bluuebunny/crossref_metadata_2025 huggingface dataset:
Precise location of the fault plane and the onset of the main rupture of the 2005 West Off Fukuoka Prefecture earthquake
Authors: Takenaka Hiroshi , Nakamura Takeshi , Yamamoto Yosuke , Toyokuni Genti , Kawase Hiroshi
Published: August 2014

Near-source strong-motion records of the 2005 West Off Fukuoka Prefecture earthquake have two remarkable features. One is the presence of a relatively long period pulse with large amplitude on the fault-normal component of the velocity and displacement records, which is the result of the forward rupture directivity. The other is that the records show several seconds of small but increasing amplitude arrival (“initial rupture phase”) followed by the onset of the main energy release (“main rupture phase”). We first determined the precise geometry of the fault plane of this earthquake by examining the horizontal particle motion of the mainS-wave portion on the records, as follows: the strike is N304°E, and the dip angle is 87°. The dip direction of the fault plane is northeast, and the surface intersection of the fault plane passes by the eastern coast of Genkai Island. We also obtained the relative location of the onset of the main rupture with respect to the hypocenter, and the mean rupture velocity between them. The distance between them is 5.1 km, the onset of the main rupture is located southeast above the hypocenter. The mean rupture velocity along the straight path is 1.4 km/s. It is found that the main rupture began 3.6 sec later from the origin time, at the central point between the hypocenter and Genkai Island. Our results suggest that Genkai Island directly suffered the strong effects of the forward rupture directivity during the earthquake.
Rupture process of the 2005 West Off Fukuoka Prefecture, Japan, earthquake
Authors: Horikawa Haruo
Published: August 2014

The 2005 West off Fukuoka Prefecture, Japan, earthquake (MS 6.7) is a moderate-size crustal event. The rupture process of this earthquake was inferred from strong motion data. It is observed regardless of epicentral distance and azimuth that the initialP-wave with a small amplitude continued for 2.5–4 s, suggesting prominent initial rupture. The duration of the initial rupture was estimated to be 3.3 s from travel time analysis. Inversion analysis shows that the initial rupture continued for 3.5 s and the overall rupture finished within 10 s. An area of large slip with two peaks of slip amount appeared to the southeast of the hypocenter, and the location of the large-slip area is consistent with the origin of the main rupture inferred from travel time analysis. Small amount of slip was found at and around the hypocenter, and the rupture velocity was slow there. The seismic moment of this earthquake was estimated to be 5.7 × 1018 Nm (Mw6.4). The maximum stress drop calculated from the derived slip distribution exceeded 10 MPa. An area of negative stress drop expanded, corresponding to the distribution of small slip. Forward modeling of the observed waveforms suggests that the negative stress drop is not fully attributable to poor resolution of inversion analysis for small amount of slip. Since dynamic stress drop should be positive around the hypocenter so that rupture propagates over the entire fault, it is plausible that the negative stress drop appeared after healing.
Simulation of strong motions in Fukuoka City during the 2005 West Off Fukuoka Prefecture Earthquake with special reference to thick Quaternary sediments around the Kego fault
Authors: Satoh Toshimi , Kawase Hiroshi
Published: August 2014

We simulate velocity records at two stations in the building damaged area near the Kego fault in Fukuoka City by 1-D wave propagation theory during the 2005 West Off Fukuoka Prefecture Earthquake, Japan. Here we use the pre-Tertiary bedrock wave deconvolved from the record observed at a K-NET station outside of the damaged area. The observed velocity waveforms and pseudo velocity response spectra in the period range from 0.7 to 10 seconds in the predominant direction (N20°E) components are reasonably reproduced. Velocity pulses with a period of about 1 to 2 seconds in observed velocity waveforms at two stations are found to be amplified by the Quaternary sediments above the pre-Tertiary bedrock. After we confirmed the validity of our approach through the simulation, we predict the peak ground velocity (PGV) distribution around the Kego fault by considering 1-D response of Quaternary sediments at each site. The predicted PGV distribution of N20?E components is largest (about 80 cm/s) in the northeast side of the Kego fault and agrees well with the building damage distribution. Our result shows that the 1-D site responses of Quaternary sediments mainly contributed to the difference of PGVs inside and outside of the damaged area in Fukuoka City.
Stress change prior to the major events in the 1989 earthquake swarm off the eastern Izu Peninsula, Japan
Authors: Kawakata Hironori , Ogasawara Hiroshi , Sekiguchi Shoji , Uyama Shizuka , Mino Kazuo
Published: August 2014

We investigate a temporal change in a stress parameter of earthquakes that occurred in the 1989 swarms off the eastern Izu Peninsula in Japan. We use the energy index (EI), which have been monitored in deep South African gold mines for predicting major events, as an estimate of apparent stress that is proportional to the ratio of seismic energy (E) to seismic moment (Mo).EImeasures an excess or shortage inEwith respect to the empirical relationship betweenEandMo. We check thatEIis almost proportional to the apparent stress for the ranges ofMoand frequency for our analysis, althoughEis underestimated due to the artifact of limited frequency band of monitoring. The largest events (M= 5.2 and 5.5) took place off the tip of a vertical crack, which opened associated with magma intrusion. While the opening continued to load the source areas of theM5.2 and 5.5, we find significant decrease inEIprior to the events. Based on the experimental result that the stress decreases when yielding takes place prior to final failure, we interpret this observation as yielding in the vicinity of the large earthquake hypocenters, following a rapid increase in stress caused by magma intrusion.
Statistical studies of fast and slow Z-mode plasma waves in and beyond the equatorial plasmasphere based on long-term Akebono observations
Authors: Nishimura Y. , Ono T. , Iizima M. , Shinbori A. , Kumamoto A. , Oya H.
Published: August 2014

