報告書番号

N11058

タイトル（和文）

強震記録のインバージョン解析に基づく2011年東北地方太平洋沖地震の震源過程

タイトル（英文）

Source process of the 2011 M 9.0 off the Pacific coast of Tohoku earthquake by inversion analysis using strong-motion records

概要 （図表や脚注は「報告書全文」に掲載しております）

2011 年東北地方太平洋沖地震を対象として，震源インバージョン解析によって震源の詳細な破壊過程を推定した．主要なモーメント解放領域は，震源を中心とした約200km×200kmの範囲内にある．複数の観測記録に共通してみられる主要な波群の到達時刻を説明するために，断層面上の破壊が海溝付近に到達した後，プレート境界深部に向けて再伝播する多重震源シナリオを先験的に仮定した解析を行った結果，宮城県沖の海域では，最初の破壊伝播で1978年宮城県沖地震の震源となった領域がすべり，二度目の破壊伝播ではその東側に隣接する領域が約30秒遅れてすべったことがわかった．また海溝付近の浅いプレート境界領域では約60mの最大すべりが生じており，その大きさや位置は海底地殻変動のデータや既往の津波波源解析結果ともよい対応を示す．

概要 （英文）

The source rupture process of the 2011 M9.0 off the Pacific coast of Tohoku great earthquake is inferred from strong-motion data. A waveform inversion technique based on the empirical Green's function and the simulated annealing are applied to derive the spatial and temporal distribution of the moment density, rise time on the finite fault plane. We assumed the rupture scenario of the kind of multi-faulting, in order to interpret two distinctive strong-motion packets at a time interval of about 50 seconds shown in the acceleration records in and around Miyagi Prefecture. Since the apparent velocities of these two wave-packets are very close, the sources of them are expected to be located near each other. The rupture on the fault plane, radiated from the hypocenter, is assumed to be restarted just after arriving at the eastern edge near the trench, toward the opposite, deeper side of the fault, due to the overshoot or the successive strain energy radiation along with very long-duration slip at the shallow part of the fault. The estimated slip model indicates that the first strong-motion packet was radiated from the asperity at the source area of the 1978 M 7.4 off Miyagi earthquake at the time of rupture front from the hypocenter passing, and the second packet was generated from the eastern adjacent asperity that slipped when the second rupture front reached. On the other hand the largest slip of about 60 m was found at shallow plate-boundary near the trench, which is considered to yield a huge tsunami.

報告者

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