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Current research presented at GSA Corvallis, 2002
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Research Objectives:
The urban corridor lies within the Puget-Willamette lowland, a seismically active forearc basin overlying the Cascadia subduction zone. Major project objectives are twofold: 1) to document and understand the structural setting of the lowland, its basins and faults, and their role in accomodating contemporary deformation and seismicity; and 2) to document and understand the history of surficial processes in the lowland, as recorded in the Quaternary deposits framework and as revealed by high resolution physiographic mapping. Current research is focused in four areas:
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Click on any number or region to learn about research underway in the Pacific Northwest Urban Corridor Geologic Mapping Project study area.
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1) Fault zones and basins in the Urban Corridor
We are documenting the location, arrangement, size, and history of crustal fault zones and intervening basins beneath the Puget Lowland and Northern Willamette Valley. Major faults like the Seattle Fault and Portland Hills Fault lie directly beneath the cities. The tectonic setting and hazard is similar to SW Japan's Inland Sea, where the 1995 Kobe earthquake caused major human and economic losses.
2) Lowland surface processes and history
Lowland sedimentary basin deposits record a history of deformation and changing environments in the Lowlands. Deposits
left during the last glacial maximum cover the Puget Lowland, and related glacial outburst floods inundated the Columbia
and Willamette Valleys. In Puget Sound, the glacial stratigraphy is key to evaluating earthquake shaking intensity,
landslide susceptibility, and groundwater quality and quantity. We are using a combination of geologic mapping and
high resolution laser terrane mapping to document the distribution, thickness, and physical properties of the basin
fills, their depositional facies, and the geomorphic record of the Vashon ice advance and retreat.
3) Geology of lowland aquifers
The lowland basins commonly contain important groundwater resources. In the Willamette basin of NW Oregon, the Miocene Columbia River Basalt is an important strain marker for late Cenozoic deformation and is also a significant ground water aquifer. An interdisciplinary study is underway that combines field mapping, subsurface data, aeromagnetic surveys, paleomagnetic, and geochemical studies to document flow by flow stratigraphy, crustal faulting, and their role in controlling ground water resources.
4) Cascadia framework and geospatial databases
We are integrating crustal structure, seismicity, and deformation into a predictive tectonic model. We are also building uniform geospatial databases that are web-accessible and applicable to urban natural hazard and resource issues.
Research is nearing completion in the following areas:
5) Tyee Basin
The Tyee basin in the southern Oregon Coast Range is large, early Tertiary sedimentary basin with long recognized hydrocarbon
potential. New mapping and resource evaluation in cooperation with the Oregon Department of Geology and Mineral Industries
provides a clear picture of potential targets.
6) North Cascades
The largest historic crustal earthquake in Washington occurred in the North Cascades in 1872. Nearly completed geologic
mapping of over 10,000 square miles of rugged terrain by Rowland Tabor and his colleagues provides new insight into
its crustal structure and tectonics.
7) Geology of the Olympic Peninsula and Olympic National Park
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geologic mapping resources for the peninsula and the Geologic Story
of Olympic National Park are outlined in these pages.
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