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Published July 2013 | Published
Journal Article Open

High-resolution 3D shallow crustal structure in Long Beach, California: Application of ambient noise tomography on a dense seismic array


Ambient noise tomography has proven to be effective in resolving shallow earth structure. We applied ambient noise tomography on a dense seismic array in Long Beach, California. The array was composed of more than 5200 stations with an average spacing close to 100 m. Three weeks of passive ambient noise were crosscorrelated between each station pair, which resulted in more than 13.5 million crosscorrelations within the area. Clear fundamental-mode Rayleigh waves were observed between 0.5 and 4 Hz, which were most sensitive to structure above 1-km depth. For each station pair, we applied frequency-time analysis to determine the phase traveltime dispersion, and, for each frequency, we applied eikonal tomography to determine the Rayleigh wave phase velocity map. The eikonal tomography accounted for ray bending by tracking the wavefront and allowed uncertainties to be estimated through statistical analysis. The compilation of phase velocity maps was then used to invert for 3D shear velocity structure. The inverted model showed clear correlation with the known geologic features such as the shallow south–north velocity dichotomy and a deeper fast anomaly associated with the Newport-Inglewood fault zone. Our results can potentially be used to complement traditional active source studies.

Additional Information

© 2013 Society of Exploration Geophysicists. Manuscript received by the Editor 26 October 2012; revised manuscript received 4 March 2013; published online 1 August 2013. The authors gratefully acknowledge NodalSeismic LLC and Signal Hill Petroleum, Inc., for permitting us to use the Long Beach data. We also thank K. Wapenaar, the associate editor, A. Verdel, and two anonymous reviewers for constructive comments and V. Tsai and C. Stork for helpful discussions.

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