bluuebunny/crossref_metadata_2025 huggingface dataset:
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

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

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

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

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

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.
Environmental magnetic record and paleosecular variation data for the last 40 kyrs from the Lake Biwa sediments, Central Japan
Authors: Hayashida Akira , Ali Mohammed , Kuniko Yoshiki , Kitagawa Hiroyuki , Torii Masayuki , Takemura Keiji
Published: August 2014

We have conducted paleomagnetic and environmental magnetic analysis of a sediment piston core recovered from Lake Biwa, central Japan. Tephrochronology and AMS radiocarbon dating showed that this core covers the time period since about 40 kyr BP. The variation of paleomagnetic direction shows a good agreement with the PSV record for the last 10 kyrs from the deeper water site (BIWA SV-3; Ali et al., 1999), although the amplitudes are subdued probably due to the relatively lower accumulation rate at the shallower site. Inclination lows of the pre-Holocene interval are correlated to PSV records reported from the marine sediments off Shikoku and in the Japan Sea. In addition, the variation of magnetic mineral concentration reflects environmental changes during the last glacial period. It is suggested that the flux of fine-grained magnetite, probably associated with greater precipitation, was increased during interstadial periods. The variation of anhysteretic remanent magnetization is likely correlated to the Dansgaard-Oeschger (D-O) cycles recorded in Greenland ice cores. An apparent swing of the PSV curve is recognized at about 27 ka, but evidence for the Mono Lake excursion at 32 ka around the D-O events 6 and 7 is unclear. Combination of the detailed paleomagnetic record and the sub-Milankovitch climate cycles thus provides better resolution for understanding geomagnetic secular variation and polarity excursions in space and time.
Impact process of boulders on the surface of asteroid 25143 Itokawa—fragments from collisional disruption
Authors: Nakamura A. M. , Michikami T. , Hirata N. , Fujiwara A. , Nakamura R. , Ishiguro M. , Miyamoto H. , Demura H. , Hiraoka K. , Honda T. , Honda C. , Saito J. , Hashimoto T. , Kubota T.
Published: August 2014

The subkilometer-size asteroid 25143 Itokawa is considered to have a gravitationally bounded rubble-pile structure. Boulders appearing in high-resolution images retrieved by the Hayabusa mission revealed the genuine outcome of the collisional event involving the asteroid’s parent body. Here we report that the boulders’ shapes and structures are strikingly similar to laboratory rock impact fragments despite differences of orders of magnitude in scale and complexities of the physical processes. These similarities suggest the universal character of the process throughout the range of these scales, and the brittle and structurally continuous nature regarding the parent body of the boulders. The similarity was likely preserved because of relatively lesser comminuting processes acting on individual boulders; the close assemblages of similar appearing boulders (a boulder family) represent the impact destruction of boulders on the surface.
Gravity anomalies and the geologic block structures in and around the aftershock area of the 2007 Noto Hanto Earthquake
Authors: Honda Ryo , Hiramatsu Yoshihiro , Kono Yoshiteru , Katagawa Hideki
Published: August 2014

The 2007 Noto Hanto Earthquake occurred on 25 March. We have constructed a detailed gravity anomaly map over the Noto peninsula. Four block boundaries which are identified by morphological/geological studies are also recognized on the gravity anomaly map. Various other observations indicate that the mainshock ruptured only one of the blocks, the Kuwatsuka block, although aftershocks are distributed over two blocks, the Kuwatsuka and the Saruyama blocks. The Bouguer anomalies over the Kuwatsuka block are relatively high compared to those of the Saruyama block, i.e. the basement depth of the Kuwatsuka block is shallower than that of the Saruyama block. This difference in the basement depth is consistent with the deformation pattern observed by SAR interferometry. At the block boundary, an offset is recognized in the aftershock distribution. Based on the relationships among the gravity anomalies, the geologic structures, the aftershock distribution and the source fault, we propose that the rupture size of the earthquake was constrained by the block structure in this region.
Magnetotelluric observations around the focal region of the 2007 Noto Hanto Earthquake (Mj 6.9), Central Japan
Authors: Yoshimura Ryokei , Oshiman Naoto , Uyeshima Makoto , Ogawa Yasuo , Mishina Masaaki , Toh Hiroaki , Sakanaka Shin’ya , Ichihara Hiroshi , Shiozaki Ichiro , Ogawa Tsutomu , Miura Tsutomu , Koyama Shigeru , Fujita Yasuyoshi , Nishimura Kazuhiro , Takagi Yu , Imai Mikihiro , Honda Ryo , Yabe Sei , Nagaoka Shintaro , Tada Mitsuhiro , Mogi Toru
Published: August 2014

