Tectonic implications of a high-resolution aeromagnetic survey of the Portland basin, Oregon and Washington

Conference · Thu Apr 01 04:00:00 EST 1993 · Geological Society of America, Abstracts with Programs; (United States)

OSTI ID:5422799

Blakeley, R J; Wells, R E ^[1]; Beeson, M H ^[2]; Madin, I P ^[3]; Popowski, T ^[4]; Yelin, T S ^[5]

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1. Geological Survey, Menlo Park, CA (United States)
2. Portland State Univ., OR (United States). Geology Dept.
3. Dept. of Geology and Mineral Industries, Portland, OR (United States)
4. GeoEngineers, Redmond, WA (United States)
5. Univ. of Washington, Seattle, WA (United States). Geological Survey

A high-resolution aeromagnetic survey of the Portland-Vancouver metropolitan area was conducted by the US Geological Survey during September, 1992, to determine the location and extent of faults in the area, especially where concealed by vegetation, water, and urban development. Magnetic anomalies in this area are caused principally by three volcanic units: Eocene basaltic basement, presumably representing an accreted oceanic terrane; folded and faulted flows of the Miocene Columbia River Basalt Group; and locally erupted basalt of Plio-Pleistocene age. Linear magnetic anomalies correlate with several known faults in these rocks, while other anomalies may reflect previously unrecognized faults beneath covered areas. The northwest-striking Portland-Hills fault, which lies beneath downtown Portland and which appears to be seismically active at the M [<=] 3 level, is clearly represented in the magnetic data as an anomaly extending southeast to the Clackamas River drainage, a total distance in excess of 50 km. This fault is thought to be the southwestern boundary of a complex pull-apart zone that formed the Portland Basin. The northeastern boundary of the pull-apart zone, the frontal fault northeast of downtown Vancouver, is less apparent in the magnetic data. The overall length of the magnetic anomaly associated with the Portland Hills fault indicates that the fault is at least 50 km in length. If the Portland Hills fault is seismically active along this entire length, seismic risk to the Portland-Vancouver metropolitan area may be greater than previously suspected.

• OSTI ID: 5422799
• Report Number(s): CONF-9305259--
• Conference Information: Journal Name: Geological Society of America, Abstracts with Programs; (United States) Journal Volume: 25:5
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
AERIAL SURVEYING
DATA ANALYSIS
DEVELOPED COUNTRIES
GEOLOGIC FAULTS
GEOLOGIC FRACTURES
GEOLOGIC STRUCTURES
GEOPHYSICAL SURVEYS
MAGNETIC SURVEYS
MAPPING
NATIONAL ORGANIZATIONS
NORTH AMERICA
OREGON
SEDIMENTARY BASINS
SURVEYS
TECTONICS
US DOI
US GS
US ORGANIZATIONS
USA
WASHINGTON