bluuebunny/crossref_metadata_2025 huggingface dataset:
Age polyethism in the leaf‐cutting ant Acromyrmex subterraneus brunneus Forel, 1911 (Hym., Formicidae)
Authors: Camargo R. S. , Forti L. C. , Lopes J. F. S. , Andrade A. P. P. , Ottati A. L. T.
Published: August 2010

Abstract  This study describes and quantifies the behavioural acts of two laboratory colonies of Acromyrmex subterraneus brunneus by investigating worker age polyethism. Twenty‐nine behavioural acts were recorded during the 19‐week observation period. Young individuals performed tasks inside the nest related to brood care and care for the fungus garden, whereas older individuals performed activities outside the nest such as foraging and activities in the waste chamber. The average longevity (±SD) was 108.21 ± 3.30, 109.15 ± 1.92 and 122.71 ± 1.55 days for large, medium and small workers, respectively. The small‐sized workers presented a higher probability of reaching older age than large‐ and medium‐sized workers. This study describes task switching according to age polyethism and the relationship of physical and temporal subcastes.
Sibling cannibalism in aphidophagous ladybirds: its impact on sex‐dependent development and body weight
Authors: Omkar  , Pervez A. , Gupta A. K.
Published: August 2010

Abstract: The effects of sibling egg cannibalism on sex‐dependent development and adult body weight were determined by rearing simultaneously two groups of sibling larvae of ladybirds, viz.Propylea dissectaandCoccinella transversalisindividually. The first group included cannibals (i.e. neonates, which took a sibling egg as the first meal and later fed on aphids,Aphis craccivora) and the other included non‐cannibals (reared exclusively on aphids). The cannibal larvae developed faster with heavier adults than non‐cannibals. This expedited development and nutritional advantage (increased body weight) was greater in first instars indicating maximum benefit of sibling cannibalism to them. Sibling cannibalism was relatively more advantageous to male than to female ladybirds. Laboratory data predict that the larger size of adults in the field could possibly be the result of sibling egg cannibalism at the neonate level.
Oviposition deterrence of shoots and essential oils of Minthostachys spp. (Lamiaceae) against the potato tuber moth
Authors: Guerra P. C. , Molina I. Y. , Yábar E. , Gianoli E.
Published: August 2010

Abstract:  The potato tuber moth is a noxious pest of potato in stores, where the use of repellent plants is an environmentally sound alternative to the application of chemical pesticides. We evaluated the protective effect of native Minthostachys species (Lamiaceae) against tuber infestation by the potato tuber moth in a rustic store in Cusco, Perú. We covered potato tubers with dried shoots of Minthostachys spicata and Minthostachys glabrescens and compared tuber damage with a control treatment of maize straw. We also conducted a no‐choice oviposition bioassay in the laboratory, testing the oviposition deterrence of essential oils of M. spicata, M. glabrescens and Minthostachys mollis at natural concentrations. We recorded the number of eggs laid by mated moths on filter paper treated with essential oils of each of the three species and on two control treatments: hexane and untreated blank. Finally, we tested for differences in oviposition deterrence among five full‐sib families of potato tuber moth raised under identical conditions. We found that dried, chopped leaves and flowers of Minthostachys species reduced the percentage of tuber damage in stores in comparison with the control (5% vs. 12%), but no difference in protection was found between species. Essential oils at natural concentrations deterred moth oviposition, reducing the number of eggs laid by about 80% compared with the control treatments; again, there were no significant differences between Minthostachys species. Finally, whereas we detected among‐family variation in oviposition on filter papers treated with essential oils, no difference was found in the number of eggs laid on control substrates. Therefore, there was genetic variation for oviposition deterrence in the potato tuber moth and resistance to repellent plants might evolve thereafter.
Electroantennogram measurements of atmospheric pheromone concentration after aerial and ground application of gypsy moth mating disruptants
Authors: Thorpe K. W. , Van Der Pers J. , Leonard D. S. , Sellers P. , Mastro V. C. , Webb R. E. , Reardon R. C.
Published: August 2010

Abstract: A portable electroantennogram (EAG) sensor was used to measure relative atmospheric pheromone concentration in forest plots treated with aerial and ground applications of gypsy moth,Lymantria dispar(L.) (Lep., Lymantriidae), mating‐disruption formulations. Five treatments (Disrupt II flakes with sticker, Disrupt II flakes without sticker, Disrupt II flakes in a sticker slurry, microcapsules and hand‐applied Luretape), all applied at 75 g active ingredient per hectare and an untreated control were evaluated. Gypsy moth male catch in pheromone‐baited traps and fertilization of deployed females were suppressed in all treatments, and no females deployed in treated plots produced more than 5% fertile eggs. Relative pheromone concentrations were significantly higher in the two treatments in which flakes were aerially applied with sticker and in the microcapsule treatment. Pheromone concentration measurements in the flakes without sticker and hand‐applied treatments were not significantly different from those in the control. Mating success was negatively correlated with relative pheromone concentration. The ability of the EAG to detect differences in pheromone concentration that are correlated with mating success suggests that this could be a useful method for predicting the effectiveness of mating‐disruption treatments.
Origin of fine‐grained peridotite xenoliths from Iraya volcano of Batan Island, Philippines: deserpentinization or metasomatism at the wedge mantle beneath an incipient arc?
Authors: Arai Shoji , Kida Megumi
Published: August 2010

