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  •  30 March 2021
Open access

Electrical Conductivity in Texturally Equilibrated Fluid‐Bearing Forsterite Aggregates at 800°C and 1 GPa: Implications for the High Electrical Conductivity Anomalies in Mantle Wedges

  •  24 March 2021

Key Points

  • Electrical conductivity in texturally equilibrated brine‐bearing forsterite aggregates was measured at 800°C and 1 GPa by a novel setup

  • Three‐dimensional images were obtained by synchrotron X‐ray computed tomography to precisely determine the fluid fractions and to visualize the fluid distribution

  • Above 1.0 vol.% fluid with 5 wt.% NaCl is required to explain the high conductivity anomalies above 0.01 S/m in deep fore‐arc mantles

Open access

Thermo‐Mechanical Numerical Modeling of the South American Subduction Zone: A Multi‐Parametric Investigation

  •  15 March 2021

Key Points

  • Numerical models of South American subduction study the effect of upper‐mantle rheology, subduction interface strength and slab thermal weakening

  • The model results are compared with natural observations on slab geometry and surface velocities

  • The best‐fitting models have a nonlinear upper mantle, a weak subduction zone interface and significant slab thermal weakening

Melting Dynamics of Late Cretaceous Lamprophyres in Central Asia Suggest a Mechanism to Explain Many Continental Intraplate Basaltic Suite Magmatic Provinces

  •  15 March 2021

Key Points

  • Newly found lamprophyres in central Asia record decompression melting of pyroxenite‐bearing asthenosphere at Tp ≈ 1400°C and Pfinal ≈ 2.3 GPa

  • The decompression melting represents small‐scale mantle upwellings under a sharply thinned lithosphere

  • Edge‐driven mantle convection is a trigger for small‐volume intraplate magmatic provinces of corrugated lithospheric lower boundaries

Open access

3D Local Earthquake Tomography of the Ecuadorian Margin in the Source Area of the 2016 Mw 7.8 Pedernales Earthquake

  •  14 March 2021

Key Points

  • 3D Vp and Vp/Vs models were calculated using local earthquake tomography in the region affected by the 2016 Pedernales, Ecuador earthquake

  • Tomographic images highlight the heterogeneities of the margin affected by seamounts and ridges comprising the oceanic crust

  • Carnegie Ridge seems the main feature controlling the seismic activity and the offshore extent of large megathrust earthquakes in the region

Evidence for Fluids at the Hypocenter of the 2017 Ms 7.0 Jiuzhaigou Earthquake Revealed by Local Earthquake Tomography

  •  14 March 2021

Key Points

  • We investigate the seismogenic structure of the 2017 Ms 7.0 Jiuzhaigou earthquake using the arrival times of local earthquakes

  • The main shock and aftershocks are distributed along an unmapped branch of the easternmost end of the eastern Kunlun fault

  • The high Vp and low Vs anomalies as well as high Vp/Vs ratio near the source area suggest the presence of fluids in the cracked rocks

Open access

Eruptive Cycle and Bubble Trap of Strokkur Geyser, Iceland

  •  12 March 2021

Key Points

  • Eruptive cycle of Strokkur consists of eruption, conduit refilling, bubble trap gas accumulation and bubble collapses at depth in conduit

  • Duration of phases in the eruptive cycle linearly increases from single to sextuple eruptions, except for the conduit refilling phase

  • We infer a bubble trap at a pool geyser at 23.7 ± 4.4 m depth, 13–23 m west of the conduit feeding single to sextuple eruptions

Open access

A 3D Full Stress Tensor Model for Oklahoma

  •  12 March 2021

Key Points

  • We compute the stress field using finite element modeling by considering contributions from both gravitational and far‐field tectonic forces

  • We obtain the orientation and magnitude of the tectonic force by finding the stress field that best‐fits the observed stress observations

  • Gravitational contribution to the horizontal stress field has a comparable magnitude regarding tectonic contribution for the upper 5 km

Deep Structure of the North Natal Valley (Mozambique) Using Combined Wide‐Angle and Reflection Seismic Data

  •  12 March 2021

Key Points

  • The basement of North Natal Valley and the Mozambique Coastal Plain is of continental nature

  • The location of the COB is South of the Naude Ridge, close to the Ariel Graben location

  • These results preclude the possibility of an overlap of the Antarctica plate on the MCP and the NNV in Gondwana kinematic reconstructions

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Incorporating wind information in the inversion of co‐located pressure and seismic data for shallow elastic structure

  •  9 April 2021

Key Points

  • Wind‐direction data allow us to select time intervals of stable wind direction.

  • Selected data can be inverted for shallow elastic structure by the moving pressure model.

