bluuebunny/crossref_metadata_2025 huggingface dataset:
The central Philippine Fault Zone: Location of great earthquakes, slow events and creep activity
Authors: Besana G. M. , Ando M.
Published: August 2014

The central Philippine Fault Zone is found to be the locus of great earthquakes, a transition zone with slow slip and creep activity. This is based on the analysis and correlation of seismic historic data and detailed documentation of recent seismic events in the region. Based on this study the Guinyangan fault is defined to be the northern locked portion with recurrence interval of as short as 65 years. The Masbate fault is the central part with large and medium earthquakes accompanied by unusually large ground rupture. The north Central Leyte fault and the south Central Leyte fault, on the other hand, are characterized by aseismic creep and medium-sized events, usually with clusters of foreshocks, respectively. Unusual seismic activity both on the Masbate fault and Central Leyte fault somehow correlates well with the behavior of known slow events and creep activity. Further investigation of this region could lead to deeper understanding of impending major earthquakes, especially along the Guinyangan fault, which usually produces larger damaging events, and for further understanding of the impact of slow events and creep on the adjoining active structures.
Strong S-wave anisotropy in the aftershock region of the 2000 Tottori-ken Seibu, Japan, earthquake (Mw6.6)
Authors: Nakamura Takeshi , Takenaka Hiroshi , Suzuki Sadaomi
Published: August 2014

The 2000 Tottori-ken Seibu earthquake (Mw6.6) occurred in Tottori prefecture, western Japan on October 6, 2000. We conducted aftershock observation and analyzed S-wave anisotropy using the aftershocks M
jma2.0 to 3.5 observed at two stations near the aftershock region. The fast S-waves are polarized to almost E-W direction, which corresponds to the P-axis direction of the mainshock. The delay time of the split S-waves ranges between 20 and 100 ms. The crack density inside and outside the aftershock area is estimated from the delay time. The distribution of crack density shows a strong spatial variation and depends on the ratio of the path length inside the aftershock region against the whole path length. Assuming a uniform distribution of anisotropy inside and outside the aftershock region, the crack densities inside and outside are 0.017 and 0.007, respectively. It thus seems probable that in the aftershock region the distribution of cracks is intensive and cracks are opened due to the presence of fluids in seismogenic layers. This considerable spatial variation of anisotropy between inside and outside the aftershock region suggests that the aftershock region may have different mechanical properties from the surrounding area.
Sharply concentrated cosmic-ray excess fluxes from heliomagnetospheric nose and tail boundaries observed with neutron monitors on the ground
Authors: Nagashima K. , Kondo I. , Fujii Z.
Published: August 2014

Two kinds of sharply concentrated excess flux of cosmic rays from heliomagnetospheric nose and tail directions (right ascension α ∼ 18 hours and ∼ 6 hours) are found by the analysis of sidereal daily variation of neutron intensity (median energy Em ∼ 20 GeV) on the ground. These fluxes do not show any response to the polarity reversal of solar magnetic field at the north pole and is contradictory to the simulation of the solar modulation of galactic anisotropy, which produces sidereal variation at the Earth greater in the negative polarity state than in the positive state. This indicates that they are not of the galactic origin and would be produced on the heliomagnetospheric nose and tail boundaries where it is considered that the interaction between the galactic and solar magnetic fields could produce the cosmic-ray acceleration. The acceleration mechanism producing the polarity-independent sidereal variation against solar modulation will be discussed.
The BGS magnetic field candidate models for the 10th generation IGRF
Authors: Lesur Vincent , Macmillan Susan , Thomson Alan
Published: August 2014

In this paper we describe the derivation of the BGS candidate models for the 10th generation International Geomagnetic Reference Field. Our data set comprised quiet night-time data from the Èrsted and Champ satellites spanning 1999.2–2004.6 and observatory hourly means spanning 1999.0–2004.0. To improve the secular variation estimates for 2005.0–2010.0, predictions based on application of linear prediction filters to long series of observatory annual means were also used. These data were fitted by a spherical harmonic “parent” model with an internal field of maximum degree 36, a quadratic dependence on time up to degree 8, a linear dependence on time up to degree 12, an external field of maximum degree 2 with linear dependence on time, annual and semi-annual variations, and Dst dependence for degree 1 terms. Additionally for the external field, non-zonal degree 1 coefficients in the Geocentric Equatorial Inertial reference frame with annual variations and dependence on the Interplanetary Magnetic Field Y-component are included. The candidate models were then based, for the main field, on an extrapolation to 2005.0 of the truncated parent model, and for the secular variation, on its extrapolation to 2007.5. This latter set of coefficients was then used to generate a synthetic data set at the Earth’s surface and this set was augmented with long term linear predictions of observatory annual means, to produce the final candidate secular variation model at 2007.5.
A global distribution of sporadic E events revealed by means of CHAMP-GPS occultations
Authors: Garcia-Fernandez M. , Tsuda T.
Published: August 2014