Abstract Peridotite xenoliths from the subarc mantle, which have been rarely documented, are described from Iraya volcano of the Luzon arc, the Philippines, and are discussed in the context of wedge‐mantle processes. They are mainly harzburgite, with subordinate dunite, and show various textures from weakly porphyroclastic (C‐type) to extremely fine‐grained equigranular (F‐type). Textural characteristics indicate a transition from the former to the latter by recrystallization. The F‐type peridotite has inclusion‐rich fine‐grained olivine and radially aggregated orthopyroxene, being quite different in texture from ordinary mantle‐derived peridotites previously documented. Despite their strong textural contrast, the two types do not show any systematic difference in modal composition. The harzburgite of C‐type has ordinary mantle peridotite mineralogy; olivine is mostly Fo91–92 and chromian spinel mostly has Cr#s (= Cr/[Cr + Al] atomic ratios) from 0.3 to 0.6. Olivine is slightly more Fe‐rich (Fo89–91) and spinel is more enriched in Cr (the Cr#, 0.4–0.8) and Fe3+ in F‐type peridotites than in C‐type harzburgite. Orthopyroxene in F‐type peridotites is relatively low in CaO (<1 wt%), Al2O3 (<2 wt%) and Cr2O3 (<0.4 wt%). The F‐type peridotite was possibly formed from the C‐type one by recrystallization including local dissolution and precipitation of orthopyroxene assisted by fluid (or melt) of subduction origin. Textural characteristics, however, indicate a deserpentinization origin from abyssal serpentinite of which protolith was a C‐type peridotite. In this scenario the initial abyssal serpentinite was possibly dehydrated due to an initiation of magmatic activity beneath an incipient oceanic arc like Batan Island. The F‐type peridotite is characteristic of the upper mantle of island arc, especially of incipient arc.
Behavior of Niobium, Tantalum and other high field strength elements in adakites and related lavas from The Philippines
Authors: Prouteau Gaëlle , Maury René C. , Sajona Fernando G. , Cotten Joseph , Cotten Jean
Published: August 2010

Abstract Pliocene–Quaternary adakites and spatially and temporally associated niobium‐enriched basalts (the latter thought to be derived by melting of slab melt‐metasomatized mantle) from the Philippine island arcs have been selected for analysis of high field strength elements (HFSE). All these samples have nearly constant and chondritic Zr/Hf ratio (36.5) and slightly infrachondritic Nb/Ta ratio (14.7). We interpret adakitic magmas to be derived from the partial melting at approximately 900°C of subducted mid‐ocean ridge basalts (MORB) crust, with rutile and/or ilmenite as residual minerals. Melting calculations show that, under these conditions, slab melts should have suprachondritic Nb/Ta ratios. The obvious discrepancy with our data is attributed to insufficient knowledge of rutile‐melt partition coefficients for HFSE. Consequently, abnormal Nb/Ta or Zr/Hf ratios cannot be considered as potential markers of slab melting processes in island arcs.
Adakitic lavas in the Central Luzon back‐arc region, Philippines: lower crust partial melting products?
Authors: Yumul Graciano P. , Dimalanta Carla , Bellon Herve , Faustino Decibel V. , De Jesus Joel V. , Tamayo Rodolfo A. , Jumawan Ferdinand T.
Published: August 2010

Abstract Volcanism in the back‐arc side region of Central Luzon, Philippines, with respect to the Manila Trench is characterized by fewer and smaller volume volcanic centers compared to the adjacent forearc side‐main volcanic arc igneous rocks. The back‐arc side volcanic rocks which include basalts, basaltic andesites, andesites and dacites also contain more hydrous minerals (ie, hornblende and biotite). Adakite‐like geochemical characteristics of these back‐arc lavas, including elevated Sr, depleted heavy rare earth elements and high Sr/Y ratios, are unlikely to have formed by slab melting, be related to incipient subduction, slab window magmatism or plagioclase accumulation. Field and geochemical evidence show that these adakitic lavas were most probably formed by the partial melting of a garnet‐bearing amphibolitic lower crust. Adakitic lavas are not necessarily arc–trench gap region slab melts.
Geology of the southern Zambales Ophiolite Complex, Luzon, Philippines
Authors: Yumul Graciano P. , Dimalanta Carla B. , Jumawan Ferdinand T.
Published: August 2010

Abstract Field, geochemical and geophysical evidence show that the southern Zambales Ophiolite Complex attained its present‐day configuration through the juxtapositioning of an arc terrane (San Antonio massif) to a back‐arc crust (Cabangan massif). The San Antonio massif manifests island arc‐related characteristics (i.e. spinel XCr [Cr/(Cr + Al)] >0.60; mostly plagioclase An92–95; pyroxene crystallizing ahead of plagioclase; orthopyroxene as an early, major crystallizing phase) which cannot be directly parental to the Cabangan massif transitional mid‐ocean ridge basalt to island arc tholeiitic volcanic carapace. The two massifs are believed to be separated by a left‐lateral strike–slip fault, the Subic Bay Fault Zone. Apart from the presence of highly sheared, allochthonous outcrops, the Subic Bay Fault Zone is generally defined by northwest–southeast trending magnetic and bouguer anomalies. The San Antonio massif was translated southward from the northern part of the Zambales Ophiolite Complex through the Subic Bay Fault Zone. This resulted into its suturing with the Cabangan massif and could have led to the formation of the present‐day Subic Bay.
Comparative study of platinum‐group elements in the Coto and Acoje blocks of the Zambales Ophiolite Complex, Philippines
Authors: Zhou Mei‐Fu , Yumul Graciano P. , Malpas John , Sun Min
Published: August 2010