On 25 March 2007, a damaging earthquake (M
j 6.9) occurred near the west coast of the Noto Peninsula, Central Japan. A wideband magnetotelluric (MT) survey was carried out in the onshore area of the source region immediately after the mainshock, with the aim of imaging the heterogeneity of the crustal resistivity structure. The final observation network had consisted of 26 sites. As a preparatory step for imaging three-dimensional features of the resistivity around the focal region, we constructed two-dimensional resistivity models along five profiles using only the TM mode responses, in order to reduce three-dimensional effects. Four profiles are perpendicular to the fault strike, and a fifth profile is parallel to the strike through the mainshock epicenter. Significant characteristics of the resistivity models are: (1) beneath the mainshock hypocenter, there is a conductive body which spreads to the eastern edge of the active aftershock region; (2) a resistive zone is located in the gap of the aftershock distribution between the mainshock hypocenter and the largest eastern aftershock; (3) one of the largest aftershock occurred at the boundary of the resistive zone described above. These results suggest that the deep conductors represent fluid-filled zones and that the lateral heterogeneity could have controlled the slip distribution on the fault plane.
Numerical simulation of the tsunami generated by the 2007 Noto Hanto Earthquake and implications for unusual tidal surges observed in Toyama Bay
Authors: Abe Ikuo , Goto Kazuhisa , Imamura Fumihiko , Shimizu Katsuyoshi
Published: August 2014

We conducted a numerical analysis of the tsunami generated by the 2007 Noto Hanto Earthquake (Mj= 6.9) that occurred on 25 March 2007 near the Noto Peninsula on the northwest coast of Honshu Island, Japan. Our numerical simulation reproduced well the behaviors of the tsunami as recorded at the Wajima tidal observatory and showed that the computed tsunami arrived in Toyama Bay more than 1 h after the earthquake. However, a crew of a small boat in the bay felt the shock and, despite calm weather conditions, their boat capsized just 3 min after the earthquake. Although abnormal tidal surges were recorded at several locations around Toyama Bay, the timing of these is inconsistent with the surges being a direct result of the tsunami generated at the source area of the earthquake. We used “backward wave propagation analysis” to estimate the likely source area of the abnormal tidal surges in the bay and carried out the a simulation of landslide-induced tsunami. Our conclusion is that these abnormal tidal surges were likely caused by a submarine landslide on the steep sea floor on the western side of Toyama Bay.
Comparison of early aftershock sequences for the 2004 Mid-Niigata and 2007 Noto Hanto earthquakes in central Japan
Authors: Mori Jim , Kano Yasuyuki , Enescu Bogdan
Published: August 2014

We examined continuously recorded seismograms of the 2004 Mid-Niigata and 2007 Noto Hanto earthquakes to compare the early aftershocks for these two similar earthquakes in central Japan. Although the two mainshocks had similar size, depth, and focal mechanisms, the aftershock levels were quite different, with the Niigata case being much stronger. The results of our analyses show that the early aftershock occurrences for the two events were quite similar for the first several minutes. About 7 minutes after the Niigata mainshock, significantly enhanced aftershock triggering began and continued for the duration of that aftershock sequence. We speculate that the change that occurred in the Niigata region may be due to fluid effects in the fault zone.
Shear-driven kinetic Alfven wave in the plasma sheet boundary layer
Authors: Tiwari B. V. , Mishra R. , Varma P. , Tiwari M. S.
Published: August 2014

Shear-driven kinetic Alfven waves (KAWs) at the plasma sheet boundary layer (PSBL) were investigated for substorm events in the presence of a parallel electric field using the general loss-cone distribution function. Using a kinetic approach, we derived the expressions for dispersion relation and growth length of the KAW in the presence of the parallel electric field using the general loss-cone distribution function for both, weak and strong shear regimes. The frequency of the KAW obtained is in agreement with observed values of 0.1–4 Hz in the PSBL. The results explain the generation of the energetic KAWs at the PSBL by the shear at substorm onset. The parallel electric field associated with the energetic KAWs at substorm onset may heat the field-aligned electrons, leading to parallel electron energisation that ultimately causes an intense aurora. The electric field along magnetic field lines enhances the frequency of KAW but decreases the growth length in the case of weak shear. We also found that the parallel electric field can reflect KAW towards the PSBL. The loss-cone distribution index changes the profiles of frequency and growth length plots of the shear-driven KAW. Hence, the loss-cone distribution function is an important factor in the excitation of KAW in the active region of the magnetosphere, such as the PSBL and the auroral acceleration region.
Analytic model of upper tropospheric clouds in the tropical Hadley cell
Authors: Tanaka Kyoko K. , Yamamoto Tetsuo , Watanabe Sei-ichiro , Nakajima Kensuke
Published: August 2014