  • If wind data were not available, one can still make a good estimate for structure by analyzing the high‐pressure‐end of data.

The Brittle‐Ductile Transition in Porous Limestone: Failure Mode, Constitutive Modeling of Inelastic Deformation and Strain Localization

  •  9 April 2021

Key Points

  • New triaxial and CT data are presented on Indiana limestone of porosity 16%.

  • Digital Volume Correlation reveals several complex failure modes involving shear bands through the brittle‐ductile transition.

  • The onset of inelastic compaction in dual porosity allochemical limestones is in agreement with the normality condition.

An alternative approach for constraining 3D‐displacements with InSAR, applied to a fault‐bounded groundwater entrainment field in California

  •  8 April 2021

Key Points

  • In 2017, up to 12 cm of LOS displacement occurred at the Whitewater groundwater entrainment site.

  • We compare methods for inferring 3D velocities from 1D InSAR measurements.

  • The Garnet Hill Fault experienced increased right‐lateral sense of shear in some areas.

High Resolution 3‐D Shear Wave Velocity Model of Northern Taiwan via Bayesian Joint Inversion of Rayleigh Wave Ellipticity and Phase Velocity with Formosa Array

  •  8 April 2021

Key Points

  • A new 3‐D Vs model of northern Taiwan is constructed using Rayleigh wave H/V ratios and phase velocities

  • The addition of H/V ratio measurements allows detailed shallow crustal structure to be resolved with sub‐kilometer depth resolution

  • The resolved fine crustal structures provide new geometrical constraints on basin formation and orogeny dynamics

Radiometric temperature determination in nongray bridgmanite: applications to melting curve and post‐perovskite transition boundary in the lower mantle

  •  8 April 2021

Key Points

  • Thermal radiation spectra record nongray interaction with bridgmanite in laser‐heated diamond anvil cells

  • Radiometric temperature of nongray bridgmanite in laser‐heated diamond anvil cells is up to 5‐10 % off the maximum sample temperature

  • Extant melting curves and experimental phase transition boundaries in the bridgmanite system contain this systematic error in temperature

Advanced InSAR Tropospheric Corrections from Global Atmospheric Models that Incorporate Spatial Stochastic Properties of the Troposphere

  •  7 April 2021

Key Points

  • An improved InSAR troposphere correction method proposed, based on Global Atmospheric Models (GAM), that considers spatial stochastic properties of the troposphere at different altitude levels for better weighting the GAM samples.

  • Comparisons with three other GAM corrections (PyAPS, d‐LOS, and GACOS) show a significant reduction in average standard deviation of corrected interferograms and better time‐series analysis results.

  • The results demonstrate the importance of considering horizontal heterogeneities and spatial stochastic models of the troposphere when using GAM‐corrections.

Plate‐boundary kinematics of the Afrera linkage zone (Afar) from InSAR and seismicity

  •  7 April 2021

Key Points

  • InSAR time‐series and seismicity analyses of deformation at the Afrera Plain linkage zone in Northern Afar, Ethiopia

  • Time‐series show fault slip accommodated through stick‐slip and creep along en‐echelon NS‐striking faults

  • Varying fault behavior could be influenced by elevated heat flows and hydrothermal circulation near the magmatic segments

Constraints on mantle viscosity from intermediate‐wavelength geoid anomalies in mantle convection models with plate motion history

  •  7 April 2021

Key Points

  • We use convection models with plate motion history to constrain the mantle viscosity, both its relative variations and absolute values.

  • Strong plate and weak plate margins with non‐uniform viscosity are critical in reproducing the geoid and surface plate motion.

  • The lower mantle viscosity is ∼1.3‐2.5× 10^22 Pa·s and ∼30 and ∼600‐1000 times higher than that in the transition zone and asthenosphere.

Seismic visibility of eclogite in the Earth's upper mantle – implications from high pressure‐temperature single‐crystal elastic properties of omphacite

  •  7 April 2021

Key Points

  • Single‐crystal elastic properties of omphacite were measured for the first time at high P‐T conditions.

  • Undeformed eclogite is seismically invisible at 210‐300 km 400‐500 km depth range.

  • Modeled seismic anisotropy of deformed eclogite can be as high as 4‐5% in the uppermost mantle.

Formation of Nanocrystalline and Amorphous Materials Causes Parallel Brittle‐viscous Flow of Crustal Rocks:Experiments on Quartz – Feldspar Aggregates

  •  5 April 2021

Key Points

  • Strain localizes into viscous slip zones that delimit coarser‐grained, cataclastic lenses.

  • Viscous flow is enabled by a microstructural transformation from microcrystalline to nanocrystalline, partly amorphous material in the slip zones.