With the advent of the GPS/MET mission, the atmospheric sciences were given a new tool to enhance studies related to global and seasonal variations of different atmospheric parameters. In particular, it has proof valuable for the study of the ionospheric irregularities in the E layer, which before were performed basically on a local basis by ground based instruments. Using similar techniques applied to GPS/MET data to process the 50 Hz sampling rate GPS data to study the E layer electron density distribution, this work shows the global and seasonal distributions of the ionospheric irregularities of electron density, during high solar activity, by using the CHAMP satellite GPS data from January 1st 2002 to May 31st 2004. As pointed out by several theories on the E layer and previous studies with ground based data, the results presented here show that these irregularities have strong geographical and seasonal dependence, with enhancements in the auroral regions, in mid-latitudes and during the summer season.
Nighttime enhancement of the amplitude of geomagnetic sudden commencements and its dependence on IMF-Bz
Authors: Araki T. , Keika K. , Kamei T. , Yang H. , Alex S.
Published: August 2014

We present a statistical study of the diurnal variation of the occurrence frequency of geomagnetic sudden commencements (SCs) observed at Kakioka (geomagnetic latitude, θ = 27.4°). SCs with an H-component amplitude (ΔH) larger than 40 nT occur more frequently in the nighttime than the daytime, while those with smaller amplitudes (ΔH < 39 nT) occur more frequently in the daytime. Three large amplitude SCs (ΔH = 85, 117 and 145 nT at Kakioka) were analyzed in detail. All three exhibited larger amplitudes during the nighttime at all low latitudes except those near the dayside equator. A statistical study reveals that the averaged amplitudes are slightly larger in the daytime at Alibag (θ = 10.2°) but considerably larger in the nighttime at three higherlatitude Japanese stations, Kanoya (θ = 21.9°), Kakioka and Memambetsu (θ = 35.4°). Case studies of two moderate amplitude SCs which occurred at the same UT indicate that nighttime SC amplitudes at low latitudes are slightly (considerably) larger than daytime amplitudes when the interplanetary magnetic field (IMF) points northward (southward). We suggest that the diurnal variation of SC amplitudes can be explained by a combination of field aligned and resultant ionospheric currents produced during the main impulse of SCs.
Simulation of the high-degree lithospheric field recovery for the Swarm constellation of satellites
Authors: Maus S. , Lühr H. , Purucker M.
Published: August 2014

A primary objective of the Swarm constellation mission is to resolve the lithospheric magnetic field with the best achievable accuracy in order to bridge the spectral gap between satellite and airborne/marine magnetic surveys. In a series of end-to-end simulations, the possibilities of high degree field recovery were investigated. The proposed constellation consists of a higher and a lower pair of satellites. It was soon found that a constellation as such does not yet guarantee improved high degree field recovery. Of crucial importance is the orbit constellation of the lower pair of satellites. If the lower satellites follow each other, as investigated in Constellation 1, the gain of a constellation turns out to be marginal, compared to a single satellite. For Constellation 2, the lower satellites were separated in the E/W direction. In this setup, one can use the instantaneous E/W magnetic field gradient between the satellites, as well as the N/S along track gradients. Incorporating this vector gradient information results in significantly improved field resolution. Indeed, the final simulation suggests that the envisaged Swarm constellation will enable the recovery of the lithospheric field to beyond spherical harmonic degree 130.
Introducing localized constraints in global geomagnetic field modelling
Authors: Lesur Vincent
Published: August 2014

A set of functions is defined that can be used for modelling the internal part of the geomagnetic field. These functions are represented in term of spherical harmonics of a given maximum degreeLand are centred at specific latitudes and longitudes. The number of functions needed and the positions of their centres are such that any potential field of maximum spherical harmonic degreeLcan be modelled. Formulae are obtained to transform between the potential field representation using these functions and a classic spherical harmonic representation. The shape of these functions can be optimized to make them reasonably localized, and from there it is shown how a localized constraint can be applied to an internal geomagnetic field model. The technique is demonstrated by means of models built from a few months of the Swarm mission synthetic data set.
Subsidence monitoring within the Athens Basin (Greece) using space radar interferometric techniques
Authors: Parcharidis Is. , Lagios E. , Sakkas V. , Raucoules D. , Feurer D. , Le Mouelic S. , King C. , Carnec C. , Novali F. , Ferretti A. , Capes R. , Cooksley G.
Published: August 2014

The application of conventional SAR Interferometry (InSAR) together with the two techniques of subcentimeter accuracy, the Stacking and the Permanent Scatterers (PS) Interferometry, were used to study the ground deformation in the broader area of Athens for the period 1992 to 2002. Using the Stacking interferometric method, 55 ERS-1&2 SAR scenes, between 1992 and 2002, were acquired producing 264 differential interferograms. Among these only 60 were finally selected as fulfilling certain criteria. The co-seismic deformation associated with the Athens Earthquake (Mw = 5.9, September 7, 1999) was excluded from the analytical procedure in an attempt to present results of only aseismic character. In total ground subsidence results of about 12 mm in the southern suburbs of Athens, but higher value of about 40 mm in the northern ones for the period 1992–2002. Based on the PS technique, a precise average annual deformation rate-map was generated for the period 1992–1999, ending just before the Athens earthquake event. Both circular and elongated-shape areas of subsidence are recognizable especially in the northern part of the Athens Basin (3–4 mm/yr), as well as at its southern part (1–3 mm/yr). In addition, a rate of 2–3 mm/yr is also yielded for some part of the Athens city center. Subsidence rates of 1–2 mm/yr are measured at the western part of the basin over an area of old mining activities, and around the newly built Syntagma Metro Station. The correlation of the observed deformation patterns with respect to the spatial distribution of water pumping, older mining activities, metro line tunneling and other local geological parameters is examined and discussed.
A comparative study of the bottomside profile parameters over Wuhan with IRI-2001 for 1999–2004
Authors: Chen Huajiao , Liu Libo , Wan Weixing , Ning Baiqi , Lei Jiuhou
Published: August 2014

