A record section for a large earthquake shows clear first P arrivals out to about…
PHYSICS · Subjective · Fermi University Physics · Oscillations, Waves & Acoustics · Earth, Climate & Energy Physics · Seismology, tectonics and geodynamics
The Solid Earth, Ch Rays and travel times: from arrivals to a layered planet
Problem
A record section for a large earthquake shows clear first P arrivals out to about 103∘ epicentral distance, then no direct P arrivals at the travel time predicted by continuing the direct P curve, between about 103∘ and 142∘; beyond 142∘, later arrivals (identified as PKP) appear. Someone argues: "the missing arrivals between 103∘ and 142∘ show that the deep mantle strongly absorbs P energy over that range of distances, since the wave loses all its energy there." Evaluate this claim. State what actually causes the gap and why it is not evidence of absorption.