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August 8, 2024, 19:15


Today （ 8 ） a magnitude 7 ． 1 earthquake occurred at 16:43 in the Hyuga Sea. Seismic activity has remained active since then. Step-like changes associated with this earthquake have been observed at strain stations.

The Japan Meteorological Agency (JMA) held an extraordinary meeting of the Evaluation and Study Group on Earthquakes along the Nankai Trough to discuss the relationship between this earthquake and the Nankai Trough earthquake.

This earthquake was evaluated as a reverse fault type earthquake with a pressure axis in the west-northwest ・ east-southeast direction, with a moment magnitude of 7 ． 0, caused by a partial displacement of the boundary between the land plate and the Philippine Sea plate in the assumed hypocenter region of the Nankai Trough earthquake.

0 In the statistical data of past large earthquakes in the world, of the 1 ， 437 cases of earthquakes of moment magnitude 7 ． 0 or greater that occurred between 1904 and 2014, the subsequent occurrence of a moment magnitude 8 class or greater earthquake in the same region were 6 cases within 7 days of the occurrence of the first earthquake, and the frequency of subsequent occurrences decreases with time. This data includes the 2011 （ 2011 ） Tohoku Earthquake （ Moment Magnitude 9 ． 0 ） cases where a Moment Magnitude 7 class earthquake occurred two days before the earthquake occurred. In the world cases, the frequency of an earthquake of moment magnitude 7 ． 0 or greater occurring in the same area within 7 days after an earthquake of moment magnitude 7 0 or greater occurs is about 1 in several hundred times.

These facts suggest that the likelihood of occurrence of a large-scale earthquake is relatively higher in the assumed epicenter region of the Nankai Trough earthquake than in normal times.

There is diversity in Nankai Trough earthquakes, and the epicenter area of a large-scale earthquake may be limited to the vicinity of this earthquake, or it may extend over the entire Nankai Trough.

In the event of the largest earthquake, strong tremors are expected over a wide area from the Kanto region to the Kyushu region, and high tsunami are expected along the Pacific coast from the Kanto region to the Okinawa region.

Please take disaster prevention measures according to future calls from the government and local governments.

The JMA will continue to carefully monitor crustal activity along the Nankai Trough.

*Moment magnitude is the magnitude obtained by closely examining the scale of displacement of the epicenter fault. It may be different from the magnitude reported by the Japan Meteorological Agency in earthquake information.
*The Evaluation and Review Committee is working together with the existing Tokai Region Earthquake Disaster Prevention Measures Enhancement Area Judging Committee.



From now on, the status of crustal activities and other information will be published in "Nankai Trough Earthquake Related Explanatory Information".


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