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Portland Hills Fault

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Figure 3. Isopach map of the Hillsboro Formation. The Portland Hills fault zone is buried under Missoula Flood deposits at the western margin of the Portland basin (Madin, 1990). Cooper and Bull mountains are Columbia River Basalt Group exposures uplifted during the Pleistocene (after Wilson [1998a])

Figure 3. Isopach map of the Hillsboro Formation. The Portland Hills fault ... Available to Purchase

Published: 01 April 2003
Figure 3. Isopach map of the Hillsboro Formation. The Portland Hills fault zone is buried under Missoula Flood deposits at the western margin of the Portland basin ( Madin, 1990 ). Cooper and Bull mountains are Columbia River Basalt Group exposures uplifted during the Pleistocene (after Wilson
Journal Article

Late Pleistocene and Holocene Tectonics of the Portland Basin, Oregon and Washington, from High-Resolution Seismic Profiling Available to Purchase

Thomas L. Pratt, Jackson Odum, William Stephenson, Robert Williams, Shawn Dadisman, Mark Holmes, Brian Haug
Published: 01 August 2001
Bulletin of the Seismological Society of America (2001) 91 (4): 637–650.
DOI: https://doi.org/10.1785/0119990085
... of marine profiles along 40 km segments of the Columbia and Willamette Rivers and two 1.5-km-long land profiles across the East Bank and Portland Hills fault zones. The marine profiles show a strong reflector as deep as 85 m that correlates with the unconformity at the base of unconsolidated, late...
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View PDF for article title, Late Pleistocene and Holocene Tectonics of the <span class="search-highlight">Portland</span> Basin, Oregon and Washington, from High-Resolution Seismic Profiling
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Journal Article

Seismotectonics of the Portland, Oregon, region Available to Purchase

Thomas S. Yelin, Howard J. Patton
Published: 01 February 1991
Bulletin of the Seismological Society of America (1991) 81 (1): 109–130.
DOI: https://doi.org/10.1785/BSSA0810010109
... margin of the Portland basin. The western margin has been previously recognized as a zone of dextral strike-slip faulting, known as the Portland Hills Fault Zone. The epicenter of the 1962 earthquake is located between the two fault zones and lies approximately 15 km NE of downtown Portland. Our...
View PDF for article title, Seismotectonics of the <span class="search-highlight">Portland</span>, Oregon, region
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Journal Article

Gravity Study through the Tualatin Mountains, Oregon: Understanding Crustal Structure and Earthquake Hazards in the Portland Urban Area Available to Purchase

Richard J. Blakely, Marvin H. Beeson, Kenneth Cruikshank, Ray E. Wells, Ansel Johnson, Ken Walsh
Published: 01 August 2004
Bulletin of the Seismological Society of America (2004) 94 (4): 1402–1409.
DOI: https://doi.org/10.1785/012003045
...Richard J. Blakely; Marvin H. Beeson; Kenneth Cruikshank; Ray E. Wells; Ansel Johnson; Ken Walsh Abstract A high-resolution gravity survey through the Tualatin Mountains (Portland Hills) west of downtown Portland exhibits evidence of faults previously identified from surface geologic...
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View PDF for article title, Gravity Study through the Tualatin Mountains, Oregon: Understanding Crustal Structure and Earthquake Hazards in the <span class="search-highlight">Portland</span> Urban Area
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Journal Article

Tectonic setting of the Portland-Vancouver area, Oregon and Washington: Constraints from low-altitude aeromagnetic data Available to Purchase

