bluuebunny/crossref_metadata_2025_split huggingface dataset:
Linear scaling and periodicity on the measures of global and local scale complexities of total electron content dynamics
Authors: Kumar C. V. Anil , Eapen Suja 
Published: April 2013

AbstractIn this paper, we compare the local and global dynamics of total electron content (TEC) by analyzing Lyapunov exponents and correlation dimensions. The internal structure of the underlying system is studied using TEC data from the solar minimum years 2007–2008. The mutual information, false nearest neighbors, and space‐time separation of both local and global snapshots are estimated and analyzed. It indicates that although the internal dynamics changes with season, the pattern of variation over the seasons remains identical for both the years, suggesting that the characteristics of these changes might be predictable. We report the evidence of a linear scaling with slope 0.00187 and a periodicity with period of 1 year on measures of global and local scale complexities of TEC dynamics. This behavior appears to be a universal phenomenon unaffected by change of cycles and amount of information influencing the complexity, since they are almost constant over the 2 years. The global Lyapunov exponent increases linearly over a year, whereas the local Lyapunov exponent increases up to the middle of the year, attains greatest local complexity, and then decreases. This suggests that local prediction is more reliable than the global one. The estimated invariants characterize the complex dynamics as it evolve from local time to global time and also provide information to the system's heterogeneity. The features such as presence of multiple attractors, linear scaling, and nearly regular seasonal periodicity may have practical consequences and could yield insights into the internal dynamics of TEC and the modeling of its variations.
Equatorial ionospheric electrodynamic perturbations during Southern Hemisphere stratospheric warming events
Authors: Olson M. E. , Fejer B. G. , Stolle C. , Lühr H. , Chau J. L. 
Published: April 2013

AbstractWe use ground‐based and satellite measurements to examine, for the first time, the characteristics of equatorial electrodynamic perturbations measured during the 2002 major and 2010 minor Southern Hemisphere sudden stratospheric warming (SSW) events. Our data suggest the occurrence of enhanced quasi 2 day fluctuations during the 2002 early autumnal equinoctial warming. They also show a moderately large multi‐day perturbation pattern, resembling those during arctic SSW events, during 2002 late equinox, as the major SSW was weakening. We also compare these data with extensive recent results that showed the fundamentally important role of lunar semidiurnal tidal effects on low latitude electrodynamic perturbations during arctic SSW events.
Empirical relationship between electron precipitation and far‐ultraviolet auroral emissions from DMSP observations
Authors: Sotirelis Thomas , Korth Haje , Hsieh Syau‐Yun , Zhang Yongliang , Morrison Daniel , Paxton Larry 
Published: April 2013

AbstractAuroral emissions observed in the far‐ultraviolet wavelength range are compared with measurements of the coincident precipitating electrons and ions that produce the emissions in a large‐scale correlative study. The auroral emissions and particle precipitation are observed with the Special Sensor Ultraviolet Spectrographic Imager and SSJ5 detectors, respectively, both onboard the DMSP F16 satellite. Coincident observations along the same magnetic field line in the Northern Hemisphere are assembled from two consecutive winters (during 2005–2007). A numerical fit to 27,922 coincident observations provides an empirical relationship between the electron energy flux and the intensity of Lyman‐Birge‐Hopfield long emissions, JEe = 4.90 ⋅108 (eV s–1 sr–1 cm–2)/R ILBHL (valid in the absence of significant ion fluxes: JEe > 10 JEion). A fit to 1308 coincident observations provides the relationship between the average electron energy and the Lyman‐Birge‐Hopfield short to Lyman‐Birge‐Hopfield long emission ratio, <Ee > = 19.6 keV exp(–2.34 ILBHS / ILBHL) (valid from 3 to 19.6 keV). These resulting empirical relationships permit the energy flux and average energy of precipitating electrons to be inferred from far‐ultraviolet imagery, in the absence of significant ion precipitation.
The ionospheric Sq current system obtained by spherical harmonic analysis
Authors: Stening R. J. , Winch D. E. 
Published: April 2013

