We collect rms amplitude data from band-passed seismograms using group velocity windows.
Data from 13 stations yielded 1488,1 Hz, Pg/Lg amplitude ratios within a box covering western China and surrounding areas.
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The advantage of using ratio data is that relative source and site effects are similar to one another, while path effects retain large variations.
Disadvantages include interpretation difficulty and the large number of correction "surfaces" that must be calculated and stored.