in the Pacific Ocean east of Honshu, Japan, at 04:52 UTC on Monday, November 9 (1:52 p.m. Japan time), according to the US Geological Survey (USGS). No tsunami threat was reported, and there were no immediate reports of casualties or damage.
Source: USGS via The Watchers
The USGS located the epicentre about 106 kilometres (66 miles) east-northeast of Hasaki, a coastal city in Chiba prefecture, at a shallow depth of 24.2 kilometres, at coordinates 36.2 degrees north and 141.8 degrees east. The USGS event reference is us7000tx1f.
Japan's Meteorological Agency (JMA) gave a preliminary magnitude of 5.9 for the same event, at about 1:52 p.m. local time off the coast of Ibaraki prefecture, northeast of Tokyo, at a depth of about 10 kilometres, according to reports citing the agency. The JMA reported seismic intensity 3 on Japan's 0-to-7 scale in parts of Miyagi, Fukushima, Ibaraki and Tochigi prefectures, and NHK reported obvious shaking in those prefectures, with intensity 2 recorded in Tokyo's Arakawa and Adachi wards. Early figures from different agencies often differ before seismologists complete their reviews.
Source: JMA via China News Service / Business Today
The USGS issued a green PAGER alert for the earthquake, indicating a low likelihood of casualties or damage, and put the estimated maximum shaking intensity at IV, with three public felt reports submitted at the time of its update. Its significance index for the event was 501 on a scale running to 1,000, based on magnitude, felt reports and estimated impact.
Monitoring summaries based on the USGS data said there was no tsunami threat associated with this earthquake, and the JMA issued no tsunami warning. Business Today's report of the JMA announcement also carried no immediate reports of casualties, property damage or disruption to transport or essential services. That is the position in the sources checked as this report was prepared; Japanese authorities were expected to complete further assessments.
A second offshore quake off the same coast in four days
The same stretch of Japan's Pacific coast was shaken on Friday, November 6, by a magnitude 6.1 earthquake centred southeast of Hasaki, which was also felt in Tokyo and also produced no tsunami alert and no damage reports. Monday's event is a separate earthquake — a different epicentre, northeast rather than southeast of Hasaki, and a smaller magnitude — not an update to Friday's story.
What is solid
- A magnitude 5.7 earthquake occurred at 04:52 UTC on November 9, 106 km east-northeast of Hasaki at 24.2 km depth, per the USGS (event us7000tx1f)
- No tsunami threat or tsunami warning was reported for this event (USGS-based monitoring summaries; JMA reports)
- USGS PAGER issued a green alert, indicating a low likelihood of casualties or damage, and no casualties or damage had been reported in the sources checked
What is only claimed
- The JMA's preliminary reading differed from the USGS solution — magnitude 5.9 and depth about 10 km, against the USGS 5.7 and 24.2 km; agencies' initial figures are routinely revised
- Shaking levels also differ by measure: the USGS estimated maximum intensity IV from felt reports, while the JMA reported intensity 3 in parts of four prefectures and intensity 2 in two Tokyo wards
Japan sits along the Pacific Ring of Fire, where the Pacific plate interacts with neighbouring plates in subduction zones and transform faults, making the country one of the most seismically active in the world. Its monitoring and early-warning systems are built for events of this size, and offshore quakes of magnitude 5 to 6 off the Honshu coast are recorded regularly.
What happens next: the JMA routinely watches for aftershocks after a quake of this size, and both agencies may revise the earthquake's parameters as more data arrives. A smaller magnitude 4.6 event was also recorded in the same offshore area minutes later, at 05:01 UTC, in USGS-based monitoring reports. Any verified casualty or damage report from Japanese authorities would be carried as a follow-up.