bluuebunny/crossref_metadata_2025 huggingface dataset:
Resolving static offsets from high-rate GPS data: the 2003 Tokachi-oki earthquake
Authors: Larson Kristine M. , Miyazaki Shin’ichi
Published: August 2014

The M
w 8.0 2003 Tokachi-oki earthquake offshore Hokkaido is the largest earthquake observed to date by a dense GPS network (GEONET). These GPS data are important both for resolving the geodetic signature of the earthquake itself and studies of postseismic deformation. Because GPS positions are generally estimated by averaging 24 hours of observations, it can be difficult to separate the effects of the earthquake and early postseismic deformation. In order to address this difficulty, a Kalman filtering methodology is developed that allows the estimation of the static offsets for the mainshock, its largest aftershock, and postseismic deformation in the first 24 hours. The static offsets computed for this study can be used for earthquake rupture studies while the early postseismic data can be used to evaluate frictional properties of the fault.
In-situ stress at the northern portion of the Chelungpu fault, Taiwan, estimated on boring cores recovered from a 2-km-deep hole of TCDP
Authors: Yabe Yasuo , Song Sheng-Rong , Wang Chien-Ying
Published: August 2014

We have investigated the depth variation in the stress state at the northern part of the Chelungpu fault, Taiwan, which slipped during the 1999 Chi-Chi earthquake (Mw7.6). In-situ stress around the fault was estimated based on the stress memory of rocks recovered from five depths (739–1316 m) of a 2-km-deep-hole. The borehole intersects a fault zone at a depth of 1111 m (FZ1111), which is the best candidate for the Chelungpu fault. Our main results are: (1) theSHmaxdirection is parallel to the slip for the Chi-Chi earthquake and agrees with those of the local, regional, or tectonic scales estimated from various stress indicators; (2) significant aspects of the stress field are identical to those of paleostress; (3) the horizontal differential stress was significantly reduced just above FZ1111, which may be attributable to the existence of a significantly deformable zone at this depth.
Initial observations of auroras by the multi-spectral auroral camera on board the Reimei satellite
Authors: Obuchi Yasuyuki , Sakanoi Takeshi , Yamazaki Atsushi , Ino Tomohiro , Okano Shoichi , Kasaba Yasumasa , Hirahara Masafumi , Kanai Yoshikazu , Takeyama Norihide
Published: August 2014

The small Japanese scientific satellite Reimei was launched successfully from Baikonur Space Center into a sun-synchronous (noon-midnight meridian) polar orbit at an altitude of ∼630 km on August 23, 2005. Auroral fine structure observations have been performed by the multi-spectral auroral camera (MAC) and electron/ion spectrum analyzers (ESA/ISA) on board Reimei. The MAC is a three channel camera system used to simultaneously observe the temporal dynamics of the auroral fine structure at the wavelengths of 428 nm (N2
+ 1NG), 558 nm (O), and 670 nm (N2 1PG). Since its successful launch, Reimei has been operated continuously and produced lots of unique data on the auroral fine structures with the MAC and ESA/ISA. The initial observation data from MAC has shown the temporal dynamics of auroral fine structure, such as the vortex street, appearing in the poleward edge of the auroral oval. The significant differences in the auroral shapes between the MAC channels suggest the existence of different emission processes. Further, the height profiles of the aurora and airglow are clearly seen in the image data in the limb direction. It is expected that the various mechanisms and dynamics of auroral fine structures can be investigated by analyzing the Reimei observation data.
Aftershock observation of the Noto Hanto earthquake in 2007 using ocean bottom seismometers
Authors: Yamada Tomoaki , Mochizuki Kimihiro , Shinohara Masanao , Kanazawa Toshihiko , Kuwano Asako , Nakahigashi Kazuo , Hino Ryota , Uehira Kenji , Yagi Takeo , Takeda Naoto , Hashimoto Shinichi
Published: August 2014

The Noto Hanto earthquake in 2007 (M
j 6.9) occurred on March 25, 2007 near the west coast of the Noto peninsula, Honshu, Japan. To study the aftershock activity under the sea, we deployed pop-up type ocean bottom seismometers (OBSs) from April 5 to May 8, 2007. We combined data from ten ocean bottom and four onshore seismic stations located around the rupture area of the earthquake and determined the preliminary distribution of the aftershocks. Most of the offshore aftershocks are located in a depth range between 2 and 10 km, and no earthquakes are observed in the lower crust. Hypocenters of deep events occurring at depths greater than 5 km are confined to an area northeastward from the largest aftershock in offshore region. Most of the aftershocks aligned along a high angle and southeast dipping plane, which is consistent with the geometry of the active faults revealed by previous seismic reflection surveys.
Magnetic properties and archeointensity determination on Pre-Columbian pottery from Chiapas, Mesoamerica
Authors: Morales Juan , Goguitchaichvili Avto , Acosta Guillermo , González-Moran Tomas , Alva-Valdivia Luis , Robles-Camacho Jasinto , del Sol Hernández-Bernal Ma.
Published: August 2014

