bluuebunny/crossref_metadata_2025 huggingface dataset:
Electron density measurement under the influence of auroral precipitation and electron beam injection during the DELTA campaign
Authors: Wakabayashi M. , Ono T.
Published: August 2014

The direct observation of electron number density was successfully carried out using an impedance probe onboard the S310-35 sounding rocket during the DELTA (Dynamics and Energetics of the Lower Thermosphere in Aurora) campaign, which provided the altitude profile along the rocket trajectory in a diffuse aurora. The plasma density profile showed clear density enhancements due to the auroral precipitation as well as artificial ionizations induced by the electron beam injection. The enhanced ionization due to the electron beam experiment was too high to be determined by means of the detection of the UHR (Upper Hybrid Resonance) frequencies. To overcome this difficulty, SHR (Sheath Resonance) frequency and sheath capacitance values were used to deduce the plasma density in the artificially ionized region. Based on the SHR analysis method, we were able to determine the maximum density to be 2·106 cm−3 at the altitude of 98.9 km; this measurement was ascribed to the artificial ionization by the 1-keV electron beam in comparison with the results of particle detector instrument on-board the S310-35. The data analysis of the sheath capacitance was able to distinguish the natural ionization region from the artificial one. The impedance probe measurement was able to evaluate the ionospheric conductivities which have important properties for evaluating the Joule heating process in the thermosphere. Both Pedersen and Hall conductivities showed distinctive enhancement around an altitude of 128 km which were due to the auroral particle precipitation.
Seismic velocity variations on the San Andreas fault caused by the 2004 M6 Parkfield Earthquake and their implications
Authors: Li Yong-Gang , Chen Po , Cochran Elizabeth S. , Vidale John E.
Published: August 2014

Repeated earthquakes and explosions recorded at the San Andreas fault (SAF) near Parkfield before and after the 2004M6 Parkfield earthquake show large seismic velocity variations within an approximately 200- m-wide zone along the fault to depths of approximately 6 km. The seismic arrays were co-sited in the two experiments and located in the middle of a high-slip part of the surface rupture. Waveform cross-correlations of microearthquakes recorded in 2002 and subsequent repeated events recorded a week after the 2004M6 mainshock show a peak of an approximately 2.5% decrease in seismic velocity at stations within the fault zone, most likely due to the co-seismic damage of fault-zone rocks during dynamic rupture of this earthquake. The damage zone is not symmetric; instead, it extends farther on the southwest side of the main fault trace. Seismic velocities within the fault zone measured for later repeated aftershocks in the following 3–4 months show an approximate 1.2% increase at seismogenic depths, indicating that the rock damaged in the mainshock recovers rigidity—or heals—through time. The healing rate was not constant but was largest in the earliest post-mainshock stage. The magnitude of fault damage and healing varies across and along the rupture zone, indicating that the greater damage was inflicted and thus greater healing is observed in regions with larger slip in the mainshock. Observations of rock damage during the mainshock and healing soon thereafter are consistent with our interpretation of the low-velocity waveguide on the SAF being at least partially softened in the 2004M6 mainshock, with additional cumulative effects due to recurrent rupture.
Initial studies of high latitude magnetic field data during different magnetospheric conditions
Authors: Cersosimo D. O. , Wanliss J. A.
Published: August 2014

We investigate the statistical properties of high-latitude magnetometer data for differing geomagnetic activity. This is achieved by characterizing changes in the nonlinear statistics of the geomagnetic field, by means of the Hurst exponent, measured from a single ground-based magnetometer station. The long-range statistical nature of the geomagnetic field at a local observation site can be described as a multifractional Brownian motion, thus suggesting the statistical structure required of mathematical models of magnetospheric activity. We also find that, in general, the average Hurst exponent for quiet magnetospheric intervals is smaller than that for more active intervals.
Detecting horizontal gradient of sound speed in ocean
Authors: Kido Motoyuki
Published: August 2014

We propose a new approach to monitor the horizontal gradient of sound speed in ocean for its correction on seafloor positioning using the GPS/acoustic technique. The new method requires five seafloor transponders to solve five parameters: δx, horizontal position of a transponder array; δt, a common delay in traveltimes due to the stratified component of sound speed; ∇
t, the gradient of traveltime delays among the transponders associated with the sound speed gradient. We also numerically evaluate the geometrical strength of the five transponders’ layout and observation point to avoid possible trade-off among the parameters.
Polarization analysis of a Pi2 pulsation using continuous wavelet transform
Authors: Kulesh M. , Nosé M. , Holschneider M. , Yumoto K.
Published: August 2014

In this contribution, we extend a series of previous works focused on an investigation of signal’s polarization attributes using the continuous wavelet transform, where we proposed a method to map instantaneous polarization attributes of multicomponent signals in the wavelet domain and explicitly relate these attributes with the wavelet transform coefficients of the analyzed signal. In this work, we applied our polarization method to an examination of characteristics of Pi2 pulsations. We have shown some merits of the use of the continuous wavelet transform for the Pi2 pulsations’ analysis. First, we used our polarization method for the geomagnetic field data from the MSR, KAK, GUA, SMA, BLM and LAQ observatories and showed some correlations between the polarization parameters of pulsation and the station’s position (nightside or dayside). Secondly, we considered the signal’s north components of a pair of stations and demonstrated a time-frequency variations of the phase difference between two stations during the pulsation.
Rayleigh-Taylor instability after giant impacts: Imperfect equilibration of the Hf-W system and its effect on the core formation age
Authors: Sasaki Takanori , Abe Yutaka
Published: August 2014

