A two‐layer attenuation model for the upper mantle at short periods

Abstract

Estimates of maximum mean P‐wave attenuation (described by the quality factor Qα) are used to make a two‐layer model of Qα in the period range 0.125–1 s for the northwest Pacific subducting region. A shallow highly attenuating layer (Qα ≈ 150) of only 85 km thickness overlays a less attenuating layer to a depth of 450 km (Qα > 1000). The added bandwidth made available by the use of array data yields key information for testing the validity of textbook models predominantly based on extrapolation from longer period data. We find that seismic attenuation at short periods appears to behave differently to long‐period attenuation. This reversal is represented by a modification to the absorption band model obtained from longer period data. Copyright 1995 by the American Geophysical Union.