bluuebunny/crossref_metadata_2025_split huggingface dataset:
Postseismic deformation following the 2005 West Off Fukuoka Prefecture Earthquake (M7.0) derived by GPS observation
Authors: Nakao Shigeru , Takahashi Hiroaki , Matsushima Takeshi , Kohno Yuhki , Ichiyanagi Masayoshi 
Published: August 2014

AbstractWe constructed a temporary GPS network around the aftershock area of the 2005 West Off Fukuoka Prefecture Earthquake (M7.0) in order to investigate the characteristics of its postseismic deformation. Our GPS network data, as well as the GEONET data, were analyzed using Bernese GPS software. We detected notable postseismic deformation in horizontal components close to the fault plane. The observed maximum displacement was 5.6 cm at the GNKI site on Genkaijima Island. A logarithmic law was adapted to the coordinate time series data, revealing decay times from 2 to 23 days, similar to those obtained for the 2003 Tokachi-oki Earthquake (M8.0). The amount of postseismic slips on the fault was assessed using the coseismic fault model proposed by the Geographical Survey Institute (GSI). We derived an optimum fault model of postseismic slip on the shallow (less than 3 km depth) portion of the fault. Our findings indicate that postseismic slip occurred only in shallow parts of the coseismic fault.
Three-dimensional seismic velocity structure as determined by double-difference tomography in and around the focal area of the 2005 West off Fukuoka Prefecture earthquake
Authors: Hori M. , Matsumoto S. , Uehira K. , Okada T. , Yamada T. , Iio Y. , Shinohara M. , Miyamachi H. , Takahashi H. , Nakahigashi K. , Watanabe A. , Matsushima T. , Matsuwo N. , Kanazawa T. , Shimizu H. 
Published: August 2014

Abstract
On March 20, 2005 the West off Fukuoka Prefecture earthquake (magnitude of 7.0 on the JMA scale) occurred in southeastern Japan. The earthquake fault was a left-lateral strike-slip having a nearly vertical fault plane and a strike in the WNW-ESE direction. The largest aftershock with a magnitude of 5.8 (JMA) followed 1 month later. To gain more detailed aftershock data, several teams from different Japanese universities jointly installed a number of temporary seismic stations and positioned Ocean Bottom Seismometers (OBSs) immediately above the focal area. Double-difference tomography was used to estimate the three-dimensional (3D) (Zhang and Thurber, 2003) velocity structures in and around the focal area based on the travel time data collected during seismic observations. The high-velocity regions estimated by the inversion are located on the edge of the aftershock area and on the shallow part of asperity, as inferred from the slip distribution. Conversely, the V
p/V
s ratio is not always as high as that found at the location of the asperity. This finding suggests that the construction of the medium is not uniformly elastic but complex, with different relations between elastic constants and strength.
Deep crustal structure along the Niigata-Kobe Tectonic Zone, Japan: Its origin and segmentation
Authors: Nakajima Junichi , Hasegawa Akira 
Published: August 2014

AbstractA seismic tomography study has revealed a detailed three-dimensional seismic velocity structure along a highstrain-rate zone, the Niigata-Kobe Tectonic Zone (NKTZ), located in Japan. The results show that the depth extent of the low-velocity zone varies along the NKTZ. We divided the NKTZ into three regions on the basis of the velocity structure. A low-velocity anomaly observed in the lower crust beneath the southwestern part of the NKTZ is probably attributable to the fluids derived from the Philippine Sea slab, while a prominent low-velocity anomaly extending from the upper crust to the uppermost mantle in the volcanic region, the middle part of the NKTZ, may be caused by the existence of melts and a higher-temperature condition that results from magmatic activity. The northeastern part exhibits low-velocity anomalies in the upper crust and the uppermost mantle, which are probably due to the thick sediment and fluids related to the back-arc volcanism, respectively. The strength of the crust and uppermost mantle along the NKTZ may have been weakened by the concentration of the fluids, which in turn facilitates the large contraction there. The heterogeneous structures revealed in this study suggest that the origin of the high-strain-rate zone varies along the NKTZ.
Equatorial electrojet in the East Brazil anomaly region
Authors: Rastogi R. G. , Yumoto K. 
Published: August 2014

