[U-16] 2024年能登半島地震(2:E)

[U16-P05] The 2024 Noto Earthquake: Large Slip from Slow Initial Rupture in a Fluid-rich Fault Zone

マ ザンフォン¹、ゼン ホンユ^1,2、ルオ ハイペン¹、リュー ぜミン³、ジャン ユ¹、*青木 陽介⁴、ワン ウェイタオ³、伊東 優治⁴、リュー ミンチェ²、チュイ ヤン⁵、ユン サンホ^6,2,1、ヒル エマ^1,2、ウェイ シェンジ^1,2,7 (1.南洋理工大学シンガポール地球観測所、2.南洋理工大学アジア地球環境学科、3.中国地震局地球物理研究所、4.東京大学地震研究所、5.河海大学地球科学科、6.南洋理工大学電気工学科、7.中国科学院地質地球物理研究所)

キーワード：能登半島地震、震源過程、地震の始まり

Seismic hazard evaluation at critical infrastructures, such as nuclear power plants, urges a deeper understanding of the fundamental physics that governs the initiation, propagation, and termination of damaging earthquakes. The 2024 moment magnitude (Mw) 7.5 Noto Peninsula earthquake produced great hazards and was generated by a complex rupture process. We derived high-resolution 3D surface deformation of the event using dense space geodetic (SAR/InSAR) observations, which reveals two major deformation zones separated by ~40 km along the coast of the Peninsula. Our static slip model, inverted from geodetic data, and finite fault slip model, constrained by both geodetic and seismic data, suggest that shallow slip exceeded 10 m on an offshore fault and that peak stress drop was greater than 10 MPa. A calibrated back-projection using teleseismic array high-frequency data shows that the rupture was extremely slow around the hypocenter for ~20 s before it propagated bilaterally at speeds of 3.4 km/s and 2.8 km/s towards the southwest and northeast, respectively. The slow start of the rupture coincides with the seismic swarm that surged since 2020 due to lower crust fluid supply, suggesting that high pore fluid pressure contributed to slowing down the initial rupture. These observations suggest a distinct coseismic slip behavior reflecting high heterogeneity in fault properties within a fluid-rich fault zone. The earthquake was accompanied by intense high-frequency seismic radiation and strong ground shaking. The Peak Ground Acceleration (PGA) exceeded 2.6G at a site less than 40km from the nuclear power plant. Large stress accumulation together with rough fault geometry and/or friction are likely responsible for the exceedingly large high-frequency radiation, which is mostly responsible for devastating damages.