bluuebunny/crossref_metadata_2025_split huggingface dataset:
Source parameters of the May 29, 2004 South Korea earthquake (ML 5.2)
Authors: Park Sun-Cheon , Mori Jim 
Published: August 2014

AbstractA 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

Abstract
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

Abstract
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.
Crustal structure of the ocean-island arc transition at the mid Izu-Ogasawara (Bonin) arc margin
Authors: Nishizawa Azusa , Kaneda Kentaro , Nakanishi Ayako , Takahashi Narumi , Kodaira Shuichi 
Published: August 2014

Abstract
Wide-angle refraction experiments were conducted to reveal the crustal structure at the transition between the intra-oceanic island arc crust of the mid Izu-Ogasawara (Bonin) arc and the backarc oceanic crust of the Shikoku Basin. The island arc crust consists of an upper crust about 5 km thick with a P-wave velocity <6.0 km/s, a middle crust 5 km thick with a P-wave velocity of 6.0–6.3 km/s, and a lower crust 10 km thick with a P-wave velocity of 6.8–7.2 km/s. The total crustal thickness is about 20 km. The thickness thins to approximately 6 km over a distance of 30 km at the western margin of the Izu-Ogasawara arc (IOA). These features are very similar to those of the northern IOA, which indicates that the crustal structure is relatively constant within 200 km at the northern and mid IOA. The Kinan Escarpment, a 500-km-long fault with a maximum offset of 800 m, characterizes the transition zone between the IOA and Shikoku Basin. The seismic crustal model indicates that the escarpment is a fault which tears the whole oceanic crust along the western margin of the IOA. However, no significant differences exist in the crustal structure on either side of the escarpment, and the Kinan Escarpment seems to be a zone of the structural weakness from its birth.
Determination of the 30-year creep trend on the Ismetpaşa segment of the North Anatolian Fault using an old geodetic network
Authors: Kutoglu H. S. , Akcin H. 
Published: August 2014

Abstract
The Ismetpaşa segment of the North Anatolian Fault was ruptured during both the 1944 (M w = 7.2) Gerede and 1951 (M w = 6.9) Kurşunlu earthquakes. The field studies carried out in the aftermath of these two major earthquakes showed that the Ismetpaşa segment had experienced a creep movement. To monitor the surface creep, a geodetic network with six control points was established on the segment. This network was observed three times—in 1972, 1982 and 1992. Based on our evaluations of those observations, the creep on the segment was geodetically determined to be 1.02 cm/year (1972–1982) and 0.93 cm/year (1982–1992) respectively. In 1999, the North Anatolian Fault experienced two major shocks—the M w = 7.4 Gölcük and M w = 7.2 Düzce earthquakes—both on the western part of the Ismetpaşa fault. Using the global positioning system, our surveying team observed the network one more time in 2002 to assess whether these earthquakes affected the creep of the Ismetpaşa segment, or not. The evaluation of the observations revealed a creep of 0.78 cm/year for the period 1992–2002. This result reveals that the creep of the segment has decreased in a linear fashion between 1972 and 2002 and that it had not been triggered by the Gölcük and Düzce earthquakes.
Structural pattern at the northwestern sector of the Tepic-Zacoalco rift and tectonic implications for the Jalisco block, western Mexico
Authors: Urrutia-Fucugauchi Jaime , González-Morán Tomás 
Published: August 2014

