bluuebunny/crossref_metadata_2025 huggingface dataset:
On the submarine communication cable JASC ground self-potential stability
Authors: Starjinsky Sergey S. , Nikiforov Valerian M.
Published: August 2014

This investigation was undertaken for searching the source of linear trends in JASC submarine cable data over the time interval of 6 years and estimating the electrode noise level. One of the reasons for a trend is probably the potential instability in the cable ground, which happened because the titanium electrodes of the ground were placed in sea water that is electrochemically active. To study this phenomenon, we have registered the voltage variations of three titanium JASC cable electrodes, which were closely spaced (≈15 cm) and placed at a depth of ≈15 m near the coast for 70 days, synchronously with JASC cable voltage observations. The electrode noise level and coherence between channels were estimated and linear trends in electrode pair voltage variation were revealed. The estimated linear trend magnitude is about 0.28 mV/day, which is comparable with 0.21 mV/day earlier observed in JASC submarine cable data. We concluded that the linear trend in JASC cable data is, at least partly, probably caused by the titanium electrodes potential variations. This linear trend should be registered simultaneously with JASC cable voltage observation, keeping in mind the possibility of finding a procedure for removing it, in order to enhance the signal/noise ratio in data.
Onshore-offshore seismic transect from the eastern Nankai Trough to central Japan crossing a zone of the Tokai slow slip event
Authors: Kodaira Shuichi , Iidaka Takashi , Nakanishi Ayako , Park Jin-Oh , Iwasaki Takaya , Kaneda Yoshiyuki
Published: August 2014

In the summer of 2001, an onshore-offshore integrated seismic survey was carried out along a 485 km long profile crossing the eastern Nankai Trough and central Japan from the western edge of the Izu island arc. Seismic velocity and reflectivity images showongoing subduction of repeated ridges. Two ridges are clearly resolved, the Paleo Zenisu-south ridge and -north ridge located between the Nankai Trough and central Japan. The two subducting ridges are 12 km thick by 40 km wide, and 20 km thick by 60 km wide, respectively. We propose that the north ridge may have prevented the eastward propagation of co-seismic slip during the 1944 earthquake due to strong coupling. Highly reflective subducting oceanic crust is imaged at 25–45 km depth beneath central Japan, and has a 2 km high dome structure at 30–40 km depth, indicating an even deeper ridge structure. This highly reflective subducted oceanic crust overlaps with the high Poisson’s ratio zone imaged in a seismic tomography study. From these relations, we propose that the Tokai silent slip can be attributed to a high pore pressure zone, which significantly extends the conditionally stable region at the top of the subducted crust.
Repeating short- and long-term slow slip events with deep tremor activity around the Bungo channel region, southwest Japan
Authors: Hirose Hitoshi , Obara Kazushige
Published: August 2014

We report the repeating occurrence of short- and long-term slow slip events (SSE) which are accompanied by deep tremor activity around the Bungo channel region, southwest Japan. Both of these activities are detected by NIED Hi-net, which is composed of densely distributed observatories equipped with a set of tiltmeter and a high-sensitivity seismograph. Since the short-term SSE is small in magnitude, GPS can detect only the long-term SSE. Some of these episodes have nearly the same surface deformation pattern. This shows the existence of ‘slow slip patches’ on a plate interface, where the episodic slow slip is the characteristic slip behavior. We observe a change in periodicity and size of the short-term episode after the onset of the long-term SSE. Moreover, the long-term slow slip accelerates when the short-term activity takes place. This suggests that there is an interaction between these two types of SSEs.
Triggering sequence of large aftershocks of the Mid Niigata prefecture, Japan Earthquake in 2004 by static stress changes
Authors: Miyazawa Masatoshi , Mori Jim , Iio Yoshihisa , Shibutani Takuo , Matsumoto Satoshi , Katao Hiroshi , Ohmi Shiro , Nishigami Kin’ya
Published: August 2014

Following the Mid Niigata prefecture Earthquake (MJMA6.8) in 2004, 4 large aftershocks (MJMA6.3, 6.0, 6.5, 6.1) occurred: three within 40 minutes and one after 4 days. We examine the possibility for the triggering of this sequence of large aftershocks by static stress changes. For the close spatial triggering, it is important to have information about the fault geometries, slip distribution, and focal mechanisms. We determine the fault plane orientations from the aftershock distributions. Slip distributions of the mainshock and the largest aftershock are obtained by seismic waveform inversions of local strong-motion records. Mechanisms for the events are taken from MT solutions. The temporal variations of Coulomb failure function changes (Δ CFF) are calculated on the fault planes of the aftershocks before their rupture. Positive Δ CFF values (0.06–0.3 MPa) are obtained around the hypocenters on the fault planes, indicating the possibility that static triggering from the main event and following aftershocks can explain the occurrence of subsequent aftershocks.
A tectonic interpretation of NW-SE strike-slip faulting during the 2004 off the Kii peninsula earthquakes, Japan: Probable tear of the Philippine Sea plate
Authors: Miyoshi Takayuki , Ishibashi Katsuhiko
Published: August 2014

