Numerical simulation of piezomagnetic changes associated with hydrothermal pressurizationNumerical simulation of piezomagnetic changes associated with hydrothermal pressurization
We have developed a computer program to calculate geomagnetic field changes due to the piezomagnetic effect, which is caused by hydrothermal pressurization. The program uses the distribution of pore fluid pressure that is the result of a numerical simulation for hydrothermal fluid circulation after magma intrusion. First, we present a mathematical formulation of three-dimensional (3-D) effective stress equilibrium equations that contain the hydrostatic buoyancy effects of the pore fluid and the seepage force associated with fluid flow. Then, we develop a 3-D finite element program for solving the elastic effective stress field using the spatial distribution of body forces resulting from both gravity and seepage force, with appropriate boundary conditions. On the basis of the solved elastic effective stress field, the distributions of stress-induced magnetization were estimated from the linear piezomagnetism to calculate the piezomagnetic effect on the ground. We examined the results of numerical experiments on the effects of permeability and the influence of a caprock as important factors in changing the physical state within a volcanic edifice. From these evaluations, we found that both effects influence not only the amount of piezomagnetic anomalies, but also the duration time of the anomalous piezomagnetic field. Finally, our method was applied to actual volcanomagnetic field variations observed at the Merapi Volcano in Indonesia. As a result, our model reasonably explained the observed pattern of variations.
各種検索
サポート
ヘルプ