  • Both viscous and brittle processes have to operate in parallel to accommodate deformation

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free access

The development and evaluation of the Earth Gravitational Model 2008 (EGM2008)

Key Points

  • Document the development of first ever gravity model to degree 2190
  • Demonstrate EGM2008's performance
  • Compare EGM2008 with other models

Open access

ITRF2014: A new release of the International Terrestrial Reference Frame modeling nonlinear station motions

Key Points

  • ITRF2014 benefits from accurate modeling of station annual and semiannual displacements
  • ITRF2014 benefits from accurate modeling of postseismic deformations for sites affected by major earthquakes
  • Leading to the determination of accurate and robust secular frame and site velocities

more >
Open access

Mapping Deep Electrical Conductivity Structure in the Mount Isa region, Northern Australia: Implications for Mineral Prospectivity

Key Points

  • Magnetotelluric data reveal crustal architecture of the eastern margin of the Proterozoic Mount Isa Province
  • Magnetotelluric models demonstrate spatial correlation between the crustal‐scale Carpentaria conductivity anomaly and the Gidyea Suture zone
  • Crustal‐penetrating structures act as potential pathways for transporting metalliferous fluids to form mineral deposits in the upper crust

Open access

Dynamic weakening of serpentinite gouges and bare surfaces at seismic slip rates

Key Points

  • Gouge friction approaches that of bare surfaces at high normal stress
  • Dehydration reactions and bulk melting in serpentinite in < 1 m of slip
  • Flash heating causes dynamic frictional weakening in gouge and bare surfaces

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Three‐Dimensional Crustal Architecture Beneath the Sikkim Himalaya and Its Relationship to Active Deformation

Key Points

  • Importance of the 3‐D deformation of the crust in the continent‐continent collision regime is highlighted
  • Clear observation of the ramp‐flat‐ramp geometry of the MHT has been made as well that of the regional scale heterogeneity within the crust
  • The Role of transverse tectonics in shaping the observed structure in the Sikkim Himalaya is proposed

Plain Language Summary

Sikkim is an Indian state between Nepal and Bhutan. The style of convergence between India and Eurasia changes from head‐on collision (Nepal Himalaya) to oblique convergence (Eastern Himalaya) across this region (Sikkim Himalaya). We study the crustal structure of this region using broadband seismological data recorded by a local network of stations. The Main Himalayan Thrust (MHT) separates the downgoing Indian Plate from the overriding Himalayan wedge. The MHT and the other major discontinuities within the crust, viz., the Moho and the midcrustal discontinuity are seen to dip northward. But all of these discontinuities also have higher‐order lateral variations. The MHT has a ramp‐flat‐ramp geometry with two ramps in the Lesser Himalaya and the Tethyan Himalaya, respectively. The ramp in the Lesser Himalaya is like a dome and upwarps the overlying thrust faults. The thickness and average shear wave velocity of underthrusting Indian crust is very similar to that of the Peninsular Indian crust. The Moho also has dome‐like structure separated by elongated, deeper sections trending NW‐SE. We conjecture that these alternate shallow and deep segments of the Moho are a consequence of several cycles of strike‐slip displacements on transverse faults known to be active here.

free access

The development and evaluation of the Earth Gravitational Model 2008 (EGM2008)

Key Points

  • Document the development of first ever gravity model to degree 2190
  • Demonstrate EGM2008's performance
  • Compare EGM2008 with other models

Open access

Philippine Sea and East Asian plate tectonics since 52 Ma constrained by new subducted slab reconstruction methods

Key Points

  • Twenty‐eight East Asia subducted slabs mapped from tomography and unfolded to constrain plate reconstructions
  • Slab evidence for a subducted 8000 × 2500 km “East Asian Sea” that existed between the Pacific and Indian Oceans in the early Cenozoic
  • Miocene arc‐arc collision between the northern Philippine Sea plate and the Ryukyu‐SW Japan Eurasian margin ~15–20 Ma

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Single‐station automated detection of transient deformation in GPS time series with the relative strength index: A case study of Cascadian slow slip

Key Points

  • We develop a single‐station automated transient detection algorithm based on the RSI
  • The transient detections agree well with previous studies in Cascadia
  • Transient detections are correlated with tremor and correlation attenuates with slab depth

Open access

ITRF2014: A new release of the International Terrestrial Reference Frame modeling nonlinear station motions

Key Points

  • ITRF2014 benefits from accurate modeling of station annual and semiannual displacements
  • ITRF2014 benefits from accurate modeling of postseismic deformations for sites affected by major earthquakes
  • Leading to the determination of accurate and robust secular frame and site velocities

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