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The relationship of source parameters of ridge-crest and transform earthquakes to the thermal structure of oceanic lithosphere

1979; Elsevier BV; Volume: 55; Issue: 1-2 Linguagem: Inglês

10.1016/0040-1951(79)90337-8

1879-3266

Sean C. Solomon, Norman C. Burr,

Geological and Geochemical Analysis

The source parameters of large earthquakes on ridge crests and transform faults are closely related to the thermal and mechanical properties of oceanic lithosphere. Several characteristics of these earthquakes (including magnitude, seismic moment M0, apparent stress η\̄gs and stress drop Δσ) are synthesized according to local plate velocity v and, for transforms, to ridge—ridge offset L and average fault width W estimated by Brune's method. For ridge-crest (normal faulting) events: (1) the maximum M0 decreases with v; (2) this decrease may be attributed to a particular isotherm limiting the depth of seismic failure if the largest crestal earthquakes are located 10–20 km off-axis; a constancy of the product of Δσ and fault length for these events is implied; (3) η\̄gs shows no systematic variation with v. For transform events: (1) the maximum M0 decreases with v; (2) the maximum M0 appears to increase with the maximum age contrast across the transform; (3) η\̄gs does not clearly depend on either v or L; (4) the maximum estimated W(v) decreases with v; (5) for fixed v, W(L) increases with L; (6) the largest earthquakes on long transforms occur near the transform center; (7) an inversion of slip rate and magnitude data for 60 transforms supports the hypothesis that seismic failure occurs only at temperatures below a fixed value, and gives a nominal value of 100°–150° C to this limiting isotherm. Neither stress drops nor apparent stresses are resolvably different for ridge crest and transform fault earthquakes.