bluuebunny/crossref_metadata_2025_split huggingface dataset:
Scales of Stress Heterogeneity Near Active Faults in the Santa Barbara Channel, Southern California
Authors: Persaud Patricia , Pritchard Edward H. , Stock Joann M. 
Published: January 2020

AbstractThe Santa Barbara Channel represents the offshore portion of the Ventura Basin in Southern California. Ongoing transpression related to a regional left step in the San Andreas Fault has led to the formation of E‐W trending en‐echelon fault systems that accommodate localized shortening across the basin. Recent studies have suggested that faults within the channel could be capable of a multisegment rupture and producing a Mw 7.7–8.1 tsunamigenic earthquake. However, dynamic rupture models producing these results do not account for stress heterogeneity. With only sparse information available on the stress field in this region, further borehole‐derived stress constraints are essential for obtaining a more comprehensive understanding of the hazards related to the complex fault systems. We used caliper logs from 19 wells obtained from industry to identify stress‐induced borehole breakouts beneath the Holly and Gail oil platforms in the channel. Our newly developed forward modeling technique provides constraints on the orientations and relative magnitudes of the three principal stresses. At Gail, we determine a reverse faulting stress regime (SHmax = 1.7; Shmin = 1.6; SV = 1.0) and an SHmax azimuth of N45°E. Our results are consistent with local structures, which reflect deeper regional scale trends, and with similar studies onshore nearby. At Holly, an SHmax rotation from ~N36°W to ~N57°E occurs across ~100 m depth in a single well and differs from nearby results, indicating that short‐length scale (<10 km laterally and <1 km in depth) stress heterogeneity is associated with complex changes in fault geometry.
The Henkel Petrophysical Plot: Mineralogy and Lithology From Physical Properties
Authors: Enkin Randolph J. , Hamilton Tark S. , Morris William A. 
Published: January 2020

AbstractThe Henkel plot (logarithm of magnetic susceptibility versus density of rock samples) reveals that most rocks fall on either a “magnetite trend” or a “paramagnetic trend.” Interpretation of gravity and magnetic surveys is improved when the mineralogical and lithological basis of these trends is understood. We present a quantitative mineralogical mixing model, involving the components QFC (quartz‐feldspar‐calcite), FM (ferromagnesian silicates), and M (magnetite) and discuss the geological processes which produce or modify these mixtures. Igneous rocks mostly plot on the magnetite trend, where the FM/M ratio is about 10. The density‐susceptibility mineralogical mixing model is compatible with the CIPW mineral calculation for igneous classification from chemical analyses. Sedimentary and metamorphic processes usually involve oxidation, reduction, and/or iron loss, all which are magnetite‐destructive and lead to petrophysical measurements along the paramagnetic trend where FM/M > 1,000. Mineralization, with the introduction of sulfides and oxides, leads to dense rocks which do not plot along the magnetite nor paramagnetic trends. This quantitative analysis provides a method to integrate geological processes in the interpretation of geophysical surveys.
Topographic Fingerprint of Deep Mantle Subduction
Authors: Briaud Arthur , Agrusta Roberto , Faccenna Claudio , Funiciello Francesca , van Hunen Jeroen 
Published: January 2020

AbstractThe dynamic topography links with the mantle structures at various temporal and spatial scales. However, it is still unclear how it relates to the dynamics of subducting lithosphere when plates reach the mantle transition zone and lower mantle. Seismic tomography images show how slab morphologies vary from sinking subvertically into the lower mantle, to lying flat above the upper‐lower mantle discontinuity, to thickening in the shallow lower mantle. These slab shapes have been considered to be the result of variable interaction of the slab with the upper‐lower mantle discontinuity at ~670 km depth. Previous studies show that periodic deep slab dynamics can explain a variety of enigmatic geological and geophysical observations such as periodic variations of the plate velocities, trench retreat and advance episodes, and the scattered distribution of slab dip angle in the upper mantle. In this study, we use two‐dimensional subduction models to investigate the surface topography expression and its evolution during slab transition zone interaction. Our models show that topography does not depend on slab morphology; indeed, the dynamic topography cannot distinguish between a slab sinking straight into the lower mantle and slab stagnation at the upper‐lower mantle boundary. However, topographic oscillations are related to episodes of the trench advance and retreat, which in turn are linked to the slab folding behavior at transition zone depths. Our results suggest that the surface transient signal observed by geological studies could help to detect deep subduction dynamics.
Improved Global Nonlinear Surface Mass Variation Estimates From Geodetic Displacements and Reconciliation With GRACE Data
Authors: Wu Xiaoping , Haines Bruce J. , Heflin Michael B. , Landerer Felix W. 
Published: January 2020

