Seismicity changes related to a water injection experiment in the Nojima Fault Zone

Abstract A water injection experiment was carried out by the scientific drilling program named the 'Nojima Fault Zone Probe' during the two periods 9–13 February and 16–25 March 1997. The pumping pressure at the surface was approximately 4 MPa. The total amount of injected water was 258 m³. The injection was made between depths of 1480 m and 1670 m in the Disaster Prevention Research Institute, Kyoto University (DPRI) 1800 m borehole drilled into the Nojima Fault zone. A seismic observation network was deployed to monitor seismic activity related to the water injections. Seismicity suddenly increased in the region not far from the injection hole 4 or 5 days after the beginning of each water injection. These earthquakes were likely to be induced by the water injections. Most of the earthquakes had magnitudes ranging from −2 to +1. Numerous earthquakes occurred during the first injection, but only one could be reliably located and it was approximately 2 km north of the injection site. Between the two injection periods, earthquakes concentrated in the region approximately 1 km northwest of the injection site. During and after the second injection experiment, earthquakes were located approximately 1.5 km west of the injection site. Those earthquakes were located approximately 3 km or 4 km from the injection point and between 2 km and 4 km in depth. Values of intrinsic permeability of 10⁻¹⁴–10⁻¹⁵ m² were estimated from the time lapse of the induced seismic activity. The coefficient of friction in the area where the induced earthquakes occurred was estimated to be less than 0.3.     

Identification of the source caldera for the Middle Miocene ash-flow tuffs in the Kii Peninsula based on apatite trace-element composition

A large caldera cluster consisting of at least four calderas (Omine, Odai, Kumano-North and Kumano calderas) existed in the central–southern part of the Kii Peninsula approximately 14–15 Ma. On the other hand, thick Middle Miocene ash-flow tuffs, referred to as the Muro Ash-flow Tuff and the Sekibutsu Tuff Member, are distributed in the northern part of the Kii Peninsula. Although these tuffs are considered to have erupted from the caldera cluster in the central-southern Kii Peninsula, identifying the source caldera in the cluster has been controversial because of similarities in the petrological characteristics and identical radiometric ages of the volcaniclastic rocks of these calderas. We successfully discriminated the characteristics of the eruptive products of each caldera in the caldera cluster based on the apatite trace-element compositions of the pyroclastic dikes and ash-flow tuffs of the calderas. We also demonstrated that the source caldera of at least the lower main part of the Muro Ash-flow Tuff and the Sekibutsu Tuff Member was the Odai Caldera, which is located in the central Kii Peninsula. Our findings show possible correlations among the pyroclastic conduits and ash-flow tuffs of the caldera-fill and/or outflow deposits, even in cases where they have been densely welded and diagenetically altered. This method is useful for the study of deeply eroded ancient calderas.     

A complete introduction to the SCJ proposal and its commentary on the development of seismically resilient cities

In modern society, the population, wealth and social functions are increasingly concentrated in a few large cities. Such concentration brings about efficiency while at the same time it increases the vulnerability of the society. To address this issue, the Science Council of Japan (SCJ) published a proposal entitled “Shape Cities and Societies Safer against Severe Earthquakes”. It makes a variety of suggestions for enhancing the seismic resilience of large cities, including: (1) comprehensive thinking based on the latest scientific knowledge and rich imagination; (2) selection of sites suitable for residence and social activities; (3) introducing the urban seismic coefficient; (4) promoting the enhancement of the seismic performance of buildings and civil structures; (5) easing the concentration of population and functions; (6) building communities that enable shelter and escape; (7) resilient technology of information and communication system and its effective utilization; (8) preparation and implementation of emergency response after earthquakes; (9) development and application of new structural seismic technology; (10) learning from domestic and foreign earthquake disasters and launching of international cooperation and knowledge sharing and (11) taking actions from a multidisciplinary perspective. The proposal is introduced in this paper.     

Errors in response calculations for extensional vibrations of bars

The transient extensional vibrations of a slender and uniform bar, which is clamped at one end and is subjected to an axial force at the other free end, are investigated by applying three methods: the Laplace transform method, the normal mode and Newmark β methods in conjunction with the finite element method (FEM); the errors caused by the spatial discretization of the FEM and the direct integration of the Newmark β method are studied and compared with those of the previous paper where the flexural vibrations of a cantilever beam were considered. The reason why the extensional vibration problem is investigated here is that the condition seems to be severe due to the closeness of adjacent natural frequencies, the larger values of natural frequencies and the smaller number of nodal variables of the FEM in comparison with those of the flexural vibration problem. The numerical results show that the errors in response of the extensional vibration problem are large. However, if one follows the criterion proposed in this paper, accurate response is obtainable by the Newmark β method, which requires less computer time than either of the other methods mentioned above.     

A quenched carbonaceous composite (QCC) grain model for the interstellar 220 NM extinction hump

The dependence of the wavelength of peak absorption of dust grains on the grain size is investigated analytically by using an oscillator model for the absorption band. The peak wavelength of a weak absorption band is much less sensitive to the grain size than that of a strong band. This is explained by the fact that the surface mode, which is excited in the strong absorption band, is not raised in the weak absorption band. A quenched carbonaceous composite (QCC) synthesized from hydrocarbon plasma is found to have a weak absorption band at 220 nm. The absorption peak wavelength of the QCC grains falls well in the range of 217±7 nm even if the grain size runs from 5 to 100 nm. This is compatible with the observed constancy of the 220 nm hump (217±5 nm). By contrast, the absorption peak of graphite grains, which have a strong band around 280 nm and have been investigated as candidates for the hump, is very sensitive to the grain size. A quite narrow range of the grain size is required to account for the observed 220 nm feature. A weak absorption model, such as the QCC grains, is suggested to be a more likely candidate for the 220 nm extinction hump than a strong absorption model, such as graphite grains.Paper presented at the IAU Third Asian-Pacific Regional Meeting, held in Kyoto, Japan, between 30 September–6 October, 1984.     