In order to investigate spatial and temporal variations of fast and slow Z-mode waves frequently observed in the equatorial plasmasphere, statistical studies have been performed by using plasma wave observation data obtained by the Akebono satellite within a period from 1989 to 1995. It has been clarified that fast and slow Z-mode waves are intensified within ±5° of geomagnetic latitudes in an altitude range from 6000 km to the apogee (10500 km) of the satellite without obvious local time dependence. Long-term averaged intensity of fast Z-mode waves has almost the same orders of magnitude as that of slow Z-mode waves. These results indicate that significant part of fast Z-mode waves are not produced by the linear mode conversion process from slow Z-mode waves, but excited by more direct process. Furthermore, the region of intensified fast and slow Z-mode waves has been spread in a wider geomagnetic latitude range of ±10° during geomagnetic storms. These evidences suggest that one of the possible free energy sources is ring current particles injected into the equatorial region of the plasmasphere during geomagnetic storms.
3-D electromagnetic induction studies using the Swarm constellation: Mapping conductivity anomalies in the Earth’s mantle
Authors: Kuvshinov Alexei , Sabaka Terence , Olsen Nils
Published: August 2014

An approach is presented to detect deep-seated regional conductivity anomalies by analysis of magnetic observations taken by low-Earth-orbiting satellites. The approach deals with recovery of C-responses on a regular grid and starts with a determination of time series of external and internal coefficients of the magnetic potential. From the coefficients, time series of the magnetic vertical component and of the horizontal divergence of the horizontal components are synthesized on the grid and the C-responses are determined by means of signal processing of the corresponding time series. For validation of the approach, 3 years of realistic synthetic data at simulated orbits of the forthcoming Swarm constellation of 3 satellites have been used. To obtain the synthetic data for a given 3-D conductivity Earth’s model a time-domain scheme has been applied which relies on a Fourier transformation of the inducing field, and on a frequency domain forward modelling. The conductivity model consists of a thin surface layer of realistic conductance and a 3-D mantle that incorporates a hypothetic deep regional anomaly beneath the Pacific Ocean plate. To establish the ability of the approach to capture the geometry of the mantle heterogeneities used in the forward approach, numerical experiments have been undertaken using various satellite combinations, sampling periods of the resulting time series, and numbers of internal coefficients. The possibility of the approach to map anomalies in the mantle using satellite data that contain contributions from the core and lithosphere, from the magnetosphere and ionosphere (and their Earth-induced counterparts), as well as payload noise has been investigated. The model studies have shown that C-responses obtained on a regular grid might be used to map regional deep-seated conductivity anomalies. Moreover, it has been demonstrated that these C-responses are successfully recovered from magnetic data collected by the proposed Swarm constellation of 3 satellites.
Modeling and analysis of solar wind generated contributions to the near-Earth magnetic field
Authors: Vennerstrom S. , Moretto T. , Rastätter L. , Raeder J.
Published: August 2014

Solar wind generated magnetic disturbances are currently one of the major obstacles for improving the accuracy in the determination of the magnetic field due to sources internal to the Earth. In the present study a global MHD model of solar wind magnetosphere interaction is used to obtain a physically consistent, divergence-free model of ionospheric, field-aligned and magnetospheric currents in a realistic magnetospheric geometry. The magnetic field near the Earth due to these currents is analyzed by estimating and comparing the contributions from the various parts of the system, with the aim of identifying the most important aspects of the solar wind disturbances in an internal field modeling context. The contribution from the distant magnetospheric currents is found to consist of two, mainly opposing, contributions from respectively the dayside magnetopause currents and the cross-tail current. At high latitudes the field-aligned component is of partidular interest in connection with internal field-modelling. In the altitude regime of 400–800 km (typical for low Earth orbit satellites) the ionospheric currents are found to contribute significantly to the disturbancance, and account for more than 90% of the field-aligned disturbance. The magnetic disturbance field from field-aligned currents (FACs) is basically transverse to the main field, and they therefore contribute with less than 2% to the disturbance in total field intensity. Inhomogeneity in ionospheric conductance is identified as the main cause of main-field disturbance in the field-aligned direction. These disturbances are associated with the ionospheric Pedersen currents, and may introduce systematic errors in internal field models.
Curl-B technique applied to Swarm constellation for determining field-aligned currents
Authors: Ritter Patricia , Lühr Hermann
Published: August 2014