Richard J. Blakely, Ray E. Wells, Thomas S. Yelin, Ian P. Madin, Marvin H. Beeson
Journal: GSA Bulletin
Published: 01 September 1995
GSA Bulletin (1995) 107 (9): 1051–1062.
DOI: https://doi.org/10.1130/0016-7606(1995)107<1051:TSOTPV>2.3.CO;2
... southwest of the Tualatin Mountains corresponds closely with another mapped fault and with mixed reverse and strike-slip faulting during a seismic swarm (M ≤ 3) in 1991. We believe these and other anomalies in the aeromagnetic data reflect the Portland Hills fault zone, believed to be the southwestern...
View PDF for article title, Tectonic setting of the <span class="search-highlight">Portland</span>-Vancouver area, Oregon and Washington: Constraints from low-altitude aeromagnetic data
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Probabilistic seismic damage and loss assessment methodology for wastewater network incorporating modeling uncertainty and damage correlations Available to Purchase

Mohammad S Alam, M.EERI, Barbara G Simpson, M.EERI, Andre R Barbosa, M.EERI, Jaehoon Jung, Nishant Parulekar
Published: 01 August 2023
Earthquake Spectra (2023) 39 (3): 1435–1472.
DOI: https://doi.org/10.1177/87552930231180642
... deterministic earthquake scenarios, including a moment magnitude M6.8 Portland Hills Fault and M8.1, M8.4, M8.7, and M9.0 Cascadia Subduction Zone (CSZ) events. As spatial-correlation models of pipeline damage were non-existent in the literature and local information on costs to repair the pipes was limited...
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Book Chapter

Strike-slip faults in the western Columbia River flood basalt province, Oregon and Washington Available to Purchase

Author(s)
James L. Anderson, Terry L. Tolan, Ray E. Wells
Book: The Columbia River Flood Basalt Province
Publisher: Geological Society of America
Published: 01 August 2013
DOI: 10.1130/2013.2497(13)
... flows have been deformed by both folding and strike-slip faulting within the Klickitat Valley basin. Pleistocene-age deposits are known to be cut by both the Luna Butte and Portland Hills faults. Strike-slip earthquake focal mechanisms have also been determined for some faults. ...
Abstract
View PDF for content titled, Strike-slip <span class="search-highlight">faults</span> in the western Columbia River flood basalt province, Oregon and Washington
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The pattern of deformation in the western part of the Columbia River flood basalt province contains two key components: (1) anticlinal uplifts of the Yakima Fold Belt with east-northeast to west-southwest trends, and (2) strike-slip fault zones with dominantly northwest trends. It is the abundance and regional extent of the latter that distinguish this area from other parts of the province. There are many northwest-striking, right-lateral, strike-slip faults in the interval from the Willamette Valley eastward to Umatilla (123°W to 119°W longitude). Some of these faults are only a few kilometers long, whereas others are of regional extent (&gt;100 km). Conjugate northeast-striking, left-lateral, strike-slip faults have also been identified but are far less numerous. Local variations in the stress field within basins have produced sets of subsidiary structures by transtension and transpression. These occur where fault zones change trend with respect to the NNW-SSE–oriented maximum principal compressive stress. Strike-slip faulting was active early in the history of the Yakima Fold Belt uplifts, at least by emplacement of the Columbia River Basalt Group lavas, but after the Yakima Fold Belt uplift, spacing had already been firmly established. It is probable that many of these faults are episodically reactivated basement structures that have repeatedly undergone cycles of emergence, burial by flood basalts, and reemergence. Strike-slip deformation appears to have happened simultaneously within the Yakima Fold Belt uplifts and adjacent synclinal basins. However, the pattern and magnitude of deformation differ significantly in the basins compared to the uplifts. The Yakima Fold Belt uplifts have been segmented and shifted many kilometers by strike-slip faults, while displacements within adjacent basins are orders of magnitude less. Within Yakima Fold Belt uplifts, reversals of vergence sometimes occur wherein the frontal (forelimb) thrusts and fold asymmetry switch from one side of the uplift to the other. These changes are accommodated by cross-trending, right-lateral, strike-slip faults of regional extent. The pattern of strike-slip deformation as mapped within basins in many cases appears to be immature and lacking in interconnection. Eruptive vents in the Simcoe backarc volcanic field and Boring lavas are often aligned along strike-slip faults. Pliocene-age Simcoe lava flows have been deformed by both folding and strike-slip faulting within the Klickitat Valley basin. Pleistocene-age deposits are known to be cut by both the Luna Butte and Portland Hills faults. Strike-slip earthquake focal mechanisms have also been determined for some faults.

