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Event
AEG Oregon Chapter - October 2023 Meeting
Abstract:
We present a new geologic map of the greater Portland-Vancouver metropolitan area, which occupies the tectonically active lowland between the Coast Range and Cascade volcanic arc. The map synthesizes the geology of 51 7.5 quadrangles, mapped at 1:24,000 scale since 1989 in a cooperative effort among the USGS, Oregon Department of Geology and Mineral Industries, and Washington Geological Survey. The map covers accreted basalt basement of the Coast Range and onlapping Paleogene marine strata; younger rocks of the western Cascade arc; flood basalt of the Miocene Columbia River Basalt Group (CRBG); post-CRBG fill of the Portland, Tualatin, and northern Willamette basins; and the Quaternary Boring volcanic field. Missoula flood deposits and mega-landslide complexes are widespread. We compiled the map from digital sources in an ArcGIS geodatabase (USGS GeMS; Geologic Map Schema) at 1:24,000 scale, including 18 quadrangles of previously unpublished mapping. We resolved gaps and overlaps, fixed mapping errors, and removed tiny polygons to produce a 1:63,360-scale map. The structure of the map area is dominated by the Holocene-active, NW-trending Gales Creek and Quaternary-active Portland Hills dextral-oblique fault systems that accommodate northward motion of the Cascadia fore-arc. The 60-km-long Gales Creek Fault, about 35 km west of Portland, forms the boundary between the Coast Range and the Tualatin basin, which is at least 5 km deep based on companion geophysical surveys. The Portland Hills fault system bounds the NW-striking Tualatin Mountains uplift that separates the Portland Basin from the Tualatin basin. Continued subsidence of the Tualatin and Portland basins is suggested by Columbia River Basalt at 300-400 m below sea level in the basins. This map provides a framework for an improved understanding of a variety of earth science issues; including earthquake hazards from crustal faulting and strong ground shaking, aquifer storage and recovery systems in the CRBG, natural gas storage at the Mist gas field, Columbia River ecosystems, and the terroir of well-known American Viticultural Areas in northwest Oregon.
Speaker Bio:
Ray Wells has 40 years of experience as a USGS field geologist and geophysicist documenting the structure, tectonic evolution, and earthquake hazards of the Cascadia subduction margin of the northwest U.S. More broadly, he applies geologic mapping, GPS, potential fields, and paleomagnetism to examine Cascadia in the context of the plate tectonic evolution of the North American Cordillera, processes of terrane accretion and transport, and the structure of circum-Pacific source regions of great subduction earthquakes. He was the Geological Society of America's Florence Bascom Awardee for Geologic Mapping in 2017, and he received GSA's Geophysics Division George P. Woollard Award for application of geophysics to geologic problems in 2022.
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LocationOld Market Pub (View)
6959 SW Multnomah Blvd.
Portland, OR 97223
United States
Timezone: America/Los_Angeles Online Access Information After you have registered for the event, the online access information for the Zoom meeting will be provided on the order confirmation page and email. Please make sure you copy this link prior to the meeting start time.
Categories
| Kid Friendly: No |
| Dog Friendly: No |
| Non-Smoking: Yes! |
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Contact
| Owner: Oregon AEG |
| On BPT Since: Nov 06, 2016 |
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| AEG Oregon |
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