We have developed a two-dimensional analytic model that describes the behavior of upper tropospheric clouds in the tropical Hadley cell. The behavior of the model is characterized by two dimensionless parameters: one is proportional to the temperature lapse rate, and the other is relevant to the initial altitude of the cloud particles. We derived analytic expressions for the motion and evaporation of the cloud particles and calculate various cloud properties, such as the cloudiness and the column water content. We found that the outflow from the convective regions spreads out and generates a cirrus layer whose coverage has a maximum at the tropopause: the cloudiness is as large as 0.5–1 in the vicinity of the tropopause for small cloud particles with radii of less than 5 μm. We suggest that the thin cirrus clouds observed near the tropopause in the tropic region are formed by the advection of cloud particles supplied from the ITCZ. Because of its simpleness, the present model may play a role in diagnosing cloud properties in climate models that are used to study climate changes over a long time span.
Instrumentation and performance evaluation of the XRS on SELENE orbiter
Authors: Shirai K. , Okada T. , Yamamoto Y. , Arai T. , Ogawa K. , Shiraishi H. , Iwasaki M. , Arakawa M. , Grande M. , Kato M.
Published: August 2014

The x-ray fluorescence spectrometer (XRS) on board Japanese lunar polar orbiter SELENE (Kaguya) will provide global distribution of major elemental composition on the lunar surface in energy range of characteristic K-α x-ray line emission for Mg, Al, Si, Ca, Ti, and Fe. These measurements will contribute to research of lunar origin and its evolution. The XRS shows a good energy resolution within 200 eV at 5.9 keV relying on charge coupled device (CCD) as photon energy dispersive detector. Total collective area of 100 cm2 for main detector facing the lunar surface is composed of 16 CCD chips. Instrumentation of the XRS and its performance evaluated in laboratory are presented.
Ground calibration of the high-sensitivity SELENE lunar magnetometer LMAG
Authors: Shimizu Hisayoshi , Takahashi Futoshi , Horii Naoki , Matsuoka Ayako , Matsushima Masaki , Shibuya Hidetoshi , Tsunakawa Hideo
Published: August 2014

Ground calibration experiments of the SELENE high sensitivity fluxgate Lunar Magnetometer (LMAG) have been performed in order to determine the alignment, sensitivity, and offset of the sensors (MGF-S). It is checked out that the sensors are orthogonal to each other within 0.4 degrees, and the linearity of the ambient magnetic field and the output from the sensors are confirmed. Also, the temperature dependences of the offset and sensitivity are examined but no clear signatures of temperature dependencies can be seen. SELENE has an in-flight calibration system in order to determine the direction of the magnetometer routinely. The magnetic fields generated by the sensor alignment monitor coil (SAM-C) system are used for the in-flight calibration. The magnetic field distributions generated by SAM-C are determined and the accuracy of determination of the magnetometer position and direction is estimated. Multiple measurements will allow us to determine the direction of MGF-S with about 0.1-degree accuracy. Appropriate corrections from the results of the ground and in-flight calibrations will allow us to recover the magnetic field near the moon with accuracy about 0.1 nT.
A new model of lunar crust: asymmetry in crustal composition and evolution
Authors: Arai Tomoko , Takeda Hiroshi , Yamaguchi Akira , Ohtake Makiko
Published: August 2014

Earlier models of lunar crustal formation as a simple flotation of ferroan anorthosites (FAN) do not account for the diverse crustal composition revealed by feldspathic lunar meteorites and granulites in the Apollo samples. Based on the integrated results of recent studies of lunar meteorites and global chemical and mineralogical maps, we propose a novel asymmetric crust model with a ferroan, noritic, nearside crust and a magnesian, troctolitic farside crust. Asymmetric crystallization of a primordial magma ocean can be one possibility to produce a crust with an asymmetric composition. A post-magma-ocean origin for a portion of the lunar crust is also possible and would account for the positive eNd value for FAN and phase equilibria. The formation of giant basins, such as the South Pole-Aitken (SPA) basin may have significant effects on resurfacing of the early lunar crust. Thus, the observed surface composition of the feldspathic highland terrane (FHT) represents the combined results of magma ocean crystallization, post-magma-ocean magmatism and resurfacing by basin formation. The Mg/(Mg+Fe) ratios, rock types, and mineral compositions of the FHT and the South Pole-Aitken basin Terrane (SPAT) obtained from the KAGUYA mission, coupled with further mineralogical and isotopic studies of lunar meteorites, will facilitate an assessment of the feasibility of the proposed crust model and improve understanding of lunar crustal genesis and evolution.
A new index to monitor temporal and long-term variations of the equatorial electrojet by MAGDAS/CPMN real-time data: EE-Index
Authors: Uozumi T. , Yumoto K. , Kitamura K. , Abe S. , Kakinami Y. , Shinohara M. , Yoshikawa A. , Kawano H. , Ueno T. , Tokunaga T. , McNamara D. , Ishituka J. K. , Dutra S. L. G. , Damtie B. , Doumbia V. , Obrou O. , Rabiu A. B. , Adimula I. A. , Othman M. , Fairos M. , Otadoy R. E. S. ,   MAGDAS Group
Published: August 2014

