bluuebunny/crossref_metadata_2025_split huggingface dataset:
Tsunami source of the 2004 off the Kii Peninsula earthquakes inferred from offshore tsunami and coastal tide gauges
Authors: Satake Kenji , Baba Toshitaka , Hirata Kenji , Iwasaki Shin-Iti , Kato Teruyuki , Koshimura Shunichi , Takenaka Jun , Terada Yukihiro 
Published: August 2014

Abstract
Tsunamis from the 2004 off the Kii Peninsula earthquakes (M 7.1 and 7.4) were recorded on offshore tsunami gauges, a GPS tsunami gauge and eight bottom-pressure gauges, as well as coastal tide gauges located south of Honshu and Shikoku. The maximum amplitudes on the GPS and bottom-pressure gauges were several to ten cm, while those on tide gauges were up to 0.9 m. We first computed tsunami waveforms from the earthquake source models proposed Yamanaka (2004) and Yagi (2004) from seismic waveform analysis, and compared them with the observed waveforms. For the first event (foreshock), both models produce similar waveforms with the observations. For the second event (mainshock), the waveforms computed from the Yamanaka model is closer to the observed waveforms, but there are still discrepancies between the observed and computed waveforms. We then performed tsunami waveform inversions to estimate the water height distributions in the source area. The foreshock source is ≈1600 km2 with the maximum water height of 0.2 m. The estimated tsunami source area for the mainshock, ≈3600 km2 with the maximum of 0.6 m, extends ≈60 km toward northwest and ≈40 km southwest from the epicenter along the aftershock distribution, suggesting that multiple faulting was involved in the mainshock.
Response of the equatorial electrojet to solar flare related X-ray flux enhancements
Authors: Manju G. , Viswanathan K. S. 
Published: August 2014

Abstract
The response of ionospheric E-region electric fields and currents to solar flare related X-ray flux enhancements are studied at the magnetic equatorial location of Trivandrum (8.5°N, 77°E; dip 0.5°N) using VHF (54.95 MHz) coherent backscatter radar observations in the altitude region of 95–110 km conducted during daytime. The amplitude of the Solar Flare Effects (SFE) observed in the earth’s magnetic field variations at Trivandrum have been examined in relation to that at Alibag and it is found that the ratio of the SFE amplitudes at the two stations lies in the range of 1.8–2.6. The backscattered power of the VHF radar showed a substantial reduction during the peak phase of all the strong X-rank flares studied. It has also been observed that there is a sharp fall in the ratio of the field line integrated Hall conductivity (σ2) to the field line integrated Pedersen conductivity (σ1) in the dynamo region "Equation missing" during strong flare times in relation to normal times. The time variations of mean Doppler frequency (f

D
) of the backscattered signals have been observed to indicate a fall close to the peak phase of the strong flare events. Another new result is the radar observed presence of westward electric field for a long duration of 2–3 hours during a partial counter electrojet (CEJ) event that occurred on one of the days (8 July 1992) studied. The implications of the observations are discussed in detail.
High-resolution maps of Coda Q in Japan and their interpretation by the brittle-ductile interaction hypothesis
Authors: Jin Anshu , Aki Keiiti 
Published: August 2014

Abstract
Using seismograms recorded at 582 Hi-net stations for earthquakes located within 30 km from each station, we measured coda Q for frequency bands of 1–2, 2–4, 4–8, 8–16, and 16–32 Hz, respectively. Then coda Q maps are constructed with average station spacing of 20 km over Japan, except the Hokkaido Island. The most striking feature of the obtained maps is the significant spatial variation within Japan, up to a factor of 3 for the lower frequency bands, as well as its strong frequency dependence. Such high spatial resolution was not possible to achieve without the high density and sensitivity of the Hi-net. We found several low coda Q regions for frequency band of 1–2 Hz including the southwestern Shikoku, eastern Shimane-western Tottori along the Japan Sea coast and the disjointed spots along the Pacific coast from the Kanto-Tokai region to southern edge of the Kii-peninsula. However, the most conspicuous low coda Q zone is a narrow belt from Niigata towards south-west to the Biwa lake along the Japan Sea coast. This low Q zone appears at frequency bands of both 1–2 and 2–4 Hz, and it coincides with the zone of high deformation rate revealed from the GPS data. For frequency bands 4–16 Hz (2–4 Hz in Kyushu), the low coda Q areas agree with volcanic and geothermal areas. For frequency band of 16–32 Hz, the coda Q is distributed nearly uniformly throughout the study area.
Three dimensional velocity structure around aftershock area of the 2004 mid Niigata prefecture earthquake (M6.8) by the Double-Difference tomography
Authors: Korenaga Masahiro , Matsumoto Satoshi , Iio Yoshihisa , Matsushima Takeshi , Uehira Kenji , Shibutani Takuo 
Published: August 2014