Abstract The Zambales Ophiolite Complex (ZOC), Philippines, includes two geochemically distinct, ophiolitic assemblages: the high‐Al chromitite‐bearing Coto Block and high‐Cr chromitite‐bearing Acoje Block. This paper reports a comparative platinum‐group element (PGE) study of these two blocks. The PGE data were obtained using Ni‐sulfide fire assay preconcentration combined with inductively coupled plasma mass spectrometry (ICP‐MS) measurement. Podiform chromitites in the Acoje Block have higher Cu, Ir, Ru and Rh contents than their equivalents in the Coto Block, although chromitites from both have similar Pt and Pd contents. The PGE mantle‐normalized patterns of dunites from the two blocks are also different: dunites from the Coto Block are depleted in Pt, whereas those from the Acoje Block have a relatively flat pattern. The data demonstrate that Coto and Acoje Blocks have different origins in terms of their source region and partial melting processes. This study implies that the ZOC is a paired ophiolite belt formed in an island arc and back‐arc basin environment.
Gravity variations along the Southeast Bohol Ophiolite Complex (SEBOC), Central Philippines: Implications on Ophiolite Emplacement
Authors: Barretto Jenny Anne L. , Dimalanta Carla B. , Yumul Graciano P.
Published: August 2010

Abstract The basement complex of Bohol Island consists of the Southeast Bohol Ophiolite Complex (SEBOC), Cansiwang Melange and Alicia Schist. The SEBOC is a complete, but dismembered ophiolite with outcrops generally trending northeast– southwest and dipping north‐west. The harzburgite units of the SEBOC are almost always observed to be thrusted onto the Cansiwang Melange, which in turn is thrusted onto the Alicia Schist. Bouguer gravity values on Bohol range from about +60 mGal in the west to +120 mGal in the east, in the region to the north‐east of the SEBOC outcrops. Based on the present distribution of the SEBOC units and their thrust fault relationship with the Cansiwang Melange and Alicia Schist, it is proposed that the SEBOC was emplaced by onramping towards the south‐eastward direction. However, the orientation of the Bouguer highs suggests that the thrusting direction of the ophiolite units is towards the south‐west and not towards the south‐east.
Shear partitioning in the Philippines: Constraints from Philippine Fault and global positioning system data
Authors: Aurelio Mario A.
Published: August 2010

Abstract The Philippine Fault is a major left‐lateral structure formed in an island arc setting. It accommodates a component of the oblique convergence between the Philippine Sea Plate and the Philippine archipelago. This observation is quantified through a series of global positioning satellite experiments between 1991 and 1996. The formation of the Fault marks the onset of a new geodynamic regime in the Philippine region. In the central Philippines, this event corresponds to the creation of a new tectonic boundary separating the Philippine Mobile Belt and the Philippine Sea Plate, following the latter's kinematic reorganization that occurred around 4 Ma ago. During this event, the Philippine Sea Plate changed its relative movement with respect to Eurasia from a northward to a north‐westward motion, favoring the formation of a Philippine Fault–Philippine Trench system under a shear partitioning mechanism.
Forearc deformation and tectonic significance of the ultramafic Molucca central ridge, Talaud islands (Indonesia)
Authors: Bader Anne Gaëlle , Pubellier Manuel
Published: August 2010

Abstract The Molucca Sea is a narrow basin located south of Mindanao (Philippines) and underlined by a north‐south ophiolitic ridge. This ridge represents the outer ridge of the Sangihe subduction zone and emerges by uplift in the central part of the basin, in the Talaud Islands. Field studies indicate that forearc sediments rest uncomformably on (i) a dismembered ophiolitic series and (ii) thick melanges. Structural analysis indicates two deformation events, one of which is oriented east‐west coaxial with the present state of strain. We interpret the earlier (N20°E) direction as a thrusting event that affected an ophiolitic basement associated with the edge of the Celebes Sea. Thrusting within the oceanic crust and sediments also generated olistostromes (melanges). The style of deformation is characterized by flattened rhombs of peridotites which exists in situ in the upper section of the crustal sequence and were also found inside the melange. Incipient Sangihe subduction around 15 Ma uplifted the deformed crust and buried the melanges beneath the forearc sediments. Recent east‐west shortening during subduction of the Snellius Plateau reactivated the melanges within thrusts cutting the forearc series.
Cooling and inferred exhumation history of the Ryoke metamorphic belt in the Yanai district, south‐west Japan: Constraints from Rb–Sr and fission‐track ages of gneissose granitoid and numerical modeling
Authors: Okudaira Takamoto , Hayasaka Yasutaka , Himeno Osamu , Watanabe Koichiro , Sakurai Yasuhiro , Ohtomo Yukiko
Published: August 2010

Abstract The Ryoke metamorphic belt in south‐west Japan consists mainly of I‐type granitoids and associated low‐pressure/high‐temperature metamorphic rocks. In the Yanai district, it has been divided into three structural units: northern, central and southern units. In this study, we measured the Rb–Sr whole‐rock–mineral isochron ages and fission‐track ages of the gneissose granodiorite in the central structural unit. Four Rb–Sr ages fall in a range of ca 89–87 Ma. The fission‐track ages of zircon and apatite are 68.9 ± 2.6 Ma and 57.4 ± 2.5 Ma (1σ error), respectively. Combining the newly obtained ages with previously reported (Th–)U–Pb ages from the same unit, thermochronologic study revealed two distinctive cooling stages; 1) a rapid cooling (> 40°C/Myr) for a period (~7 Myr) soon after the peak metamorphism (~ 95 Ma) and 2) the subsequent slow cooling stage (~ 5°C/Myr) after ca 88 Ma. The first rapid cooling stage corresponds to thermal relaxation of the intruded granodiorite magma and its associated metamorphic rocks, and to the uplift by a displacement along low‐angle faults which initiated soon after the intrusion of the magma. Uplift by the later stage deformation having formed large‐scale upright folds resulted in progress of the exhumation during the first stage. The average exhumation velocity of the stage is ≥ 2 mm/yr. During the second stage, the rocks were not accompanied by ductile deformation and were exhumed with the rate of 0.1–0.2 mm/yr. The difference in the exhumation velocity between the first and second cooling stages resulted from the difference in the thickness of the crust and in the activity of ductile deformation between the early and later stages of the orogenesis.
Primordial helium isotope signature from Plio–Quaternary alkaline basalts in Yemen
Authors: Orihashi Yuji , Nagao Keisuke , Al‐Jailani Ashraf , Hanan Barry B.
Published: August 2010

