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In situ observations of velocity changes in response to tidal deformation from analysis of the high-frequency ambient wavefield

Hillers, G. and Retailleau, L. and Campillo, M. and Inbal, A. and Ampuero, J.-P. and Nishimura, T. (2015) In situ observations of velocity changes in response to tidal deformation from analysis of the high-frequency ambient wavefield. Journal of Geophysical Research. Solid Earth, 120 (1). pp. 210-225. ISSN 2169-9313. doi:10.1002/2014JB011318.

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We report systematic seismic velocity variations in response to tidal deformation. Measurements are made on correlation functions of the ambient seismic wavefield at 2–8 Hz recorded by a dense array at the site of the Piñon Flat Observatory, Southern California. The key observation is the dependence of the response on the component of wave motion and coda lapse time τ. Measurements on the vertical correlation component indicate reduced wave speeds during periods of volumetric compression, whereas data from horizontal components show the opposite behavior, compatible with previous observations. These effects are amplified by the directional sensitivities of the different surface wave types constituting the early coda of vertical and horizontal correlation components to the anisotropic behavior of the compliant layer. The decrease of the velocity (volumetric) strain sensitivity S_θ with τ indicates that this response is constrained to shallow depths. The observed velocity dependence on strain implies nonlinear behavior, but conclusions regarding elasticity are more ambiguous. The anisotropic response is possibly associated with inelastic dilatancy of the unconsolidated, low-velocity material above the granitic basement. However, equal polarity of vertical component velocity changes and deformation in the vertical direction indicate that a nonlinear Poisson effect is similarly compatible with the observed response pattern. Peak relative velocity changes at small τ are 0.03%, which translates into an absolute velocity strain sensitivity of S_θ≈5 × 10^3 and a stress sensitivity of 0.5 MPa^(−1). The potentially evolving velocity strain sensitivity of crustal and fault zone materials can be studied with the method introduced here.

Item Type:Article
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URLURL TypeDescription
Inbal, A.0000-0001-8848-7279
Ampuero, J.-P.0000-0002-4827-7987
Additional Information:© 2014 American Geophysical Union. Received 23 May 2014. Accepted 26 Nov 2014. Accepted article online 5 Dec 2014. Published online 7 Jan 2015. We thank D. Agnew for providing us with the predicted tidal strain, and the water well and meteorological data, from PFO. We appreciate discussions with P.A. Johnson, M.L. Doan, E. Daub, and G. Renaud. This work was supported by the European Research Council (Advanced grant Whisper L27507). G. Hillers acknowledges support through a Heisenberg fellowship from the German Research Foundation (Hi 1714/1-1). Figures were made using Generic Mapping Tools (GMT) [Wessel and Smith, 1998] with global multiresolution topography (GMRT) [Ryan et al., 2009]. We thank X. Briand for his outstanding and timely computational assistance that underpinned much of this work and O. Coutant for providing the waveform synthetics. We thank the Associate Editor, N. Nakata, and an anonymous reviewer for their comments that helped to improve the manuscript. The field experiment was funded by USGS grant G11AP20056. Retrieval of the original seismograms from the IRIS Data Management Center is sufficient to understand, evaluate, replicate, and build upon the reported research.
Group:Seismological Laboratory
Funding AgencyGrant Number
European Research Council (ERC)Whisper L27507
Deutsche Forschungsgemeinschaft (DFG)Hi 1714/1-1
Subject Keywords: tidal deformation; tidal strain; ambient noise monitoring; nonlinear in situ response; velocity change monitoring
Issue or Number:1
Record Number:CaltechAUTHORS:20150327-081714465
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Official Citation:Hillers, G., L. Retailleau, M. Campillo, A. Inbal, J.-P. Ampuero, and T. Nishimura (2015), In situ observations of velocity changes in response to tidal deformation from analysis of the high-frequency ambient wavefield, J. Geophys. Res. Solid Earth, 120, 210–225, doi:10.1002/2014JB011318.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:56158
Deposited By: Ruth Sustaita
Deposited On:27 Mar 2015 16:31
Last Modified:10 Nov 2021 20:55

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