Abstract
The 2004 mid Niigata prefecture earthquake with M6.8 occurred in the north of central part of Japan. It was a reverse fault by the regional compression stress field in NW-SE direction. Several aftershocks with M≥6 were occurred. The large aftershocks occurred on plural fault planes. The plane was either parallel or normal to the main shock one. We estimated three dimensional velocity structures in and around the focal area of the earthquake by using a Double Difference tomography method. The arrival time data were picked from seismograms at the deployed seismic stations settled by Kyoto and Kyushu universities in collaboration, NIED, ERI, and JMA. The velocity structure showed that a low velocity zone existed in the northwest part of the aftershock area. On the contrary, the velocity in the southeast became high. Moreover, the fault plane of the main shock inferred from the aftershock distribution was located at the velocity boundary.
Geomagnetic paleointensity over 1.2 Ma from deep-tow vector magnetic data across the East Pacific Rise
Authors: Yamamoto Michiko , Seama Nobukazu , Isezaki Nobuhiro 
Published: August 2014

Abstract
Deep-tow vector magnetic data have been acquired across the fast-spreading southern East Pacific Rise 18°S and inverted to magnetization intensity variations. Vector magnetic data are used to determine continuous magnetic intensity within intervals of constant polarity over the Matuyama and Brunhes periods up to the Cobb Mountain event at 1.19 Ma. A comparison of our deep-tow vector data and a sediment core-derived geomagnetic paleointensity timescale suggests that the short-wavelength magnetic anomaly signal is indeed of geomagnetic origin and can be used to date the seafloor with a high resolution. The crustal age determined from our date reveals a highly asymmetric spreading rate for the recent period (since 0.3 Ma).
Rupture process by waveform inversion using simulated annealing and simulation of broadband ground motions
Authors: Shiba Yoshiaki , Irikura Kojiro 
Published: August 2014

AbstractA source inversion method using very fast simulated annealing is proposed to estimate the earthquake rupture process, and associated radiation of broadband strong ground motions. We invert the displacement and velocity motions separately to estimate the spatio-temporal distributions of effective stress and moment. The developed method is applied to the near-source strong motions in the frequency range up to 5 Hz from the 1997 Izu-Hanto Toho-Oki earthquake (Mjma 5.9). Results of the displacement inversion indicate that for this earthquake the seismic moment is mainly released from the shallower region and the northern area from the hypocenter. Similar results are obtained from the velocity inversion, and the variation of the effective stress also exhibits a similar behavior to the moment distribution. Based on the inversion results, we propose a characterized source model that consists of the finite number of asperities and a background area with uniform effective stresses. The broadband ground motion simulation demonstrates that the characterized source model successfully reproduces the observed ground motions in spite of the simplification of actual (inverted) source process. This suggests our proposed inversion method and source characterization process are suitable for the strong-motion prediction that reflects the high-frequency radiation from an actual earthquake.
1-D resistivity structures of the oceanic crust around the hydrothermal circulation system in the central Mariana Trough using Magnetometric Resistivity method
Authors: Tada Noriko , Seama Nobukazu , Goto Tada-nori , Kido Motoyuki 
Published: August 2014