Hf-W chronometry provides constraints on the timing of planetary accretion and differentiation, as the segregation of a metal core from silicates should induce strong fractionation of Hf from W. In most previous studies, it was assumed that a giant impact would perfectly reset the Hf-W chronometer. Here, we show the difficulty of achieving perfect equilibration of the Hf-W system. Perfect equilibration requires iron to split into small droplets. However, since the sedimentation velocities of small droplets are low, the Rayleigh-Taylor instability between the upper metal-containing and lower metal-free layers results in quick overturning of the layers, unless iron droplets were uniformly distributed in the entire mantle. Therefore, the lower metal-free layers cannot be equilibrated. We calculated the isotopic evolution of the Hf-W system, taking into account the partial resetting of this chronometer. Our study led to three conclusions: (1) collision conditions and the number of giant impact events affect the age estimation of core formation, (2) the Earth’sWisotope ratio indicates that more than two-tenths of the volume of the protoearth’s mantle must have been equilibrated at each giant impact, and (3) Mars should have experienced a late, extensive equilibration event; it could have been a single giant impact.
A compound linear discriminant method for small-magnitude seismic events and its application to the North Korea seismic event of October 9, 2006
Authors: Che Il-Young , Jun Myung-Soon , Jeon Jeong-Soo
Published: August 2014

On October 9, 2006, a seismic event (mb3.9) occurred in North Korea, which was later announced as a nuclear test. We studied the seismic event from the viewpoint of seismological discrimination withouta prioriinformation of the source. This paper presents a compound discriminant method that enhances the ability to distinguish between earthquakes and explosions on the Korean Peninsula. The method includes four single discriminants based on seismic spectral amplitude ratios. These discriminants are used as single variables in a multivariate statistical analysis to derive a compound linear discriminant function that optimally separates the two populations. Short-period vertical component seismograms recorded by seismo-acoustic array (CHNAR) are used for the method. Combining the mutually complementary discrimination abilities of the single methods improves the discriminant power and lowers the probability of misclassification to 1.7% for the data sets. Using this compound method, we were able to identify the North Korea seismic event as explosion-induced. This discrimination technique can be applied automatically to new observations and extended to other seismic arrays or networks. The combination of these seismic discriminants with infrasound observations will increase our ability to detect surface explosions on the Korean Peninsula.
Numerical study of electrostatic electron cyclotron harmonic waves due to Maxwellian ring velocity distributions
Authors: Umeda Takayuki
Published: August 2014

Excitation of electrostatic electron cyclotron harmonic (ECH) waves is studied by performing linear dispersion analysis and particle-in-cell computer simulation. The ECH wave emissions can be excited by a positive slope in a velocity distribution function perpendicular to the ambient magnetic field, such as that due to a loss cone or ring velocity distribution. However, there exists no analytic expression for integration of Maxwellian ring velocity distribution functions. Here we present a method to solve the linear dispersion relations of Maxwellian ring velocity distribution functions with numerical integration. The obtained dispersion relations are confirmed by particle-in-cell simulation.
Occurrence of quasi-periodic slow-slip off the east coast of the Boso peninsula, Central Japan
Authors: Ozawa Shinzaburo , Suito Hisashi , Tobita Mikio
Published: August 2014

An analysis of Global Positioning System (GPS) data revealed south-southeastward transient deformation caused by the expected slow-slip near the Boso peninsula, central Japan, approximately 5 years after a similar event in 2002. An area of aseismic slip with a moment magnitude of 6.6 was estimated off the Boso peninsula, adjacent to the area of associated seismic activity. The 2007 aseismic slip started from around August 10, expanded slightly to the north, and gradually ceased activity over a period of about 10 days. This rupture process is different from those of the last two events in which the slow-slip area moved from north to south. However, the three slow-slip events detected by the GPS array verify the hypothesis that the Boso slow-slips occur quasi-periodically in a certain area, accompanied by seismic swarms. The factors causing the slight differences in the rupture process, magnitude, recurrence time, and slip area among the observed slow-slip events remain unclear.
Horizontal deformation in South Korea from permanent GPS network data, 2000–2003
Authors: Hamdy Ahmed M. , Park Pil-Ho , Lim Hyung-Chul
Published: August 2014