As part of the effort to establish an archeointensity variation curve for Mesoamerica, 13 archeologically well-identified pottery samples belonging to the Ocozocoautla site (Chiapas) were studied. Analyzed samples consist of ‘ofrenda type’ pottery fragments found in several caves. Three archeological intervals are involved: 450-100 B.C., 200–550 A.D. and 550–900 A.D. The Thellier method in its modified form was applied to small fragments previously embedded in salt pellets. Raw intensity values were further corrected for cooling rate effects. The common time-consuming TRM anisotropy correction protocol was substituted by an alternative approach during the paleointensity experiments. Forty-two specimens, belonging to six samples, yielded high-quality Thellier determinations. The NRM fraction f used for paleointensity determination ranges between 0.42 to 0.99, and the quality factor q (Coe et al., 1978) varies from 4 to 59, being normally greater than 5. These results correspond to data of good quality. The mean archeointensity values per pottery fragments range from 14.6±1.5 to 59.5±13.8 μT, while the corresponding virtual axial dipole moments range from 2.5±0.3 to 10.0±2.4 × 1022 A m2. These new data, although not numerous, are of high quality and definitively contribute to the Mesoamerican, still insipient, archeointensity database.
Rock magnetism and microscopy of the Jacupiranga alkaline-carbonatitic complex, southern Brazil
Authors: Alva-Valdivia Luis M. , Perrin M. , Rivas-Sánchez María L. , Goguitchaichvili Avto , López-Loera Héctor , Lopes Omar Ferreira , Bonás Thiago Bastos
Published: August 2014

This study of the Cajati deposit provides evidence that the ore was neither purely hydrothermal, nor volcanic in origin, as previous workers have proposed. The ores were formed from magnetite-rich magmas, hydrothermally altered and intruded at an indicated crustal depth in excess of 500 m. The mineralogical and textural association between magnetite and magnesioferrite in the carbonatite, and between the titanomagnetite and magnesioferrite-Ti mineralization in the pyroxenite of hedenbergite, seems to be analog mineralizations strongly related to the ionic substitution of Fe2+ by Mg. Relatively high Q ratios (≥5) for Jacupirangite-pyroxenite may indicate a thermo remanent magnetization (TRM) by the ore during post-metamorphic cooling, however it can also be developed from chemical remanent magnetization (CRM). Vector plots for the pyroxenite samples show reasonably linear and stable magnetic components. The intensity decay curves show that only two components of magnetizations are likely present. Continuous susceptibility measurements with increasing temperature show that the main magnetic phase seems to be magnetite. Maghemite is probably produced during the cooling process. Susceptibility recorded from low temperature (liquid nitrogen (-196°C)) to room temperature produces typical curves, indicating Verwey transition of magnetite. Hysteresis parameters point out that nearly all values fall in a novel region of the Day plot, parallel to but below magnetite SD + MD mixing curves.
Ground effects of space weather investigated by the surface impedance
Authors: Pirjola Risto , Boteler David , Trichtchenko Larisa
Published: August 2014

The objective of this paper is to provide a discussion of the surface impedance applicable in connection with studies of geomagnetically induced currents (GIC) in technological systems. This viewpoint means that the surface impedance is regarded as a tool to determine the horizontal (geo)electric field at the Earth’s surface, which is the key quantity for GIC. Thus the approach is different from the traditional magnetotelluric viewpoint. The definition of the surface impedance usually involves wavenumber-frequency-domain fields, so inverse Fourier transforming the expression of the electric field in terms of the surface impedance and the geomagnetic field results in convolution integrals in the time and space domains. The frequency-dependent surface impedance has a high-pass filter character whereas the corresponding transfer function between the electric field and the time derivative of the magnetic field is of a low-pass filter type. The relative change of the latter transfer function with frequency is usually smaller than that of the surface impedance, which indicates that the geoelectric field is closer to the time derivative than to the magnetic field itself. An investigation of the surface impedance defined by the space-domain electric and magnetic components indicates that the largest electric fields are not always achieved by the plane wave assumption, which is sometimes regarded as an extreme case for GIC. It is also concluded in this paper that it is often possible to apply the plane wave relation locally between the surface electric and magnetic fields. The absolute value of the surface impedance decreases with an increasing wavenumber although the maximum may also be at a non-zero value of the wavenumber. The imaginary part of the surface impedance usually much exceeds the real part.
Source process for complex fault system of the 2007 Chuetsu-oki, Niigata, Japan, earthquake
Authors: Nakamura Takeshi , Ishihara Yasushi , Yamanaka Yoshiko , Kaneda Yoshiyuki
Published: August 2014

The 2007 Chuetsu-oki earthquake occurred in the offshore area of Niigata Prefecture, central Japan, on 16 July 2007. The aftershock distribution shows two fault planes, dipping to the northwest and southeast, respectively, which form a cross-sectional “V” pattern. We analyze the kinematic source process for the two fault planes consistent with the aftershock distribution using teleseismic body waveform data. Our results indicate that the mainshock initiated rupture on both faults northeast of their intersection and that the rupture propagated unilaterally southwestward along the southeast-dipping fault. The maximum slip is 1.6 m on the southeastdipping fault, and the seismic moments of northwest- and southeast-dipping faults are 8.0 × 1017N m (Mw5.9) and 7.5 × 1018N m (Mw6.5), respectively. The forward modeling of geodetic displacement from the obtained fault model is consistent with the GPS and InSAR measurements. Successive conjugate reverse faults around the source region are identified from the reflection seismic sections. We presume that stress changes and complicated structures in property and geometry around the source region are the dominant causal factors for generating the complexity of coseismic fault system.
Development of a distributed backup system and a recovery system for telemetric seismic data
Authors: Uehira Kenji
Published: August 2014