AbstractAn earlier comprehensive analysis of geomagnetic tides by Winch is revisited to display changes in the current systems with season and longitude. The data used come from the quiet Sun years 1964–1965. We choose to present some total equivalent current systems, being the sum of the external and internal parts derived in the spherical harmonic analysis. The latitudes and local times of the current system foci are generally in agreement with other workers. The amplitudes of the current system vortices follow an annual variation with maximum in summer. The longitude variations of the vortex amplitudes vary as the inverse of the magnetic field strength at both equinoxes but have different variations at the solstices. Other longitude maxima which have been reported in the equatorial electrojet intensity were not found. We examine in detail the “invasions” of the summer current systems across the equator, identifying these as signatures of field‐aligned currents (FACs). The tilting of current contours with respect to the equator is interpreted as being due to midday FACs. As others have found, the identification of afternoon FACs is more difficult. The seasonal swap‐over of FAC directions occurs not in September but in October–November.
Statistical comparison of isolated and non‐isolated auroral substorms
Authors: Liou Kan , Newell Patrick T. , Zhang Yong‐Liang , Paxton Larry J. 
Published: April 2013

AbstractThe present study compares isolated and non‐isolated substorms in terms of their global morphology and energy deposition. The analysis is based on a list of geomagnetic substorm onsets identified with magnetometer data from SuperMAG and published previously by Newell and Gjerlove (2011a). Isolated substorms are defined as those with separation of two consecutive onsets no less than 3 h. The auroral data are obtained from the global ultraviolet imager (GUVI) on board the TIMED satellite and are rebinned into typical magnetic latitude‐magnetic local time maps. The auroral maps are then averaged in 1 min intervals to show the dynamic change of the aurora. The three phases of the substorm are clearly demonstrated in both isolated and non‐isolated substorms. However, there are noticeable differences between the two types of substorms: (1) While the nighttime auroral power for both types of substorms slightly increases in the growth phase, isolated (non‐isolated) substorms are associated with smaller (greater) nighttime auroral power. (2) In the expansion phase, isolated substorms are associated with greater and more explosive energy release than non‐isolated substorms. (3) The time for the recovery phase is ~2 times longer for isolated than for non‐isolated substorms. (4) The winter‐to‐summer auroral power ratio is approximately constant throughout the three substorm phases and the ratio is larger for isolated (~30%) than that for non‐isolated (~10%) substorms. It is also found that the polar cap area increases during the growth phase until ~10 min prior to the magnetic substorm onset and decreases rapidly thereafter. The decrease is found to result from the closure of the nightside polar cap associated with substorm expansion. It is found that the observed differences between the two types of substorms simply reflect the differences in the solar wind and EUV drivers. Thus, we conclude that there is no intrinsic difference between isolated and non‐isolated substorms in terms of auroral energy release and subsequent auroral power decay.
Response of the equatorial and low‐latitude ionosphere to an intense X‐class solar flare (X7/2B) as observed on 09 August 2011
Authors: Sripathi S. , Balachandran N. , Veenadhari B. , Singh R. , Emperumal K. 
Published: April 2013

AbstractIn this paper, we present response of equatorial and low‐latitude ionosphere to an intense solar flare of class X7/2B that peaked at 08:05 UT on 09 August 2011 in the solar cycle 24. Global positioning system total electron content (TEC) observations in the sunlit hemisphere show enhancement of ~3 TEC units, while geomagnetic H component observations indicate sudden decrease and increase in their strength at equatorial and low‐latitude stations, respectively, at several stations in the sunlit hemisphere. In addition, equatorial electrojet strength over Indian region reveals commencement of counter electrojet. Simultaneous Canadian Advanced Digital Ionosonde observations at Tirunelveli, an equatorial station in India, show the disappearance of ionogram echoes during the flare event indicating absorption of radio signals in the D region. Strong equatorial blanketing type Es layer was observed in the ionogram records at Tirunelveli prior to the occurrence of the solar flare that continued for several hours though it became weak/absent during the flare event. Ionogram records on the control day show regular F layer movement without any blanketing type Es layer. Very low frequency (VLF) observations at Allahabad, an Indian low‐latitude station, show enhanced VLF amplitude signal during the same time revealing the sudden enhancement of D region ionization. Using the observations presented here, an attempt has been made to study the impact of the solar flares on the electrodynamics of the equatorial and low‐latitude ionosphere.
Sporadic E layer development and disruption at low latitudes by prompt penetration electric fields during magnetic storms
Authors: Abdu M. A. , Souza J. R. , Batista I. S. , Fejer B. G. , Sobral J. H. A. 
Published: April 2013