The 2004 off the Kii peninsula earthquakes (M
w 7.5 for the main shock) occurred within the subducting Philippine Sea (PHS) plate near its boundary, the Nankai trough, southwest Japan. The rupture mode of the foreshock-main shock-aftershock sequence was complicated, a combination of ENE-WSW striking (almost trough parallel) reverse faulting beneath the trough and NW-SE trending (almost trough normal) strike-slip faulting mostly on the landward side of the former. In this paper, we discuss the tectonic meaning of this NW-SE running strike-slip fault. We examined hypocenter distribution and focal mechanisms of slab earthquakes from October 1997 through September 2004 and confirmed a NW-SE striking tear of the PHS slab beneath the middle part of the Kii Peninsula pointed out by Miyoshi and Ishibashi (2004). According to the Earthquake Research Committee (2004) there is a NW-SE trending structural discontinuity in the PHS crust to the southeast of the main shock epicenter. Putting all features together, we interpret that there is a NW-SE striking fracture within the PHS plate continuously from the Nankai trough region to the slab beneath the Kii Peninsula, and that a partial rupture of this fracture occurred during the off the Kii peninsula earthquakes together with trough-parallel reverse faulting. It should be noted that two disastrous M 7-class slab earthquakes seem to have occurred along this tear beneath the peninsula in 1899 and 1952.
Mass and moment of inertia constraints on the lunar crustal thickness: Relations between crustal density, mantle density, and the reference radius of the crust-mantle boundary
Authors: Hikida Hajime , Mizutani Hitoshi
Published: August 2014

The gravity inversion for the lunar crustal thickness needs three parameters: the crustal density, mantle density, and the reference radius of the crust-mantle boundary. The assumption of crust and mantle densities is found to significantly affect on the resultant crustal thickness variations. Moreover, the recent seismic analyses suggest the possibility of thinner crustal thickness around the Apollo 12 site than that proposed in the Apollo-era, on which the previous gravity inversions relied upon. Therefore the validity of the assumption used in previous gravity-inversion studies must be re-examined in detail. By using a simple three-layered mass model of the Moon including a uniform crust, mantle, and core, we determine possible combinations of the three parameters, satisfying the mass and moment of inertia constraints. The results show that the set of the parameters used in Neumann et al. (1996) can be consistent with mass and moment of inertia constraints, while those in Wieczorek and Phillips (1998) does not satisfy the constraints.
Candidate main-field models for producing the 9th generation IGRF
Authors: Mandea Mioara
Published: August 2014

This paper presents the various candidate models used in deriving the 9th generation IGRF. Based on notes submitted to the IAGA working group V-MOD with the Gauss coefficients, a brief description of the data used and the method of modelling for each of the candidate models is given. The six candidate models for epoch 1995.0 and the five for epoch 2000.0 are presented. Improvements gained by the new models are also discussed.
Magnetic field modelling from scalar-only data: Resolving the Backus effect with the equatorial electrojet
Authors: Holme R. , James M. A. , Lühr H.
Published: August 2014

It is well known that models of the global geomagnetic field constructed from only measurements of the field intensity suffer from large errors arising from the Backus or perpendicular error effect. Knowledge of the location of the magnetic dip equator is in principal sufficient to eliminate this error. We investigate constraining the location of the dip equator using observations of the equatorial electrojet in intensity measurements made from the CHAMP satellite. While the models generated are inferior compared with models obtained from oriented three-component vector data, they may be of sufficient quality to allow construction of future global geomagnetic reference models in the absence of vector data.
Fault model of the 2005 Fukuoka-ken Seiho-oki earthquake estimated from coseismic deformation observed by GPS and InSAR
Authors: Nishimura Takuya , Fujiwara Satoshi , Murakami Makoto , Suito Hisashi , Tobita Mikio , Yarai Hiroshi
Published: August 2014

On 20 March 2005, the Fukuoka-ken Seiho-oki (the 2005 West off Fukuoka Prefecture) earthquake (MJMA7.0) occurred in northern Kyushu, western Japan. We used coseismic deformation observed by GPS and InSAR to construct a fault model. The uniform slip model of rectangular dislocation in an elastic half-space suggests ∼1.4 m of left-lateral strike slip faulting on a near-vertical fault. The fault strike is 298 degrees and its southeastern edge was strongly constrained by the displacement at a permanent GPS station located on Shikanoshima, which is consistent with the aftershock distribution. We estimated slip distribution on a planar fault and found the maximum slip of ∼1.9 m near the surface. Large slip is concentrated at depths of 0 to 10 km in an along-strike range from the hypocenter to 10 km east-southeast of it.
Source processes of the 2005 West Off Fukuoka Prefecture earthquake and its largest aftershock inferred from strong motion and 1-Hz GPS data
Authors: Kobayashi Reiji , Miyazaki Shin’ichi , Koketsu Kazuki
Published: August 2014

