bluuebunny/crossref_metadata_2025_split huggingface dataset:
Paleomagnetism of the late Cenozoic basalts from northern Patagonia
Authors: Mena Mabel , Ré Guillermo H. , Haller Miguel J. , Singer Silvia E. , Vilas Juan F. 
Published: August 2014

AbstractLate Cenozoic volcanic rocks outcrop in the northern Patagonia Extrandina. Lava flows, characterized as olivine and alkaline basalts, belong to intraplate volcanism. We report paleomagnetic and rock-magnetic studies carried out on Late Cenozoic basalts belonging to the Cráter, Mojón and Moreniyeu Formations. The paleomagnetic sampling comprised 75 sites in lava flows and dikes from the Cráter Formation, three sites in a lava flow from the Mojón Formation and three sites in a lava flow from the Moreniyeu Formation. Alternating field (AF) and thermal detailed demagnetization techniques were used. Most of the samples have a viscous component. The AF procedure was more effective than thermal demagnetization in destroying viscous components and in defining the characteristic remanent magnetizations. Demagnetization curves and rock-magnetic studies suggest that the main remanence carrier is Ti-poor magnetite. Radiometric K-Ar ages were performed on these basalts. The radiometric ages are 0.8±0.1 Ma from outcrops located at Cerro Fermín and 1.9±0.4 Ma from outcrops at Cerro Negro, both at the Cráter Formation. These ages suggest an early-middle Pleistocene age for the lava flows from Cerro Fermín, and a late Pliocene to early Pleistocene age for the Cerro Negro lava flows. Based on the magnetic polarity temporal scale, the Cerro Fermín lava flows have registered the beginning of the Brunhes Chron, while the Cerro Negro basalts could have been extruded during the Olduvai Subchron. The K-Ar radiometric age of the Moreniyeu Formation (1.6±0.2 Ma) suggests an early Pleistocene age for this lava flow. The reverse polarity of its virtual geomagnetic poles (VGPs) is in agreement with the predominant one during the Matuyama Chron and suggests that the Moreniyeu Formation constitutes another volcanic event clearly separate from those of the Cráter Formation. The K-Ar radiometric age of the Mojón Formation (3.3±0.4 Ma) locates it in the middle Pliocene. The VGP polarity would be correlated with some reverse subchron located in Gauss Chron or with the end of the Gilbert Chron. The petrographical and geochemical similarities between the studied basalt and the Somuncura plateau basalts (late Oligocene-early Miocene, located northern and eastern of the study area), together with the time lapsed among between the Mojón and Cráter basalt extrusion suggest the presence in the area of a temporarily extensive thermal anomalies.
Paleomagnetism of the latest Cretaceous-Paleocene intrusive suite of the Mezcala district, southern Mexico
Authors: Molina Garza Roberto S. , Valdivia Luis Alva 
Published: August 2014

AbstractPaleomagnetic data from three plutons of the latest Cretaceous to early Tertiary Mezcala intrusive suite, of the Mezcala mining district in northern Guerrero State, in southern Mexico, are characterized by well-defined near univectorial magnetizations of both normal and reverse polarities. The magnetizations reside primarily in a ferromagnetic cubic phase (magnetite or maghemite) and partly in hematite. Within-site dispersion is relatively small, but between-site dispersion is not. The overall mean for 9 selected sites is of D=318.5° and I=47.1° (k=18.5; α95=12.3°), and is discordant with respect to the reference direction for North America. The discordance may be explained by tilt down-to-the-northeast of the structural block that contains the intrusive suite of about 40° about a NW-SE trending axis, or perhaps more likely and based on additional geological evidence, by a combination of ∼20° of counterclockwise rotation about a vertical axis and a smaller amount of tilt. Vertical-axis-rotation is supported by paleomagnetic data from nearby localities, whereas a small magnitude of tilt is supported by geological field relations. This result is consistent with the hypothesis that Laramide structures of the Guerrero-Morelos platform were reactivated by a younger deformation event, and that there is a deformation event superimposed that involves lateral slip. The contrasting orientation of NW-SE trending structures within the Mezcala mining district affecting the plutons, and N-S trending Laramide structures, suggests that the discordant paleomagnetic directions are best explained by a combination of tilt and rotation.
Relative paleointensity of the geomagnetic field over the last 21,000 years BP from sediment cores, Lake El Trébol (Patagonia, Argentina)
Authors: Gogorza C. S. G. , Irurzun M. A. , Chaparro M. A. E. , Lirio J. M. , Nunez H. , Bercoff P. G. , Sinito A. M. 
Published: August 2014