A new index, EE-index (EDst, EU, and EL), is proposed to monitor temporal and long-term variations of the equatorial electrojet by using theMAGDAS/CPMN real-time data. The mean value of the H component magnetic variations observed at the nightside (LT = 18–06) MAGDAS/CPMN stations along the magnetic equatorial region is found to show variations similar to those of Dst; we defined this quantity as EDst. The EDst can be used as a proxy of Dst for the real-time and long-term geospace monitoring. By subtracting EDst from the H component data of each equatorial station, it is possible to extract the Equatorial Electrojet and Counter Electrojet components, which are defined as EU and EL, respectively.
Relation between structure and low-temperature geothermal systems in Fukuoka city, southwestern Japan
Authors: Saibi Hakim , Nishijima Jun , Hirano Tomohiro , Fujimitsu Yasuhiro , Ehara Sachio
Published: August 2014

The Fukuoka area is located in the southwestern part of Japan. The Yokote-Ijiri area, located in the southern part of Fukuoka city, has several low-temperature geothermal systems, including eleven hot springs. From 1996 to 2008, the Fukuoka area was investigated by gravity survey, using Scintrex CG-3 and CG-3M gravimeters, in an attempt to delineate its subsurface structure. The surveys were intended to improve the understanding of the relation between the geothermal systems and the subsurface structure as well as to locate the active faults in the surveyed area, which are responsible for generating large earthquakes. The gravity data were analyzed using integrated gradient interpretation techniques, such as the Horizontal Gradient (HG), Tilt Derivative (TDR), and Euler deconvolution methods. With these techniques, many faults were detected, including the famous Kego fault, which is an active fault in Fukuoka city. A 2-D gravity model was constructed to show the relationship between the faults and the geothermal systems. The results of the present study will hopefully lead to an understanding of the relationships between the interpreted faults and the location of the low-temperature geothermal systems and possibly aid in future geothermal exploration of the area.
Resistivity structure around the focal area of the 2004 Rumoi-Nanbu earthquake (M 6.1), northern Hokkaido, Japan
Authors: Ichihara Hiroshi , Honda Ryo , Mogi Toru , Hase Hideaki , Kamiyama Hiroyuki , Yamaya Yusuke , Ogawa Yasuo
Published: August 2014

The Rumoi-Nanbu earthquake (M6.1) occurred in northern Hokkaido, Japan, on December 14, 2004. We conducted MT surveys along three profiles in and around the focal area to delineate and decipher the structural features of the seismogenic zone. The inverted 2-D resistivity images of the three sections comprised two layers: an upper conductive layer and a lower resistive layer. The boundary of these layers lay at a depth of approximately 3–5 km. A comparison with the surface geology and drilling data revealed that the upper conductive layer and the lower resistive layer corresponded to the Cretaceous—Tertiary sedimentary rocks and older basement rocks, respectively. A clear upheaval of the layer boundary was found along the profile at the center of the focal area. In addition, borehole data indicated an obvious increase in the Young’s modulus toward the lower layer. Therefore, the elastic properties with a complex geometry around the focal zone tended to vary; this probably depicts the zone of stress accumulation that triggered the earthquake.
Fault model of the 2007 Noto Hanto earthquake estimated from coseismic deformation obtained by the distribution of littoral organisms and GPS: Implication for neotectonics in the northwestern Noto Peninsula
Authors: Hiramatsu Yoshihiro , Moriya Kazuyoshi , Kamiya Takahiro , Kato Michio , Nishimura Takuya
Published: August 2014

We investigate the coseismic vertical crustal movement along the northern and western coast of the Noto Peninsula caused by the Noto Hanto earthquake on March 25, 2007, from the distribution of supra-, mid- and infra-littoral organisms. The highest uplift of 44 cm is observed at Akakami and the maximum subsidence of 8 cm at Fukami. We construct a rectangular fault model with a uniform slip in elastic half-space using both the coseismic vertical displacement estimated from the distribution of these organisms and the coseismic crustal deformation obtained by GPS. The model shows a reverse fault with a right-lateral slip of 1.3 m in a 18.6 km×14.5 km area. The seismic moment is 1.0×1019 N m (MW6.6) using a rigidity of 30 GPa. The geometry of the source fault is consistent with the distribution of aftershocks and active faults, and the fault is restricted to the central area of the aftershock area. Relationships among the fault, the distribution of aftershocks, active faults, and geological blocks around the source area suggest that geological structures restrict the fault size of the earthquake. By considering an inclined altitudinal distribution of marine terraces and the coseismic vertical crustal deformation detected in this study, we estimate that the recurrence of earthquakes during the past 120 kyr would produce a vertical crustal deformation of ≈12 m and the background tectonic uplift would reach ≈28 m.
An experiment of predicting Total Electron Content (TEC) by fuzzy inference systems
Authors: Akyilmaz O. , Arslan N.
Published: August 2014

