Borehole water and hydrologic model around the Nojima fault, SW Japan

The active fault drilling at Nojima Hirabayashi after the 1995 Hyogoken-nanbu (Kobe) earthquake (M_JMA = 7.2) provides us with a unique opportunity to investigate subsurface fault structure and the in-situ properties of fault and fluid. The borehole intersected the fault gouge of the Nojima fault at a depth interval of 623 m to 625 m. The lithology is mostly Cretaceous granodiorite with some porphyry dikes.The fault core is highly permeable due to fracturing. The borehole water was sampled in 1996 and 2000 from the depth interval between 630 and 650 m, just below the fault core. The chemical and isotopic compositions were analyzed. Carbon and oxygen isotope ratios of carbonates from the fault core were analyzed to estimate the origin of fluid.The following conclusions were obtained. (1) The ionic and isotopic compositions of borehole water did not change from 1996 to 2000. They are mostly derived from local ground water as mentioned by Sato and Takahashi [Sato, T., Takahashi, M., 2000. Chemical and isotopic compositions of groundwater obtained from the Hirabayashi well. Geological Survey of Japan Interim Report No. EQ/00/1, 187–192.]. (2) Geochemical speciation revealed that the borehole water was derived from a relatively deep reservoir, which may be situated at a depth of 3 to 4 km where the temperature is about 80–90 °C. (3) The shallower part of the Nojima fault (shallower than the reservoir depth) has not been healed from the hydrological viewpoints 5 years after the event, in contrast to the rapid healing detected by S wave splitting [Tadokoro, K., Ando, M., 2002. Evidence for rapid fault healing derived from temporal changes in S wave splitting, Geophys. Res. Lett., 29, 10.1029/2001GL013644.]. (4) Precipitation of calcite from the present borehole water since drilling supports the idea of precipitation of some calcite in coseismic hydraulic fractures in the fault core [Boullier, A-M., Fujimoto, K., Ohtani, T., Roman-Ross, G., Lewin, E., Ito, H., Pezard, P., Ildefonse, B., 2004. Textural evidence for recent co-seismic circulation of fluids in the Nojima fault zone, Awaji Island, Japan., Tectonophysics, 378, 165–181.]. (5) Carbon and oxygen isotope ratios of calcite indicated that the meteoric water flux had been localized at the fault core. (6) A difference in the carbon isotope ratio between the footwall and the hanging wall suggests that the fault has been acted as a hydrologic barrier, although the permeability along the fault is still high.     

Long-term patterns in the diets of Japanese temperate bassLateolabrax japonicus larvae and juveniles in Chikugo estuarine nursery ground in Ariake Bay, Japan

Larval and juvenile Japanese temperate bass (Lateolabrax japonicus) samples were collected from a wide range of spatial gradients (covering a distance of approximately 30 km) in Chikugo estuary, Ariake Bay, Japan over a period of 8 yr (1997–2004) in order to observe changes in diet. Gut contents were studied by separating, identifying, counting, and estimating the dry weight of prey organisms. Copepod samples were collected during each cruise to observe the numerical composition, abundance, and biomass in the estuary. Considerable spatial and temporal variations were observed in copepod distributions in ambient water and the diets of the fish. Two distinctly different copepod assemblages were identified in the estuary: One in the upper estuarine turbidity maximum (ETM), dominated by a single speciesSinocalanus sinensis and the other in the lower estuary consisting of a multispecies assemblage, dominated byOithona davisae, Acartia omorii, Paracalanus parvus, andCalanus sinicus. The gut content composition of the fish in the upper estuary was dominated byS. sinensis, while in the lower estuary, it consisted ofP. parvus, O. davisae, andA. omorii. Within the size group analyzed (13.0–27.0 mm SL), the smaller individuals were found to feed on a mixed diet composed of smaller prey. The diets gradually shifted to bigger prey composed predominantly ofS. sinensis for larger size groups. Greater proportions of empty guts were recorded in the smaller individuals and dropped with increasing fish size. Higher dry biomass of copepods in the environment, as well as higher dry weights of gut contents, were recorded in the upper estuary, indicating that the upper estuarine ETM areas are important nursery grounds for the early life stages of the Japanese temperate bass. The early life stages of the Japanese temperate bass are adapted to use the upstream nursery grounds and ascending to the nursery areas to useS. sinensis is one of the key survival strategies of the Japanese temperate bass in the Chikugo estuary.     

A new direction finding technique for auroral VLF hiss based on the measurement of time differences of arrival at three spaced observing points

A newly developed direction finding (DF) technique for auroral hiss based on the measurement of time differences of wave arrival was carried out in 1978 at Syowa Station (geomag. lat. -70.4°), Antarctica and its two slave unmanned observing points located at about 20 km distances from Syowa. The auroral hiss signals (0.3–100 kHz) received at the two spaced points were transmitted to Syowa by a wide-band telemeter of 2 GHz. The arrival time difference of auroral hiss between Syowa and each spaced point was automatically determined by cross-correlating the waveforms of the received signals, and then the incident and azimuthal angles were measured with an accuracy of about 10°.It has been found that the new DF technique can determine localized exit regions at the ionospheric level which show rapid temporal movements. A comparison of the DF results with ground-based auroral data has shown that impulsive type auroral hiss with a wide-band frequency range has not emerged from the whole region of a bright aurora but from some localized regions of bright electron auroras at the ionospheric level, and that the arrival directions of auroral hiss change rapidly in accordance with the auroral movements.     

Comparative energetics analysis of CCM2 with different horizontal resolutions

 Comprehensive global energetics analysis is carried out for the NCAR CCM2 with different horizontal resolutions of R15, T42, T63, and T106 to assess the effect of various model truncations on the global energetics characteristics in climate models. Both the energy levels and energy transformations are examined over the zonal wave number domain during a northern winter and summer. In addition to the simulated atmosphere, the ECMWF global analysis during 1986 to 1990 is analyzed for comparison using the same diagnostic scheme. Previous studies have revealed that zonal kinetic energy is supplied by synoptic disturbances in terms of the zonal-wave interactions of kinetic energy. According to our result, however, such an energy flow from eddies to zonal motions is valid only for zonal wave numbers up to about 30. We find that the zonal-wave interactions of kinetic energy change sign beyond wave number 30 where the energy is transformed from zonal to eddies for both the ECMWF and CCM2-T106. The large-scale zonal motions are diffusive against the short waves beyond wave number 30, which may well be parameterized by various forms of the diffusion schemes. We suggest from this result that the atmospheric disturbances with wave numbers lower than 30 are necessary to represent accurately the two-way interactions between zonal and eddy motions, because these waves can actively influence the behavior of the zonal motions. Based on this finding, we suggest that the model resolution of R15 is inadequate for climate studies from the energetics point of view, and that resolution of T42 is the minimum requirement to represent the general circulation adequately. Some other discrepancies are discussed in detail for the coarse resolution climate models. Received: 15 July 1996/Accepted: 3 January 1997     

Spectral and intensity variations in cygnus X-3 by the Astronomical Netherlands Satellite

Measurements obtained with the Utrecht (1–8 keV) and Cambridge (1–28 keV) instruments on board the Astronomical Netherlands Satellite are discussed. Particularly, the 4.8 hr period is investigated.Paper presented at the COSPAR Symposium on Fast Transients in X- and Gamma-Rays, held at Varna, Bulgaria, 29–31 May, 1975.