AbstractAnalysis of the aeromagnetic anomalies over the northwestern sector of the Tepic-Zacoalco rift documents a NE-SW pattern of lineaments that are perpendicular to the inferred NW-SE boundary between the Jalisco block and the Sierra Madre Occidental. The boundary lies within the central sector of the Tepic-Zacoalco rift immediately north of the Ceboruco and Tepetiltic stratovolcanoes and extends up to the San Juan stratovolcano, where it intersects the NE-SW magnetic anomaly lineament that runs toward the Pacific coast (which intersects two volcanic centers). This N35°E lineament separates the central rift zone of low amplitude mainly negative anomalies (except those positive anomalies over the stratovolcanoes) from the zone to the north and west characterized by high amplitude positive long wavelength anomalies. The NE-SW lineament is parallel to the western sector of the Ameca graben and the offshore Bahia de Banderas graben and to the structural features of the Punta Mita peninsula at the Pacific coast, and thus seems to form part of a regional NE-SW pattern oblique to the proposed westward or northwestward motion of the Jalisco block. The orientation of this regional structural pattern at the northern end of the Tepic-Zacoalco rift seems consistent with proposed dominant SW-directed extension along the rift during the Pliocene and Quaternary, rather than with NW-SE lateral strike-slip faulting. The orthogonal pattern that characterizes the northernmost boundary of the Tepic-Zacoalco rift is oblique to the pattern observed in the Grande de Santiago river (which conforms the northern limit of the rift) and for the central-eastern sectors of the Ameca graben (south of the rift). This spatial arrangement of major lineaments and structural elements points to a complex tectonic history for the region that includes the rifting of the Gulf of California and margin deformation due to plate convergence and kinematic re-organization events, and which may have resulted in distinct episodes of left-lateral, right-lateral and normal faulting in Neogene times, as proposed in recent studies.
Magnetostratigraphy of the Cretaceous/Tertiary boundary and early Paleocene sedimentary sequence from the Chicxulub Impact Crater
Authors: Rebolledo-Vieyra Mario , Urrutia-Fucugauchi Jaime 
Published: August 2014

Abstract
We report on the magnetostratigraphy of the Chicxulub crater impact breccias and first 15 meters of the Paleocene sedimentary sequence recovered in three boreholes of the UNAM Scientific Drilling Program. Three geomagnetic polarity zones are documented in the impact breccias and sedimentary sequence, which span from chron 29R to 28N. For the 15 m interval they represent ∼2.5 Ma, which yields low apparent sedimentary rates for boreholes UNAM-5 (110 km from the center of the crater) and UNAM-7 (127 km from the center of the crater). The carbonate sedimentary sequence can be associated to a shallow basin depositional environment. In these boreholes the thickness between the 29R and the 29N chrons is just 0.5 m, suggesting that during the 100 ka from the K/T boundary to the polarity transition sediments were not deposited or eroded. Within borehole UNAM-6 (152 km from the center of the crater) it appears that sediments containing chron 29N are missing, the lack of the upper breccias, the long duration of a reversal event within the base of the sequence and low apparent sedimentary rate of 3.3 m/Ma, suggests a hiatus within the impact breccias and the basal Paleocene sedimentary sequence. Magnetic susceptibility logs confirm absence of the upper breccias at UNAM-6 borehole. Magnetic susceptibility values increase towards the base of the sequence, suggesting that basement and melt clasts were subjected to a low temperature hydrothermal alteration.
Hydrocarbon-induced magnetic contrasts in some Venezuelan and Colombian oil wells
Authors: Costanzo-Alvarez Vincenzo , Aldana Milagrosa , Díaz Marisel , Bayona Germán , Ayala Carolina 
Published: August 2014

Abstract
In this work we present a review of our current research on the subject of near-surface hydrocarbon-induced magnetic contrasts. Samples are drill cuttings from number of Venezuelan and Colombian oil fields, and some soils from an oil prospective area. Results from rock magnetic, electronic paramagnetic resonance (EPR), extractable organic matter (EOM) and scanning electron microscopy (SEM) are discussed in light of new experiments. Two types of magnetic susceptibility (MS) anomalies have been recognized in oil well samples (i.e. A and B-like). A-like anomalies are probably associated to a reducing environment caused by the underlying reservoirs, whereas B-like anomalies might reflect lithological contrasts. Samples from A-like anomalous levels reveal the restrictive presence of authigenic spherical aggregates of submicronic Fe-rich magnetic crystals. Peaks of organic matter free radical concentration (OMFRC) and EOM are also observed at depth levels that lie close to those with A-like anomalies. Hysteresis ratios J
rs/Js and H
cr/Hc could be used as additional criteria to recognize A-like magnetic contrasts. In soil samples, MS and OMFRC anomalies coincide with peaks of ethane concentration and an area underneath where source rock has reached appropriate conditions of pressure and temperature to generate hydrocarbons (Cretaceous kitchen). Different types of crude oils and subsurface structures could have also a direct effect on the observed amplitude of A-like anomalies.
Review of magnetism and heavy metal pollution studies of various environments in Argentina
Authors: Chaparro Marcos A. E. , Gogorza Claudia S. G. , Chaparro Mauro A. E. , Irurzun María A. , Sinito Ana M. 
Published: August 2014