AbstractSpatiotemporal coverage gaps and the nature of distant signature sources in Global Navigation Satellite System (GNSS) and The Gravity Recovery and Climate Experiment (GRACE) data require global inversions of data combinations for cross validation and complete and continuous monitoring of surface water mass variations. For spectral completeness, accurate data‐based degree‐1 surface mass variation coefficient or equivalent geocenter motion estimates are also desired but very difficult to obtain. To improve the reliability of such estimates, we carry out a new effort to combine different space geodetic technique data in a Kalman filter and time series approach to Terrestrial Reference Frame realization using an advanced formulation. With origin at the center of mass of the Earth system, the new parameterization now includes site displacements in the state vector explicitly for realistic assessment of their covariance matrices. More robust geocenter motion results are achieved when the displacement information is combined further with GRACE gravity data in a unified inversion. Previously, various systematic effects in GNSS data resulted in rather large discrepancies in global surface mass change estimates when compared with those from GRACE gravity data. Here, we show that significantly improved GNSS data after reprocessing and the refined Estimating the Circulation and Climate of the Ocean (ECCO) bottom pressure model reveal a global surface mass variation pattern that has been largely reconciled with that from GRACE data.
Formulation of a Triaxial Three‐Layered Earth Rotation: Theory and Rotational Normal Mode Solutions
Authors: Guo Zhiliang , Shen WenBin 
Published: January 2020

AbstractIn this study, we formulated a triaxial three‐layered anelastic Earth rotation theory considering various core‐mantle couplings, including the pressure and gravitational couplings acting on the elastic inner core by the outer core and mantle, and the viscoelectromagnetic couplings between the outer core and mantle and between the outer and inner cores. With this formulation, using the eigenvalue method, we solved four rotational normal modes, including the Chandler Wobble (CW), Free Core Nutation (FCN), Free Inner Core Nutation (FICN), and the Inner Core Wobble (ICW). The triaxiality of the actual Earth has notable effects on rotational normal modes, that is, 0.005, 0.0,
0.071, and 1.174 d (mean solar days), respectively, for the CW, FCN, FICN, and ICW. In the case that the triaxiality is bigger, for instance, if the Earth's equatorial dynamical ellipticity were
, which is 1 order of magnitude larger than the presently determined ellipticity (
), the CW and ICW periods will be lengthened by 3.579 and 94.912 d, and the FICN period will be decreased by 0.591 d. Based on our present knowledge, the numerical solutions of the four normal modes under the new rotation frame suggest that the periods of CW, FCN, FICN, and ICW are, respectively, 432.2, 429.9, 934.0, and 2,718.7 d. Our theory for Earth can be extended to other planets in our solar system.
Salinity Affects Topsoil Organic Carbon Concentrations Through Regulating Vegetation Structure and Productivity
Authors: Xue Lian , Jiang Junyan , Li Xiuzhen , Yan Zhongzheng , Zhang Qian , Ge Zhenming , Tian Bo , Craft Christopher 
Published: January 2020