Analysis of continuous GPS data 2000–2003 at 50 stations of the Korean GPS Network (KGN) suggests that the southern part of the Korean peninsula is tectonically more stable than other regions in the Eastern Asia. The average velocity was ∼1.5 mm/yr and the average overall strain rate was around −0.3 × 10−9str/yr. The obtained velocity field indicates the presence of anticlockwise rotation of the whole region with respect to Daejeon station (DAEJ), in the central part of South Korea. It also showed that KM-OB (Kyonggi Massif and the Okchon Basin) and YM-TB (Yeongnam Massif and Taebaeksan Basin) have left-lateral shearing movements. Both movements were confirmed by the deformation analysis of the KGN horizontal velocity field using the infinitesimal plate theory. The results show that South Korea moves toward the WNW direction with a velocity of 0.9 mm/yr with a slow anticlockwise rotation. The strain field in South Korea indicates the existence of both compression and tension. The compression and extension axes have WSW-EWE and NNW-SSE directions, respectively.
A simulation study of effects of GRACE orbit decay on the gravity field recovery
Authors: Yamamoto Keiko , Otsubo Toshimichi , Kubo-oka Toshihiro , Fukuda Yoichi
Published: August 2014

The effects of satellite ground track changes of GRACE on monthly gravity field recoveries are investigated. In the case of a gravity field recovery using a relatively short period of a month or so, the variation of ground tracks affects the precision of the gravity field solutions. It is a serious problem when the solutions are employed for detecting temporal gravity changes which are almost at their detection limits. In this study, the recoveries of four-weekly gravity fields are simulated and the relation between the recovery precision and the ground track is investigated. The result shows that the GRACE ground track of the year 2003 was in good condition for four-week gravity field recovery, but it will sometimes appear as worse cases as the orbit altitude decays. In those cases, the global standard deviations of geoid height errors will be about one order worse than the best case. From our simulation, ground tracks of around altitudes of 473, 448, 399, 350 and 337 km give insufficient spatial resolutions, even for gravity field recovery up to degree 30.
Very low frequency earthquakes excited by the 2004 off the Kii peninsula earthquakes: A dynamic deformation process in the large accretionary prism
Authors: Obara Kazushige , Ito Yoshihiro
Published: August 2014

Anomalous seismic events were observed after the occurrence of the foreshock (Mw=7.2) and the main shock (Mw=7.5) of the 2004 off the Kii peninsula earthquakes. These anomalous events are characterized by very low-frequency energy of around 10 seconds with almost no higher-frequency energy and are considered the same as the very low-frequency (VLF) earthquakes discovered by Ishihara (2003) in some places along the Nankai trough, southwest Japan. The VLF seismic activity is mainly coincident with the aftershock area of the 2004 off the Kii peninsula earthquakes; however a minor activity was also excited in the southern Kii channel area. The VLF seismograms sometimes include higher-frequency wave trains with amplitudes much smaller than that of regular aftershocks. This indicates that VLF earthquakes have different source properties from the regular earthquakes. The centroid moment tensor analysis for one of the larger events suggests that the source depth is very shallow and the focal mechanism is the reverse faulting. These features suggest that the event occurs on the well-developed reverse fault system in the large accretionary prism near the Nankai trough. The swarm activity of VLF earthquakes might be considered as a chain-like occurrence of slips on the reverse fault system and thus the signature of a dynamic deformation process in the accretionary prism.
Urgent aftershock observation of the 2004 off the Kii Peninsula earthquake using ocean bottom seismometers
Authors: Sakai Shin’ichi , Yamada Tomoaki , Shinohara Masanao , Hagiwara Hiroko , Kanazawa Toshihiko , Obana Koichiro , Kodaira Shuichi , Kaneda Yoshiyuki
Published: August 2014

The 2004 off the Kii Peninsula earthquake occurred on September 5, 2004. Knowing the precise aftershock distribution is important for understanding the mechanism of this earthquake. However, the hypocenter of the main shock was located more than 100 km offshore from the nearest station of the land observation network. In the three days after the main shock, we started ocean bottom seismometer (OBS) observation in order to determine the precise distribution of the aftershocks. We assumed a seismic velocity structure for the hypocenter calculation, based on the results of previous seismic refraction study. The station corrections were incorporated to locate the hypocenter precisely. The hypocenters located within an area covered by five OBSs show relatively small errors. It is found that the OBS-located hypocenters are located about 5.5 km east-southeast from those by JMA and the depth range of the aftershocks is about 5–25 km just beneath the Nankai trough axis. The aftershock hypocenters can be grouped into two clusters at different depths of about 10 km and about 20 km. It is inferred that the main shock also has a depth of 5–25 km. Since this extent of the main shock was larger than one of the oceanic crust of the Philippine Sea plate, the fault plane of the main shock extended at the upper most mantle of the Philippine Sea plate. Although we cannot assign the actual fault plane of the main shock form our observation results, it is clarified that intra-plate earthquakes occurred near the trench region. Our OBS result supports that the main shock was the earthquake not at the plate boundary but within the bending Philippine Sea plate near the trough axis.
Temporal changes in seismic velocity of the crust around Iwate volcano, Japan, as inferred from analyses of repeated active seismic experiment data from 1998 to 2003
Authors: Nishimura Takeshi , Tanaka Satoru , Yamawaki Teruo , Yamamoto Hidekazu , Sano Takashi , Sato Minemori , Nakahara Hisashi , Uchida Naoki , Hori Shuichiro , Sato Haruo
Published: August 2014