Abstract
In recent years, the number of studies of pollution and magnetic proxies for environmental pollution in developed countries, especially European and North American countries, has gradually increased from the 80’s to date. Despite this trend that shows a positive interest in taking care of the environment and researching into the environmental impact of several human activities, pollution studies in Latin American countries have been reducing in number. Moreover, studies of magnetic proxies for pollution are scarce; in particular, studies of this nature has been carried out in Argentina over the past few years by Chaparro and coworkers. Studies of magnetic enhancement in soils due to the burning mechanism are discussed and the results of burnt soils affected by fires of different nature and natural soils are compared, taking into account their magnetic carriers. Nevertheless, this article deals mainly with the first studies of magnetic proxies for pollution conducted in a province in Argentina. Soils, lagoon and stream sediments from three areas were studied. These areas comprise La Plata, Chascomús, and Tandil districts. The influence of pollution was investigated in Tandil and La Plata, revealing magnetic enhancement and the presence of pollutants only in Tandil soils. On the other hand, stream and lagoon sediments were studied in La Plata and Chascomús. Magnetic carriers and the contents of some heavy metals were identified and investigated in both areas separately. Magnetic parameters show distinctive points and wide areas affected by pollution. Furthermore, this magnetic inference is supported by high contents of heavy metals, especially lead and zinc. Finally, a new statistical study of multiple correlation analysis concerning data from La Plata and Chascomús areas was tried in order to investigate the existence of a linear relation between sets of several magnetic parameters and several chemical variables.
Present-day crustal motion in northeast China determined from GPS measurements
Authors: Meng Guojie , Shen Xuhui , Wu Jicang , Rogozhin Eugene A. 
Published: August 2014

Abstract
GPS measurements carried out between 1997 and 2005 at 37 stations distributed throughout northeast China place indicate the presence of constraints on the present-day crustal motion in this region. Velocity vectors relative to Eurasia are very small, only 1.58 mm/yr on average, indicating that the region is generally stable. With the exception of five stations that show significant motion at the 95% confidence level, the insignificant motion of most stations precludes a clear association of their velocities with the rotation of a separate rigid microplate, suggesting that northeast China belongs to Eurasia plate. The velocities of several stations in the southwestern corner of the studied region consistently point to the southeast. This is most probably a distant effect of the eastward motion of northern Tibet. Small velocities of the stations of around the time of the 1999 M

W
= 7.1 and 2002 M

W
= 7.3 deep-focus earthquakes, which occurred in Wangqing county, suggest that these earthquakes did not cause wide-spread deformations to the shallow crust.
GPS observations of post-storm TEC enhancements at low latitudes
Authors: Kutiev Ivan , Otsuka Yuichi , Saito Akinori , Watanabe Shigeto 
Published: August 2014

Abstract
In a previous work (J. Geophys. Res., 110(A01308), 1–11, 2005), the authors developed an original approach to the processing of total electron content (TEC) data obtained by GPS signals from the Japan receiver network. This approach includes removing the diurnal and seasonal variation carried by 27-day medians and the solar rotation periodicity. The relative deviations of TEC from the median—from all measured locations at a given hour—were then approximated by a regression line along the main prolongation of the Japan islands, between latitudes 24° and 45°N. The two variables of the regression line, the average value at the center and the slope were obtained as a time series, and their behavior during geomagnetic storms in the period 2000–2002 were analyzed. One interesting result was the observed enhancement of TEC at the end of the recovery phase of the storms. The slope variations clearly showed that this enhancement started from the south and was interpreted as a poleward expansion of equatorial crest. In the present paper we further analyze this post-storm phenomenon, adding foF2 data from Japanese Kokubunji and Okinawa ionosondes. We also show the latitude extension of the poleward expansion by using lat/UT contour plots. The results confirm that most of the post-storm TEC enhancements are part of the equatorial crest region which extends poleward during nighttime. In some cases, the enhanced TEC structures develop by separating from the crest region. Daytime TEC enhancements were also observed. Their structures are not confined to the equatorial crests region, but occupy the whole latitude range considered in this study. TEC post-storm enhancements were generally found to be in agreement with foF2 variations.
The influence of pore fluids on seismic wave velocities under high temperature and high pressure conditions: Development of a new technique with gas apparatus at AIST, Japan
Authors: Kitamura Keigo , Masuda Koji , Takahashi Miki , Nishizawa Osamu 
Published: August 2014

