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Record Details

Record 37 of 732
Topographic form of the Coast Ranges of the Cascadia Margin in relation ot coastal uplift rates and plate subduction
External Online Source: doi:10.1029/93JB03236
Author and Affiliation:
Kelsey, Harvey M.(Humboldt State University, Arcata, California, United States)
Engebretson, David C.(Western Washington University, Bellingham, Washington, United States)
Mitchell, Clifton E.(University of Oregon, Eugene, Oregon, United States)
Ticknor, Robert L.(Western Washington University, Bellingham, Washington, United States)
Abstract: The Coast Ranges of the Cascadia margin are overriding the subducted Juan de Fuca/Gorda plate. We investigate the extent to which the latitudinal change in attributes related to the subduction process. These attributes include the varibale age of the subducted slab that underlies the Coast Ranges and average vertical crustal velocities of the western margin of the Coast Rnages for two markedly different time periods, the last 45 years and the last 100 kyr. These vertical crustal velocities are computed from the resurveying of highway bech marks and from the present elevation of shore platforms that have been uplifted in the late Quaternary, respectively. Topogarphy of the Coast Ranges is in part a function of the age and bouyancy of the underlying subducted plate. This is evident in the fact that the two highest topographic elements of the Coast Rnages, the Klamath Mountains and the Olympic Mountains, are underlain by youngest subducted oceanic crust. The subducted Blanco Fracture Zone in southernmost Oregon is responsible for an age discontinuity of subducted crust under the Klamath Mountains. The norhtern terminus of hte topographically higher Klamaths is offset to the north relative to the position of the underlying Blanco Fracture Zone, teh offset being in the direction of migration of the farcture zone, as dictated by relative plate motions. Vertical crustal velocities at the coast, derived from becnh mark surveys, are as much as an order of magnitude greater than vertical crustal velocities derived from uplifted shore platforms. This uplift rate discrepancy indicates that strain is accumulating on the plate margin, to be released during the next interplate earthquake. In a latitudinal sense, average Coast Rnage topography is relatively high where bench mark-derived, short-term vertical crustal velocities are highest. Becuase the shore platform vertical crustal velocities reflect longer-term, premanent uplift, we infer that a small percentage of the interseismic strain that accumulates as rapid short-term uplift is not recovered by subduction earthquakes but rather contributes to rock uplift of the Coast Ranges. The conjecture that permanent rock uplift is related to interseismic uplift is consistent with the observation that those segments of the subduction zone subject to greater interseismic uplift rates are at approximately the same latitudes as those segments of the Coast Ranges that have higher magnitudes of rock uplift over the long term.
Publication Date: Jun 10, 1994
Document ID:
19950057697
(Acquired Dec 28, 1995)
Accession Number: 95A89296
Subject Category: GEOPHYSICS
Document Type: Journal Article
Publication Information: Journal of Geophysical Research (ISSN 0148-0227); 99; B6; p. 12,245-12,255
Publisher Information: United States
Financial Sponsor: NASA; United States
Description: 11p; In English
Distribution Limits: Unclassified; Publicly available; Unlimited
Rights: Copyright
NASA Terms: COASTAL RANGES (CA); GEOLOGICAL FAULTS; PLATES (TECTONICS); SUBDUCTION (GEOLOGY); TOPOGRAPHY; DISCONTINUITY; ELEVATION; GEOCHRONOLOGY; LATITUDE; SEISMOLOGY; STRESS-STRAIN RELATIONSHIPS
Imprint And Other Notes: Journal of Geophysical Research vol. 99, no. B6 p. 12,245-12,255 June 10, 1994
Miscellaneous Notes: Research sponsored by National Science Foundation
Availability Source: Other Sources
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