bluuebunny/crossref_metadata_2025_split huggingface dataset:
Early and middle Matuyama geomagnetic excursions recorded in the Chinese loess-paleosol sediments
Authors: Yang Tianshui , Hyodo Masayuki , Yang Zhenyu , Ding Lin , Fu Jianli , Mishima Toshiaki 
Published: August 2014

Abstract
A detailed paleomagnetic and rock-magnetic investigation on the early and middle Matuyama loess-paleosol sediments has been carried out at the Baoji section, Shaanxi province, southern Chinese Loess Plateau. Our new magnetostatigraphy revises the position of the lower Olduvai boundary from L27 to S26. Seven shortlived geomagnetic excursions, tentatively named as E1, E2, E3, E4, E5, E6, and E7, have been recognized in the L13, S22, L26, L27, S29, and upper and middle parts of L32, respectively. Results of the anisotropy of low-field magnetic susceptibility (AMS) show that the studied loess-paleosol sediments retain the primary sedimentary fabric. Rock magnetic experiments reveal that the sediments from the excursional and polarity transitional intervals have the same magnetic characteristics as those from the surrounding normal and reversed polarity intervals. Assuming a constant accumulation rate between polarity boundaries, these seven excursions are estimated to be at about 1.11 Ma (E1), 1.58 Ma (E2), 1.92 Ma (E3), 2.11 Ma (E4), 2.25 Ma (E5), 2.35 Ma (E6), and 2.42 Ma (E7) Ma. The E1 and E2 in the middle Matuyama Chron can be correlated with the Punaruu and Stage 54 (Gilsa) excursions, respectively. The E4, E5, and E7 in the early Matuyama Chron can be correlated with the Réunion II, Réunion I, and cryptochron C2r.2r-1 (X-subchron), respectively. The E3 in the lower Olduvai subchron and E6 in the early Matuyama Chron have no comparable events. At present they can only be correlated with the anomalous directions observed in the Osaka Bay core (Biswas et al., 1999). Therefore, further investigations are necessary to support their global occurrences. The present result together with the two late Matuyama excursions dated at about 0.89 Ma and 0.92 Ma (Yang et al., 2004) show that the Baoji section yields at least nine Matuyama excursions which, along with the results of the study, suggests that eight excursions occur at 0.9–2.2 Ma (Channell et al., 2002), thereby providing evidence that the short-lived geomagnetic excursions may also be a basic characteristic of the geomagnetic field during the Matuyama Chron.
Magnetizations of the seamounts in the Izu-Ogasawara arc with special reference to the origin of their normal polarity biases
Authors: Ueda Yoshio 
Published: August 2014

Abstract
Magnetizations of the seamounts in the Izu-Ogasawara arc are calculated using correlation analyses of magnetic anomalies and topographic data. The calculated results of the seamounts in the Sitito-Iozima ridge (present volcanic front) show normal magnetizations with a mean value of 5.10±1.38 A/m. The results also show that the majority of the seamounts in the Nisi-Sitito ridge, which are Pliocene and Middle Miocene in origin, are magnetized in a normal magnetic field direction with a mean value of 2.74±1.07 A/m. Seamounts in the Kyushu-Palau ridge, which are Oligocene in origin, also show predominantly normal polarities, with a mean of 2.67±0.71 A/m. For such a polarity bias to be explained by induced magnetization components (IM), including viscous remanent magnetization (VRM), the intensity of IM should be comparable to the mean of 2.74 A/m. However, no significant differences in the standard deviations of magnetization intensities are recognized between the seamounts in the Nisi-Sitito Ridge and those in the Sitito-Iozima Ridge, contrary to expectations if the normal polarity bias is IM in origin. Three-dimensional (3-D) multi-block model analyses are also applied to 25 seamounts having magnetization directions considerably different from those of the present magnetic field to estimate the normally and reversely magnetized volumes of the seamounts. The results show that 88% (22/25) of the seamounts have relatively greater volumes of normal magnetization compared to reverse magnetization. The IM component estimated from the 3-D multi-block model is a maximum of 0.66 A/m, which is too small to explain the observed normal polarity bias. A possible alternative explanation for the observed normal polarity bias may be enhanced volcanic activity during normal magnetic periods, although this is difficult to justify theoretically at the present time.
Size-frequency statistics of boulders on global surface of asteroid 25143 Itokawa
Authors: Michikami Tatsuhiro , Nakamura Akiko M. , Hirata Naru , Gaskell Robert W. , Nakamura Ryosuke , Honda Takayuki , Honda Chikatoshi , Hiraoka Kensuke , Saito Jun , Demura Hirohide , Ishiguro Masateru , Miyamoto Hideaki 
Published: August 2014

