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Seismic coupling and uncoupling at subduction zones

Ruff, Larry and Kanamori, Hiroo (1983) Seismic coupling and uncoupling at subduction zones. Tectonophysics, 99 (2-4). pp. 99-117. ISSN 0040-1951. doi:10.1016/0040-1951(83)90097-5.

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Seismic coupling has been used as a qualitative measure of the “interaction” between the two plates at subduction zones. Kanamori (1971) introduced seismic coupling after noting that the characteristic size of earthquakes varies systematically for the northern Pacific subduction zones. A quantitative global comparison of many subduction zones reveals a strong correlation of earthquake size with two other variables: age of the subducting lithosphere and convergence rate. The largest earthquakes occur in zones with young lithosphere and fast convergence rates, while zones with old lithosphere and slow rates are relatively aseismic for large earthquakes. Results from a study of the rupture process of three great earthquakes indicate that maximum earthquake size is directly related to the asperity distribution on the fault plane (asperities are strong regions that resist the motion between the two plates). The zones with the largest earthquakes have very large asperities, while the zones with smaller earthquakes have small scattered asperities. This observation can be translated into a simple model of seismic coupling, where the horizontal compressive stress between the two plates is proportional to the ratio of the summed asperity area to the total area of the contact surface. While the variation in asperity size is used to establish a connection between earthquake size and tectonic stress, it also implies that plate age and rate affect the asperity distribution. Plate age and rate can control asperity distribution directly by use of the horizontal compressive stress associated with the “preferred trajectory” (i.e. the vertical and horizontal velocities of subducting slabs are determined by the plate age and convergence velocity). Indirect influences are many, including oceanic plate topography and the amount of subducted sediments. All subduction zones are apparently uncoupled below a depth of about 40 km, and we propose that the basalt to eclogite phase change in the down-going oceanic crust may be largely responsible. This phase change should start at a depth of 30–35 km, and could at least partially uncouple the plates by superplastic deformation throughout the oceanic crust during the phase change.

Item Type:Article
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URLURL TypeDescription DOIArticle
Kanamori, Hiroo0000-0001-8219-9428
Additional Information:© 1983 Elsevier Science Publishers B.V. Revised December 20, 1981; received by Publisher May 19, 1983. We have benefited from discussions and comments, both general and specific, with: D.L. Anderson, H.K. Eissler, B.H. Hager, J. Kelleher, and L.R. Sykes. We thank S. Stein and G. Davies for their reviews. This research was supported by the National Science Foundation (EAR 78-11973) and NASA (Geodynamics, NSG-7610). Contribution nr. 3668, Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125.
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NSFEAR 78-11973
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Caltech Division of Geological and Planetary Sciences3668
Issue or Number:2-4
Record Number:CaltechAUTHORS:20141216-104428055
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Official Citation:Larry Ruff, Hiroo Kanamori, Seismic coupling and uncoupling at subduction zones, Tectonophysics, Volume 99, Issues 2–4, December 1983, Pages 99-117, ISSN 0040-1951, (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:52861
Deposited By: Tony Diaz
Deposited On:16 Dec 2014 18:49
Last Modified:10 Nov 2021 19:44

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