bluuebunny/crossref_metadata_2025_split huggingface dataset:
Topside electron density profiles observed at low latitudes by COSMIC and compared with in situ ion densities measured by C/NOFS
Authors: Lai Pei‐Chen , Burke William J. , Gentile L. C. 
Published: April 2013

AbstractElectron density height profiles (EDPs) play critical roles in accurately tracing the propagation of radio frequency signals through the topside ionosphere. The Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) satellites were designed to provide this information during GPS radio occultation events. However, due to the reliance of COSMIC data reduction on inverse Abel transformations, questions persist about the accuracy of its EDP products. The Communication/Navigation Outage Forecasting System (C/NOFS) satellite in a low‐inclination orbit offers new opportunities for empirically testing the accuracy of topside EDPs from COSMIC over the altitude range 400 to 800 km. We report here on the results of a feasibility study covering the interval 24–25 October 2011 in which a large magnetic storm occurred. We identified universal times when C/NOFS passed within 6° × 60° rectangles centered at the latitudes and longitudes of the tangent line for COSMIC EDPs. We also compared COSMIC EDPs with those predicted by two widely used models. Our analysis shows that during a very large fraction of the available events, ion densities measured by C/NOFS were in closer agreement with COSMIC EDPs than were model predictions at the same altitudes. We also use the COSMIC and C/NOFS data sets to assess stormtime effects on the low‐latitude ionosphere. During the main phase of the storm both local densities and vertical total electron content rose on the dayside, but decreased on the nightside. During recovery both quantities quickly reverted toward their quiet‐time levels.
Inner magnetospheric heavy ion composition during high‐speed stream‐driven storms
Authors: Forster D. R. , Denton M. H. , Grande M. , Perry C. H. 
Published: April 2013

AbstractIon composition data, taken by the Combined Release and Radiation Effects Satellite Magnetospheric Ion Composition Spectrometer instrument, are investigated across eight high‐speed solar wind‐stream‐driven storms (HSSs) during 1991. The HSSs are identified using solar wind data from OMNI alongside geomagnetic indices, and the behavior of ions in the energy range 31.2–426.0 keV is investigated. A case study of the single HSS event that occurred on 30 July 1991 is performed, and superposed epoch analyses of five events are conducted. The data show evidence of a local minimum (dropout) in the flux and partial number density of ionic species H+, He+, He++, and O+ close to the onset of magnetospheric convection. The flux and number density rapidly fall and then recover over a period of hours. The initial rapid recovery in number density is observed to consist primarily of lower‐energy ions. As the number density reaches its maximum, the ions show evidence of energization. Heavy ion‐to‐proton ratios are observed to decrease substantially during these HSS events.
Evaluation of 1‐D and 3‐D seismic models of the Pacific lower mantle with S, SKS, and SKKS traveltimes and amplitudes
Authors: Thorne Michael S. , Zhang Yang , Ritsema Jeroen 
Published: April 2013

AbstractIn this study, we analyzed the seismic phases S, SKS, and SKKS from 31 deep‐focus earthquakes in the Tonga‐Fiji region recorded in North America between epicentral distances of 85° and 120°. The differential traveltimes and amplitude ratios for these phases reveal clear epicentral distance trends not predicted by standard one‐dimensional (1‐D) reference Earth models. The increase of the S/SKS amplitude ratio up to a factor of 10 is accompanied by an increase of the S‐SKS differential traveltime of up to 10 s. SKKS‐SKS differential traveltimes of 2–3 s and SKKS/SKS amplitude ratios of a factor of 2–4 across the epicentral range have maxima near 107°. We examined these observations using full (1‐D and 3‐D) waveforms for three 1‐D seismic velocity profiles for the central Pacific region and for the tomographic model S40RTS including modifications: different regularization parameters, great‐circle path azimuthal variation, strength of S wave velocity perturbations, S wave velocity gradients in the lower mantle, and ultra–low velocity zones. To explain these data, we constructed a hybrid model that combines both features of S40RTS and short‐wavelength features from the 1‐D profiles. The large‐scale seismic structure is represented by S40RTS. Embedded within S40RTS are a 20 km thick ultra–low velocity zone at the core‐mantle boundary near the source side and a 200 km thick negative velocity gradient zone near the receiver side of the paths. Our analysis demonstrates that the S wave velocity structure of the Pacific large low shear‐velocity province cannot be interpreted solely by global tomographic or regional modeling approaches in exclusion of each other.
Volcanic eruption monitoring by thermal image correlation: Pixel offsets show episodic dome growth of the Colima volcano
Authors: Walter Thomas R. , Legrand Denis , Granados Hugo Delgado , Reyes Gabriel , Arámbula Raúl 
Published: April 2013

