High Resolution Imagery at the Source Physics Experiment Using Large Seismic Arrays

Date: 4/25/2019

Time: 02:30 PM

Room: Cascade I

We use several methods of seismic interferometry to obtain highly detailed images at the site of the Source Physics Experiment (SPE). SPE is a series of experiments in varying geologies with the objective of obtaining a physics-based understanding of how seismic waves are created at and scattered near seismic sources. Phase I of the experiment involved chemical explosions in granite, with waves traveling across volcanics, carbonates and alluvium. Phase II of the experiment is currently ongoing and involves chemical explosions in dry alluvium geology (DAG). The records vary dramatically as energy passes through the different geologies. To separate source-specific effects from those due to geological structure, we need precise 3D models at scales ranging from tens of meters to tens of kilometers.

In April 2016, a large, dense array of 996 geophones were deployed south of the Phase I source point. In December 2018, a second deployment of 500 instruments was deployed around the DAG site. In each case, several weeks of continuous data were recorded, capturing ambient noise, distant earthquakes and records of the experimental sources, providing a rich and diverse data collection.

We apply several interferometric techniques: Source interferometry (SI) uses the explosions as rich sources of high frequency, high signal energy. Coda interferometry (CI) isolates the energy from the scattered wavefield. Ambient noise correlation (ANC) uses the energy of the ambient background field. In each case, the data recorded at one seismometer are correlated with the data recorded at another to obtain an estimate of the Green's function (GF) between the two. These GFs are then inverted to obtain the final seismic image. Our objective is to obtain a 3D model that is precise enough to calculate synthetics matching the scattering effects seen in the data.

Presenting Author: Eric Matzel

Authors