We have examined temporal changes in seismic velocity of the crust through repeated active seismic experiments at Iwate volcano, Japan, where a significant volcanic activity and an M6.1 earthquake were observed in 1998. We apply a cross spectrum moving window technique to seismic data recorded at eight stations for the six explosions detonated from1998 to 2003. The seismic velocity at the frequency range of 3-9 Hz decreased by about 1% during the three months including the occurrence of M6.1 earthquake. The seismic velocity gradually increased, and about one third of the decrease was recovered by 2002. Then, the seismic velocity decreased again in 2003. Spatio-temporal changes in the volumetric strains predicted from the M6.1 fault mechanism and the volcanic pressure sources are well correlated with the seismic velocity changes observed in 1998. However, the predicted stress fields are not completely matched with the observed velocity changes from 1998 to 2003. This inconsistency may be due to unknown regional tectonic stress field and/or localized stress fields induced by volcanic pressure sources. It should be noted that the observed velocity changes indicate frequency dependent characteristics although the mechanism is not yet understood.
A simulation analysis to optimize orbits for a tropical GPS radio occultation mission
Authors: Mousa Ashraf , Aoyama Yuichi , Tsuda Toshitaka
Published: August 2014

Space-based Radio Occultation (RO) measurements using a GPS receiver on a low Earth orbiter (LEO) provide accurate atmospheric refractivity profiles. EQUatorial Atmospheric Research Satellite (EQUARS) is a planned satellite mission carrying a GPS receiver for RO measurements, whose main focus is to study the vertical coupling process in the equatorial atmosphere and ionosphere through upward propagating atmospheric waves. This paper presents a model simulation to determine the best practical orbital parameters of a LEO satellite for GPS occultation, which provides dense occultation coverage from 20°S to 20°N and sparser coverage extending to 30°S and 30°N. Constellations of 29 GPS satellites are computed every 10 sec using the six Keplerian parameters based on real almanac data, while various orbits of LEO satellite are computed by varying orbital parameters, especially orbital altitude and inclination. Then, the occultation events are simulated under the assumption that the ray path between the occulting GPS and LEO satellites is a straight line. The simulation analysis shows that altitude and inclination angle of orbit are considered as principal parameters among the Keplerian parameters to accomplish the RO measurements in the equatorial region. Taking into account the long-lived mission, an avoidance of ionospheric F-layer influences, and practical antenna field of view, the best practical orbit for RO measurement in the equatorial region has an altitude of 750 km and an inclination of 20°. LEO on this orbit is expected to provide 530 RO events per day. The analysis also shows that three LEOs in that orbit with 120° separation can provide atmospheric profiles at least once every 6 h within 1000 km from an arbitrary station in the equator.
Crucial effect of system compliance on the maximum stress estimation in the hydrofracturing method: Theoretical considerations and field-test verification
Authors: Ito Takatoshi , Igarashi Akira , Kato Harumi , Ito Hisao , Sano Osam
Published: August 2014

Why do the currently available data sets from field hydrofracturing tests indicate that the measured re-opening pressure lies close to the shut-in pressure far more often than can reasonably be expected? In order to explain such a strange phenomenon, it is necessary to take into consideration two additional factors, those of (1) a residual aperture of fracture and (2) hydraulic compliance of the test equipment, both of which are ignored in the conventional theory of hydraulic fracturing. The residual aperture causes pressure penetration into the fracture prior to opening, and its effect is to reduce the re-opening pressure by a factor of two from the value expected when the conventional theory is used. The conventional theory implies that the fracture always begins to open at a borehole pressure less than the shut-in pressure. However, due to the effect of large hydraulic compliance, the reopening pressure measured in the conventional manner becomes larger than the true reopening pressure and approaches the shut-in pressure. Contrary to this, the reopening pressure measured using the test equipment with sufficiently small compliance represents a good estimate of the true reopening pressure. This pressure is related to the maximum horizontal stress S
H, and its measured value allows us to estimate the value of S
H.
Conductivity, electric field and electron drift velocity within the equatorial electrojet
Authors: Rastogi R. G. , Chandra H.
Published: August 2014

Rocket-borne in-situ measurements of electron density and current density made from Thumba, India, on four occasions between 1966 and 1973 and on one flight from Peru in 1965 are studied along with the corresponding ground magnetometer data. The Cowling conductivity is computed using the yearly mean magnetic field values of 1965 and the atmospheric density values from the MSIS 1986 model. The rocket-borne measurements from Thumba cover different geophysical conditions of strong, moderate and partial counter-electrojet events. The vertical profiles of the measured current density and electron density are presented along with the computed Cowling conductivity, electron drift velocity and electric field. The peak current density occurred at 106–107 km over Thumba and at 109 km over Peru compared to 104 km over Brazil. Cowling conductivity peaks occurred at 102 km over Huancayo and 101 km over Thumba, while electron drift velocity and electric field peaks occurred at approximately 105–107 km over Thumba, 108 and 110 km over Huancayo and 104 km over Brazil, respectively. While the electron density near the level of peak current density shows some variability, electron drift velocity and electric field show large variability. We conclude that the local electric field plays an important role in the spatial and temporal variability of the strength of the electrojet.
Full particle simulation of a perpendicular collisionless shock: A shock-rest-frame model
Authors: Umeda Takayuki , Yamazaki Ryo
Published: August 2014

