TRACKING THE PROGRESS OF THE USARRAY TRANSPORTABLE ARRAY:
SURFACE WAVE TOMOGRAPHY FROM AMBIENT SEISMIC NOISE AND TELESEISMIC EVENTS ACROSS WESTERN US

Center for Imaging the Earth's Interior
Department of Physics, University of Colorado at Boulder 		 

Fan-Chi Lin, Morgan P. Moschetti, Michael H. Ritzwoller, Nikolai M. Shapiro, Yingjie Yang and Weisen Shen

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Introduction   |   Phase and Group Velocities   |   3-D Isotropic Model of Western US   |   Azimuthal Anisotropy    |   References   
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PHASE and GROUP VELOCITIES

 Western US surface wave tomography

We present a new method of surface wave tomography based on applying the eikonal equation to observed phase traveltime surfaces computed from seismic ambient noise. The source¨C receiver reciprocity in the ambient noise method implies that each station can be considered to be an effective source and the phase traveltime between that source and all other stations is used to track the phase front and construct the phase traveltime surface. Assuming that the amplitude of the waveform varies smoothly, the eikonal equation states that the gradient of the phase traveltime surface can be used to estimate both the local phase speed and the direction of wave propagation. For each location, we statistically summarize the distribution of azimuthally dependent phase speed measurements based on the phase traveltime surfaces centred on different effective source locations to estimate both the isotropic and azimuthally anisotropic phase speeds and their uncertainties. Fan-chi Lin applied this method using more than 800 USArray across Western US. Here we displayed love wave speed maps for periods at 12s, 24s, 36s and 50s Results of Rayleigh Wave Azimuthal Anisotropy derived by this mothod is shown here. The azimuthal anisotropy picture is for 12s, 24s and 36s.

12 s LOVE WAVE PHASE VELOCITIES      24 s LOVE WAVE PHASE VELOCITIES


                     

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      This project is funded by the National Science Foundation - EAR 0450082.
All data was obtained from the IRIS Data Management Center.