The diurnal, seasonal, and solar activity variations of the bottomside ionospheric profile parameters B0 and B1 are studied using electron density profiles measured over Wuhan (30.4°N, 114.4°E) of China with a DGS- 256 Digisonde during 1999–2004. Comparisons are made with the International Reference Ionosphere model (IRI-2001) using both the standard option (B0-Tab and B1-Tab) and the Gulyaeva’s option (B0-Gul and B1- Gul). The results show that: (1) observed B0 has distinct diurnal and seasonal variations, while observed B1 changes little with season. The value of B0 is larger in summer than that in equinox and winter, especially for daytime. In winter and equinox, B0 also presents morning and afternoon collapses as reported by Lei et al. (2004). (2) B0 increases about 18.6 km from low solar activity (LSA) to high solar activity (HSA). B1 in HSA is smaller than that in LSA before 10:00 LT and with an opposite tendency during the rest time. (3) Observed B0 is in better agreement with B0-Gul than with B0-Tab, though the B0-Gul overestimates during 09:00 to 17:00 LT in equinox and summer. B0-Tab is 12–20 km larger than the observations over Wuhan almost all the time.

Meanwhile, B1-Tab is in good agreement with the observations.
Airglow and other F-layer variations in the Indian sector during the geomagnetic storm of February 5–7, 2000
Authors: Mukherjee G. K.
Published: August 2014

A CCD based all-sky imaging system was used to monitor various nightglow emissions (OI 630-nm, OI 557.7- nm, OI 777.4-nm, Na (589.3-nm) and hydroxyl (OH) airglow) at a low latitude station, Kolhapur (16.8°N, 74.2°E, dip lat 10.6°N) in India to study the characteristics of night airglow variations observed during the period of a moderate/weak geomagnetic storm with SSC (Storm Sudden Commencement) commencing at 15:42 UT (21:12 IST (Indian Standard Time = UT + 5.5 hrs)) on February 5, 2000. The images on the night of February 6 show the development of strong ionization anomaly (EIA) with bright intensity regions in OI 630-nm and the signature of rising bubbles with very low intensity. Though the signature of ionospheric plasma bubbles were not observed on the night of February 7, the OI 630-nm images showed the presence of large scale enhanced airglow moving to the southeast direction. The speed was significantly fast (≈300 m/s). There were bright intensity regions also observed in OI 557.7-nm airglow, but no intensity enhancement was seen in other mesospheric emissions (Na (589.3-nm) and hydroxyl (OH) airglow ) during this magnetic disturbance. The ionosonde observations at the nearby station, Visakhapatnam (lat. 17.67°N, long. 83.32°E) also showed enhancement in electron density parameter ((foF2)2) at the station on each night compared to the night of February 4–5 (quiet day) around the same time interval maximizing around 23:00 IST on the night of February 7. The Total Electron Content (TEC) fluctuations obtained from GPS phase delays between two L-band signals (L1 = 1575 MHz and L2 = 1227 MHz) showed no enhancement at night at four mid latitude stations in Japan. However, noontime TEC values were enhanced on February 6 and 7 with maximum intensity occurring on February 7. It is inferred that enhanced storm time effects in the ionosphere were mainly confined to the low latitude region, the effects were subdued in the mid latitude stations.
Magnetic storm effects at equatorial electrojet stations
Authors: Rastogi R. G.
Published: August 2014

It is shown that there are distinctly two different mechanisms for the interaction of solar wind with the earth’s magnetosphere to produce electric field in the ionospheric heights at low and middle latitudes. A persistent or slowly varying southward Interplanetary magnetic field i.e. negative IMF-Bz generates dawn to dusk electric field at polar latitudes and a westward (dusk to dawn) electric field at dayside electrojet region which is anti-Sq in direction. A rapid increase of IMF-Bz (northward turning) imposes a westward (dusk to dawn) electric field at all latitudes of the dayside hemisphere. The process involved is the imposition of -V × Bz electric field at the magnetosphere transmitted instantaneously to the magnetic equator through the polar latitudes. The changes in the H field at ground are largest at stations close to the magnetic equator and the midday longitudes. During magnetic storms, associated with the southward IMF-Bz, there are definite enhancements in the decrease of H field at the dayside equatorial electrojet stations. These changes may be coincident with the development of auroral or magnetospheric ring currents. These enhancements may be observed during the main phase as well as during the recovery phase of the magnetic storm, but the essential condition is that the IMF-Bz has to be steadily significant southward. Sometimes during the storm period abnormally large changes in H field at day side equatorial electrojet regions are observed associated with large sudden changes in IMF-Bz following the second mechanism of solar wind magnetospheric interaction. Thus the equatorial magnetic storm effects are due to combined effects of disturbance ring current, slow and steady IMF-Bz as well as due to sudden large changes in IMF-Bz.
Investigation of the Onikobe geyser, NE Japan, by observing the ground tilt and flow parameters
Authors: Nishimura Takeshi , Ichihara Mie , Ueki Sadato
Published: August 2014