The full kinetic dynamics of a perpendicular collisionless shock is studied by means of a one-dimensional electromagnetic full particle simulation. The present simulation domain is taken in the shock rest frame in contrast to the previous full particle simulations of shocks. Preliminary results show that the downstream state falls into a unique cyclic reformation state for a given set of upstream parameters through the self-consistent kinetic processes.
Spatial variation of lithospheric heterogeneity on the globe as revealed from transverse amplitudes of short-period teleseismic P-waves
Authors: Kubanza Mungiya , Nishimura Takeshi , Sato Haruo
Published: August 2014

We systematically characterized the medium heterogeneity of the lithosphere by analyzing transverse-component amplitudes of teleseismic P-waves from shallow earthquakes in short periods of 0.5 to 4 Hz. Normalized transverse amplitudes, which are less affected by a layered structure, were measured at each station of the IRIS GSN network. The data revealed significant regional differences in lateral heterogeneity of the lithosphere, with small amplitudes observed at stations on stable continents and large normalized transverse amplitudes observed in seismically active regions, such as island arcs or collision zones. These spatial changes are consistent with the tectonic settings of each station. However, large normalized transverse amplitudes were also observed in regions of very low seismicity and in regions where no seismic activity has been recognized, which may indicate the existence of medium heterogeneity in the lithosphere that has been formed in ancient times.
Preliminary dielectric and rock magnetic results for a set of prehistoric Amerindian pottery samples from different Venezuelan Islands
Authors: Costanzo-Alvarez V. , Suárez N. , Aldana M. , Hernández M. C. , Campos C.
Published: August 2014

Potsherds from 7 Venezuelan islands have been studied using a two-fold magneto/dielectric technique in order to identify clay sources and characterize different stages of pottery craftsmanship. This is the first study of archeological material using this technique. Petrographic analyses appear to agree with the clusters of data identified in scatter plots of initial magnetic susceptibility versus saturation isothermal remanent magnetization (SIRM), and natural remanent magnetization (NRM). Thus, these magnetic parameters appear to be suitable for describing clay source characteristics. Effective magnetic grain sizes, investigated via stability analyses of SIRM and anystheretic remanent magnetization (ARM) upon alternating field (AF) demagnetization, and SIRM acquisition and AF demagnetization crossover plots, seem to be related to different steps of pottery craftsmanship, namely clay preparation, finishing and firing. Thermomagnetic curves might also provide valuable information about original firing conditions. A scatter plot of SIRMs intersections versus maximum current depolarization temperatures and average activation energies, shows a coarse correlation due perhaps to the fact that these rock magnetic and dielectric data are both associated to pore-related features.
Subsurface Chemistry of the Imbrium Basin Inferred from Clementine UVVIS Spectroscopy
Authors: Otake Hisashi , Mizutani Hitoshi
Published: August 2014

Since ejecta around an impact crater is excavated from a depth, its mineralogy and chemistry will provide us with information on the composition of the pre-impact subsurface. The depth from which crater ejecta were excavated was determined from laboratory experiments, field studies, and a simplified quantitative model (Z-model and the scaling law of ejection velocity). Based on the results of these studies, it is believed that surface material of an ejecta blanket between 1.1 and 1.5 radii from the crater was excavated from a depth of 0.13 to 0.15 radii. The following results were obtained from combining the surface and subsurface basalt distributions with crater-counting ages for the mare basalt, we obtained the following results: (1) The averages of TiO2 and FeO increased with time from the Imbrian to the Eratosthenian periods, which is represented by a continuous trend curve on the TiO2-FeO graph: (2) volcanic activities in Mare Imbrium drastically decreased and basalts changed from a low-Ti to high-Ti content around the transition of the Imbrian to Eratosthenian period: (3) basalts with less than 3 wt% TiO2 erupted in succession mainly in the Imbrian period.
A method for representing a geomagnetic total force field in a small region with special attention to discontinuities of data
Authors: Yamazaki Ken’ichi , Oshiman Naoto
Published: August 2014

In order to represent the total force field variation in a narrow region as precisely as possible, the calculation process of NOC, which is frequently used in geomagnetic field modeling, was improved. An iterative procedure was introduced to avoid the effect of data missing in some time series. The presented procedures are applied to monthly averaged data of the geomagnetic total force field during 1980–1997 in Japan. Some local changes are detected using this model. One of them may be related to an earthquake that took place near the site.
Undersea co-seismic crustal movements associated with the 2005 Off Miyagi Prefecture Earthquake detected by GPS/acoustic seafloor geodetic observation
Authors: Matsumoto Yoshihiro , Fujita Masayuki , Ishikawa Tadashi , Mochizuki Masashi , Yabuki Tetsuichiro , Asada Akira
Published: August 2014