Abstract
Four cores from Lake El Trébol (Patagonia, Argentina) have been used to estimate regional geomagnetic paleointensity. The rock magnetic studies indicate that the magnetic mineralogy of the clay-rich sediments is dominated by pseudo-single domain magnetite in a range of grain sizes and concentration which are suitable for paleointensity studies. The remanent magnetisation at 20 mT (NRM20 mT) has been normalised using the an-hysteric remanent magnetisation at 20 mT (ARM20 mT), the saturation of the isothermal remanent magnetisation at 20 mT (SIRM20 mT) and the low field magnetic susceptibility (k). Coherence function analysis indicates that the normalised records are free of environmental influences. Our paleointensity (NRM20 mT/ARM20 mT) versus age curve shows good agreement with published record from another lake in Argentina and with records from other parts of the world, suggesting that, in suitable sediments, paleointensity of the geomagnetic field can give a globally coherent, dominantly dipolar signal.
Paleomagnetism of the Pleistocene Tequila Volcanic Field (Western Mexico)
Authors: Ceja Maria Rodríguez , Goguitchaichvili Avto , Calvo-Rathert Manuel , Morales-Contreras Juan , Alva-Valdivia Luis , Elguera José Rosas , Fucugauchi Jaime Urrutia , Granados Hugo Delgado 
Published: August 2014

Abstract
This paper presents new paleomagnetic results from 24 independent cooling units in Tequila area (western Trans-Mexican Volcanic Belt). These units were recently dated by means of state-of-the-art 40Ar-39Ar method (Lewis-Kenedy et al., 2005) and span from 1130 to 150 ka. The characteristic paleodirections are successfully isolated for 20 cooling units. The mean paleodirection, discarding intermediate polarity sites, is I = 29.6°, D = 359.2°, k = 26, α95 = 7.1°, n = 17, which corresponds to the mean paleomagnetic pole position P
lat = 85.8°, Plong = 84.3°, K = 27.5, A95 = 6.9°. These directions are practically undistinguishable from the expected Plestocene paleodirections, as derived from reference poles for the North American polar wander curve and in agreement with previously reported directions from western Trans-Mexican Volcanic Belt. This suggests that no major tectonic deformation occurred in studied area since early-middle Plestocene to present. The paleosecular variation is estimated trough the study of the scatter of virtual geomagnetic poles giving S
F = 15.4 with S
U = 19.9 and S
L = 12.5 (upper and lower limits respectively). These values are consistent with those predicted by the latitude-dependent variation model of McFadden et al. (1991) for the last 5 Myr. The interesting feature of the paleomagnetic record obtained here is the occurrence of an intermediate polarity at 671 ± 13 ka which may correspond the worldwide observed Delta excursion at about 680–690 ka. This gives the volcanic evidence of this event. Two independent lava flows dated as 362 ±13 and 354 ±5 ka respectively, yield transitional paleodirections as well, probably corresponding to the Levantine excursion.
Correlation between paleosol-soil magnetic signal and climate
Authors: Orgeira M. J. , Compagnucci R. H. 
Published: August 2014