AbstractEstimating the magnitude of dome eruptions is one of the main challenges in volcano monitoring. Although modern monitoring networks are in place at many dome‐building volcanoes, the type and occurrence of explosive activity and the scale of the eruptions are commonly estimated by visual inspection. Quantifying the deformation of dome‐building volcanoes and the occurrence of explosions is highly valuable, not only for enabling the provision of early warnings but also for facilitating an understanding of the physics of explosive volcanoes, as demonstrated by this study of one of the most active volcanoes in Mexico. The Volcán de Colima is currently experiencing a phase of viscous dome growth, which is associated with episodic “Vulcanian” eruptions and rock falls. Little is known about the dynamics of this dome, its growth rates, or the scale of the associated explosions. We present the results from an analysis of nighttime time‐lapse infrared images and compare these data with local seismic amplitude recordings. By digital image correlation, we track temperature features in infrared images. Images taken before and after the explosions reveal the location of the hot dome to be subject to significant and systematic lateral pixel offsets. Dome deformation is shown to occur intermittently every 3–4 h, with lateral displacements exceeding 0.3 m within periods of less than 120 s. Only the thermally elevated regions of the western dome, which may represent a coulée‐like flow, are displaced. This movement is often, but not always, associated with seismic amplitude peaks. Therefore, our analysis of the infrared image correlation suggests the occurrence of aseismic dome‐deformation episodes, thereby challenging the current understanding of dome growth and/or the appropriateness of commonly used volcano surveillance techniques.
The breakup of East Gondwana: Assimilating constraints from Cretaceous ocean basins around India into a best‐fit tectonic model
Authors: Gibbons Ana D. , Whittaker Joanne M. , Müller R. Dietmar 
Published: April 2013

AbstractPublished models for the Cretaceous seafloor‐spreading history of East Gondwana result in unlikely tectonic scenarios for at least one of the plate boundaries involved and/or violate particular constraints from at least one of the associated ocean basins. We link East Gondwana spreading corridors by integrating magnetic and gravity anomaly data from the Enderby Basin off East Antarctica within a regional plate kinematic framework to identify a conjugate series of east‐west‐trending magnetic anomalies, M4 to M0 (~126.7–120.4 Ma). The mid‐ocean ridge that separated Greater India from Australia‐Antarctica propagated from north to south, starting at ~136 Ma northwest of Australia, and reached the southern tip of India at ~126 Ma. Seafloor spreading in the Enderby Basin was abandoned at ~115 Ma, when a ridge jump transferred the Elan Bank and South Kerguelen Plateau to the Antarctic plate. Our revised plate kinematic model helps resolve the problem of successive two‐way strike‐slip motion between Madagascar and India seen in many previously published reconstructions and also suggests that seafloor spreading between them progressed from south to north from 94 to 84 Ma. This timing is essential for tectonic flow lines to match the curved fracture zones of the Wharton and Enderby basins, as Greater India gradually began to unzip from Madagascar from ~100 Ma. In our model, the 85‐East Ridge and Kerguelen Fracture Zone formed as conjugate flanks of a “leaky” transform fault following the ~100 Ma spreading reorganization. Our model also identifies the Afanasy Nikitin Seamounts as products of the Conrad Rise hotspot.
Outgassing: Influence on speed of magma fragmentation
Authors: Richard Dominique , Scheu Bettina , Mueller Sebastian P. , Spieler Oliver , Dingwell Donald B. 
Published: April 2013