We have been carrying out seafloor geodetic observations at two reference points situated off Miyagi Prefecture, northeastern Japan, using the GPS/Acoustic combination technique. Comparison of position estimates before and after the 2005 Off-Miyagi Prefecture Earthquake revealed a co-seismic crustal movement as large as 10 cm eastward at the site approximately 10 km from the epicenter, while no prominent movement was found at another site located 60 km away from the epicenter. The results at these two sites are consistent with crustal deformation calculated from the rectangular dislocation model on the fault derived from crustal movements observed at GEONET stations on land.
Trap thickness and the subtrappean structures related to mode of eruption in the Deccan Plateau of India: results from magnetotellurics
Authors: Patro B. P. K. , Sarma S. V. S.
Published: August 2014

Deccan trap thickness is an important parameter in understanding the eruption process of flood basalts (65 My). A magnetotelluric study was carried out in Deccan Volcanic Province (DVP) of the Indian Peninsular shield during 1998–1999. Modeling results clearly revealed variations both in the thickness of the Deccan traps and in their resistivity from the west coast to the eastern boundary of DVP. The thickness of the traps in DVP decreases from about 1.8 km in the west to a few hundred meters (approx. 400 m) towards the east. The traps also exhibit considerable variation in resistivity, with higher resistivities (approx. 150–200 ohm-m) in the western half and lower resistivities (approx. 50–100 ohm-m) in the eastern half of DVP. Two significant fissure/fracture zones have been detected in DVP; these may have acted as conduits for the outpouring of Deccan lavas in addition to the primary structures along the west coast and the Narmada-Son lineament (NSL) zones.
Statistical study of medium-scale traveling ionospheric disturbances observed with the GPS networks in Southern California
Authors: Kotake Nobuki , Otsuka Yuichi , Ogawa Tadahiko , Tsugawa Takuya , Saito Akinori
Published: August 2014

Using global positioning system (GPS) data taken from 350 dual-frequency GPS receivers in Southern California in 2002, we investigated two-dimensional maps of total electron content (TEC) perturbations with a time resolution of 30 s and a spatial resolution of 0.15°×0.15° in longitude and latitude to reveal statistical characteristics of medium-scale traveling ionospheric disturbances (MSTIDs). We found that MSTIDs can be categorized into three types. One type is daytime MSTIDs, which frequently occur in winter and equinoxes. Since most of the daytime MSTIDs propagated southeastward, we speculate that the daytime MSTIDs could be caused by atmospheric gravity waves in the thermosphere. A second type is nighttime MSTIDs, which frequently occur in summer. Nighttime MSTIDs propagate southwestward. This propagation direction is consistent with the idea that polarization electric fields could play an important role in generating nighttime MSTIDs. The third is dusk MSTIDs, which frequently occur in summer and propagate northwestward. Dusk MSTIDs could be caused by gravity waves originating from the sunset terminator because they have wavefronts almost parallel to the sunset terminator.
In situ stress measurement by the stress relief technique using a multi-component borehole instrument
Authors: Mukai Atsushi , Yamauchi Tsuneo , Ishii Hiroshi , Matsumoto Sigeo
Published: August 2014

We have developed a two-dimensional method for calculating principal stresses on a plane by measuring strain changes obtained by the stress relief technique using a multi-component borehole instrument. If the ratio of the radius of the core to that of the borehole is 1.4–2.0, a uniform strain change occurs in any stress field due to the overcoring. It is therefore desirable that the radius of the core obtained by overcoring is larger than that of the borehole by a few orders of magnitude. We applied the proposed calculation method to a stress measurement performed at the Hishikari mine, southwest Japan. The maximum and minimum principal stresses were determined to be 5.0 and −0.2 MPa, respectively. The nearly vertical stress was estimated to be 1.5 MPa, which was merely 30% of the predicted vertical stress (5.6 MPa). One of causes of the small vertical stress obtained in this study is considered to be the limitation of the two-dimensional method for calculating principal stresses.
Analysis of pressure waves observed in Sakurajima eruption movies
Authors: Yokoo Akihiko , Ishihara Kazuhiro
Published: August 2014

Four eruption movies of Sakurajima volcano taken in the 1980s are analyzed. Pressure waves associated with these eruptions are identified by changes in luminance using a new image processing method. Results of the processing determined the apparent speeds of these waves at approximately 342–574 m/s. Further, spatial characteristics of the pressure waves are quantitatively investigated to estimate the source conditions of volcanic explosions.
Milestones of the IAGA International Service of Rapid Magnetic Variations and its contribution to geomagnetic field knowledge
Authors: Curto J. J. , Cardús J. O. , Alberca L. F. , Blanch E.
Published: August 2014

The Service of Rapid Magnetic Variations (RMV) was created by the International Association of Geomagnetism and Aeronomy (IAGA) with the aim of obtaining an overall view of the temporal and spatial distribution of RMV as a base for further study of these phenomena. The Ebro Observatory participated in the creation of this service and has been administering it from the beginning; consequently, the histories of these two organizations are intertwined.
Evidence for an elevated 410 km discontinuity below the Luzon, Philippines region and transition zone properties using seismic stations in Taiwan and earthquake sources to the south
Authors: Wright C. , Kuo B.-Y.
Published: August 2014

