Finite-Difference Algorithm for 3D Orthorhombic Elastic Wave Propagation

Date: 4/24/2019

Time: 06:00 PM

Room: Grand Ballroom

Many earth materials and minerals are seismically anisotropic; however, due to the weakness of anisotropy and for simplicity, the earth is often approximated as an isotropic medium. Specific circumstances, such as in shales, tectonic fabrics, or oriented fractures, for example, require the use of anisotropic simulations in order to accurately model the earth. An orthorhombic medium is characterized by three mutually orthogonal symmetry planes comprising a dense system of vertically-aligned microfractures superimposed on a finely-layered horizontal geology, which can be reduced to an elastic stress-strain constitutive relationship containing nine independent moduli comprising a set of nine, coupled, first-order, linear, inhomogeneous partial differential equations. A new massively parallel 3-D full seismic waveform simulation algorithm within the principle coordinate system of an orthorhombic material, which is a specific form of anisotropy common in layered, fractured media, has been developed.

This FD code is used to support the modeling component of the Source Physics Experiment (SPE), a series underground chemical explosions at the Nevada National Security Site. The data from the experiments are used to help determine event signatures that vary depending on geology, yield and depth of burial. An improved anisotropic model has been developed using observations from the SPE Phase I experiments and tomographic inversion. The velocity parameters obtained from the tomographic inversion are used in the FD code to simulate all six experiments of Phase I using a point moment source at the source depth. The observed data is then compared to the synthetic data. The observations are also inverted with simulated Green’s Functions to obtain the source time functions.

Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia LLC, a wholly owned subsidiary of Honeywell International Inc. for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.

Presenting Author: Richard P. Jensen

Authors