AbstractPredicting explosive eruptions remains an outstanding challenge. Knowledge of the controlling parameters and their relative importance is crucial to deepen our understanding of conduit flow dynamics and accurately model the processes involved. This experimental study sheds light on one important parameter—outgassing—and evaluates its influence on magma fragmentation behavior. We perform fragmentation experiments based on the shock tube theory at room temperature on natural pyroclastic material with a connected porosity ranging from 15% to 78%. For each sample series, we determine the initial pressure (P) required to initiate magma fragmentation (fragmentation threshold, Pth). Furthermore, we measure the permeability of each sample for P < Pth and the fragmentation speed for P > Pth. A significant loss of initial pressure, caused by outgassing in samples with permeability ≥1e–12 m2, is observed within the fragmentation time scale (a few milliseconds). The samples are classified into: (a) dome/conduit wall rocks and (b) pumice/scoria. Substantial outgassing during fragmentation leads to higher fragmentation thresholds. Experimental fragmentation speeds are significantly higher than the modeled fragmentation speeds for high‐permeability dome/conduit wall rocks, but lower for high‐permeability pumices. Experimental fragmentation speeds for low‐permeability dome/conduit wall rocks and low‐permeability pumice/scoria are as expected. We also find that low‐porosity, low‐permeability, altered dome/conduit wall rocks fragment at significantly higher speeds than expected. Because fragmentation threshold and fragmentation speed are among the determining parameters for the initiation, sustainment and cessation of an eruption, outgassing should be considered in the modeling of magma fragmentation dynamics.
Missing great earthquakes
Authors: Hough Susan E. 
Published: April 2013

AbstractThe occurrence of three earthquakes with moment magnitude (Mw) greater than 8.8 and six earthquakes larger than Mw 8.5, since 2004, has raised interest in the long‐term global rate of great earthquakes. Past studies have focused on the analysis of earthquakes since 1900, which roughly marks the start of the instrumental era in seismology. Before this time, the catalog is less complete and magnitude estimates are more uncertain. Yet substantial information is available for earthquakes before 1900, and the catalog of historical events is being used increasingly to improve hazard assessment. Here I consider the catalog of historical earthquakes and show that approximately half of all Mw ≥ 8.5 earthquakes are likely missing or underestimated in the 19th century. I further present a reconsideration of the felt effects of the 8 February 1843, Lesser Antilles earthquake, including a first thorough assessment of felt reports from the United States, and show it is an example of a known historical earthquake that was significantly larger than initially estimated. The results suggest that incorporation of best available catalogs of historical earthquakes will likely lead to a significant underestimation of seismic hazard and/or the maximum possible magnitude in many regions, including parts of the Caribbean.
Causes and mechanisms of the 2011–2012 El Hierro (Canary Islands) submarine eruption
Authors: Martí Joan , Pinel Virginie , López Carmen , Geyer Adelina , Abella Rafael , Tárraga Marta , Blanco María José , Castro Antonio , Rodríguez Carmen 
Published: April 2013

AbstractEl Hierro eruption started on 10 October 2011 after an unrest episode that initiated on 17 July 2011. This is the first eruption in the Canary Islands that has been tracked in real time. Although being submarine and not directly observable, the data recorded allowed its reconstruction and to identify its causes and mechanisms. Seismicity, surface deformation, and petrological data indicate that a batch of basanitic magma coming from a reservoir located at a depth of about 25 km below the El Hierro Island was emplaced at shallower depth creating a new reservoir about 10–12 km above, where magma evolved until the initiation of the eruption. The characteristics of seismicity and surface deformation suggest that the necessary space to accumulate magma at this shallower position, which coincides with the crust/mantle boundary beneath El Hierro, was created in about 2 months by elastic deformation and magma‐driven fracturing of the crust. After this first intrusion episode, part of the magma started to migrate laterally toward the SE for nearly 20 km, always keeping the same depth and following a path apparently controlled by stress barriers created by tectonic and rheological contrasts in the upper lithosphere. This lateral migration of magma ended with a submarine eruption at about 5 km offshore from the southern corner of El Hierro Island. The total seismic energy released during the unrest episode was of 8.1 × 1011 J, and the total uplift previous to the onset of the eruption was of 40 mm. Combining geological, geophysical, and petrological data and numerical modeling, we propose a volcanological model of the causes and mechanisms of El Hierro eruption that shows how the stress distribution in the crust beneath El Hierro, which was influenced by rheological contrasts, tectonic stresses, and gravitational loading, controlled the movement and eruption of magma. We also discuss the implications of this model in terms of eruption forecast in the Canary Islands.
Rupture dynamics and ground motion from 3‐D rough‐fault simulations
Authors: Shi Zheqiang , Day Steven M. 
Published: April 2013