The constellation of the Swarm satellites provides for the first time the opportunity to determine field-aligned currents in the ionosphere uniquely. This is achieved by employing the curl-B relation of Ampere’s law directly to measurements of a satellite pair flying side-by-side. The new technique is applied to a set of consistent magnetic field and current data generated by a global magnetospheric model. Using a realistic Swarm constellation the current distribution is determined along the orbit from the synthetic magnetic field data. The resulting currents are tested against the input currents. The agreement between input model and recovered field-aligned currents is excellent and much improved compared to the single-satellite estimates. Due to the spatial separation of the sampling points, only the distribution of large-scale field-aligned currents can be determined. These investigations demonstrate one important aspect of the broad capabilities provided by the upcoming space mission.
Two-layer Q
s
structure of the slab near the southern Kurile trench
Authors: Maeda Takahiro , Sasatani Tsutomu
Published: August 2014

We estimate Q
s values (quality factor for S-wave) of the slab near the southern Kurile trench by using seismic data observed at ocean bottom seismometer (OBS) stations from selected local earthquakes. The seismic rays pass mainly through the slab and this enable us to directly estimate the slab Q
s values. The spectral inversion and coda normalization method are applied to these data. The estimated Q
s values from the two methods are nearly the same and increase with frequencies. However, these Q
s values are not high enough to explain the abnormal distribution of ground motion that has been recognized as abnormal distribution of seismic intensities at the Japanese arc. Thus we propose a two-layer Q
s structure of the slab to explain the both facts, our slab Q
s values and the abnormal distribution of ground motion. The two-layer Q
s structure consists of the upper layer with not so high Q
s values (39f
1.0) and lower layer with very high Q
s values (500f
1.0); the upper layer has a thickness of about 50 km. Seismic activity is restricted only within the upper layer of the two-layer Q
s structure. This may mean that the two-layer Q
s structure reflects the different material property between the upper and lower layer of the slab.
A study of the storm event on October 21–22, 1999 by the MHD simulation
Authors: Park K. S. , Ogino T.
Published: August 2014

We carried out a high resolution three-dimensional magnetohydrodynamic (MHD) simulation of the interaction between the solar wind and the Earth’s magnetosphere during a strong magnetic storm on October 21–22, 1999. The input to the simulation was from WIND solar wind observations. As the IMF is strongly southward (−20 nT to −30 nT) for 6 hours, the geomagnetic field lines in the dayside magnetopause are eroded to the geosynchronous orbit (GEO) region by reconnection. The associated magnetic flux is transferred from the dayside magnetosphere to the tail. The reconnection region still appears near GEO region on the dayside magnetopause, even though the IMF B
z component becomes small or northward, because of the influence of the strong IMF B
y (30 nT). IMF lines can successively reconnect with the naked and large geomagnetic field line in the dayside flank regions. Thus, the cross polar cap potential is maintained to be large value and convection in the ionosphere is enhanced. The cross polar cap potential is governed by IMF B
y as well as B
z (ф ≈250 kV for B
z ≈ −20 nT and ф ≈ 300 kV for B
z ≈ − 30 nT), and it saturates during the strong southward IMF. A large energy flux enters the ionosphere at very low latitudes (50°) and the inner edge of the plasma sheet becomes very close to the Earth X = −3.2 R
E for a strong magnetic storms. The open-closed boundary extends to 60° latitudes on the nightside, 72° on the dayside, 62° on dawn, and 66° on dusk. Enhanced energy flux appears at low latitudes (50°) on the nightside in simulation. Moreover, the energy flux in the dusk region (19 MLT) appears down to 55° latitude in simulation, which is consistent with the low latitude boundary of the 0.02-20 keV particles detected by TED of the NOAA-15. A convective electric field, which is penetrating to the Earth-side of the NENL, is almost comparable to that of the solar wind. The present MHD simulation study give reasonable results even for extreme conditions and thereby its usefulness is demonstrated as a physical model for space weather studies.
Time scheduling of magnetic surveys in mid-latitudes with respect to forecasting geomagnetic activity
Authors: Hejda Pavel , Bochníček Josef , Horáček Josef , Nejedlá Jaroslava
Published: August 2014

The quality of magnetic surveys is essentially influenced by the geomagnetic activity. As the in situ measurements are usually limited to very short time period, they must be compared with observatory continuous registrations. When reducing measurements one makes an assumption that diurnal variations of the magnetic field are identical at both the station and the reference observatory. During magnetically quite periods, this assumption is satisfied to an acceptable extent. However, under high geomagnetic activity, the error may easily exceed the acceptable limit. Our analysis indicates that, in mid-latitudes, magnetic surveys should not be made, if some of the Kp values are over 5. Long-term and medium-term forecasts of geomagnetic activity are based on known periodicities (11-year, half-year and 27-day). Short-term forecasts are based on the knowledge of the actual conditions on the Sun, in the solar wind and in the interplanetary magnetic field. Regional Warning Centres, associated in the International Space Environment Service (ISES) deal with forecasts of geomagnetic activity. Links to all 12 centres can be obtained through http://www.ises-spaceweather.org/about_ises/index.html.
Geomagnetic survey and geomagnetic model research in China
Authors: Gu Zuowen , Zhan Zhijia , Gao Jintian , Han Wei , An Zhenchang , Yao Tongqi , Chen Bin
Published: August 2014