Image
Post–Columbia River Basalt Group (CRBG) sedimentary overburden (0–15 Ma) isochore map generated as the difference between digital elevation model (DEM)–derived topography and top CRBG structure map. The northeast extension of the Portland Hills fault is shown southeast of Dutch Canyon. Thickness packages &lt;~1 km diameter are likely an interpolation artifact. Contour interval = 50 m. Location of the Columbia River shown for reference. BV—Beaverton fault; CM—Canby-Molalla fault; SOF—Sylvan-Oatfield fault; PH—Portland Hills fault; EB—East Bank fault; PHBL—Prune Hill/Blue Lake fault; LL—Lacamas Lake fault. Fault acronyms follow Figure 1.

Post–Columbia River Basalt Group (CRBG) sedimentary overburden (0–15 Ma) is... Open Access

Published: 21 April 2021
Figure 8. Post–Columbia River Basalt Group (CRBG) sedimentary overburden (0–15 Ma) isochore map generated as the difference between digital elevation model (DEM)–derived topography and top CRBG structure map. The northeast extension of the Portland Hills fault is shown southeast of Dutch Canyon
Image
▴ Aerial view of downtown Portland, showing the location of the Marriott—site of the 2010 SSA Annual Meeting—and the Portland Hills fault. The trace of the fault is based on an analysis of aeromagnetic data by Rick Blakely, USGS. There appears to be a stepover in the fault in downtown Portland. Where else would a seismologist want to be? Photo courtesy of Northern Light Studio.

▴ Aerial view of downtown Portland, showing the location of the Marriott—si... Available to Purchase

Published: 01 March 2010
Figure 1. ▴ Aerial view of downtown Portland, showing the location of the Marriott—site of the 2010 SSA Annual Meeting—and the Portland Hills fault. The trace of the fault is based on an analysis of aeromagnetic data by Rick Blakely, USGS. There appears to be a stepover in the fault in downtown
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(a) Topography of the Portland area, Oregon. Bold black-and-white dashed line indicates the Portland light-rail tunnel, extending through the Portland Hills. Light black lines indicate mapped faults (Beeson et al., 1989, 1991; Madin, 1990; Yeats et al. 1996) and are dashed where inferred and dotted where concealed. White dotted lines AA′ comprise the aeromagnetic lineation taken from Figure 2b and discussed in text. O, Oatfield fault; S, Sylvania fault; P, Portland Hills fault. (b) Aeromagnetic anomalies of the Portland area. White dotted lines AA′ indicate a northwest-striking lineation discussed in text.

(a) Topography of the Portland area, Oregon. Bold black-and-white dashed li... Available to Purchase

Published: 01 August 2004
Figure 2. (a) Topography of the Portland area, Oregon. Bold black-and-white dashed line indicates the Portland light-rail tunnel, extending through the Portland Hills. Light black lines indicate mapped faults (Beeson et al. , 1989 , 1991 ; Madin, 1990 ; Yeats et al. 1996 ) and are dashed
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(A) Generalized geology of the Portland and Tualatin basins, adapted from Blakely et al. (2000), McPhee et al. (2014), after Walker and MacLeod (1991), and Wells et al. (1994). GC—Gales Creek fault; BV—Beaverton fault; SOF—Sylvan- Oatfield fault; CM—Canby Molalla fault; PH—Portland Hills fault; EB—East Bank fault; PHBL—Prune Hill/Blue Lake fault; LL—Lacamas Lake fault. White squares indicate major cities; small purple square indicates location of Eocene Waverly Heights basalt. Locations of cross sections A–A′ (Fig. 11) and B–B′ (Fig. 13) shown. (B) PB—Portland basin; TB—Tualatin basin; NWB—Northern Willamette Basin.

