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Understanding the amplitudes of noise correlation measurements

Tsai, Victor C. (2011) Understanding the amplitudes of noise correlation measurements. Journal of Geophysical Research B, 116 (B9). Art. No. B09311. ISSN 0148-0227. doi:10.1029/2011JB008483.

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Cross correlation of ambient seismic noise is known to result in time series from which station-station travel-time measurements can be made. Part of the reason that these cross-correlation travel-time measurements are reliable is that there exists a theoretical framework that quantifies how these travel times depend on the features of the ambient noise. However, corresponding theoretical results do not currently exist to describe how the amplitudes of the cross correlation depend on such features. For example, currently it is not possible to take a given distribution of noise sources and calculate the cross correlation amplitudes one would expect from such a distribution. Here, we provide a ray-theoretical framework for calculating cross correlations. This framework differs from previous work in that it explicitly accounts for attenuation as well as the spatial distribution of sources and therefore can address the issue of quantifying amplitudes in noise correlation measurements. After introducing the general framework, we apply it to two specific problems. First, we show that we can quantify the amplitudes of coherency measurements, and find that the decay of coherency with station-station spacing depends crucially on the distribution of noise sources. We suggest that researchers interested in performing attenuation measurements from noise coherency should first determine how the dominant sources of noise are distributed. Second, we show that we can quantify the signal-to-noise ratio of noise correlations more precisely than previous work, and that these signal-to-noise ratios can be estimated for given situations prior to the deployment of seismometers. It is expected that there are applications of the theoretical framework beyond the two specific cases considered, but these applications await future work.

Item Type:Article
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Tsai, Victor C.0000-0003-1809-6672
Additional Information:© 2011 American Geophysical Union. Received 23 April 2011; revised 17 June 2011; accepted 29 June 2011; published 24 September 2011. The author thanks R. Snieder, F.‐C. Lin, G. A. Prieto, M. P. Moschetti, L. Ramirez, D. E. McNamara, two anonymous reviewers and the Associate Editor for helpful comments. This research was supported by a Mendenhall postdoctoral fellowship from the U.S. Geological Survey.
Group:Seismological Laboratory, Keck Institute for Space Studies
Funding AgencyGrant Number
Subject Keywords:attenuation; noise correlation; surface-wave amplitudes
Issue or Number:B9
Record Number:CaltechAUTHORS:20111025-085851425
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Official Citation:Tsai, V. C. (2011), Understanding the amplitudes of noise correlation measurements, J. Geophys. Res., 116, B09311, doi:10.1029/2011JB008483.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:27397
Deposited On:25 Oct 2011 20:17
Last Modified:09 Nov 2021 16:48

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