The geomagnetic survey at 135 stations in China were carried out in 2003. These stations are with better environmental condition and small magnetic field gradient (<5 nT/m). In the field survey, the geomagnetic declination D, the inclination I and the total intensity F were measured. Ashtech ProMark2 differential GPS (Global Positioning System) was used in measuring the azimuth, the longitude, the latitude and the elevation at these stations. The accuracy of the azimuth is 0.1′. The geomagnetic survey data were reduced using the data at geomagnetic observatories in China. The mean standard deviations of the geomagnetic reduced values are: <1.5 nT for F, <0.5′ for D and I. Using the geomagnetic data which include the data at 135 stations and 35 observatories in China, and the data at 38 IGRF (International Geomagnetic Reference Field) calculation points in China’s adjacent regions, the Taylor polynomial model and the spherical cap harmonic model were calculated for the geomagnetic field in China. The truncation order of the Taylor polynomial model is 5, and its original point is at 36.0°N and 104.5°E. Based on the geomagnetic anomalous values and using the method of spherical cap harmonic (SCH) analysis, the SCH model of the geomagnetic anomalous field was derived. In the SCH model, the pole of the spherical cap is at 36.0°N and 104.5°E, and the half-angle is 30°, the truncation order K= 8 is determined according to the mean square deviation between the model calculation value and the observation value, the AIC (Akaike Information Criterion) and the distribution of geomagnetic field.
New Slovak geomagnetic repeat station network
Authors: Valach Fridrich , Vaczyova Magdalena , Dolinsky Peter
Published: August 2014

Six geomagnetic repeat stations were established over the territory of Slovakia. The locations of the observation points were chosen in a way to provide long time series of geomagnetic measurements at the same places (or nearly the same ones). Thus the series start in the middle of the 19th century. In this paper, the long time series of three geomagnetic elements D, H and I are reviewed. Results of the last geomagnetic measurements at the six observation points (reduced to the 2004.5 epoch) are presented and linear models of the distribution of geomagnetic elements and of their secular variations are shown.
Crustal movement of Antarctica and Syowa Station based on GPS measurements
Authors: Ohzono Mako , Tabei Takao , Doi Koichiro , Shibuya Kazuo , Sagiya Takeshi
Published: August 2014

In Antarctica, sea level rise and crustal uplift have occurred due to ice sheet melting and mantle response since the Last Glacial Maximum (LGM). The International GNSS Service (IGS) provides continuous data at nine sites on the Antarctic plate, and we analyzed data obtained from these sites between 1998 and 2003. Additional data were acquired by campaign observations around Syowa Station carried out by the Japanese Antarctic Research Expedition (JARE). Five sites around Syowa Station have been repeatedly occupied since 1998. Our analysis of the IGS data demonstrates that the Antarctic continent behaves as a rigid plate. Vertical components indicate an uplift of about 1.3–7.0 mm/year at almost all sites, which are attributed to the postglacial rebound. However, some observed velocities disagree with the predictions of glacial isostatic adjustment (GIA) models. It will be necessary to incorporate our results into the modeling of ice sheet melting. Around Syowa Station, the campaign GPS result is basically consistent with the IGS data analysis, thereby demonstrating that GPS observations properly represent the ongoing crustal movement around Syowa Station. However, the GPS results show some disagreement with the VLBI observations; this discrepancy will need to be sorted out using local tie observations that should be carried out in the near future.
Crustal heterogeneity around the Nagamachi-Rifu fault, northeastern Japan, as inferred from travel-time tomography
Authors: Nakajima Junichi , Hasegawa Akira , Horiuchi Shigeki , Yoshimoto Kazuo , Yoshida Takeyoshi , Umino Norihito
Published: August 2014

An M=5 earthquake occurred on September 15, 1998, in the Nagamachi-Rifu fault (NRF), northeastern Japan. In the aftermath of this event, many seismograph stations were constructed temporarily around the fault, forming a dense network of stations with a spatial separation of 5 km. We report here our estimation of the three-dimensional velocity structures of the P and S waves using arrival-time data recorded at these stations with the aim of understanding the heterogeneous structure around the NRF. Low-Velocity and high Poisson’s ratio anomalies are imaged in the lower crust beneath the volcanic area, which are probably associated with the partially molten materials conveyed through the upwelling flow in the mantle wedge. A distinct low-velocity anomaly, which is explainable by the existence of H2O-filled pores, is observed in the mid crust at the deeper extension of the NRF. Two low-velocity anomalies that are probably associated with the remnants of magmatic activity that formed the Shirasawa caldera and with the existence of thick late-Cenozoic sedimentary layers are observed at depths shallower than 10 km in the hanging wall of the NRF. Our results successfully characterize the major features of the complex velocity structure around the NRF, with implications for the existence of fluid-rich regions in the mid to lower crust.
Oscillating motion of the Jovian Great Red Spot and Numerical Experiments with IG equation
Authors: Asada Tadashi , Miyazaki Isao
Published: August 2014

Position measurements of the Great Red Spot (GRS) on recent digital images of Jupiter were carried out to detect the longitudinal and latitudinal motion of the GRS. Its longitudinal oscillating motion may be interpreted as two types. One has a 57-day period and no latitudinal motion, the other has 86 days and probably has latitudinal motion. In 86 days, oscillation, the GRS seems to locate equatorward when it moves relatively westward, and poleward when it moves eastward. Numerical Experiments of the Intermediate Geostrophic (IG) equation show the same results for the motion of an eddy, and that a kind of wave collides with the eddy when it changes relative longitudinal motion from eastward to westward.
Electron temperature variation associated with the auroral energy input during the DELTA campaign
Authors: Abe Takumi , Oyama Koh-Ichiro , Kadohata Akihiro
Published: August 2014