P waves from earthquakes south of Taiwan, recorded by seismic stations within and around Taiwan, were used to define two average wavespeed models WPSP01 and WPSP02 for the upper mantle and transition zone below the Luzon region. Wavespeeds are characteristic of oceanic upper mantle. The 410-km discontinuity, however, appears to be elevated to about 325 km depth, based on clear identification of the travel-time branch produced by refraction within the transition zone, and estimates of its first and second derivatives with respect to distance. A plausible explanation is low temperatures within the subducted South China Sea plate. The data also imply relatively low wavespeed jumps of 0.6–1.0% and 1.1–1.5% respectively across the elevated 410-km discontinuity and a lower discontinuity at 676 km depth, and high wavespeed gradients in the transition zone. Phase-weighted stacking on a cluster of short-period seismograms with first arrival energy from within the transition zone provides independent support for the validity of the models; later arrivals are detected close to the predicted times and slownesses for energy emerging from the lowermost upper mantle and the top of the lower mantle. An additional arrival on the stacks may be caused by a localized discontinuity near 530 km depth.
Automatic seismic wave arrival detection and picking with stationary analysis: Application of the KM2O-Langevin equations
Authors: Nakamula Sho , Takeo Minoru , Okabe Yasunori , Matsuura Masaya
Published: August 2014

An automatic detection and a precise picking of the arrival times of seismic waves using digital seismograms are important for earthquake early detection systems. Here we suggest a new method for detecting and pickingP-andS-wave signals automatically. Compared to methods currently in use, our method requires fewer assumption with properties of the data time series. We divide a record into intervals of equal lengths and check the “local and weak stationarity” of each interval using the theory of the KM2O-Langevin equations. The intervals are stationary when these include only background noise, but the stationarity breaks abruptly when a seismic signal arrives and the intervals include both the background noise and theP-wave. This break of stationarity makes us possible to detectP-wave arrival. We expand the method for picking ofS-waves. We applied our method to earthquake data from Hi-net Japan, and 90% ofP-wave auto-picks were found to be within 0.1 s of the corresponding manual picks, and 70% ofS-wave picks were within 0.1 s of the manual picks. This means that our method is accurate enough to use as a part of the seismic early detection system.
Thermal and hydrostatic structure of the protoplanetary nebula exposed to stellar radiation and stellar wind from the central star
Authors: Yun Young Seok , Emori Hiroyuki , Nakazawa Kiyoshi
Published: August 2014

A model for a nebula exposed to the radiation and stellar wind from the central star has been examined. T Tauri stars commonly have disks and stellar wind, though we have no theoretical model on nebular thermal structure under the wind. The aims of this paper are to propose a theoretical nebula model, and to perform mathematical analysis on the geometrical structure and temperature distribution of a passive nebula. Its geometrical surface is determined by the dynamical pressure of the stellar wind. The nebular surface is assumed to be a black body surface, heated by the incident stellar photon flux. We obtain temperature from the equation of energy balance between the stellar radiation upon this nebular surface and the black body radiation from it. The temperature distribution in passive disks is insensitive to the wind strength and is almost identical even if the wind strength changes by five orders of magnitude. The nebula temperature is not expressed by a simple power law function of the distance from the central star. This is an important difference between our results and those of previous works. Since the nebula surrounding a T Tauri star is influenced by stellar wind, our model may be more appropriate than any other simple single power law temperature for passive protoplanetary nebulae.
Gravitational energy release in an evolving Earth model
Authors: Roberts Paul H. , Kono Masaru
Published: August 2014

The energy budget of the Earth’s core balances the heat lost through cooling with the sum of gravitational, latent heat and radioactive sources (if any). The gravitational and latent heat sources are due to the freezing of core mix onto the surface of the inner core. Gravitational energy is released because the light components of core mix that are released during freezing are buoyant, and rise as they rejoin the fluid core. This source of energy can be regarded as part of the total gravitational energy released as the entire Earth cools and contracts. The main purpose of this paper is to present a new method of evaluating the total energy release. The method is applied to two Earth models. Both show that the gravitational source that stirs the fluid core is less than 30% of the total gravitational energy released through the contraction of the Earth as it cools.
A new type of a three-component spinner magnetometer to measure the remanence of rocks at elevated temperature
Authors: Wack Michael , Matzka Jürgen
Published: August 2014

A new instrument to continuously determine the remanent magnetisation of standard paleomagnetic (inchsized) rock samples during heating and cooling (continuous thermal demagnetisation) was developed. The design as an off-axis spinner magnetometer (i.e. the samples rotate on a circular path in a radial distance to the spinning axis) allows the simultaneous measurement of several samples and offers a way to determine the full vector of magnetisation. Six fluxgate sensors are used to record three gradients of the magnetic fields caused by the samples and the vector of remanence is determined by regression analysis of the gradient signals. The sensitivity of the instrument is 2·10−7 Am2. Hot air is circulating through copper pipes which heat the samples by thermal radiation to avoid magnetic fields which would arise from direct electrical heating. Currently, the measurements are restricted to a maximum of 350°C. The instrument was tested with oceanic basalt samples that were given an artificial remanence. Some continuous thermal demagnetisation experiments of this artificial remanence and of the natural remanent magnetisations are shown for oceanic basalts.
The 2004 Las Campanas/Lowell Observatory campaign II. Surface properties of Hayabusa target Asteroid 25143 Itokawa inferred from Hapke modeling
Authors: Lederer S. M. , Domingue D. L. , Thomas-Osip J. E. , Vilas F. , Osip D. J. , Leeds S. L. , Jarvis K. S.
Published: August 2014

