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The files contain phase-velocity maps of Love and Rayleigh waves
derived from USArray data for the period 2006-2013 using
noise-tomography techniques. This set of phase-velocity maps are
referred to as "USANT13".

This is an update to the maps "USANT12" that were published
as part of the paper:

Ekstrom, G., Love and Rayleigh phase-velocity maps, 5-40 s,
of the western and central USA from USArray data,
Earth Planet. Sci. Lett. (2013), 
http://dx.doi.org/10.1016/j.epsl.2013.11.022

There is a separate file for phase velocity at
each period and for each wave type (L or R).

Each file contains a line close to the beginning that looks like 
#PVELREF: x.xxxx
This line gives the reference phase velocity for the anomaly
values that follow.

The files contain values of phase velocity for latitude-longitude
pixels. Variations are given in percent. The format of the data is 
latitude, longitude, pixel size in degrees, percent deviation.
The latitude and longitude refer to the center of the pixel.

The pixel map is referenced to geocentric coordinates.  Therefore
the latitude should be corrected to the ellipsoid if maps are 
plotted in geographic coordinates.

Please cite the EPSL paper if you make use of the USANT12 or
USANT13 maps.
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GE 2014-05-03
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