We simultaneously inverted strong motion and 1-Hz GPS data recorded during the 2005 west off Fukuoka prefecture earthquake (M
JMA 7.0) for its source process. The data at a GPS station near the source region provided strong constraint on the fault geometry and asperity area. The resultant slip distribution suggests a single asperity close to the Genkai island, where many houses were severely damaged. The maximum slip is 1.4 m, and the total seismic moment is 1.0 × 1019 Nm (M
W 6.6). We also inverted strong motion data recorded during the largest aftershock (M
JMA 5.8). The resultant slip distribution shows two asperities on the fault plane. The maximum slip in the major asperity is 0.12 m and the total seismic moment is 2.0 × 1017 Nm (M
W 5.5). The main shock and largest aftershock may cause stress change on the Kego fault, which is a major fault running through the city of Fukuoka.
Initial-rupture fault, main-shock fault, and aftershock faults: Fault geometry and bends inferred from centroid moment tensor inversion of the 2005 west off Fukuoka prefecture earthquake
Authors: Ito Yoshihiro , Obara Kazushige , Takeda Tetsuya , Shiomi Katsuhiko , Matsumoto Takumi , Sekiguchia Shoji , Hori Sadaki
Published: August 2014

The 2005 west off Fukuoka prefecture earthquake (M
JMA = 7.0) occurred on March 20, 2005 in northwest Kyusyu, Japan. The fault geometry and rupture propagation of the main shock are investigated by applying the centroid moment tensor (CMT) inversion method to densely-distributed broadband seismic network data. An accurate distribution of small aftershocks is also examined by a double-difference method. The source fault of the main shock whose moment magnitude was 6.6 had a strike of 123°, and the rupture propagated in the southeast direction. We obtain forty-four CMT solutions of the main shock and aftershocks with a moment magnitude greater than 3.5. For the main shock, the fault strike estimated using P-wave first-motion polarities differs from that of the moment tensor solution by 13° in the counterclockwise direction. Some aftershocks with a moment tensor solution similar to the focal mechanism of the main shock derived from the P-wave first motions are distributed north of the epicenter of the main shock. The largest aftershock with a strike of 8° in the clockwise direction, which differs from that of the CMT solution of the main shock, was located south of the main shock. These changes in the fault strike play an important role in the initiation and termination of the rupture process of the main shock.
Source process and near-source ground motions of the 2005 West Off Fukuoka Prefecture earthquake
Authors: Asano Kimiyuki , Iwata Tomotaka
Published: August 2014

A large shallow crustal earthquake occurred at the western off-shore of Fukuoka Prefecture, northern Kyushu, Japan, at 10:53 on March 20, 2005 (JST). Source rupture processes of the mainshock and the largest aftershock on April 20, 2005, are estimated by the kinematic waveform inversion of strong motion seismograms. The rupture of the mainshock started with relatively small slip, and the largest slip was observed at the southeast of the hypocenter. The inverted source models showed that both of the ruptures of the mainshock and the largest aftershock mainly propagated to southeast from the hypocenters, and the rupture area of those events did not overlap each other. Three-dimensional ground motion simulation by the finite difference method considering three-dimensional bedrock structure was also conducted to see the spatial variation of the near-source ground motion of the mainshock. The result of the simulation shows that expected groud motions are relatively large in and arround Genkai Island, Shikanoshima Island, and the center of Fukuoka City compared to the other area because of the rupture heterogeneity and the deep basin structure in Fukuoka City.
The generalized Bouguer anomaly
Authors: Nozaki Kyozo
Published: August 2014

This paper states on the new concept of the generalized Bouguer anomaly (GBA) that is defined upon the datum level of an arbitrary elevation. Discussions are particularly focused on how to realize the Bouguer anomaly that is free from the assumption of the Bouguer reduction densityρB, namely, theρB-free Bouguer anomaly, and on what is meant by theρB-free Bouguer anomalyin relation to the fundamental equation of physical geodesy. By introducing a new concept of the specific datum level so that GBA is not affected by the topographic masses, we show the equations of GBA upon the specific datum levels become free fromρBand/or the terrain correction. Subsequently utilizing these equations, we derive an approximate equation for estimatingρB. Finally, we show how to compute a Bouguer anomaly on the geoid by transforming the datum level of GBA from the specific datum level to the level of the geoid. These procedures yield a new method for obtaining the Bouguer anomaly in the classical sense (say, the Bouguer disturbance), which is free from the assumption ofρB. We remark that GBA upon theρB-free datum levelis the gravity disturbance and that the equation of it has a tie to the fundamental equation of physical geodesy.
Geomagnetic effects of high-density plasma with southward magnetic field in the interplanetary coronal mass ejection observed on May 2–3, 1998
Authors: Adachi Haruka , Sakurai Tohru , Marubashi Katsuhide
Published: August 2014

This paper aims to clarify the effect of high-density plasma in interplanetary coronal mass ejection (ICME) observed during the May 2–3, 1998 geomagnetic storm. The examination is performed based on the estimation of Dst index, which is calculated with the observed solar wind parameters of the ICME. The estimated Dst index variation is compared with Dst index variation provided by the World Data Center for Geomagnetism, Kyoto (WDC, Kyoto). From this examination, we find that the trend of the estimated Dst is in good agreement with that of the provided Dst when the thresholds are taken into account for both the solar wind plasma density and the dawn-to-dusk solar wind electric field, as 30 #/cc and 0.49 mV/m, respectively. From the result, we can conclude that the effect of high-density plasma is important on the enhancement of geomagnetic storm as well as the effect of the other solar wind parameters, such as the interplanetary magnetic field (IMF) Bz and solar wind velocity. On the other hand, the solar source of the magnetic field of this ICME is examined. The magnetic field structure of the ICME is examined by fitting the flux rope model to the observed magnetic field and solar wind speed. The results are compared with the magnetic structure of the bases of coronal helmet streamers. From this comparison we can find that the magnetic structure of the interplanetary flux rope is in good agreement with that of the neutral line of the base of coronal helmet streamers. The result suggests that if we look for the causes of geomagnetic storm we should take into account both the plasma structure and the magnetic structure of the base of coronal helmet streamers.
An empirical model of ionospheric foE over Wuhan
Authors: Yue Xinan , Wan Weixing , Liu Libo , Ning Baiqi
Published: August 2014

