TY - JOUR
T1 - New aeromagnetic data reveal large strike-slip (?) faults inthe Northern Willamette Valley, Oregon
AU - Blakely, R. J.
AU - Wells, R. E.
AU - Tolan, T. L.
AU - Beeson, M. H.
AU - Trehu, A. M.
AU - Liberty, L. M.
PY - 2000
Y1 - 2000
N2 - 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 (M 1 ) 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.
AB - 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 (M 1 ) 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.
KW - Aeromagnetic surveys
KW - Cascadia subduction zone
KW - Earthquakes
KW - Fault zones
KW - Tectonics
KW - Willamette Valley
UR - http://www.scopus.com/inward/record.url?scp=84879883376&partnerID=8YFLogxK
U2 - 10.1130/0016-7606(2000)112<1225:NADRLS>2.0.CO;2
DO - 10.1130/0016-7606(2000)112<1225:NADRLS>2.0.CO;2
M3 - Article
AN - SCOPUS:84879883376
SN - 0016-7606
VL - 112
SP - 1225
EP - 1233
JO - Bulletin of the Geological Society of America
JF - Bulletin of the Geological Society of America
IS - 8
ER -