The Puget Sound Aeromagnetic Survey

Previous research shows that many of the earthquake-producing faults in the Puget Lowland region lie concealed beneath water, glacial deposits, and other cover. To illuminate these hidden hazards and further describe the upper part of the earth's crust, the U.S. Geological Survey conducted an airborne magnetic study of the entire Puget Lowland region during the spring and summer of 1997. This aeromagnetic survey was the centerpiece project of the 1997 Puget Sound Urban Hazards Initiative and a cooperative effort between the Urban Hazards Initiative, the National Cooperative Geologic Mapping Program, and the National Earthquake Hazards Reduction Program.

The aeromagnetic survey was conducted by Sander Geophysics Limited, a Canadian company under contract to the U.S. Geological Survey. The survey covers an area of about 12,000 square miles, extending from the Canadian border to south of Olympia and including the cities of Seattle, Tacoma, Everett, Bremerton, Olympia, and Bellingham. The aircraft flew along parallel lines spaced only 0.25 miles apart (a total distance of 43,000 miles) and at an altitude as low as permitted by safety considerations, generally only 800 feet above the ground. Interpretation of these aeromagnetic data, in conjunction with other geologic and geophysical information, will provide critical first-order information needed to assess the earthquake hazards posed by crustal faults in the Puget Lowland region.