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The mechanics of deep-focus faulting

Authors
Journal
Tectonophysics
0040-1951
Publisher
Elsevier
Publication Date
Volume
8
Issue
2
Identifiers
DOI: 10.1016/0040-1951(69)90085-7
Disciplines
  • Earth Science
  • Geography

Abstract

Abstract In the new global tectonics the lithosphere slab, flawed by normal faults formed near the oceanic trenches, is convected down into the mantle to form the seismic zone for deep-focus earthquakes. The dominant stress at depth is the shear stress exerted along the length of the lithosphere slab. This implies that about half of the old faults will be oriented approximately perpendicular to the axis of least compressive stress, forming favourable sites for fluid intrusion. Inasmuch as the outer face of the down-warped lithosphere lithosphere is a region where partial melting is to be expected, melt will be intruded into those faults to form a sequence of lubricated planes available for deep-focus faulting. Faulting is presumably initiated by the “slipping off” (possibly activated by creep) of the contact points between the two faces of the fault. The fault-plane solutions for such shocks should yield P-axes aligned with the dip of the seismic zone and T-axes perpendicular to the zone, although circumstances where the axes are interchanged can arise. The former orientation appears to be the dominant one observed.

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