A coastal acoustic tomography experiment in the Tokyo Bay

Eight sets of coastal acoustic tomography (CAT) systems were deployed during November 29 to December 10, 2002 at the coasts on both sides of Tokyo Bay to measure tidal current structures at 15-rain interval.Sound transmission across the Tokyo Bay (between Yokohama and Chiba)was successfillly traced,even under severe interference from ship generated wakes and bubbles.Tidal current fields changing from northward to southward flow are well reconstructed by the inverse analysis of travel-time difference data for a period with the best sound transmission condition. It is suggested that the CAT is the most powerful tool to continuously map tidal current fields in the coastal seas with heavy shipping traffic and fisheries activity.     

Interpretation of landslide distribution triggered by the 2005 Northern Pakistan earthquake using SPOT 5 imagery

The 2005 northern Pakistan earthquake (magnitude 7.6) of 8 October 2005 occurred in the northwestern part of the Himalayas. We interpreted landslides triggered by the earthquake using black-and-white 2.5-m-resolution System Pour l’Observation de la Terre 5 (SPOT 5) stereo images. As a result, the counts of 2,424 landslides were identified in the study area of 55 by 51 km. About 79% or 1,925 of the landslides were small (less than 0.5 ha in area), whereas 207 of the landslides (about 9%) were large (1 ha and more in area). Judging from our field survey, most of the small landslides are shallow rock falls and slides. However, the resolution and whitish image in the photos prevented interpreting the movement type and geomorphologic features of the landslide sites in detail. It is known that this earthquake took place along preexisting active reverse faults. The landslide distribution was mapped and superimposed on the crustal deformation detected by the environmental satellite/synthetic aperture radar (SAR) data, active faults map, geological map, and shuttle radar topography mission data. The landslide distribution showed the following characteristics: (1) Most of the landslides occurred on the hanging-wall side of the Balakot–Garhi fault; (2) greater than one third of the landslides occurred within 1 km from the active fault; (3) the greatest number of landslides (1,147 counts), landslide density (3.2 counts/km²), and landslide area ratio (2.3 ha/km²) was found within Miocene sandstone and siltstone, Precambrian schist and quartzite, and Eocene and Paleocene limestone and shale, respectively; (4) there was a slight trend that large landslides occurred on vertically convex slopes rather than on concave slopes; furthermore, large landslides occurred on steeper (30° and more) slopes than on gentler slopes; (5) many large landslides occurred on slopes facing S and SW directions, which is consistent with SAR-detected horizontal dominant direction of crustal deformation on the hanging wall.     

Evolving fluid composition during prograde metamorphism in subduction zones: A new approach using carbonate-bearing assemblages in the pelitic system

The changing XCO₂ in fluids during the progressive metamorphism in Sanbagawa belt of the Cretaceous subduction zone, Japan, was estimated by a newly proposed method. The subduction zone meta-sediments are characterized commonly by four-phase assemblages in the CaO–NaAlO₂–KAlO₂–Al₂O₃ system with excess quartz and a CO₂–H₂O binary fluid phase. Using the common assemblage of calcite–albite–muscovite–clinozoisite, XCO₂ of the fluid was estimated to be from about 0.0001–0.0005 (the lowest grade chlorite zone), through 0.004–0.01 (garnet zone), 0.01–0.05 (albite–biotite zone) to 0.06–0.2 (oligoclase–biotite zone).The paragenetic relationship of meta-sediments from the subduction zones was compared in a wide P–T range to cover the stability fields of aragonite and jadeite. As a result, an excellent P–T–XCO₂ relationship was delineated to serve as a quantitative monitor for the evolving fluid composition during the progressive metamorphism in subduction zones.     

Symmetropy of earthquake patterns: asymmetry and rotation in a disordered seismic source

We demonstrate that the idea of symmetropy can be used for quantification of earthquake patterns. The symmetropy can be considered as a measure of asymmetry. A pattern is richer in asymmetry when the symmetropy is smaller. The specific results of its applications are obtained as follows. In a discrete model of a seismic source with self-organized criticality, the spatial patterns of earthquakes during critical states and sub-critical states are distinguished by the behaviour of the symmetropy: sub-critical patterns show that the symmetropy is approximately a constant but this has various values during critical states. The critical patterns show asymmetric property without any asymmetric force from the outside and without asymmetric intracellular rule. We show that the emergence of asymmetric patterns is a generic feature of dynamic ruptures in our model. Such a generic asymmetry results from the model which is an inherently discrete system consisting of finite-sized cells. These cells may represent geometrical disordered fault zones. We further discuss rotational motions that generate seismic rotational waves. In micromorphic continuum theory, such rotations are attributed to dynamic ruptures in disordered systems. We note that the concept of disorder in this theory is expressed by a set of finite-sized microstructures and is consistent with the concept of disorder modelled in the present study. Thus, we suggest that the spatially asymmetric patterns of earthquakes might be related to the rotational motions, because both come from dynamic ruptures in a discrete fault zone without a well-defined continuum limit.     