Abstract
An examination of the geomagnetic field variations at equatorial stations in South America has shown that the daily range of the northward field, H, is about 30% larger in Peru than in Brazil. The midday H field vector in Brazil shows a large westward tilt, corresponding to large westward declination at the station. A significant meridional trans-equatorial current system is suggested for the observed anomaly. The longitudinal variation in the equatorial electrojet current strength is suggested to be due to the corresponding variation in the ionospheric electric field rather than to the electrical conductivity.
Vertical velocity from the Korean GPS Network (2000–2003) and its role in the South Korean neo-tectonics
Authors: Hamdy Ahmed M. , Park Pil-Ho , Jo Bong Gon 
Published: August 2014

Abstract
In the absence of adequate leveling observations in South Korea, the vertical deformation has been investigated using the Korean Global Positioning System (GPS) Network data (2000-2003). Although the vertical components of the GPS velocities have been rarely used in crustal deformation studies because of their high noise level, the processing strategy employed here enhances the data quality and eliminates the seasonal effect. The obtained vertical velocity field shows that the maximum vertical velocity in the ITRF 97 reference frame is 3.3 mm/year (subsidence), which reflects a relatively low level of seismic activity in South Korea. Two deformation patterns were recognized; subsidence in the Okchun Basin, and uplift in its adjacent areas. This subsidence is due to the collision of Kyonggi Massif and Okchun Basin (part of the South China block) against the Yongnam Massif and Taebaeksan Basin (part of the North China block).
Volcanic origin of the 1741 Oshima-Oshima tsunami in the Japan Sea
Authors: Satake Kenji 
Published: August 2014

Abstract
The generation mechanism of the 1741 Oshima-Oshima tsunami, which is considered to be the most destructive tsunami that has ever originated in the Japan Sea, has been the subject of much debate. The tsunami caused about 2,000 casualties along the Hokkaido and northern Honsu coasts and inflicted damage as far as the Korean Peninsula. The tsunami source is located between recent tsunamigenic earthquakes, but there is no historical record of an earthquake in 1741. In contrast, the records indicate volcanic activity of Oshima-Oshima, including a large-scale sector collapse, although the volume change associated with the subaerial landslide is too small to explain the observed tsunami heights. Recent marine surveys indicate that the landslide extended to the ocean bottom with a volume change of about 2.5 km3, nearly an order of magnitude larger than the subaerial slide. On the basis of mapped bathymetry, the generation of the tsunami is calculated using a simple kinematic landslide model. The tsunami propagation is computed in two different grids—a 6″ grid around the source and a 1′ grid for the entire Japan Sea. A parameter search of the model shows that the observed tsunami heights are best explained by a horizontal slide velocity of 40 m/s and a rise time of 2 min. The large vertical drop of the landslide and the coupling of the submarine landslide and tsunami are the main factors responsible for the large tsunami.
Sudden commencements in the X and Y fields at equatorial stations in the African sector
Authors: Rastogi R. G. 
Published: August 2014

Abstract
This paper describes the mean direction of the H vector due to Sq (solar quiet) and SC (sudden commencement) at equatorial stations Addis-Ababa (geographical longitude: 39°E) and at M’Bour (17°W). The Sq (H) vector aligns fairly well with the direction of the dip declination (D), and the SC (H) vector aligns along the dipole declination (Ψ) minus the dip declination D. At M’Bour, which is situated in the Atlantic Anomaly region, both the Sq (H) and the SC (H) vectors were along 32°W of N, while the dip as well as the dipole declinations were 9°W. Thus, the normal and the disturbance current in the Atlantic region is modulated by some additional meridian currents, resulting in a large increase in the westward Y, the source of which cannot be currently estimated from only one station, M’Bour. This problem requires further investigation.
Surface wave analysis with beamforming
Authors: Tanimoto Toshiro , Prindle Kenton 
Published: August 2014

Abstract
It is well known that off-great-circle path propagation causes a technical difficulty for surface wave analysis in higher frequency ranges. We propose a new approach that combines a beamforming technique and two-station phase velocity measurement to resolve this problem. Beamforming allows us to determine the correct azimuth of incoming surface waves which can be taken into account in phase velocity measurement. Beamforming results also support that a plane-wave approximation is mostly acceptable for frequencies up to about 50–60 mHz (millihertz), although evidence of multipathing is occasionally recognized in beamforming results as multiple peaks. Application of this correction scheme for Rayleigh-wave data in Southern California seems to make the largest impact on the results of azimuthal anisotropy. Effects are not large for frequencies up to 30 mHz but fast velocity axes in azimuthal anisotropy maps change significantly for higher frequencies.
Geomagnetic jerks from the Earth’s surface to the top of the core
Authors: Chambodut Aude , Eymin Céline , Mandea Mioara 
Published: August 2014

