bluuebunny/crossref_metadata_2025_split huggingface dataset:
Seismic vertical array analysis of the velocity structure and phase decomposition during aftershocks of the 2007 Chuetsu-oki earthquake
Authors: Yoshida Kunikazu 
Published: August 2014

Abstract
A velocity profile derived from PS-logging was examined using the mainshock and aftershock records from KK5 and KSH seismic vertical arrays in the Kashiwazaki-Kariwa nuclear power plant, which is located on the focal region. A seismic phase decomposition analysis method was applied to aftershock vertical array records. Peak frequencies of spectral ratios of the aftershock records from the KSH array between various depths were slightly different from those of theoretical transfer functions. A comparison of observed and theoretical S-wave travel times at various depths indicated that travel times for the mainshock measured by picking S-wave arrival times were identical to the theoretical travel times calculated from the PS-logging profile, although travel times for the aftershocks were different from the theoretical travel times. The decomposition analysis of seismic vertical array records from KK5 array for a small aftershock shows that a clear wave packet of surface waves follows just after the direct S-wave arrival. In contrast, a decomposition analysis of the KSH array records show that a wave packet of surface waves are not clearly discernable.
Equatorial GPS ionospheric scintillations over Kototabang, Indonesia and their relation to atmospheric waves from below
Authors: Ogawa Tadahiko , Miyoshi Yasunobu , Otsuka Yuichi , Nakamura Takuji , Shiokawa Kazuo 
Published: August 2014

Abstract
Using Global Positioning System (GPS) satellites, we have been conducting equatorial ionospheric scintillation observations at Kototabang, Indonesia since January 2003. Scintillations caused by equatorial plasma bubbles appear between 2000 and 0100 LT in equinoctial months with a seasonal asymmetry, and their activity decreases with decreasing solar activity. A comparison between scintillation index (S
4) and Earth’s brightness temperature (T
bb) variations suggests that the scintillation activity can be related to tropospheric disturbances over the Indian Ocean to the west of Kototabang. To understand better the reasons of day-to-day variability of S
4, we analyze S
4, T
bband lower thermospheric neutral wind ("Equation missing") data. The results show that S
4 fluctuates with periods of about 2.5, 5, 8, 14 and 25 days, possibly due to atmospheric waves from below and that similar periods are also found in the T
bband "Equation missing" variations. Using a general circulation model, we made numerical simulations to determine the behavior of neutral wind in the equatorial thermosphere. The results indicate the following: (1) 2- to 20-day waves dissipate rapidly above about an altitude of 125 km, and 0.5- to 3-hour waves become predominant above 100 km, (2) zonal winds above 200 km altitude are, on the whole, eastward during sunset-sunrise, (3) zonal wind patterns due to short-period (1–4 h) atmospheric gravity waves (AGWs) above 120 km altitude change day by day, exhibit wavy structures with scale lengths of about 30–1000 km and, as a whole, move eastward at about 100−1 while changing patterns over time. These simulations suggest that the Rayleigh-Taylor instability responsible for plasma bubble generation can be seeded by AGWs with short periods of about 0.5–3 h, and that background conditions necessary for this instability are modulated by planetary-scale atmospheric waves propagating up to an altitude of about 120 km from below.
Relative effects of electric field and neutral wind on positive ionospheric storms
Authors: Balan N. , Alleyne H. , Otsuka Y. , Vijaya Lekshmi D. , Fejer B. G. , McCrea I. 
Published: August 2014

Abstract
The paper studies the relative importance of penetrating eastward electric field (PEEF) and direct effects of equatorward neutral wind in leading to positive ionospheric storms at low-mid latitudes using observations and modeling. The observations show strong positive ionospheric storms in total electron content (TEC) and peak electron density (N
max) at low-mid latitudes in Japan longitudes (≈125°E–145°E) during the first main phase (started at sunrise on 08 November) of a super double geomagnetic storm during 07–11 November 2004. The model results obtained using the Sheffield University Plasmashpere Ionosphere Model (SUPIM) show that the direct effects of storm-time equatorward neutral wind (that reduce poleward plasma flow and raise the ionosphere to high altitudes of reduced chemical loss) can be the main driver of positive ionospheric storms at low-mid latitudes except in N
max around the equator. The equatorward wind without PEEF can also result in stronger positive ionospheric storms than with PEEF. Though PEEF on its own is unlikely to cause positive ionospheric storms, it can lead to positive ionospheric storms in the presence of an equatorward wind.
Gravity waves in the equatorial thermosphere and their relation to lower atmospheric variability
Authors: Miyoshi Yasunobu , Fujiwara Hitoshi 
Published: August 2014

