A Parallel Tool for Numerical Approximation of 3D Electromagnetic Surveys in Geophysics

Abstract

Abstract. This paper presents an edge-based parallel code for the data computation that arises when applying one of the most popular electromagnetic methods in geophysics, namely, the controlled-source electromagnetic method (CSEM). The computational implementation is based on the linear Edge Finite Element Method in 3D isotropic domains because it has the ability to eliminate spurious solutions and is claimed to yield accurate results.The framework structure is able to exploit the embarrassingly-parallel tasks and the advantages of the geometric flexibility as well as to work with three different orientations for the dipole, or excitation source, on unstructured tetrahedral meshes in order to represent complex geological bodies through a local refinement technique. We demonstrate the performance and accuracy of our tool on the Marenostrum supercomputer (Barcelona Supercomputing Center) through scaling tests and canonical tests, respectively.

Improving edge finite element assembly for geophysical electromagnetic modelling on shared-memory architectures

“…1. Marine CSEM [8] The 3D CSEM modelling is typically solved in frequency domain at low frequency (∼ 1Hz), which involves the numerical solution of Maxwell's equations in stationary regimes in an unbound domain Γ [4].…”

“…Following the works by [3] and [4], the edge finite element equation for CSEM modelling can be expressed as follows:…”

“…PETGEM is developed as open-source at Computer Applications in Science & Engineering of Barcelona Supercomputing Center. Detailed information about PETGEM, such as software stack, main functionalities and capabilities, are described in [4], [5].…”

“…Therefore, parts of the assembly process eligible for vectorizing are the following: computation of stiffness and mass matrices, b e computation, Gauss points computation, basis functions computation and electric field computation. Here, our main target was avoid the use of loops in the numerical formulation by [3], [4] and [5]. As consequence, in the new version of the code all operations can be developed in a matrix-vector manner, which significantly reduces the memory access (indirect addressing) and therefore the computation time.…”

“…Furthermore, the 3D modelling of geophysical EM problems can easily overwhelm single core computing resources [3]. To alleviate these issues we present a set of node-level optimizations to perform the assembly of edge finite element matrices that arise in 3D geophysical electromagnetic modelling on shared-memory architectures.…”