ML20151P833

Strain Accumulation in Western Washington & Southwestern British Columbia, Presented at 880506-08 Meeting in Seattle,Wa

ML20151P833
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Site:	Trojan File:Portland General Electric icon.png
Issue date:	05/06/1988
From:	Lisowski M, Prescott W, Savage J INTERIOR, DEPT. OF, GEOLOGICAL SURVEY
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References
NUDOCS 8808100202
Download: ML20151P833 (1)

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1 Strain Accumulation in Western Washington and Southwestern British Columbia M. Lisowski. J.C. Savage, W.H. Prescott (All at USGS, Menlo Park, CA 94025), and H.

Dragert (Pacific Geoscience Centre, P.O. Box 6000, Sidney, B.C. VSL 4B2)

Analysis of repeated measurements of geodetic networks in western Washington and southwestern British Columbia indicates active horizontal deformation along the Casca-dia subduction zone, with maximum contraction approximately parallel to the N71*E convergence direct.on of the Juan de Fuca plate given by the NUVEL-1 global plate model. Across the Strait of Juan de Fuca the average shear strain rate (dilatation not determined) is 0.19 a 0.06 rad /yr between 1$92 and 19S6 and 0.14 0.06 rad /yr be-tween 1942 and 19$6 with maximum contraction in a N70'E610*directio;.. Across the Puget Lowlands near Seattle the average principal strain rates (extension reckoned posi-tive) are 0.03 = 0.02 strain /yr and -0.03 0.01 strain /yr with maximum contraction in a N69'Ei7' direction. In the Olympic Mountains the average principal strain rates are 0.07 a 0.06 strain /yr and -0.09 0.06 pstrain/yr with maximum contraction in a N5S'Ea9' direction. The orientation of the principal strains and the average rate of shear strain accumulation (i = is - 52 ) in the networks can be roughly reproduced by a simple dislocation model of the Cascadia subduction zone that has the shallow portion of the plate interface locked to a position near the Washington coastline.

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