Abstract
Using a general circulation model that contains the region from the ground surface to the upper thermosphere, we have examined characteristics of gravity waves in the equatorial thermosphere. At an altitude of 150 km, the dominant periods of gravity waves for zonal wave number 20 (zonal wavelength λ
x
≈ 2000 km), 40 (λ
x
≈ 1000 km) and 80 (λ
x
≈ 500 km) are 3, 1.5 and 1 h, respectively. For individual zonal wave numbers, the corresponding dominant period becomes shorter at higher altitudes due to dissipation processes in the thermosphere, such as molecular viscosity and ion drag force, indicating that gravity waves with a larger horizontal phase velocity (larger vertical wavelength) can penetrate into the thermosphere. The longitudinal variation of gravity wave activity in the equatorial thermosphere and upward propagation of gravity waves from the lower atmosphere were also studied. The longitudinal distribution of gravity wave activity in the thermosphere is quite similar to that of gravity wave activity in the lower atmosphere and the cumulus convective activity in the tropical troposphere. Our results indicate that the strong energy flux due to gravity waves from the enhanced cumulus convective activity propagates upward into the upper thermosphere. The relation between the wind fluctuation associated with gravity waves and the ionospheric variation is discussed. Fluctuations of the neutral zonal wind with periods of 1–2 h are significant in the 200- to 300-km height region, and its amplitude sometimes exceeds 50 m s−1. These results suggest that upward propagating gravity waves can affect the ionospheric variation in the F-region.
Thickness variation of the sedimentary cover in the South Western Desert of Egypt as deduced from Bouguer gravity and drill-hole data using neural network method
Authors: Zaher Mohamed Abdel , Senosy M. M. , Youssef M. M. , Ehara Sachi 
Published: August 2014

Abstract
The Bouguer anomaly map of scale 1:500,000 and the lithological logs of more than 120 deep wells distributed in the Southern part of Western Desert of Egypt were used to determine the thickness of the sedimentary cover containing the main sandstone water formation. The predominant structures affecting both the basement rock and the sedimentary cover were also studied. Gravity stripping approach was applied to separate density anomalies within the sedimentary fill from the influence of deeper levels in the crystalline crust. The study indicated that the surface of the basement rock is highly rugged and mostly controlled by structures causing variation of the sedimentary cover thickness from location to other all over the area. Isopach maps were constructed based on the Artificial Neural Network (ANN) model which is considered a best method for that operation. The maximum thickness of sandstone formations is recorded at west Oweinat, southwest of Aswan, Dakhla oasis and west of Qena town. As this formation is the main water aquifer in the study area, therefore these locations are characterized by the presence of huge amount of ground water. Accordingly, these areas must be taking the priority in the programs of sustainable development in southern Egypt.
Location of the North Magnetic Pole in April 2007
Authors: Newitt L. R. , Chulliat A. , Orgeval J. -J. 
Published: August 2014

Abstract
Observations have been made at five locations in the vicinity of the North Magnetic Pole (NMP). These were used in four different analyses—virtual geomagnetic pole, simple polynomial, spherical cap harmonic, best fitting grid—to derive positions of the NMP. The average position at 2007.3 was 83.95°N, 120.72°W, with a positional uncertainty of 40 km. This position is only 27 km from the pole position given by the CHAOS magnetic model. The NMP continues to move in a northwesterly direction but its drift speed has stabilized at just over 50 km per year. The number of direct observations is insufficient to determine if the NMP has started to decelerate.
Assessment of radar interferometry performance for ground subsidence monitoring due to underground mining
Authors: Ng Alex Hay-Man , Chang Hsing-Chung , Ge Linlin , Rizos Chris , Omura Makoto 
Published: August 2014

