bluuebunny/crossref_metadata_2025 huggingface dataset:
Paleomagnetism of the Ishikoshi Andesite: a Middle Miocene paleomagnetic pole for northeastern Japan and tectonic implications
Authors: Hoshi Hiroyuki , Teranishi Yuki
Published: August 2014

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

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

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

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

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.
Three-dimensional velocity structure in the source region of the Noto Hanto Earthquake in 2007 imaged by a dense seismic observation
Authors: Kato Aitaro , Sakai Shinichi , Iidaka Takashi , Iwasaki Takaya , Kurashimo Eiji , Igarashi Toshihiro , Hirata Naoshi , Kanazawa Toshihiko ,   Group for the aftershock observations of the 2007 Noto Hanto Earthquake
Published: August 2014

The velocity structure and accurate aftershock distributions of the Noto Hanto Earthquake in 2007 (thrust type) are elucidated by inverting the arrival times from 917 aftershocks using double-difference tomography. P-wave velocity (V

p
) of the hanging wall in the southeast appears to be higher than that of the footwall in the northwest, and the high-V

p
body of the hanging wall has a relatively high V

p
/V

s
ratio. Conversely, the low-V

p
body in the footwall appears to have a low V

p
/V

s
ratio at depths greater than 3 km. Aftershocks associated with the mainshock fault are roughly distributed along this velocity boundary between the hanging wall and footwall. Near-surface thin layers with significantly low V

p
and high V

p
/V

s
are imaged in a northwest direction from the mainshock epicenter. A likely explanation is that the mainshock fault plane was reactivated as a reverse fault in terms of the inversion tectonics due to the crustal shortening which initiated from the late Miocene. Both the mainshock hypocenter and the vertical alignment of aftershocks beneath it are located in the low-V

p
and low-V

p
/V

s
zones, indicating the potential presence of water-filled pores. Crustal stretching and shortening in and around the Noto Peninsula have created complex structures, including weak high-dip angle faults, almost vertical faults, and low velocity zones, which can potentially affect the seismic activities around the source region.
Auroral radio emission and absorption of medium frequency radio waves observed in Iceland
Authors: Sato Yuka , Ono Takayuki , Iizima Masahide , Kumamoto Atsushi , Sato Natsuo , Kadokura Akira , Miyaoka Hiroshi
Published: August 2014

In order to study the generation and propagation processes of MF auroral radio emissions (referred to as auroral roar and MF burst) in the polar ionosphere, an Auroral Radio Spectrograph (ARS) system was installed at Husafell station in Iceland (invariant latitude: 65.3°). Data analysis of man-made transmissions also provides useful information for the ionosphere study as well as an investigation of auroral radio emissions since the propagation character of MF radio waves changes depending on electron-neutral collisions in the bottomside ionosphere. Thus, ionospheric absorption is examined in comparison with the solar zenith angle and auroral phenomena. The results indicate that the ARS data can be used to detect ionization occurring at distant regions. In late 2006, the ARS detected one auroral roar and twoMF bursts, which were identified as left-handed polarized waves. Results of data analysis, including other auroral data and particle spectra observed by the DMSP satellite, suggest that the MF bursts are generated by electrons with an average energy of several keV associated with auroral breakup. On the other hand, the auroral roar is generated as upper hybrid waves by relatively low-energy electrons over the observation site and propagates downward, being converted into L-O mode electromagnetic waves.
Ionospheric hole behind an ascending rocket observed with a dense GPS array
Authors: Furuya Tomoaki , Heki Kosuke
Published: August 2014

An ascending liquid-fuel rocket is known to make a hole in the ionosphere, or localized electron depletion, by leaving behind large amounts of neutral molecules (e.g. water) in the exhaust plume. Such a hole was made by the January 24, 2006 launch of an H-IIA rocket from Tanegashima, Southwestern Japan, and here we report its observation with a dense array of Global Positioning System receivers as a sudden and temporary decrease of total electron content. The observed disturbances have been compared with a simple numerical model incorporating the water diffusion and chemical reactions in the ionosphere. The substantial vanishing of the ionosphere lasted more than one hour, suggesting its application as a window for ground-based radio astronomical observations at low frequencies.
An improved scheme for modeling the reflectance spectra of space-weathered regoliths
Authors: Nimura Tokuhiro , Hiroi Takahiro , Pieters Carle M.
Published: August 2014