Abstract
We present preliminary results of an electromagnetic survey over a region of hydrothermal circulation in the spreading axis of the central Mariana Trough. The Magnetometric Resistivity (MMR) method is used to determine the electrical resistivity structure of the oceanic crust around the hydrothermal system. 1-D electrical resistivity structure is calculated from the relation between the amplitude of magnetic field and source-receiver separation. The amplitudes of magnetic field variation of ocean bottom magnetometers (OBMs) placed on axis are larger than those of OBMs about 700 m away from the spreading axis, for source-receiver separations larger than 400 m. We estimated two resistivity structure models: one for the axial OBMs, and another for the off-axis OBMs. A region of lower resistivity between depths of 100–300 m is identified in the on-axis model. The hydrothermal source of the Alice Springs Field probably exists beneath the spreading axis, and the size of this source is smaller than 700 m. Lower resistivities at a depth of 50 m are identified in both the on-axis and the off-axis models, suggesting that the porosity in the uppermost oceanic crust is largest at this depth.
Magnetization intensity mapping on Unzen Volcano, Japan, determined from high-resolution, low-altitude helicopter-borne aeromagnetic survey
Authors: Okubo Ayako , Tanaka Yoshikazu , Utsugi Mitsuru , Kitada Naoto , Shimizu Hiroshi , Matsushima Takeshi 
Published: August 2014

Abstract
On September 18, 2002, we conducted a high-resolution, low-altitude helicopter-borne aeromagnetic survey at two flight altitudes, using spiral trajectories for the first time, over Unzen Volcano in the framework of the Unzen Scientific Drilling Project (USDP). This study obtained more detailed and new information than the previous aeromagnetic studies in Unzen volcano about the geological features, for understanding the history and eruption mechanism of the Unzen volcano. Therefore, we conducted a magnetization intensity mapping on the volcano, on the assumption that the magnetic anomalies are caused by the terrain magnetized in the same direction as the present Earth’s magnetic field and the magnetization intensity varies only laterally. This map shows good agreement with the geologic features, especially the hydrothermal alteration zone and the collapsed pyroclastic deposits. In addition, even in the area covered by lavas, the magnetization intensities show various values corresponding to each eruption event. It may be considered that the differences in magnetic properties reflect different oxygen fugacity in rocks during their cooling time period. Local magnetization lows on Heisei-Shinzan suggest that the Heisei lava produced by the 1991–1995 eruption has not yet been cooled enough.
Comprehensive paleomagnetic study of a succession of Holocene olivine-basalt flow: Xitle Volcano (Mexico) revisited
Authors: Alva-Valdivia Luis M. 
Published: August 2014

AbstractA detailed paleomagnetic study of a young Late Holocene olivine-basalt flow from the Xitle volcano in the southern Basin of Mexico was completed to evaluate the consistency and reliability of the record derived from fresh well-preserved and exposed lava flows. One-hundred oriented standard paleomagnetic cores corresponding to 10 different lava effusion episodes were collected from unit-flow V. Thermomagnetic analyses show that bulk magnetic properties and remanence is carried in most cases by Ti-poor titanomagnetite, presumably resulting from oxy-exsolution processes during the initial flow cooling. Unblocking temperature and coercivity suggests pseudo-single domain magnetic grains for these (titano)magnetites. Thermal and alternating field demagnetizations show well-defined univectorial magnetizations. Most sites present a mean direction with small angular dispersion around the dipolar direction for central Mexico. The overall mean direction (N= 10, Dec = 1.1°, Inc = 34.1°,k= 531 and α95= 2.1°) is characterized by small angular dispersion and inclination close to the dipolar value for the locality. Anisotropy ofmagnetic susceptibility lineation agrees with the geologically-inferred flow direction. Various samples from the 10 lava flows were selected for Thellier paleointensity experiments because of their stable remanent magnetization and relatively low within-site dispersion. According to reliability parameters, the obtained paleointensities are of reasonably good quality. Nine mean paleointensities range between 48.6 and 73.9μT. The overall mean paleointensity of 59.9–7.7μT is higher than the present-day field of 43μT, consistent with the global data for this time-period. Most samples presented alteration during the cooling rate test, and no correction was made to these samples. Those samples on which cooling-rate correction was applied give a flow mean lower than the raw paleointensity data, as was expected.
Diffusion of crustal deformation from disturbances arising at plate boundaries—a case of the detachment beneath the Izu Peninsula, central Honshu, Japan—
Authors: Takahashi Kana , Seno Tetsuzo 
Published: August 2014