Daytime half-hourly values of the critical frequency of the ionosphericE-layer,f oE, obtained at Wuhan Ionospheric Observatory (geographic 114.4°E, 30.6°N; 45.2°dip), China, during the whole interval of 1957–1991 and 1999–2004 have been used to develop an empirical model. The model, including variations with local time, day number and solar cycle, is in agreement with the observations. A comparison between our model and IRI and Titheridge’s model has also been made. Statistically, our model gives a better performance than IRI and Titheridge’s model because data set is obtained with our own station. Both the IRI and Titheridge’s model overestimatef oEespecially in May to September months. Combing with past investigations, we suggest that overestimation of ionospheric parameters by IRI may be a common feature in East Asia. This result is very helpful for both the correction of IRI in East Asia and the development of Chinese Reference Ionosphere (CRI) model.
The Swarm End-to-End mission simulator study: A demonstration of separating the various contributions to Earth’s magnetic field using synthetic data
Authors: Olsen Nils , Haagmans Roger , Sabaka Terence J. , Kuvshinov Alexei , Maus Stefan , Purucker Michael E. , Rother Martin , Lesur Vincent , Mandea Mioara
Published: August 2014

Swarm, a satellite constellation to measure Earth’s magnetic field with unpreceded accuracy, has been selected by ESA for launch in 2009. The mission will provide the best ever survey of the geomagnetic field and its temporal evolution, in order to gain new insights into the Earth system by improving our understanding of the Earth’s interior and climate. An End-to-End mission performance simulation was carried out during Phase A of the mission, with the aim of analyzing the key system requirements, particularly with respect to the number of Swarm satellites and their orbits related to the science objectives of Swarm. In order to be able to use realistic parameters of the Earth’s environment, the mission simulation starts at January 1, 1997 and lasts until re-entry of the lower satellites five years later. Synthetic magnetic field values were generated for all relevant contributions to Earth’s magnetic field: core and lithospheric fields, fields due to currents in the ionosphere and magnetosphere, due to their secondary, induced, currents in the oceans, lithosphere and mantle, and fields due to currents coupling the ionosphere and magnetosphere. Several independent methods were applied to the synthetic data to analyze various aspects of field recovery in relation to different number of satellites, different constellations and realistic noise sources. This paper gives an overview of the study activities, describes the generation of the synthetic data, and assesses the obtained results.
Using global magnetospheric models for simulation and interpretation of Swarm external field measurements
Authors: Moretto T. , Vennerstrøm S. , Olsen N. , Rastätter L. , Raeder J.
Published: August 2014

We have used a global model of the solar wind magnetosphere interaction to model the high latitude part of the external contributions to the geomagnetic field near the Earth. The model also provides corresponding values for the electric field. Geomagnetic quiet conditions were modeled to provide simulated external contributions relevant for internal field modeling. These have proven very valuable for the design and planning of the upcoming multi-satellite Swarm mission. In addition, a real event simulation was carried out for a moderately active time interval when observations from the Ørsted and CHAMP sattelites were available. Comparisons between the simulation results and the satellite observations for this event demonstrate the current level of validity of the global model. We find that the model reproduces quite well the region 1 current system and nightside region 2 currents whereas it consistently underestimates the dayside region 2 currents and overestimates the horizontal ionospheric closure currents in the dayside polar cap. Furthermore, with this example we illustrate the great benefit of utilizing the global model for the interpretation of Swarm external field observations and, likewise, the potential of using Swarm measuremnets to test and improve the global model.
Global lithospheric magnetic field modelling by successive regional analysis
Authors: Thébault E.
Published: August 2014

Present lithospheric field models, like the MF4 and CM4, are produced by least squares estimation using spherical harmonic basis functions with global support. Accounting for the different properties of magnetic data at low and high latitudes, a method that can take regional differences into account is proposed. Using four years of CHAMP satellite data, a detailed lithospheric magnetic field snapshot is obtained at 400 km altitude over the entire sphere by stitching together a dense coverage of regional models. The individual forward models computed on a quasi-regular grid over the Earth are then transformed to spherical harmonics by direct integration. Despite the stitching procedure, the long wavelength lithospheric features are correctly reproduced and small scale features are well resolved. Without regularization, the resulting model is stable to spherical harmonic degree 56. In addition to accounting for regionally varying noise levels, the proposed technique is also well suited to deal with incomplete data coverage issues when combining satellite with near surface data. The method could therefore make an important contribution to one of the main goals of the Swarm mission: to close the spectral gap between satellite and near-surface magnetic surveys.
A reexamination of pitch angle diffusion of electrons at the boundary of the lunar wake
Authors: Nakagawa Tomoko , Iizima Masahide
Published: August 2014