AbstractAn investigation of low‐latitude sporadic E layers during magnetic storms shows that the formation and disruption of these layers are strongly controlled by the magnetospheric electric fields that penetrate to equatorial ionosphere. It is observed that a prompt penetration electric field (PPEF) of westward polarity that dominates the nightside ionosphere can cause formation of sporadic E layers near 100 km, while a PPEF of eastward polarity that dominates the dayside and eveningside can lead to disruption of an Es layer in progress. It is shown that a vertical Hall electric field, induced by the primary zonal PPEF, in the presence of the storm‐associated enhanced conductivity of the night E layer, can be responsible for vertical ion velocity convergence sufficient to influence the Es layer formation. A downward polarity of the Hall electric field leads to Es layer formation, while an upward polarity causes the Es layer disruption. An interplay of magnetic storm associated prompt penetration electric field and energetic particle precipitation is evident in the observed Es layer response features in the region of the South Atlantic/American magnetic anomaly reported here.
Origins of oblique‐slip faulting during caldera subsidence
Authors: Holohan Eoghan P. , Walter Thomas R. , Schöpfer Martin P.J. , Walsh John J. , van Wyk de Vries Benjamin , Troll Valentin R. 
Published: April 2013

AbstractAlthough conventionally described as purely dip‐slip, faults at caldera volcanoes may have a strike‐slip displacement component. Examples occur in the calderas of Olympus Mons (Mars), Miyakejima (Japan), and Dolomieu (La Reunion). To investigate this phenomenon, we use numerical and analog simulations of caldera subsidence caused by magma reservoir deflation. The numerical models constrain mechanical causes of oblique‐slip faulting from the three‐dimensional stress field in the initial elastic phase of subsidence. The analog experiments directly characterize the development of oblique‐slip faulting, especially in the later, non‐elastic phases of subsidence. The combined results of both approaches can account for the orientation, mode, and location of oblique‐slip faulting at natural calderas. Kinematically, oblique‐slip faulting originates to resolve the following: (1) horizontal components of displacement that are directed radially toward the caldera center and (2) horizontal translation arising from off‐centered or “asymmetric” subsidence. We informally call these two origins the “camera iris” and “sliding trapdoor” effects, respectively. Our findings emphasize the fundamentally three‐dimensional nature of deformation during caldera subsidence. They hence provide an improved basis for analyzing structural, geodetic, and geophysical data from calderas, as well as analogous systems, such as mines and producing hydrocarbon reservoirs.
Heterogeneous rupture in the great Cascadia earthquake of 1700 inferred from coastal subsidence estimates
Authors: Wang Pei‐Ling , Engelhart Simon E. , Wang Kelin , Hawkes Andrea D. , Horton Benjamin P. , Nelson Alan R. , Witter Robert C. 
Published: April 2013

AbstractPast earthquake rupture models used to explain paleoseismic estimates of coastal subsidence during the great A.D. 1700 Cascadia earthquake have assumed a uniform slip distribution along the megathrust. Here we infer heterogeneous slip for the Cascadia margin in A.D. 1700 that is analogous to slip distributions during instrumentally recorded great subduction earthquakes worldwide. The assumption of uniform distribution in previous rupture models was due partly to the large uncertainties of then available paleoseismic data used to constrain the models. In this work, we use more precise estimates of subsidence in 1700 from detailed tidal microfossil studies. We develop a 3‐D elastic dislocation model that allows the slip to vary both along strike and in the dip direction. Despite uncertainties in the updip and downdip slip extensions, the more precise subsidence estimates are best explained by a model with along‐strike slip heterogeneity, with multiple patches of high‐moment release separated by areas of low‐moment release. For example, in A.D. 1700, there was very little slip near Alsea Bay, Oregon (~44.4°N), an area that coincides with a segment boundary previously suggested on the basis of gravity anomalies. A probable subducting seamount in this area may be responsible for impeding rupture during great earthquakes. Our results highlight the need for more precise, high‐quality estimates of subsidence or uplift during prehistoric earthquakes from the coasts of southern British Columbia, northern Washington (north of 47°N), southernmost Oregon, and northern California (south of 43°N), where slip distributions of prehistoric earthquakes are poorly constrained.
Numerical investigation of the interplay between wall geometry and friction in granular fault gouge
Authors: Rathbun Andrew P. , Renard François , Abe Steffen 
Published: April 2013