Abstract
We carry out numerical simulation of disturbance propagation within a plate floating over a viscous layer based on the 2-dimensional equations of Lehner et al. (1981). We apply the results to the anomalous crustal movements in central Honshu that followed the dike intrusion event between Miyakejima and Kozushima in the mid of 2000. We assume that the anomalous crustal movements represent diffusive transfer of a slip on the detachment beneath the Izu Peninsula, that occurred at the time of the dike intrusion event, over thin viscous layers such as the fault gouge of nearby great interplate earthquakes (Seno, 2005). From the arrival times of the disturbance in the Tokai district, the diffusion coefficient is determined to be 50–150 m2/s, and the viscosity of the fault gouge to be 1013–1015 Pa s. This value of viscosity is significantly smaller than that of the asthenosphere, and would probably be caused by the elevation of pore fluid pressure close to the lithostatic in the rupture zones of nearby great earthquakes. The serpentinized wedge mantle landward of the rupture zones may also constitute part of the thin viscous layers.
Caldera geometry determined by the depth of the magma chamber
Authors: Kusumoto Shigekazu , Takemura Keiji 
Published: August 2014

Abstract
The depth of the magma chamber is shown to be an important factor governing the initial type, scale, and collapse of a caldera. The collapse of the magma chamber is approximated by the contraction of a sphere in an elastic medium, and the distribution of plastic and/or rupturing area on the surface is calculated using the Coulomb failure criterion under the assumption of an elastic-perfectly plastic material. It is found that the necessary contraction for the formation of a caldera is described by fifth-power polynomial expression of the depth of the magma chamber, and that the radius and geometry of the caldera are dependent on the depth of the magma chamber.
A study of smoothed TEC precision inferred from GPS measurements
Authors: Liu Zhizhao , Gao Yang , Skone Susan 
Published: August 2014

Abstract
The availability of a large amount of TEC data derived from dual frequency GPS measurements observed by GPS reference networks provides a great opportunity for ionosphere studies. In order to obtain better accuracy for the derived TEC, a data smoothing technique is usually employed to take advantage of both code pseudorange and carrier phase GPS measurements. The precision of TEC data therefore is dependent on the smoothing approach. However little work has been done to evaluate the precision of the smoothed TEC data obtained from different smoothing approaches. This investigation examines the properties of two popularly used smoothing approaches and develops the closed-form formulas for estimating the precision of the smoothed TEC data. In addition, a previously proposed approximate formula for estimating TEC precision is also evaluated against its closed-form formula developed in this paper. The TEC precisions derived from the closed-form precision estimation formulas for approaches I and II are analyzed in a numerical test. The results suggest that approach II outperforms approach I and the precision of TEC data smoothed by approach II is higher than approach I. For approach I, a numerical test is also conducted to compare the precision difference between the closed-form and approximate formulas for estimating TEC precision. The comparison indicates that TEC derived from the closed-form formula have better precisions than the approximate formula. Analysis also reminds users that extra cautions should be taken when using the approximate formula in order to avoid the precision divergence phenomenon.
Understanding the concept of outlier and its relevance to the assessment of data quality: Probabilistic background theory
Authors: Monhor Davaadorjin , Takemoto Shuzo 
Published: August 2014

Abstract
In recent years an increasing interest in the studies on outlier can be observed, however, for the time being there exists no general definition of outlier. In the present paper we introduced a generic descriptive definition of outlier. We observed that the outlier problems had so far been treated in statistical way without paying proper attention to probabilistic-theoretic backgrounds. In view of this gap, we made an attempt to establish a probabilistic background theory. Within this framework, the large deviations are considered as probabilistic-theoretic model of outlier, and the interrelationship of the laws of large numbers, the central limit theorems and the large deviations are clarified. These considerations are specialized for the case of statistical sample, which is important from the point of view of the assessment of data quality. Some methodological and historical aspects of geodesy, geophysics and astronomy are mentioned, too. We revealed that the data analysis carried out by Kepler in the process of discovery of his famous elliptic law of planetary motion has relevance to the outlier problem. This methodologically interesting fact is a new result in the history of geosciences. We established that the accuracy of Chebyshev inequality increases as the deviation of the random variable involved from its expectation, increases. The possibility of application of Chebyshev inequality to the outlier problem is pointed out.
Three-dimensional structure of Vp, Vs and Vp/Vs in the upper crust of the Marmara region, NW Turkey
Authors: Bariş Şerif , Nakajima Junichi , Hasegawa Akira , Honkura Yoshimori , Ito Akihiko , Üçer S. Balamir 
Published: August 2014