Velocity distribution of the solar wind electrons injected into the lunar wake boundary is re-examined by using a simple model structure of inward electric field. The electrons that were flowing along the magnetic field lines undergo pitch angle scattering due to the electric field component perpendicular to the magnetic field. The electrons obtain perpendicular speeds twice as much as the drift speed. On the basis of the GEOTAIL observations of the whistler mode waves and strahl electrons, the intensity of the electric field and the thickness of the wake structure are estimated to be 28-40 mVm-1 and less than 20 km, respectively.
GPS measurements of horizontal deformation across the Lai Chau—Dien Bien (Dien Bien Phu) fault, in Northwest of Vietnam, 2002-2004
Authors: Cong Duong Chi , Yun Hong-Sic , Cho Jae-Myoung
Published: August 2014

Global Positioning System (GPS) measurements from Feb. 2002 through Mar. 2004 were used to estimate the recent crustal movement along the Lai Chau—Dien Bien (Dien Bien Phu) fault (LC-DBF) system in the Northwest of Vietnam. Four GPS campaign data were processed to estimate ITRF2000 and local horizontal velocities, as well as extensive and compressive strain rates across the LC-DBF. ITRF2000 velocities are consistent with east-southeastward movement of Sundaland i.e. Indochina. Local velocities did not reveal much left-lateral strike-slip of the fault system and the derived strain rates were insignificantly different from zero at 95% confidence.
Re-estimation of tsunami source of the 1952 Tokachi-oki earthquake
Authors: Satake Kenji , Hirata Kenji , Yamaki Shigeru , Tanioka Yuichiro
Published: August 2014

Previous studies indicate that the source area of the 2003 Tokachi-oki earthquake (M 8.0) was smaller than the comparable 1952 Tokachi-oki earthquake (M 8.2) source. We reinverted the 1952 tsunami waveforms, by adopting higher-resolution tsunami simulation method, and estimating and correcting for clock errors of tide gauges from comparison of the 1952 and 2003 tsunami waveforms. The estimated slip distribution indicates that the 1952 tsunami source area was indeed larger than the 2003 source. The distributions of measured and computed coastal tsunami heights also support this conclusion.
Simulations of SH wave scattering due to cracks by the 2-D finite difference method
Authors: Suzuki Yuji , Kawahara Jun , Okamoto Taro , Miyashita Kaoru
Published: August 2014

We simulate SH wave scattering by 2-D parallel cracks using the finite difference method (FDM), instead of the popularly used boundary integral equation method (BIEM). Here special emphasis is put on simplicity; we apply a standard FDM (fourth-order velocity-stress scheme with a staggered grid) to media including tractionfree cracks, which are expressed by arrays of grid points with zero traction. Two types of accuracy tests based on comparison with a reliable BIEM, suggest that the present method gives practically sufficient accuracy, except for the wavefields in the vicinity of cracks, which can be well handled if the second-order FDM is used instead. As an application of this method, we also simulate wave propagation in media with randomly distributed cracks of the same length. We experimentally determine the attenuation and velocity dispersion induced by scattering from the synthetic seismograms, using a waveform averaging technique. It is shown that the results are well explained by a theory based on the Foldy approximation for crack densities of up to about 0.1. The presence of a free surface does not affect the validity of the theory. A preliminary experiment also suggests that the validity will not change even for multi-scale cracks.
A numerical analysis of seismic waves for an anisotropic fault zone
Authors: Nakamura Takeshi , Takenaka Hiroshi
Published: August 2014

In this study we examine the effects of anisotropy on the seismic wavefield in a fault zone from computation of the synthetic seismograms for a simple fault zone model and a variety of seismic wave sources. The fault zone is modeled by a homogeneous vertical layer with transverse isotropy, induced by cracks, sandwiched between isotropic half-spaces (host rocks). The symmetry axis of the transverse isotropy is horizontal and perpendicular to the fault zone strike. We calculate the synthetic seismograms for this anisotropic fault zone model using a semianalytical method, the propagator matrix method. The synthetic seismograms show a later phase arriving after the main shear-wave in the horizontal component perpendicular to the fault zone strike at most stations near the fault zone. It is the slower shear-wave (qS2) and its reverberation. The amplitude of this phase and the time delay from the main shear-wave arrival are proportional to the degree of anisotropy, which suggests that observing such phase in field measurements may imply the presence of an anisotropic fault zone. We also perform the shear-wave splitting measurements by applying the cross-correlation method to the synthetic seismograms for various sources. For a strike-slip source, the synthetic seismograms show that the wavefield is more affected by the velocity structure than by the degree of anisotropy, which makes it difficult to estimate the anisotropic (shearwave splitting) parameters. For normal and dip-slip fault sources with the strike parallel to or striking against the fault zone, the effects of anisotropy is so dominant that the anisotropic fault zone can be detected. These results suggest that the determination of the anisotropic properties in the fault zone would require an appropriate station deployment and the source type information.
One-dimensional spherical elementary current systems and their use for determining ionospheric currents from satellite measurements
Authors: Juusola Liisa , Amm Olaf , Viljanen Ari
Published: August 2014