Fast, low-cost Internet lines have recently become available that rapidly transfer seismometer data. However, as in any fast transfer system, gaps frequently occur during data transmission. There are many causes for missing data packets at the receiving end, where is the data center side. I have developed a system that is meant to solve this problem. When the telemetry or the system is down at the data center end, data recovery is possible if the data are stored locally at each station. This means that the missing data can be re-sent after the required repairs have been made at the data center end. Therefore, I developed a concept of a distributed backup system that can store seismometer data for over 1 year locally at each station and developed a new protocol called “WIN Raw Data Recovery Protocol (WRRP)” for the efficient re-transmission of missing data.
Seismic structure of the subducting seamounts on the trench axis: Erimo Seamount and Daiichi-Kashima Seamount, northern and southern ends of the Japan Trench
Authors: Nishizawa Azusa , Kaneda Kentaro , Watanabe Naoko , Oikawa Mitsuhiro
Published: August 2014

We present detailed P-wave velocity models of subducting seamounts from two wide-angle seismic experiments across the Erimo Seamount and Daiichi-Kashima Seamount, northern and southern ends of the Japan Trench. Common characteristics of the velocity models of the seamounts are that the maximum crustal thicknesses of the seamounts are 12–17 km thicker than a typical oceanic crust and that Pn velocities beneath the seamounts are approximately 7.7 km/s, i.e., slower then those of the neighboring area. These features are very similar to the crustal models for the seamounts produced by the Cretaceous off-ridge volcanism on the Pacific Basin.
Numerical simulations of the solar corona and Coronal Mass Ejections
Authors: Poedts Stefaan , Jacobs Carla , van der Holst Bart , Chané Emmanuel , Keppens Rony
Published: August 2014

Numerical simulations of Coronal Mass Ejections (CMEs) can provide a deeper insight in the structure and propagation of these impressive solar events. In this work, we present our latest results of numerical simulations of the initial evolution of a fast CME. For this purpose, the equations of ideal MagnetoHydroDynamics (MHD) have been solved on a three-dimensional (3D) mesh by means of an explicit, finite volume solver, where the simulation domain ranges from the lower solar corona up to 30R
e. In order to simulate the propagation of a CME throughout the heliosphere, a magnetic flux rope is superposed on top of a stationary background solar (MHD) wind with extra density added to the flux rope. The flux rope is launched by giving it an extra initial velocity in order to get a fast CME forming a 3D shock wave. The magnetic field inside the initial flux rope is described in terms of Bessel functions and possesses a high amount of twist.
Characteristics of deformation structure around the 2007 Niigata-ken Chuetsu-oki earthquake detected by multi-channel seismic reflection imaging
Authors: No Tetsuo , Takahashi Narumi , Kodaira Shuichi , Obana Koichiro , Kaneda Yoshiyuki
Published: August 2014

A multi-channel seismic reflection (MCS) survey was conducted to investigate the tectonic structure off Niigata, which caused the 2007 Niigata-ken Chuetsu-oki earthquake, using the research vessel (R/V) KAIREI of the Japan Agency for Marine-Earth Science and Technology. Based on the results of data processing and interpretation of available data, three areas are identified according to seismic characteristics. The most deformed area is located on the continental shelf near the source region of the 2007 Niigata-ken Chuetsu-oki earthquake, i.e., the area east of the Yoneyama-Ogi Uplifts. A remarkable growth of folds, including fault-related folds, and a strong reflector dipping east is identifiable by localized strain concentrations. The second area is located between the Yoneyama-Ogi Uplifts and the Jouetsu Knoll in the Toyama Trough. Although the deformation of deposits in the second area was smaller than in the first area, folds are identified. The third area is located toward the west of the Jouetsu Knoll in the Toyama Trough. No significant deformed structures developed in this area. Based on the interpretation of stratigraphy obtained in previous studies, seismic characteristics, and well data, the development of an anticline was initiated by a compression field after about 3.6 Ma. In particular, the deformation of sedimentary layers by the compression field occurred rapidly after about 1.3 Ma. Folds have grown larger toward the east after about 1.3 Ma. In addition, subsidence of about 0.2 s in sedimentary layers can be seen at the western margin of the Yoneyama-Ogi Uplifts, suggesting that tectonic movement related to reverse faulting has advanced there very recently. From aftershock distribution on a depth section on line S-2 near the hypocentral region, most hypocenters were determined to be below the strong reflector. This result suggests that fold growth has accompanied past large earthquakes, such as the 2007 Niigata-ken Chuetsu-oki earthquake.
Local multi-polar expansions in potential field modeling
Authors: Minchev B. , Chambodut A. , Holschneider M. , Panet I. , Schöll E. , Mandea M. , Ramillien G.
Published: August 2014