Japanese sounding rocket “S-310-35” was launched from Andøya Rocket Range in Norway on December 13, 2004 during Dynamics and Energetics of the Lower Thermosphere in Aurora (DELTA) campaign, in which the rocket-borne in-situ measurements and ground-based measurements were coordinated to conduct a comprehensive observation of the upper atmospheric response against the auroral energy input. The Fast Langmuir Probe (FLP) was installed on the sounding rocket to study thermal structure and energy balance of the plasma by measuring the electron temperature in the polar lower ionosphere. The FLP observations indicate that the electron temperatures were found to be remarkably high in an altitude range from 106 km to 114 km during the ascending phase of the rocket. The lowest part of this high temperature region might be affected by artificial electron beam which was generated by the N2 temperature instrument on the same rocket. On the other hand, a small increase of the electron temperature was observed at the altitude from 114 to 119 km in the descending phase. This is possibly the first time that both the temperature increase and density fluctuation that may be caused by the Farley-Buneman instability were detected by in-situ observation.
An aspect of the subsurface structure of the Burdur-Isparta area, SW Anatolia, based on gravity and aeromagnetic data, and some tectonic implications
Authors: Dolmaz M. Nuri
Published: August 2014

Gravity and aeromagnetic analyses were conducted in the Burdur-Isparta area of Turkey in order to identify the subsurface structure and tectonics of the region independent of surface cover. The analytic signal of the aeromagnetic anomalies was first calculated to delineate the source fields of these anomalies. The magnetic signatures were found to correlate well with the intrusives associated with the subduction of the African oceanic lithosphere and with the ophiolitic nappes in the region. The residual aeromagnetic anomalies mostly orientate in the N-S direction, implying the presence of remanent magnetization. Based on the shape analysis of aeromagnetic anomalies, the region appears to have rotated clockwise. The magnetic anomalies were found to continue upward to 5 km a.s.l. The upward continued map shows deep effects of the sub-crustal magnetic sources. Based on the Bouguer gravity anomalies, the thickness of the crust in the study area is between 33 and 37.5 km. Major extensive NE- and NW- as well as N-trending faults are identified that coincide with the Lake Burdur, Lake Beysehir and Kovada grabens, respectively. Lake Egirdir is also devoid of any magnetic sources. As a final step, the maxima of the horizontal gradient of the gravity data were calculated. The maxima show that the major geological formations and the structural trends in the area are remarkable. The boundaries of the various geological formations can be identified based on the boundary analysis of the gravity and the analytic signal of the aeromagnetic data. The change in the nature of the anomalies reflects the imprints of intense deformation associated with major tectonic activity of the African-Eurasian plate convergence zone.
Moment release budget at oblique convergence margin as revealed by the 2004 Sumatra-Andaman earthquake
Authors: Oishi Makiko , Sato Tamao
Published: August 2014

Based on the model of oblique convergence, we predicted the slip rate on the megathrust plate boundary in the western Sunda arc and compared it with the slip distribution of the 2004 M
w 9.0 Sumatra-Andaman earthquake. The slip directions on the megathrust plate boundary, which are necessary for predicting the slip rate, were determined using the fault plane solutions of medium-sized earthquakes occurring for the last 30 years in the 2004 rupture zone. At long wavelengths the predicted slip rate correlates well with the latitudinal variation of the coseismic slip, suggesting that kinematics described by the model of oblique convergence operated over a long interseismic period and that the seismic coupling coefficient has been generally uniform along the strike of the rupture zone. Using the data for the same period of time, we estimated the total seismic moment released by the earthquakes on the Sumatra fault and its submarine continuation located on the backarc side of the Nicobar and Andaman islands. The ratio of the observed seismic moment to the seismic moment predicted from the model of oblique convergence is small. The residual may either be stored for generation of future earthquakes or was taken up by the fault creep at shallow depths.
Cathodoluminescence and fluid inclusion analyses of mineral veins within major thrusts in the Shimanto accretionary complex: evidence of hydraulic fracturing during thrusting
Authors: Mukoyoshi Hideki , Hirono Tetsuro , Sekine Kotaro , Tsuchiya Noriyoshi , Soh Wonn
Published: August 2014

To elucidate fluid-rock interaction in a seismogenic zone along a plate-subduction boundary, we investigated the occurrence of mineral veins within the major thrusts in the Shimanto accretionary complex and examined their microstructures using a cathodoluminescence technique. We found discriminative structures, for example, a jigsaw-puzzle structure, within the quartz veins in the thrusts, which could indicate that hydraulic fracturing occurred by abnormal pore-fluid pressure during thrusting. Pore pressure values, estimated quantitatively by fluid inclusion analyses, were 3–27 MPa higher than the surrounding parts, which may be direct evidence of abnormal pore-fluid pressure. High pore-fluid pressures and subsequent hydraulic fracturing may play an important role within major thrusts along a plate-subduction boundary.
Automation of absolute measurement of the geomagnetic field
Authors: Auster H. U. , Mandea M. , Hemshorn A. , Pulz E. , Korte M.
Published: August 2014