The method of 1D spherical elementary current systems (SECS) is a new way for determining ionospheric and field-aligned currents in spherical geometry from magnetic field measurements made by a low-orbit satellite. In contrast to earlier methods, the full ionospheric current distribution, including both divergence-free and curl-free horizontal currents, as well as field-aligned currents, can be determined. Placing infinitely many 2D SECSs of identical amplitudes at a constant latitude results in two types of 1D SECSs, which are independent of longitude, and by superposition can reproduce any ionospheric and field-aligned current system with the same property. One type of the 1D SECSs is divergence-free and toroidal with a poloidal magnetic field, and the other type is curl-free and poloidal. Associated with the divergence of the curl-free type are radial currents. The magnetic field of the combined curl-free 1D SECS and field-aligned currents is toroidal and restricted to the region above the ionosphere. Ionospheric currents are determined by placing several 1D SECSs at different latitudes and choosing their amplitudes in such a way that their combined magnetic field as closely as possible fits the one measured by the satellite. The 1D SECS method has been tested using both modeled and real data from the CHAMP satellite, and found to work excellently in 1D cases.
Measurement quality estimation of proton-precession magnetometers
Authors: Denisov A. Y. , Denisova O. V. , Sapunov V. A. , Khomutov S. Y.
Published: August 2014

A method for calculating quality estimation of the magnetic field value measured by proton-precession magnetometers from data of single measurement is presented. This method is appropriate for frequency measurement algorithms which process time-series of signal’s zero crossing. Expressions for measurement error estimation are obtained taking into account signal decay and correlated noise. Presented formulas allow a result reliability to be estimated immediately in single measurement and give an opportunity for complex control of a device performance. Correlation and relaxation corrections are given. It was experimentally tested that the standard deviation of measurements is in a good qualitative agreement with presented error estimation.
Influence of magnetic field variations on measurements by magnetometers using averaging algorithms
Authors: Denisova O. , Sapunov V. , Denisov A.
Published: August 2014

The article is devoted to features of modulus magnetic field measurements by means of proton magnetometers. Inertial characteristics of the magnetometers and dynamic errors of variable magnetic field measurements are discussed. Three basic magnetometers averaging algorithms, processing zero crossing times of free precession, are compared. Theoretical and some numerical estimations of the algorithms work are presented for the linear, square and harmonic variations of magnetic field.
Modelling of spatial-temporal changes of the geomagnetic field in Japan
Authors: Ji Xiaoli , Utsugi Mitsuru , Shirai Hiroki , Suzuki Akira , He Jinlan , Fujiwara Satoshi , Fukuzaki Yoshihiro
Published: August 2014

A geomagnetic regional model is constructed to provide a spatial-temporal variation of three orthogonal components (X, Y, Z) in Japan. In order to obtain a high temporal and spatial resolution, Natural Orthogonal Components (NOC) analysis and Spherical Cap Harmonic (SCH) analysis were employed to produce a spatial-temporal model based on the observed data from geomagnetic observatories and continuous geomagnetic stations. Using this model, we calculated the secular variation between 1999 and 2004 in Japan. The root mean square (RMS) scatter of the model is less than 3 nT, which indicates a good agreement between calculated and input data.
Sharp and seismically transparent inner core boundary region revealed by an entire network observation of near-vertical PKiKP
Authors: Kawakatsu Hitoshi
Published: August 2014

We present an entire network observation of near-vertical PKiKP from the Japanese seismic network, Hi-net. The record section of an intermediate depth (298 km) earthquake in Mariana (2001/07/03 13:10:43, Mw 6.5) shows remarkably clear arrivals of PKiKP in an epicentral distance range of 14–24 degrees. From more than 170 individual picks of PKiKP, we performed array analyses of PKiKP-related seismic phases to infer the structure near the inner core boundary (ICB) with unprecedented high quality. Both PKiKP and PcP showed strong similarity in waveforms up to a frequency of 2 Hz. Both amplitude and waveform analyses indicate that the ICB may be as sharp as the CMB and no thicker than 2 km. The slant stack for a 1–2 Hz frequency band, where PKiKP and PcP show energy peaks and where the background noise level is ∼3% of PKiKP, indicated no conspicuous phase other than SKiKP. We also noted that no gradual energy build-up of the inner core scattering signal was observed. Thus, this part of the inner core appears highly transparent seismically in this frequency range. In the 0.5–1.0 Hz frequency band (10–15% noise level), we observed one possible reflection phase from a slightly dipping (∼5°) reflector/discontinuity inside of the inner core around a depth of 470 km below the ICB (3% reflection). However, this phase may be due to pPKiKP water/crustal layer reverberations. Other than this, there appears to be no sharp (∼5 km thick) horizontal discontinuity in the top 400 km part of the inner core whose reflection amplitude is larger than ∼2%.
Preliminary results of rocket attitude and auroral green line emission rate in the DELTA campaign
Authors: Iwagami Naomoto , Komada Sayaka , Takahashi Takao
Published: August 2014

