What acoustic phenomenon causes the shadow zone for P-wave arrivals at epicentral angles between 100° and 140°?

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Quizplus · Accepted Answer

The shadow zone is an area in which seismographs do not detect P-waves from earthquakes due to their bending within Earth's layers. This bending or refraction of P-waves is caused by the gradual increase in velocity with depth within the Earth's crust, mantle, and core. At epicentral angles between 100° and 140°, P-waves are refracted at such an angle that they do not reach the surface within this zone, creating the P-wave shadow zone.

What Acoustic Phenomenon Causes the Shadow Zone for P-Wave Arrivals