Abstract Isotopic compositions of He, Ne and Ar were measured on Plio–Quaternary alkaline basalts of Marib–Sirwah and Shuqra volcanic fields in Yemen, south‐western Arabian Peninsula. Very high 3He/4He isotope ratios were found in olivine phenocrysts of some Quaternary alkaline basalts in both volcanic fields, located on the margin of the dispersed Afar mantle plume, compared with the Afar–Ethiopian province in the center of the mantle plume. This suggests that the Afar mantle plume source may consist of common component (C or focal zone (FOZO)) with variable primordial 3He/4He ratio rather than high μ mantle (HIMU) component. The three component mixing C as the Afar mantle plume, depleted mantle (DM) as upper mantle and lithospheric mantle with a hybrid enriched mantle I–II (EM I–EM II) characteristics may be adequate to explain He–Sr–Nd–Pb isotope variation for the Afar–Arabian Cenozoic volcanics. The occurrence of high 3He/4He ratios in the Marib–Sirwah volcanic field appears to show that the primitive basaltic magma, derived from the margin of the dispersed trous‐like Afar mantle plume during 15–0 Ma, was not by contamination of lithospheric and upper mantle materials in comparison with that from the center of the Afar mantle plume as a result of relatively low thermal anomaly.
Deformation processes in the shallow levels of an accretionary prism: The Mesozoic Torlesse Terrane, South Island, New Zealand
Authors: Kano Ken‐Ichi , Konishi Yusaku
Published: August 2010

Abstract The deformation style of the Torlesse Terrane along the southern Kaikoura coast, South Island, New Zealand, records shallow level deformation processes within an accretionary prism during the Early Cretaceous. The beds exhibit complicated structural features resulting from multistage deformations in a lithological unit, that were intimately related with the dewatering and lithification of terrigenous sediments. The earliest phase of deformation throughout the transect studied was the development of pinch‐and‐swell structures and boudinage fabrics due to layer‐parallel extension while the beds were poorly consolidated. This was followed locally by mesoscopic tight to close recumbent folding. The beds are cut locally by two phases of mudstone intrusions. The earlier phase was initiated by ‘in situ’ fluidization of mudstone layers, whereas the later phase represented intrusion of siliceous claystone probably derived from an overpressured decollement. Minor faults at high‐angles to bedding by layer‐normal shortening then disrupted the beds throughout the transect. The deformation was followed by formation of meso‐ and macroscopic scale open to gentle folds by layer‐parallel shortening. Kilometer‐scale differential stratal rotations were produced during the final main tectonic phase that occurred in association with post‐accretion Neogene regional disturbance.
Strain and tilt changes measured during a water injection experiment at the Nojima Fault zone, Japan
Authors: Fujimori Kunio , Ishii Hiroshi , Mukai Atsushi , Nakao Shigeru , Matsumoto Shigeo , Hirata Yasuhiro
Published: August 2010

Abstract In order to make geophysical and geological investigations of the Nojima Fault on Awaji Island, Japan, three boreholes measuring 1800 m, 800 m and 500 m deep were drilled into the fault zone. The fault is one of the seismic source faults of the 1995 Hyogo‐ken Nanbu earthquake of M7.2. A new multicomponent borehole instrument was installed at the bottom of the 800 m borehole and continuous observations of crustal strain and tilt have been made using this instrument since May 1996. A high‐pressure water injection experiment within the 1800 m borehole was done in February and March 1997 to study the geophysical response, behavior, permeability, and other aspects of the fault zone. The injection site was located approximately 140 m horizontally and 800 m vertically from the instrument. Associated with the water injection, contraction of approximately 0.7 × 10−7 str (almost parallel to the fault) and tilt of approximately 1 × 10‐7 rad in the sense of upheaval toward the injection site were observed. In addition to these controlled experiments, the strainmeter and tiltmeter also recorded daily variations. We interpret strain and tilt changes to be related to groundwater discharge and increased ultra‐micro seismicity induced by the injected water.
Electrokinetic phenomena associated with a water injection experiment at the Nojima fault on Awaji Island, Japan
Authors: Murakami Hideki , Hashimoto Takeshi , Oshiman Naoto , Yamaguchi Satoru , Honkura Yoshimori , Sumitomo Norihiko
Published: August 2010

Abstract Self‐potential variations were measured to estimate the magnitude of electrokinetic and hydrological parameters (zeta potential and permeability) of the Nojima Fault zone in Awaji, Japan. The study observed self‐potential variations that seemed to be associated with water flow from the injection well to the fracture zone, which were induced by turning the injection on and off. Amplitudes of the variations were a few to 0.03 V across 320–450 m dipoles. These variations can be explained well with an electrokinetic model. The quantity k/ζ (permeability/zeta potential) is in the range 1.6 × 10−13− 5.4 × 10−13 m2/V. Permeability of the Nojima fault zone can be estimated as approximately 10−16–10−15 m2 on the assumption that the zeta potential is in the range –0.01 to –0.001 V.
In situ stress measurements in NIED boreholes in and around the fault zone near the 1995 Hyogo‐ken Nanbu earthquake, Japan
Authors: Ikeda Ryuji , Iio Yoshihisa , Omura Kentaro
Published: August 2010

