Publisher： John Wiley & Sons Inc
E-ISSN： 2156-2202|92|B3|2647-2661
ISSN： 0148-0227
Source： Journal Of Geophysical Research, Vol.92, Iss.B3, 1987-03, pp. : 2647-2661
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Abstract
Analysis of the travel times and amplitude range distributions of both compressional and shear wave arrivals on 15 closely spaced refraction profiles reveals a significant, systematic, and symmetric dependence of average layer 2 velocities on their distance to the north and south of the Hawaiian ridge. Beyond the flexural arch surrounding the ridge the velocity‐depth solutions indicate a normal layer 2. Within the arch (approximately 155 km from the ridge) the average elastic velocities in layer 2 are lowered by 0.8–0.9 ± 0.2 km/s. Within 75 km of the ridge the average velocities are again normal. Elastic and elastic‐plastic flexural models for the regional compensation of the Hawaiian islands predict tensional stress drops of 0.8 kbar in the upper lithosphere for the region having lowered velocities in layer 2, which are similar in magnitude with laboratory measurements of the confining pressure drop necessary to reduce velocities in porous basalts by 0.5 km/s. A significant inverse relationship (correlation coefficient of 0.818) exists between the average elastic velocities in the upper 1.0 km of the igneous crust and the strain in the upper crust calculated from these flexural models. The correlation between lowered average velocities in layer 2 and increased tensional stresses and strains suggest that crack opening in the upper crust accompanies the flexure. These observations are the first reported for a midplate load and corroborate previous suggestions from seismic and flexural data at subduction zones.
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