We present an analysis of Hapke photometric modeling applied to uniform ground-based UBVRIJHK broadband data of asteroid 25143 Itokawa collected over a wide range of solar phase angles (4°–130°) during the 2004 apparition (Thomas-Osip et al., this issue, hereafter Paper I). Our photometric analyses indicate that Itokawa has a blocky surface with properties different from other, albeit larger, S-class asteroids studied using similar Hapke modeling analyses. Images from the Hayabusa spacecraft affirm the Hapke modeling results, demonstrating the ability of Hapke photometric modeling to predict a rocky asteroid surface correctly; this is the first time that a predicted rocky surface has been observed by a spacecraft. The single particle scattering functions are dominantly forward scattering, suggesting the surface material is composed primarily of clear particles whose scattering is dictated by the particle’s surface as opposed to internal scatterers (more typical of S-class asteroids), while the opposition parameters indicate that the regolith may be more compact than most of the limited number of asteroids visited by spacecraft to date. The roughness properties, single particle scattering properties, and opposition surge characteristics are all indicative of a surface where multiple scattering does not play a major role in defining the photometric properties of the regolith.
Fault model of the 2007 Noto Hanto earthquake estimated from PALSAR radar interferometry and GPS data
Authors: Fukushima Yo , Ozawa Taku , Hashimoto Manabu
Published: August 2014

The 2007 Noto Hanto earthquake (M
w 6.6) is the first major earthquake in inland Japan since the launch of the Japanese ALOS satellite. Interferometric synthetic aperture radar successfully mapped the coseismic displacements from both ascending and descending orbits in and around the earthquake epicentral region. The line-of-sight displacements toward the satellite from the ascending and descending orbits amount to about 50 and 20 cm, respectively. The interferograms as well as the GPS data of the GEONET network are inverted in order to determine the slip distribution on the source fault. The dip and strike angles of the preferred model are 48° and N51°E, respectively, and its fault slip area reaches the seafloor. The dip angle is not well constrained in our tested range between 40° and 60°. The dominant slip area is located just above the hypocenter, at depths between 4 and 10 km. Many aftershocks seem to have occurred on and around the area of dominant slip.
Radiated energy from the Noto Hanto, Japan, earthquake of March 25, 2007, and its aftershock
Authors: Izutani Yasuo
Published: August 2014

The Noto Hanto earthquake of March 25, 2007, is a shallow reverse-faulting event with M
w = 6.7. We analyze transverse component accelerograms of the main shock and an aftershock (M
w = 3.6) recorded at 10 strong motion observation stations. The hypocenter of the aftershock is located very close to that of the main shock and the epicentral distances of the stations are between 15 and 65 km. We calculate spectral ratio between records of the main shock and the aftershock in order to obtain source spectral ratio by empirically removing the effects of wave propagation path and surface layers at the stations. Thus obtained source spectral ratio is inconsistent with that expected for the self-similar omega-square source model assuming constant stress drop. Fitting omega-square source spectral ratio with variable corner frequency to the observed spectral ratio, the radiated energy and the corner frequency for the main shock and the aftershock are estimated. The radiated energy is 6.8 × 1014 J for the main shock and 6.7 × 109 J for the aftershock. The energy-to-moment ratios for the main shock and the aftershock are 5.0 × 10−5 and 2.1 × 10−5. This scale-dependence of the energy-to-moment ratio is similar to that obtained previously for shallow strike-slip earthquakes and reverse-faulting earthquakes in Japan. The relationship between the seismic moment, M
0, and the corner frequency, f
0, is M
0 ∝ f
0
−3.3±0.2
.
Constrained simultaneous algebraic reconstruction technique (C-SART) —a new and simple algorithm applied to ionospheric tomography
Authors: Hobiger Thomas , Kondo Tetsuro , Koyama Yasuhiro
Published: August 2014

A simple and relatively fast method (C-SART) is presented for tomographic reconstruction of the electron density distribution in the ionosphere using smooth fields. Since it does not use matrix algebra, it can be implemented in a low-level programming language, which speeds up applications significantly. Compared with traditional simultaneous algebraic reconstruction, this method facilitates both estimation of instrumental offsets and consideration of physical principles (expressed in the form of finite differences). Testing using a 2D scenario and an artificial data set showed that C-SART can be used for radio tomographic reconstruction of the electron density distribution in the ionosphere using data collected by global navigation satellite system ground receivers and low Earth orbiting satellites. Its convergence speed is significantly higher than that of classical SART, but it needs to be speeded up by a factor of 100 or more to enable it to be used for (near) real-time 3D tomographic reconstruction of the ionosphere.