scholarly journals The spatial and temporal evolution of the Portland and Tualatin forearc basins, Oregon, USA

Geosphere ◽  
2021 ◽  
Author(s):  
Darby P. Scanlon ◽  
John Bershaw ◽  
Ray E. Wells ◽  
Ashley R. Streig
Keyword(s):  
Metropolitan Area ◽  
Late Eocene ◽  
Normal Faults ◽  
Coast Range ◽  
Accommodation Space ◽  
Columbia River Basalt ◽  
Tectonic Framework ◽  
Portland Metropolitan Area ◽  
Forearc Basins ◽  
Columbia River Basalt Group

The Portland and Tualatin basins are part of the Salish-Puget-Willamette Lowland, a 900-km-long, forearc depression lying between the volcanic arc and the Coast Ranges of the Cascadia convergent margin. Such inland seaways are characteristic of warm, young slab subduction. We analyzed the basins to better understand their evolution and relation to Coast Range history and to provide an improved tectonic framework for the Portland metropolitan area. We model three key horizons in the basins: (1) the top of the Columbia River Basalt Group (CRBG), (2) the bottom of the CRBG, and (3) the top of Eocene basement. Isochore maps constrain basin depocenters during (1) Pleistocene to mid-Miocene time (0–15 Ma), (2) CRBG (15.5–16.5 Ma), and (3) early Miocene to late Eocene (ca. 17–35 Ma) time. Results show that the Portland and Tualatin basins have distinct mid-Miocene to Quaternary depocenters but were one continuous basin from the Eocene until mid-Miocene time. A NW-striking gravity low coincident with the NW-striking, fault-bounded Portland Hills anticline is interpreted as an older graben coincident with observed thickening of CRBG flows and underlying sedimentary rocks. Neogene transpression in the forearc structurally inverted the Sylvan-Oatfield and Portland Hills normal faults as high-angle dextral-reverse faults, separating the Portland and Tualatin basins. An eastward shift of the forearc basin depocenter and ten-fold decrease in accommodation space provide temporal constraints on the emergence of the Coast Range to the west. Clockwise rotation and northward transport of the forearc is deforming the basins and producing local earthquakes beneath the metropolitan area.

scholarly journals Multiple Holocene Earthquakes on the Gales Creek Fault, Northwest Oregon Fore-Arc

2020 ◽  
Author(s):  
Alison E. Horst ◽  
Ashley R. Streig ◽  
Ray E. Wells ◽  
John Bershaw
Keyword(s):  
Seismic Hazard ◽  
Metropolitan Area ◽  
Timing Constraints ◽  
Willamette Valley ◽  
Accommodation Space ◽  
Structural Relationships ◽  
Buried Soil ◽  
Portland Metropolitan Area ◽  
Holocene Activity ◽  
The U.S

ABSTRACT Several potentially hazardous northwest-striking faults in and around the Portland basin, within the fore-arc of Cascadia, are classified as Quaternary active by the U.S. Geological Survey, but little is known about their Holocene activity. We present new earthquake-timing constraints on the Gales Creek fault (GCF), a 73 km long, northwest-trending fault with youthful geomorphic expression located about 35 km west of Portland. We excavated a paleoseismic trench across the GCF in the populated northern Willamette Valley and document three surface-rupturing earthquakes from stratigraphic and structural relationships. Radiocarbon samples from offset stratigraphy constrain these earthquakes to have occurred ∼1000, ∼4200, and ∼8800 calibrated years before the present. The penultimate earthquake back-tilted a buried soil into the hillslope creating accommodation space that was infilled by a colluvial deposit. The most recent earthquake faulted and formed a fissure within the penultimate colluvial deposit. Our results suggest that the GCF has a recurrence interval of ∼4000 yr, and if the full 73 km length were to rupture, it would result in an Mw 7.1–7.4 earthquake, providing a significant seismic hazard for the greater Portland metropolitan area.