The Total Electron Content (TEC) is predicted by fuzzy inference systems for various station-satellite pairs. GPS data from the GRAZ, HFLK, LINZ, MOPI and UZHL permanent stations are processed in order to obtain the vertical total electron content (VTEC) using differenced carrier-smoothed code observations. The quality of the VTEC prediction was studied on 9 and 11 September 2005 (DOY 252 and 254). The predictions were computed for 5, 10 and 15 min intervals. The mean accuracies of predictions are about 0.1, 0.2 and 0.3 TECU for these time intervals. More than 98% of the VTEC is successfully recovered with the proposed prediction method.
Summer-time nocturnal wave characteristics in mesospheric OH and O2 airglow emissions
Authors: Guharay A. , Taori A. , Taylor M.
Published: August 2014

The mesospheric temperature mapper (MTM) measurements on mesospheric OH (6, 2) and O2 (0, 1) band emissions from Maui, Hawaii during July, 2002 show significant day-to-day variability. The nocturnal variability reveals prominent wave signatures with a periodicity ranging from 6 to 13 h. For better characterization of the nocturnal wave in the data, a Krassovsky’s η (∼|η|e

iφ) analysis was carried out. Deduced Krassovsky parameters show significant variability, with ranges of |η| ∼ 1.7–3.9 for the OH data and ∼4.3–13 for the O2 data. The phase values of Krassovsky parameters exhibit larger variability, with variations from approximately −91° to +23° for the OH data and −45° to −10° for the O2 data. Comparison of these values with existing observations and models show large deviations from model values and relatively better agreements with the observed values reported by other investigators. The deduced vertical wavelength from |η| and φ indicates that our data is mostly dominated by upward propagating waves with occasional high values ≥100 km, implying possible evanescent waves.
Rupture process of the 2007 Notohanto earthquake by using an isochrones back-projection method and K-NET/KiK-net data
Authors: Pulido Nelson , Aoi Shin , Fujiwara Hiroyuki
Published: August 2014

We estimated the source process of the 2007/3/25 Notohanto earthquake using a new method for source imaging based on an “isochrones-backprojection” of observed seismograms in the source region (IBM). The IBM differs from conventional earthquake source modeling approaches in that no inversion procedures are required. The idea of IBM is to directly back-project amplitudes of seismogram envelopes around the source into a space image of the earthquake rupture. The method requires the calculation of isochrones times at every station used for source imaging, for a set of grids points distributed within the source fault plane. Total grid “brightness” is calculated by adding all observed waveform envelope amplitudes at every station, for every isochrone line crossing the grid, in order to produce an image of the total fault plane brightness distribution. Our source imaging results of the Notohanto earthquake show two large brightness regions; the first region is located 10 km above the hypocenter, and the second region is located at the bottom of the northern end of the fault plane. These regions approximately correspond to large slip areas obtained by a conventional inversion approach. Our method has the capability to quickly map asperities of large earthquakes using observed strong motion data.
Automatic determination of source parameters of the 2007 Noto Hanto earthquake
Authors: Wu Changjiang , Horiuchi Shigeki
Published: August 2014

Large earthquakes have been observed to be caused by the rupture of several asperities. The rapid determination of source parameters is hence of great importance for correctly determining shaking intensities or evaluating the strong motion distribution generated by a large earthquake. This study shows that we can automatically preprocess strong motion data using automaticP- andS-phase pickers, determine the focal mechanism, and identify the fault plane from two nodal planes. A real-time simulation is performed for the 2007 Noto Hanto earthquake. Using our automatic fault plane identificator, we were able to identify one of the nodal planes with a strike of 62° and a dip of 70° within a 30-s interval from the beginning of focal mechanism determination to the end of waveform inversion. Results from automatic inversions showed that the slip was confined to a shallow portion with a maximum slip of about 3 m. The total seismic moment released in 10 s was 2.0×1018N m, which corresponds to a moment magnitude of 6.8.
Temporal variations of crustal structure in the source region of the 2007 Noto Hanto Earthquake, central Japan, with passive image interferometry
Authors: Ohmi Shiro , Hirahara Kazuro , Wada Hiroo , Ito Kiyoshi
Published: August 2014

