2021年3月4日〜5日に発生したニュージーランド・ケルマディック島付近の地震について (first report: 2021/03/05, last update: 2021/03/05)
Earthquake summary on 5th March, 2021, Kermadec islands, New Zealand

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1. 地震の概要 Summary of earthquake


 一連の地震で最初に発生したMw7.3のイベントでは,ニュージーランド国内で有感であったことが報告されています[2].ただし,Mw7.4やMw8.1の地震では揺れは限定的だったようです.一方,本地震に関連して津波警戒情報が発出されました[3].新型コロナ感染症に伴う行動制限(オークランド:Alert Level 3,その他:Level 2)[4]が課された中での津波警戒情報でしたので,津波避難情報は行動制限より優先されるとの情報もあわせて発信されました.

 On March 5, 2021 (local time in New Zealand), a series of earthquakes occurred near Kermadic Island, New Zealand, starting with a Mw7.3 earthquake event, followed by a Mw7.4 earthquake and the largest Mw 8.1 earthquake within six hours, according to the USGS[1]. The first Mw7.3 event occurred in the offshore near the North Island of New Zealand, while the subsequent Mw7.4 and Mw8.1 events occurred near Kermadic Island, about 1000 km north-northeast of the North Island. The USGS estimated that the Mw 7.3 earthquake was a lateral fault with a depth of about 20 km, but GeoNet[2], a seismic network in New Zealand, reported that the depth was about 90 km. The Mw7.4 and Mw8.1 earthquakes that occurred near Kermadec Island are both estimated to have been reverse fault earthquakes with an east-west compressive component. Although the estimated depths of the hypocenter of both earthquakes vary, the hypocenter of the Mw8.1 earthquake is estimated to be shallower around 10km depth. These earthquakes are aligned along the Hikurangi Trough to Kermadec Trough, which is a convergence zone of the Pacific Plate and the Australian Plate, and Mw8.1 earthquake is consistent in the occurence at the plate boundary[1].

 The first Mw7.3 event in the series of earthquakes was reported to have been felt within New Zealand[2]. However, the shaking in the Mw7.4 and Mw8.1 earthquakes seems to have been limited. On the other hand, a tsunami advisory was issued in relation to this earthquake[3]. The tsunami advisory was issued under the situation of activity restrictions (Alert Level 3 in Auckland, Level 2 in other areas)[4] due to the COVID-19, so the tsunami evacuation information was also issued as a priority overriding the activity restrictions.

謝辞 Acknowledgment

 本報告では,GeoNet/GNS ScienceならびにUSGSの地震情報を使用致しました.記して感謝致します.
 In this report, I used event summary of GeoNet/GNS Science, and USGS. I appreciate for the efforts.

参考文献 References

[1] USGS: Latest Earthquakes. Link

[2] GeoNet: Geological hazard information for New Zealand.Link

[3] NEMA: National Enmergency Management Agency.Link

[4] New Zealand Government: Unite against COVID-19.Link

文責 後藤浩之 (Hiroyuki Goto)京都大学防災研究所 DPRI Kyoto University

Mail to : gotocatfish.dpri.kyoto-u.ac.jp (@は半角の@に置き換えて下さい)