August 13th, 2024, 3:30 P.M. JST Announcement.
［Summary］
At approximately 4:43 pm on August 8th, a magnitude 7.1 earthquake occurred with its epicenter at Hyuga Sea.
Following the occurrence of this earthquake, it was thought that the possibility of a large-scale earthquake occurring in the assumed focal region of the Nankai Trough earthquake was relatively higher than usual, and therefore an emergency Nankai Trough earthquake information (Massive Earthquake Warning) was issued at 7:15 p.m. on August 8th.
Since the earthquake on the 8th, no seismic activity or crustal movement that would indicate a particular change in the locking status of the plate boundary has been observed in the assumed focal region of the Nankai Trough earthquake.
Please continue to take disaster prevention measures in accordance with calls from the national and local governments, etc.
［Text］
At approximately 16:43 on August 8th, a magnitude 7.1 (moment magnitude 7.0) earthquake occurred with its epicenter at Hyuga Sea.
Seismic activity continues to be active near the epicenter of this earthquake.
The number of earthquakes (preliminary figures) that occurred in the expected epicenter of the Nankai Trough earthquake (including the area surrounding the epicenter of the August 8 earthquake) with a seismic intensity of 1 or higher from 4:00 p.m. on the 8th to 12:00 noon today (13th) is as follows:
8th 16:00 to 24:00 8 times (Intensity 6-low: 1 time, Intensity 2:02 times, Intensity 1:05 times)
9th 00:00 to 24:00 11 times (Intensity 3:01 times, Intensity 2:02 times, Intensity 1:08 times)
10th 00:00 to 24:00 2 times (Intensity 2:01 times, Intensity 1:01 times)
11th 00:00 to 24:00 2 times (Intensity 3:01 times, Intensity 1:01 times)
12th 00:00 to 24:00 1 time (Intensity 1:01 times)
13th 00:00 to 12:00 0 times
Additionally, step-like changes associated with the magnitude 7.1 earthquake have been observed at strain observation points, but so far no changes have been observed beyond those usually seen after earthquakes.
Changes associated with deep low-frequency earthquake (microtremor) activity in the Kii Peninsula and Ise Bay have been observed by nearby strain meters, but this is a phenomenon that has been seen repeatedly in the past.
As such, since the occurrence of the earthquake on the 8th, no seismic activity or crustal movement that would indicate a particular change in the locking state of the plate boundary has been observed in the expected focal region of the Nankai Trough earthquake.
After examining the relationship between the August 8 earthquake and a Nankai Trough earthquake, it was determined that the possibility of a large-scale earthquake occurring in the expected focal region of the Nankai Trough earthquake is relatively higher than usual, and therefore an emergency Nankai Trough earthquake information (Massive Earthquake Warning) was issued at 7:15 p.m. on August 8.
The government is calling on areas where disaster prevention measures for the Nankai Trough earthquake are being promoted to reconfirm their daily earthquake preparations for one week after the earthquake on the 8th, and to be prepared to evacuate immediately if they feel shaking.
Please continue to take disaster prevention measures in accordance with calls from the government and local governments.
The Japan Meteorological Agency will continue to carefully monitor trends in crustal activity along the Nankai Trough.
*The moment magnitude is a value obtained by examining the scale of the displacement of the earthquake source fault.
It may differ from the magnitude reported by the Japan Meteorological Agency in earthquake information, etc.
2024年8月13日15時30分 発表
【概要】
８月８日１６時４３分頃に日向灘を震源とするマグニチュード７．１の地震が発生しました。この地震の発生に伴って、南海トラフ地震の想定震源域では、大規模地震の発生可能性が平常時に比べて相対的に高まっていると考えられたことから、８月８日１９時１５分に南海トラフ地震臨時情報（巨大地震注意）を発表しました。８日の地震の発生後、南海トラフ地震の想定震源域ではプレート境界の固着状況に特段の変化を示すような地震活動や地殻変動は観測されていません。引き続き、政府や自治体などからの呼びかけ等に応じた防災対応をとってください。
【本文】
８月８日１６時４３分頃に日向灘を震源とするマグニチュード７．１（モーメントマグニチュード７．０）の地震が発生しました。この地震の震源付近では、その後も地震活動は活発な状態が続いています。
８日１６時から本日（１３日）１２時までに南海トラフ地震の想定震源域（８月８日の地震の震源域周辺を含む）で発生した震度１以上を観測した地震の回数（速報値）は次の通りです。
８日１６時から２４時まで ８回（震度６弱：１回、震度2時2分回、震度1時5分回）
９日００時から２４時まで １１回（震度3時1分回、震度2時2分回、震度1時8分回）
１０日００時から２４時まで ２回（震度2時1分回、震度1時1分回）
１１日００時から２４時まで ２回（震度3時1分回、震度1時1分回）
１２日００時から２４時まで １回（震度1時1分回）
１３日００時から１２時まで ０回
また、ひずみ観測点では、マグニチュード７．１の地震に伴うステップ状の変化が観測されていますが、地震後に通常みられる変化以外は今のところ観測されていません。紀伊半島及び伊勢湾の深部低周波地震（微動）活動に伴う変化が付近のひずみ計等で観測されていますが、これまでにも繰り返しみられている現象です。
このように、８日の地震の発生後、南海トラフ地震の想定震源域ではプレート境界の固着状況に特段の変化を示すような地震活動や地殻変動は観測されていません。
８月８日の地震と南海トラフ地震との関連性について検討した結果、南海トラフ地震の想定震源域では、大規模地震の発生可能性が平常時に比べて相対的に高まっていると考えられたことから、８月８日１９時１５分に南海トラフ地震臨時情報（巨大地震注意）を発表しました。
政府では、南海トラフ地震防災対策推進地域に対して、８日の地震発生から１週間、日頃からの地震への備えの再確認や、揺れを感じたら直ちに避難できる態勢をとるよう呼びかけています。引き続き、政府や自治体などからの呼びかけ等に応じた防災対応をとってください。
気象庁では、引き続き注意深く南海トラフ沿いの地殻活動の推移を監視します。
※モーメントマグニチュードは、震源断層のずれの規模を精査して得られるマグニチュードです。気象庁が地震情報等で、お知らせしているマグニチュードとは異なる値になる場合があります。