In the remote detection of mineral compositions of planetary surface materials on airless bodies, space weathering is an obstacle which makes reflectance spectra redder and darker and weakens spectral features. This study attempts to model an effect of space weathering due to vapor coating by accounting for the change in surface reflectivity of regolith particles wherein nanophase-reduced iron (npFe0) particles are concentrated on their surfaces. When applied to a suite of reflectance spectra of lunar soils having different degrees of space weathering, this model can estimate the degrees of space weathering in terms of the thicknesses of the coating layer and provide an absorption coefficient spectrum of the host material.
Gamma-ray spectrometer (GRS) for lunar polar orbiter SELENE
Authors: Hasebe Nobuyuki , Shibamura Eido , Miyachi Takashi , Takashima Takeshi , Kobayashi Masanori , Okudaira Osamu , Yamashita Naoyuki , Kobayashi Shingo , Ishizaki Takeshi , Sakurai Kunitomo , Miyajima Mitsuhiro , Fujii Masayuki , Narasaki Keisuke , Takai Shigeki , Tsurumi Katsuhiro , Kaneko Hiroshi , Nakazawa Michio , Mori Kunishiro , Gasnault Olivier , Maurice Sylvestre , d’Uston Claude , Reedy Robert C. , Grande Manuel
Published: August 2014

The high-precision gamma-ray spectrometer (GRS) on the lunar polar orbiter SELENE is designed to measure 200 keV—12 MeV gamma rays in order to determine elemental compositions of the lunar surface. The GRS consists of a large germanium (Ge) crystal as a main detector and a massive bismuth germanate crystal and a plastic scintillator as anticoincidence detectors. The Ge detector is cooled by a Stirling cryocooler with its compressor attached to a passive radiator facing the cold space. The cooling system maintains the Ge detector below 90 K during the observation. The flight model of the GRS has achieved an energy resolution of 3.0 keV (FWHM) at 1333 keV. Energy spectra obtained by the GRS will show sharp gamma-ray lines whose energies identify the elements and whose intensities determine the concentrations of the elements, permitting global mapping of the elemental abundances in the sub-surface of the Moon. The elemental maps obtained by the GRS with such high-energy resolution enable us to study lunar geoscience problems.
Electromagnetic compatibility (EMC) evaluation of the SELENE spacecraft for the lunar radar sounder (LRS) observations
Authors: Kumamoto A. , Ono T. , Kasahara Y. , Goto Y. , Iijima Y. , Nakazawa S.
Published: August 2014

In order to achieve the lunar subsurface sounding and planetary radio wave observations by the Lunar Radar Sounder (LRS) onboard the SELENE spacecraft, strict electromagnetic compatibility (EMC) requirements were applied for all instruments and the whole system of the spacecraft. In order to detect the lunar subsurface echoes from a depth of 5 km, the radiated emission (RE) limit was determined to be −10 dBμV/m and the common-mode (CM) current limit to be 20 dBμA. The EMC performance of the spacecraft was finally evaluated in the system EMC test held from Oct. 20 to Oct. 22, 2005. There is no broadband noise but some narrowband noises at a level above the CM-current limit in a frequency range from 4 to 6 MHz, in which radar soundings are operated. Based on the noise spectrum within 4–6 MHz, the noise level of FMCW radar sounder is estimated to be 14 dB lower than the CM-current limit. In the SELENE EMC test, the following new techniques were introduced: (1) systematic control and evaluation of CM-current noises were first performed to improve the spacecraft EMC performance; (2) onboard battery operation was utilized for reduction of ambient broadband noises during EMC measurements.
Low-energy charged particle measurement by MAP-PACE onboard SELENE
Authors: Saito Yoshifumi , Yokota Shoichiro , Asamura Kazushi , Tanaka Takaaki , Akiba Ryota , Fujimoto Masaki , Hasegawa Hiroshi , Hayakawa Hajime , Hirahara Masafumi , Hoshino Masahiro , Machida Shinobu , Mukai Toshifumi , Nagai Tsugunobu , Nagatsuma Tsutomu , Nakamura Masato , Oyama Koh-ichiro , Sagawa Eiichi , Sasaki Susumu , Seki Kanako , Terasawa Toshio
Published: August 2014