AbstractWe perform three‐dimensional (3‐D) numerical calculations of dynamic rupture along non‐planar faults to study the effects of fault roughness on rupture propagation and resultant ground motion. The fault roughness model follows a self‐similar fractal distribution over length scales spanning three orders of magnitude, from ~102 to ~105 m. The fault is governed by a strongly rate‐weakening friction, and the bulk material is subject to Drucker‐Prager viscoplasticity. Fault roughness promotes the development of self‐healing rupture pulses and a heterogeneous distribution of fault slip at the free surface and at depth. The inelastic deformation, generated by the large dynamic stress near rupture fronts, occurs in a narrow volume around the fault with heterogeneous thickness correlated to local roughness slopes. Inelastic deformation near the free surface, however, is induced by the stress waves originated from dynamic rupture at depth and spreads to large distances (>10 km) away from the fault. The present simulations model seismic wave excitation up to ~10 Hz with rupture lengths of ~100 km, permitting comparisons with empirical studies of ground‐motion intensity measures of engineering interest. Characteristics of site‐averaged synthetic response spectra, including the distance and period dependence of the median values, absolute level, and intra‐event standard deviation, are comparable to appropriate empirical estimates throughout the period range 0.1–3.0 s. This class of model may provide a viable representation of the ground‐motion excitation process over a wide frequency range in a large spatial domain, with potential applications to the numerical prediction of source‐ and path‐specific effects on earthquake ground motion.
Quartz grain boundaries as fluid pathways in metamorphic rocks
Authors: Kruhl Jörn H. , Wirth Richard , Morales Luiz F. G. 
Published: April 2013

AbstractTEM and SEM/FIB sequential imaging of quartz grain boundaries from contact and regional metamorphic rocks show that most of the grain boundaries are open on the nanometer scale. Three types of voids occur. (i) Roughly 40–500 nm wide open zones parallel to the grain boundaries. They are suggested to be caused by general volume reduction as a result of anisotropic cooling contraction at temperatures decreasing below ca. 300°C, the threshold temperature of diffusion in quartz and of decompression expansion at pressures decreasing below several hundred MPa. (ii) Cavities of variable shape and up to micrometer size along the open grain boundaries and (iii) cone‐shaped, nanometer‐sized depressions at sites where dislocation lines meet the open grain boundaries. The latter two types are generated by dissolution–precipitation processes. Open grain boundaries, cavities, and depressions form a connected network of porosity, which allows fluid circulation and may affect physical properties of the rocks. The same process is suggested to occur along grain and phase boundaries in other rocks as exemplified in this study, and it should be expected along intracrystalline cracks or cleavage planes.
Waveform tomography in 2.5D: Parameterization for crooked‐line acquisition geometry
Authors: Smithyman B. R. , Clowes R. M. 
Published: April 2013

