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Manuscript Title: A finite element program package for magnetotelluric modelling.
Authors: E. Kisak, P. Silvester
Program title: H-PARALLEL FEMT-2D
Catalogue identifier: ACSG_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 10(1975)421
Programming language: Fortran.
Computer: IBM 360/75.
Operating system: OS/360 WITH HASP II.
Program overlaid: yes
RAM: 50K words
Word size: 32
Keywords: Geophysics, Magnetotelluric, Finite element, Laplace, Helmholtz, H-parallel, H-polarization, E-parallel, E-polarization, Cuthill-mckee, Sparse matrices.
Classification: 13.

Subprograms used:
Cat Id Title Reference
ACSJ_v1_0 ZFORMATS CPC 10(1975)421

Nature of problem:
Telluric and magnetotelluric response over two dimensional resistivity anomalies and topographic variation in the H-parallel case.

Solution method:
The high-order triangular finite element method is used with polynomials of degree up to six. The resultant linear system of equations is not solved by an iterative process; rather, the complex symmetric positive- definite coefficient matrix is factorized into LDL T. The generation of nodes is mostly automatic and is followed by reordering according to the reverse Cuthill-Mckee algorithm to improve matrix profile and thus greatly reduce storage requirements. Surface electric field values are computed with the matrix representation of the normal derivative operator.

Restrictions:
The usual assumptions of magnetotelluric modelling are assumed. Only geological structures having infinite length in one direction are treated. It is assumed that all boundaries within the problem region can be well approximated by straightline segments.

Unusual features:
Data in the BLOCK DATA BLOCK1 of the program are punched in Z format, a feature of the IBM FORTRAN IV. This BLOCK DATA can be generated in other formats using the prorgam ZFORMATS described in this paper and which must be suitably modified.

Running time:
The execution times are greatly problem-dependent. The sample problem of a vertical fault described in the long write-up and involving the solution of a complex linear system of 235 unknowns required 25 s in total CPU time on the IBM 360/75 computer.