Viscoelastic behaviour and temporal fractal properties of lherzolite and marble: possible extrapolation from experimental results to the geological time-scale

The viscoelastic relaxation behaviour of lherzolite and marble and their temporal fractal properties are studied. Based on the high‐temperature viscoelastic behaviour for these rock types derived from the time–temperature superposition principle, the relaxation function for the viscoelastic behaviour of lherzolite and marble can be expressed as a flow law from a power‐law function of temperature‐reduced time given by normalizing the various temperature behaviours, with a non‐integer exponent. The relaxation function is thus time‐scale invariant, i.e. there is a temporal fractal property to the temperature‐reduced time. Their rheological behaviour over geological time‐scales at low temperature can be extrapolated from the experimental high‐temperature behaviour based on the temporal fractal property. Our derived flow law satisfies not only transient behaviour but also steady‐state behaviour.     

Evidence of Microbial Activity in the Formation of Manganese Wads at the Asahidake Hot Spring in Hokkaido, Japan

Abstract. Mt. Asahidake is an active volcano, with more than 90 active wells, in the Daisetsu volcanic group located in central Hokkaido, Japan. Wells along the Yukomanbetsu-sawa River showed high manganese concentrations and associated manganese deposits. These deposits consist of manganese oxides, and the concentration of iron is very low except for one sample collected from the upper reach of the river. Most of the wet samples showed basal diffraction characteristic of todorokite (9.6 Å). Cultivation tests showed that microorganisms were responsible for the oxidation of dissolved Mn²⁺ in the Asahidake hot spring. The dissolved Mn²⁺ concentration in the sterilized hot spring water was unchanged after four days, whereas the Mn²⁺ concentration in the sterilized hot spring water with a small amount of fresh manganese wad was decreased to zero after three days, and manganese oxide formed. This result implies that the activity of microorganism oxidizes dissolved Mn²⁺ and forms manganese oxide at the Asahidake manganese deposits. In addition to Komanoyu hot spring and Yunotaki Falls, this is the third report of microbial activity forming considerable deposits of manganese oxides in hot spring waters.     

Relationships between Volcanism, Hydrothermal Alteration and Epithermal Gold-Silver Mineralization in the Muka Mine Area in the Kitami Metallogenic Province, Hokkaido, Japan

Abstract: Neogene magmatism in the Muka mine area in the Kitami metallogenic province was characterized on the basis of K-Ar age data by felsic–to–mafic terrestrial extrusive and intrusive volcanism from Late Miocene to Early Pliocene. The geology of the Muka mine area comprises the Upper Cretaceous-Paleocene Yubetsu Group, consisting primarily of sandstone and shale; Upper Miocene Ikutahara Formation, consisting of clastic and felsic volcaniclastic rocks and Kane-hana Lava (rhyolite) of 7. 5 Ma; Upper Miocene Yahagi Formation, consisting of clastics, felsic volcaniclastics and rhyolite lavas; Late Miocene andesite and rhyolite dikes (Chidanosawa Rhyolite of 7. 2 Ma and Hon-Mukagawa Andesite of 6. 6 Ma); Lower Pliocene Hakugindai Lava (basalt: 4. 0 Ma); and Quaternary System. The volcanism consists of earlier Late Miocene felsic extrusive activity during the sedimentation of the Ikutahara Formation, later Late Miocene felsic extrusive and intrusive activities during the sedimentation of the Yahagi Formation and intermediate intrusive activity after the sedimentation of the Yahagi Formation and Early Pliocene mafic extrusive activity. The Muka gold-silver ore deposit occurs primarily in the felsic volcaniclastic rocks and Kanehana Lava of the Ikutahara Formation and in Hon-Mukagawa Andesite. These wall–rocks, the clastic rocks of the Ikutahara Formation and the clastic and felsic volcaniclastic rocks of the Yahagi Formation were affected to various extents by hydrothermal alteration. The hydrother-mal alteration can be divided into two stages (early and late) based on the modes of occurrence and mineral assemblages. Early hydrothermal alteration is characterized by regional and vein-related alterations associated with epithermal gold-silver mineralization in a near-neutral hydrothermal system. Regional alteration can be subdivided into a zeolite zone (mordenite+adularia±heulandite–clinoptilolite series mineral±smectite±quartz°Cristobalite±opal–CT) and a smectite zone (smec–tite±quartz±opal–CT). Vein-related alteration can be subdivided into a K-feldspar zone (quartz+adularia±illite±interstratified illite/smectite±pyrite), an illite zone (quartz+illite°Chlorite±interstratified illite/smectite±smectite±pyrite) and an interstratified illite/smectite zone (quartz+interstratified illite/smectite±smectite±pyrite). The adularization age of 6. 8 Ma in the K-feldspar zone that developed in Kanehana Lava hosting ore veins coincides well with the epithermal gold-silver mineralization age of 6. 6 Ma. Late hydrothermal alteration is characterized by a kaolinite zone (kaolinite±dickite±alunite±quartz°Cristobalite± tridymite±pyrite) in an acid hydrothermal system, and cuts early alteration zones such as the K-feldspar zone. Other modes of occurrence of acid alteration are a 7Å halloysite-kaolinite vein in the hydrothermal explosion breccia dike and smectite–kaoli–nite veins along joint planes of Kanehana Lava. The style of the gold-silver deposit associated with early near-neutral hydrothermal alteration is a low-sulfidation epithermal type. The low-sulfidation epithermal gold-silver mineralization of 6. 6 Ma in the vicinity of the Muka ore deposit was essentially accompanied by felsic volcanic activity during the sedimentation of the Yahagi Formation, and was closely related both temporally and spatially to the felsic intrusive activity of Chidanosawa Rhyolite of 7. 2 Ma. The related hydrother-mal activity of the gold-silver mineralization took place at intervals of approximately 0. 4–0. 6 Ma after the volcanic activity related to the mineralization.     

