東北日本太平洋下のプレート境界近傍で発生する地震のスケーリング則

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  • 山下 哲央
    東北大学大学院理学研究科地震・噴火予知研究観測センター
  • 岡田 知己
    東北大学大学院理学研究科地震・噴火予知研究観測センター
  • 松澤 暢
    東北大学大学院理学研究科地震・噴火予知研究観測センター
  • 長谷川 昭
    東北大学大学院理学研究科地震・噴火予知研究観測センター

書誌事項

タイトル別名
  • Scaling Law of Earthquakes along the Plate Boundary East off Northeastern Japan
  • トウホク ニホン タイヘイヨウ カ ノ プレート キョウカイ キンボウ デ ハッセイ スル ジシン ノ スケーリングソク

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抄録

We estimated the scaling relation, i. e. MO (seismic moment)-fC (corner frequency) relation, of small to moderate-sized earthquakes east off northeastern Japan. We used spectral ratio method to accurately estimate fC from observed spectra of earthquakes. We calculated spectral ratios of all the event pairs with spatial separations less than the hypocenter location errors, and estimated fC values by fitting them with theoretical spectral ratios. Seismic moments were estimated from the JMA (Japan Meteorological Agency) magnitudes. We also estimated spatial variation of the scaling relation along the plate boundary of the subduction zone. Obtained scaling relation was compared with the scaling law derived by Nadeau and Johnson (1998) in which seismic coupling coefficient was assumed to be 100%. Obtained MO-fC samples are somewhat scattered and the distribution range corresponds to seismic coupling coefficients of 1 to 100%. The range corresponds to stress drops of 0.1 to 10MPa. Regional variations of stress drops are also observed. In particular, lower stress drops are estimated in and around the fault area of the 1896 Sanriku tsunami earthquake. Higher stress drops are obtained for the deeper portion (deep thrust zone) of the plate boundary. This tendency of higher stress drops for deeper events can be explained by the difference in physical properties (i. e., rigidity) which depend on depth. The MO-fC relation also varies along the arc. Areas with higher stress drops are distributed in and around the asperities of some large earthquakes. These events with higher stress drops might occur off the plate boundary and/or on the plate boundary in and around the asperities.

収録刊行物

  • 地震　第２輯

    地震　第２輯 56 (4), 457-469, 2004

    公益社団法人 日本地震学会

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