The attitude of a sounding rocket launched in the DELTA (Dynamics and Energetics of the Lower Thermosphere in Aurora) campaign was determined with IR horizon sensors and geomagnetic sensors. Since the payload was separated into two portions, two sets of attitude sensors were needed. A new IR sensor was developed for the present experiment, and found the zenith-angle of the spin-axis of the rocket with an accuracy of 2°. By combining information obtained by both type of sensors, the absolute attitudes were determined. The auroral green line emission rate was measured by a photometer on board the same rocket launched under active auroral conditions, and the energy flux of the auroral particle precipitation was estimated.
Rocket observation of energetic electrons in the low-altitude auroral ionosphere during the DELTA campaign
Authors: Ogasawara K. , Asamura K. , Takashima T. , Saito Y. , Mukai T.
Published: August 2014

This paper reports on properties of energetic electrons observed by the Auroral Particle Detector (APD) on board the sounding rocket S-310-35, which was launched from And/0ya Rocket Range, Norway, at 0033:00 UT on 13 December 2004 during the DELTA campaign. The APD was designed to measure energy spectra of energetic electrons in the range of 3.5 to 65 keV every 10 ms using avalanche photodiodes. The measurement was done at altitudes of 90–140 km (apogee height of the rocket flight), which corresponded to the collisional interaction region of precipitating electrons with the atmospheric constituents. The overall profile of energetic electron precipitations was consistent with auroral images taken from the ground. The downward fluxes almost always exceeded those of upward electrons, and the ratio of downward to upward fluxes increased with energy and also with altitude. This is reasonably understood in terms of the effect of collisions between the energetic electrons and the atmospheric constituents. An interesting feature in energy spectra of precipitating electrons is the existence of non-thermal electrons at higher energies, regardless of inside or outside of auroral arcs. In order to predict the incident downward spectra at the top of the atmosphere, we have applied an analytic method of Luhmann (1976) to evaluate the collisional effect on the electron spectra. As a result, most of the observed energy spectra of precipitating electrons are well expressed by kappa distributions with the thermal energy of a few hundreds of eV and kappa of 5–8, while the spectrum inside a strong arc is better fitted by the sum of a Maxwellian distribution on the lower energy side and a power law at higher energies. To the authors’ knowledge, this is the first direct and reliable measurement of energy spectra of electrons in the 10-keV energy range in the auroral ionosphere.
Dynamics and Energetics of the Lower Thermosphere in Aurora (DELTA)—Japanese sounding rocket campaign—
Authors: Abe Takumi , Kurihara Junichi , Iwagami Naomoto , Nozawa Satonori , Ogawa Yasunobu , Fujii Ryoichi , Hayakawa Hajime , Oyama Koh-ichiro
Published: August 2014

Japanese sounding rocket “S-310-35” was launched from And/0ya Rocket Range in Norway on December 13, 2004 during Dynamics and Energetics of the Lower Thermosphere in Aurora (DELTA) campaign, in which the rocket-borne in-situ measurements and ground-based measurements were coordinated to carry out a comprehensive observation of the thermospheric response against the auroral energy input. The instruments on board the rocket successfully performed their measurements during the flight, and thereby the temperature and density of molecular nitrogen, auroral emission rate, and the ambient plasma parameters were derived. Simultaneous measurements by the ground-based instruments provided neutral wind, neutral temperature, the auroral images and the ionospheric parameters near the rocket trajectory. This paper introduces science objectives, experimental outline, and preliminary scientific results of the DELTA campaign and explains geophysical condition at the time of the rocket launch, while the companion papers in this special issue describe more detailed results from each instrument.
The contribution of sprites to the global atmospheric electric circuit
Authors: Füllekrug Martin , Rycroft Michael J.
Published: August 2014

The global static electric field in the global atmospheric electric circuit resulting from mesospheric sprite discharges is inferred from a coupled model for the global static and dynamic electric fields derived from Maxwell’s equations. It is found that the global atmospheric electric field from individual sprites is ≲ 44 mV/m, which can be measured with conventional ULF/ELF radio wave antennas at frequencies ≲ 4 Hz.
Low-frequency variability of a two-layer ocean forced by periodic winds
Authors: Sakamoto Toshihiro
Published: August 2014

To seek the variability of the oceanic subtropical gyre on interannual and longer time scales we have conducted numerical experiments with a two-layer quasigeostrophic model in a square basin bounded by no-slip walls. We find that when the amplitude of annually periodic wind forcing is increased, the time series of the total energy exhibit a transition to chaos in such a manner that the response frequency constitutes a quasi-devil’s staircase against the forcing amplitude; in particular, the n-cycles appear in descending order of n. The low-frequency modes may thus be produced by seasonal winds. Since, however, the power of the subharmonics is much weaker than that with the forcing frequency, their energy would be concealed by noise in the presence of stochastic wind forcing. The present result is in contrast with the case of the time-independent forcing in which we observe the intrinsic frequencies probably associated with the wave propagation, frequency locking and a cascade of period-doubling bifurcations.
Simulation study on nonlinear frequency shift of narrow band whistler-mode waves in a homogeneous magnetic field
Authors: Katoh Yuto , Omura Yoshiharu
Published: August 2014