The passive image interferometry technique is applied to the continuous seismic waveform data obtained around the source region of the 2007 Noto Hanto Earthquake, central Japan. We computed the autocorrelation function (ACF) of band-pass filtered seismic noise portion recorded with each short-period seismometer at several seismic stations for 1 day each. In some stations, comparison of each 1-day ACF shows temporal evolutions of the ACF, which are interpreted as the change of seismic velocity structure in the volume considered. Sudden changes of ACF are detected to be associated with the occurrence of the main shock in one station of the four stations analyzed. Gradual changes of ACFs in the preceding 2 weeks of the main shock are also recognized in two stations, which would be of great importance for understanding the stress state before the occurrence of earthquakes.
Spherical cap harmonic analysis of magnetic variations data from mainland Australia
Authors: Stening R. J. , Reztsova T. , Ivers D. , Turner J. , Winch D. E.
Published: August 2014

Spherical cap harmonic analysis (SCHA) has been applied to geomagnetic data from an array of magnetometers deployed across the Australian mainland during 1989–90 in order to examine features of the ionospheric S
q current system. The external contours, corresponding to ionospheric currents, are generally in good agreement with the data in that the direction of current flow is perpendicular to the measured horizontal magnetic field. The derived internal (induced) current systems are less reliable but exhibit fairly consistent behaviour on some occasions. As the S
q current system whorl passes over Australia, the reversed internal current whorl lags by a bit less than an hour. When the external system moves off the continent into the Indian Ocean, the derived internal system sometimes appears to remain over the continent for about two hours but this is found to be caused by the large coastal effect in the west. The variations obtained from the analysis at particular sites are compared with the original data and give generally good agreement. Internal and external variations at several sites are derived and behave as expected to some extent. In particular we find that the internal component of the vertical element adds to the external component on the west coast but subtracts from it on the east coast. Further analyses are performed using data from the CM4 model. The SCHA gives a separation of internal and external components in good agreement with the original for the horizontal CM4 magnetic fields while the agreement is not so good for the vertical component.
Response of piezoelectric lead zirconate titanate detector to oblique impact with hypervelocity iron particles
Authors: Takechi S. , Onishi T. , Minami S. , Miyachi T. , Fujii M. , Hasebe N. , Mori K. , Nogami K. , Ohashi H. , Sasaki S. , Shibata H. , Iwai T. , Grün E. , Srama R. , Okada N.
Published: August 2014

A cosmic dust detector using piezoelectric lead zirconate titanate (PZT) is currently being developed for use onboard a spacecraft for the BepiColombo mission. The characteristics of the PZT detector were studied by carrying out hypervelocity impact measurements with iron particles supplied by a Van de Graaff accelerator. The measurements with particle velocities of less than 5 km/s showed a linear relationship between the output voltages obtained from the detector and the particle momenta. This linear relationship obtained was almost independent of the impact angle between the particle and the PZT surface.
The intensity of the geomagnetic field in the late-Archaean: new measurements and an analysis of the updated IAGA palaeointensity database
Authors: Biggin Andrew J. , Strik Geert H. M. A. , Langereis Cor G.
Published: August 2014

We firstly present the results of a detailed palaeointensity study performed on 54 samples from 9 volcanic units of late Archaean age (2724-2772 Ma) from the Pilbara Craton, Western Australia. These results were severely affected by magnetomineralogical alteration occurring during the laboratory heating process necessitating the application of a correction procedure. The correction allowed results from three lavas to pass strict selection criteria but we deem that only one of these exhibits sufficient internal consistency to be considered moderately reliable. It yields a virtual dipole moment of 47±6 ZAm2which is 60% of the present-day value. We combine this determination with a filtered dataset from the updated IAGA (International Association of Geomagnetism and Aeronomy) palaeointensity database, PINT08. Directional secular variation has recently been shown to have changed fundamentally since the Archaean, probably as a consequence of inner core growth since that time. However, here we argue that it is still unclear whether this evolution was accompanied by a single long timescale change in average poloidal field intensity. While the distribution of Precambrian palaeointensity determinations as a whole is significantly lower than that for the last 300 Myr, we show that this finding largely reflects data from the Proterozoic aeon. The distribution of more ancient measurements from the late Archaean-earliest Proterozoic is indistinguishable from that of the last 300 Myr which might suggest that a ‘Proterozoic dipole low’ period existed between two periods of higher field intensity. Were this pattern of long-term geomagnetic intensity variation to be supported by the addition of new data in the future, then it could indicate a related three-stage evolution in core dynamics, namely: vigorous thermal convection caused by high core-mantle heat flux early in the Earth’s history, weaker thermal convection later as the heat flux fell, and finally, strong compositional convection since the inner core nucleated.
Cenozoic and Mesozoic basalts from Egypt: a preliminary survey with a view to paleointensity
Authors: Perrin M. , Saleh A. , Alva-Valdivia L.
Published: August 2014

