scholarly journals Rheologic constraints on the upper mantle from 5 years of postseismic deformation following the El Mayor-Cucapah earthquake

2016 ◽  
Vol 121 (9) ◽  
pp. 6809-6827 ◽  
Author(s):  
T. T. Hines ◽  
E. A. Hetland
Keyword(s):  
Upper Mantle ◽  
Postseismic Deformation

scholarly journals Upper mantle rheology from GRACE and GPS postseismic deformation after the 2004 Sumatra-Andaman earthquake

2010 ◽  
Vol 11 (6) ◽  
pp. n/a-n/a ◽  
Author(s):  
I. Panet ◽  
F. Pollitz ◽  
V. Mikhailov ◽  
M. Diament ◽  
P. Banerjee ◽  
...  
Keyword(s):  
Upper Mantle ◽  
Postseismic Deformation ◽  
Mantle Rheology ◽  
Andaman Earthquake

scholarly journals MCMC inversion of the transient and steady-state creep flow law parameters of dunite under dry and wet conditions

2021 ◽  
Vol 73 (1) ◽  
Author(s):  
Sagar Masuti ◽  
Sylvain Barbot
Keyword(s):  
Activation Energy ◽  
Steady State ◽  
Upper Mantle ◽  
Physical Mechanism ◽  
Transient Creep ◽  
Steady State Creep ◽  
Postseismic Deformation ◽  
Nonlinear Stress ◽  
Dry And Wet Conditions ◽  
Flow Law

AbstractThe rheology of the upper mantle impacts a variety of geodynamic processes, including postseismic deformation following great earthquakes and post-glacial rebound. The deformation of upper mantle rocks is controlled by the rheology of olivine, the most abundant upper mantle mineral. The mechanical properties of olivine at steady state are well constrained. However, the physical mechanism underlying transient creep, an evolutionary, hardening phase converging to steady state asymptotically, is still poorly understood. Here, we constrain a constitutive framework that captures transient creep and steady state creep consistently using the mechanical data from laboratory experiments on natural dunites containing at least 94% olivine under both hydrous and anhydrous conditions. The constitutive framework represents a Burgers assembly with a thermally activated nonlinear stress-versus-strain-rate relationship for the dashpots. Work hardening is obtained by the evolution of a state variable that represents internal stress. We determine the flow law parameters for dunites using a Markov chain Monte Carlo method. We find the activation energy $$430\pm 20$$ 430 ± 20   and $$250\pm 10$$ 250 ± 10  kJ/mol for dry and wet conditions, respectively, and the stress exponent $$2.0\pm 0.1$$ 2.0 ± 0.1 for both the dry and wet cases for transient creep, consistently lower than those of steady-state creep, suggesting a separate physical mechanism. For wet dunites in the grain-boundary sliding regime, the grain-size dependence is similar for transient creep and steady-state creep. The lower activation energy of transient creep could be due to a higher jog density of the corresponding soft-slip system. More experimental data are required to estimate the activation volume and water content exponent of transient creep. The constitutive relation used and its associated flow law parameters provide useful constraints for geodynamics applications. Graphical Abstract

scholarly journals Thin crème brûlée rheological structure for the Eastern California Shear Zone

Geology ◽  
2020 ◽  
Author(s):  
Shaozhuo Liu ◽  
Zheng-Kang Shen ◽  
Roland Bürgmann ◽  
Sigurjón Jónsson
Keyword(s):  
Shear Zone ◽  
Upper Mantle ◽  
Lower Crust ◽  
Near Field ◽  
Plate Boundary ◽  
Postseismic Deformation ◽  
Decadal Time Scale ◽  
Eastern California Shear Zone ◽  
Transient Rheology ◽  
Transient Viscosity

Since the occurrence of the 1992 CE Mw 7.3 Landers and 1999 Mw 7.1 Hector Mine earthquakes in the Mojave Desert (California, USA), postseismic deformation following both earthquakes has been intensively studied, and models with a strong crust overlying a low-viscosity mantle asthenosphere have been favored. However, we recently found that the near-field postseismic transients after the two earthquakes have lasted longer than previously thought, which requires a revision of the postseismic modeling. Our new modeling results based on the revised postseismic transients show that: (1) the effective viscosity of the lower crust beneath the Mojave region at the decadal time scale is ~2 × 1020 Pa·s (transient viscosity ~2 × 1019 Pa·s), i.e., only ~5 times that of the underlying mantle asthenosphere, and (2) the transient viscosity of the upper mantle exhibits a time-dependent increase, providing fresh geodetic evidence for frequency-dependent rheology (e.g., Andrade or extended Burgers rheology). The inferred transient rheology for the first year agrees well with that obtained for the July 2019 Mw 6.4 and Mw 7.1 Ridgecrest earthquakes ~180 km north of the two Mojave events. Our modeling results support a thin crème brûlée model for the Eastern California Shear Zone (part of the Pacific-North America plate boundary) in which both the lower crust and the upper mantle exhibit ductility at decadal time scales.

Water Gas May Not Shift in Deep Earth

2020 ◽  
Author(s):  
Nore Stolte ◽  
Junting Yu ◽  
Zixin Chen ◽  
Dimitri A. Sverjensky ◽  
Ding Pan
Keyword(s):  
Formic Acid ◽  
Upper Mantle ◽  
Free Energy Calculations ◽  
Water Gas Shift ◽  
Ab Initio Molecular Dynamics ◽  
Water Gas Shift Reaction ◽  
Carbon Carrier ◽  
Deep Earth ◽  
Shift Reaction ◽  
Water Gas

The water-gas shift reaction is a key reaction in Fischer-Tropsch-type synthesis, which is widely believed to generate hydrocarbons in the deep carbon cycle, but is little known at extreme pressure-temperature conditions found in Earth’s upper mantle. Here, we performed extensive ab initio molecular dynamics simulations and free energy calculations to study the water-gas shift reaction. We found the direct formation of formic acid out of CO and supercritical water at 10∼13 GPa and 1400 K without any catalyst. Contrary to the common assumption that formic acid or formate is an intermediate product, we found that HCOOH is thermodynamically more stable than the products of the water-gas shift reaction above 3 GPa and at 1000∼1400 K. Our study suggests that the water-gas shift reaction may not happen in Earth’s upper mantle, and formic acid or formate may be an important carbon carrier, participating in many geochemical processes in deep Earth.<br>

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