We study frequency variation of a coherent whistler-mode wave in a homogeneous magnetic field by a selfconsistent simulation model. Simulation results show that an injected whistler-mode wave packet grows due to an instability driven by temperature anisotropy and the amplified wave packet triggers emissions with frequency shift during its propagation. We clarify that the resonant currents J
E and J
B due to the nonlinear wave-particle interaction play significant roles in both wave growth and frequency variation. Based on the simulation results, we show that the range of the frequency shift in a homogeneous system is quantitatively estimated by the trapping frequency V
T of trapped electrons; in a case that the original frequency of the wave packet is 0.62Ωe and V
T=4.05 × 10−2
c, the lower and upper frequencies are estimated to be 0.565Ωe and 0.685Ωe, respectively. The results of the present study reveal that the role of nonlinear trapping is significant in the elementary process of VLF triggered emissions in the equatorial region of the magnetosphere.
Identifying block rotations from remanent magnetization effect: Example from northern Central Turkey
Authors: Bilim Funda , Ates Abdullah
Published: August 2014

One of the difficulties in interpreting magnetic anomaly data is the distortion caused by rock body magnetization. There have been several successful studies carried out on the estimation of body magnetization based on the correlation of the Bouguer and magnetic anomaly data. A number of other significant research projects have aimed at identifying the effect of remanent magnetization in magnetic data only. In this paper, we present a threedimensional method for determining the body magnetization direction by means of comparing the amplitude of the analytic signal with the horizontal gradient of pseudogravity of magnetic anomaly using the correlation coefficient equation. The method has been successfully applied to test cases and is applied here to the aeromagnetic anomalies located in northern Central Turkey. Anomalies displaying individual polarities were separated out and correlated with themselves using the correlation coefficient equation. Counter-clockwise rotations in the range of 3° and 174° were determined. Clockwise rotations were determined in the range of 19° and 153°. The inclination of the body magnetization directions for one of the blocks was estimated to be 68.4°, while all other blocks had a low inclination angle of body magnetization in the range of 32° to 57°. These results may imply that these blocks gained their magnetizations when Turkey was at low latitudes. Possible buried faults are also identified. The results reported here comply with the new mobilistic theory.
Ionospheric measurements during the total solar eclipse of 11 August 1999
Authors: Chandra H. , Sharma Som , Lele P. D. , Rajaram G. , Hanchinal Arun
Published: August 2014

A number of radio experiments were conducted at Ahmedabad (23°N, 73°E) with the aim of studying the ionospheric effects of the total solar eclipse of 11 August 1999. Rapid radio soundings from the ionosonde were made on the eclipse day and on control days. A riometer was operating at 30 MHz, and field strength measurements along the three oblique incidence paths of Colombo-Ahmedabad (11905 kHz), Bombay-Ahmedabad (558 kHz) and Rajkot-Ahmedabad (810 kHz) were also made. A reduction of about 20% was observed in the minimum frequency of reflection from the ionosonde (fmin), which indicates a reduction in D-region ionization. The critical frequency of the E-layer was not measurable beyond 1600 h IST on eclipse day due to the strong blanketing sporadic-E, but there is a 20% decrease in the critical frequency of the F1-layer. Although there was no change in the minimum virtual height of the F-layer on eclipse day, there appears to have been a decrease in the height of maximum ionization (hpF2) during the eclipse, indicating a reduction in the thickness of the F-layer. The signal strength of the Colombo-Ahmedabad path shows an initial rapid increase with the start of the eclipse (indication of a decrease in ionization in the D- and lower E-regions), but subsequently decreases until the maximum of the eclipse (excessive deviative absorption because of the wave penetrating to the E-region). The field strength measurements of the Bombay-Ahmedabad path show a large fading after sunset as the sky wave also appeared. On eclipse day the fading started about an hour earlier. Riometer recordings also show a higher signal during eclipse day, which again indicates an eclipse-associated decrease in ionization.
Modelling the disturbance caused by a dc-electrified railway to geomagnetic measurements
Authors: Pirjola Risto , Newitt Larry , Boteler David , Trichtchenko Larisa , Fernberg Peter , McKee Lorne , Danskin Donald , van Beek Gerrit Jansen
Published: August 2014

Magnetic fields created by a dc-electrified railway are a nuisance to the operation of a geomagnetic observatory and also disturb other electromagnetic studies. Theoretical formulas that enable quantitative estimates of the magnetic effect of a dc railway including leakage currents in the ground are presented in this paper. They are illustrated by numerical examples. The validity of the theoretical model was verified by measurements carried out in the vicinity of a nearly north-south railway in Calgary, Canada. The earth structure in that area is approximately layered, which is an assumption included in the theoretical model. The agreement between the measured magnetic fields due to trains and the theoretical values is good. Numerical computations indicate that magnetic fields larger than the maximum allowable noise level (assumed to be about 10 pT) at today’s magnetic observatories may extend to distances of tens of kilometres from a railway. We have prepared computer programs based on the theoretical formulas in the MatLab, Octave, FORTRAN and IDL languages, in which the locations (i.e. the latitudes and the longitudes) of the point of observation, of the feeding substations and of the trains, together with the feeding and leakage currents and the heights of the feeding lines, can be given as inputs.