MAP-PACE (MAgnetic field and Plasma experiment-Plasma energy Angle and Composition Experiment) is one of the scientific instruments onboard the SELENE (SELenological and ENgineering Explorer) satellite. PACE consists of four sensors: ESA (Electron Spectrum Analyzer)-S1, ESA-S2, IMA (Ion Mass Analyzer), and IEA (Ion Energy Analyzer). ESA-S1 and S2 measure the distribution function of low-energy electrons below 15 keV, while IMA and IEA measure the distribution function of low energy ions below 28 keV/q. Each sensor has a hemispherical field of view. Since SELENE is a three-axis stabilized spacecraft, a pair of electron sensors (ESA-S1 and S2) and a pair of ion sensors (IMA and IEA) are necessary for obtaining a three-dimensional distribution function of electrons and ions. The scientific objectives of PACE are (1) to measure the ions sputtered from the lunar surface and the lunar atmosphere, (2) to measure the magnetic anomaly on the lunar surface using two ESAs and a magnetometer onboard SELENE simultaneously as an electron reflectometer, (3) to resolve the Moon-solar wind interaction, (4) to resolve the Moon-Earth’s magnetosphere interaction, and (5) to observe the Earth’s magnetotail.
Ray-traced troposphere slant delays for precise point positioning
Authors: Hobiger Thomas , Ichikawa Ryuichi , Takasu Tomoji , Koyama Yasuhiro , Kondo Tetsuro
Published: August 2014

Precise satellite orbits and clock information for global navigation satellite systems (GNSS) allow zero-difference position solutions, also known as precise point positioning (PPP) to be calculated. In recent years numerical weather models (NWM) have undergone an improvement of spatial and temporal resolution. This makes them not only useful for the computation of mapping functions but also allows slant troposphere delays from ray-tracing to be obtained. For this study, such ray-traced troposphere corrections have been applied to code and phase observations of 13 sites from the International GNSS Service (IGS) receiver network, which are located inside the boundaries of the Japanese Meteorological Agency (JMA) meso-scale weather model, covering a period of 4 months. The results from this approach are presented together with a comparison to standard PPP processing results. Moreover the advantages and caveats of the introduction of ray-traced slant delays for precise point positioning are discussed.
Deformation of the Augustine Volcano, Alaska, 1992–2005, measured by ERS and ENVISAT SAR interferometry
Authors: Lee Chang-Wook , Lu Zhong , Kwoun Oh-Ig , Won Joong-Sun
Published: August 2014

The Augustine Volcano is a conical-shaped, active stratovolcano located on an island of the same name in Cook Inlet, about 290 km southwest of Anchorage, Alaska. Augustine has experienced seven significant explosive eruptions—in 1812, 1883, 1908, 1935, 1963, 1976, 1986, and in January 2006. To measure the ground surface deformation of the Augustine Volcano before the 2006 eruption, we applied satellite radar interferometry using Synthetic Aperture Radar (SAR) images from three descending and three ascending satellite tracks acquired by European Remote Sensing Satellite (ERS) 1 and 2 and the Environment Satellite (ENVISAT). Multiple interferograms were stacked to reduce artifacts caused by atmospheric conditions, and we used a singular value decomposition method to retrieve the temporal deformation history from several points on the island. Interferograms during 1992 and 2005 show a subsidence of about 1–3 cm/year, caused by the contraction of pyroclastic flow deposits from the 1986 eruption. Subsidence has decreased exponentially with time. Multiple interferograms between 1992 and 2005 show no significant inflation around the volcano before the 2006 eruption. The lack of a pre-eruption deformation signal suggests that the deformation signal from 1992 to August 2005 must have been very small and may have been obscured by atmospheric delay artifacts.
Geohazard assessment from satellite magnetic data modeling—with examples from the Arctic Margin along the Canada Basin and the Korean Peninsula along 40°N (latitude) parallel
Authors: Taylor Patrick T. , Kim Hyung Rae , Kutina Jan , Johnson G. Leonard
Published: August 2014

Long-wavelength, relative high-amplitude-magnetic anomalies obtained at satellite altitudes have provided an understanding of the nature of the deeper crust of the Earth. We have studied two such long-wavelength anomalies in regions of high stress—one with a large and one with a lower amplitude anomaly. The first feature is on the Canada Basin continental margin in the Northwest and Yukon Territories, Canada (magnetic anomaly range: 19 nT to −6 nT at 350-km altitude). This area is also the focus of significant stress and earthquake activity. We interpret this anomaly and associated tectonic activity with this region’s position at or near the fulcrum of the scissors-like opening of the Canada Basin in the mid-Mesozoic Era. The second is a section along the 40°N (latitude) parallel crossing the Korean Peninsula (magnetic anomaly range: <−2 nT to >3 nT at 350-km altitude), where an east-west fracture zone has been proposed to extend from northeastern China, across the Korean Peninsula, Sea of Japan and (Northern) Japan.
Subsurface structure of the Myojin Knoll pumiceous volcano obtained from multichannel seismic reflection data
Authors: Tsuru Tetsuro , Okuda Ayumi , No Tetsuo , Kaneda Yoshiyuki , Tamaki Kensaku
Published: August 2014

