ديدگاه نوين در مدلسازي عددي تغيير شكلهاي پوسته زمين قسمت اول : نظريه

A New Method for Numerical Modeling of Crustal Deformations, Part One: Theory

This research presents a numerical tool for estimation of subduction zonesʹ behavior during interseismic periods. This approach is based on the least-squares method to derive slippage vectors at subduction fault. The spatial distribution of under ground coupling could be investigated in detail through inverse analysis of geodetic data. During an interseismic period, a region at an intermediate depth remains locked, while the shallower and deeper portions are decoupled, and a steady slip proceeds there. The steady slip could be detected by micro-earthquakes continuously occurring in these two portions. The standard equations of Inverse Problems offer a straightforward way for finding slippage vectors at the interface of two converging plates. One of the new aspects of the current study is evaluation of Greenʹs function operator matrix by means of FEM. Greenʹs function operators are functions of some fundamental parameters such as Tectonic Forces and Far-field Treatment, which are regarded in the present Inverse analysis. To implement fault sliding in a continuum-based FEM code, Split Node Technique as a simple and efficient method is applied. This method does not increase the number of degrees of freedom and no net forces or moments are induced on the finite element mesh. As other common Inverse problems, singularity of coefficient matrix is the main problem. This problem particularly emerges if the number of degrees of freedom is too large. The numerical procedure returns a set of slippage vectors that are not correct. Singular Value Decomposition (SVD) diagnoses precisely what the problem is. In some cases, SVD will not only diagnose the problem, it will also solve it.