High‐frequency seismic attenuation of oceanic P and S waves in the western Pacific

Analyses of oceanic P and S data from an earthquake in the Kuril Islands which occurred along the trend of a 1500‐km‐long ocean bottom hydrophone array deployment near Wake Island have yielded constraints on high‐frequency seismic attenuation in the western Pacific. Spatial attenuation and Q were determined for group velocities between 8.2 and 3.0 km/s and for frequencies between 2.5 and 22.5 Hz. There is greater attenuation of oceanic P than oceanic S at all frequencies suggesting either the presence of significant bulk attenuation in the lithosphere or that oceanic P propagates as a leaky mode. The apparent attenuation of oceanic P and S is distance‐dependent, with lower attenuation beyond 30° Δ. The apparent Q of oceanic P increases with frequency as Q ∼ ƒ 0.7 , from about 300 at 2.5 Hz to 1500 at 17.5 Hz. The apparent Q of oceanic S increases with frequency as Q ∼ ƒ 1.1 , from about 400 at 2.5 Hz to 3000 at 22.5 Hz.