Abstract The 1995 Hyogo‐ken Nanbu (Kobe) earthquake, M7.2, occurred along the north‐east–south‐west trending Rokko–Awaji Fault system. Three boreholes of 1001 m, 1313 m and 1838 m deep were drilled in the vicinity of the epicenter of the earthquake. Each borehole is located at characteristic sites in relation to active faults and the aftershock distribution. In particular, the Nojima–Hirabayashi borehole [Hirabayashi National Research Institute for Earth Science and Disaster Prevention (NIED) drilling] in Awaji Island was drilled to a depth of 1838 m, approximately 320 m southeast from the surface rupture of the Nojima Fault, and it crosses fracture zones below a depth of 1140 m. In situ stress measurements by the hydraulic fracturing method were conducted in these boreholes within 1.5 years after the earthquake. Measurement results suggest the following: (i) Differential stress values are very small, approximately 10 MPa at a depth of 1000 m at each site; (ii) the orientation of maximum horizontal compression is almost the same in the boreholes, perpendicular to the surface trace of the faults, north‐west–south‐east; (iii) fault types estimated from the state of stress differ among these sites; and (iv) the differential stress value just beneath the fault fracture zone decreases abruptly to one‐half of that above the fault zone in the Hirabayashi NIED drilling. These features support the idea that the shear stress along the Rokko–Awaji Fault system decreased to a low level just after the earthquake.
In situ stress measurements in a borehole close to the Nojima Fault
Authors: Tsukahara Hiroaki , Ikeda Ryuji , Yamamoto Kiyohiko
Published: August 2010

Abstract In situ stress was measured close to the fault associated with the 1995 Kobe Earthquake (Hyogo‐ken Nanbu earthquake; January 1995; M7.2) using the hydraulic fracturing method. The measurements were made approximately 2 years after the earthquake. The measured points were approximately 40 m from the fault plane at depths of about 1500 m. The maximum and the minimum horizontal compressive stresses were 45 MPa and 31 MPa, respectively. The maximum compressive stress and the maximum shear stress are very small in comparison with those of other seismically active areas. The azimuth of the maximum horizontal compressive stress was estimated from the observed azimuths of well bore breakouts at depths between 1400 m and 1600 m and was found to be N135° (clockwise). The maximum stress axis is perpendicular to the fault strike, N45°. These features are interpreted in terms of a small frictional coefficient of the fault. The shear stress on the fault was released and dropped almost to zero during the earthquake and it has not yet recovered. Zero shear stress on the fault plane resulted from the perpendicular orientation of one of the principal stress to the fault plane.
Stresses at sites close to the Nojima Fault measured from core samples
Authors: Yamamoto Kiyohiko , Yabe Yasuo
Published: August 2010

Abstract The Nojima Fault in Awaji, Hyogo prefecture, Japan, was ruptured during the 1995 Hyogo‐ken Nanbu earthquake (MJMA = 7.2). Toshima is located close to the fault segment, in which a large dislocation has been observed on the Earth’s surface. Ikuha is near the southern end of the buried fault that extends from the surface rupture. Stresses are measured on core samples taken at depths of 310 m, 312 m and 415 m at Toshima and a depth of 351 m at Ikuha. The measured stresses show that both sites are in the field of a strike–slip regime, but compression dominates at Toshima. Defining the relative shear stress as the maximum shear stress divided by the normal stress on the maximum shear plane, the relative shear stress ranges from 0.42 to 0.54 at Toshima and is approximately 0.32 at Ikuha. While the value at Ikuha is moderate, those at Toshima are comparably large to those in areas close to the inferred fault of the 1984 Nagano‐ken Seibu earthquake. Value amounts greater than 0.4 suggest that there are areas of large relative shear stress along faults, thus having the potential to generate earthquakes. Provided that the cores are correctly oriented, the largest horizontal stresses at shallow depths are in the direction from N113°E to N139°E at Toshima and N74°E at Ikuha, indicating that the fault does not orient optimally for the stress field at both sites. The slip is known to be predominant in the right‐lateral strike–slip component. Although this slip may appear contradictory to the stress field at Toshima, the slip direction is found to be parallel to the measured stresses resolved on the fault plane for the first approximation. The ratio of shear stress to normal stress on the fault plane is roughly estimated to be greater than zero and smaller than 0.3 near Toshima.
Seismic observations in the DPRI 1800 m borehole drilled into the Nojima Fault zone, south‐west Japan
Authors: Nishigami Kin’Ya , Ando Masataka , Tadokoro Keiichi
Published: August 2010

Abstract Seismometers were installed at three depths in the Disaster Prevention Research Institute, Kyoto University (DPRI) 1800 m borehole drilled into the Nojima Fault zone, southwest Japan. The waveforms recorded by these seismometers are rather simple compared with those recorded at the DPRI 800 m borehole or on the ground surface. These data should be well suited for detecting fault zone‐trapped waves and estimating the fault zone structure and its temporal variation related to the healing process of the ruptured fault. Typical waveforms trapped in the fault zone were observed by a surface seismographic array across the Nojima Fault just after the 1995 Hyogo‐ken Nanbu earthquake (Kobe earthquake). Among the wave data recorded in the DPRI 1800 m borehole, however, clear evidences of fault zone‐trapped waves have not yet been found, and further studies are continuing. The present study outlines the observation system in the DPRI 1800 m borehole, which will make it easier to access and analyze the borehole data.
Resistivity mapping using the VLF‐MT method around surface fault ruptures of the 1995 Hyogo‐ken Nanbu earthquake, Japan
Authors: Yamaguchi Satoru , Murakami Takahisa , Inokuchi Hiroo
Published: August 2010

