Welcome to the new version of CaltechAUTHORS. Login is currently restricted to library staff. If you notice any issues, please email coda@library.caltech.edu
Published September 2013 | Published
Journal Article Open

Spurious velocity changes caused by temporal variations in ambient noise frequency content


Ambient seismic noise cross-correlations are now being used to detect temporal variations of seismic velocity, which are typically on the order of 0.1 per cent. At this small level, temporal variations in the properties of noise sources can cause apparent velocity changes. For example, the spatial distribution and frequency content of ambient noise have seasonal variations due to the seasonal hemispherical shift of storms. Here, we show that if the stretching method is used to measure time-shifts, then the temporal variability of noise frequency content causes apparent velocity changes due to the changes in both amplitude and phase spectra caused by waveform stretching. With realistic seasonal variations of frequency content in the Los Angeles Basin, our numerical tests produce about 0.05 per cent apparent velocity change, comparable to what Meier et al. observed in the Los Angeles Basin. We find that the apparent velocity change from waveform stretching depends on time windows and station-pair distances, and hence it is important to test a range of these parameters to diagnose the stretching bias. Better understanding of spatiotemporal noise source properties is critical for more accurate and reliable passive monitoring.

Additional Information

© The Authors 2013. Published by Oxford University Press on behalf of The Royal Astronomical Society. Accepted 2013 April 23; Received 2013 April 22; In original form 2013 February 18. We thank Fan-Chi Lin and Dongzhou Zhang for helpful discussions. We thank the editorMichael Ritzwoller and two anonymous reviewers for their comments that improved the manuscript. The facilities of the Southern California Earthquake Data Center (SCEDC), and the Southern California Seismic Network (SCSN), were used for access to waveforms data required in this study. This work is partially supported by the NSF/EAR-0838247 and Southern California Earthquake Center (12064).

Attached Files

Published - Geophys._J._Int.-2013-Zhan-1574-81.pdf


Files (4.3 MB)
Name Size Download all
4.3 MB Preview Download

Additional details

August 22, 2023
October 24, 2023