Abstract
The surface of asteroid 25143 Itokawa is covered with numerous boulders although gravity is very small compared with that of other asteroids previously observed from spacecraft. Here we report the size-frequency statistics of boulders on the entire surface of Itokawa based on high-resolution images (1 pixel ≈0.4 m) obtained by the Hayabusa spacecraft. There are 373 boulders larger than 5 m in mean horizontal dimension on the entire surface—0.393 km2—and the number density is nearly 103/km2. The cumulative boulder size distribution on the entire surface has a power-index of −3.1 ± 0.1. For the east and west sides and the head and body portions of Itokawa, the power-index of the size distributions and the number densities of boulders of these areas are thought to be similar from the statistical point of view. A global mapping of boulders shows that there is no apparent correlation in the locations of boulders and craters. The ratio of the total volume of the boulders to the total excavated volume of the craters on Itokawa is ≈25% when only craters larger than 50 m in mean diameter are considered, and this ratio is extremely larger than that on Eros and the Moon, respectively. The origin of boulders on the surface of Itokawa was examined quantitatively by calculating the number of boulders and the size of the largest boulder using a model based on impact cratering experiments. The result indicated that the boulders on the surface of Itokawa cannot solely be the product of craters. Our results suggest that the boulders originated from the disruption of the larger parent body of Itokawa, as has been described in previous papers (Fujiwata et al., Science, 312, 1330–1334, 2006; Saito et al., Science, 312, 1341–1344, 2006).
Source model of the 2007 Noto-Hanto earthquake (Mw 6.7) for estimating broad-band strong ground motion
Authors: Kurahashi Susumu , Masaki Kazuaki , Irikura Kojiro 
Published: August 2014

AbstractA source model for estimating broad-band ground motions from the 2007 Noto-Hanto earthquake (Mw6.7) is estimated from a comparison of the observed records of the mainshock and synthesized motions based on the characterized asperity model using the empirical Green’s function method. The observed records of aftershocks used as the empirical Green’s functions are carefully selected to have almost the same radiation characteristics and source distance as the asperities of the mainshock. The best-fit source model consists of two asperities of different size. A large one is located just above the hypocenter, with an area of 6.3×6.3 km2and stress drop of about 26 MPa. A smaller one is located north-east of the large one, with an area of 3.6×3.6 km2and stress drop of about 10 MPa. The stress drop of the large one is about twofold higher than the average values of inland crustal earthquakes so far estimated, while that of smaller one is almost average. We found that the remarkable directivity pulses from the source model struck the northern part of the Noto peninsula, causing heavy damage in some towns there.
Analysis of the tsunami generated by the 2007 Noto Hanto earthquake
Authors: Tanioka Yuichiro 
Published: August 2014

Abstract
The 2007 Noto Hanto earthquake generated a small tsunami that was recorded at several tide gauge stations along the coast of the Japan Sea. The most important feature of this tsunami is that two waveforms recorded at the Wajima and Noto tide gauge stations, which are located 30 km apart, showed very different later phases—the large later phases recorded at Noto were not observed at Wajima. Numerical simulation of the tsunami indicated that the difference was caused by the shallow water bathymetry around the Noto peninsula. The large tsunami that was amplified at a few tens of kilometers off the north coast of the Noto peninsula propagated towards the Noto tide gauge station, but not towards the Wajima station. This study indicates that the propagation of a tsunami caused by a shallow earthquake beneath a coastal area is significantly affected by the local bathymetry. A comparison of the observed and computed tsunami waveforms indicated that the slip amount of the fault was 0.8 m. The seismic moment of the Noto Hanto earthquake was calculated to be 0.94 × 1019 N m (M
w 6.6).
Postseismic displacements following the 2007 Noto peninsula earthquake detected by dense GPS observation
Authors: Hashimoto Manabu , Takahashi Hiroaki , Doke Ryosuke , Kasahara Minoru , Takeuchi Akira , Onoue Kenusuke , Hoso Yoshinobu , Fukushima Yo , Nakamura Kajuro , Ohya Fumio , Honda Ryo , Ichiyanagi Masayoshi , Yamaguchi Teruhiro , Maeda Takahiro , Hiramatsu Yoshihiro 
Published: August 2014