The satellite era brings new challenges in the development and the implementation of potential field models. Major aspects are, therefore, the exploitation of existing space- and ground-based gravity and magnetic data for the long-term. Moreover, a continuous and near real-time global monitoring of the Earth system, allows for a consistent integration and assimilation of these data into complex models of the Earth’s gravity and magnetic fields, which have to consider the constantly increasing amount of available data. In this paper we propose how to speed up the computation of the normal equation in potential filed modeling by using local multi-polar approximations of the modeling functions. The basic idea is to take advantage of the rather smooth behavior of the internal fields at the satellite altitude and to replace the full available gravity or magnetic data by a collection of local moments. We also investigate what are the optimal values for the free parameters of our method. Results from numerical experiments with spherical harmonic models based on both scalar gravity potential and magnetic vector data are presented and discussed. The new developed method clearly shows that very large datasets can be used in potential field modeling in a fast and more economic manner.
A theory of rock core-based methods for in-situ stress measurement
Authors: Yamamoto Kiyohiko
Published: August 2014

The behavior of the inelastic strain of rocks under the loading of compression reflects the history of stresses applied to the rocks. A number of methods based on this rock property of stress memory have been proposed for measuring in-situ stress. The magnitudes of in-situ stress can be determined from drilled core samples by deformation rate analysis (DRA); in other words, rocks do have the property of in-situ stress memory. In general, the inelastic strain of rocks increases with an increase in applied stress difference. The Keiser effect observed in laboratory experiments is explained as the behavior of the inelastic strain of this well-known mode. However, this effect cannot be the mechanism of the in-situ stress memory because the effect does not potentially allow us to determine the magnitudes of previously applied stress. Here, I theoretically show that rocks exhibit another mode of inelastic strain under axial loading of compression—if locally concentrated stresses in rocks relax to some extent under in-situ stress at depth. The magnitudes of in-situ stress can be determined from the behavior of this mode of inelastic strain under axial loading. The results of DRA suggest that this hypothesis is actually valid and that it is not only valid for the DRA, but also for the other rock core-based methods used for measuring in-situ stress.
Calculation of the piezomagnetic field arising from uniform regional stress in inhomogeneously magnetized crust
Authors: Yamazaki Ken’ichi
Published: August 2014

This paper describes a simple procedure for the calculation of the piezomagnetic field arising from uniform regional stress in heterogeneously magnetized crust. There exists a strong similarity between the spatial distributions of anomalies in the geomagnetic total force values arising from magnetization structures in the Earth’s crust and those arising from piezomagnetic signals that arise from there. This similarity enables us to compute the piezomagnetic field due to uniform regional stress without the need to determine the explicit structure of magnetization intensities in the crust. This situation is similar to that of “reduction to the pole”, which is commonly used to interpret magnetic survey data. An explicit formula is presented that gives the 2-D spectrum of the piezomagnetic field from that of local magnetic anomalies; the formula is then applied to synthetic data. Calculated values are compared with the exact solution of the piezomagnetic field in order to assess the efficacy of the proposed method. The comparison verifies that calculations performed using the formula yield sufficiently accurate values for practical use.
An attempt to infer information on planetary wave by analyzing sporadic E layers observations
Authors: Zuo Xiaomin , Wan Weixing , Zhao Guangxin
Published: August 2014

In this paper we presented two typical global 6-day planetary wave oscillations occurring in sporadic E layers. By analyzing the f
o
E
s time series observed from several ionosonde stations on the basis of the methods suggested by Haldoupis and Pancheva (2002), we computed estimates for the PW propagation direction, zonal wave number and phase velocity. We obtained results that the 6-day PW, with zonal wave number about 1, propagates westward, which are in agreement with those reported from radar and satellite neutral wind MLT measurements. The results provide experimental evidence for a close relationship between PWs and midlatitude E
s. In addition, the study proves the validity of E
s observations measured routinely and rather reliably with a dense global network of digital ionosondes used as an alternative means of studying large-scale neutral atmospheric dynamics in the MLT region.
Crustal thickness beneath the Ryukyu arc from travel-time inversion
Authors: Nakamura Mamoru , Umedu Nozomi
Published: August 2014

First P-wave arrival times recorded by the seismic network in the Ryukyu arc were analyzed in order to image the lateral variation in crustal thickness beneath the Ryukyu arc. The results indicate a low P
n velocity (7.5 km/s) in the Ryukyu arc and a relatively high P
n velocity (7.9 km/s) in the Okinawa Trough. The crustal thickness changes between the northern-and-central Ryukyu arc (range 23–27 km) and the southern Ryukyu arc (range 29–44 km). The crustal thickness of the former is consistent with that in the northern-and-central Okinawa Trough, suggesting a flat Moho stretching from the Okinawa Trough to the Ryukyu arc. This flat Moho extends uniformly over a wide area. In contrast, the crustal thickness in the southern Ryukyu arc is consistent with the characteristics of the crustal structure whereby the Moho becomes shallower in the vicinity of the axis of the Okinawa Trough and deepens remarkably with increasing distance from the axis in the southern Ryukyu arc. These differences would be caused by the difference in rifting style between the northern-and-central Okinawa Trough and the southern Okinawa Trough.
Earthquake hazard assessment in seismogenic systems through Markovian artificial neural network estimation: an application to the Japan area
Authors: Herrera C. , Nava F. A.
Published: August 2014

