Azimuthally Dependent Scattering of High Frequency Vertical Component Seismic Data at the Large N Array, Source Physics Experiment

Date: 4/24/2019

Time: 04:15 PM

Room: Cascade I

The Large-N array of the Source Physics Experiment (SPE) consisted of 496 vertical component geophones that recorded the seismic wave field produced by the SPE-5 buried chemical explosion. One of the goals of the Large-N experiment was geophysical characterization of the subsurface, which relies on coherent wave field processing methods. However, preliminary observations of the data showed a high degree of azimuthally dependent seismic scattering, hindering surface wave analysis. For the work presented here, we quantify the azimuthal dependence of the wave field scattering to guide future coherent wave field processing methods. Specifically, we form ten linear arrays, with various source-receiver azimuths, from a subset of the Large-N stations. For each linear array, we evaluate wave field coherence as a function of frequency and inter-station distance. For P waves, we observe that there is a strong azimuthal dependence of wave coherence, with the highest degree of scattering occurring in a northwest/southeast propagation direction. This suggests that there are structural elements beneath the Large-N array that affect the direct source to receiver body wave ray path. We also observe that the scattering of the post-P energy displays a coherence that is dependent on both frequency and azimuthal direction. This energy is preferentially coherent in the southwest-to-northeast propagation direction, consistent with the strike of the steeply dipping boundary fault adjacent to the northeast side of the Large-N array at low frequencies (<10 Hz). At higher frequencies, the azimuthally dependent wave coherence diminishes, suggesting that the scattering of high frequency portion of the post-P wave field is independent of the large-scale geologic structure at this site.

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: Andréa Darrh

Authors