AbstractThe influence of surface roughness is central in understanding the behavior of various types of shear zones including faults, landslides, and deformation in glacial till. All of these systems contain a non‐planar rough wall, which interacts with either a gouge zone or another wall. We use the 3‐D discrete element method (DEM) to investigate both the effect of boundary roughness and friction. Granular non‐cohesive gouge is sandwiched between rough walls with large grooves, or smooth walls composed of spherical particles that can be adjusted to control roughness. Roughness and gouge properties are scaled to laboratory friction experiments. We vary friction between the particles and the wall and monitor shear strength, height, coordination number, distribution, and orientation of particle forces, localization, and porosity distribution in the shear zone. We find that, on the first‐order, strength is controlled by particle‐particle friction and mechanical coupling of the fault zone wall to the gouge. Rough boundaries (RMS roughness > grain radius) force more shear within the gouge zone, dilating the layer and sliding more grains, which leads to large stress necessary to shear the layer. When large amplitude roughness is removed, and roughness is at the grain‐scale, the coupling, and thus the strength, is controlled by both wall and particle friction as well as fine‐scale boundary roughness. These differences are reflected in profiles of shear within the gouge zone and offset at the boundary in smooth models. From our simulations, we quantify how and why rough natural faults will have a higher overall strength.
Imaging the shallow crust with local and regional earthquake tomography
Authors: Biryol Cemal B. , Leahy Garrett M. , Zandt George , Beck Susan L. 
Published: April 2013

AbstractWhile active‐source imaging (seismic reflection, refraction) is typically used to image the shallow crust, these techniques tend to suffer from energy penetration problems in complex tectonic regimes, resulting in poor imaging. Further, active sources (such as air guns or vibroseis) tend to be band limited, resulting in poor signal‐to‐noise ratio at low frequencies (1–10 Hz). Recent studies suggest that earthquake data may be able to solve these imaging problems. However, conventional earthquake tomography typically aims to image the upper mantle and lithosphere, where typical station spacing (tens of km) and array aperture (hundreds of km) have resulted in the maximum resolution. In this study, we take advantage of the small‐scale and 250 m station spacing of the LaBarge Passive Seismic Experiment to determine whether local and regional earthquake tomographies can be used to constrain structure in the top 5 km of the crust. We also study how the inclusion of finite‐frequency effects impacts the final images. Our results indicate that local and regional events provide substantial improvements over teleseismic events alone, with approximately 500 m resolution both vertically and laterally in the upper most 5 km. We also find that inclusion of finite‐frequency data between 1 and 10 Hz plays a key role in maintaining resolution in the shallowest portion of the model.
Ages and relative sizes of pre‐2004 tsunamis in the Bay of Bengal inferred from geologic evidence in the Andaman and Nicobar Islands
Authors: Rajendran C. P. , Rajendran Kusala , Andrade Vanessa , Srinivasalu S. 
Published: April 2013