In this study we conducted observations of the Onikobe geyser, NE Japan, by deploying a tiltmeter and an acoustic sensor close to the vent, a flow pressure sensor at the conduit exit, and measuring water temperature at ground level. The data from these instruments are consistent with the model of geysers which involves effusion process of boiling due to depressurization. During the observation period, the geyser generally effused water for about 90 s every 10 mins, although during certain periods these times randomly shortened to about 60 s and 6 mins, respectively. Tilt records show a strong correlation with the short and long effusion times, reflecting water movement in at least two chambers beneath the vent. We are able to empirically predict the duration of effusion from tilt data, although flow pressure does not vary with effusion time.
Long-term seafloor geomagnetic station in the northwest Pacific: A possible candidate for a seafloor geomagnetic observatory
Authors: Toh H. , Hamano Y. , Ichiki M.
Published: August 2014

For two years, geomagnetic variations have been measured at the seafloor in the northwest Pacific. The seafloor data consist of the geomagnetic vector field measured by a three-component fluxgate magnetometer and the absolute scalar total force measured by an Overhauser (1953) magnetometer with attitude measurements for both orientation and tilt. Using the attitude data, the geomagnetic data at a site in the northwest Pacific (41o06′08″N, 159°57′47″E, -5580 m), hereafter referred to as NWP, were converted into the same reference frame as land and satellite measurements. Short-period variations of the converted vector data were examined by Hamano’s (2002) global time domain analysis method, which showed compatibility of the seafloor geomagnetic observatory data with the existing land observatory network. The smooth and gradual change of the Earth’s main field (i.e., the geomagnetic secular variation) was also found consistent with those predicted by the latest International Geomagnetic Reference Field (IGRF-10; IAGA, 2005) and by Ørsted Satellite (Olsen, 2002) for not only the scalar field but also the vector field. This means that observation of the geomagnetic vector secular variation is now feasible on the seafloor.
Application of GPS in geomagnetic survey
Authors: Gu Zuowen , Zhan Zhijia , Gao Jintian , Yao Tongqi , Han Wei
Published: August 2014

When measuring the geomagnetic declination, the azimuth of the reference mark must be measured. This paper briefly describes the principle of measuring the azimuth by the differential GPS (Global Positioning System), several test observations of GPS and the results. In geomagnetic survey in China during 2002~2003, GPS was used in measuring the azimuth. Field observations by GPS were carried out during the period that satellite signals were better received. The statistical results of the GPS data at 135 stations in China show that the difference of the azimuths between 2 GPS measurements at various stations is 0.0″~5.9″ and the average is 1.6″. The azimuthal accuracy measured by GPS in this paper is 0.1′, and it is much better than the azimuthal accuracy 1.0′ given by Newitt et al. (1996). The observation results show that the azimuths measured by GPS are accurate and reliable; they are not related to the time-space changes. The geomagnetic declinations D at various stations were obtained based on the azimuths measured by GPS, and the standard deviation of the reduced value of D was < 0.4′. Using the reduced values, the 8-order spherical cap harmonic model and the 5-order Taylor polynomial model in China for D were obtained. In geomagnetic survey, GPS is also used in measuring the longitude, the latitude and the elevation at various stations.
Deformation and „deformation quiescence” prior to the Chi-Chi earthquake evidenced by DInSAR and groundwater records during 1995–2002 in Central Taiwan
Authors: Yen Jiun-Yee , Chen Kun-Shan , Chang Chung-Pai , Ng Sin Mei
Published: August 2014

Deformation of Central Taiwan between 1997 and 2002 was investigated using radar interferometry to construct the deformation rate time series before, during, and after the Chi-Chi earthquake. The deformation rate time series was compared to the time series of groundwater level in the monitoring wells of Yuanlin and Tzushan in order to investigate the relation between the geodetic observations and the groundwater levels. The deformation pattern of Central Taiwan generally forms a half-elliptical pattern, with the eastern half of the elliptical shape cut away by the north-south trending Chelungpu fault. Along a selected profile of 10 km near the Chelungpu Fault of Central Taiwan, the differential range change was measured and recalculated into deformation rates. The year-to-year deformation rates near the Chi-Chi earthquake ranged between 1.5 and 3 cm/year in most years except for the years between 1999 and 2000, which showed more than 5 cm/year deformation rates along the profile. Prior to the high deformation rate shown during the coseismic image pair, the deformation rate was low, as shown on the other image pairs. This variation in deformation rate coincides with the recorded trend in the level of groundwater in two monitoring wells in the Yuanlin area. The low deformation rate prior to the Chi-Chi earthquake may—partially—be explained by this lowering in groundwater level.
Integrated gradient interpretation techniques for 2D and 3D gravity data interpretation
Authors: Saibi Hakim , Nishijima Jun , Ehara Sachio , Aboud Essam
Published: August 2014

