震源の不均質すべりを考慮した半経験的地震動評価

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書誌事項

タイトル別名
  • Semi-Empirical Synthesis of Strong Ground Motions for the Description of Inhomogeneous Faulting
  • シンゲン ノ フキンシツスベリ オ コウリョシタ ハン ケイケンテキ ジシンド

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抄録

Stochastic models specified by statistical source parameters have been proposed to describe the details of fault plane irregularities. The statisical parameters have been estimated through the analysis of strong-motion records by using these models. In the study herein, a new semi-empirical method is developed to estimate strong ground-motions in the short period range, taking into account the fault plane irregularities.<br>The fault plane of large earthquake is assumed to consist of some small segments with a specific size, which is called fault patch size. The displacement Dij of each segment is divided into two parts. One is the average displacement D0 over the fault plane and the other is the deviation ΔDij from D0. Seismic wave SL(t) due to D0 and the seismic wave SS(t) due to ΔDij are synthesized separately as follows:<br>SL(t)=nΣi=1nΣj=1nΣk=1(Re/Rij)Se(t-τijk)<br>SS(t)=nΣi=1nΣj=1κij(Re/Rij)Se(t-τij1)<br>where Se(t) shows an observed seismic wave of element earthquake, of which fault area should be consistent with the fault patch size, Re is the source to site distance of the element earthquake, Rij is a distance from each segment on the fault plane to the site, and τijk is a delay time in relation to rupture propagation and travel time of seismic waves.<br>SL(t) can be derived based on the similarity conditions of source parameters and n is determined from the cubic root of the seismic-moment ratio between the large and the element earthquakes. κij is introduced as a ratio between the deviation ΔDij of each segment on the fault plane and the displacement of element earthquake, and is assumed to be a probabiristic parameter of normal distribution with average of 0 and with standard deviation of SD. SD shows the degree of inhomogeneity of displacement on the fault plane. The final result of synthesized strong ground-motion can be expressed as a sum of SL(t)and SS(t).<br>The new method is applied to synthesis of strong ground motions at Akita during the 1983 Nihonkai-chubu earthquake (M=7.7) and the relations among SD and some statistical parameters of other stochastic fault models are discussed theoretically.

収録刊行物

  • 地震　第２輯

    地震　第２輯 40 (1), 77-88, 1987

    公益社団法人 日本地震学会

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