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Pacific Northwest Geologic Mapping and Urban Hazards

Richard J. Blakely


U.S. Geological Survey
Western Region Earth Surface Processes Team
345 Middlefield Road, MS 989
Menlo Park, CA

Telephone- (650) 329-5316
Fax- (650) 329-5133


My research interests focus on the application of gravity and magnetic techniques to geologic and tectonic problems throughout the Western U.S. The volcanic terrane that underlies much of the Puget Sound-Willamette Valley urban corridor is well suited for these techniques. Young deposits, water, and vegetation conceal hazardous faults in this region, but the same faults often offset underlying volcanic bedrock. Geophysical techniques thus can "see" through the concealing cover to facilitate mapping and characterizing of these structures.


My recent work in Cascadia has been at various geophysical fronts. Over the past decade, the USGS has systematically acquired high-resolution aeromagnetic data throughout much of the Oregon and Washington forearc, and these data have proven useful in mapping and characterizing known and undiscovered faults. In Seattle, for example, high-resolution aeromagnetic data serve as a proxy for subsurface geologic maps over the headwall of the Seattle fault zone, known to be capable of a M7 earthquake. Using geologic mapping and high-resolution seismic reflection data, we were able to map various strands of the fault zone with high spatial resolution. Similarly, much of the Portland area is underlain by Columbia River basalt, and faults that offset this volcanic unit produce magnetic anomalies that permit mapping the faults over long distances. Gravity anomalies, on the other hand, are particularly helpful in estimating the three-dimensional attributes of sediment-filled basins, useful information in predicting ground motion during future earthquakes.


This site is maintained by the Pacific Northwest Urban Corridor Geologic Mapping Project, part of the Geology, Minerals, Energy and Geophysics Science Center

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