４月３日台湾近海大地震について
本日、台湾東側近海でマグネチュード７．５（暫定値）の大きな地震が発生しました。この地震で日本の沖縄地方でも津波が到達しました。台湾の花蓮市で最大震度６強の大きな揺れが観測され、被害が出ています。また、台湾の首都台北でも震度５弱が観測されました。台湾では１９９９年９月２１日に台湾中部で大きな地震が発生し、死者２４１５人、負傷者１３０６人の被害が発生しました。当時、台湾の震度階級では震度７は無かったのですが、震度７相当の揺れが観測されていました。現在の台湾における震度階級に７があるのかわかりませんが、今回の地震で建物が崩れ、山崩れが発生しています。日本の気象庁が発表している震度７（激震）の被害は、「家屋の倒壊が30%以上に及び, 山くずれ, 地割れ, 断層などを生じる.」です。後日、今回の地震の最大深度は変更されるかもしれません。今回の台湾地震の被害が最小に留められることを願っております。
今回の地震はプレート型地震でしょうか？
台湾の北端から北ではフィリピン海プレートがユーラシアプレートの下に沈み込んでいます。台湾の大きな地震はプレート型地震が多いのですが、今回の地震の震源は非常に浅いので、どのような仕組みで地震が発生したのか、解明が待たれます。今回の台湾地震は８時５８分（日本時間、以下同じ）にマグネチュード７．５の地震が発生し、次いで９時１１分にマグネチュード６．６、９時３５分にマグネチュード６．３の地震が発生していました。震源は３回ともほぼ同じ位置（１回目：北緯23.8度/東経121.7度、２回目：北緯24.1度/東経121.7度、３回目：北緯24.2度/東経121.7度）でしたが、少しずつ北に移動していることが明確でした。また、最初の２回の震源は「ごく浅い」深度でしたが、３回目は深度２０ｋｍと深くなりました。まるで、プレート境界上部から下部へ震源が移動しているようです。ただ、能登半島地震のような複数の活断層が連続して動いた可能性もあるので、地震対策のためにも発生のメカニズム解明が待たれます。
日本の地震災害時、台湾はよく援助を申し出てくれました。
日本は東日本大震災を始め、多くの大きな地震災害が発生しています。最近では１月１日に発生した能登半島地震が記憶に新しい大地震でした。もちろん、日本国内の地震災害の対応・援助に尽力すべきですが、台湾は常に日本の地震災害に援助の手を差し伸べてくれました。まだ台湾の地震や津波被害の全貌は明らかになっていません。もし大きな被害が発生していたのであれば、個人でできることをしたいと思っています。
#台湾 #地震 #津波
Regarding the April 3rd earthquake near Taiwan
Today, a large earthquake with a magnitude of 7.5 (tentative value) occurred near the eastern coast of Taiwan. This earthquake caused a tsunami to reach the Okinawa region of Japan. Large tremors with a maximum seismic intensity of 6+ were observed in Hualien City, Taiwan, causing damage. In addition, a seismic intensity of lower 5 was observed in Taipei, the capital of Taiwan. In Taiwan, a large earthquake occurred in central Taiwan on September 21, 1999, resulting in 2,415 deaths and 1,306 injuries. At that time, Taiwan did not have a seismic intensity level of 7, but tremors equivalent to intensity 7 were observed. I don't know if Taiwan is currently on a seismic intensity scale of 7, but this earthquake has caused buildings to collapse and landslides to occur. The Japan Meteorological Agency has announced that the damage caused by a seismic intensity 7 (severe earthquake) is ``30% or more of houses will collapse, and it will cause landslides, cracks in the ground, faults, etc.'' The maximum depth of this earthquake may change at a later date. We hope that the damage caused by this Taiwan earthquake will be kept to a minimum.
Is this earthquake a plate-type earthquake?
North of the northern tip of Taiwan, the Philippine Sea Plate is subducting beneath the Eurasian Plate. Most of the major earthquakes in Taiwan are plate-type earthquakes, but the epicenter of this earthquake was very shallow, so we are waiting to find out how the earthquake occurred. In this Taiwan earthquake, a magnitude 7.5 earthquake occurred at 8:58 a.m. (Japan time, same hereafter), followed by a magnitude 6.6 earthquake at 9:11 a.m., and a magnitude 6.3 earthquake at 9:35 a.m. It was occurring. The epicenter was at almost the same location all three times (1st: 23.8 degrees north latitude/121.7 degrees east longitude, 2nd earthquake: 24.1 degrees north latitude/121.7 degrees east longitude, 3rd earthquake: 24.2 degrees north latitude/121.7 degrees east longitude), but gradually moved northward. It was clear that they were moving. In addition, the epicenters of the first two earthquakes were at "very shallow" depths, but the third one was deeper, at a depth of 20 km. It seems as if the epicenter is moving from the upper part of the plate boundary to the lower part. However, there is a possibility that multiple active faults moved in succession, as in the case of the Noto Peninsula Earthquake, so elucidation of the mechanism behind the occurrence is needed for earthquake countermeasures.
During the earthquake disaster in Japan, Taiwan often offered assistance.
Japan has experienced many major earthquake disasters, including the Great East Japan Earthquake. Recently, the Noto Peninsula earthquake that occurred on January 1st was a major earthquake that is still fresh in our memory. Of course, Japan should make every effort to respond and provide assistance to earthquake disasters in Japan, but Taiwan has always extended a helping hand to Japan's earthquake disasters. The full extent of Taiwan's earthquake and tsunami damage is still not clear. If major damage had occurred, I would like to do what I can as an individual.
#Taiwan #earthquake #tsunami
