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New aeromagnetic data reveal large strike-slip (?) faults inthe Northern Willamette Valley, Oregon

Geological Society of America Bulletin

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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 (M1) 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 occured on a left-stepping restraining bend along the Mount Angel-Gales Creek fault zone.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
New aeromagnetic data reveal large strike-slip (?) faults inthe Northern Willamette Valley, Oregon
Series title:
Geological Society of America Bulletin
Volume
112
Issue:
8
Year Published:
2000
Language:
English
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Geological Society of America Bulletin
First page:
1225
Last page:
1233
Number of Pages:
9