Abstract
A comparison of the index of potential water storage (PWS) with the magnetic properties of soils in Russia and of Argentina and China paleosols suggests the existence of one or two climatic thresholds that affect the formation, preservation or depletion of ferrimagnetic minerals. Soils characterized by a positive PWS are wetted during an important part of the year, creating an appropriate environment that favors the depletion of ferrimagnetic minerals due to mainly reductive dissolution. Such soils are characterized by a depletion of detrital ferrimagnetic minerals, as observed in Argentinean soils and paleosols. On the other hand, a negative PWS prevents highly reducing conditions in the soil, and the detrital ferrimagnetic minerals are preserved. The environmental conditions of these soils allow the formation of (superparamagnetic) pedogenic minerals, together with the preservation of lithogenic minerals. These conditions produce a net magnetic enhancement of the soil, as observed in Russia and China. The second threshold in PWS could be at a positive value. Above this second threshold, the water content of the soil during practically the whole year could allow the formation of (superparamagnetic) pedogenic minerals. This threshold could explain differences in the magnetic enhancement or depletion of Argentina soils characterized by a positive PWS.
A geomagnetic total intensity anomaly originated from lightning-induced isothermal remanent magnetization: case of the Yatsugatake Magnetic Observatory, central Japan
Authors: Shimizu Hisayoshi , Koyama Takao , Koyama Shigeru , Utada Hisashi 
Published: August 2014

Abstract
Magnetic total intensity anomaly maps of the Yatsugatake Magnetic Observatory, central Japan, in 1975, 1982 and 2005 are examined. The magnetic environment seems to be stable during this period except for the appearance of an anomalous thin patch-pair in the middle part of the observatory sometime between 1975 and 1982. The peak-to-peak amplitude of the patch-pair is about 80 nT at 2 m above ground level. The magnetization induced by the horizontal electric current in the ground due to the lightning which hit the observatory area in July 1981 is a probable cause for the patch-pair. Modeling confirmed that the characteristics of the patch-pair are well reproduced by model magnetizations that represent lightning-induced isothermal remanent magnetization acquired from horizontal lightning electric current in the ground. The required maximum magnetization to explain the peak-to-peak amplitude of the patch-pair is estimated to be in the range of 10 to 40 A/m.
Micro-tilt changes preceding summit explosions at Semeru volcano, Indonesia
Authors: Nishi Kiyoshi , Hendrasto Muhamad , Mulyana Iyan , Rosadi Umar , Purbawinata Mas Atje 
Published: August 2014

Abstract
A two-axis tiltmeter installed at the summit of Semeru volcano, Indonesia, reveals two different modes of deformation, short-term and longer-term. The short-term variations are inflations precursory to the occurrence of summit explosions. The time intervals between the explosions range from several minutes to several tens of minutes, and the maximum precursory tilt change observed is about 0.1–0.2 μrad. This change in tilt is interpreted to reflect a shallow pressurization source, just beneath the active crater. The longer-term tilt changes are displayed over a period of several days to weeks, and a steady inflation during a period of nearly 2 weeks preceded the occurrence of pyroclastic flows on December 22, 2005. Both short-term and longer-term changes are confined to the radial tilt component, pointing toward the active crater and conduit. To explain both of these tilt changes we propose relatively shallow conduit pressurization, although at somewhat deeper levels in the case of longer-term deformation. The causative mechanisms involve gas exsolution, microlite crystallization, and rheological stiffening, which results in greater flow resistance and dynamic pressure in the upper conduit, thus causing the edifice tilts observed. The gas pore pressure in the magma builds until the threshold required to trigger explosive fragmentation is reached.
Atmospheric stability at 90 km, 78°N, 16°E
Authors: Hall C. M. , Aso T. , Tsutsumi M. 
Published: August 2014

Abstract
We employ observations obtained from a meteor wind radar to derive ambipolar diffusion coefficients, neutral temperatures, temperature gradients and, subsequently, Brunt-Väisälä frequencies at an altitude of 90 km over Svalbard (78°N, 16°E). The derived values showed a good agreement with independent measurements at each step of the analysis. Current atmospheric models are based on sparse data obtained at such high latitude, so these results represent a viable alternative for incorporating in subsequent studies of atmospheric dynamics, particularly if the derived monthly variabilities are included. The Brunt-Väisälä frequencies are then combined with wind shear measurements to estimate horizontally averaged gradient Richardson Numbers (Ri). We find Ri to be consistently larger in summer than winter due to wind shears being similarly larger in winter and augmented by the inverse seasonal variation in Brunt-Väisälä frequency. These seasonal variations result in Ri indicative of dynamic stability in summer and instability in winter. The variabilities in wind shear and Brunt-Väisälä frequency are then included to—albeit more qualitatively—illustrate the distribution between stability and static and dynamic instabilities as a function of season, using a novel portrayal pioneered by Zink and Vincent (J. Geophys. Res., 109, doi:10.1029/2003JD003992, 2004). The resulting picture is discussed in the framework of current conceptions of distribution of turbulent energy dissipation with height and season and of current opinion of the mesopause structure at 78°N.
Change of strain rate and seismicity in the Chubu district, central Japan, associated with a Tokai slow event
Authors: Kobayashi Tomokazu , Hashimoto Manabu 
Published: August 2014