Abstract
Rapid changes in the magnetic field characterised by an abrupt change in the secular variation have been named “secular variation impulses” or “geomagnetic jerks”. Three of these events, around 1968, 1978 and 1990, occurred during the time-span covered by the comprehensive model CM4 (Sabaka et al., 2002, 2004). This model, providing the best temporal resolution between 1960 and 2002 as well as a fine separation of the different magnetic sources, can be used to study rapid phenomena of internal origin. In order to analyse these events all over the globe, synthetic time series were obtained from the CM4 model between 1960–2002. Geomagnetic jerks are detected here as a rapid movement of the zero isoline of the second field derivative. Analysis of the area swept out by this isoline as a function of time allows us to map the spatial extent of jerks though time, and to identify an event around 1985 that is localized in the Pacific area. At the core surface, we compute the fluid flows under the frozen-flux and tangentially geostrophic assumptions. The flows do not exhibit any special pattern at jerk times, but instead show a smooth temporal evolution over the whole time period. However, the mean amplitude of the dynamical pressure associated with these flows present maxima at each jerk occurrence and helps to confirm the identification of a jerk in 1985.
Paleomagnetism of the Datong monogenetic volcanoes in China: paleodirection and paleointensity during the middle to early Brunhes Chron
Authors: Yamamoto Y. , Tsunakawa H. , Shaw J. , Kono M. 
Published: August 2014

Abstract
Paleomagnetic measurements were conducted on Datong volcanic rocks from China, which are thought to have formed in the mid to early Brunhes Chron. Meaningful site-mean paleodirections were obtained from 21 sites which are considered to represent 17 independent cooling units. They give a mean VGP (virtual geomagnetic pole) position of (76.5°N, 7.9°E) with A95=7.7° (N=17), which is statistically distinct from geographic north. This dataset also yields an ASD (angular standard deviation) of 17.2° around the mean VGP position. Because the paleodirections form two clusters, the samples may record the paleomagnetic field during two different short periods and therefore may not average out paleosecular variation. Paleointensity measurements were conducted using three different methods. The DHT and LTD-DHT Shaw methods, the Thellier method, and the microwave Thellier method were applied to 119, 29 and 73 specimens respectively, and they give 66, 16 and 12 successful results (success rates are 55, 55 and 16%). From the LTD-DHT Shaw dataset, eight acceptable site-mean paleointensities are obtained. They give an average VDM (virtual dipole moment) of 3.79±1.94x 1022 A m2. This is 56% lower than the average VDM of 5.91±1.74x 1022 A m2 (N=14) calculated from the selected Thellier data from the latest paleointensity database using the same criteria. One possible reason for this difference might be systematic overestimations of paleointensities by the Thellier method on volcanic rocks.
Paleointensities from Tertiary basalts, Inner Mongolia and Hebei Province, northeastern China
Authors: Tanaka Hidefumi , Takahashi Naho , Zheng Zhong 
Published: August 2014

Abstract
A paleointensity study using the Thellier’s method was made on Tertiary basaltic rocks in Inner Mongolia and Hebei Province, northeastern China. K-Ar ages were previously reported for all the rocks, which range around 6–8 Ma and 28–32 Ma. Sample selection was based on total quality of remanence behavior and rock magnetism. High stability to AF and thermal demagnetization, small difference between the heating and cooling curves of magnetic susceptibility vs. temperature measurements, and PSD to SD characteristics in the Day plot of the hysteresis parameters were required. Experiments in vacuum using Coe’s procedure were applied to 54 specimens from nine flows. Experiments were successful for 34 specimens, giving seven flow mean paleointensities. Excluding two flow means (in one flow, only two specimens from the same sample survived and in the other, the within-site error amounts to 42%) the final success rate was 29 out of 54 (54%), which is not low. The obtained results range from 54 to 65 μT, except for one lava which gave 23 μT. These results indicate that although the paleointensity in the Tertiary was generally smaller than the present-day value, there were large fluctuations in the dipole moment, and paleointensities of the present-day level were often attained.
Magnetic petrology and its implication for magma mixing of the 1991–1995 dacite at Unzen volcano, Japan
Authors: Saito Takeshi , Ishikawa Naoto 
Published: August 2014

