In:
Journal of Geophysical Research: Solid Earth, American Geophysical Union (AGU), Vol. 93, No. B5 ( 1988-05-10), p. 4773-4783
Abstract:
Residual sphere images from deep earthquakes not only detect the presence of slab‐associated velocity anomalies but also lend insight into the flow and deformation of lithosphere subducted into the lower mantle. We have compared travel times from deep events in the Kuril and Mariana arcs with the seismic velocity anomalies implied by kinematical models that thicken the slab perpendicular to its plane by reducing the vertical velocity of the flow with depth. We assume that the details of the deformation (whether the slab buckles, imbricates, fragments, etc.) are averaged out along the ray paths, and hence our models constrain the scale, not the mode, of slab thickening. The deep event travel times are best fit by undeformed models, but the ability of the residual sphere method to resolve slab thickness is limited by ray bending effects. Although the Mariana times are consistent with advective thickening factors of 5 or more, factors larger than 3 are ruled out by the Kuril data. For all models examined, the data require that slab material extends to depths of 900–1000 km. Global tomographic models and regional studies which delineate high‐velocity anomalies in the lower mantle beneath zones of Cenozoic subduction are consistent with our results, as is recent work on pulse distortion by slab gradients. Comparison of observed and predicted rates of seismic moment release suggests that if substantial advective thickening does occur, it is largely aseismic.
Type of Medium:
Online Resource
ISSN:
0148-0227
DOI:
10.1029/JB093iB05p04773
Language:
English
Publisher:
American Geophysical Union (AGU)
Publication Date:
1988
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