abstract

An earlier work (Herreraet al.:Earth Planets Space,58, 973–979, 2006) introduced two new methods for seismic hazard evaluation in a geographic area with distinct, but related, seismogenic regions. These two methods are based on modeling the transition probabilities ofstates, i.e. patterns of presence or absence of large earthquakes, in the regions, as a Markov chain. This modeling is, in turn, based on a straightforward counting of observed transitions between states. Thedirectmethod obtains transition probabilities among states that include events with magnitudesM≥Mr, whereMris a specified threshold magnitude. Themixedmethod evaluates probabilities for transitions from a state withM≥Mrmto a state withM≥MrM, whereMrm<MrM. Both methods gave very good results when applied to the Japan area, with the mixed method giving the best results and an improved magnitude range. In the work presented here, we propose other methods that use the learning capacity of an elementary neuronal network (perceptron) to characterize the Markovian behavior of the system; these neuronal methods,directandmixed, gave results ∼7 and ∼6% better than the counting methods, respectively. Method performance is measured using grading functions that evaluate a tradeoff between positive and negative aspects of performance. This procedure results in a normalized grade being assigned that allows comparisons among different models and methods.
The Upper Atmosphere and Plasma Imager/the Telescope of Visible Light (UPI/TVIS) onboard the Kaguya spacecraft
Authors: Taguchi M. , Sakanoi T. , Okano S. , Kagitani M. , Kikuchi M. , Ejiri M. , Yoshikawa I. , Yamazaki A. , Murakami G. , Yoshioka K. , Kameda S. , Miyake W. , Nakamura M. , Shiokawa K.
Published: August 2014

The Upper Atmosphere and Plasma Imager (UPI) was placed in a lunar orbit in order to study both the Moon and Earth. The UPI consists of two telescopes: a Telescope of Extreme Ultraviolet (TEX) and a Telescope of Visible Light (TVIS), which are both mounted on a two-axis gimbals system. The TVIS is equipped with fast catadioptric optics and a high-sensitivity CCD to image swift aurora and dark airglow in the terrestrial upper atmosphere. TVIS has a field-of-view equivalent to the Earth’s disk as seen from the Moon. The spatial resolution is about 30 km × 70 km on the Earth’s surface at auroral latitudes. The observation wavelengths can be changed by selecting different bandpass filters. Using the images of the northern and southern auroral ovals taken by TVIS, the intensities and shapes of the conjugate auroras will be quantitatively compared. Using the airglow imaging, medium- and large-scale ionospheric disturbances will be studied. In this paper, the instrumental design and performance of TVIS are presented.
Nonlinear thermoremanence corrections for Thellier paleointensity experiments on single plagioclase crystals with exsolved magnetites: a case study for the Cretaceous Normal Superchron
Authors: Usui Yoichi , Nakamura Norihiro
Published: August 2014

Single plagioclase paleointensity experiment has been an excellent tool to reliably estimate ancient geomagnetic field intensity. Although transparent plagioclases with magmatic nanophase magnetites have shown their potential for paleointensity estimation, in most cloudy plagioclases with exsolved magnetites, the problems of strong anisotropy as rod-shape magnetites, the hyperbolic tangential saturation of thermoremanence (TRM), and slow cooling of host plutons need to be addressed. In this paper, we propose experimental schemes to address these problems with considerations of error estimation and uncertainty for paleointensity experiments on exsolved magnetite. First, in order to experimentally check the effect of the hyperbolic tangential saturation of TRM, we performed Thellier simulation experiments using laboratory total TRM as simulated natural remanence (NRM). Single cloudy plagioclases were sampled from early Cretaceous granite in the Kitakami massif, Northeast Japan. We designed the experiment where the total TRM and the partial TRMs in the Thellier experiments were acquired under different field intensities. For these experiments, correction for hyperbolic tangential TRM acquisition yielded precise field intensity estimations. Next, Thellier experiments on NRM of the crystals from the same granite were performed as a demonstration of correction schemes for both magnetic anisotropy and hyperbolic tangential TRM acquisition. Precise determination of anisotropy tensor seems to be the major challenge for single plagioclase paleointensity estimation with exsolved magnetite.
The seasonal and solar cycle variations of electron density gradient scale length, vertical drift and layer height during magnetically quiet days: Implications for Spread F over Trivandrum, India
Authors: Manju G. , Devasia C. V. , Ravindran Sudha
Published: August 2014

A study has been carried out on the behaviour of electron density gradient scale length, L, vertical drift and layer height, around post sunset hours, during the magnetically quiet days of summer, winter and equinox seasons of solar maximum (2002) and minimum years (1995), using ionosonde data of Trivandrum (8.5°N, 76.5°E, dip = 0.5°N) in the Indian longitude sector. The results indicate a clear seasonal and solar cycle variation in all the three parameters. Further, the seasonal variation of equatorial Spread F (ESF) during the above period is examined in terms of the relative roles of L, the vertical drift and layer height (of the F layer) in the triggering of the collisional Rayleigh-Taylor instability. The results, show for the first time, that L also plays an important role, in controlling the quiet time seasonal and solar cycle variability of ESF; whereas in earlier studies this parameter had been taken to be constant. The detailed results are presented and discussed.
A numerical study on amplitude characteristics of the terdiurnal tide excited by nonlinear interaction between the diurnal and semidiurnal tides
Authors: Huang Chun Ming , Zhang Shao Dong , Yi Fan
Published: August 2014