AbstractGeologic evidence along the northern part of the 2004 Aceh‐Andaman rupture suggests that this region generated as many as five tsunamis in the prior 2000 years. We identify this evidence by drawing analogy with geologic records of land‐level change and the tsunami in 2004 from the Andaman and Nicobar Islands (A&N). These analogs include subsided mangrove swamps, uplifted coral terraces, liquefaction, and organic soils coated by sand and coral rubble. The pre‐2004 evidence varies in potency, and materials dated provide limiting ages on inferred tsunamis. The earliest tsunamis occurred between the second and sixth centuries A.D., evidenced by coral debris of the southern Car Nicobar Island. A subsequent tsunami, probably in the range A.D. 770–1040, is inferred from deposits both in A&N and on the Indian subcontinent. It is the strongest candidate for a 2004‐caliber earthquake in the past 2000 years. A&N also contain tsunami deposits from A.D. 1250 to 1450 that probably match those previously reported from Sumatra and Thailand, and which likely date to the 1390s or 1450s if correlated with well‐dated coral uplift offshore Sumatra. Thus, age data from A&N suggest that within the uncertainties in estimating relative sizes of paleo‐earthquakes and tsunamis, the 1000 year interval can be divided in half by the earthquake or earthquakes of A.D. 1250–1450 of magnitude >8.0 and consequent tsunamis. Unlike the transoceanic tsunamis generated by full or partial rupture of the subduction interface, the A&N geology further provides evidence for the smaller‐sized historical tsunamis of 1762 and 1881, which may have been damaging locally.
Chemical controls on fault behavior: Weakening of serpentinite sheared against quartz‐bearing rocks and its significance for fault creep in the San Andreas system
Authors: Moore Diane E. , Lockner David A. 
Published: April 2013

AbstractThe serpentinized ultramafic rocks found in many plate‐tectonic settings commonly are juxtaposed against crustal rocks along faults, and the chemical contrast between the rock types potentially could influence the mechanical behavior of such faults. To investigate this possibility, we conducted triaxial experiments under hydrothermal conditions (200–350°C), shearing serpentinite gouge between forcing blocks of granite or quartzite. In an ultramafic chemical environment, the coefficient of friction, μ, of lizardite and antigorite serpentinite is 0.5–0.6, and μ increases with increasing temperature over the tested range. However, when either lizardite or antigorite serpentinite is sheared against granite or quartzite, strength is reduced to μ ~ 0.3, with the greatest strength reductions at the highest temperatures (temperature weakening) and slowest shearing rates (velocity strengthening). The weakening is attributed to a solution‐transfer process that is promoted by the enhanced solubility of serpentine in pore fluids whose chemistry has been modified by interaction with the quartzose wall rocks. The operation of this process will promote aseismic slip (creep) along serpentinite‐bearing crustal faults at otherwise seismogenic depths. During short‐term experiments, serpentine minerals reprecipitate in low‐stress areas, whereas in longer experiments, new Mg‐rich phyllosilicates crystallize in response to metasomatic exchanges across the serpentinite‐crustal rock contact. Long‐term shear of serpentinite against crustal rocks will cause the metasomatic mineral assemblages, which may include extremely weak minerals such as saponite or talc, to play an increasingly important role in the mechanical behavior of the fault. Our results may explain the distribution of creep on faults in the San Andreas system.
Precise relative earthquake location using surface waves
Authors: Michael Cleveland K. , Ammon Charles J. 
Published: April 2013

AbstractEarthquake locations provide a fundamental tool for seismological investigations. While dense seismic networks can provide robust locations, accuracy and precision of these locations suffer outside dense networks. This is particularly true in offshore areas, where location analysis relies heavily on distant seismic observations. We present a method for estimating precise relative seismic source epicentroid locations using surface waves. Several reasons, including lower velocities and strength of the signal at distance, make use of surface waves for event location appealing. We focus on the Panama Fracture Zone region and relocate 81 strike‐slip earthquakes to produce tectonically consistent epicentroid locations. The resulting pattern of earthquakes more clearly delineates recently active regional structures than original body‐wave locations. The mean shift between the US Geological Survey National Earthquake Information Center epicenter and our epicentroids is about 14 km (the median is about 11 km), and typical origin time changes are generally less than ±2 s. We find that north of 6.5°N, the plate boundary motion is split across two roughly north‐south striking structures, the Panama and Balboa Fracture zones. For the last 36 years, slip along these two structures roughly matches slip along the Panama Fracture Zone to the south (from 4.5°N to 6.25°N), but the Balboa Fracture zone has roughly three times the moment than the northern Panama Fracture Zone. Our analyses show that observed Rayleigh‐wave signal‐to‐noise ratios for moderate‐to‐large shallow earthquakes are suitable for applying the procedure and that Rayleigh‐wave observations form a self‐consistent set of constraints on the relative location of earthquake centroids.