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  •  27 May 2021
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Limitations in One‐Dimensional (an)Elastic Earth Models for Explaining GPS‐Observed M2 Ocean Tide Loading Displacements in New Zealand

  •  26 May 2021

Key Points

  • M2 ocean tide loading displacements in New Zealand are inferred from GPS observations

  • Estimates for the North Island are not reproduced by models combining ocean tide loading and a 1D (an)elastic Earth structure

  • Spatially coherent residual displacements of ∼0.4 mm (2%) are likely due to lateral Earth structure associated with Pacific Plate subduction

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Direct Velocity Inversion of Ground Penetrating Radar Data Using GPRNet

  •  20 May 2021

Key Points

  • We propose a deep learning-based electromagnetic velocity inversion for GPR zero-offset data

  • Tests on synthetic examples show accurate velocity inversion results

  • Applications to field data yield predictions that agree with the velocity models derived from previous physics-based inversion studies

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Episodic Earthquake Swarms in the Mineral Mountains, Utah Driven by the Roosevelt Hydrothermal System

  •  20 May 2021

Key Points

  • We find 1,100 earthquakes in the Mineral Mountains, Utah during 2016–2019 using a matched-filter method and 75 earthquake templates

  • Fluctuations of the seismicity rate with periods of burst-like activity followed by quiescence shows 15 swarm-like sequences

  • Spatial and temporal evolution of burst-like seismicity is related to fluid diffusion with possible episodes of aseismic slip

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The Proliferation of Induced Seismicity in the Permian Basin, Texas

  •  20 May 2021

Key Points

  • 45,009 earthquakes and 10,208 quarry blasts are identified in the Permian Basin region during 2000–2017

  • Small magnitude (M < 1) and larger magnitude earthquakes missed from prior analyses can be characterized 100s of km from the TXAR array

  • Seismicity near Pecos, Texas, is primarily driven by wastewater disposal at wells deeper than 1.5 km

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What Triggers Caldera Ring‐Fault Subsidence at Ambrym Volcano? Insights From the 2015 Dike Intrusion and Eruption

  •  18 May 2021

Key Points

  • Ground displacement at Ambrym in February 2015 was caused by a dike intrusion, deflating reservoir, and normal slip on a caldera ring-fault

  • Extracting at most 7% of the magma from Ambrym's reservoir suffices to reactivate the caldera ring-faults

  • Normal slip along Ambrym's ring-fault can occur during moderate-sized eruptions, resulting in subsidence and further caldera development

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Quantifying Eruptive and Background Seismicity, Deformation, Degassing, and Thermal Emissions at Volcanoes in the United States During 1978–2020

  •  18 May 2021

Key Points

  • In the United States, 96 of 161 volcanoes have at least one type of detected activity (seismicity, deformation, and gas or thermal emissions)

  • Forty-five percent of volcanoes with thermal emissions are only seen by medium-spatial resolution satellites (<100 m/pixel)

  • Each volcano has an Activity Intensity Level; a higher score from multiple data types indicates a greater likelihood of magmatic activity

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Moment Tensors of Ring‐Faulting at Active Volcanoes: Insights Into Vertical‐CLVD Earthquakes at the Sierra Negra Caldera, Galápagos Islands

  •  17 May 2021

Key Points

  • Dip slip along curved ring faults at volcanoes generates Mw > 5 earthquakes dominated by a compensated-linear-vector-dipole component

  • We propose a method for estimating ring-fault parameters by moment tensor inversion using long-period seismic data

  • Our estimation of ring-fault parameters of earthquakes at the Sierra Negra caldera yields results consistent with geodetic observations

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Global Volume Distribution for Subaerial Volcanism on Earth

  •  17 May 2021

Key Points

  • The continuous distribution of global subaerial volcanism on Earth is modeled and quantified

  • The distribution displays an initial (erupted volume < 170 Mm3) log-normal section, followed by a power law section encompassing several orders of magnitude

  • Power law—distributed eruption volumes may rule out the possibility of short-term deterministic forecasts of the size of an impending eruption

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Topographic Amplification of Crustal Subsidence by the Rainwater Load of the 2019 Typhoon Hagibis in Japan

  •  17 May 2021

Key Points

  • We estimate water vapor distribution in the 2019 super typhoon Hagibis with a dense GNSS network in Japan and compare it with precipitation

  • We estimate the distribution of rainwater load by the typhoon using the observed crustal subsidence, which exceeds the total precipitation

  • The discrepancy possibly reflects the amplification of subsidence due to selective deployment of the GNSS stations in concave terrains

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Crustal and upper‐mantle structure below Central and Southern Mexico

  •  3 June 2021

Key Points

  • A three-dimensional full seismic waveform model of Central and Southern Mexico for 5–50 s periods was constructed via adjoint methods

  • The shear wave velocity model indicated two continuous anomalies in the shallow upper mantle and the lower crust

  • These anomalies were associated with the ultra-slow seismic velocity zones and the high conductivity regions where slow earthquakes have been identified.

