Two graphics showing how P-waves emitted by a virtual source traveled
P waves emitted by a virtual source (yellow star) with a lag-time of 1.34 seconds. The left panel is a snapshot of the 2–8 Hz band-passed wavefield observed at each station (after simple cross-correlation) and the right panel is the beamed wavefield observed at each station (after processing). Credit: Castellanos et al. [2020], Figure 7
Source: Journal of Geophysical Research: Solid Earth

Seismic interferometry uses the Earth’s background vibrations (ambient noise) to reconstruct coherent waves traveling between pairs of seismic stations. However, because of the nature of the ambient noise field, most of the seismic energy that is radiated from a station propagates horizontally in the form of surface waves. Body waves also exist within the ambient noise, but these arrivals are difficult to observe and consequently have only been measured in a few studies.

Castellanos et al. [2020] analyzed ambient noise data from a high-density oil-industry survey in Long Beach, California, USA, to reconstruct over 12 million diving P waves which they then used to map the crustal structure beneath the 5,200-node array.

The tomographic images generated by their study attest to the reliability of noise-derived body waves to map the subsurface velocity structure.  These high-frequency arrivals provide resolution capable of illuminating small structural variations caused by faults that would have been otherwise invisible to conventional surface wave studies.

Citation: Castellanos, J. C., Clayton, R. W., & Juarez, A. [2020]. Using a time‐based subarray method to extract and invert noise‐derived body waves at long beach, California. Journal of Geophysical Research: Solid Earth, 125, e2019JB018855.

—Martha K. Savage, Editor, JGR: Solid Earth

Text © 2020. The authors. CC BY-NC-ND 3.0
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