Numerous phases of igneous activity took place in Egypt during the Mesozoic and the Cenozoic but no paleointensity results have ever been published from these rocks. Therefore a preliminary survey was conducted in the northern part of Egypt and in Sinai to test the suitability of these basalts for paleointensity determinations. Three Oligo-Miocene sites have been sampled north of Cairo: Abu Zaabal, Qatrani, and 6th of October City. In Sinai, we sampled Jurassic basalts in Wadi Budra and Oligo-Miocene rocks from Wadi Nukhul. The main magnetic carriers of these rocks are titanomagnetites with varying Ti content. Large secondary components are present in most middle Jurassic basalts and discrepancies remain in the directional analysis so this sill cannot be used for paleointensity experiments and the associated poles should not be considered for paleomagnetic reconstructions either. Directional analysis of the Oligo-Miocene basalts is very straightforward and updated mean VGPs have been calculated from the Cairo area (68.9°N, 91.3°E; Kappa = 274; A95 = 3.7) and from Wadi Nukhul (72.7°N, 13.4°E; Kappa = 528; A95 = 5.4). Pseudo-paleointensity results obtained as well from stable Egypt as from Sinai are promising, with values lower or similar (between 29 to 58 μT) to present-day field intensity.
First archeointensity results from Portuguese potteries (1550-1750 AD)
Authors: Hartmann Gelvam A. , Trindade Ricardo I. F. , Goguitchaichvili Avto , Etchevarne Carlos , Morales Juan , Afonso Marisa C.
Published: August 2014

Geomagnetic field variations at archeomagnetic timescales can be obtained from well-dated heated structures and archeological potsherds. Here, we present the first archeointensity results obtained on Portuguese ceramics (1550 to 1750 AD) collected at Brazilian archeological sites. The results are compared to those obtained from Western Europe and currently available geomagnetic field models. Continuous thermomagnetic and IRM acquisitions curves indicate that Ti-poor titanomagnetite is responsible for the remanence in these ceramic fragments. Five fragments (24 samples) out of twelve analyzed yielded reliable intensity estimates. The row archeointensity data were corrected for TRM anisotropy and cooling rate effect. The mean dipole moments are obtained for three different age intervals: 1550±30 AD, 1600±30 AD and 1750±50 AD. Mean intensities vary from 37.9±4.2 μT to 54.8±7.6 μT in agreement with the previously reported data for 1550 AD and 1750 AD. Relatively weaker, but still highly dispersed, values were obtained for 1600 AD ceramics.
Controlled atmosphere vibrating thermo-magnetometer (CatVTM): a new device to optimize the absolute paleointensity determinations
Authors: Poidras Thierry , Camps Pierre , Nicol Patrick
Published: August 2014

The laboratory of paleomagnetism of Montpellier (France) has developed a new one-axis vibrating thermal magnetometer dedicated to the study of physical properties of natural rocks remanence. Among its key characteristics, this apparatus allows both measurement of the magnetization moment on the interval from room temperature to 700°C with a precision of 2 × 10-9 A m2 and acquisition of a total or a partial thermo-remanent magnetization using a steady field from -100 up to 100 μT. Another point that is worth noting is that one can apply a controlled atmosphere by means of argon flux to prevent oxidation of the studied sample during heating. We report here a technical description of this new instrument and review some specific applications in absolute paleointensity surveys.
Low-temperature magnetic properties of andesitic rocks from Popocatepetl stratovolcano, Mexico
Authors: Kosterov Andrei , Conte Gennaro , Goguitchaichvili Avto , Urrutia-Fucugauchi Jaime
Published: August 2014

To contribute to the growing database of magnetic properties of rocks and minerals at cryogenic temperatures, we have measured magnetization, low-field susceptibility, and hysteresis loops as a function of temperature between 2 K (10 K for hysteresis) and 300 K for twelve representative samples from a suite of volcanic rocks of predominantly andesitic composition erupted by the Popocatepetl stratovolcano, Mexico. High temperature susceptibility measurements have yielded Curie points (T
C) mostly between 430 and 550°C, two samples additionally containing a magnetic phase with T
C of 300-320°C, and one sample—with 140-170°C. Hysteresis measurements at room temperature have revealed invariably the presence of a low-coercivity mineral with coercive force ranging from 10 to 20 mT. This suggests that NRM of Popocatepetl rocks is carried by an intermediate titanomagnetite of composition between approximately TM04 and TM20. Thermal demagnetization of SIRM given at 2 K displays no evidence for the Verwey transition, further showing that samples are essentially magnetite free. At the same time, an inflection between 30-50 K reported previously for intermediate titanomagnetites (Moskowitz et al., EPSL, 157, 141-149, 1998) is seen in all studied Popocatepetl samples except one. As well, below 50 K the coercive force increases sharply with decreasing temperature reaching up to 100 mT at 10 K. On the other hand, examining the behavior of low-field susceptibility at cryogenic temperatures shows that susceptibility signal is dominated by intermediate titanomagnetites only in a part of our samples. In four out of 12 samples, however, susceptibility signal appears to be due to a hemoilmenite phase containing about 20 mole% of hematite. Caution is thus advised when interpreting low-temperature susceptibility data in terms of magnetic mineralogy.
Paleomagnetic behavior of volcanic rocks from Isla Socorro, Mexico
Authors: Sbarbori Elise , Tauxe Lisa , Goguitchaichvili Avto , Urrutia-Fucugauchi Jaime , Bohrson Wendy A.
Published: August 2014

