T210 Earthquakes, Faults, and Fault Systems in the Pacific Northwest

Tuesday, 24 October 2017
8:00 AM - 12:00 PM
Chelan 4

FINDING FAULTS ALONG HOOD CANAL: FIELD-BASED INSIGHTS FROM FIVE YEARS OF GEOLOGIC MAPPING

Paper number: T210-9
Program: Technical Sessions
Time: 10:00 AM – 10:15 AM

Authors

Abstract

Five years of 1:24,000-scale geologic mapping along Hood Canal provides insight into Quaternary deformation related to the Seattle fault zone, Dabob Bay fault zone, Saddle Mountain deformation zone, and the Hood Canal fault.

The Seattle fault: Evidence for the extension of the Seattle Fault west of Green and Gold mountains includes exposures of dissimilar deposits juxtaposed along the projected fault zone. There, older glacial and nonglacial deposits are exposed south of the fault, whereas relatively young Whidbey Formation is exposed just north of the fault. Near the fault, Whidbey Formation deposits are tightly folded— deformation is likely tectonic because the formation appears largely undeformed away from the fault.

West of Hood Canal, several east-west trending, subvertical strike-slip faults represent a change in character of the Seattle Fault. This orientation and style of faulting differs from that observed to the east, and suggests complex and enigmatic fault mechanics as the fault nears the Olympic Mountains.

Alluvial terraces within drainages on the western Kitsap Peninsula may record co-seismic sedimentation, which preserved organic material that appears to increase in age with elevation.

Dabob Bay fault zone: This inferred right-lateral fault zone may connect the Seattle Fault to the south with the Bon Jon Pass fault to the north in the area of the Olympic-Wallowa Lineament. On the Toandos Peninsula, the fault deforms deposits as young as Olympia age (MIS 3) at one exposure. Based on the spatial distribution of bedrock exposures and passive seismic data, the fault appears to step over to the north on the Bolton Peninsula making a basin.

Saddle Mountain deformation zone: Between the mapped location of the Saddle Mountain deformation zone and the Hamma Hamma River, tectonically sheared zones in Crescent Formation basalts may be an extension of these faults to the northeast. Approximately three miles northeast of Price Lake, two parallel, linear erosional valleys expose shear zones that contain both right- and left-lateral slickensides.

Hood Canal fault: Small discontinuous faults are observed on the western side of Hood Canal and appear to parallel the inferred Hood Canal fault, yet no evidence confidently supports the existence of this fault zone.

Geological Society of America Abstracts with Programs. Vol. 49, No. 6

doi: 10.1130/abs/2017AM-303441

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