3D SEM Modeling of Wave Propagation at the Source Physics Experiment Phase II Site to Quantify Shear Wave Generation by Explosions at Short Distance (<3km)
Shear wave energy has been observed for most underground explosions which are classically modeled as isotropic sources. Shear waves are likely to be produced by any deviation of the actual source from an ideal isotropic source and by wave propagation in a complex subsurface where reflections and refraction will transfer seismic energy from P to S-wave. In this study, we use 3D full waveform modeling enabled by the code SPECFEM3D (Komatitsch & Tromp, 1999) to quantify the effect of different subsurface features on P/S ratio. Our goal is to explain some of the scatter observed for P/S ratio for small events and at short event-to-station distances that challenges discrimination methods (Pyle & Walter, 2019). SPECFEM3D is based on the Spectral Element Method (SEM) which is a direct numerical method that has benefited from advances in numerical methods and (super)computers over the last two decades.
Our modeling is compared to data recorded by a dense Large-N array of a series of well-instrumented chemical explosions in the Yucca Flat basin (Nevada), Phase II of the Source Physics Experiment (SPE). The four explosions of the series were carried-out in quaternary alluvium overlying tertiary tuff and Paleozoic basement rocks. A subsurface model was built using a local geological framework model and different models of seismic velocities were tested, some coming from seismic analyses, some from tomographic studies. We further varied the velocity of each geological unit in the model using Gaussian and Von Karman distributions to account for random heterogeneities. The accuracy of our modeling is assessed with different convergence tests. We compare modeled P/S ratios and peak velocities of the transverse component to the data to constraint our modeling. We found that the contrast between the tuff and the sedimentary layer is key in matching the peak velocity of the transverse component observed in the data with synthetics.
Session: Advances in Seismoacoustic Methods for Explosion Monitoring II
Type: Oral
Room: Cedar
Date: 4/22/2022
Presentation Time: 10:15 AM Pacific
Presenting Author: Carene Larmat
Student Presenter: No
Additional Authors
Carene Larmat Presenting Author Corresponding Author carene@lanl.gov Los Alamos National Laboratory |
Ting Chen tchen@lanl.gov Los Alamos National Laboratory |
J. Rubin Abrams rabrams12@math.arizona.edu University of Arizona |
Asher May asher.may.98@gmail.com University of New Mexico |
Richard Alfaro-Diaz raalfarodiaz@lanl.gov Los Alamos National Laboratory |
Charlotte Rowe char@lanl.gov Los Alamos National Laboratory |
W. Scott Phillips wsp@lanl.gov Los Alamos National Laboratory |
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3D SEM Modeling of Wave Propagation at the Source Physics Experiment Phase II Site to Quantify Shear Wave Generation by Explosions at Short Distance (<3km)
Category
Advances in Seismoacoustic Methods for Explosion Monitoring
Description