The Obama geothermal field is located on the western part of Kyushu Island, Japan. This area has importance due to its high geothermal content which attracts sporadic researchers for study. In 2003 and 2004, Obama was covered by gravity surveys to monitor and evaluate the geothermal field. In this paper, the surveyed gravity data will be used in order to delineate and model the subsurface structure of the study area. Gradient methods such as analytic signal and vertical derivatives were applied to the gravity data. The available borehole data and the results of the gradient interpretation techniques were used to model the Obama geothermal field. In general, the obtained results show that the gradient interpretation techniques are useful to obtain geologic information from gravity data.
Simultaneous ground-based and satellite observations of Pc5 geomagnetic pulsations: A case study using multipoint measurements
Authors: Sung S.-K. , Kim K.-H. , Lee D.-H. , Takahashi K. , Cattell C. A. , André M. , Khotyaintsev Y. V. , Balogh A.
Published: August 2014

Pc5 pulsations with a latitude-independent frequency of ∼2.8 mHz (period ∼6 min) were observed with ground-based magnetometers in the morning sector (0700–1000 local time) from 0730 to 0810 UT, April 29, 2001. The pulsations exhibited an amplitude peak and a ∼180° phase change at ∼67° geomagnetic latitude. A vortex structure of the equivalent ionospheric current system was also observed centered at the geomagnetic latitude between 67° and 71°. During the Pc5 event, the Polar spacecraft was located near the morningside magnetic equator and crossed magnetic field lines conjugate to the ground stations at which the pulsations were strong. Polar observed ∼2.8 mHz pulsations in the radial electric field and compressional magnetic field components. Since toroidal mode Alfvén waves in the magnetosphere are characterized by an electric field perturbation in the radial direction, the simultaneous presence of pulsations in both components indicates that a field line resonance (FLR) was driven by compressional pulsations. The ground H component at the station conjugate to Polar and the radial electric field perturbation at Polar oscillated with a great similarity without a phase delay. From an analysis of the ground-satellite data, we suggest that the ground perturbations are associated with toroidal mode Alfvén waves rather than compressional mode propagating across magnetic field lines. In addition, we discuss the source of the compressional perturbations observed at Polar using solar wind and geosynchronous data.
Seafloor displacement at Kumano-nada caused by the 2004 off Kii Peninsula earthquakes, detected through repeated GPS/Acoustic surveys
Authors: Kido Motoyuki , Fujimoto Hiromi , Miura Satoshi , Osada Yukihito , Tsuka Kentaro , Tabei Takao
Published: August 2014

In 2004, we started monitoring crustal deformation at Kumano-nada in the Nankai trough using the GPS/Acoustic technique. We observed a large southward seafloor displacement of ∼30 cm associated with the off Kii Peninsula earthquake, which occurred in September 2004, between our two survey campaigns in August and November 2004. The observed seafloor displacement is larger than that predicted from a slip model derived solely from GPS measurements on land. This may indicate the earthquake fault is slightly shallower and extends move to the NW than previously estimated.
EISCAT observational results during the DELTA campaign
Authors: Nozawa S. , Ogawa Y. , Brekke A. , Tsuda T. , Hall C. M. , Miyaoka H. , Kurihara J. , Abe T. , Fujii R.
Published: August 2014

This paper aims at describing the ionospheric conditions during the DELTA (Dynamics and Energetics of the Lower Thermosphere in Aurora) campaign period based on EISCAT radar observations conducted at Tromsø (69.6°N, 19.2°E). We conducted EISCAT UHF radar observations on December 5 and from December 8 to December 13, 2004 with a beam-scanning mode for a total of 74 hours. Except for December 8 during a 2 hr interval operation, we operated the EISCAT UHF radar for 12 hour intervals everyday to make it possible to derive semidiurnal tidal amplitudes and phases in the lower thermosphere. Observed electron densities and derived electric fields by the EISCAT UHF radar indicate that magnetospheric activity was high during the period from December 5 to 13 except for the night of December 13. Derived semidiurnal amplitudes during December 9–12, 2004 exhibited a day to day variation at and below 110 km, while the corresponding phase was relatively stable over the four days except for the zonal component on December 12. Neutral and electron temperatures measured by the DELTA rocket were compared with neutral/ion and electron temperatures from the EISCAT UHF radar observations. Comparison of neutral/ion temperatures show some agreement, while poor agreements were found for the electron temperature. Possible causes of the discrepancy are discussed.
A new model for the fault beneath the sedimentary basin in the 1891 Nobi earthquake
Authors: Nakano Masaru , Miyakoshi Jun’ichi , Yamaoka Koshun
Published: August 2014

We have investigated the geometry and detailed location of the Gifu-Ichinomiya (GI) fault, a buried fault considered to have ruptured during the 1891 Nobi earthquake. Based on an inversion of coseismic vertical displacements obtained by leveling surveys, we obtain an inclined fault plane showing a reverse fault-type mechanism, rather than the vertical fault plane assumed in previous models. The fault dips 60? to the east and its slip during the earthquake is estimated to have been 1.48 m along the fault dip. The fault is located 5 km east of the location assumed in the previous models. Recent earthquakes have been scattered along the new fault location, not the previously estimated one. Focal mechanisms of the earthquakes that have occurred around the fault are dominated by a reverse fault component, which is consistent with the focal mechanism of the GI fault obtained by the inversion of coseismic displacements. The seismic intensity distribution calculated using the new fault geometry and location explains well the distribution of observed damage caused by the 1891 Nobi earthquake.
Two parallel trench-normal fault planes within the Pacific slab associated with the 1994 and 2000 Kurile earthquakes as revealed by simultaneous relocation of their main shocks and aftershocks
Authors: Harada Tomoya , Ishibashi Katsuhiko
Published: August 2014

