| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
U.S. GEOLOGICAL SURVEY GEOPHYSICS PROGRAM AK-50 UNIVERSITY OF WASHINGTON, SEATTLE, WASHINGTON 98195
Abstract
Earthquake hypocenters within the subducting Juan de Fuca plate beneath Washington and northern Oregon are interpreted as showing that the direction of plate dip changes from northeast beneath the Puget Sound region to east-southeast beneath southwestern Washington. The shallowest hypocenters within the Juan de Fuca plate are between 30- to 40-km depth, and the distribution of these events strikes north-northeast from near the mouth of the Columbia River to the northern Olympic Mountains. The distribution of hypocenters between 40 to 50 km generally strikes parallel with the shallowest events, but shows a significant broadening beneath the eastern Olympic Mountains and Puget Sound. Events with depths greater than 50 km south of the 1965 Seattle earthquake (mb = 6.5) strike north-northeast, approximately parallel with the shallower distributions; however, north of this event, the distribution of these deeper hypocenters strikes northwest. This change in the distribution of earthquake hypocenters reflects an upward arching of the Juan de Fuca plate plate beneath Puget Sound compared with the depth of the plate beneath southwestern Washington. The T axis calculated for the 1949 South Puget Sound earthquake (MS = 7.1) is oriented to the southeast, and the 20° plunge of the T axis is in good agreement with the plate dip angle determined from the earthquake hypocenters. We conclude that the 1949 earthquake resulted at least in part from down-dip tensional forces within the subducting Juan de Fuca plate. One consequence of the change in the direction of plate dip is that volcanic front in Washington is everywhere perpendicular to the dip of the Juan de Fuca plate.
This article has been cited by other articles:
|
|
 |
|
  I. G. Wong Low Potential for Large Intraslab Earthquakes in the Central Cascadia Subduction Zone Bulletin of the Seismological Society of America, October 1, 2005; 95(5): 1880 - 1902. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
A. F. McNeill, M. G. Bostock, G. C. Rogers, and J. C. Shragge The Effect of Forearc Mantle Serpentinization on Ground Motions from Megathrust and Intraslab Events in the Cascadia Subduction Zone Bulletin of the Seismological Society of America, February 1, 2004; 94(1): 147 - 154. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 W. Hildreth, J. Fierstein, and M. Lanphere Eruptive history and geochronology of the Mount Baker volcanic field, Washington GSA Bulletin, June 1, 2003; 115(6): 729 - 764. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 L. C. McNeill, C. Goldfinger, R. S. Yeats, and L. D. Kulm The effects of upper plate deformation on records of prehistoric Cascadia subduction zone earthquakes Geological Society, London, Special Publications, January 1, 1998; 146(1): 321 - 342. [Abstract] [PDF]
|
|
|
|
|
|
W. D. Stanley, S. Y. Johnson, A. I. Qamar, C. S. Weaver, and J. M. Williams Tectonics and seismicity of the southern Washington Cascade Range Bulletin of the Seismological Society of America, February 1, 1996; 86(1A): 1 - 18. [Abstract] [PDF]
|
|
|
|
|
|
E. RIEKEN and R. L. THIESSEN Three-dimensional model of the Cascadia subduction zone using earthquake hypocenters, western Washington Bulletin of the Seismological Society of America, December 1, 1992; 82(6): 2533 - 2548. [Abstract] [PDF]
|
|
|
|
|
|
B. P. COHEE, P. G. SOMERVILLE, and N. A. ABRAHAMSON Simulated ground motions for hypothesized Mw = 8 subduction earthquakes in Washington and Oregon Bulletin of the Seismological Society of America, February 1, 1991; 81(1): 28 - 56. [Abstract] [PDF]
|
|
|
|
|
|
J. HAVSKOV, S. MALONE, D. MCCLURG, and R. CROSSON Coda Q for the state of Washington Bulletin of the Seismological Society of America, August 1, 1989; 79(4): 1024 - 1038. [Abstract] [PDF]
|
|
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
