報告書番号

N08007

タイトル（和文）

2007年新潟県中越沖地震の震源過程の解明と広帯域強震動評価

タイトル（英文）

Source Process and Broadband Strong Motions during the Niigata-ken Chuetsu-oki Earthquake in 2007

概要 （図表や脚注は「報告書全文」に掲載しております）

東京電力柏崎刈羽原子力発電所および周辺地域に被害をもたらした2007年新潟県中越沖地震(M6.8)の震源過程を解明するために，震源近傍の強震記録を用いた震源インバージョン解析を実施するとともに，得られた震源モデルを特性化し，柏崎サイトの観測強震記録を対象とした広帯域強震動シミュレーションをおこなうことで，設定した震源モデルの妥当性を検証した．その結果，震源断層面上には3つの空間的に独立したアスペリティ（相対的にモーメント解放量が大きい領域）が存在し，特性化震源モデルにおけるアスペリティの総面積は，断層全体の約25％を占めることを明らかにした．またアスペリティ上の実効応力は20～25MPaであり，平均的な値の1.2～1.5倍程度の大きさであった．提案した特性化震源モデルは，柏崎サイト内の原子炉各号機の基礎版上観測記録を精度よく再現できることを示した．

概要 （英文）

Detailed source rupture process is inferred for the 2007 Niigata-ken Chuetsu-oki earthquake (M6.8) from regional strong-motion records. For an initial fault model we assume the southeast dipping rectangular fault of 30 km long and 17 km wide, referring to aftershock distribution relocated through the data from ocean bottom seismometers. The spatio-temporal variation for the seismic moment and the rise time on the fault plane are estimated using the inversion technique composed of the very fast simulated annealing (VFSA) and the empirical Green's function method. The aftershock of M4.4 which occurred at 21:08 on 16 July is employed as an empirical Green's function. Strong-motion records of two horizontal components from 18 stations, which are located within 50 km from the center of the main shock fault, are used for the inversion. The optimal solution estimated from the inversion analysis shows that three separated asperity areas are recognized, which correspond to three pulses appeared in the strong motion records observed at near-source stations. For rupture time distribution, we find that rupture accelerates abruptly on the third asperity which is most distant from the hypocenter, and the local rupture velocity seems to exceed the S-wave velocity. We further construct the characterized source model which describes the generation of the broadband strong motions based on the inversion result, and estimate the strong motions during the main shock at the Kashiwazaki-Kariwa nuclear power station. By assuming radial rupture propagation with individual rupture speed at each asperity, several strong-motion records observed in the NPS site are synthesized well through the characterized source model in which the effective stress on the asperity roughly distributes from 20 to 25 MPa.

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