Snell's Law governs seismic ray refraction at a velocity interface: sin(i)/V1 = sin(r)/V2, where i is the angle of incidence in the upper (slower) layer and r is the angle of refraction in the lower (faster) layer. Since the ray bends away from the normal (refraction angle > incidence angle here, 45°>30°), the lower layer must have a higher velocity.
Applying Snell's Law: sin(i)/V1 = sin(r)/V2, so V2 = V1 × sin(r)/sin(i) = 2.0 km/s × sin(45°)/sin(30°) = 2.0 × (0.7071/0.5) = 2.0 × 1.4142...
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