The Myojin Knoll is a submarine volcano that has a classically beautiful conical-shaped silicic caldera whose surface is covered by pumice. To determine the tectonic structure inside the caldera wall and beneath the caldera floor of this pumicious submarine volcano, we carried out a structural interpretation study using newly collected deep-penetrating multichannel seismic (MCS) reflection data. We also conducted a detailed velocity analysis of the MCS data, which facilitated the interpretation study. The results demonstrate that approximately 90% of the caldera wall is composed of pumiceous volcanic breccia. This finding supports those of previous researchers who, based on seafloor observations, single-channel seismic reflection, and gravity and geomagnetic data, concluded the Myojin Knoll is a knoll having a pumiceous caldera wall underlain by a pre-caldera rhyolitic stratovolcano edifice. We also determined a down-warping reflector approximately 800 m beneath the caldera floor. A seismic unit immediately above the reflector has a higher P-wave velocity than the pumice units and shows a chaotic seismic reflection pattern. We interpreted the reflector to be the bottom of a possible shallow magma chamber where the magma would undergo repeated expansion and contraction as a result of recurrent eruption activities.
A conservative and non-oscillatory scheme for Vlasov code simulations
Authors: Umeda Takayuki
Published: August 2014

A new numerical positive interpolation technique for conservation laws and its application to Vlasov code simulations are presented. In recent Vlasov simulation codes, the Vlasov equation is solved based on the numerical interpolation method because of its simplicity of algorithm and its ease of programming. However, a large number of grid points are needed in both configuration and velocity spaces to suppress numerical diffusion. In this paper we propose a new high-order interpolation scheme for Vlasov simulations. The current scheme is non-oscillatory and conservative and is well-designed for Vlasov simulations. This is compared with the latest interpolation schemes by performing one-dimensional electrostatic Vlasov simulations.
An improved regularization method for estimating near real-time systematic errors suitable for medium-long GPS baseline solutions
Authors: Luo Xiaowen , Ou Jikun , Yuan Yunbin , Gao Jinyao , Jin Xianglong , Zhang Kefei , Xu Huajun
Published: August 2014

It is well known that the key problem associated with network-based real-time kinematic (RTK) positioning is the estimation of systematic errors of GPS observations, such as residual ionospheric delays, tropospheric delays, and orbit errors, particularly for medium-long baselines. Existing methods dealing with these systematic errors are either not applicable for making estimations in real-time or require additional observations in the computation. In both cases, the result is a difficulty in performing rapid positioning. We have developed a new strategy for estimating the systematic errors for near real-time applications. In this approach, only two epochs of observations are used each time to estimate the parameters. In order to overcome severe ill-conditioned problems of the normal equation, the Tikhonov regularization method is used. We suggest that the regularized matrix be constructed by combining the a priori information of the known coordinates of the reference stations, followed by the determination of the corresponding regularized parameter. A series of systematic errors estimation can be obtained using a session of GPS observations, and the new process can assist in resolving the integer ambiguities of medium-long baselines and in constructing the virtual observations for the virtual reference station. A number of tests using three medium- to long-range baselines (from tens of kilometers to longer than 1000 kilometers) are used to validate the new approach. Test results indicate that the coordinates of three baseline lengths derived are in the order of several centimeters after the systematical errors are successfully removed. Our results demonstrate that the proposed method can effectively estimate systematic errors in the near real-time for medium-long GPS baseline solutions.
Ultra-rapid UT1 measurement by e-VLBI
Authors: Sekido Mamoru , Takiguchi Hiroshi , Koyama Yasuhiro , Kondo Tetsuro , Haas Rüdiger , Wagner Jan , Ritakari Jouko , Kurihara Shinobu , Kokado Kensuke
Published: August 2014

The latency of UT1 measurement with Very Long Baseline Interferometry (VLBI) has been greatly reduced by using e-VLBI technology. VLBI observations on the baseline formed by the Kashima 34-m and the Onsala 20-m radio telescopes achieved ultra-rapid UT1 measurements, where the UT1 result was obtained within 30 min after the end of the observing session. A high speed network and a UDP-based data transfer protocol ‘Tsunami’ assisted the high data rate and long-distance data transfer from Onsala to Kashima. The accuracy of the UT1 value obtained from the 1-h single baseline e-VLBI experiment has been confirmed to be as the same level with the rapid combined solution of Bulletin-A. The newly developed technology is going to be transferred to the regular intensive VLBI sessions, and it is expected to contribute to the improved latency and accuracy of UT1 data.
First GPS-TEC evidence for the wave structure excited by the solar terminator
Authors: Afraimovich E. L.
Published: August 2014