In this paper a device is presented to measure the geomagnetic field vector absolutely and automatically. In contrast to the standard DI-Flux measurement procedure our automation approach is based on the rotation of a three-component fluxgate magnetometer about precisely monitored axes without using a non-magnetic theodolite. This method is particularly suitable for automation because it only requires exact knowledge of the axes orientations. Apart from this, requirements on mechanical precision are moderate. The design of the facility is presented, and mechanical, optical and magnetic limitations are discussed. First promising results of measuring the Earth’s magnetic field absolutely and automatically with the new device at Niemegk observatory are discussed.
Density distribution in medium-sized icy satellites of giant planets
Authors: Czechowski Leszek , Leliwa-Kopystynski Jacek
Published: August 2014

We discuss processes that determine the distribution of density in the medium-sized icy satellites (MIS). Gravitational differentiation, porosity and phase transitions lead to a spherical distribution, while thermal convection, large impacts and tidal deformation can result in a non-spherical distribution. According to our previous research, convective patterns in MIS can consist of one or two convective cells for radiogenic and tidal heating. The shift of the center of mass ΔrCM and the ratio of moments of inertia IZ/IXY are calculated using a numerical model of convection. A new dimensionless number C is introduced to describe the deformation of the surface. We found that ΔrCM can reach ≈0.5% of the satellite radius for the one-cell pattern. With the two-cell pattern the moment of inertia, IZ, can be reduced by ≈0.4%. The impact cratering could be one cause of significant changes in ΔrCM and IZ /IXY but only for the smallest of the MIS. Tidal deformation could result in the enhancement of mass redistribution caused by other mechanisms.
Interseismic deformation of the Nankai subduction zone, southwest Japan, inferred from three-dimensional crustal velocity fields
Authors: Tabei Takao , Adachi Mari , Miyazaki Shin’ichi , Watanabe Tsuyoshi , Kato Sayomasa
Published: August 2014

We have studied crustal deformation in the Nankai subduction zone, southwest Japan, based on three-dimensional GPS velocity fields. Oblique subduction of the Philippine Sea plate has caused two different modes of deformation of the overriding plate: interseismic crustal shortening in the direction of plate convergence, and permanent lateral movement of the forearc. The block boundary dividing the forearc is the Median Tectonic Line (MTL); however, we assumed that its shallower portion is fully or partially locked to a certain depth. The plate boundary and the MTL are represented by many rectangular faults. We carried out inversion analyses with a priori information to estimate simultaneously slip deficit rates at those rectangular faults, together with the rate of lateral movement of the forearc. The results show that the seismogenic subduction faults at a depth of 5–25 km are strongly locked. As for the transition zone at 25–35 km, the inversion analysis results in stronger locking than shown in previous studies, especially when the vertical velocity data are weighted. The rates of lateral forearc movement and slip deficit at the MTL are nearly comparable but in a reverse sense to each other. This shows that the shallower portion of the MTL is strongly locked but that stationary aseismic slip is occurring in the deeper part.
Geodetic constraint on the slip distribution of the 2006 Central Kuril earthquake
Authors: Takahashi Hiroaki , Kasahara Minoru
Published: August 2014

We have investigated the slip distribution of the 15 November 2006 Central Kuril earthquake off Simushir Island using continuous GPS data. A dense GPS network on Hokkaido Island, northern Japan, and Sakhalin Island detected coseismic horizontal displacements of ~9 mm despite large epicentral distances of about 900–1200 km. Eastward displacements at the sites decrease to the south, and this spatial distribution feature constrains the slip on the three subfaults. Our data suggest that little slip has occurred in the southern and northern parts, but that a 6-m slip has occurred in the center of the focal region. This interpretation fits well with the detailed slip distribution inferred from teleseismic waveform inversions. The total seismic moment, 2.8 × 1021 N m, is approximately the value indicated using by the Global CMT solution. Our result implies that there remains a seismic gap between this event and the 1952 great Kamchatkan earthquake that is large enough for anM> 8 earthquake.
Calibration of amplification factors using KiK-net strong-motion records: toward site effective estimation of seismic intensities
Authors: Hayashida Takumi , Tajima Fumiko
Published: August 2014

Estimated seismic intensities using conventional relationships are not always in agreement with those observed at specific sites. We investigate subsurface amplification factors using the KiK-net strong-motion data recorded both in the borehole and on the ground surface and attempt to estimate more accurate intensities at a given site. Here the amplification factors are evaluated using the ratios of peak velocity amplitudesVsurf/Vborthat are calculated from records on the ground surface and in the borehole. The ratios (amplification factors) decrease with hypocentral distance in general, but the attenuation characteristics vary from station to station. At stations where large amplifications are observed, the ratios show large scatter relative to the empirical amplification formulas. The variation is also affected by the incident direction of seismic waves as well as the hypocentral distance. We derived empirical amplification formulas ofVsurf/VbedwhereVbedis the peak velocity on the engineering bedrock as a function of hypocentral distance at individual stations (i.e. specific sites) in place of the conventionally used amplification constants. The estimated intensities using the site-effective formulas show substantial improvement at most of the stations in comparison with those calculated using conventional formulas.
Evolution of the concept of Sudden Storm Commencements and their operative identification
Authors: Curto J. J. , Araki T. , Alberca L. F.
Published: August 2014