Abstract
This paper describes the results from the recently launched SAR satellites for the purpose of subsidence monitoring over underground coal mine sites in the state of New South Wales, Australia, using differential interferometric synthetic aperture radar (DInSAR) technique. The quality of the mine subsidence monitoring results is mainly constrained by noise due to the spatial and temporal decorrelation between the interferometric pair and the phase discontinuities in the interferogram. This paper reports on the analysis of the impact of these two factors on the performance of DInSAR for monitoring ground deformation. Simulations were carried out prior to real data analyses. SAR data acquired using different operating frequencies, for example, X-, C- and L-band, from the TerraSAR-X, ERS-1/2, ENVISAT, JERS-1 and ALOS satellite missions, were examined. The simulation results showed that the new satellites ALOS, TerraSAR-X and COSMO-SkyMed perform much better than the satellites launched before 2006. ALOS and ENVISAT satellite SAR images with similar temporal coverage were searched for the test site. The ALOS PALSAR DInSAR results have been compared to DInSAR results obtained from ENVISAT ASAR data to investigate the performance of both satellites for ground subsidence monitoring. Strong phase discontinuities and decorrelation have been observed in almost all ENVISAT interferograms and hence it is not possible to generate the displacement maps without errors. However these problems are minimal in ALOS PALSAR interferograms due to its spatial resolution and longer wavelength. Hence ALOS PALSAR is preferred for ground subsidence monitoring in areas covered by vegetation and where there is a high rate ground deformation.
Effect of troposphere slant delays on regional double difference GPS processing
Authors: Nordman Maaria , Eresmaa Reima , Boehm Johannes , Poutanen Markku , Koivula Hannu , Järvinen Heikki 
Published: August 2014

Abstract
The demand for geodetic time series that are accurate and stable is increasing. One factor limiting their accuracy is troposphere refraction, which is hard to model and compute with sufficient resolution, both in time and space. We have studied the effect of numerical weather model (NWM)-derived troposphere slant delays and the most commonly used mapping functions, Niell and Vienna, on Global Positioning System (GPS) processing. Six months of data were calculated for a regional Finnish network, FinnRef, which consists of 13 stations, using Bernese v. 5.0 in double difference mode. The results showed that when site-specific troposphere zenith delays or gradients are not estimated, the use of NWM-based troposphere delays improved the repeatabilities of all three components of station positions (north, east and up) statistically significantly and up to 60%. The more realistic troposphere model also reduces the baseline length dependence of the solution. When site-specific troposphere delays and the horizontal gradients were estimated, there was no statistically significant improvement between the different solutions.
Characteristic activity and migration of episodic tremor and slow-slip events in central Japan
Authors: Obara Kazushige , Sekine Shutaro 
Published: August 2014

AbstractContinuous seismic data and tilt measurements in the Aichi and Mie regions of central Japan indicate significant migration of episodic non-volcanic deep tremors and short-term slow-slip events on the subducting plate interface at the deeper extension of the mega-thrust earthquake seismogenic zone. These episodic tremor and slip (ETS) events occur in two concentrated regions on either side of Ise Bay at recurrence intervals of approximately every 6 months throughout 2004 and 2005, separated by a distinct tremor gap. A migrating tremor episode from the southern edge of the Mie region in January 2006, however, is found to have crossed aseismic Ise Bay along a continuous 200 km long strike of the subducting Philippine Sea Plate. Coincident with the migration of tremors, very low frequency earthquakes with a predominant frequency of 0.05 Hz and tilt changes lasting for a few days were detected. Inversion analysis of the tilt data indicates that at least five reverse faultings with an average slip length of 1 cm took place on the plate boundary, migrating from southwest to northeast, equivalent to a total moment release of Mw6.2. The tremor seismicity gap at Ise Bay is attributed to the presence of a small ridge in the Philippine Sea Plate that blocks most propagating ETS events. The 2006 episode propagated orthogonal to the majority of ETS event in this region, and was found not to be obstructed by the ridge structure.
Relations between the thermal properties and porosity of sediments in the eastern flank of the Juan de Fuca Ridge
Authors: Goto Shusaku , Matsubayashi Osamu 
Published: August 2014