AbstractA method for 2.5D viscoacoustic waveform tomography that can be applied to generate 2D models of velocity and attenuation from inversion of refraction waveforms on land seismic reflection data acquired along crooked roads is developed. It is particularly useful for typical crustal reflection surveys. First‐arrival travel time tomography is applied using a 3D method, but with constraints on the intermediate 3D velocity model; the result is the starting model for the next step. A 2.5D frequency‐domain full‐waveform inversion stage parameterizes 3D geometry in the seismic source and receiver arrays, with the assumption that the velocity and attenuation models are homogeneous in the out‐of‐plane direction. This approach results in superior results compared to a strictly 2D approach when the acquisition line is crooked, with a moderate increase in computational cost. A case study using data acquired in the Nechako Basin in south‐central British Columbia, Canada, exemplifies and validates the procedure. The velocity model derived from 2.5D waveform tomography is compared with that from a previous study in which 2D waveform tomography was applied to the same data set and with results from 3D travel time tomography. The resolution and accuracy of the velocity model from 2.5D waveform tomography are demonstrated to be greater than those from travel time or 2D waveform tomography. A model of viscoacoustic attenuation, which was not possible in the 2D case, is also generated. These models are interpreted jointly to highlight features of geological interest, such as a sedimentary basin, basement rocks, and faults, from surface to about 3 km depth.
Modified Jeffery model: Influence of particle concentration on mineral fabric in moderately concentrated suspensions
Authors: Jezek Josef , Schulmann Karel , Paterson Scott 
Published: April 2013

AbstractA modified Jeffery model involving particle interactions allows the simulation of preferred orientation of crystals and the anisotropy of magnetic susceptibility in magmatic flow with up to 40% of rigid particle fraction. Numerical simulations are compared to analogue and natural fabrics. A study of the role of particle concentration shows that the increasing percentage of crystal fraction in dilute suspensions leads to progressive attenuation of the fabric intensity and cyclicity. At high strains in simple shear flow, the lineation converges to a constant value close to the shear plane. With increasing particle concentration, the fabric diverges from the shear direction reflecting the effect of increased crystal tiling. The model can be applied to quantify mineral preferred orientations of crystal mushes in magmatic fabric studies.
3‐D multiobservable probabilistic inversion for the compositional and thermal structure of the lithosphere and upper mantle. I:a prioripetrological information and geophysical observables
Authors: Afonso J. C. , Fullea J. , Griffin W. L. , Yang Y. , Jones A. G. , D. Connolly J. A. , O'Reilly S. Y. 
Published: April 2013

Traditional inversion techniques applied to the problem of characterizing the thermal and compositional structure of the upper mantle are not well suited to deal with the nonlinearity of the problem, the trade‐off between temperature and compositional effects on wave velocities, the nonuniqueness of the compositional space, and the dissimilar sensitivities of physical parameters to temperature and composition. Probabilistic inversions, on the other hand, offer a powerful formalism to cope with all these difficulties, while allowing for an adequate treatment of the intrinsic uncertainties associated with both data and physical theories. This paper presents a detailed analysis of the two most important elements controlling the outputs of probabilistic (Bayesian) inversions for temperature and composition of the Earth's mantle, namely thea prioriinformation on model parameters,ρ(m), and the likelihood function,L(m). The former is mainly controlled by our current understanding of lithosphere and mantle composition, while the latter conveys information on the observed data, their uncertainties, and the physical theories used to relate model parameters to observed data.The benefits of combining specific geophysical datasets (Rayleigh and Love dispersion curves, body wave tomography, magnetotelluric, geothermal, petrological, gravity, elevation, and geoid), and their effects onL(m), are demonstrated by analyzing their individual and combined sensitivities to composition and temperature as well as their observational uncertainties. The dependence of bulk density, electrical conductivity, and seismic velocities to major‐element composition is systematically explored using Monte Carlo simulations. We show that the dominant source of uncertainty in the identification of compositional anomalies within the lithosphere is the intrinsic nonuniqueness in compositional space. A general strategy for definingρ(m) is proposed based on statistical analyses of a large database of natural mantle samples collected from different tectonic settings (xenoliths, abyssal peridotites, ophiolite samples, etc.). This strategy relaxes more typical and restrictive assumptions such as the use of local/limited xenolith data or compositional regionalizations based on age‐composition relations. We demonstrate that the combination of ourρ(m) with aL(m) that exploits the differential sensitivities of specific geophysical observables provides a general and robust inference platform to address the thermochemical structure of the lithosphere and sublithospheric upper mantle. An accompanying paper deals with the integration of these two functions into a general 3‐D multiobservable Bayesian inversion method and its computational implementation.