Electrical conduction and polarization of calcite single crystals

The electrical conductivity and polarization properties of calcite single crystals with three orientations, namely, a (00.1) plane perpendicular to the crystallographic c axis (10.0) plane parallel to the crystallographic c axis, and a (10.4) cleavage plane, were studied by both complex impedance and thermally stimulated depolarization current (TSDC) measurements. Conductivities for (00.1)-, (10.0)-, and (10.4)-oriented single calcite crystals at 400–600?°C were 1.16?×?10^?7?–?1.05?×?10^?5, 7.40?×?10^?8?–?4.27?×?10^?6, and 4.27?×?10^?7?–?2.86?×?10^?5 Ω^?1 m^?1, respectively, and the activation energies for conduction were 112, 103, and 101?kJ?mol^?1, respectively. The TSDC spectra verified the electrical polarizability of calcite crystals. The activation energy for depolarization, estimated from TSDC spectra, of the (00.1)-, (10.0)-, and (10.4)-oriented calcite substrates were 112, 119, and 114?kJ?mol^?1, respectively. Considering the correlation between the processes of conduction and electric polarization, we proposed the mechanisms of conduction and polarization in calcite on the assumption of oxide ion transport.     

Radiocesium in Ponds in the Near Zone of Fukushima Dai-ichi NPP

The article presents the results of studying radiocesium concentration and distribution between dissolved and particulate forms in ponds in the near zone of Fukushima Dai-ichi NPP NPP after the 2011 accident. The total concentration of ¹³⁷Cs in pond water and its variations are shown to be largely governed by the concentration of particulate matter being as high as 68 Bq/L, compared with 5 Bq/L in solution. The values of the distribution coefficient K_d in the ponds are similar to those in rivers and in large flow-through lakes in the accidentally polluted zone at Fukushima Dai-ichi NPP. The contributions of the main competing ions K⁺ and NH ₄ ⁺ to radiocesium desorption from solid particles into solution were similar for the ponds; however, their relative effect on dissolved radiocesium concentration varied over time because of variations in ammonium concentration.     

Impacts of different diffusion scenarios for mitigation technology options and of model representations regarding renewables intermittency on evaluations of CO2 emissions reductions

This paper evaluated the impacts of climate change mitigation technology options on CO₂ emission reductions and the effects of model representations regarding renewable intermittency on the assessment of reduction by using a world energy systems model. First, different diffusion scenarios for carbon dioxide capture and storage (CCS), nuclear power, and wind power and solar PV are selected from EMF27 scenarios to analyze their impacts on CO₂ emission reductions. These technologies are important for reducing CO₂ intensity of electricity, and the impacts of their diffusion levels on mitigation costs are significant, according to the analyses. Availability of CCS in particular, among the three kinds of technologies, has a large impact on the marginal CO₂ abatement cost. In order to analyze effects of model representations regarding renewables intermittency, four different representations are assumed within the model. A simplistic model representation that does not take into consideration the intermittency of wind power and solar PV evaluates larger contributions of the energy sources than those evaluated by a model representation that takes intermittency into consideration. Appropriate consideration of renewables intermittency within global energy systems models will be important for realistic evaluations of climate change mitigation scenarios.     

Production and degradation of fluorescent dissolved organic matter derived from bacteria

Dynamics of fluorescent dissolved organic matter (FDOM) in ocean environments has received attention over the past few decades. Although it has appeared that in situ production of oceanic FDOM is mainly due to bacteria, the production and bio- and photodegradation processes of bacterial FDOM have not been elucidated. In this study, a culture experiment with bacteria was carried out to assess the production and biodegradation processes of bacterial FDOM. Photodegradation of bacterial FDOM and dissolved organic carbon (DOC) was also examined by exposure to a solar simulator. Bacterial FDOM consists of six components which were determined by parallel factor analysis (PARAFAC). Fluorescence intensities of protein-like FDOM increased with the bacterial biomass, but the increases of humic-like FDOM lagged behind the protein-like FDOM by 5–10 days. Exposure to simulated sunlight caused significant decreases in fluorescence intensities of all components; 52–94% of the initial intensities were lost during 24 h. While, the DOC concentration exhibited a small decrease through the experiment (1.9–11.1%). These results showed that photodegradability of bacteria derived DOC was much less than the fluorescence, indicating that the lifetime of bacteria-derived DOC is much longer than the length estimated by the fluorescence. The role of photobleached FDOM derived from bacteria may be significant in the biogeochemical cycle at the surface layer.     

The infrared and ultraviolet absorptions of micro-organisms and their relation to the Hoyle-Wickramashinghe hypothesis

Absorption of yeast andE. coli in the infrared and ultraviolet regions and that of diatomaceous soil in the infrared region have been obtained. Electron microscope photographs of aggregates ofE. coli have also been obtained. These results are discussed in relation to the Hoyle-Wickramasinghe hypothesis regarding the nature of interstellar grains.Department of Nuclear Engineering