A fully nonlinear numerical tidal model has been developed with the aim of presenting amplitude features of the terdiurnal tide excited by nonlinear interaction between the diurnal and semidiurnal tides. Since the superposition of the migrating diurnal and semidiurnal tidal solutions from the GSWM-00 (Global Scale Wave Model 2000) is taken as the initial disturbance for this nonlinear model, the diurnal and semidiurnal tides are allowed to nonlinearly interact with each other. The analyses on the simulations show that the migrating terdiurnal tide can be significantly excited by the nonlinear interaction between the diurnal and semidiurnal tides in the mesosphere and lower thermosphere (MLT) region, especially above 90 km, and have pronounced amplitudes (wind speeds over 15 m s−1 and temperature over 10 K) in the lower thermosphere (90–110 km). In addition, its amplitudes vary strongly with season and maximize during equinoctial months at low and middle latitudes, and its zonal wind component is larger than the meridional wind component. Simultaneously, the diurnal and semidiurnal tides exhibit evident variations, indicating that the wave-wave and wave-mean flow interactions are the important cause of the tidal variability. Our calculations also illustrate the remarkable alteration of the background fields induced by the mean flow/tidal interaction, implying this interaction should be comprehensively considered in describing global atmospheric dynamic and thermal structures in the MLT region.
Procrustean solution of the 9-parameter transformation problem
Authors: Awange J. L. , Bae K. -H. , Claessens S. J.
Published: August 2014

The Procrustean “matching bed” is employed here to provide direct solution to the 9-parameter transformation problem inherent in geodesy, navigation, computer vision and medicine. By computing the centre of mass coordinates of two given systems; scale, translation and rotation parameters are optimised using the Frobenius norm. To demonstrate the Procrustean approach, three simulated and one real geodetic network are tested. In the first case, a minimum three point network is simulated. The second and third cases consider the over-determined eight- and 1 million-point networks, respectively. The 1 million point simulated network mimics the case of an air-borne laser scanner, which does not require an isotropic scale since scale varies in the X, Y, Z directions. A real network is then finally considered by computing both the 7 and 9 transformation parameters, which transform the Australian Geodetic Datum (AGD 84) to Geocentric Datum Australia (GDA 94). The results indicate the effectiveness of the Procrustean method in solving the 9-parameter transformation problem; with case 1 giving the square root of the trace of the error matrix and the mean square root of the trace of the error matrix as 0.039 m and 0.013 m, respectively. Case 2 gives 1.13×10−12 m and 2.31×10−13 m, while case 3 gives 2.00×10−4 m and 1.20 × 10−5 m, which is acceptable from a laser scanning point of view since the acceptable error limit is below 1 m. For the real network, the values 6.789 m and 0.432 m were obtained for the 9-parameter transformation problem and 6.867 m and 0.438 m for the 7-parameter transformation problem, a marginal improvement by 1.14%.
Integrating potential fields with remote sensing data for geological investigations in the Eljufra area of Libya
Authors: Saadi Nureddin Mohamed , Watanabe Koichiro , Imai Akira , Saibi Hakim
Published: August 2014

In this study, we successfully integrated geological data, potential field data, and remote sensing data with the aim of investigating and improving our knowledge of the structural setting of the Eljufra area, northwestern Libya. SPOT-5 panchromatic band and digital elevation models (DEM) were used to construct surface shaded maps, and gravity and aeromagnetic surveys were used to provide information on subsurface structures and the nature of intrusive bodies. The results revealed that the prevailing trend of lineaments is NNW-SSE and NNE-SSW. A Bouguer anomaly map revealed that horst and graben blocks occur inside the large graben. An analytic signal method was applied to the aeromagnetic data to estimate locations and the minimum depths to the contact. A comparison of gravity and magnetic data provided information on hydrothermally altered basalt and sediment density. An anticlinal structure was detected in the western part of the study area. The effects of faults on basalt rocks indicated geological time for volcanic activity.
Quantitative description of oscillatory zoning in basaltic to dacitic plagioclases from the Shirahama Group, Japan
Authors: Tsune Akira , Toramaru Atsushi
Published: August 2014

New criteria related to the origin of oscillatory zoning (OZ) in plagioclase are presented. We compare the OZs in basaltic to those of dacitic plagioclases in the tholeiitic series volcanic rocks of the Shirahama Group, Izu Peninsula, Japan. Nomarski differential interference contrast (NDIC) images of the etched thin sections are used to measure zone thicknesses of the OZs. The normalized standard deviations per data series of the thicknesses are then calculated. We found that the average thicknesses are almost constant (mostly from 2 to 3 μm) through all the rock samples. This constancy corresponds to our idea that the length of oscillation, D/V (D: diffusivity in the melt; V: growth velocity of plagioclase) is almost constant for a variety of melt viscosity because strong dependences on the viscosity of D and V are canceled out in D/V. Consequently, we concluded that the growth of the OZ is basically controlled by an interface kinetics mechanism. In contrast, the plagioclases in SiO2-rich rocks have the following features: (1) larger standard deviations, (2) abundant erode-like zones, and (3) large oscillation amplitudes. These features reveal that the OZ patterns of plagioclases in more silicic magmas are disturbed due to change of the environmental parameters under the magma dynamics.
Precise remote-monitoring technique of water volume and temperature of a crater lake in Aso volcano, Japan: implications for a sensitive window of a volcanic hydrothermal system
Authors: Terada Akihiko , Hashimoto Takeshi , Kagiyama Tsuneomi , Sasaki Hisashi
Published: August 2014

