Recent Tectonics of the Blanco Ridge, Eastern Blanco Transform Fault Zone
Marine Geophysical Researches 21: 423–450, 2000. 423 © 2000 Kluwer Academic Publishers. Printed in the Netherlands. Recent tectonics of the Blanco Ridge, eastern blanco transform fault zone Robert P. Dziak1, Christopher G. Fox2, Robert W. Embley2, John L. Nabelek3, Jochen Braunmiller3 & Randolph A. Koski4 1Cooperative Institute for Marine Resources Studies, Oregon State University, Hatfield Marine Science Center, Newport, OR 97365, USA 2National Oceanic and Atmospheric Administration, Pacific Marine Environmental Laboratory, Hatfield Marine Science Center, Newport, OR 97365, USA 3College of Ocean and Atmospheric Sciences, Oregon State University, Corvallis, OR 97331, USA 4United States Geological Survey, MS999 345 Middlefield Rd, Menlo Park, CA 94025, USA Received 25 August 1998; accepted 23 May 2000 Key words: Blanco transform fault zone, earthquakes, ridge formation, submersible Abstract Bathymetric, hydro-acoustic, seismic, submersible, and gravity data are used to investigate the active tectonics of the eastern Blanco Transform Fault Zone (BTFZ). The eastern BTFZ is dominated by the ∼150 km long transform-parallel Blanco Ridge (BR) which is a right-lateral strike- slip fault bordered to the east and west by the Gorda and Cascadia Depressions. Acoustic locations, fault-parameter information, and slip vector estimates of 43 earthquakes (Mw ≥ 3:8) that occurred along the eastern BTFZ over the last 5 years reveal that the Blanco Ridge is a high-angle right-lateral strike-slip fault, with a small component of dip-slip motion, where the Juan de Fuca plate is the hanging wall relative to the Pacific plate. Furthermore, the Cascadia and Gorda basins are undergoing normal faulting with extension predominantly oblique to the transform trend.
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