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Seasonal variations of observed noise amplitudes at 2–18 Hz in southern California

Hillers, G. and Ben-Zion, Y. (2011) Seasonal variations of observed noise amplitudes at 2–18 Hz in southern California. Geophysical Journal International, 184 (2). pp. 860-868. ISSN 0956-540X. doi:10.1111/j.1365-246X.2010.04886.x.

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We show that noise amplitudes at frequencies above 1 Hz exhibit strong seasonal variations in a broad southern California region. The results are based on 3-component seismic data recorded between 2002 and 2009 by 30 stations. Focusing on continuous 6-hr night-time segments, the seismograms are bandpass-filtered in nine frequency bands between 2 and 18 Hz. Squared amplitudes are median-filtered to reduce the influence of earthquake signals and integrated to yield half-hourly noise energy estimates. The 6-hr minimum energy values are converted back to ground velocity and used as representative daily noise level amplitudes. Notwithstanding various trends, drifts and other transient complexities, a common feature of the resulting time series in both the horizontal and vertical components are annual amplitude changes at all examined frequencies and all stations. The strength of amplitude variations shows no correlation with distance from the coast and some particularly clear seasonal changes are seen near topographic features in arid uninhabited areas. Comparison to meteorological data suggests that the main sources for the high-frequency noise field are variations of temperature and wind at the surface. In addition to acting directly on topographic irregularities and other surface features, these sources (and especially temperature changes) may also generate high-frequency noise by inducing multitudinous small-scale failures in the shallow crust.

Item Type:Article
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URLURL TypeDescription DOIArticle
Ben-Zion, Y.0000-0002-9602-2014
Additional Information:© 2010 The Authors. Geophysical Journal International © 2010 RAS. Accepted 2010 November 9. Received 2010 September 20; in original form 2010 May 20. Article first published online: 22 Dec. 2010. The seismograms used in this study were obtained from the Southern California Earthquake Data Center (SCEDC). We thank the scientists involved with recording and making the data available. GH thanks the computing staff at Caltech Seismolab for their continuous assistance. GH was supported in part by the Gordon and Betty Moore Foundation and by a postdoctoral fellowship with Jean-Paul Ampuero at Caltech. This is Caltech Tectonic Observatory Contribution 134. YBZ acknowledges support from the National Science Foundation (grant 354 EAR-0908903) and the Southern California Earthquake Center. The manuscript benefited from constructive comments of Norm Sleep, Keith Koper, an anonymous referee and Editor Cindy Ebinger. Some figures were made using GMT (Wessel & Smith 1998).
Group:Caltech Tectonics Observatory
Funding AgencyGrant Number
Gordon and Betty Moore FoundationUNSPECIFIED
Southern California Earthquake Center (SCEC)UNSPECIFIED
Subject Keywords:Geomechanics; Elasticity and anelasticity; Fracture and flow; Site effects; Wave scattering and diffraction; Wave propagation
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Caltech Tectonics Observatory134
Issue or Number:2
Record Number:CaltechAUTHORS:20110228-152223780
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Official Citation:Hillers, G. and Ben-Zion, Y. (2011), Seasonal variations of observed noise amplitudes at 2–18 Hz in southern California. Geophysical Journal International, 184: 860–868. doi: 10.1111/j.1365-246X.2010.04886.x
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:22558
Deposited By: Tony Diaz
Deposited On:03 Mar 2011 19:44
Last Modified:09 Nov 2021 16:06

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