Abstract
In order to study the effects of different pore fluids on elastic-wave velocities, we developed a new system for measuring elastic wave velocities (V

p
and V

s
) under high-pressure conditions up to 200 MPa and high-temperature conditions up to 200°C using a gas-medium high-pressure and high-temperature apparatus. During the V

p
and V

s
measurements, we can also control the pore pressures from outside the rock samples. We measured V

p
and V

s
of the Berea sandstone samples under three different pore-fluid conditions including dry (without pore-fluids), in the presence of pore water, and in the presence of pore gas. Here we describe our new measurement technique and establish the capacity of the gas apparatus and measurement technique and their potentialities for the solution of geological problems.
Strong ground motions recorded by a near-source seismographic array during the 16 August 2005 Miyagi-Ken-Oki, JAPAN, earthquake (Mw 7.2)
Authors: Nakahara Hisashi , Sawazaki Kaoru , Takagi Nobumasa , Nishimura Takeshi , Sato Haruo , Fujiwara Hiroyuki 
Published: August 2014

Abstract
An earthquake of Mw 7.2 took place on August 16, 2005 at a plate boundary between the Pacific plate and the North American plate off the coast of Miyagi Prefecture, Northeast Japan. During the Miyagi-Ken-Oki event, we succeeded in recording strong ground motions at six stations in a seismograhic array with an epicentral distance of about 70 km, where we have been operating seven strong-motion seismometers in an aperture of about 500 m since April 2004. The predominant period of the ground motion was shorter than 0.3 s. The peak ground acceleration exceeded 1.7 g at a station where non-linear site response may have occurred during the mainshock. The short-period strong ground motions show a large spatial variation, with up to a ten-fold difference in amplitude even within the array. However, there is a similarity between waveforms registered at different stations for periods longer than 0.4 s. Therefore, the difference in the ground motions may be mainly attributed to the difference in the shallow structure just beneath the stations.
Nonlinear site response from the 2003 and 2005 Miyagi-Oki earthquakes
Authors: Tsuda Kenichi , Steidl Jamison 
Published: August 2014

Abstract
We estimate nonlinear site response by comparing site response estimates from the 16 August 2005 Mj=7.2 and 26 May 2003 Mj=7.0 Miyagi-Oki earthquakes with site response estimates from aftershocks of the 2003 event. Site response is solved by a spectral inversion technique to separate source, path, and site components. The constraint motion in the inversion is a regional attenuation model derived from fitting the spectra of data recorded at borehole KiK-net stations in the region and a theoretical source spectrum for each event determined using the same borehole stations. Site response is calculated at the surface of the KiK-net and K-NET stations. In general, the average aftershock site response is larger than for the two mainshocks, especially at a higher frequency. When comparing site response with input ground motion level, the predominant frequency and the site response values tend to decrease as the level of input ground motion increases.
Precise aftershock distribution of the 2005West Off Fukuoka Prefecture Earthquake (Mj=7.0) using a dense onshore and offshore seismic network
Authors: Uehira Kenji , Yamada Tomoaki , Shinohara Masanao , Nakahigashi Kazuo , Miyamachi Hiroki , Iio Yoshihisa , Okada Tomomi , Takahashi Hiroaki , Matsuwo Norimichi , Uchida Kazunari , Kanazawa Toshihiko , Shimizu Hiroshi 
Published: August 2014

AbstractThe 2005 West Off Fukuoka Prefecture Earthquake (Mj=7.0) occurred on March 20, 2005 in the northern part of Kyushu, Japan. To study the aftershock activity, we deployed eleven pop-up type ocean bottom seismometers (OBSs), sixteen locally recorded temporary stations, and eight telemetered temporary stations in and around the epicenter region. We combined data from these stations and permanent stations located around the aftershock area, and determined the hypocenter of the mainshock and aftershocks. The mainshock was in the northwestern central part of the aftershock region, at a depth of 9.5 km. The mainshock was on a left-lateral strike-slip fault. Aftershocks were located in a depth range of 1–16 km and laterally extend for about 25 km in a NW-SE direction. We found that the aftershocks fell into four groups. This might be due to the heterogeneous structure in the source region. In the group that includes the mainshock, we estimated two fault planes bordering on the depth of the mainshock. There are 10-degree differences in both strike and dip angles between the lower and upper planes. From the aftershock distribution and the focal mechanisms, the rupture first propagated downward, and then propagated upward.