Using TEC measurements from the global network of GPS receivers, we have obtained the first evidence for the wave structure excited by the solar terminator (ST), moving over the USA, Europe, and Japan. Two main types of the observed TEC disturbance were found: large-scale (LS) 60-min variations with an amplitude of about 0.5–1 TECU and medium-scale (MS) 15-min variations with an amplitude of about 0.05–0.1 TECU. The first type of disturbances was predicted in theoretical investigations and registered earlier using different methods of ionosphere radio sounding. The second type of the observed TEC disturbance is wave packets (WPs) generated when the time derivative of TEC is at its maximum. These WPs have duration of about 1–2 h and a time shift of about 1.5–2.5 h after the ST appearance at an altitude of 100 km. That ST-generated wave packets have been found for the first time. LS TEC disturbances and MS WPs are space-fixed along the ST line over a distance exceeding 1600 km.
Magnetic poles and dipole tilt variation over the past decades to millennia
Authors: Korte M. , Mandea M.
Published: August 2014

Due to the strong dipolar character of the geomagnetic field the shielding effect against cosmic and solar ray particles is weakest in the polar regions. We here present a comprehensive study of the evolution of magnetic and geomagnetic pole locations and the Earth’s magnetic core field in both polar regions over the past few years to millennia. North and south magnetic poles change independently according to the asymmetric complexity of the field in the two hemispheres, and the changes are not correlated to variations of the dipole axis. The recent, strong acceleration of the north magnetic pole motion appears to be linked to a reverse flux patch at the coremantle boundary, and an increasing deceleration of the pole over the next years seems likely. Over the whole studied period of 7000 years two periods of comparatively high velocity of the north magnetic pole are observed at 4500 BC and 1300 BC, based on the presently available data and models. Geographic latitudes and longitudes of magnetic and geomagnetic poles based on the studied geomagnetic field models are available together with animations of the poles and polar field behaviour from our webpage http://www.gfz-potsdam.de/geomagneticfield/poles.
TEC anomalies—Local TEC changes prior to earthquakes or TEC response to solar and geomagnetic activity changes?
Authors: Afraimovich Edward L. , Astafyeva Elvira I.
Published: August 2014

A number of papers have reported on deviations of daily values of the maximum electron concentration of the ionospheric F
2 layer and/or total electron content (TEC) in the vicinity of an earthquake’s epicenter some time prior to the quake. Owing to the importance of this problem, a question of a “locality” of those effects is emerging. To study this issue we have developed a method based on the calculation of global electron content and of local electron content in “check-region” with low seismic activity. The effect of TEC day-to-day changes before strong earthquakes is analyzed in this work. It is shown that in some cases this effect might be a reflection of global changes of the ionization caused by the 27-day variations as well as other fast alterations due to solar and geomagnetic activity changes. We discuss the problem of certain data corrections that permit local changes to be distinguished from global ones.
Scaling of characterized slip models for plate-boundary earthquakes
Authors: Murotani Satoko , Miyake Hiroe , Koketsu Kazuki
Published: August 2014

We characterized source rupture models with heterogeneous slip of plate-boundary earthquakes in the Japan region. The slip models are inferred from strong-motion, teleseismic, geodetic, or tsunami records. For the identification of asperities in the slip models, we found that the area of subfaults retrieved with slips of >1.5 times the total average slip provides a size approximately equivalent to the characterized asperity by Somervilleet al.(1999). We then carried out regression analyses of the size and slip for the rupture area and asperity. The obtained scaling relationship to the seismic moment indicates that rupture areaS, average slipD, and combined area of asperitiesSaare 1.4, 0.4, and 1.2 times larger, respectively, than those of crustal earthquakes. In contrast, the ratios of the size and slip between the asperities and rupture area (Sa/SandDa′/D) are the same for plateboundary earthquakes as for crustal earthquakes. The above analyses indicate that plate-boundary and crustal earthquakes share similar source characteristics.
Tsunami waveform inversion of the 2007 Bengkulu, southern Sumatra, earthquake
Authors: Fujii Yushiro , Satake Kenji
Published: August 2014

