Abstract
Using 17 seismic stations in French Polynesia, we study the propagation of high‐frequency Pn waves in the Central and South‐Central Pacific. This study is prompted by the presence of striking Pn wave phases on the seismograms of the Hawaii earthquakes recorded in the Tuamotu and Society islands (Tahiti), almost 40° away. The Pn velocity inferred from these observations (7.95±0.03 km/s) is in good agreement with the values obtained in the North Pacific by Walker (1977a, b) and shows the existence over most of the Pacific basin of a remarkably efficient Pn wave guide of relatively low velocity. Compared to Pn, Sn waves are much less efficiently transmitted. The Pn velocities measured from intraplate earthquakes in the South‐Central Pacific suggest the presence of a 2–3% anisotropy in the wave guide, the direction of maximum velocity being parallel to the trend of the island chains. All these observations are interpreted as evidence of the presence of minimum velocity channels within the subcrustal lithosphere and a discussion of the models which can account for these features is presented.
Published Version
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