A high-resolution Digital Surface Model and a commercial digital camera have enabled precise and continuous monitoring of the crater lake at Aso volcano. From July 2006 onwards, infrared (IR) thermometry has been used with this system, enabling more accurate measurements of lake volume and temperature based on simple and intensive observations than has been possible in any other previous studies. The heat discharge remained largely constant at approximately 220 MW, with the exception of an abrupt increase to 280 MW that coincided with a rapid decrease in the water level in August 2007. Simultaneously, an increase in temperature at a shallow depth was suggested by other observations. The crater lake was found to respond to even slight changes in volcanic fluid supply, which can be well quantified by our method. Thus, a crater lake can be monitored more precisely than subaerial fumaroles whose energy estimation is often accompanied by large uncertainties. Our monitoring technique of a crater lake provides information on the subsurface hydrothermal system beneath it, for which any in-situ measurements are practically impossible.
Digital beacon receiver for ionospheric TEC measurement developed with GNU Radio
Authors: Yamamoto Mamoru
Published: August 2014

A simple digital receiver named “GNU Radio Beacon Receiver (GRBR)” was developed for the satelliteground beacon experiment to measure the ionospheric total electron content (TEC). The open-source software toolkit for the software defined radio, GNU Radio, is utilized to realize the basic function of the receiver and perform fast signal processing. The software is written in Python for a LINUX PC. The open-source hardware called Universal Software Radio Peripheral (USRP), which best matches the GNU Radio, is used as a frontend to acquire the satellite beacon signals of 150 and 400 MHz. The first experiment was successful as results from GRBR showed very good agreement to those from the co-located analog beacon receiver. Detailed design information and software codes are open at the URL http://www.rish.kyoto-u.ac.jp/digitalbeacon/
Holocene ages and inland source of wood blocks that emerged onto the seafloor during the 2007 Chuetsu-oki, central Japan, earthquake
Authors: Kaneda Heitaro , Nakata Makoto , Hosoo Yoshihiro , Sugiyama Yuichi , Okamura Yukinobu
Published: August 2014

At least 300 tons of subrounded to well-rounded wood blocks emerged onto the seafloor at a water depth of 70–100 m during the 2007 M
w 6.6 Chuetsu-oki, central Japan, earthquake. Radiocarbon dating and taxonomic identification of eight of those wood blocks suggest that they were transported from inland during the middle to late Holocene, buried by subsequent sedimentation, and brought up onto the seafloor in 2007, most likely by submarine liquefaction induced by strong shaking. In particular, all eight blocks gave ages older than 2500 cal yr BP, implying the possibility that the 2007 earthquake was the first earthquake during the last two millennia to have caused shaking strong enough to induce submarine liquefaction in the 2007 meizoseismal area. However, we cannot rule out the possibility of multiple large earthquakes after approximately 2 ka, if the buried wood sources cannot be emptied by a single earthquake. Further studies are required to examine paleoseismic implications of the emergence of these wood blocks in 2007.
VHF radar observations of nighttime F-region field-aligned irregularities over Kototabang, Indonesia
Authors: Otsuka Y. , Ogawa T. , Effendy
Published: August 2014

We report, for the first time, continuous observations of the nighttime F-region field-aligned irregularities (FAIs) over Indonesia. A VHF radar with operating frequency of 30.8 MHz and peak power of 20 kW has been operated at Kototabang (0.20°S, 100.32°E; dip latitude 10.4°S), Indonesia since February 2006. Five beams were allocated between ±54° in azimuth around geographic south (126°–234°). From the continuous observation from February 2006 to November 2007, we found that FAIs appeared frequently at pre-midnight between March and May and at post-midnight between May and August. The pre-midnight FAIs coincided well with GPS scintillation observed at the same site. Seasonal and local time variations of the pre-midnight FAI occurrence are consistent with those of equatorial plasma bubbles reported in previous studies (e.g., Maruyama and Matuura, 1984). These results indicate that the pre-midnight FAIs could be associated with the equatorial plasma bubbles. On the other hand, seasonal and local time variations of the post-midnight FAIs were inconsistent with those of the plasma bubbles. The features of the post-midnight FAIs can be summarized as follows: (1) The post-midnight FAIs are not accompanied by GPS scintillations. (2) Most of the post-midnight FAI regions do not show propagation, but some of them propagate westward. (3) Echo intensity of the post-midnight FAIs was weaker than that of the pre-midnight FAIs. These features are similar to those of the FAI echoes that have been observed at mid-latitude (e.g., Fukao et al., 1991). At Kototabang, Fukao et al. (2004) have firstly observed FAIs that resemble those at mid-latitude. The present paper reports statistical characteristics of the mid-latitude-type FAIs observed at Kototabang.
Kelvin waves in stratosphere, mesosphere and lower thermosphere temperatures as observed by TIMED/SABER during 2002–2006
Authors: Forbes Jeffrey M. , Zhang Xiaoli , Palo Scott E. , Russell James , Mertens Christopher J. , Mlynczak Martin
Published: August 2014