AbstractWe have been conducting dense GPS observation in and around the epicentral region of the 2007 Noto peninsula earthquake since March 25, 2007, in order to detect postseismic displacements. Continuous observation has been underway at 12 sites to fill the gap of GEONET. Preliminary analysis of data up to early May shows that initial postseismic displacement rapidly decayed within 20 days after the occurrence of the mainshock. Horizontal displacements do not exceed 20 mm even at sites above the aftershock zone for this period. We also found a maximum uplift of about 20 mm there. Inversion of postseismic displacements with the variable slip model suggests a nearly right-lateral afterslip of less than 5 cm on the shallow portion of the source fault. Fitting a theoretical function to a time series of coordinate changes also suggests that the observed postseismic displacements might have been generated by afterslip.
Exploring the feasibility of on-site earthquake early warning using close-in records of the 2007 Noto Hanto earthquake
Authors: Wu Yih-Min , Kanamori Hiroo 
Published: August 2014

AbstractIn view of the remarkable success of the Japan Meteorological Agency earthquake early warning system (developed jointly with the National Research Institute for Earth Science and Disaster Prevention) during the 2007 Noto Hanto earthquake, we explore the use of an on-site early warning method with the hope of eventually enhancing the existing system for more robust and faster warning. We determined two early warning parametersτcandPdusing the K-NET and KiK-net data for the 2007 Noto Hanto earthquake as well as 20 large earthquakes in Japan. An extended method suggests a possibility of using the initial displacement amplitude data for faster warning. For the two nearby sites at the epicentral distances of 7 and 19 km of the 2007 Noto Hanto earthquake, an early warning can be ideally issued at 2.27 and 5.46 s, respectively, before the peak ground motion velocity occurs at the site.
Temporal variation of sound speed in ocean: a comparison between GPS/acoustic and in situ measurements
Authors: Kido Motoyuki , Osada Yukihito , Fujimoto Hiromi 
Published: August 2014

Abstract
The GPS/acoustic technique applied to seafloor geodesy intrinsically measures integrated sound speed along a trajectory of an acoustic signal as well as the position of a seafloor transponder array. We present here a generalized expression of sound speed variation in terms of a traveltime residual normalized to the vertical component. With this expression, residual traveltimes to any seafloor transponders will have a same value regardless of their depths and slant angles. This is valid even for the case having horizontal gradient in sound speed structure; the gradient affects only on positioning of a transponder array and not on the estimate of sound speed just beneath the observation point. We monitored temporal variation of this quantity through a GPS/acoustic survey and compared it with in situ expendable bathythermograph (XBT) measurements periodically carried out during the survey. We found that the relative change of the two independent measurements are in good agreement within 5% of the typical amplitude of temporal variation.
Laboratory experiments of particle size effect in X-ray fluorescence and implications to remote X-ray spectrometry of lunar regolith surface
Authors: Maruyama Yoko , Ogawa Kazunori , Okada Tatsuaki , Kato Manabu 
Published: August 2014

Abstract
We performed laboratory experiments to investigate the effect of particle size in X-ray fluorescence (XRF) with respect to interpreting remote X-ray spectrometry. To simulate microscopic roughness of the uppermost surface of lunar regolith, we used powdery specimens of crashed rocks ranging 25 to 500 μm in size and flat rock plates for comparison. Our results show that XRF intensities from powdery specimens decrease relative to those from flat plates by up to 50%, especially for larger particle size and at increasing source-to-surface-to-detector angle (phase angle). Corrections should be required for elemental analysis by XRF spectrometry in the SELENE ‘ Kaguya’ and other planetary orbiter missions.
Plasma wave observation using waveform capture in the Lunar Radar Sounder on board the SELENE spacecraft
Authors: Kasahara Yoshiya , Goto Yoshitaka , Hashimoto Kozo , Imachi Tomohiko , Kumamoto Atsushi , Ono Takayuki , Matsumoto Hiroshi 
Published: August 2014