AbstractWe applied a 3-D seismic tomography inversion algorithm to arrival-time data obtained, during 18 years from 1985 to 2002, from local seismic networks and aftershock studies in the Marmara region, in order to better understand the upper crustal structure of the complex tectonic region. We integrated all the available data set into a common data set and relocated the events, using a 1-D velocity model. We then selected 3,949 earthquakes and obtained 92355 arrival times, in total, consisting of 59,313P-wave and 33,042S-wave arrival times. In this paper we present detailed crustal structures forV p,V sandV p/V sratios from the surface down to 15 km depth with good resolution in terms of the hit count analysis of seismic rays, the checkerboard and restoring resolution tests for the studied region. The results obtained from the inversion suggest that the western part of the North Anatolian Fault Zone shows strong lateral heterogeneity. We concluded that no clear pattern exists between the distribution of microearthquakes and aftershocks and the velocity perturbations presented in this paper. This is probably due to complex tectonic and geological structures. Large coseismic slip associated with the two recent strong earthquakes was found to correspond to higher velocity anomalies, as was often found recently. On the other hand, low velocity values correspond to the sedimentary units or the alluvium regions, as supported by the low resistivity and gravity values. Thus the results presented in this paper are quite consistent with the other data such as gravity, resistivity and magnetic anomalies, indicating that our model is reliable and efficient and it should be useful for further interpretation of tectonic and geological problems in this region. It should be pointed out, however, that the results ofS-wave perturbations andV p/V sratio could not be discussed in detail because of insufficient quality of theS-wave data and the reliability of the results is not very high. Nonetheless, the fact that recent large Izmit earthquake and moderate aftershocks that occurred in or around the high velocity zones near the low velocity region suggests that high velocity regions found in the area close to Istanbul in the Marmara Sea and also at the Iznik-Mekece fault are potential sites for strain energy accumulation and release.
A synoptic study of VLF sudden phase anomalies recorded at Visakhapatnam
Authors: Khan Ibrahim , Devi M. Indira , Arunamani T. , Madhusudhana Rao D. N. 
Published: August 2014

Abstract
A synoptic survey of Sudden Phase Anomalies (SPAs) observed in the phase variation measurements of 16 kHz VLF transmissions from Rugby (England) made at Visakhapatnam (India) has been carried out. These Sudden Ionospheric Disturbances caused during solar flares are examined in relation to flare time enhancements of X-ray radiation fluxes. It is found that nearly 81% of SPAs recorded have accompanying X-ray enhancements and in 80% of the cases Hα flares and microwave bursts also occur concurrently. Using SPA magnitudes and flare time X-ray flux values, the threshold level of X-ray flux to induce an SPA has been estimated as 1.5⊙×10−3 ergs/cm2/s. In majority of the events, the change in reflection height during the flare is observed to be less than 4 kms. Other SPA characteristics like onset times, growth and relaxation times etc. have also been studied. These results are consistent with those obtained for other propagation paths.
The observation of ULF emissions at Nakatsugawa in possible association with the 2004 Mid Niigata Prefecture earthquake
Authors: Ohta Kenji , Watanabe Nobuo , Hayakawa Masashi 
Published: August 2014

Abstract
The observation of ULF/ELF electromagnetic emissions at Nakatsugawa, Gifu, has indicated that ULF emissions in the frequency below 0.1 Hz take place about two-three weeks before the 2004 Mid Niigata Prefecture earthquakes. The most important support to this is based on the goniometric direction finding for those ULF emissions in the period of October 2–6, which indicates their azimuth being very close to the epicenters of the earthquake. So, these ULF emissions on October 2–6 are likely to be associated with the 2004 Mid Niigata Prefecture earthquake.