Temperature measurements from the SABER instrument on the TIMED spacecraft are used to elucidate the properties of Kelvin waves and other equatorial oscillations over the altitude range 20–120 km during 2002–2006. The dominant Kelvin waves transition from long periods (52–10 days) and short wavelengths (9–13 km) in the stratosphere, to shorter periods (2–3 days) and longer wavelengths (35–45 km) in the 80–120 km height region. Ultra-Fast Kelvin Waves (UFKW) with periods of 2.5–4.5 days intermittently exist at amplitudes of order 3–10 K between 80–120 km during all months of the year, with variability at periods typically in the 20–60 day range. An Intra-seasonal oscillation (ISO) of zonal mean temperatures also exists with periods 20–60 days that may be driven by Eliassen-Palm Flux Divergences (EPFD) due, at least in part, to UFKW and migrating diurnal tides.
Diurnal and intraseasonal variation of UTLS vertical wind disturbance in the equatorial region and its relation to tropospheric convective activities
Authors: Kozu Toshiaki , Kodama Yasu-Masa , Shibagaki Yoshiaki , Shimomai Toyoshi , Kawashima Masayuki , Alexander Simon P.
Published: August 2014

Vertical wind variations in the Upper Troposphere and Lower Stratosphere (UTLS) measured by the Equatorial Atmosphere Radar (EAR) at Kototabang, Sumatra, between 2003 and 2005 but mainly in 2004, have been statistically analyzed to study the characteristics of wind variances associated with convective activity, which is related to gravity wave generation and propagation. The analyses are intended to characterize relatively short period disturbances of less than 12 hours and an energy propagation direction of a relatively high elevation angle, and to relate vertical wind variations to convective activity close to the EAR. Correlation analyses between vertical wind variations and rainfall show that the wind variances have a clear diurnal variation indicating probable effects of tropospheric convection. They also show some intraseasonal variation. However, there are no significant correlations with the Out-going Long-wave Radiation (OLR) anomaly. The correlations between variances at UT and LS suggest that the UTLS coupling of vertical wind variation through upward propagation of gravity wave is similarly evident in the afternoon during both the active and the inactive phase of OLR that is a proxy of large-scale convective activity.
Soft computing methods for geoidal height transformation
Authors: Akyilmaz O. , Özlüdemir M. T. , Ayan T. , Çelik R. N.
Published: August 2014

Soft computing techniques, such as fuzzy logic and artificial neural network (ANN) approaches, have enabled researchers to create precise models for use in many scientific and engineering applications. Applications that can be employed in geodetic studies include the estimation of earth rotation parameters and the determination of mean sea level changes. Another important field of geodesy in which these computing techniques can be applied is geoidal height transformation. We report here our use of a conventional polynomial model, the Adaptive Network-based Fuzzy (or in some publications, Adaptive Neuro-Fuzzy) Inference System (ANFIS), an ANN and a modified ANN approach to approximate geoid heights. These approximation models have been tested on a number of test points. The results obtained through the transformation processes from ellipsoidal heights into local levelling heights have also been compared.
Gravity structure of Akan composite caldera, eastern Hokkaido, Japan: Application of lake water corrections
Authors: Hasegawa Takeshi , Yamamoto Akihiko , Kamiyama Hiroyuki , Nakagawa Mitsuhiro
Published: August 2014

Akan volcano, eastern Hokkaido, Japan, is characterized by a rectangular-shaped caldera (Akan caldera: 24 km by 13 km) with a complex history of caldera-forming eruptions during the Quaternary. A new Bouguer anomaly map of the caldera is presented on the basis of a gravity survey around Akan volcano. As part of and in addition to this survey, we applied gravimetry over the frozen caldera lake including lake water corrections. The Bouguer map shows the distribution of at least three sub-circular minima indicative of multiple depressions inside the caldera. Lake water corrections, performed by a numerical integration method using rectangular prisms, sharpen edges of the sub-circular minima. This gravity feature is consistent with geological investigations suggesting that caldera-forming eruptions of Akan volcano occurred from at least three different sources. It is concluded that Akan caldera can be described as a composite caldera with three major depressed segments.
Global co-seismic displacements caused by the 2004 Sumatra-Andaman earthquake (Mw 9.1)
Authors: Fu Guangyu , Sun Wenke
Published: August 2014

This paper presents and discusses the global co-seismic displacements caused by the 2004 Sumatra-Andaman earthquake, using quasi-static dislocation theory for a spherically symmetric earth model (Sun et al., 1996). Theoretical calculations are performed with a heterogeneous slip distribution fault model based on Ammon et al. (2005). Results show that the co-seismic horizontal displacements are large to the north-east and southwest of the fault plane. Even as far as 6000 km from the epicenter, more than 1 millimeter co-seismic horizontal displacements raised from the earthquake. This paper has three contributions: to validate the fault model (Ammon et al., 2005) by geodetic data; to interpret the displacements observed by GPS; and to provide a reference for other researchers or for other geodetic applications. Overall, the modelled and observed displacements basically agree with each other in both the near field and far field. The calculated displacements are a generally smaller than the observed ones, since considerable moment is released by slow-slips and/or aftershocks which has not been included in the fault model.