The 1994 Hokkaido-Toho-Oki (M
w 8.3) and the 2000 Nemuro-Hanto-Oki (M
w 6.8) earthquakes have been regarded as great/large intraslab events within the subducted Pacific plate along the southern Kurile trench. Determining which nodal planes of their mechanism solutions are actual fault planes and whether or not the 2000 event occurred on the southwestern extension of the 1994 fault plane have been problematic. In order to clarify these points, we examine the relative location of their main-shock and aftershock distributions accurately by simultaneous relocation of their hypocenters using the Modified Joint Hypocenter Determination (MJHD) method. The result clearly shows that the two earthquakes occurred on trench-normal shallow-dipping fault planes within the Pacific slab, apart from and parallel to each other. Therefore, the 2000 earthquake was not a rupture on the deeper extension of the 1994 fault plane, but one on another fault plane. A large intraslab earthquake (M
w 7.8; depth, about 100 km) occurred to the northwest of the 1994 event in 1978, and two trench-normal fracture zones exist outside the trench to the southeast of the 1994 and 2000 events. Therefore, these three intraslab great/large earthquakes are considered to have been ruptures along pre-existing trench-normal weak zones within the subducted Pacific plate.
Substorm time scales from polar cap convection measurements
Authors: Jayachandran P. T. , MacDougall J. W.
Published: August 2014

A recent study by Jayachandran et al. (Geophys. Res. Lett., 30, 2064, 2003) reported repeated and detectable changes in the polar cap convection associated with substorms. We report here our use of ionospheric convection measurements to determine the time scales of growth, expansion, and recovery/reconfiguration associated with the substorms. The average time scales, determined from polar cap convection, associated with growth, expansion, and recovery are 31.6, 22.4, and 38.8 min, respectively. A comparison of the growth and expansion time scales determined from the convection measurements with those determined from the geosynchronous satellite measurements revealed interesting differences. The growth time scale determined from the ionospheric convection measurement is smaller than that of the time scale determined from geosynchronous measurements, whereas the expansion time scale determined using the ionospheric convection is much larger than that of the time scale determined using the geosynchronous measurements. The implications of the results in the Magnetosphere-Ionosphere (M-I) coupling are discussed.
Surface wave propagation in a fluid saturated incompressible porous half-space lying under two layers of different liquids
Authors: Kumar Rajneesh , Hundal B. S.
Published: August 2014

A study of surface wave propagation in a fluid saturated incompressible porous half-space lying under a double-layer consisting of non-homogeneous and homogeneous liquids is presented. The frequency equation connecting the phase velocity with wave number is derived. Special cases as: (i) Rayleigh type surface waves in an incompressible poro-elastic half-space lying under a uniform layer of a homogeneous liquid, (ii) Rayleigh type surface waves in an incompressible poro-elastic half-space lying under a uniform layer of a non-homogeneous liquid and (iii) Rayleigh type surface waves propagating along the free surface of a fluid saturated incompressible porous elastic half-space, are investigated. Numerical results with graphical presentations of the variations of phase velocity with wave number for different cases are also included.
A numerical simulation of ionospheric and atmospheric variations associated with the Sumatra earthquake on December 26, 2004
Authors: Shinagawa H. , Iyemori T. , Saito S. , Maruyama T.
Published: August 2014

In the Sumatra earthquake that occurred on December 26, 2004, significant ionospheric variations were detected immediately after the earthquake in both the TEC (total electron content) data of GPS (Global Positioning System) and the ionosonde data. A magnetic pulsation with a period of about 4 min was also observed in Phimai, Thailand. Recent studies have suggested that these events are associated with acoustic waves excited by a sudden large-scale displacement of the sea surface around the epicenter. In order to study these phenomena quantitatively, a time-dependent two-dimensional nonhydrostatic compressible atmosphere-ionosphere model has been used and compared with relevant data. By modeling in sea surface perturbation, we were able to reproduce an atmospheric oscillation with a period of about 4 min in the upper atmosphere above the epicenter. The electron density variations observed by GPS/TEC and by ionosondes were also reproduced fairly well. We found that the observed TIDs (traveling ionospheric disturbances) with long periods are caused by the ducted thermospheric gravity waves produced in the thermosphere through acoustic pulse from the epicenter. The good overall agreement between the simulation results and observations indicates that numerical simulation with the nonhydrostatic compressible atmosphere-ionosphere model could be a useful tool to investigate the relationship between variations in the upper atmosphere and various sources of disturbances in the lower atmosphere.
Preliminary report on crustal deformation surveys and tsunami measurements caused by the July 17, 2006 South off Java Island Earthquake and Tsunami, Indonesia
Authors: Kato Teruyuki , Ito Takeo , Abidin Hasanuddin Z. , Agustan
Published: August 2014