Asbtract

We performed tsunami waveform inversions for the Bengkulu, southern Sumatra, earthquake on September 12, 2007 (M
w 8.4 by USGS). The tsunami was recorded at many tide gauge stations around the Indian Ocean and by a DART system in the deep ocean. The observed tsunami records indicate that the amplitudes were less than several tens of centimeters at most stations, around 1 m at Padang, the nearest station to the source, and a few centimeters at the DART station. For the tsunami waveform inversions, we adopted 20-, 15- and 10-subfault models. The tsunami waveforms computed from the estimated slip distributions explain the observed waveforms at most stations, regardless of the subfault model. We found that large slips were consistently estimated at the deeper part (>24 km) of the fault plane, located more than 100 km from the trench axis. The largest slips of 6–9 m were located about 100–200 km northwest of the epicenter. The deep slips may have contributed to the relatively small tsunami for its earthquake size. The total seismic moment is calculated as 4.7 × 1021 N m (M
w = 8.4) for the 10-subfault model, our preferred model from a comparison of tsunami waveforms at Cocos and the DART station.
Rupture process during the 2007 Noto Hanto earthquake (MJMA 6.9) and strong-motion simulation in the source region
Authors: Shiba Yoshiaki
Published: August 2014

The source rupture process during the 2007 Noto Hanto earthquake is inferred using a broadband waveform inversion technique based on the empirical Green’s function and the simulated annealing. The spatio-temporal distributions of the moment density and rise time on the fault are estimated from displacement motions in the frequency range from 0.1 to 2 Hz, and effective stress distribution is derived from the velocity motions in the frequency range up to 5 Hz. Results from the displacement inversion indicate that the seismic moment is mainly released from a single asperity with an area of 10 × 10 km2, and total moment release is estimated to be about 1.3 × 1019 N m. The velocity inversion shows that the high effective stress area distributes on and around the asperity, in particular at the deep periphery of it. The broadband strong motions determined using the conventional source model composed of only the moment distribution are compared with those calculated by considering both moment and effective stress separately. The fit between observed acceleration motions and synthetic ones from both source models are generally good in the frequency range up to 10 Hz, and no evident difference is recognized.
Rupture process of the 2007 Noto Hanto earthquake: waveform inversion using empirical Green’s function
Authors: Nozu Atsushi
Published: August 2014

A waveform inversion study was conducted to reveal the rupture process of the 2007 Noto Hanto, Japan, earthquake using near-source strong ground motion records. To avoid uncertainty in the subsurface structure in and around the source region when calculating Green’s functions, I used the aftershock records as empirical Green’s functions. To ensure that the path and the site effects are shared between the ground motions from the mainshock and those from aftershocks, the mainshock fault plane was divided into four domains, each of which was allocated to one of the aftershocks used as the empirical Green’s function events. The result of the inversion indicated that the rupture process included the break of two asperities. The first asperity, located close to the JMA hypocenter, was broken soon after the rupture started. This was followed by an extension of the rupture and the subsequent break of the second shallow asperity. The total moment of the mainshock was estimated to be 1.96E+19 N m, which is roughly consistent with the moment estimated by the F-net (1.36E+19 N m). Agreement between the observed and synthetic ground motions is quite satisfactory.
Observation of ground motions of aftershocks of the 2007 Noto Hanto earthquake in Monzenmachi, the Wajima city, for estimation of site amplification
Authors: Yamanaka Hiroaki , Motoki Kentaro , Yamada Nobuyuki , Sugawara Tatsuya , Mabuchi Yumi , Seo Kazuoh
Published: August 2014

Heavy damage occurred in Monzenmachi, the Wajima city, in the northern part of the Noto peninsula during the 2007 Noto Hanto earthquake with an M
j of 6.9. The area is located along a river and sandwiched by mountains at the northern and southern ends of a Quaternary narrow valley 1–2 km wide. The seismic intensity observed in the area was 6 upper during the main shock. In this study, we conducted observations of ground motions during aftershocks in Monzenmachi to understand local site effects in the vicinity of the seismic intensity station. We installed 11 accelerometers in three areas of Monzenmachi, Hashiride, Touge, and Kuroshima. In each area, three or five stations were chosen for a deployment of a linear array across the areas with heavy damage. The analysis was performed using aftershock records observed during events with M
j of 2.3–4.4. The spectral ratio of records from the station near the seismic intensity station to a reference station on Tertiary layers shows a dominant peak at a period of 1 s. We also found distinct peaks at periods of 0.4–0.7 s in the spectral ratios at the sites in the areas with heavy damage. In contrast, no dominant peaks were identified at the stations at the foot of the mountains. This clearly indicates that site amplification effects play an important role in defining the damage distribution in an area. Similar peaks were found in the H/V spectra of microtremors at the aftershock observation sites, though the peak amplitudes of the microtremor H/Vs are smaller than those of the S-wave spectral ratios.
Groundwater level changes related to the ground shaking of the Noto Hanto Earthquake in 2007
Authors: Itaba Satoshi , Koizumi Naoji , Matsumoto Norio , Takahashi Makoto , Sato Tsutomu , Ohtani Ryu , Kitagawa Yuichi , Kuwahara Yasuto , Sato Takashi , Ozawa Kunio
Published: August 2014

