Identifying block structure in the Pacific Northwest, USA

Journal of Geophysical Research
By:  and 



We have identified block structure in the Pacific Northwest (west of 116°W between 38°N and 49°N) by clustering GPS stations so that the same Euler vector approximates the velocity of each station in a cluster. Given the total number k of clusters desired, the clustering procedure finds the best assignment of stations to clusters. Clustering is calculated for k= 2 to 14. In geographic space, cluster boundaries that remain relatively stable as k is increased are tentatively identified as block boundaries. That identification is reinforced if the cluster boundary coincides with a geologic feature. Boundaries identified in northern California and Nevada are the Central Nevada Seismic Belt, the west side of the Northern Walker Lane Belt, and the Bartlett Springs Fault. Three blocks cover all of Oregon and Washington. The principal block boundary there extends west-northwest along the Brothers Fault Zone, then north and northwest along the eastern boundary of Siletzia, the accreted oceanic basement of the forearc. East of this boundary is the Intermountain block, its eastern boundary undefined. A cluster boundary at Cape Blanco subdivides the forearc along the faulted southern margin of Siletzia. South of Cape Blanco the Klamath Mountains-Basin and Range block extends east to the Central Nevada Seismic Belt and south to the Sierra Nevada-Great Valley block. The Siletzia block north of Cape Blanco coincides almost exactly with the accreted Siletz terrane. The cluster boundary in the eastern Olympic Peninsula may mark permanent shortening of Siletzia against the Intermountain block.

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Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Identifying block structure in the Pacific Northwest, USA
Series title Journal of Geophysical Research
DOI 10.1002/2015JB012277
Volume 120
Issue 11
Year Published 2015
Language English
Publisher American Geophysical Union
Contributing office(s) Earthquake Science Center
Description 12 p.
First page 7905
Last page 7916
Country United States
State California, Idaho, Nevada, Oregon, Washington
Online Only (Y/N) N
Additional Online Files (Y/N) N
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