Abstract Distinctive fault ruptures, the Nojima Fault and Ogura Fault, appeared along the northwestern coast of Awaji Island at the time of the 1995 Hyogo‐ken Nanbu earthquake (Kobe earthquake). In order to delineate the shallow resistivity structures around the faults just after they formed, Very Low Frequency Magnetotelluric (VLF‐MT) surveys were made at five sites along the Nojima Fault and at one site along the Ogura Fault. Fourteen transects were made at the one site on the Ogura Fault, and another transect covers the area between the two faults. Changes in apparent resistivity or phase, or both, commonly occur when crossing the surface location of one of the faults, except for the northern transects at OGR‐0 on the Ogura Fault. Apparent resistivity values of less than 100 Ωm were observed for Tertiary and Quaternary sediments and values larger than 200 Ωm for granitic rocks. The resistivity structures are related to the morphological characteristics of the fault ruptures. Remarkably conductive zones (less than 10 Ωm in apparent resistivity and 30–40 m in width) were found where the surface displacement is distinct and prominent along a single fault plane. If remarkably conductive zones were formed at the time of the 1995 Hyogo‐ken Nanbu earthquake, the results provide a good constraint on the dimensions of a conductive zone near the surface that was made by one earthquake. Alternatively, if characteristic resistivity structures existed prior to the earthquake, the conductive zone was probably formed by some tens of earthquakes in relatively modern times. In this case, this phenomenon is inferred to be a concentration of fracturing in a narrow zone and is associated with the formation of clay minerals, which enhance rock conductivity.
Long‐term temperature monitoring in a borehole drilled into the Nojima Fault, southwest Japan
Authors: Yamano Makoto , Goto Shusaku
Published: August 2010

Abstract Long‐term monitoring of temperature distribution in an active fault zone was carried out using the optical fiber temperature‐sensing technique. An optical fiber cable was installed in a borehole drilled into the Nojima Fault in Awaji Island, south‐west Japan, and the temperature profile to a depth of 1460 m had been measured for 2.5 years (July 1997–January 2000). Although the obtained temperature records showed small temporal variations due to drifts of the measurement system all along the cable, local temperature anomalies were detected at two depths. One at around 80 m seems to correspond to a fracture zone and may be attributed to groundwater flow in the fracture zone. This anomaly had been stable throughout the monitoring period, whereas the other anomaly at around 500 m was a transient one. The water level in the borehole could be estimated from the diurnal temperature variations in the uppermost part of the borehole and may provide information on the hydrological characteristics of the fault zone, which is connected to the borehole through perforations on the casing pipe. Except for these minor variations, the temperature profile had been very stable for 2.5 years. The conductive heat flow calculated from this profile and the thermal conductivity measured on core samples increases with depth, probably resulting from errors in thermal conductivity due to sampling problems and/or from advective heat transfer by regional groundwater flow. Assuming that the middle part of the borehole (less fractured granite layer) is least affected by these factors, heat flow at this site is estimated to be approximately 70 mW/m2.
A trial for monitoring temporal variation of seismic velocity using an ACROSS system
Authors: Yamaoka Koshun , Kunitomo Takahiro , Miyakawa Koji , Kobayashi Kazunori , Kumazawa Mineo
Published: August 2010

Abstract The temporal variation of seismic velocity near the Nojima Fault, which ruptured during the 1995 Kobe earthquake (Hyogo‐ken Nanbu earthquake), was detected using an accurately controlled routine‐operated seismic source (ACROSS). The source generates elastic waves by a centrifugal force of an eccentric mass rotating around an axis. The mass is driven with an AC servomotor whose angular position is accurately controlled with reference to a very accurate global positioning system (GPS) clock. The error of the mass’ position is less than 0.002 radian and does not accumulate. As a result, the source generates sinusoidal waves of very narrow spectral peaks enabling their detection with an excellent signal‐to‐noise ratio. Although the stability of the rotation is quite excellent, a large daily variation was found, which seems to be caused by changes in atmospheric temperature. The daily variation was 10% in amplitude and 0.1 radian in phase of the signal observed at the 800 m borehole seismometer. A significant variation was found to be due to that of coupling between the rotational source and the foundation made of reinforced concrete in which the source was situated. In order to make a correction on the signal of the 800 m borehole seismometer, the vibration of the foundation was measured and modeled assuming a rigid body movement. The correction successfully reduced the daily variation by approximately 90%, resulting in a variation of 1% in amplitude and 0.01 radian in phase. The phase variation of 0.01 radian corresponds to 100 μs and less than 0.1% in velocity over 1000 m between the source and the receiver.
Estimating the permeability of the Nojima Fault Zone by a hydrophone vertical seismic profiling experiment
Authors: Kiguchi Tsutomu , Ito Hisaso , Kuwahara Yasuto , Miyazaki Teruki
Published: August 2010