The Geological Survey of Japan, AIST has been monitoring groundwater using the observation network of about 40 stations in and around the Kinki and Tokai districts for earthquake prediction research. The Noto Hanto Earthquake in 2007 (MJMA6.9) occurred in the northwestern part of the Noto Hanto Peninsula, Japan on March 25, 2007. The epicentral distance to the nearest and furthest observation well is about 100 km and 400 km, respectively. Changes in groundwater level related to the Noto Hanto Earthquake were detected at many stations. Most of these were changes in the long-term trend and/or short-term oscillation; there were a few steplike changes. The coseismic static volumetric strain changes calculated from the fault model ranged between 10−9and 10−10at most of the observation stations. These changes were therefore considered to be groundwater changes caused by the ground shaking because groundwater level sensitivity to crustal volumetric strain is a few centimeters to 10−8strain at the most. We compared the coseismic groundwater level changes for the Noto Hanto Earthquake with those for five recent large earthquakes and obtained rough characteristics of the effect of the ground shaking on the groundwater level at each of the observation stations.
Groundwater changes associated with the 2004 Niigata-Chuetsu and 2007 Chuetsu-oki earthquakes
Authors: Itaba Satoshi , Koizumi Naoji , Toyoshima Tsuyoshi , Kaneko Masashi , Sekiya Kazuyoshi , Ozawa Kunio
Published: August 2014

The Geological Survey of Japan, AIST, has been monitoring groundwater in and around the Kinki and Tokai districts for earthquake prediction research. The Niigata Prefectural Office has also been observing groundwater for monitoring land subsidence in Niigata Prefecture. The 2004 Niigata-Chuetsu (MJMA6.8) and 2007 Chuetsuoki (MJMA6.8) earthquakes occurred in Niigata Prefecture, Japan, on October 23, 2004 and July 16, 2007, respectively. The two earthquakes have a similar magnitude, epicenter, and mechanism. At many of the observation wells, we detected changes in groundwater level or pressure related to the two earthquakes, but no clear precursory changes. At all of our observation wells in Niigata Prefecture, trend changes were observed after coseismic step-like changes for both of the earthquakes. At some of the stations in and around the Kinki and Tokai districts, coseismic trend changes and/or step-like changes were observed. The pattern of the changes were almost similar for the two earthquakes. Those changes were considered to be caused not by the static crustal deformation but by the ground shaking.
Long-baseline quasi-real time kinematic GPS data analysis for early tsunami warning
Authors: Daud Mohd Effendi , Sagiya Takeshi , Kimata Fumiaki , Kato Teruyuki
Published: August 2014

Real time monitoring of wave height in the ocean far from the coast can contribute to mitigation of a tsunami disaster. Here we demonstrate that early detection of a damaging tsunami can be achieved using a new long baseline kinematic GPS method, by tracking the anomalous changes in sea surface heights. The movement of a GPS buoy relative to a base station with a baseline length of 500 km has been monitored in quasi-real time mode, and the tsunami waves caused by the 5 September 2004 Off Kii Peninsula earthquake, Japan, have been successfully resolved. Based on the continuous analysis of GPS buoy data for 8 days, the average scattering of the low-pass filtered 1-Hz GPS buoy heights after tidal correction are about 3.4 cm and 1.2 cm for typhoon and calm weather, respectively. That is precise enough to detect tsunami waves with an amplitude of over 30 cm even under typhoon conditions. The long baseline can ensure an adequate evacuation time for people living on the coast.
Coseismic fault model of the 2008 Iwate-Miyagi Nairiku earthquake deduced by a dense GPS network
Authors: Ohta Yusaku , Ohzono Mako , Miura Satoshi , Iinuma Takeshi , Tachibana Kenji , Takatsuka Kota , Miyao Kayo , Sato Toshiya , Umino Norihito
Published: August 2014

A large earthquake ofMj7.2 occurred on June 14, 2008, beneath the border between Iwate and Miyagi prefectures in northeastern Japan. We propose a simple rectangular fault model based on a dense GPS network, including continuous GPS sites run by four agencies, to describe the coseismic deformation. The coseismic displacements are estimated by kinematic PPP (precise point positioning) analysis. Near the hypocenter, colocated independent instruments (integrated accelerogram and kinematic PPP) measure the same large displacement caused by the mainshock. The fault model explains the observations well and reproduces the observed complex spatial pattern, especially around the northern part of the focal area, which is the focus of a debate on whether or not the coseismic slip occurred on the Dedana fault system. Our results show that no major slip on the Dedana fault system occurred. The estimated amount of moment release was equivalent toMw6.9, and the maximum slip reached 3.5 m on the southern sub-fault.
A paleointensity study on middle Miocene to Pliocene volcanic rocks from south-eastern Spain
Authors: Calvo-Rathert M. , Goguitchaichvili A. , Vegas-Tubía N.
Published: August 2014