In this paper, we review the evolution of both, the concept and the operative methods of detection of Storm Commencements (SC’s) and we introduce suggestions for future improvements. Finally, a more precise definition of the events with consequences in terminology and detection is proposed.
Hypocenter distribution of plate boundary zone off Fukushima, Japan, derived from ocean bottom seismometer data
Authors: Shinohara Masanao , Hino Ryota , Yoshizawa Takashi , Nishino Minoru , Sato Toshinori , Suyehiro Kiyoshi
Published: August 2014

Microearthquake observation using Ocean Bottom Seismometers (OBSs) was carried out to obtain a detailed distribution of microearthquakes beneath the area off Fukushima, in the middle section of the Japan Trench in the summer of 1997. The observation period spanned approximately one month. Almost all of the well-determined hypocenters occurred in the vicinity of the plate boundary in this region (approximately 100 km landward of the trench axis), while seismicity is markedly lower between this area and the trench itself. The seaward limit of the high seismicity region is close to the western end of the zone of direct contact between the oceanic crust and the overriding landward crust. Twenty-nine earthquakes were recorded within the overriding landward plate. Twelve earthquakes were recorded about 30 km below the plate boundary, and form a landward dipping plane that appears to be an up-dip continuation of the lower plane of the double seismic zone. The microseismicity characteristics of the plate boundary region are interpreted to be controlled by the geometry and physical properties of the plate interface. The seismic activity in the lower seismic plane near the trench is considered to relate to bending of the subducting plate and to dehydration of serpentinized Pacific Plate mantle.
Estimation of picked-up lunar ions for future compositional remote SIMS analyses of the lunar surface
Authors: Yokota Shoichiro , Saito Yoshifumi
Published: August 2014

In situ measurement of Moon-originating ions picked-up in orbit round the Moon is expected to provide valuable information regarding the thin lunar atmosphere and surface. Secondary ions sputtered by the solar wind ions reflect the surface abundance. Global composition mapping of the lunar surface may be thus achieved by measuring the sputtered ions as one would perform laboratory SIMS.We studied the dynamics of picked-up lunar ions when the Moon was exposed to the solar wind. Our model’s source mechanism involved photoionization of the lunar exospheric atoms, photon-stimulated ion desorption, and ion sputtering. We propose that an intense flux of picked-up lunar ions (104 /cm2 sec) exists at an altitude of 100 km, for nearly a quarter of the orbit. The ion flux originating from the lunar surface is mono-directional and mono-energetic, and is distinguishable from that of lunar atmospheric origin whose energy spectra correspond to their spatial distribution. Our calculation suggested that ion measurements in orbit round the Moon enable remote SIMS analyses.
Co-seismic strain-steps associated with the 2004 off the Kii peninsula earthquakes-Observed with Ishii-type borehole strainmeters and quartz-tube extensometers
Authors: Asai Yasuhiro , Okubo Makoto , Ishii Hiroshi , Aoki Harumi , Yamauchi Tsuneo , Kitagawa Yuuichi , Koizumi Naoji
Published: August 2014

The 2004 off the Kii peninsula earthquakes (Mj7.1 and Mj7.4) occurred at the Nankai trough, on 5 September 2004. Clear strain-steps associated with these earthquakes were observed with Ishii-type borehole strainmeters and quartz-tube extensometers in the Tokai and Kinki districts. We investigated the spatial and depth distribution of the observed principal strain changes and compared the observed strain-steps and theoretical calculations at all observatories. The following results were obtained: the observed strain-steps at all observatories are generally consistent with the polarities of the theoretical values, and the observed strain-step increases with depth at the same place. As for the Togari site, the following relationships are obtained: the strain-step and the tidal strains increase with depth and increasing of the modulus of elasticity, namely, hardness of rock. We consider that the geological structure around the observatory may cause a modification of the strain field.
Difference in the initial slopes of the P-wave envelope waveforms of the main shock M7.4 and foreshock M7.1 of the 2004 off the Kii peninsula earthquakes
Authors: Odaka Toshikazu , Nakamura Hiromitsu , Ashiya Kimitoshi
Published: August 2014

We made a close investigation about the initial rising slopes of the envelope waveforms of the P-wave ground motion by using data for recent earthquakes. We have found that the P-wave initial slopes decrease almost linearly with increasing epicentral distance over the wide range of distance. This linear relation looks to be independent of the earthquake magnitudes and focal depths though the dispersion of data is somewhat large. We have found that the P-wave initial slopes of the foreshock M7.1 of the 2004 off the Kii peninsula earthquakes are very sharp. To the contrary, the slope of the main shock M7.4 is quite gentle. The main shock was preceded by a small event that occurred about 6.7 seconds before the main shock. This pre-event was generated near the initiation point of the main fracture. We are speculating that the difference in the initial slope between the foreshock and main shock may reflect the difference in the time variation of the stress drop at the early stage of the fracture and that the small pre-shock may be responsible for the slow rising of the initial P-wave motion of the main shock.
Inversion analysis of the 2004 off the Kii peninsula earthquakes using seismic intensity data
Authors: Kanda Katsuhisa , Takemura Masayuki
Published: August 2014