Abstract A multi‐offset hydrophone vertical seismic profiling (VSP) experiment was done in a 747 m deep borehole at Nojima Hirabayashi, Hyogo prefecture, Japan. The borehole was drilled to penetrate the Nojima Fault, which was active in the 1995 Hyogo‐ken Nanbu earthquake. The purpose of the hydrophone VSP is to detect subsurface permeable fractures and permeable zones and, in the present case, to estimate the permeability of the Nojima Fault. The analysis was based on a model by which tube waves are generated when incident P‐waves compress the permeable fractures (or permeable zones) intersecting the borehole and a fluid in the fracture is injected into the borehole. Permeable fractures (or permeable zones) are detected at the depths of tube wave generation, and fracture permeability is calculated from the amplitude ratio of tube wave to incident P‐wave. Several generations of tube waves were detected from the VSP sections. Distinct tube waves were generated at depths of the fault zone that are characterized by altered and deformed granodiorite with a fault gouge, suggesting that permeable fractures and permeable zones exist in the fault zone. Tube wave analysis shows that the permeability of the fault gouge from 624 m to 625 m is estimated to be approximately 2 × 10−12 m2.
Examination of mineral assemblage and chemical composition in the fracture zone of the Nojima Fault at a depth of 1140 m: Analyses of the Hirabayashi NIED drill cores
Authors: Matsuda Tatsuo , Arai Takashi , Ikeda Ryuji , Omura Kentaro , Kobayashi Kenta , Sano Hiroyuki , Sawaguchi Takashi , Tanaka Hidemi , Tomita Tomoaki , Tomida Naoto , Hirano Satoshi , Ymazaki Akiko
Published: August 2010

Abstract A 1800 m deep borehole was drilled at Nojima Hirabayashi, Japan to penetrate through the Nojima Fault, which was activated at the time of the 1995 Hyogo‐ken Nanbu earthquake (Kobe earthquake). Three fracture zones were recognized in cores at approximate depths of 1140 m, 1300 m and 1800 m. The mode of distribution of fault rocks, minerals and chemical elements were analyzed in an interval between depths of 1108 m and 1161 m, focusing on the fracture zone at the depth of 1140 m. Foliated blue‐gray fault gouge constituted the central part of the fracture zone. The degree of fracturing appeared to be greater in the hanging wall than in the footwall. The relative amounts of minerals were estimated qualitatively. In the analyzed interval, not only were quartz, orthoclase, plagioclase, biotite and hornblende detected in the parent rock (granodiorite), but also kaolinite, smectite, laumontite, stilbite, calcite, ankerite and siderite, which are related to hydrothermal alteration. In particular, biotite disappeared both in the hanging wall and footwall across the central fault zone; it disappeared over a wider range in the hanging wall than in the footwall. The amounts of major chemical elements were analyzed quantitatively. Concentrations of Al2O3, Fe2O3, MnO, TiO2, and P2O5 all decreased throughout the interval except at some points. H2O+ and CO2 increased throughout the interval. Na2O increased in the region outside the central plane, whereas MgO and CaO increased in the hanging wall and decreased in the footwall. SiO2 and K2O decreased in the hanging wall and increased in the footwall. These results elucidate the higher degree of fracturing and chemical changes present in the hanging wall of the 1140 m fracture zone than in the footwall.
Crack‐filling clays and weathered cracks in the DPRI 1800 m core near the Nojima Fault, Japan: Evidence for deep surface‐water circulation near an active fault
Authors: Uda Shin‐Ichi , Lin Aiming , Takemura Keiji
Published: August 2010

Abstract Crack‐filling clays and weathered cracks were observed in the Disaster Prevention Research Institute, Kyoto University (DPRI) 1800 m cores drilled from the Nojima Fault Zone, which was activated during the 1995 Hyogo‐ken Nanbu earthquake (Kobe earthquake). The crack‐filling clays consist mainly of unconsolidated fine‐grained materials that fill opening cracks with no shear textures. Most of the cracks observed in the DPRI 1800 m cores are yellow‐brown to brown in color due to weathering. Powder X‐ray diffraction analyses show that the crack‐filling clays are composed mainly of clay minerals and carbonates such as siderite and calcite. Given that the top of the borehole is approximately 45 m above sea level, most of the core is far below the stable groundwater table. Hence, it is suggested that the crack‐filling clays and weathered cracks in the cores taken at depths of 1800 m were formed by the flow of surface water down to the deep fractured zone of the Nojima Fault Zone during seismic faulting.
ESR and ICP analyses of the DPRI 500 m drill core samples penetrating through the Nojima Fault, Japan
Authors: Fukuchi Tatsuro , Imai Noboru
Published: August 2010

Abstract The Disaster Prevention Research Center, Kyoto University (DPRI) 500 m drilling core samples from the Nojima Fault, which caused the 1995 Hyogo‐ken Nanbu earthquake in Japan, were analyzed using electron spin resonance (ESR) and inductively coupled plasma (ICP). The fault gouge of the Nojima Fault zone, measuring approximately 50 mm in width, is located at a depth of about 388.4 m from the surface along the 500 m core samples. Electron spin resonance measurements of the fault gouge have revealed that a quartet ESR signal in montmorillonite and the hyperfine structure of an Al center in quartz were reduced to 31–36% of the initial intensity by heating, while an E′ center in quartz, which is often used for Quaternary fault dating, had been reduced to only 70% of the initial value. According to a computer simulation on the decay of ESR signals by frictional heating, the ESR intensity pattern measured in the fault gouge does not coincide with the calculated pattern for dry faults with a planar slip surface because the temperature on the fault plane must rise above the melting point of the fault blocks. However, for fault gouge containing pore water, the temperature in the fault gouge cannot rise above the boiling temperature of water, approximately 310–370°C under a pore water pressure of 10–20 MPa. If pore water in the fault gouge was boiled to approximately 350°C by frictional heating and the boiled water diffused into the fault gouge, the ESR intensity pattern could be explained. Alternatively, the ESR intensity of Fe3+ increases in the dark gray fault gouge and is consistent with ICP data. This result is also consistent with the increased magnetic susceptibility in the fault gouge. Furthermore, using inductively coupled plasma mass spectrometry (ICP‐MS), a 208Pb anomaly was detected in the fault gouge, which can be probably explained by the generation of 220Rn gases in the Earth’s crust. This 208Pb anomaly means that the fault gouge zone had been in radioactive disequilibria.
ESR analysis of the Nojima fault gouge, Japan, from the DPRI 500 m borehole
Authors: Matsumoto Hiroshi , Yamanaka Chihiro , Ikeya Motoji
Published: August 2010