Thirteen middle-Miocene to Pliocene volcanic sites, belonging to four different types of volcanism (calc-alkaline volcanism, potassic calc-alkaline and shoshonitic volcanism, lamproitic volcanism and basaltic alkaline volcanism), have been sampled in south-eastern Spain for paleointensity determinations. Rock-magnetic studies yield low-Ti titanomagnetite as the main carrier of remanence, showing also the presence of titanohematites in several cases. Analysis of hysteresis parameters indicates a PSD domain structure. Paleointensity determinations were performed with the Coe (1967) method. Of the 90 paleointensity determinations carried out, 29 provide successful determinations which fulfil selection criteria; most of these were in samples of lamproitic volcanism. Only four lamproitic sites out of the 13 studied ones yield reliable results. All have a similar age of approximately 7 M.y. Virtual dipole moments (VDM) of three of these display values between approximately 4·1022 A m2 and 8·1022 A m2, thus providing new paleointensity data for a time interval (between 4 and 8 M.a.), with a lack of Thellier-type paleointensity determinations. The fourth site shows a much lower paleointensity of 1.6·1022 A m2, and may correspond to a polarity transition, in accordance with its paleo-directional results.
Paleomagnetic and rock-magnetic study on volcanic units of the Valsequillo Basin: implications for early human occupation in central Mexico
Authors: Goguitchaichvili Avto , Pozzo Ana Lillian Martin-Del , Rocha-Fernandez Jose Luis , Urrutia-Fucugauchi Jaime , Soler-Arechalde Ana Maria
Published: August 2014

Alleged human and animal footprints were found within the upper bedding surfaces of the Xalnene volcanic ash layer that outcrops in the Valsequillo Basin, south of Puebla, Mexico (Gonzalez et al, 2005). The ash has been dated at 40 ka by optically stimulated luminescence analysis, thereby providing new evidence that America was colonized earlier than the Clovis culture (about 13.5 Ma). We carried out paleomagnetic and rock magnetic analysis on 18 Xalnene ash block and core samples collected at two distinct localities and 19 standard paleomagnetic cores belonging to nearby monogenetic volcanoes. Our data provide evidence that both the volcanic lava flow and Xalnene ash were emplaced during the Laschamp geomagnetic event spanning from about 45 to 39 ka.
Seismo-acoustic location method for small-magnitude surface explosions
Authors: Che Il-Young , Shin Jin Soo , Kang Ik Bum
Published: August 2014

The aims of this study were to develop an improved method using infrasound observations at multiple seismoacoustic arrays for locating small-magnitude surface explosions at regional distances and to apply the method to ground-truth blasting events for validation. The location method is based on a nonlinear grid search using the travel times and back azimuths of infrasonic signals generated from the surface explosions and on seismic parameters that are independently determined by routine seismic monitoring systems. Specifically, the method utilizes wind-corrected infrasonic azimuths in grid searching to constrain the grids according to nearness to feasibly real observations. Ground-truth events were recorded by a seismo-acoustic station temporarily operated inside an open-pit mine and then used to investigate the improvement by the location method. The method improved the locating of ground-truth events by approximately 50% compared to the seismic location results.
Properties of matrices included in the calculation of geomagnetically induced currents (GICs) in power systems and introduction of a test model for GIC computation algorithms
Authors: Pirjola Risto
Published: August 2014

“Geomagnetically induced currents” (GICs) in ground-based networks are a manifestation of space weather and a potential source of problems to the systems. Exact matrix equations, which are summarized in this paper, for calculating GICs in a power system were formulated in the 1980s. These equations are reformulated here to show how they lead to a direct relation between GICs and the horizontal geoelectric field. Properties of the matrices, which enable the derivation of physical features of the flow of the GICs in a power system, are considered in detail. A specific aim of this study was to show that the ratio of the GICs obtained at a station under two different geophysical situations is independent of the total earthing resistance at that particular station. The behavior of the elements of the transfer matrix between geovoltages and GICs confirms the earlier result that it is sufficient to make a calculation of a small grid around the site if the GIC values at one site are of interest. Using the developed technique, I have calculated the GICs of the old configuration of the Finnish 400-kV grid.