Abstract
The empirical relations of the thermal properties (thermal conductivity, heat capacity, specific heat, and thermal diffusivity) to the porosity and mineral composition of clay and sandy sediments recovered in the eastern flank of the Juan de Fuca Ridge are examined using the observed thermal properties, index properties, and mineral composition of the sediments. Observed thermal conductivity-porosity relations are explained using the geometric mean model. The observed relations of heat capacity and specific heat, respectively, to porosity are given by the arithmetic mean formula. A new model for the sediment thermal diffusivity-porosity relation is proposed based on models of thermal conductivity and heat capacity. This model, expressed by the geometric mean model with a correction function for the porosity and heat capacities of grain sediment and pore-filling fluid, explains the observed thermal diffusivity-porosity relations. These thermal property models are applicable to thermal properties of other sediment lithology types and are useful as standard models for estimating the thermal properties of marine sediment.
Site-specific correlation of GPS height residuals with soil moisture variability using artificial neural networks
Authors: Ogaja Clement 
Published: August 2014

Abstract
Historical time series generated from GPS sites reveal significant seasonal variations in the vertical direction. It is well known that continental waters (soil moisture, snow, ground water) mass redistribution is one of the potential contributors to these observed seasonal variations although their actual loading effects on GPS results are least well understood. A number of hydrology model outputs exist with a fair degree of uncertainty. Studies of interrelations between anomalous vertical variations observed at geodetic sites and hydrology model outputs are useful, in particular, as the hydrology models continue to be refined. In this paper, artificial neural networks is proposed for correlating GPS height residuals with the soil moisture variability. Time series from eight sites of the global GPS network are used to correlate with the soil moisture information from the US National Oceanographic and Atmospheric Administration (NOAA) Climate Prediction Center’s land data assimilation system (CPC LDAS). The results show the feasibility of the neural interpretation in terms of the correlation coefficients (∼0.6) and root mean square errors (about 15% of residual range). Other geodetic time series can be used for the same purpose, such as from SLR, VLBI, and absolute gravity.
Aftershock distribution of the 26 December 2004 Sumatra-Andaman earthquake from ocean bottom seismographic observation
Authors: Araki Eiichiro , Shinohara Masanao , Obana Koichiro , Yamada Tomoaki , Kaneda Yoshiyuki , Kanazawa Toshihiko , Suyehiro Kiyoshi 
Published: August 2014

AbstractWe deployed an OBS network in February–March 2005 in the rupture area of the Sumatra Andaman earthquake on 26 December 2004. We placed 17 short-term OBSs and two long-term OBSs, and recovered OBSs after observation for 19–22 days. The hypocenter distribution from 10-day data of 17 OBS revealed the detailed structure of aftershock seismicity offshore of Sumatra Island. Aftershock seismicity associated with the subducting slab starts 40 km inward from the Sunda trench axis; it ceases at 50 km depth beneath the Aceh Basin, approximately 240 km inward from the trench axis. Aftershocks in 120–170 km from the trench axis consist of a surface with a dip of 10–12° dominated by a dip-extension type mechanism. Beyond the southwestern edge of the Aceh Basin, the aftershock activity becomes higher, and dominated by dip-slip type earthquakes, with a slightly increased dipping angle of 15–20°. Three along-arc bands of shallow seismicity were identified at 70 km inward from the Sumatra trench, 110 km inward from the trench, and in the south of the Aceh Basin. These locations correspond to steep topographic slopes in the accretionary prism, suggesting the present evolutional activity of the accretionary prism offshore Sumatra Island.
Large surface wave of the 2004 Sumatra-Andaman earthquake captured by the very long baseline kinematic analysis of 1-Hz GPS data
Authors: Ohta Yusaku , Meilano Irwan , Sagiya Takeshi , Kimata Fumiaki , Hirahara Kazuro 
Published: August 2014