(A) Generalized geology of the Portland and Tualatin basins, adapted from ... Open Access

Published: 21 April 2021
—Portland Hills fault; EB—East Bank fault; PHBL—Prune Hill/Blue Lake fault; LL—Lacamas Lake fault. White squares indicate major cities; small purple square indicates location of Eocene Waverly Heights basalt. Locations of cross sections A–A′ ( Fig. 11 ) and B–B′ ( Fig. 13 ) shown. (B) PB—Portland basin; TB
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Structural contour map of base Columbia River Basalt Group (CRBG). Regions of higher elevation (cool colors) along the Portland Hills separate the Portland and Tualatin basins. The base CRBG surface is exposed in outcrop around Dutch Canyon and the southwest margin of the Tualatin basin. Contour interval = 100 m. Dashed faults are inferred as in Wells et al. (2020a). Location of the Columbia River shown for reference. BV—Beaverton fault; CM—Canby-Molalla fault; SOF—Sylvan-Oatfield fault; PH—Portland Hills fault; EB—East Bank fault; PHBL—Prune Hill/Blue Lake fault; LL—Lacamas Lake fault. Refer to Figure 4 for surface control data. Diagonal-hatch pattern represents structurally complex southern portion of the Tualatin basin. Cross-hatch pattern denotes exposed pre-CRBG sedimentary rock. Fault acronyms follow Figure 1.

Structural contour map of base Columbia River Basalt Group (CRBG). Regions ... Open Access

Published: 21 April 2021
. Contour interval = 100 m. Dashed faults are inferred as in Wells et al. (2020a) . Location of the Columbia River shown for reference. BV—Beaverton fault; CM—Canby-Molalla fault; SOF—Sylvan-Oatfield fault; PH—Portland Hills fault; EB—East Bank fault; PHBL—Prune Hill/Blue Lake fault; LL—Lacamas Lake fault
Image
Regional geologic map of the Portland-Salem, Oregon area showing crustal seismicity, 1993 Scotts Mills earthquake focal mechanism, and area of Figures 3 and 4 (modified from Blakely et al., 2000). Abbreviations: PHF—Portland Hills fault; BF—Beaverton fault; GCF—Gales Creek fault (red lines); MAF—Mount Angel fault; NF—Newberg fault.

Regional geologic map of the Portland-Salem, Oregon area showing crustal se... Open Access

Published: 06 February 2020
Figure 2. Regional geologic map of the Portland-Salem, Oregon area showing crustal seismicity, 1993 Scotts Mills earthquake focal mechanism, and area of Figures 3 and 4 (modified from Blakely et al., 2000 ). Abbreviations: PHF—Portland Hills fault; BF—Beaverton fault; GCF—Gales Creek fault
Image
Structural contour map of top Columbia River Basalt Group (CRBG). The top CRBG surface is exposed along the Portland Hills anticline, which separates the Portland and Tualatin basins, and along the southwestern margin of the Tualatin basin. Cool colors reflect higher elevations, and warm colors reflect lower elevations. Contour interval = 100 m. Dashed faults are inferred as in Wells et al. (2020a). Location of the Columbia River shown for reference. BV—Beaverton fault; CM—Canby-Molalla fault; SOF—Sylvan-Oatfield fault; PH—Portland Hills fault; EB—East Bank fault; PHBL—Prune Hill/Blue Lake fault; LL—Lacamas Lake fault. Refer to Figure 4 for surface control data. Diagonal-hatch pattern represents structurally complex southern portion of the Tualatin basin. Cross-hatch pattern denotes exposed pre-CRBG sedimentary rock. Fault acronyms follow Figure 1.