AbstractMagnetic petrologic analyses were carried out on lava samples from the lava dome of the 1991–1995 eruption of Unzen volcano, Japan. As a result, three kinds of titanomagnetites with different Curie temperatures were identified and the difference between the samples from the lava dome which grew exogenously and endogenously were revealed. Titanomagnetites withTc of 460–500°C and 380–400°C are the predominant magnetic minerals. In addition, a titanomagnetite withTc of ∼540°C, but in low concentration, is also present. The exogenous lava samples contain more titanomagnetite withTc of 380–400°C and less microphenocrysts of titanomagnetites than the endogenous samples. The equilibrium temperature of 900–920°C, 780–820°C and 720°C is estimated from titanomagnetite withTc of 380–400°C, 460–500°C and 540°C, respectively. We suggest that these titanomag-netites are probably formed by magma mixing and eruption processes. Titanomagnetite withTc of 460–500°C was derived from felsic magma (780–820°C) in a shallow chamber. Titanomagnetite withTc of 380–400°C was produced from the mixed magma (900–920°C). After being squeezed out from the reservoir, a small amount of titanomagnetite withTc of ∼540°C was crystallized.
Paleomagnetism of the Ishikoshi Andesite: a Middle Miocene paleomagnetic pole for northeastern Japan and tectonic implications
Authors: Hoshi Hiroyuki , Teranishi Yuki 
Published: August 2014

Abstract
To determine a Middle Miocene paleomagnetic pole for northeastern Japan and discuss its tectonic implications, we obtained new paleomagnetic results from Middle Miocene (about 14 Ma) dacite and andesite flows of the Ishikoshi Andesite. Characteristic remanent magnetizations were isolated from 12 lava sites by means of detailed alternating field and thermal demagnetizations. Analysis of demagnetization results and rock magnetic experiments indicated that magnetite or Ti-poor titanomagnetite is the main magnetic carrier. We obtained a formation mean direction (D = 9.2°, I = 65.9°, α95 = 7.3°, k = 40.5, N = 11) and compared it with published paleomagnetic results from other areas of northeastern Japan to discuss tectonic rotation. This comparison provided a mean paleomagnetic pole (85.9°N, 236.6°E, A
95 = 6.2°, K = 115.9, N = 6) that we consider represents the Middle Miocene pole for northeastern Japan. It is statistically indistinguishable from coeval poles for southwestern Japan, South Korea, and northern China, and we therefore conclude that northeastern Japan as a whole has not been subjected to tectonic rotation since the Middle Miocene. A reassessment of geologic and paleomagnetic data suggests that a previous model of the Late Miocene or later counterclockwise rotation of northeastern Japan is based on tilt-uncorrected paleomagnetic directions from tilted rock units.
Characteristics of crustal magnetic structures in the Tsushima (Ulleung) and Japan Basins from vector magnetic anomalies
Authors: Kato Hiroyuki , Isezaki Nobuhiro , Park Chan Hong , Kim Chang Hwan , Nakanishi Masao 
Published: August 2014

Abstract
Magnetic surveys by a Deep-tow Three-Component Magnetometer (DTCM) were conducted in the northeastern part of the Japan Basin and the central part of the Tsushima (Ulleung) Basin. Magnetic lineations are recognized clearly in the former area, whereas they were not recognized by previous studies in the latter area. The high-quality vector magnetic anomaly data obtained by DTCM enables the precise determination of the strikes of magnetic lineations and the positions of magnetic boundaries. Magnetic anomalies measured by DTCM show the characteristics of linear magnetic anomalies in both basins. The strikes of magnetic lineations are N47°E in the Japan Basin and N82°E in the Tsushima Basin. The estimated magnetization intensities of magnetic source models constructed from the amplitudes of analytic signal calculated from vector anomalies and the crustal structures determined by seismic studies are similar to those of typical extrusive basalt in both basins. The observed anomalies in the Japan Basin contain a short wavelength anomaly which cannot be explained by the model. Their ages may be chrons C5Cr (16.726–17.277 Ma), C5Dn (17.277–17.615 Ma), C5Dr (17.615–18.281 Ma), and sub-chron C5Dr.1n which was identified by a paleomagnetic study. The estimated half-spreading rate is 2.0 cm/yr, which is slower than that estimated by previous study. The observed anomalies in the Tsushima Basin show that there is a partial magnetization high. This may indicate that not all of the sources of magnetic lineations in the Tsushima Basin changed to low magnetization by the effect of thick sediment cover and the intrusions of a large amount of dikes after the formation.
A newly-identified spectral reflectance signature near the lunar South pole and the South Pole-Aitken Basin
Authors: Vilas Faith , Jensen Elizabeth A. , Domingue Deborah L. , McFadden Lucy A. , Runyon Cassandra J. , Mendell Wendell W. 
Published: August 2014

