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Book Chapter

Aseismic Deformation Within Oceanic Lithosphere1

By
Matthew H. Salisbury
Matthew H. Salisbury
Department of Geology, University of Washington, Seattle, Washington 98105.
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Published:
January 01, 1974

Abstract

The existence of ridge transform faults and the near absence of fan-shaped magnetic-anomaly patterns suggest that seafloor spreading is a spatially incremental process. This concept requires that spreading-velocity contrasts exist across ridge transform faults and that the fracture zones beyond ridge transform structures contain a small component of strike slip motion. Magnetic-anomaly patterns in the North Pacific confirm this motion and give 0.55 cm/year as its average measure; this value is in close agreement with theory. These patterns demonstrate further that the plate segments into which the oceanic crust is divided by the great fracture zones move with different angular velocities and erratic spreading directions. Topographic persistence of fracture zones, patterns of submarine volcanism, and the "branching lines," here interpreted as a consequence of a change in spreading direction on an array of active fracture zones, are further evidence of deformation within the plate interiors.

The low seismicity of the fracture zones is the result of high pore pressure, intense brecciation, and serpentinization that cause a drastic reduction in shear strength in the fracture zones. The oceanic crust is considered as a distinct mechanical and seismic province which is cut by thin zones of extremely low shear strength and in which major deformation can occur continuously and aseismically. Crustal rigidity in such a system is the adjusting rigidity of a logjam. The concept of rigid plates is thus only a useful approximation to a dynamically complex crust.

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Contents

AAPG Memoir

Plate Tectonics—Assessments and Reassessments

Charles F. Kahle
Charles F. Kahle
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American Association of Petroleum Geologists
Volume
23
ISBN electronic:
9781629812182
Publication date:
January 01, 1974

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