Abstract
The waveform capture (WFC) instrument is one of the subsystems of the Lunar Radar Sounder (LRS) on board the SELENE spacecraft. By taking advantage of a moon orbiter, the WFC is expected to measure plasma waves and radio emissions that are generated around the moon and/or that originated from the sun and from the earth and other planets. It is a high-performance and multifunctional software receiver in which most functions are realized by the onboard software implemented in a digital signal processor (DSP). The WFC consists of a fast-sweep frequency analyzer (WFC-H) covering the frequency range from 1 kHz to 1 MHz and a waveform receiver (WFC-L) in the frequency range from 10 Hz to 100 kHz. By introducing the hybrid IC called PDC in the WFC-H, we created a spectral analyzer with a very high time and frequency resolution. In addition, new techniques such as digital filtering, automatic filter selection, and data compression are implemented for data processing of the WFC-L to extract the important data adequately under the severe restriction of total amount of telemetry data. Because of the flexibility of the instruments, various kinds of observation modes can be achieved, and we expect the WFC to generate many interesting data.
Telescope of extreme ultraviolet (TEX) onboard SELENE: science from the Moon
Authors: Yoshikawa I. , Yamazaki A. , Murakami G. , Yoshioka K. , Kameda S. , Ezawa F. , Toyota T. , Miyake W. , Taguchi M. , Kikuchi M. , Nakamura M. 
Published: August 2014

Abstract
The Upper Atmosphere and Plasma Imager (UPI) is to be launched in 2007 and sent to the Moon. From the lunar orbit, two telescopes are to be directed towards the Earth. The Moon has no atmosphere, which results in there being no active emission near the spacecraft; consequently, we will have a high-quality image of the near-Earth environment. As the Moon orbits the Earth once a month, the Earth will also be observed from many different directions. This is called a “science from the Moon”. The two telescopes are mounted on a two-axis gimbal system, the Telescope of Extreme ultraviolet (TEX) and Telescope of Visible light (TVIS). TEX detects the O II (83.4 nm) and He II (30.4 nm) emissions scattered by ionized oxygen and helium, respectively. The targets of extreme-ultraviolet (EUV) imaging are the polar ionosphere, the polar wind, and the plasmasphere and inner magnetosphere. The maximum spatial and time resolutions are 0.09 Re and 1 min, respectively.
Southern Ocean mass variation studies using GRACE and satellite altimetry
Authors: Kuo Chung-Yen , Shum C. K. , Guo Jun-yi , Yi Yuchan , Braun Alexander , Fukumori Ichiro , Matsumoto Koji , Sato Tadahiro , Shibuya Kazuo 
Published: August 2014

Abstract
The Southern Ocean is a major link between the world oceans via complicated processes associated with the melting and accumulation of the vast Antarctic ice sheets and the surrounding sea ice. The Southern Ocean sea level is poorly observed except from recent near-polar orbiting space geodetic satellites. In this study, the Southern Ocean mass variations at the seasonal scale are compared using three independent data sets: (1) the Gravity Recovery And Climate Recovery Experiment (GRACE) observed ocean bottom pressure (OBP), (2) steric-corrected satellite altimetry (ENVISAT) and, (3) the Estimating the Circulation and Climate of the Ocean (ECCO) model OBP data. The height difference between sea level derived from altimetry and steric sea level contains the vertical displacement of the Earth surface due to elastic loading. Here we provide a formulation of this loading term which has not been considered previously in other studies and demonstrate that it is not negligible, especially for regional studies. In this study, we first conduct a global comparison using steric-corrected JASON-1 altimetry with GRACE to validate our technique and to compare with recent studies. The global ocean mass variation comparison shows excellent agreement with high correlation (∼0.81) and with discrepancies at 3–5 mm RMS. However, the discrepancies in the Southern Ocean are much larger at 12–17 mm RMS. The mis-modeling of geocenter variations and the second degree zonal harmonic (J
2) degrade the accuracy of GRACE-derived mass variations, and the choice of ocean temperature data sets and neglecting the loading correction on altimetry affect the OBP comparisons between GRACE and altimetry. This study indicates that the satellite observations (GRACE and ENVISAT) are capable of providing an improved constraint of oceanic mass variations in the Southern Ocean.
Analysis of gravity field variations derived from Superconducting Gravimeter recordings, the GRACE satellite and hydrological models at selected European sites
Authors: Neumeyer J. , Barthelmes F. , Kroner C. , Petrovic S. , Schmidt R. , Virtanen H. , Wilmes H. 
Published: August 2014