A large earthquake (Mw=7.7) along a plate boundary occurred in the south of Java Island on July 17, 2006, and caused a significant tsunami. We made GPS observations and tsunami heights measurements during the period from July 24 to August 1, 2006. The earthquake seems to be due to an interplate low angle reverse faulting, though there might be a possibility of high angle faulting within the subducting lithosphere. Crustal deformation distribution due to the earthquake, aided by tsunami heights measurements, might clarify which would be the case. We occupied 29 sites by GPS in the area of southern Java encompassing the area from 107.8 E to 109.50 E. These sites were occupied once before the earthquake. However, we were not able to detect significant coseismic displacements. The obtained displacements, most of which span several years, show ESE direction in ITRF2000 frame. This represents the direction of Sunda block motion. The tsunami heights measured at 11 sites were 6–7 m along the southern coast of Java and indicate that the observed heights are systematically higher than those estimated from numerical simulations that are based on seismic data analysis. This might suggest that fault offsets might have been larger—nearly double—than those estimated using seismic analysis. These results lead us to an idea that the rupture was very slow. If this is the case, the earthquake might have been a “tsunami earthquake” that is similar to the one that occurred on June 2, 1994 in the east of the present earthquake.
Dynamic rupture propagation on a 2D fault with fractal frictional properties
Authors: Ide Satoshi
Published: August 2014

We study dynamic rupture propagation on a 2D fault with a spatially heterogeneous slip-weakening friction law under a homogeneous stress condition. The slip-weakening distanceDcis determined based on fault topography, characterized by the fractal dimension σ and a normalized slip-weakening distanceDc0. Assuming different combination of these parameters, we carry out a large number of dynamic rupture simulations to discuss event size statistics and the scaling relations of macroscopic parameters such as seismic moment, rupture velocity, seismic energy, and radiation efficiency. All stopped events obey an approximately power-law size-number relation. However, statistically self-similar rupture propagation is observed only for selfsimilar fault topography with σ = 1, where the average rupture velocity is controlled byDc0. This suggests that a power-law size-number relation does not simply mean the self-similarity of rupture process. Both upper and lower fractal limits in fault topography disturb the power-law statistics and the lower fractal limit results in excess of events of the characteristic size. The facts that slow ruptures can radiate large seismic energy and that fast ruptures are not always efficient suggest the importance of local acceleration, deceleration, and arrest of rupture. We also show that the spatial regularity of slip-weakening distance is essential to make the above results.
Contribution of heat outputs from high- and low-temperature hydrothermal sources to the neutrally buoyant plume at the TAG hydrothermal mound, Mid-Atlantic Ridge
Authors: Goto Shusaku , Gamo Toshitaka , Chiba Hitoshi , Fujioka Kantaro , Mitsuzawa Kyohiko
Published: August 2014

We provide an estimation of the heat output necessary to generate the neutrally buoyant plume above the TAG hydrothermal mound, Mid-Atlantic Ridge, located at 26°N, using a model of plume rise in a density-stratified environment with crossflow. The estimated heat output is 460 ± 40 MW. Previous studies have estimated that the heat outputs from high-temperature hydrothermal discharge and low-temperature diffuse flow at the TAG hydrothermal mound are 90 ± 20 MW and at least 780 MW, respectively. Consequently, the contribution of diffuse flow to make the neutrally buoyant plume is 370 ± 60 MW, which accounts for approximately 80% of the heat output to the neutrally buoyant plume. As this contribution is less than 50% of the total heat output from the diffuse flow, it is likely that more than 50% of the heat output from the diffuse flow dissipates in the ambient current.
Feasibility study on the potential of satellite altimetry for detecting seismic geoid changes due to the 2004 Sumatra-Andaman earthquake
Authors: Hayashi Yutaka , Hirata Kenji , Kuragano Tsurane , Sakurai Toshiyuki , Takayama Hiromi , Hasegawa Yohei , Hamada Nobuo
Published: August 2014

Sea surface height data obtained by satellite altimetry from Jason-1 and TOPEX/Poseidon were analyzed to explore the possibility of a seismic geoid change due to the 2004 Sumatra-Andaman earthquake. This analysis identified a weakly positive geoid change in a region between the trench and outer arc. A subsequent investigation of the characteristics of this coseismic geoid change based on the dislocation theory revealed that a positive peak should indicate the upper edge of the high-slipped area or asperity and that a negative peak is responsible for the lower edge of the earthquake fault. An attempt at modeling the difference in the sea level anomaly failed to explain the observation since a large scatter in the original dataset obstructed its confirmation.
Two-dimensional resistivity structure of the fault associated with the 2000 Western Tottori earthquake
Authors: Yamaguchi Satoru , Murakami Hideki , Iwamoto Hisanori , Takemoto Kazuhiro , Kitada Kazuya , Shiozaki Ichiro , Oshiman Naoto , Katoh Shigehiro
Published: August 2014