AbstractWe have evaluated temporal variation in strain rates in the Chubu and Kinki districts, central Japan, between 1997 and 2004 using continuous GPS data of GEONET. We found that strain rates throughout the southern part of Chubu district, including the Yoro fault and Nobi fault zone, have significantly deviated from the secular crustal deformation pattern since at least 2001. The results of an inversion procedure show that the strain rate change can be well explained by a slow slip beneath the Tokai area, suggesting that the Tokai slow event has significantly affected the crustal deformation not only in the Tokai area but also in an area located more than 100 km from the main slip area of the event. We also found that the seismicity rate has clearly decreased by approximately 50% around the Yoro fault since the latter half of 2000. The δCFF inferred from our Tokai slow slip model agrees with the observed reduction in seismicity. These results were interpreted as indicating that the seismicity, which has been decreasing for several years, is controlled by the reduction in the shear stressing-rate due to the Tokai slow slip.
An efficient boundary integral equation method applicable to the analysis of non-planar fault dynamics
Authors: Ando Ryosuke , Kame Nobuki , Yamashita Teruo 
Published: August 2014

Abstract
We develop a novel and efficient boundary integral equation method based on the spatio-temporal formulation for the two-dimensional dynamic and quasistatic analyses of an earthquake fault in a single scheme. A major advantage of this method is its applicability to the analysis of non-planar faults with the same degree of accuracy as to that of planar faults. Calculation time and memory requirement are reduced through the employment of asymptotic representations of the integration kernels appearing in the convolution integral. Asymptotic kernels are factorized into terms dependent on space or time alone, resulting in efficient numerical computations. In addition, the dependence on time is found to vanish in the asymptotic kernels far behind the S-wave front, which also contributes to the time-saving efficiency of the calculations. We show that, in a dynamic analysis, if a 3% error is allowed for the slip rate, computation time and memory requirement are reduced by 25% and 45%, respectively, in an in-plane fault case, and by 60% and 75%, respectively, in an anti-plane fault case. This method can be employed as a powerful numerical tool in simulating an entire earthquake cycle consisting of both quasi-static and dynamic processes with a more realistic non-planar geometry of faults.
Development of airglow temperature photometers with cooled-CCD detectors
Authors: Shiokawa K. , Otsuka Y. , Suzuki S. , Katoh T. , Katoh Y. , Satoh M. , Ogawa T. , Takahashi H. , Gobbi D. , Nakamura T. , Williams B. P. , She C.-Y. , Taguchi M. , Shimomai T. 
Published: August 2014

Abstract
We have developed three airglow temperature photometers with cooled-CCD detectors. The photometers measure rotational temperatures using the airglow emissions of OH and O2 near the mesopause region (altitude: 80s-100 km). The photometers also measure six other airglow and auroral lines at wavelengths of 557.7, 630.0, 777.4, 589.3, 427.8, and 486.1 nm. The CCD detectors are used to distinguish the emission lines in these airglow bands, similarly to those used by the Spectral Airglow Temperature Imagers (SATI). In this paper, we describe the configuration of the photometers, their calibration, the data processing to extract rotational temperatures and emission intensities from the measured airglow spectra, as well as the initial deployment at Platteville, Colorado (40.2°N, 255.3°E), when their observations were compared with the concurrent and nearly collocated observations by a sodium lidar. We obtain a good correlation and some systematic difference of temperatures from the photometers and the lidar, and discuss possible causes of the temperature difference.
The first lidar observations of the nighttime sodium layer at low latitudes Gadanki (13.5°N, 79.2°E), India
Authors: Kumar Y. Bhavani , Prasanth P. Vishnu , Rao D. Narayana , Murthy M. Sundara , Krishnaiah M. 
Published: August 2014

