Po/So Phases: Propagation Velocity Across a 1,500-km-Long, Deep Ocean Hydrophone Array

摘要

Po/So phases from numerous earthquakes along the margin of the Northwestern Pacific Basin were successfully recorded by a 1,5000 by a 1,5000-km-long ocean bottom hydrophone (OBH) array deployed for two months near Wake Island. Data from ten shallow-focus (<100km) events at 20 deg (2,2000 km) to 34 deg (3,8000 km) epicentral distance were used to compute propagation velocities across the array for the onsets of Po and So. The values found are 7.96 + or - 0.05 km/s for Po and 4.58 + or - 0.06 km/s for So. Travel-time intercepts associated with these velocities are, respectively, - 7.21 plus or minus 2.40 s and - 12.84 plus or minus 7.61 s. These velocities are significantly lower than those previously reported for the Northwestern Pacific using single station data. Although the low velocities and negative intercepts could simply be the result of bias in the data, they might also be due to the effects of azimuthal anisotropy along travel paths, or to increasing propagation velocity with lithospheric age, or to a different mode of propagation near the source. Keywords: Primary seismic wave velocity; Earthquake epicenters; Wave propagation; Reprints. (EDC)