Abstract
Signal analysis of Galileo images of the Moon suggests the presence of an absorption band centered near 0.7 μm in the reflectance spectra of areas located adjacent to the equatorward walls of lunar craters at latitudes ranging from −58 to −78°, and areas contained in the South Pole-Aitken Basin. We propose three potential explanations: an Fe2+→Fe3+ charge transfer transition in oxidized iron in clinopyroxenes (high-Ca bearing pyroxenes) or phyllosilicates (Fe- and Mg-bearing sheet silicates containing adsorbed H2O and interlayer OH−), or an effect of titanium in ilmenite (a common lunar opaque material). No identification of the mineralogy is conclusive. The presence and nature of the absorption feature could be confirmed using AMICA images of the lunar far side from the Japanese mission Hayabusa, spectroscopic results from the Japanese mission Selene scheduled for launch in 2007, or the Moon Mineralology Mapper on the Indian mission Chandrayaan-1.
Highly resolved distribution of aftershocks of the 2007 Noto Hanto Earthquake by a dense seismic observation
Authors: Sakai Shin’ichi , Kato Aitaro , Iidaka Takashi , Iwasaki Takaya , Kurashimo Eiji , Igarashi Toshihiro , Hirata Naoshi , Kanazawa Toshihiko ,   group for the joint aftershock observation of the 2007 Noto Hanto Earthquake
Published: August 2014

Abstract
The 2007 Noto Hanto Earthquake occurred on March 25, 2007, in the Noto Peninsula, central Japan. A half day after the main shock, we started installing temporary seismic stations in order to determine the precise locations of its aftershocks. Ten universities and two research institutes deployed 88 temporary seismic stations in and around the source area. The observation lasted for about 2 months. We relocated 1318 aftershocks with arrival time corrections at each station. The relocated hypocenters show relatively small errors—less than 0.2 km in the horizontal direction and less than 0.4 km depth. Most of the relocated hypocenters are about 2.0 km shallower than those determined by JMA. The distribution of the aftershocks forms a southeast-dipping plane. The main shock is located at the bottom part of their distribution. The precise aftershock distribution extends into a shallower area than the original, and it coincides with sea floor-ward extension of the active faults previously known from a sonic reflection survey. Heterogeneous distribution of the aftershocks on the fault plane shows low seismicity just above the main shock hypocenter, and middle-size aftershocks are distributed on the periphery of the main shock. A precursory event (M 4.4) that occurred 0.6 s before the main rupture is located close to the M 2.2 foreshock that occurred 12 min before it.
Crustal deformation associated with the Noto Hanto Earthquake in 2007 in Japan
Authors: Ozawa Shinzaburo , Yarai Hiroshi , Tobita Mikio , Une Hiroshi , Nishimura Takuya 
Published: August 2014

Abstract
The Global Positioning System (GPS) network in Japan detected coseismic deformation from the 2007 Noto Hanto earthquake (M
w = 6.9). The result indicates a 21-cm southwestward displacement and a 7-cm upheaval at the GPS site near the epicenter. Synthetic Aperture Interferometry (InSAR) shows an approximately 50-cm movement toward the “Daichi” satellite, in ascending orbit, near the epicenter. The estimated fault slip distribution based on GPS and InSAR results shows a large slip area ranging up to 2 m near and northeast of the hypocenter. The slip area beneath the Sea of Japan southwest of the hypocenter also shows large slippage of around 2 m. Aftershocks are distributed in the asperity area and its vicinity, demonstrating that the asperity hypothesis clearly does not hold completely for this earthquake. Computed vertical displacements using the model are consistent with the geomorphological evidence of long-term uplift.