Nonlinear Effects on Linear Seismic Source Inversions From Simulations of Underground Chemical Explosions

Date: 4/24/2019

Time: 06:00 PM

Room: Grand Ballroom

Linear moment tensor inversion is a common method used in seismology to understand the characteristics of the seismic source model. However, underground explosions nonlinearly affect the surrounding earth materials through plastic deformation, breaking rocks, and spall. Although nonlinear algorithms can accurately simulate very near field ground motions, they are computationally expensive and unnecessary for far field wave simulations. Linearized seismic wave propagation codes, on the other hand, are computationally efficient and can accurately model the far-field linear wavefield, despite their simplification of the seismic source. Thus, it is advantageous to understand the conditions under which a purely linear analysis of far-field seismic waveforms is sufficiently accurate and when nonlinear analysis is critical. We have coupled Sandia’s nonlinear algorithms to a linearized elastic wave propagation code using time-varying boundary conditions, to pass information from the nonlinear domain to the linear one. We find the purely linear seismic moment tensor and source time functions that optimally fit the waveforms produced by the nonlinear source and investigate how well these purely linear methods can adequately fit the synthesized data from nonlinear sources. We will present results showing the effects of geological materials, nearby structures, and frequency on linear source parameters for earth models with simulated chemical explosions at various scaled depths of burial. We will also discuss how well the linear source models are able to reconstruct the waveforms from the nonlinear source in the various scenarios.

Sandia National Laboratories is a multimission laboratory managed and operated by National Technology & 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: Leiph Preston

Authors