The direction and magnitude of the geomagnetic field vary both spatially and temporally and undergo significant departures from that of a geocentric axial dipole. In order to properly characterize persistent behaviors, time-averaged field models must be based on the highest quality data. Here we present full-vector paleomagnetic data for volcanic units exposed in the southeast quadrant of the island of Socorro, Mexico. We carried out a joint expedition between the Scripps Institution of Oceanography and the Universidad Nacional Autónoma México to Isla Socorro in January of 2005 during which we collected oriented paleomagnetic samples from 21 sites, representing as many as 10 different volcanic units (the oldest of which is ~540 ka). We subjected over 100 specimens to the most up-to-date paleointensity methods, and included the standard reliability checks. In an earlier study, Bohrson et al. (1996) proposed a series of widespread eruptive events, based on similarities of argon/argon dates. Paleointensity from specimens that conform to the strictest acceptance criteria are available from both the (unoriented) original sample collection and our fully oriented (but as yet undated) new collection. Correlation between the two collections is however problematic. The time-averaged direction from Socorro is consistent with that expected from a geocentric axial dipole, and the time-averaged intensity is 30.0±7.1 μT, equivalent to a virtual axial dipole moment (VADM) of 67.6±16.0 ZAm2.
Analyzing the variation of embedding dimension of solar and geomagnetic activity indices during geomagnetic storm time
Authors: Mirmomeni M. , Lucas C.
Published: August 2014

Cyclic solar activity as one of the natural chaotic phenomena has significant effects on Earth, climate, and satellites. Rapid changes in the near-Earth space environment can affect the performance and reliability of both spacecraft and ground-based systems. This can imply major problems due to communication and satellite operational anomalies. Therefore, it is meaningful to analyze solar activity and geomagnetic indices to elicit the behavior of sun as the origin of most of these chaotic phenomena. One of the most important tools for analyzing the chaotic trends is the “Embedding Dimension” (ED). In this paper, the variation of ED for solar activity indices especially during storm time for two well-known storms is considered. The first storm is the super-storm on 13 March 1989, which shuts down the power supply system in Québec, Canada and the second one is the storm caused by Coronal Mass Ejection on 11 January 1997 which causes the failure of Telstar 401 satellite. The method of this paper is based on the fact that the reconstructed dynamics of an attractor should be a smooth map, i.e. with no self intersection in the reconstructed attractor. It is shown that the Embedding Dimension (and other chaotic characteristics) of some solar and geomagnetic activity indices during these storms varies rapidly.
Gravity and magnetic constraints on the crustal structure and evolution of the Horeki seamount in the Izu-Ogasawara (Bonin) arc
Authors: Fujiwara Toshiya , Kido Yukari , Tamura Yoshihiko , Ishizuka Osamu
Published: August 2014

Data on the crustal structure, bulk composition, and eruption ages of an arc seamount were obtained in an investigation aimed at studying the spatial and temporal variations in the magma composition of an intra-oceanic arc. We conducted gravity and magnetic surveys of the Horeki seamount and evaluated the density and magnetization structure using inversion and forward modeling. The seamount is located on the back-arc side of the Izu-Ogasawara arc. This seamount has an elliptical shape, a flat summit, and satellite ridges and cones on its northern and southern flanks. The flanks are consistent with a higher density anomaly, with an estimated mean density corresponding to dense basaltic rocks. A low-density anomaly is distributed in the seamount top, indicating that the top likely consists of porous basalts or differentiated rocks. The prominent circular low Bouguer gravity anomaly, which appeared in the northern part of the flat-topped summit, indicates that a light-density material fills the summit. The main body of seamount is normally magnetized. Combined with the age of the rocks, the volcanism constructing the main body may be most robust in the Gauss chron. The deeper part of seamount may consist of intrusive rocks, with induced magnetization over remanence. The eastern part of the northern ridges is reversely magnetized, while the western part is normally magnetized. These features and the ages of the sampled rocks suggest that these ridges were constructed in the Matuyama and Brunhes chrons, respectively. The southern part of the seamount flanks shows weak normal magnetization, probably caused by the small cones with different polarities of remanent magnetization.