GEOLOGIC MAP OF THE GREATER PORTLAND METROPOLITAN AREA, OREGON AND WASHINGTON

2017 ◽  
Author(s):  
Ray E. Wells ◽  
◽  
Ralph Haugerud ◽  
Russell C. Evarts ◽  
Alan Niem ◽  
...  
Keyword(s):  
Metropolitan Area ◽  
Geologic Map ◽  
Portland Metropolitan Area

Temporally variable crustal contributions to primitive mantle-derived Columbia River Basalt Group magmas

2021 ◽  
pp. 120197
Author(s):  
James M.D. Day ◽  
Kimberley L.R. Nutt ◽  
Brendon Mendenhall ◽  
Bradley J. Peters
Keyword(s):  
Columbia River ◽  
Primitive Mantle ◽  
Columbia River Basalt ◽  
Columbia River Basalt Group

scholarly journals Seismic characteristics of polygonal fault systems in the Great South Basin, New Zealand

2020 ◽  
Vol 12 (1) ◽  
pp. 851-865
Author(s):  
Sukonmeth Jitmahantakul ◽  
Piyaphong Chenrai ◽  
Pitsanupong Kanjanapayont ◽  
Waruntorn Kanitpanyacharoen
Keyword(s):  
Three Dimensional ◽  
Late Eocene ◽  
Seismic Survey ◽  
Fault System ◽  
Normal Faults ◽  
Tier 2 ◽  
South Basin ◽  
Fault Systems ◽  
Tier 1 ◽  
Polygonal Fault

AbstractA well-developed multi-tier polygonal fault system is located in the Great South Basin offshore New Zealand’s South Island. The system has been characterised using a high-quality three-dimensional seismic survey tied to available exploration boreholes using regional two-dimensional seismic data. In this study area, two polygonal fault intervals are identified and analysed, Tier 1 and Tier 2. Tier 1 coincides with the Tucker Cove Formation (Late Eocene) with small polygonal faults. Tier 2 is restricted to the Paleocene-to-Late Eocene interval with a great number of large faults. In map view, polygonal fault cells are outlined by a series of conjugate pairs of normal faults. The polygonal faults are demonstrated to be controlled by depositional facies, specifically offshore bathyal deposits characterised by fine-grained clays, marls and muds. Fault throw analysis is used to understand the propagation history of the polygonal faults in this area. Tier 1 and Tier 2 initiate at about Late Eocene and Early Eocene, respectively, based on their maximum fault throws. A set of three-dimensional fault throw images within Tier 2 shows that maximum fault throws of the inner polygonal fault cell occurs at the same age, while the outer polygonal fault cell exhibits maximum fault throws at shallower levels of different ages. The polygonal fault systems are believed to be related to the dewatering of sedimentary formation during the diagenesis process. Interpretation of the polygonal fault in this area is useful in assessing the migration pathway and seal ability of the Eocene mudstone sequence in the Great South Basin.

Imnaha Basalt, Columbia River Basalt Group

1984 ◽  
Vol 25 (2) ◽  
pp. 473-500 ◽  
Author(s):  
P. R. HOOPER ◽  
W. D. KLECK ◽  
C. R. KNOWLES ◽  
S. P. REIDEL ◽  
R. L. THIESSEN
Keyword(s):  
Columbia River ◽  
Columbia River Basalt ◽  
Columbia River Basalt Group

scholarly journals Supplemental Material: The Chief Joseph dike swarm of the Columbia River flood basalts, and the legacy data set of William H. Taubeneck

2020 ◽  
Author(s):  
M.C. Morriss ◽  
et al.
Keyword(s):  
Pacific Northwest ◽  
Large Scale ◽  
Columbia River ◽  
Flood Basalts ◽  
Data Set ◽  
Dike Swarm ◽  
Columbia River Basalt ◽  
Legacy Data ◽  
Columbia River Basalt Group ◽  
Columbia River Flood Basalts

Supplemental Plates. Plate S1: Large-scale map of entire extent of Chief Joseph dike swarm. Also incorporates dikes of Ice Harbor, Steens, and Monument swarms. Plate S1 represents the most complete record of dikes related to Columbia River Basalt Group (CRBG) event known. Plate S2: Simplified map of CRBG-related dikes across the inland Pacific Northwest. Dikes are colored by their orientation and dike line density is also shown. Plate S3: Simplified map of CRBG-related dikes across the inland Pacific Northwest.<br>

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