Fig. 4
Geometrical configuration #1: geometry used for the covariance between a east-west and north-south travel time Cov [ τ1,τ2 ], where τ1 = τα1(x1,x2) and τ2 = τα2(x3,x4). The distance between x1 and x2 and between x3 and x4 is Δ = 10 Mm.
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