New aeromagnetic data reveal large strike-slip (?) faults in the northern Willamette Valley, Oregon

Abstract

Research Article| August 01, 2000 New aeromagnetic data reveal large strike-slip (?) faults in the northern Willamette Valley, Oregon Richard J. Blakely; Richard J. Blakely 1U.S. Geological Survey, 345 Middlefield Road, M.S. 989, Menlo Park, California 94025, USA Search for other works by this author on: GSW Google Scholar Ray E. Wells; Ray E. Wells 1U.S. Geological Survey, 345 Middlefield Road, M.S. 989, Menlo Park, California 94025, USA Search for other works by this author on: GSW Google Scholar Terry L. Tolan; Terry L. Tolan 2Department of Geology, Portland State University, Portland, Oregon 97207, USA Search for other works by this author on: GSW Google Scholar Marvin H. Beeson; Marvin H. Beeson 2Department of Geology, Portland State University, Portland, Oregon 97207, USA Search for other works by this author on: GSW Google Scholar Anne M. Trehu; Anne M. Trehu 3College of Oceanic and Atmospheric Sciences, Oregon State University, Corvallis, Oregon 97331, USA Search for other works by this author on: GSW Google Scholar Lee M. Liberty Lee M. Liberty 4Center for Geophysical Investigation of the Shallow Subsurface, Boise State University, Boise, Idaho 83725, USA Search for other works by this author on: GSW Google Scholar GSA Bulletin (2000) 112 (8): 1225–1233. https://doi.org/10.1130/0016-7606(2000)112<1225:NADRLS>2.0.CO;2 Article history received: 03 Feb 1999 rev-recd: 17 Sep 1999 accepted: 11 Oct 1999 first online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Richard J. Blakely, Ray E. Wells, Terry L. Tolan, Marvin H. Beeson, Anne M. Trehu, Lee M. Liberty; New aeromagnetic data reveal large strike-slip (?) faults in the northern Willamette Valley, Oregon. GSA Bulletin 2000;; 112 (8): 1225–1233. doi: https://doi.org/10.1130/0016-7606(2000)112<1225:NADRLS>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract High-resolution aeromagnetic data from the northern Willamette Valley, Oregon, reveal large, northwest-striking faults buried beneath Quaternary basin sediments. Several faults known from geologic mapping are well defined by the data and appear to extend far beyond their mapped surface traces. The Mount Angel fault, the likely source of the Richter magnitude (ML) 5.6 earthquake in 1993, is at least 55 km long and may be connected in the subsurface with the Gales Creek fault 25 km farther northwest. Northeast of the Mount Angel fault, a 60-km-long, northwest-striking anomaly may represent a previously unrecognized dextral-slip fault beneath the towns of Canby and Molalla. Vertical offsets along the Mount Angel fault increase with depth, indicating a long history of movement for the fault. Dominantly northwest-trending, relatively straight faults, consistent stepover geometries, offset magnetic anomalies, and earthquake focal mechanisms suggest that these faults collectively accommodate significant dextral slip. The 1993 earthquake may have occurred on a left-stepping restraining bend along the Mount Angel–Gales Creek fault zone. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.