Abstract
We report on the first lidar observations of the nighttime mesospheric sodium layer from Gadanki (13.5°N, 79.2°E) site in India. The lidar measurements of upper atmospheric sodium made on 6 nights between the 10 and 16 January 2005 are presented in this paper. The Gadanki lidar uses a Nd:YAG pumped dye laser, tuned to the sodium D2 line (589.0 nm), as a transmitter. Using the system, sodium number density profiles have been obtained with a vertical resolution of 300 m, a time sampling of 120 s. During the initial six nights of observation, the peak sodium concentration is found at a height of 95 km, and the top side scale height is usually about 2 km. On three occasions, a secondary peak was observed at heights between 87 and 92 km. Measurements at Gadanki site indicate that the mean sodium abundances appear to decrease after sunset and increase before sunrise. The average nocturnal columnar abundances were in the range 2–8.9 × 109 cm2. The nightly mean centroid heights range between 92.9 and 95.2 km and the rms widths vary between 4.3 and 4.9 km. On some nights, wave like structures in the sodium layer were observed with wavelength of about 3 km and downward phase velocities of about 1 km/hr. Four sporadic layers were observed during the initial 54 h of observation. The formation and decay of an intense sporadic sodium layer was observed on the night of 11 January 2005. The layer was found to develop between 93 and 90 km altitude and appear between 0230 and 0430 LT.
Electrical conductivity measurements of brucite under crustal pressure and temperature conditions
Authors: Fuji-ta Kiyoshi , Katsura Tomoo , Matsuzaki Takuya , Ichiki Masahiro 
Published: August 2014

Abstract
Hydrous minerals are crucial because their occurrence is associated with seismic activity through the dehydration process that occurs in the earth’s crust and/or mantle. We have developed a technique to observe the dehydration reaction of brucite using electrical conductivity variation under sealed conditions. The electrical conductivity of brucite was measured as a function of temperature. The confining pressure for the measurements was 1 GPa, which represents that of the lower crust. Two types of remarkable electrical conductivity variation were observed. During the first heating, the conductivity of the sample showed a linear variation below 700 K, as was expected from the Arrhenius equation. Once the temperature was increased to near the dehydration boundary, the sample showed a high conductivity. Even though only a small amount of H2O was formed after dehydration, bulk conductivity of the sample varied greatly, presumably caused by a combination of the presence of coexisting solid and fluid phases and a mixed electronic and ionic conduction mechanism operating in the sample.
Testing the GAD throughout geological time
Authors: Evans M. E. , Hoye G. S. 
Published: August 2014

Abstract
The suggestion that the morphology of the geomagnetic field can be tested by inspecting the statistical distribution of palaeomagnetically-determined inclination angles has been challenged on the grounds that typical plate velocities require extremely long sampling intervals—perhaps exceeding the age of the Earth—in order to adequately sample the Earth’s surface. Here, we investigate this problem by means of a random walk model and conclude that an interval equivalent to Phanerozoic time (600 Myr) is generally sufficient.
Effects of the site distribution and the prior information on the inverted geomagnetic field model: a case study applying the ABIC method to the synthetic datasets
Authors: Hatakeyama Tadahiro 
Published: August 2014

Abstract
When we use stochastic inversion and Bayesian modelling in order to obtain geomagnetic field models from paleomagnetic data, there are two major factors controlling the solution: determination of the hyperparameter and the type of the smoothing constraint on the model. To investigate contributions of the factors, we calculated some patterns of inversions from synthetic datasets from ideal and real site distributions. The ABIC (Akaike’s Bayesian Information Criteria) minimization method was used to determine the hyperparameter, and then the relationship between the hyperparameter and the ABIC index was demonstrated. Using results of an inversion of synthetic datasets with errors, the most suitable hyperparameters were found for each site distribution, and the good and stable solutions were obtained. However, when number of the sites is few or coverage of the site distribution is not uniform, it is found that the solution is not clearly determined. Moreover, it seems that the solution does not significantly depend on the type of the model constraint.