AbstractEstuarine salt marshes have been recognized as one of the most efficient carbon sinks in the biosphere, with considerable potential for climate change mitigation. However, there are still uncertainties about the response of soil carbon stocks to enhanced soil salinization caused by accelerated sea‐level rises and aggravated saltwater intrusion. We therefore conducted both field investigations in the Chongming Dongtan salt marsh of the Yangtze River Estuary, China, and manipulative experiments on marsh soils occupied, respectively, by the invasive Spartina alterniflora, and the native Phragmites australis and Scirpus mariqueter, to identify the effects of elevated soil salinity on top soil organic carbon (SOC) concentration. Our field data showed that SOC concentrations were significantly positively associated with soil salinity concentrations, annual net primary productivity, and marsh surface elevation but showed a significant negative relationship with median grain size. Compared with the two native species, S. alterniflora preferred more saline conditions and had a higher SOC concentration. Although raised flooding salinities (0–35 ppt) did not strongly affect SOC concentrations, elevated soil salinities significantly corresponded with low SOC concentrations and plant biomass in manipulative experiments. These findings indicated that soil salinity, plant species, and soil texture were key factors controlling SOC concentrations in the studied salt marsh. Moreover, soil salinity could affect SOC concentrations through regulating vegetation spatial structure and plant biomass production. The further invasion of the S. alterniflora community will exert a positive influence on SOC concentrations in the Chongming Dongtan salt marsh.
Radio Monitoring of Dynamic Processes in the Ionosphere Over China During the Partial Solar Eclipse of 11 August 2018
Authors: Guo Q. , Chernogor L. F. , Garmash K. P. , Rozumenko V. T. , Zheng Y. 
Published: January 2020

AbstractWe briefly describe the multifrequency multiple‐path radio system and illustrate its observational capabilities by performing, as an example, the study of dynamic processes that occurred in the ionosphere over China during the partial solar eclipse on August 11 2018. This system, based on the software‐defined radio technology and capable of operating in the 10‐kHz to 30‐MHz band, has been developed jointly by Harbin Engineering University, the People's Republic of China, where it is located, and V. N. Karazin National University, Ukraine. The principle of the system operation is based on measurements of a Doppler shift of frequency. The implementation of Marple's algorithm for autoregression spectrum analysis has permitted an increase in a Doppler resolution down to 0.02 Hz and in a temporal resolution down to 7.5 s. The number of radio propagation paths and their orientation depend on the specifics of problems being solved. The interpretation of the eclipse effects is complicated by processes launched by the dusk terminator. The eclipse was associated with an increase in the number of rays, the generation of oscillation processes in the atmospheric gravity wave range of periods, and with a negative Doppler shift of frequency at first and a positive shift of smaller magnitude subsequently. The solar eclipse launched ~9–14% amplitude quasiperiodic oscillations in the electron density, while a maximum decrease of order 26% was observed over the Hailar–Harbin path in the ionospheric E region. The latter value does not virtually differ from theoretical estimates.
Measuring the Earth's Synchrotron Emission From Radiation Belts With a Lunar Near Side Radio Array
Authors: Hegedus Alexander , Nénon Quentin , Brunet Antoine , Kasper Justin , Sicard Angélica , Cecconi Baptiste , MacDowall Robert , Baker Daniel 
Published: January 2020

AbstractThe high kinetic energy electrons that populate the Earth's radiation belts emit synchrotron emissions because of their interaction with the planetary magnetic field. A lunar near side array would be uniquely positioned to image this emission and provide a near real time measure of how the Earth's radiation belts are responding to the current solar input. The Salammbô code is a physical model of the dynamics of the three‐dimensional phase‐space electron densities in the radiation belts, allowing the prediction of 1‐keV to 100‐MeV electron distributions trapped in the belts. This information is put into a synchrotron emission simulator that provides the brightness distribution of the emission up to 1 MHz from a given observation point. Using Digital Elevation Models from Lunar Reconnaissance Orbiter Lunar Orbiter Laser Altimeter data, we select a set of locations near the Lunar sub‐Earth point with minimum elevation variation over various‐sized patches where we simulate radio receivers to create a synthetic aperture. We consider all realistic noise sources in the low‐frequency regime. We then use a custom Common Astronomy Software Applications code to image and process the data from our defined array, using SPICE to align the lunar coordinates with the Earth. We find that for a moderate lunar surface electron density of 250/cm
, the radiation belts may be detected every 12–24 hr with a 16,384‐element array over a 100‐km‐diameter circle. Changing electron density can make measurements 10 times faster at lunar night and 10 times slower at lunar noon.
Flying Through Uncertainty
Authors: Berger T. E. , Holzinger M. J. , Sutton E. K. , Thayer J. P. 
Published: January 2020

