Contemporary Seismicity in and around the Yakima Fold-and-Thrust Belt in Eastern Washington

Gomberg, Joan; Sherrod, Brian L.; Trautman, M.; Burns, Erick R.; Snyder, Diane

doi:10.1785/0120110065

Cited by 14 publications

(7 citation statements)

References 30 publications

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“…The region has distributed earthquake activity that appears to be elevated relative to surrounding regions (Figure ), except to the northwest in the Puget Sound region [ Ludwin et al ., ; Gomberg et al ., ]. Most seismicity is shallow, less than 4 km, but some is as deep as 25–30 km, and swarms are common.…”

Section: Interpretation Of the Velocity Fieldmentioning

confidence: 99%

Active tectonics of northwestern U.S. inferred from GPS‐derived surface velocities

et al. 2013

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[1] Surface velocities derived from GPS observations from 1993 to 2011 at several hundred sites across the deforming northwestern United States are used to further elucidate the region's active tectonics. The new velocities reveal that the clockwise rotations, relative to North America, seen in Oregon and western Washington from earlier GPS observations, continue to the east to include the Snake River Plain of Idaho and south into the Basin and Range of northern Nevada. Regional-scale rotation is attributed to gravitationally driven extension in the Basin and Range and Pacific-North America shear transferred through the Walker Lane belt aided by potentially strong pinning below the Idaho Batholith. The large rotating section comprising eastern Oregon displays very low internal deformation rates despite seismological evidence for a thin crust, warm mantle, organized mantle flow, and elevated topography. The observed disparity between mantle and surface kinematics suggests that either little stress acts between them (low basal shear) or that the crust is strong relative to the mantle. The rotation of the Oregon block impinges on Washington across the Yakima fold-thrust belt where shortening occurs in a closing-fan style. Elastic fault locking at the Cascadia subduction zone is reevaluated using the GPS velocities and recently published uplift rates. The 18 year GPS and 80 year leveling data can both be matched with a common locking model suggesting that the locking has been stable over many decades. The rate of strain accumulation is consistent with hundreds of years between great subduction events.

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Section: Interpretation Of the Velocity Fieldmentioning

confidence: 99%

Active tectonics of northwestern U.S. inferred from GPS‐derived surface velocities

et al. 2013

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“…Neither the geologic nor geodetic estimate can resolve the rate and distribution of Quaternary deformation on individual Yakima folds. However, the geodetic shortening, along with contemporary seismicity [ Blakely et al ., ; Gomberg et al ., ; Wicks et al ., ] and paleoseismic evidence [ Campbell and Bentley , ; Reidel , ; West et al ., ; Blakely et al ., ; Ladinsky , ], collectively suggests continuing tectonic development of the Yakima folds through Quaternary time.…”

Section: Location and Geologic Frameworkmentioning

confidence: 99%

Differential uplift and incision of the Yakima River terraces, central Washington State

et al. 2016

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The fault‐related Yakima folds deform Miocene basalts and younger deposits of the Columbia Plateau in central Washington State. Geodesy implies ~2 mm/yr of NNE directed shortening across the folds, but until now the distribution and rates of Quaternary deformation among individual structures has been unclear. South of Ellensburg, Washington, the Yakima River cuts a ~600 m deep canyon across several Yakima folds, preserving gravel‐mantled strath terraces that record progressive bedrock incision and related rock uplift. Here we integrate cosmogenic isochron burial dating of the strath terrace gravels with lidar analysis and field mapping to quantify rates of Quaternary differential incision and rock uplift across two folds transected by the Yakima River: Manastash and Umtanum Ridge. Isochron burial ages from in situ produced 26Al and 10Be at seven sites across the folds date episodes of strath terrace formation over the past ~2.9 Ma. Average bedrock incision rates across the Manastash (~88 m/Myr) and Umtanum Ridge (~46 m/Myr) anticlines are roughly 4 to 8 times higher than rates in the intervening syncline (~14 m/Myr) and outside the canyon (~10 m/Myr). These contrasting rates demonstrate differential bedrock incision driven by ongoing Quaternary rock uplift across the folds at rates corresponding to ~0.13 and ~0.06 mm/yr shortening across postulated master faults dipping 30 ± 10°S beneath the Manastash and Umtanum Ridge anticlines, respectively. The reported Quaternary shortening across the anticlines accounts for ~10% of the ~2 mm/yr geodetic budget, suggesting that other Yakima structures actively accommodate the remaining contemporary deformation.

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“…In three dimensions the splay faults presumably have arcuate shapes that extend outward from the main strike‐slip fault system within the OWL [e.g., Naylor et al , 1986; Kim et al , 2004]. Seismicity in the YF region does not delineate specific fault zones, so the precise relationship between YF and seismicity remains enigmatic [ Reidel et al , 1989; Gomberg et al , 2012].…”

Section: Depth Of the Faults Forming The Yf And Owlmentioning

confidence: 99%

“…In three dimensions the splay faults presumably have arcuate shapes that extend outward from the main strike-slip fault system within the OWL [e.g., Naylor et al, 1986;Kim et al, 2004]. Seismicity in the YF region does not delineate specific fault zones, so the precise relationship between YF and seismicity remains enigmatic [Reidel et al, 1989;Gomberg et al, 2012]. 6. Alternative Models [28] Previous suggestions for the formation of the YF include a simple fold-and-thrust belt or doubly vergent fold-and-thrust belt formed in response to northsouth contraction, and "wrinkle ridges" analogous to ridges formed by contraction on other planets.…”

Section: Depth Of the Faults Forming The Yf And Owlmentioning

confidence: 99%

Large‐scale splay faults on a strike‐slip fault system: The Yakima Folds, Washington State

Pratt

2012

Geochem Geophys Geosyst

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[1] The Yakima Folds (YF) comprise anticlines above reverse faults cutting flows of the Miocene Columbia River Basalt Group of central Washington State. The YF are bisected by the~1100-km-long Olympic-Wallowa Lineament (OWL), which is an alignment of topographic features including known faults. There is considerable debate about the origin and earthquake potential of both the YF and OWL, which lie near six major dams and a large nuclear waste storage site. Here I show that the trends of the faults forming the YF relative to the OWL match remarkably well the trends of the principal stress directions at the end of a vertical strike-slip fault. This comparison and the termination of some YF against the OWL are consistent with the YF initially forming as splay faults caused by an along-strike decrease in the amount of strike-slip on the OWL. The hypothesis is that the YF faults initially developed as splay faults in the early to mid Miocene under NNW-oriented principal compressive stress, but the anticlines subsequently grew with thrust motion after the principal compressive stress direction rotated to N-S or NNE after the mid-Miocene. A seismic profile across one of the YF anticlines shows folding at about 7 km depth, indicating deformation of sub-basalt strata. The seismic profile and the hypothesized relationship between the YF and the OWL suggest that the structures are connected in the middle or lower crust, and that the faults forming the YF are large-scale splay faults associated with a major strike-slip fault system.Components: 9200 words, 4 figures.

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Contemporary Seismicity in and around the Yakima Fold-and-Thrust Belt in Eastern Washington

Cited by 14 publications

References 30 publications

Active tectonics of northwestern U.S. inferred from GPS‐derived surface velocities

Active tectonics of northwestern U.S. inferred from GPS‐derived surface velocities

Differential uplift and incision of the Yakima River terraces, central Washington State

Large‐scale splay faults on a strike‐slip fault system: The Yakima Folds, Washington State

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