有限要素法による構造解析

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The stress changes which are associated with the crustal deformation have hitherto been studied by geophysists. For example, the stress changes have been calculated from such factors as the maximum displacement on the fault plane, the depth of the fault and others based on the theoretical treatment on the strike slip fault. Geologically it is believed that the thickness variation reflects the variation of the amount of vertical displacement of the crustal deformation. Numerous key beds of tuff are known in the Otadai formation of Kazusa group in the Boso Peninsula. Recent study by HIRAYAMA and SUZUKI (1968) revealed in detail the thickness variation between the Key bed O_7 and K_3 among above. According to them an elliptical sedimentary basin were developed there, its longer axis is 60 km and shorter axis is 30 km in length. The thickness of the strata between O_7 and K_3 is 6.5 m in the central part of the ellipse but decreases toward the margins. Present writer considered that the thickness variation were caused bythe crustal deformation. The writer (1970) calculated the stress changes, on the assumption that the thickness variation was equal to the variation of the vertical displacement whic was associated with the vertical force exerted under the earth crust. In this paper, the writer considered that the same thickness variation was caused by the crustal deformation as the result of the horizontal tensile force, and calculated the tensile force by finite element method. The elastic model is as follows. The writer assumed that the elastic rectangular plate (60 km in length and 30 km in height) was laid on the semiinfinite plate. Two cases were assumed. On one of the cases, the one end of the plate is fixed, the lowest part of the plate is moved laterally and the other end is moved laterally by uniform distributed tensile force. On the other cases, the small semicircle is made in the middle of the lowest part in the elastic rectangular plate, and is occupied by liquid, and other conditions are the same as the above case. Comparing with the magnitude of the vertical force by which the sedimentary basin was supposed to be caused, the result shows that the magnitude of the horizontal tensile force by which the sedimentary basin was supposed to be caused is only one-twentieth.
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有限要素法による構造解析

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