The Yellowstone‐Snake River Plain Seismic Profiling Experiment: Crustal structure of the Eastern Snake River Plain

Braile, L. W.; Smith, Robert B.; Ansorge, Jörg; Baker, Matthew R.; Sparlin, Mark A.; Prodehl, C.; Schilly, M. M.; Healy, J. H.; Mueller, St.; Olsen, Kenneth H.

doi:10.1029/jb087ib04p02597

Cited by 83 publications

(23 citation statements)

References 24 publications

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“…The estimated thickness of the elastic plate (38 ± 8 km) is approximately equal to the local crustal thickness. Seismological studies suggest that the crustal thickness is ∼42 km in the eastern Snake River Plain, ∼100 km southwest of the Hebgen Lake region [ Braile et al , 1982] and that it shallows to ∼37 km in the surrounding mountain area [ Peng and Humphreys , 1998]. This concordance suggests that the elastic plate and the viscoelastic half‐space of the VE‐1 model are identified as the crust and the upper mantle, respectively.…”

Section: Resultsmentioning

confidence: 95%

Rheology of the lithosphere inferred from postseismic uplift following the 1959 Hebgen Lake earthquake

Nishimura

Thatcher

2003

J. Geophys. Res.

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[1] We have modeled the broad postseismic uplift measured by geodetic leveling in the epicentral area of the 1959 M w = 7.3 Hebgen Lake, Montana earthquake, a normal faulting event in the northern Basin and Range province. To fit the observed uplift we calculate synthetic postseismic deformation using the relaxation response of a gravitational viscoelastic Earth to the earthquake. For a model with an elastic plate overlying a viscoelastic half-space, we find that the elastic thickness is 38 ± 8 km, which isclose to the local crustal thickness. The half-space viscosity is estimated at 4 Â 10 18±0.5 Pa s. The leveling data do not require a viscous lower crust but permit a lower bound viscosity of 10 20 Pa s. The observed broad uplift cannot be explained by physically plausible afterslip on and below the coseismic fault. However, local deformation across the coseismic surface rupture requires shallow afterslip reaching the surface. The postseismic deformation induced by the estimated viscoelastic structure decays exponentially with a time constant of $15 years. Because of coupling between the elastic layer and the viscoelastic substrate, this relaxation time is significantly longer than the 2 year Maxwell relaxation time of the viscous half-space itself. Our result suggests the importance of postseismic relaxation in interpreting high-precision global positioning system velocities. For example, our model results suggest that postseismic transient velocities from both the 1959 Hebgen Lake and the 1983 M w = 6.9 Borah Peak earthquakes are currently as large as 1-2 mm/yr.

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Section: Resultsmentioning

confidence: 95%

Rheology of the lithosphere inferred from postseismic uplift following the 1959 Hebgen Lake earthquake

Nishimura

Thatcher

2003

J. Geophys. Res.

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“…The lowermost crust along Line 1 contains a thin 7.xx layer under the southeastern portion of the line suggesting that underplating accompanied the volcanic activity in the Owyhee Plateau (Figure ). In spite of many geological similarities, the crustal structure resolved in this study is very different from the crustal structure of the ESRP [e.g., Braile et al ., ; Sparlin et al ., ]. This fact is evident in the gravity map (Figure ) that shows a large linear gravity high associated with the Snake River Plain and no coherent gravity high following the NW‐SE HLP trend (Figures and ).…”

Section: Discussionmentioning

confidence: 99%

A controlled‐source seismic and gravity study of the High Lava Plains (HLP) of Eastern Oregon