AbstractSpace weather is the main source of uncertainty in the position of all objects in low Earth orbit (LEO) below about 1,000 km. The main impact is strong variation in the neutral density of the thermosphere as it responds to radiative inputs from the Sun in the extreme ultraviolet wavelength range, energetic particle precipitation in the high‐latitude auroral zones, and global‐scale electrical currents generated during geomagnetic storms. Waves and instabilities from the lower atmosphere can also influence thermospheric density in complex ways. The variation in neutral density leads to variable drag forces on satellites flying through the thermosphere, which in turn causes orbital track changes. We currently lack the ability to accurately model and predict the neutral density changes in the thermosphere in response to space weather inputs. Operational empirical models of thermospheric density are inaccurate during space weather events, and mandate that LEO orbital tracks carry large “error ellipsoids” around all objects to account for positional uncertainty. This leads to many more “conjunction” warnings than necessary as large error ellipsoids are frequently calculated to intersect in orbit. As the LEO domain becomes more crowded with the advent of commercial “megaconstellations” we face a growing challenge to reduce orbital uncertainties by developing whole atmosphere models to enable timely and accurate forecasts of thermospheric conditions. We recommend that researchers, forecasters, and policy makers coordinate to ensure that space weather research and forecasting is tightly integrated into upcoming changes to the operational Space Traffic Management system.
Orogenesis in Paleo‐Mesoproterozoic Eastern Australia: A response to Arc‐Continent and Continent‐Continent Collision During Assembly of the Nuna Supercontinent
Authors: Gibson G. M. , Champion D. C. , Huston D. L. , Withnall I. W. 
Published: January 2020

AbstractNorthern and southern Australia preserve a common record of 1790–1655 Ma intracontinental rifting and backarc extension culminating in formation of a marginal sea that subsequently collapsed following a 1650–1640 Ma reversal in plate motion and onset of arc‐continent collision. Arc‐continent collision was accompanied by intermediate‐pressure Barrovian‐type metamorphism (6–8 kb) and widespread crustal thickening as reflected in a clockwise pressure‐temperature‐time path. Later metamorphism during the 1620–1580 Ma Isa and Olary orogenies occurred under intrusion‐enhanced lower pressure conditions (4–6 kb) and followed a counterclockwise pressure‐temperature‐time path incompatible with either significant amounts of crustal thickening or tectonic models which have Australia and Laurentia commencing collision at this time. Continent‐continent collision more likely followed on closely behind arc‐continent collision (Riversleigh Tectonic Event), precipitating a switch in crustal shortening from northeast‐southwest to west‐east as the older rift template and underlying basement structures were reactivated in a transpressive or multicollisional tectonic regime not unlike that which produced the Himalayan‐Tibet orogenic system. As in the latter, ongoing collision was accommodated by thrusting, extensional collapse and lateral extrusion of still thermally weak crust on orogen‐parallel strike‐slip faults, resulting in formation of the west‐east‐striking Isa Superbasin, isothermal decompression and granite intrusion from 1620 Ma. A comparable record of deformation, metamorphism, and magmatic intrusion from 1650 until 1600 Ma has been documented for northern and southern North America (Forward/Racklan and Mazatzal orogenies) indicating that Laurentia and Australia were likely proximal to each other throughout this period.
Topographic and Tectonic Evolution of Mountain Belts Controlled by Salt Thickness and Rift Architecture
Authors: Jourdon Anthony , Mouthereau Frédéric , Le Pourhiet Laetitia , Callot Jean‐Paul 
Published: January 2020

