Multiple Tension-Crack Model for Dilatancy : Surface Displacement, Gravity and Magnetic Change
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概要
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A macroscopic model for crustal dilatancy is presented : i.e. Gaussian distribution of small tension-cracks. The influence of a single crack is evaluated by an appropriate strain nucleus in a semi-infinite elastic medium. The effect of all the cracks is given simply by integrating it with the weight of Gaussian distribution. This is nothing but an extension of the multiple Mogi model proposed by HAGIWARA (1977b). Three kinds of cracks are adopted : (a) the spherical (i.e. the Mogi model), (b) the T33-type (horizontal penny-shaped cracks) and (c) the T11-type (vertical penny-shaped cracks). The multiple Mogi model composed of spherical cracks is mechanically equivalent to the case where tensile cracks are oriented in every direction. Mechanical distortion of the elastomagnetic half-space gives rise to changes in the gravity and magnetic fields. All these distortion-related quantities are formulated in a unified way. The multiple Mogi and T33-crack models result in changes similar to each other. The only exception is the magnetic total field change : the multiple Mogi model is dominated by overall decrease, while the multiple T33-crack one exhibits practically no field change. On the other hand, the multiple T11-crack model differs substantially from the foregoing two. The upheaval has two humps in some cases and there appears a positive region in the magnetic change. In particular, the gravity field varies remarkably as compared with the height change. The multiple tension-crack model is applicable to volcanic phenomena. It also works as a source model for swarm earthquakes in volcanic regions and certain kinds of magma reservoirs.
- 東京大学地震研究所,Earthquake Research Institute, University of Tokyo,地震研究所の論文
- 1987-02-10
東京大学地震研究所,Earthquake Research Institute, University of Tokyo,地震研究所 | 論文
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