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A new reference model for the evolution of oceanic lithosphere in a cooling Earth

  •  3 June 2021

Key Points

  • A new reference model for the evolution of normal oceanic lithosphere is proposed

  • The model is based solely on thermal conduction and yet free of unphysical boundary conditions.

  • The model incorporates the effects of incomplete viscous relaxation, radiogenic heating, and secular cooling.

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Adjoint tomography of ambient noise data and teleseismic P waves: methodology and applications to central California

  •  3 June 2021

Key Points

  • We present an alternating inversion scheme combining ambient noise traveltime adjoint tomography with teleseismic full-waveform inversion

  • We demonstrate the advantage of the alternating inversion over individual inversions using both synthetics and field data in central California

  • Our model provides new constraints on the geometry of the Isabella Anomaly and helps decipher its origin.

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Exploring GPS observations of postseismic deformation following the 2012 MW7.8 Haida Gwaii and 2013 MW7.5 Craig, Alaska earthquakes: Implications for viscoelastic Earth structure

  •  3 June 2021

Key Points

  • The postseismic transient deformation caused by the 2012 and 2013 events is characterized by both afterslip and viscoelastic relaxation

  • 5+ years of cGPS data constrain a biviscous viscosity structure in the upper mantle asthenosphere under a sliver of Western North America

  • Additional postseismic campaign GPS data suggest afterslip occurred on both a dipping and a vertical fault plane following the 2012 event

Open access

Full Waveform Inversion beneath the Central Andes: Insight into the dehydration of the Nazca slab and delamination of the back‐arc lithosphere

  •  3 June 2021

Key Points

  • Normal dip subduction of the Nazca plate beneath the Central Andes

  • Dehydration of the subducted Nazca plate, hydration of the mantle wedge and partial melting of the continental crust

  • Underthrusting of the Brazilian Shield beneath the southern Altiplano and delamination beneath the southern Puna

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Elastic geobarometry for anisotropic inclusions in anisotropic host minerals: Quartz‐in‐zircon

  •  3 June 2021

Key Points

  • A new model for elastic thermobarometry is presented that accounts for the elastic anisotropy and crystallographic orientation of minerals.

  • The anisotropic elastic model was used to evaluate the suitability of the quartz-in-zircon system for thermobarometric applications.

  • Isotropic elastic models cannot resolve the strain state of an elastically anisotropic inclusion in an elastically anisotropic host.

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High‐precision Relocation with the Burial Depths of the North Korean Underground Nuclear Explosions by Combining Pn and Pg Differential Traveltimes

  •  2 June 2021

Key Points

  • A 3-D high-precision relocation method is explored using multiple phases.

  • Accurate estimates are generated for the burial depths of the North Korean nuclear tests.

  • The yield is estimated to be 225.7 kt for the largest nuclear explosion at the NKTS based on a data-constrained burial depth of 570 m.

Open access

Predicting Geothermal Heat Flow in Antarctica with a Machine Learning Approach

  •  31 May 2021

Key Points

  • A new geothermal heat flow map of Antarctica is established by adopting a machine learning approach

  • Input features include both global and regional geological and tectonic information, and heat flow observations

  • A Gondwana reconstruction shows connections of heat flow at the conjugate margins of East Antarctica

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High Fluid‐Pressure Patches beneath the Décollement: A Potential Source of Slow Earthquakes in the Nankai Trough off Cape Muroto

  •  31 May 2021

Key Points

  • A transient borehole mud flow confirmed the existence of an overpressured aquifer beneath the Nankai Trough décollement off Cape Muroto

  • The aquifer of ∼5–10 MPa excess pore pressure was distributed over a lateral extent of hundreds of meters

  • The overpressured aquifer may have been the cause of slow earthquakes observed near the drilling site

Open access

Uplift and exposure of serpentinized massifs:Modelling differential serpentinite diapirism and exhumation of the Troodos Mantle Sequence, Cyprus

  •  30 May 2021

Key Points

  • Coupled isostatic uplift-erosion modelling explains the outcrop pattern of the Troodos mountains.

  • Contrasting extents of serpentinization within the Mantle Sequence induced differential exhumation between two serpentinite domains.

  • Uplifted serpentinite massifs worldwide, reflect the relative contributions of serpentinization-induced isostasy and tectonics.

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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

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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

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

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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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