AbstractThe role of the heterogeneous rheological architecture of rifted margins in the building of mountain belts has challenged our view of how a collisional orogen formed. We show, using two‐dimensional numerical experiments of collision built by the inversion of rifted margins, that a weak pre‐extensional evaporitic layer delays the growth of topography and the onset of syn‐orogenic sedimentary record in foreland basins. In tectonic models lacking a weak décollement layer, the orogen grows by progressive accretion of basement thrusts. With a 2‐km‐thick salt layer, the orogen develops an antiformal stack in the deep crust that is kinematically connected to a shallow thin‐skin thrust belt in the foreland as observed in many orogens. A 5‐km‐thick weak layer leads to the quasi‐absence of topography and widespread salt tectonics and obliterates thrusts propagation while promoting crust and mantle underthrusting. During convergence, the preservation of a marine seaway emphasizes that collision may involve a significant period of submarine continental accretion, which duration is controlled by the thickness of the weak décollement layer. From these experiments we infer that the thicker the salt layer, the longer the delay between the onset of far‐field shortening and the formation of the orogen. Our study explains first‐order features recognized in many orogens controlled by variable salt thickness and extension.
Value of Crowd‐Based Water Level Class Observations for Hydrological Model Calibration
Authors: Etter S. , Strobl B. , Seibert J. , van Meerveld H. J. Ilja 
Published: January 2020

AbstractWhile hydrological models generally rely on continuous streamflow data for calibration, previous studies have shown that a few measurements can be sufficient to constrain model parameters. Other studies have shown that continuous water level or water level class (WL‐class) data can be informative for model calibration. In this study, we combined these approaches and explored the potential value of a limited number of WL‐class observations for calibration of a bucket‐type runoff model (HBV) for four catchments in Switzerland. We generated synthetic data to represent citizen science data and examined the effects of the temporal resolution of the observations, the numbers of WL‐classes, and the magnitude of the errors in the WL‐class observations on the model validation performance. Our results indicate that on average one observation per week for a 1‐year period can significantly improve model performance compared to the situation without any streamflow data. Furthermore, the validation performance for model parameters calibrated with WL‐class observations was similar to the performance of the calibration with precise water level measurements. The number of WL‐classes did not influence the validation performance noticeably when at least four WL‐classes were used. The impact of typical errors for citizen science‐based estimates of WL‐classes on the model performance was small. These results are encouraging for citizen science projects where citizens observe water levels for otherwise ungauged streams using virtual or physical staff gauges.
Divergent symbiont communities determine the physiology and nutrition of a reef coral across a light-availability gradient
Authors: Wall Christopher B , Kaluhiokalani Mario , Popp Brian N , Donahue Megan J , Gates Ruth D 
Published: January 2020

Abstract
Reef corals are mixotrophic organisms relying on symbiont-derived photoautotrophy and water column heterotrophy. Coral endosymbionts (Family: Symbiodiniaceae), while typically considered mutualists, display a range of species-specific and environmentally mediated opportunism in their interactions with coral hosts, potentially requiring corals to rely more on heterotrophy to avoid declines in performance. To test the influence of symbiont communities on coral physiology (tissue biomass, symbiont density, photopigmentation) and nutrition (δ13C, δ15N), we sampled Montipora capitata colonies dominated by a specialist symbiont Cladocopium spp. or a putative opportunist Durusdinium glynnii (hereafter, C- or D-colonies) from Kāne‘ohe Bay, Hawai‘i, across gradients in photosynthetically active radiation (PAR) during summer and winter. We report for the first time that isotope values of reef corals are influenced by Symbiodiniaceae communities, indicative of different autotrophic capacities among symbiont species. D-colonies had on average 56% higher symbiont densities, but lower photopigments per symbiont cell and consistently lower δ13C values in host and symbiont tissues; this pattern in isotope values is consistent with lower symbiont carbon assimilation and translocation to the host. Neither C- nor D-colonies showed signs of greater heterotrophy or nutritional plasticity; instead changes in δ13C values were driven by PAR availability and photoacclimation attributes that differed between symbiont communities. Together, these results reveal Symbiodiniaceae functional diversity produces distinct holobionts with different capacities for autotrophic nutrition, and energy tradeoffs from associating with opportunist symbionts are not met with increased heterotrophy.