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.

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.

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

A Humanistic Approach to Outreach: Amnesty for Illegal Immigrants

1991 ◽  
Vol 13 (2) ◽  
pp. 14-16
Author(s):  
David Rymph ◽  
Linda Little
Keyword(s):  
United States ◽  
El Salvador ◽  
Political Violence ◽  
Metropolitan Area ◽  
The United States ◽  
Illegal Immigrants ◽  
The Political ◽  
The Past ◽  
Humanistic Approach ◽  
The U.S

Washington, D.C., like many major cities in the U.S., has experienced a large influx of illegal immigrants in the past decade. Hundreds of thousands of Hispanics have entered the United States, many of them fleeing from the political violence in Guatemala and El Salvador. The Washington metropolitan area may have as many as 80,000 refugees from El Salvador alone.

Seismic hazard assessment for Yanbu metropolitan area, western Saudi Arabia

2015 ◽  
Vol 8 (11) ◽  
pp. 9945-9958 ◽  
Author(s):  
S. Almadani ◽  
A. Al-Amri ◽  
M. Fnais ◽  
K. Abdelrahman ◽  
E. Ibrahim ◽  
...  
Keyword(s):  
Saudi Arabia ◽  
Seismic Hazard ◽  
Hazard Assessment ◽  
Metropolitan Area ◽  
Seismic Hazard Assessment

scholarly journals Assessing the Impact of a Distance-Based Spatial Factor on Retention in the U.S. Colleges

2021 ◽  
Vol 11 (9) ◽  
pp. 508
Author(s):  
Serkan Varol ◽  
Serkan Catma
Keyword(s):  
Higher Education ◽  
Student Retention ◽  
Postsecondary Education ◽  
Metropolitan Area ◽  
Retention Rate ◽  
Complex Problem ◽  
Institutional Perspective ◽  
Spatial Factor ◽  
The Impact ◽  
The U.S

Student retention is a wide-reaching issue that causes a concern to postsecondary institutions and policy-makers. This research aimed to examine the impact of a geo-spatial factor—distance to the closest metropolitan area—on student retention from a multi-institutional perspective, through the data collected from the Integrated Postsecondary Education Data System (2017) of the U.S. Department of Education. Using the K-means clustering technique, 329 geographically dispersed higher education institutions with similar characteristics were identified. A spatial lag model was adopted to account for spatial autocorrelation detected within the dataset. A series of hierarchical regression was then conducted to measure how well the spatial variable explained student retention rate after accounting for institutional level attributes. The student retention rate was found to decrease as a university is located away from the closest metropolitan area. This finding has crucial policy and administrative implications if analyzed within the context of rural–urban discrepancies in higher education. Extending the spatial scope of retention analysis is an important step in accurately determining the set of factors that provides a better understanding of this complex problem.

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