Structural contour map of top Columbia River Basalt Group (CRBG). The top C... Open Access

Published: 21 April 2021
, and warm colors reflect lower elevations. Contour interval = 100 m. Dashed faults are inferred as in Wells et al. (2020a) . Location of the Columbia River shown for reference. BV—Beaverton fault; CM—Canby-Molalla fault; SOF—Sylvan-Oatfield fault; PH—Portland Hills fault; EB—East Bank fault; PHBL—Prune
Image
Structural contour map of Eocene basement based primarily on gravity data from McPhee et al. (2014). The elevation is lowest in the Tualatin basin (warm colors) and shallows to the east across the Portland basin (cool colors). There is a localized basement low under the Portland Hills. Eocene basement is exposed in the vicinity of Waverly Heights (Fig. 1; Wells et al., 2020a). Contour interval = 500 m. Dashed faults are inferred as in Wells et al. (2020a). Location of the Columbia River shown for reference. B—Beaverton fault; CM—Canby-Molalla fault; SOF—Sylvan-Oatfield fault; PH— Portland Hills fault; EB—East Bank fault; PHBL—Prune Hill/Blue Lake fault; LL—Lacamas Lake fault. Refer to Figure 4 for surface control data. Diagonal-hatch pattern represents area of uncertainty in gravity-derived basement surface due to density assumptions used in the gravity inversion of McPhee et al. (2014). Fault acronyms follow Figure 1.

Structural contour map of Eocene basement based primarily on gravity data f... Open Access

Published: 21 April 2021
— Portland Hills fault; EB—East Bank fault; PHBL—Prune Hill/Blue Lake fault; LL—Lacamas Lake fault. Refer to Figure 4 for surface control data. Diagonal-hatch pattern represents area of uncertainty in gravity-derived basement surface due to density assumptions used in the gravity inversion of McPhee et al
Image
Mid-Miocene Columbia River Basalt Group (CRBG) (15.5–16.5 Ma) isochore map generated as the difference between the top and base CRBG structure maps. CRBG thickness is similar in both the Portland and Tualatin basins. Thickness packages &lt;~1 km diameter are likely an interpolation artifact. Contour interval = 50 m. Location of the Columbia River shown for reference. BV—Beaverton fault; CM—Canby-Molalla fault; SOF—Sylvan-Oatfield fault; PH—Portland Hills fault; EB—East Bank fault; PHBL—Prune Hill/Blue Lake fault; LL—Lacamas Lake fault. Cross-hatch pattern denotes exposed pre-CRBG sedimentary rock. Fault acronyms follow Figure 1.

Mid-Miocene Columbia River Basalt Group (CRBG) (15.5–16.5 Ma) isochore map ... Open Access

Published: 21 April 2021
artifact. Contour interval = 50 m. Location of the Columbia River shown for reference. BV—Beaverton fault; CM—Canby-Molalla fault; SOF—Sylvan-Oatfield fault; PH—Portland Hills fault; EB—East Bank fault; PHBL—Prune Hill/Blue Lake fault; LL—Lacamas Lake fault. Cross-hatch pattern denotes exposed pre-CRBG
Image
Cross section B–B′ depicting mid- to late Miocene structural inversion of the Portland Hills uplift. Location of cross section shown in Figure 1. Prior to Columbia River Basalt Group (CRBG) deposition, normal faulting on the Sylvan-Oatfield and Portland Hills faults resulted in a graben with uplifted flanks on either side relative to the nascent Portland and Tualatin basins (Panel C). Localized normal faulting continued up until the time of CRBG deposition, resulting in preexisting topography (Panel B). This topography played an important role in controlling CRBG flow emplacement, where basalt flows are thicker in topographic lows and thinner on relative highs (Beeson et al., 1989a). Post-CRBG emplacement, normal faults were reactivated as high-angle reverse faults, resulting in the Portland Hills uplift (Panel A). Structural inversion was likely in response to the steady clockwise rotation and northward migration of the Cascadia forearc (Wells and McCaffrey, 2013). The location of the Barber #1 exploration well constrains the thickness of Paleogene to early Miocene sedimentary rocks under the Portland Hills and is shown as a black solid line. Bedding orientations based on field mapping are depicted as tadpole with dip value (Wells et al., 2020a). Depth to basement is from McPhee et al. (2014), derived from inversion of gravity data. No vertical exaggeration. SL = sea level. Unit colors and patterns are consistent with the legend in Figure 11. Fault acronyms follow Figure 1.