Two-dimensional resistivity surveys were carried out along two profiles that were laid across earthquake faults initiated by the 2000 Western Tottori earthquake. One profile was located 7 m from a trenching pit, thereby enabling a direct comparison of resistivity cross-section with the geological cross-section and, subsequently, a precise interpretation of the resistivity structure. Features of the resistivity cross-section were found to correspond fairly well to the geological cross-section. A clear resistivity boundary between the resistive and conductive zones matches the earthquake fault that was found by the trenching survey. Variations in resistivity depend primarily on the development of fractures. Two types of conductive zones were found: (1) a clear and deep-rooted conductor that corresponds to an earthquake fault and (2) an indistinct and spatially localized conductor that corresponds to a fracture attributed by landslides and collapse. A few weak conductive zones that match with discrete earthquake faults characterize our resistivity model. This feature is different from the resistivity cross-sections found at the Nojima and Ogura Faults that appeared at the time of the 1995 Hyogo-ken Nanbu earthquake; these two latter faults are characterized by distinct single conductive zones. Based on geomorphological, geological, and seismological evidence, the earthquake fault of the 2000 Western Tottori earthquake can be classified as an immature fault. In contrast, the Nojima and Ogura Faults have been active for at least the entire Quaternary period. We conclude that the difference in the fault development stages is reflected in their different resistivity structures.
Consistency between the flow at the top of the core and the frozen-flux approximation
Authors: Whaler K. A. , Holme R.
Published: August 2014

The flow just below the core-mantle boundary is constrained by the radial component of the induction equation. In the Alfvén frozen-flux limit, thought to be applicable to the outer core on the decade timescale of interest in geomagnetism, this gives a single equation involving the known radial magnetic field and its secular variation in two unknown flow components, leading to a severe problem of non-uniqueness. Despite this, we have two specific pieces of flow information which can be deduced directly from the frozen-flux induction equation: the component of flow perpendicular to null-flux curves, contours on which the radial magnetic field vanishes, and the amount of horizontal convergence and divergence at local extrema (maxima, minima and saddle points) of the radial magnetic field. To produce global velocity maps, we make additional assumptions about the nature of the flow and invert the radial induction equation for flow coefficients. However, it is not clear a priori that the flows thus generated are consistent with what we know about them along null-flux curves and at local extrema. This paper examines that issue. We look at typical differences between the null-flux curve perpendicular flow component, and convergence and divergence values at extrema, deduced directly from the induction equation and those from the inversions, investigate the effect of forcing the inversions to produce the correct null-flux curve and extremal values, and characterise the uncertainties on the various quantities contributing. Although the differences between the flow values from the induction equation directly and obtained by inversion seem large, and imposing the direct flow information as side constraints during inversion alters the flows significantly, we also show that these differences are within the likely uncertainties. Thus, we conclude that flows obtained through inversion do not contravene the specific flow information obtained directly from the radial induction equation in the frozen-flux limit. This result should reassure the community that frozen-flux flow inversion is a consistent process, even if including the extremal-value and null-flux conditions as additional information on flow inversion is unlikely to be useful. Solving for a time-dependent core-mantle boundary field model and flow simultaneously may be a good way to produce a temporally-varying field model consistent with the frozen-flux constraint; the ability to fit the data with such a model could be used to establish the timescale over which the frozen-flux assumption is valid.
Stochastic finite-fault modeling of ground motions from the June 27, 1998 Adana-Ceyhan earthquake
Authors: Yalcinkaya Esref
Published: August 2014

In this study, acceleration time histories of the June 27, 1998 Adana-Ceyhan (Turkey) earthquake, are simulated using a stochastic modeling technique for finite faults proposed by Beresnev and Atkinson (1997). The fault length, width and the depth to the top of the fault for the earthquake are assumed 30 km, 21 km and 15 km, respectively, based on the aftershock distribution. Simulations are made for two common site classes: soil and rock. Their response characteristics are obtained from the site-specific amplification functions estimated for the weak motion seismograms at stations located in the region using spectral ratio methods. The results show that the overall agreement between simulated and observed waveforms and spectra is quite satisfying. However, significant discrepancies exist at certain stations, implying that site amplification functions play an important role in the simulation process. The effects of nonlinearity and basin edge generated surface waves do not clearly dominate on the results. The peak horizontal acceleration contours estimated using the calibrated model are consistent with the observed intensity values and the other evidences of strong ground motions.
Numerical simulation of resonant scattering of energetic electrons in the outer radiation belt
Authors: Katoh Yuto , Ono Takayuki , Iizima Masahide
Published: August 2014

Resonant diffusion processes of high energy electrons are studied numerically by using an original simulation scheme where cold electrons are treated as a fluid and hot electrons are treated as particles including fully relativistic effects. The present simulation scheme enables us to investigate the resonant scattering process in the inner magnetosphere, which has been difficult to study by using the PIC code. We investigated the variation of the distribution of electrons through the resonant diffusion process by comparing the present numerical experiment and the quasi-linear theory under the same condition of the interaction between whistler-mode waves and high energy electrons. The difference between their results suggests the importance of the verification of the theory under the realistic plasma condition corresponding to the observed parameters in the outer radiation belt.
Detection of phase disturbances of free core nutation of the Earth and their concurrence with geomagnetic jerks
Authors: Shirai Toshimichi , Fukushima Toshio , Malkin Zinovy
Published: August 2014

We detected phase disturbances of the Free Core Nutation (FCN) of the Earth directly from the analysis of the Very Long Baseline Interferometer (VLBI) observation of the Earth rotation for the period 1984–2003 by applying the Weighted Wavelet Z-Transform (WWZ) method and the Short-time Periodogram with the Gabor function (SPG) method. During the period, the FCN had two significant phase disturbances in 1992 and 1998. These epochs coincide with the reported occurrence of geomagnetic jerks.