Abstract
The 26 December 2004 Sumatra-Andaman great earthquake had a −1500 km long rupture of more than 600 seconds duration, and may have involved a complex rupture process including slow slip. We processed International GNSS Service (IGS) 1-Hz Global Positioning System (GPS) data using kinematic analysis to investigate ground motion caused by this large earthquake. Since there are few 1-Hz stations, we had to process long baseline up to several thousand kilometers long. Long baselines degrade the GPS carrier phase ambiguity resolution. Nevertheless, clear seismic surface waves of the earthquake are recorded in our longdistance kinematic GPS solutions, which are in good agreement with response-corrected broadband seismic record. Our long baseline kinematic GPS solutions clearly indicated directivity of the seismic wave associated by rupture process of this earthquake. Also at the GPS stations that are 2,000 km away from the epicenter, dynamic displacements exceeding 5–10 cm were detected. In contrast, short baseline kinematic analysis shows large strain change caused by passage of surface wave, which reaches 6 × 10-6. Based on the comparison with seismometer and spectrum analysis of GPS results, it is difficult to discuss for very long time period displacement such as with a period more than 600 seconds in this study.
GPS detection of total electron content variations over Indonesia and Thailand following the 26 December 2004 earthquake
Authors: Otsuka Y. , Kotake N. , Tsugawa T. , Shiokawa K. , Ogawa T. , Effendy  , Saito S. , Kawamura M. , Maruyama T. , Hemmakorn N. , Komolmis T. 
Published: August 2014

Abstract
We report the response of the ionosphere to the large earthquake that occurred in West Sumatra, Indonesia, at 0058 UT on December 26, 2004. We have analyzed Global Positioning System (GPS) data obtained at two sites in Sumatra and at three sites in Thailand to investigate total electron content (TEC) variations. Between 14 and 40 min after the earthquake, TEC enhancements of 1.6–6.9 TEC units (TECU) were observed at subionospheric points located 360–2000 km north of the epicenter. From the time delays of the observed TEC enhancements, we find that the TEC enhancements propagated northward from the epicenter. The time delays between the earthquake and rapid increases in TEC, which occurred near the epicenter, are consistent with the idea that acoustic waves generated by the earthquake propagated into the ionosphere at the speed of sound to cause the TEC variations. A small TEC enhancement of 0.6 TECU was observed south of the epicenter, while no TEC enhancements were seen east of the epicenter. From a model calculation, we find that this directivity of the TEC variations with respect to the azimuth from the epicenter could be caused partially by the directivity in the response of the electron density variation to the acoustic waves in the neutral atmosphere.
Changes in groundwater levels or pressures associated with the 2004 earthquake off the west coast of northern Sumatra (M9.0)
Authors: Kitagawa Yuichi , Koizumi Naoji , Takahashi Makoto , Matsumoto Norio , Sato Tsutomu 
Published: August 2014

Abstract
Associated with the 2004 earthquake off the west coast of northern Sumatra, changes in groundwater levels or pressures were observed at many observation stations in Japan which are more than 5000 km from the hypocenter. At 38 of the 45 observation stations, there were changes in groundwater levels or pressures. At the 10 observation stations in which the Ishii-type borehole strain instruments were established, changes in crustal strains were also observed. A major part of the changes in crustal strains and groundwater levels or pressures were dynamic oscillations due to a seismic wave. At some stations, coseismic or postseismic rises or drops were also observed. At five stations where both crustal stain and groundwater levels or pressures were observed, postseismic changes in groundwater levels or pressures were consistent with coseismic static steps in crustal strains. At the other five stations, postseismic changes in groundwater levels or pressures did not agree with the coseismic static steps. At two stations of these five stations, it is anticipated that the pore water pressure change in each aquifer locally occurred independently of the change in crustal strain. At another station, postseismic changes in groundwater level possessed the same characteristics as a model removing the temporary deposition. At the last two stations, the causes of the changes are unknown.