Northwest Oregon fault zones and basinsLarge, northwest-trending faults underlie northwest Oregon and the cities of the greater Portland metropolitan area. These faults (see figure below) include the Portland Hills fault zone beneath Portland, the Gales Creek fault along the east flank of the Coast Range, and the Mount Angel fault zone in the northern Willamette Valley. Scattered earthquakes occur in the region, and the Mount Angel fault was the likely source of the damaging M 5.6 Scott's Mills earthquake in 1993.
The USGS and Oregon Department of Mineral Industries are using geologic mapping, aeromagnetic and ground magnetic surveys, and subsurface studies to locate the major fault systems and determine their slip sense and history. Our knowledge of Tertiary basin strata is guiding groundwater and soil surveys in the northern Willamette Valley.
Strike slip faults in the North Willamette Valley
Portland Hills Fault zone
- Airborne hunt for faults in the Portland-Vancouver area
- Gravity studies in the Tri Met tunnel
- A tunnel Runs Through It - An Inside View of the Tualatin Mountains