Vivinavi : Yachiyo : (Japan) Yachiyo

August 14, 2024 15:30 Announced

[Summary]
A magnitude 7 ． 1 earthquake occurred at 16:43 on August 8 with its epicenter in the Hyuga Sea. After the occurrence of the earthquake on August 8, we issued a Nankai Trough Earthquake Temporary Information （ Earthquake Warning ） at 19:15 on August 8, because the possibility of a large-scale earthquake in the assumed epicenter area of the Nankai Trough earthquake was considered to have increased relative to normal conditions. After the earthquake on August 8, no seismic activity or crustal deformation has been observed in the assumed epicenter of the Nankai Trough earthquake that would indicate any particular change in the plate boundary sticking conditions. Please continue to take disaster prevention measures in response to calls from the government and local governments.

[Text]
An earthquake of magnitude 7 ． 1 （ moment magnitude 7 ． 0 ） occurred at 16:43 on August 8, centered in the Hyuga Sea. Seismic activity near the epicenter of this earthquake has remained active since then.
The number of earthquakes of seismic intensity 1 or higher that occurred in the assumed epicenter area of the Nankai Trough earthquake （ ） including the epicenter area of the August 8 earthquake from 16:00 on August 8 to 12:00 today （ August 14 ） The preliminary report ） is as follows.
8 times from 16:00 to 24:00 on the 8th （ Seismic intensity 6 ： 1 time, intensity 2 ： 2 times, intensity 1 ： 5 times ）
11 times from 00:00 to 24:00 on the 9th （ Seismic intensity 3 ： 1 time, intensity 2 ： 2 times, Seismic intensity 1 ： 8 times ）
10th 00:00 to 24:00 2 times （ Seismic intensity 2 ： 1 time, Seismic intensity 1 ： 1 time ）
11th 00:00 to 24:00 2 times （ Seismic intensity 3 ： 1 time, Seismic intensity 1 1 time ）
1 time from 00:00 to 24:00 on 12th （ Seismic intensity 1 ： 1 time ）
0 time from 00:00 to 24:00 on 13th
0 time from 00:00 to 12:00 on 14th

Also, at strain stations In addition, at strain stations, step-like changes associated with a magnitude 7 ． 1 earthquake have been observed, but no changes other than those usually seen after earthquakes have been observed so far. Shallow very low-frequency earthquakes have been observed in the Hyuga-nada Sea and off the southeast coast of Kyushu since around 9:00 p.m. on August 8. This phenomenon has been observed repeatedly in the past, but further observation ・ is needed to determine the frequency ・ of occurrence, magnitude, and other occurrence patterns. After the earthquake on March 8, crustal deformation, which is considered to be after-effects of the earthquake, was observed mainly in the southern part of Miyazaki Prefecture. Although after-effects themselves are observed after an M7-class or larger earthquake, the after-effects observed this time are considered to be within the range of normal after-effects observed after such an earthquake. It is difficult to determine the mechanism of the aftereffect variation immediately after an earthquake, and it is necessary to continue observations for a certain period of time.
In addition, changes in pore water pressure in the boreholes off the Kii Peninsula have been observed since around August 5, which are thought to be caused by crustal deformation. This phenomenon has been observed repeatedly in the past.
Thus, after the occurrence of the earthquake on August 8, no seismic activity or crustal deformation has been observed in the assumed epicenter of the Nankai Trough earthquake that would indicate any particular change in the plate boundary sticking conditions.

As a result of studying the relationship between the August 8 earthquake and the Nankai Trough earthquake, the possibility of a large-scale earthquake in the assumed epicenter area of the Nankai Trough earthquake is considered to be relatively higher than under normal conditions, and so at 19:15 on August 8, Temporary Nankai Trough Earthquake Information （ A huge earthquake warning ） was issued.
The government is calling on the Nankai Trough Earthquake Disaster Prevention Promotion Areas to reconfirm their daily earthquake preparedness and be ready to evacuate immediately if they feel a tremor for one week after the earthquake on August 8. Please continue to take disaster prevention measures in response to 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.


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Yachiyo City Hall Emergency Management Division
Address ： 312-5 Owada-Shinden, Yachiyo 276-8501
TEL ： 047-421-6716
FAX ： 047-483-1094