Establishment of Precision of Calculation for Volcanic Crustal Deformation by FEM Reproduction of Mogi-Yamakawa's Model Using FEM

• Published in: Papers in Meteorology and Geophysics Vol. 58; pp. 1 - 15
• Main Authors: Yamamoto, Tetsuya, Churei, Masaaki, Fujiwara, Kenji, Takagi, Akimichi, Sakai, Takayuki, Fukui, Keiichi
• Format: Journal Article
• Language: Japanese
• Published: Japan Meteorological Agency / Meteorological Research Institute 2007
• Subjects: Marine
• ISSN: 0031-126X; 1880-6643
• DOI: 10.2467/mripapers.58.1

Analytical solutions derived under very simplified conditions have been used to explain the crustal deformation around volcanoes. One example is Yamakawa's solution (Yamakawa, 1955), which represents surface deformation caused by small enough spherical pressure source at some depth within a semi-infinite homogeneous elastic body. However, such solutions do not exactly hold true in a real volcano, due to the volcanic edifices that project from the earth's surface, non-spherical pressure sources, inhomogeneous crustal structures, and so on. We use the finite element method (FEM) to create numerical models of a volcano for investigating crustal deformation of a real volcano. The size of the FE model or the setting of its boundary conditions will likely affect the precision of calculation for volcanic crustal deformation. Therefore, we reproduced Mogi-Yamakawa's model (or Mogi's model) using FE models of various model sizes and boundary conditions. We then quantitatively evaluated the influence of model size and boundary conditions on the precision of calculation. The results are as follows. As the FE model becomes larger, the results of FE analysis approach Yamakawa's solution, which demonstrates an improved precision of calculation. However, the smallest possible FE model is recommended so far as the necessary precision of calculation is ensured, because a large model generally produces a large number of nodes which leads to an accelerative increase in calculation time. The boundary condition of fixing bottom and side surfaces of an FE model completely is recommended because the changes in precision of calculation with distance are similar for both vertical and horizontal displacements. The vertical and horizontal sizes of the FE model remarkably affect the precision of calculation for vertical and horizontal displacements, respectively.