Abstract
If we restrict the spatial resolution to a half-wavelength of about 1500 km and the temporal resolution to 1 month, GRACE-derived temporal gravity variations can be resolved within the μgal (10-8 m/s2) range. A comparison with ground gravity measurements from selected Superconducting Gravimeter (SG) stations forming the Global Geodynamics Project (GGP) provides an independent validation. For this study, five European SGstations were selected that both cover a large test field and allow closely located SG-stations to be studied. Prior to this comparison, GRACE and SG data sets have to be reduced for the same known gravity effects due to Earth and ocean tides, pole tide, and atmosphere. After these reductions, the remaining part can be mainly attributed to mass changes in terrestrial water storage. For this reason, gravity variations derived from global hydrological models are included in the comparison of SG and GRACE results. Conversely, the hydrology models can be checked by gravity variations determined from GRACE and SG observations. For most of the SG locations investigated here, the comparison based primarily on computed correlations shows quite a good agreement among the gravity variation derived from the three different kinds of data sets: SG, GRACE, and hydrology models. The variations in SG gravity (point measurements) prove to be representative for a large area within the μgal accuracy range, if local gravity effects are removed correctly. Additionally, a methodology for an analysis of dominant common features based on the EOF-technique is proposed and illustrated. The first principal component shows strong periodicity, and the search for arbitrary periods confirms a strong common annual component, which reduces the total signal content considerably. The first eigenvector reveals common features and differences between distinct SG stations. Discrepancies between SG, GRACE, and hydrology models at individual SG stations, detected by both methods, may provide valuable hints for further investigations of respective data series.
Mapping the upper mantle discontinuities beneath China with teleseismic receiver functions
Authors: Shen Xuzhang , Zhou Huilan , Kawakatsu Hitoshi 
Published: August 2014

AbstractWe used teleseismic body waves recorded at stations of the Chinese Center of Digital Seismic Network to map the upper mantle discontinuities beneath continental China. The CRUST2.0 and anS-tomography model beneath each station were combined with the one-dimensional tracing method to convert time series of radial receiver functions to depth series. Clear signatures corresponding to the 410- and 660-km discontinuities (‘410’ and ‘660’) are visible at almost all of the stations. The averageSvelocity contrast of ‘410’ beneath the study area is close to the global average, but that for ‘660’ is smaller than the global average. The average depth of ‘410’ is 413 km, and the peak-to-peak topography is about 36 km, with regional depressions that correlate with the Datong quaternary volcano in northern China. The ‘660’ topography exhibits a peak-to-peak variation of about 43 km, and its average depth is 669 km; the depressions of the ‘660’ in northeastern, southeastern and northern China are well correlated with the past subduction around the Pacific Ocean and Philippine Sea. The width of the transition zone is also increased in the region with the deeper ‘660’. Our results would appear to indicate that there may be a low-velocity layer below a depth of approximately 600 km that may be the accumulated garnetite layer of an ancient crust above the ‘660’.
A study of VLF wave propagation characteristics in the earth-ionosphere waveguide
Authors: Indira Devi M. , Khan I. , Madhusudhana Rao D. N. 
Published: August 2014

Abstract
In the light of newly found applications for very low frequency (VLF) (3–30 kHz) measurements in the prediction of earthquakes and the detection of lightning discharges and gamma ray bursts, there has been a revival of interest in the study of VLF propagation in the earth-ionosphere waveguide. The propagation characteristics of VLF radiowaves in the earth-ionosphere waveguide critically depend upon the lower ionospheric ionization, which determines the conductivity profile of the upper boundary of the waveguide. In this context, it is potentially worthwhile to revisit the waveguide mode analysis to compute propagation parameters of long-distance VLF transmissions while taking into account different approximations to the ionospheric conductivity. We have carried out a waveguide mode analysis of 16-kHz VLF waves traveling great distances, assuming three different models for conductivity. The computational results show that at heights of less than 70 km, the change in the phase of the VLF waves due to changes in phase velocity is smaller when the ionosphere is sharply bound and assumed to have finite conductivity rather than infinite conductivity. The effect of a non-sharp or diffuse boundary at the top of the earth-ionosphere waveguide is found to cause a lowering of the height of reflection.