Imaging the Shallow Structure of the Yucca Flat at the Source Physics Experiment Phase II Site with Horizontal-to-Vertical Spectral Ratio Inversion and a Large-N Seismic Array

Session: Explosion Seismology Advances [Poster]
Type: Poster
Date: 4/29/2020
Time: 08:00 AM
Room: Ballroom
Description: 

The Source Physics Experiment (SPE) is a series of chemical explosions at the Nevada National Security Site (NNSS) with the goal of understanding seismic wave generation and propagation of underground explosions. In order to understand explosion source physics, accurate geophysical models of the SPE site are needed. Here we utilize a Large-N seismic array deployed at the SPE Phase II site to generate a shallow subsurface model. The deployment consists of 500 geophones and covers an area of approximately 2.5 x 2 km. The array is located in the Yucca Flat in the northeast corner of the NNSS, Nye County, Nevada. Using ambient noise recordings throughout the Large-N seismic array we calculate HVSR (horizontal-to-vertical spectral ratio) for Northeast-Southwest and Northwest-Southeast cross-sections at 67 stations across the array. We obtain 2D seismic images across the SPE Phase II site for the shallow structure of the basin. Our results clearly image two significant seismic impedance interfaces at ∼200-475m and ~375–800m depth. The shallower interface relates to the contrast between alluvium and Tertiary volcanic rocks. The deeper interface relates to the contrast between volcanic rocks and the Paleozoic bedrock. Our 2D subsurface models support and extend our understanding of the structure of the site. This study shows that the HVSR method in conjunction with a Large-N seismic array is a quick and effective method for investigating shallow structures.

Presenting Author: Richard A. Alfaro-Diaz

Authors