Cross section B–B′ depicting mid- to late Miocene structural inversion of t... Open Access

Published: 21 April 2021
Figure 13. Cross section B–B′ depicting mid- to late Miocene structural inversion of the Portland Hills uplift. Location of cross section shown in Figure 1 . Prior to Columbia River Basalt Group (CRBG) deposition, normal faulting on the Sylvan-Oatfield and Portland Hills faults resulted
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Considered expected IM maps: (a) PGV, (b) landslide-induced PGD, and (c) liquefaction-induced PGD maps for Portland hills fault M6.8 scenario; (d) PGV, (e) landslide-induced PGD, and (f) liquefaction-induced PGD for CSZ M9.0 scenario.

Considered expected IM maps: (a) PGV, (b) landslide-induced PGD, and (c) li... Available to Purchase

Published: 01 August 2023
Figure 6. Considered expected IM maps: (a) PGV, (b) landslide-induced PGD, and (c) liquefaction-induced PGD maps for Portland hills fault M6.8 scenario; (d) PGV, (e) landslide-induced PGD, and (f) liquefaction-induced PGD for CSZ M9.0 scenario.
Journal Article

The spatial and temporal evolution of the Portland and Tualatin forearc basins, Oregon, USA Open Access

Darby P. Scanlon, John Bershaw, Ray E. Wells, Ashley R. Streig
Journal: Geosphere
Published: 21 April 2021
Geosphere (2021) 17 (3): 804–823.
DOI: https://doi.org/10.1130/GES02298.1
...Figure 8. Post–Columbia River Basalt Group (CRBG) sedimentary overburden (0–15 Ma) isochore map generated as the difference between digital elevation model (DEM)–derived topography and top CRBG structure map. The northeast extension of the Portland Hills fault is shown southeast of Dutch Canyon...
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View PDF for article title, The spatial and temporal evolution of the <span class="search-highlight">Portland</span> and Tualatin forearc basins, Oregon, USA
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Early Miocene to late Eocene (ca. 17–35 Ma) isochore map generated as the difference between the base Columbia River Basalt Group (CRBG) and Eocene basement structure maps. Thickness packages &lt;~1 km diameter are likely an interpolation artifact. Contour interval = 500 m. Location of the Columbia River shown for reference. BV—Beaverton fault; CM—Canby-Molalla fault; SOF—Sylvan-Oatfield fault; PH—Portland Hills fault; EB—East Bank fault; PHBL—Prune Hill/Blue Lake fault; LL—Lacamas Lake fault. Cross-hatch pattern denotes exposed pre-CRBG sedimentary rock. Diagonal hatched pattern represents area of uncertainty in gravity-derived basement surface due to density assumptions used in the gravity inversion of McPhee et al. (2014). Fault acronyms follow Figure 1.

Early Miocene to late Eocene (ca. 17–35 Ma) isochore map generated as the d... Open Access

Published: 21 April 2021
of the Columbia River shown for reference. BV—Beaverton fault; CM—Canby-Molalla fault; SOF—Sylvan-Oatfield fault; PH—Portland Hills fault; EB—East Bank fault; PHBL—Prune Hill/Blue Lake fault; LL—Lacamas Lake fault. Cross-hatch pattern denotes exposed pre-CRBG sedimentary rock. Diagonal hatched pattern represents