Cox

Keller

Harder

2013

Geochem Geophys Geosyst

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[1] This study employs data collected during the High Lava Plains (HLP) controlled-source seismic experiment conducted in September 2008. In this experiment, 2612 short-period seismic recorders and 120 3-component recorders were deployed across eastern Oregon and adjacent parts of Nevada and Idaho to record 15 seismic sources. Seismic and gravity data were integrated to create 2-D crustal scale P-wave velocity and density models for the 400 km long NW-SE and N-S profiles to provide a better understanding of the crustal and upper mantle structure and ultimately the magmatic and tectonic evolution of the region. These models are the first high-resolution images beneath the path of migratory, bi-modal volcanism that dotted the High Lava Plains beginning at 16 Ma. Our models show that the crustal structure across the HLP region is similar to that of the northern Basin and Range which has experienced extension since 35 Ma but with moderate magmatic modification of the crust. A thick layer (5-7 km) of sediments and volcanics extends over most of the area and is thickest in the Harney Basin area. We interpret denser/faster material in the lower to middle crust under the southern Harney Basin area to be mafic intraplating. We have also identified a region of denser/faster material in the upper crust in the vicinity of Oregon-Idaho border. The crust thickens from 34 to 37 km, and the lower crust increases in density (2.8-2.85 g/cm 3 ), from west to east across eastern Oregon in close proximity to the interpreted position of the 0.706 Sr isotope line, suggesting a decrease in extension. In the lowermost crust below the southeastern HLP, there is relatively high velocity (7.2-7.4 km/s) and density (2.95 g/ cm 3 ) that suggests the presence of underplating. The HLP region has undergone moderate extension, and the average crustal velocity is somewhat higher than in the adjacent Basin and Range, suggesting some magmatic modification in the lower crust, but not as much as might be expected given the voluminous surface volcanism.

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“…This province is characterized by voluminous early to mid-Tertiary silicic volcanism, normal faulting, high heat flow, low P,, velocities (7.4-7.9 km/s), and thin crust (20-30 km). Seismic surveys [e.g., Braile et al, 1982] indicate an unusual crustal structure (a thin (8-10 km) upper layer underlain by anomalously thick (up to ---30 km) lower crust) that seemingly precludes significant crustal attenuation, unlike the case for typical continental rifts. The eastern half of the SRP and its southwestward extension contain a series of calderas that decrease in age to the northeast.…”

Section: Geologic Settingmentioning

confidence: 99%

Isotopic variations in continental basaltic lavas as indicators of mantle heterogeneity: Examples from the western U.S. Cordillera

Lum¹,

Leeman²,

Foland³

et al. 1989

J. Geophys. Res.

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The nature and significance of Sr and Nd isotopic variations in late Cenozoic basalts from the western U.S. Cordillera region are examined in the light of major and trace element characteristics of two end member suites from the Lunar Crater (LCVF) and the Snake River Plain (SRP) volcanic fields. Like many other late Cenozoic Basin and Range basalts, those from LCVF are mildly alkalic and have isotopic (Sr, Nd) compositions similar to those of many oceanic island basalts (OIB). SRP basaltic lavas are tholeiitic and have lower incompatible trace element contents and systematically higher 87Sr/86Sr and lower 143Nd/144Nd isotopic ratios compared to LCVF lavas. These two suites are unlikely to have any genetic relation to one another but are representative of the range of isotopic variations observed in the region. We specifically address the question of how such isotopic diversity arises. For example, (1) could all of these magmas be generated from isotopically similar source materials and then be variably contaminated by crustal material during ascent, or (2) do their isotopic compositions reflect actual heterogeneities within the underlying mantle? To answer these questions, processes of contamination were evaluated using combined major and trace element and isotopic data, and it is concluded that isotopic distinctions between SRP and LCVF basalts cannot be entirely due to contamination. Indeed, they seem to reflect compositional differences in the respective magma source regions. We interpret the LCVF magmas to represent partial melts of dominantly “asthenospheric” mantle (i.e., similar to OIB sources) which, in the case of the Basin and Range province, has presumably upwelled beneath a region of major lithospheric extension. In contrast, isotopically distinct SRP basalts could be derived from ancient or enriched mantle that most likely resides in the continental lithosphere. Thus lateral and/or vertical heterogeneities inferred to exist in the mantle beneath the western United States can be reconciled with geodynamic models that are consistent with regional tectonic evolution.

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The Yellowstone‐Snake River Plain Seismic Profiling Experiment: Crustal structure of the Eastern Snake River Plain

Cited by 83 publications

References 24 publications

Rheology of the lithosphere inferred from postseismic uplift following the 1959 Hebgen Lake earthquake

Rheology of the lithosphere inferred from postseismic uplift following the 1959 Hebgen Lake earthquake

A controlled‐source seismic and gravity study of the High Lava Plains (HLP) of Eastern Oregon

Isotopic variations in continental basaltic lavas as indicators of mantle heterogeneity: Examples from the western U.S. Cordillera

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