An inversion analysis has been developed to evaluate short-period radiation zones on an earthquake fault plane using seismic intensity data. It is robust and widely applicable even for historical earthquakes without ground motion, tsunami and geodetic data observed by instruments. It was applied to the 2004 off the Kii peninsula earthquakes that occurred in the Philippine Sea plate along the Nankai Trough. The short-period seismic wave radiation zone of each event during the 2004 off the Kii peninsula earthquakes from the inversion analysis was included in epicenter area of the corresponding aftershocks and slipped fault zone derived from the waveform inversion analysis as well. It may be also found that there were slip areas where little short period energy radiated. It also applied to the 1899/3/7 earthquake whose felt area was similar to that of the 2004 off the Kii peninsula earthquakes. However, it was indicated that the short-period radiation zones of the 1899 earthquake was located near the coast of the Kii peninsula and departed from that of the 2004 earthquake. The 1899 event might be an intermediate-depth earthquake in the Philippine Sea plate or a relative small interplate event at the west margin of the Tonankai earthquake source region.
Source parameters of the May 29, 2004 South Korea earthquake (ML 5.2)
Authors: Park Sun-Cheon , Mori Jim
Published: August 2014

A moderate earthquake with local magnitude 5.2 (ML) occurred off the eastern coast of South Korea on May 29, 2004. This earthquake is one of the largest events near the Korean Peninsula since 1978 when instrumental observations began by the Korea Meteorological Administration. We carried out modeling of regional waveforms and deconvolutions using empirical Green functions to estimate source parameters. The results of the regional waveform modeling show a reverse fault mechanism with a hypocentral depth of 8 km and seismic moment of 5 × 1016N · m, which is equivalent to Mw 5.1. Performing the empirical Green function deconvolution, we estimated a fault radius of 1.1 to 1.4 km and an average stress drop of 13.5 MPa, assuming an east dipping fault plane. Assuming a west dipping fault plane, we estimated a fault radius of 1.3 to 2.9 km and an average stress drop of 6.6 MPa.
Incoherent radar spectra in the auroral ionosphere in the presence of a large electric field: The effect of O+-O+ Coulomb collisions
Authors: Barghouthi I. A.
Published: August 2014

We have used Monte Carlo simulations of O+ velocity distributions in the high latitude F- region to improve the calculation of incoherent radar spectra in auroral ionosphere. The Monte Carlo simulation includes ionneutral, O+-O collisions (resonant charge exchange and polarization interaction) as well as O+-O+ Coulomb self-collisions. At high altitudes, atomic oxygen O and atomic oxygen ion O+ dominate the composition of the auroral ionosphere and consequently, the influence of O+-O+ Coulomb collisions becomes significant. In this study we consider the effect of O+-O+ Coulomb collisions on the incoherent radar spectra in the presence of large electric field (100 mVm-1). As altitude increases (i.e. the ion-to-neutral density ratio increases) the role of O+-O+ Coulomb self-collisions becomes significant, therefore, the one-dimensional, 1-D, O+ ion velocity distribution function becomes more Maxwellian and the features of the radar spectrum corresponding to non-Maxwellian ion velocity distribution (e.g. baby bottle and triple hump shapes) evolve to Maxwellian ion velocity distribution (single and double hump shapes). Therefore, O+-O+ Coulomb self-collisions act to isotropize the 1-D O+ velocity distribution by transferring thermal energy from the perpendicular direction to the parallel direction, however the convection electric field acts to drive the O+ ions away from equilibrium and consequently, non-Maxwellian O+ ion velocity distributions appeared. Therefore, neglecting O+-O+ Coulomb self-collisions overestimates the effect of convection electric field.
Short-term spatiotemporal variations in the aftershock sequence of the 2004 mid-Niigata prefecture earthquake
Authors: Kato Aitaro , Sakai Shinichi , Hirata Naoshi , Kurashimo Eiji , Nagai Satoru , Iidaka Takashi , Igarashi Toshihiro , Yamanaka Yoshiko , Murotani Satoko , Kawamura Tomonori , Iwasaki Takaya , Kanazawa Toshihiko
Published: August 2014

We deployed 56 temporary seismic stations within approximately a month after the occurrence of the 2004 mid-Niigata prefecture earthquake. Using manually-picked arrival data obtained from the temporary and surrounding permanent seismic stations, 1056 aftershocks have been relocated. Based on the spatiotemporal variations in the relocated aftershocks, the cluster activities associated with the mainshock and some large aftershock events are identified. The aftershocks associated with the mainshock, the largest occurred on the two steep west-dipping planes at an angle of 60° and approximately 5 km away. In contrast, the aftershocks following the event on Oct. 27 are aligned on east-dipping plane at a low angle of 25°. It is further observed that the aftershock area extended in both northeastward and southwestward directions at a later stage. The triggered seismicity around the northeast edge was more significant than that around the southwest edge. This difference could be understood by the discrepancy in the shear stress level accumulated at the dynamic shear rupture due to the mainshock.