Abstract Electron spin resonance (ESR) analyses of quartz grains in fault gouge were performed for a core sample taken from the Nojima Fault that moved during the 1995 Kobe earthquake (Hyogo‐ken Nanbu earthquake). Distribution of radiation‐induced defects in the gouge at a depth of 389.4 m was measured by extracting quartz grains from seven discrete positions within 30 mm of the fault plane on the granite side. The decrease in E′1 and Al centers was observed within 2 mm of the fault plane, suggesting partial annealing due to faulting. Partial annealing even at that depth suggested that conventional ESR dating, which is based on the hypothesis of complete annealing during faulting, was not applicable. Theoretical calculations of the temperature rise and of the thermal annealing of defects have been made by assuming a simple annealing model of heat generation on the fault plane. Thermal energy was calculated to have been approximately 8 MJ/m2 to explain the profile of the heat‐affected region. Thermal energy was much larger than the one estimated from hydrothermal solution, and corresponded to the frictional heat calculated for a normal stress of 20 MPa, a displacement of 2 m, and a frictional coefficient of 0.2.
Millennium‐scale recurrent uplift inferred from beach deposits bordering the eastern Nankai Trough, Omaezaki area, central Japan
Authors: Fujiwara Osamu , Hirakawa Kazuomi , Irizuki Toshiaki , Hasegawa Shiro , Hase Yoshitaka , Uchida Jun‐ichi , Abe Kohei
Published: August 2010

A flight of Holocene marine terraces on the southwestern coast of Cape Omaezaki of central Japan provides evidence of recurrent millennium‐scale uplift events. We reconstructed the uplift history of these terraces by using facies analysis of drill core and geoslicer samples, environmental analysis of trace fossils, and 14C age determinations. Coastal uplift can be identified by the displacement of beach deposits such as foreshore deposits, which represent the intertidal swash zone of a wave‐dominated sandy coast. Three levels of former beach deposits facing the Nankai Trough were identified near the coast in the Omaezaki area. The highest of these, dated at about 3020–2880 BC, records a maximum of 2.2–2.7 m of emergence. The middle beach surface, of minimum age 370–190 BC, shows 1.6–2.8 m of emergence. The lowest beach surface, which is older than 1300–1370 AD, records 0.4–1.6 m of emergence. Our analysis of vertical crustal deformation data during the Holocene in this region suggests that rapid and strong uplift was restricted to the southwestern coast of the Omaezaki area and was probably caused by high‐angle thrusting on subsidiary faults branching from the underlying plate boundary megathrust.
Detailed measurements of thickness and grain size of a widespread onshore tsunami deposit in Phang‐nga Province, southwestern Thailand
Authors: Fujino Shigehiro , Naruse Hajime , Matsumoto Dan , Sakakura Norihiko , Suphawajruksakul Apichart , Jarupongsakul Thanawat
Published: August 2010

Measurements of thickness and grain size along flow‐parallel transects across onshore deposits of the 2004 Indian Ocean tsunami revealed macroscopic horizontal variations and provided new insights into tsunami sedimentation. The tsunami caused severe erosion of beaches, river mouths, and the shallow seafloor along the coast of southwestern Thailand and supplied sufficient sediment to deposit a kilometer‐wide blanket of sand on the land surface. The tsunami deposits generally fine landward with some fluctuations caused by local entrainment and settlement of sediments. Sediments of medium and fine sand are restricted to a few hundreds of meters inland from their source, whereas finer grained sediments were suspended longer and deposited 1 km or more inland. Although the thickness of the tsunami deposits is strongly influenced by local topography, they generally thin landward. In areas of low‐relief topography, the rate of landward thinning is exponential and reflects the dominance of sediment supply to nearshore areas over that to areas farther inland.
Sources and depositional processes of tsunami deposits: Analysis using foraminiferal tests and hydrodynamic verification
Authors: Uchida Jun‐Ichi , Fujiwara Osamu , Hasegawa Shiro , Kamataki Takanobu
Published: August 2010

Foraminiferal tests are commonly found in tsunami deposits and provide evidence of transport of sea floor sediments, sometimes from source areas more than 100 m deep and several kilometers away. These data contribute to estimates of the physical properties of tsunami waves, such as their amplitude and period. The tractive force of tsunami waves is inversely proportional to the water depth at sediment source areas, whereas the horizontal sediment transport distance by tsunami waves is proportional to the wave period and amplitude. We derived formulas for the amplitudes and periods of tsunami waves as functions of water depth at the sediment source area and sediment transport distance based on foraminiferal assemblages in tsunami deposits. We applied these formulas to derive wave amplitudes and periods from data on tsunami deposits in previous studies. For some examples, estimated wave parameters were reasonable matches for the actual tsunamis, although other cases had improbably large values. Such inconsistencies probably reflect: (i) local amplification of tsunami waves by submarine topography, such as submarine canyons; and (ii) errors in estimated water depth at the sediment source area and sediment transport distance, which mainly derive from insufficient identification of foraminiferal tests.