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The local amplification of surface waves: A new observable to constrain elastic velocities, density, and anelastic attenuation

Lin, Fan-Chi and Tsai, Victor C. and Ritzwoller, Michael H. (2012) The local amplification of surface waves: A new observable to constrain elastic velocities, density, and anelastic attenuation. Journal of Geophysical Research B, 117 (B6). Art. No. B06302. ISSN 0148-0227. doi:10.1029/2012JB009208.

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The deployment of USArray across the continental U.S. has prompted developments within surface wave tomography to exploit this unprecedented data set. Here, we present a method to measure a new surface wave observable: broadband surface wave amplification that provides new and unique constraints on elastic velocities and density within the crust and upper mantle. The method, similar to its phase velocity counterpart referred to as Helmholtz tomography, initiates by constructing phase travel time and amplitude maps across the array for each period and earthquake. Spatial differential operators are then applied to evaluate the amplitude variation, as well as the effect of focusing/defocusing. Based on the 2-D damped wave equation, the amplitude variation corrected for focusing/defocusing is linked directly to both local amplification and intrinsic attenuation, which are separated by examining waves propagating in opposite directions. We apply the method to teleseismic Rayleigh waves observed across USArray between periods of 24 and 100 s and show that the observed amplification maps are strongly correlated with known geological features. Small-scale attenuation measurements are contaminated by wavefield complexities, but larger-scale anelastic attenuation is estimated reliably. The observed amplification maps compare well with predictions based on recent 3-D shear velocity models of the western U.S. that were produced from ambient noise and earthquake data. Notably, predictions based on models with different prescribed density structures demonstrate the potential for using estimates of local amplification to constrain not only 3-D velocity structure but also density.

Item Type:Article
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URLURL TypeDescription
Lin, Fan-Chi0000-0003-0394-6830
Tsai, Victor C.0000-0003-1809-6672
Additional Information:© 2012 American Geophysical Union. Received 7 February 2012; revised 19 April 2012; accepted 22 April 2012; published 5 June 2012. The authors wish to thank two anonymous reviewers for constructive comments and B. Schmandt and R. W. Clayton for helpful discussions. The facilities of the IRIS Data Management System, specifically the IRIS Data Management Center, were used to access the waveform and metadata required in this study. The IRIS DMS is funded through the National Science Foundation and specifically the GEO Directorate through the Instrumentation and Facilities Program of the National Science Foundation under Cooperative Agreement EAR-0552316. This research was supported by the Director’s Post Doctoral Fellowship of the Seismological Laboratory at the California Institute of Technology and by NSF grants EAR-0711526 and EAR-0844097 at the University of Colorado Boulder.
Group:Seismological Laboratory
Funding AgencyGrant Number
Caltech Seismological Laboratory Director’s Post-Doctoral FellowshipUNSPECIFIED
Subject Keywords:amplification; attenuation; surface wave; tomography
Issue or Number:B6
Record Number:CaltechAUTHORS:20120711-153922657
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Official Citation:Lin, F.-C., V. C. Tsai, and M. H. Ritzwoller (2012), The local amplification of surface waves: A new observable to constrain elastic velocities, density, and anelastic attenuation, J. Geophys. Res., 117, B06302, doi:10.1029/2012JB009208.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:32368
Deposited On:11 Jul 2012 22:58
Last Modified:09 Nov 2021 21:26

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