Western US intermountain seismicity caused by changes in upper mantle flow

Becker, T. W.; Lowry, A. R.; Faccenna, Claudio; Schmandt, Brandon; Borsa, A. A.; Yu, Chunquan

doi:10.1038/nature14867

Cited by 53 publications

(41 citation statements)

References 48 publications

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“…The residual is greatly reduced, with RMS 56 mGal, relative to the 78 mGal RMS of the observed Bouguer gravity and a 112 mGal residual associated with the starting model derived from receiver function cross‐correlation stacking. The residual gravity anomalies are likely dominated by asthenospheric mantle mass variations that our model does not account for (e.g., Becker et al, , ) and sphericity of the Earth, which produces anomalies that differ by up to tens of milligal from the Cartesian calculations used here on the scale of the conterminous U.S. The largest residuals appear to be dominated by a systematic pattern of greater asthenospheric mantle buoyancy in the west, resulting in residual anomalies mostly in the range of −150 to 50 mGal in the western U.S. but in the range −50 to 200 mGal in the east.…”

Section: Resultsmentioning

confidence: 75%

USArray Imaging of Continental Crust in the Conterminous United States

Lowry

2017

Tectonics

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The thickness and bulk composition of continental crust provide important constraints on the evolution and dynamics of continents. Crustal mineralogy and thickness both may influence gravity anomalies, topographic elevation, and lithospheric strength, but prior to the inception of EarthScope's USArray, seismic measurements of crustal thickness and properties useful for inferring lithology are sparse. Here we improve upon a previously published methodology for joint inversion of Bouguer gravity anomalies and seismic receiver functions by using parameter space stacking of cross correlations of modeled synthetic and observed receiver functions instead of standard H‐κ amplitude stacking. The new method is applied to estimation of thickness and bulk seismic velocity ratio, vP/vS, of continental crust in the conterminous United States using USArray and other broadband network data. Crustal thickness variations are reasonably consistent with those found in other studies and show interesting relationships to the history of North American continental formation. Seismic velocity ratios derived in this study are more robust than in other analyses and hint at large‐scale variations in composition of continental crust. To interpret the results, we model the pressure‐/temperature‐dependent thermodynamics of mineral formation for various crustal chemistries, with and without volatile constituents. Our results suggest that hydration lowers bulk crustal vP/vS and density and releases heat in the shallow crust but absorbs heat in the lowermost crust (where plagioclase breaks down to pyroxene and garnet resulting in higher seismic velocity). Hence, vP/vS variations may provide a useful proxy for hydration state in the crust.

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Section: Resultsmentioning

confidence: 75%

USArray Imaging of Continental Crust in the Conterminous United States

Lowry

2017

Tectonics

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“…1d), suggesting that the historically-observed spatial distribution of large earthquakes may be a short-term feature. Vertical stress variations arising from dynamic support of the topography13 are unlikely to explain asymmetric seismic activity over this length scale. Here we present results of cosmogenic sampling of bedrock fault scarps along the southwest flank of the topographic high (Fig.…”

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confidence: 94%

Orogen-scale uplift in the central Italian Apennines drives episodic behaviour of earthquake faults

Cowie

Phillips

Roberts

et al. 2017

Sci Rep

106

130

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Many areas of the Earth’s crust deform by distributed extensional faulting and complex fault interactions are often observed. Geodetic data generally indicate a simpler picture of continuum deformation over decades but relating this behaviour to earthquake occurrence over centuries, given numerous potentially active faults, remains a global problem in hazard assessment. We address this challenge for an array of seismogenic faults in the central Italian Apennines, where crustal extension and devastating earthquakes occur in response to regional surface uplift. We constrain fault slip-rates since ~18 ka using variations in cosmogenic 36Cl measured on bedrock scarps, mapped using LiDAR and ground penetrating radar, and compare these rates to those inferred from geodesy. The 36Cl data reveal that individual faults typically accumulate meters of displacement relatively rapidly over several thousand years, separated by similar length time intervals when slip-rates are much lower, and activity shifts between faults across strike. Our rates agree with continuum deformation rates when averaged over long spatial or temporal scales (104 yr; 102 km) but over shorter timescales most of the deformation may be accommodated by <30% of the across-strike fault array. We attribute the shifts in activity to temporal variations in the mechanical work of faulting.

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“…However, GIA effects diminish exponentially away from the margin of the ice sheet, and hence, they have been argued to play a minimal role south of the hinge line (James & Bent, ; Kreemer et al, ; Wu & Johnston, ). Recent studies have also argued that dynamic topography resulting from radial mantle flow impact the occurrence of earthquakes away from plate boundary (Becker et al, ; Forte et al, ).…”

Section: Introductionmentioning

confidence: 99%

“…However, GIA effects diminish exponentially away from the margin of the ice sheet, and hence, they have been argued to play a minimal role south of the hinge line (James & Bent, 1994;Kreemer et al, 2018;Wu & Johnston, 2000). Recent studies have also argued that dynamic topography resulting from radial mantle flow impact the occurrence of earthquakes away from plate boundary (Becker et al, 2015;Forte et al, 2010). Li et al (2007) calculated Coulomb stresses likely to arise from the presence of a lithosphere-craton boundary and found that regions of high Coulomb stress correlated with seismically active regions in CEUS, indicating that lateral variations of lithospheric structure is important for the occurrence of seismicity in the CEUS.…”

Section: Introductionmentioning

confidence: 99%

Role of Large‐Scale Tectonic Forces in Intraplate Earthquakes of Central and Eastern North America

Ghosh

Holt

Bahadori

2019

Geochem Geophys Geosyst

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Central and eastern United States (CEUS) have experienced large intraplate earthquakes. Yet, at present there is no comprehensive model to explain stresses, strain, and seismicity in this intraplate setting. Models to explain the intraplate stresses in CEUS include glacio‐isostatic adjustment, ridge push effects, local stresses along preexisting fracture zones, and large‐scale convection. In this paper, we present a self‐consistent model of the dynamics of CEUS that explains the stress field responsible for these intraplate earthquakes. The earthquakes represent slow, ongoing deformation associated with forces arising from a combination of lithosphere topography and structure, together with the effects of density‐driven mantle flow. Using GPS data, we calculate strain rates that are likely to arise from tectonic effects and conclude that intraplate strain rates associated with tectonic effects are unlikely to exceed 1 × 10−9 year−1. We test several models of lateral viscosity variations by comparing model stress orientation output with earthquake moment tensors, SHmax directions from stress inversion, and P axes of earthquakes. A model that satisfies stress and earthquake constraints and also strain rate magnitude constraints requires high viscosity (1025 Pa·s) craton and old oceanic lithosphere of the western Atlantic block and weaker (5 × 1024 Pa·s) accreted Appalachian terrane. Other strength contrasts within the lithosphere are likely present. Incorporation of these into future models using constraints from seismology, along with refined geodetic measurements and improved estimates of crust and upper mantle densities, is needed to further refine long‐term dynamic models and better evaluate the hazards associated with this very slow, ongoing permanent deformation within the eastern and central United States.

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Western US intermountain seismicity caused by changes in upper mantle flow

Cited by 53 publications

References 48 publications

USArray Imaging of Continental Crust in the Conterminous United States

USArray Imaging of Continental Crust in the Conterminous United States

Orogen-scale uplift in the central Italian Apennines drives episodic behaviour of earthquake faults

Role of Large‐Scale Tectonic Forces in Intraplate Earthquakes of Central and Eastern North America

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