Construction of a genomic DNA library with a TA vector and its application in cloning of the phytoene synthase gene from the cyanobacteriumSpirulina platensis M-135

INTRODUCTIONThesignalproaningschemeofmostpnsentsonarsyStasuChaseChosounder,fishfinder,etc.,deteCtsthesignaIsaanrdingt0theamPlitudethasholdafterthefilter.However,inacomplicatalandfrequenhychangingunderotCfacousticalchanne,thesta-bilityandreiabilityofthiskindofsonarsySteIndroeshamlyasanysySthenoisewhleadt0anindedion.AmplitudefaderesultingfromstrongsignalfluCtuationcauseslossofdata.InsomesyStetnS,suchasndnelocatingsonar,highrangingamCyisneded,soasinglededionschernecann0tadapttoit.Resul…     

Geothermal constraints on the hydrological regime of the TAG active hydrothermal mound, inferred from long-term monitoring

During August 1994 to March 1995, a period that included ODP Leg 158 drilling, bottom-water and sub-bottom temperatures were continuously logged by a long-term temperature monitoring system ‘Daibutsu’ at the base of the central black-smoker complex (CBC) and within the low heat flow zone at the TAG hydrothermal mound on the Mid-Atlantic Ridge. The temperature of hydrothermal fluid at CBC was also measured with a small high-temperature probe ‘Hobo’. Bottom-water temperature variations measured with Daibutsu at both sites have predominant semi-diurnal periods, causing the sub-bottom temperatures to fluctuate at these periods with reduced amplitudes and phase delays at sub-bottom depths. Seawater entrainment into the mound has been previously suggested at the low heat flow zone. We quantitatively evaluate the seawater entrainment rate at both sites from a one-dimensional numerical model, combined with a heat conduction model for the semi-diurnal variations. The entrainment rate of seawater at the base of CBC is estimated as 1.3±0.5×10⁻⁵ m/s, at least from August 17 to 30, 1994. On the other hand, the seawater entrainment rate at the low heat flow zone was undetected by long-term temperature monitoring at shallow sub-bottom depth. Nevertheless an increase in heat flow observed at the low heat flow zone during ODP drilling can be interpreted as a decrease in the entrainment rate of seawater. Before ODP Leg 158, Daibutsu measured three sub-bottom temperature anomalies at the base of CBC not derived from bottom-water temperature variations and Hobo also detected a CBC fluid temperature anomaly, indicating some natural changes in fluid flow within the mound. Daibutsu and Hobo also measured temperature anomalies during and after drilling at the ODP TAG-1 area. The Hobo temperature anomalies are inferred to have occurred when the cold fluid entrained through the drill holes at TAG-1 site reached or cooled the main fluid path to CBC. The entrained seawater through the drill holes appears to have contributed to dissolution and precipitation of anhydrite within the mound and perhaps affected the local permeability structure inside the mound. The temperature anomalies measured with Daibutsu at the base of CBC may have been induced by the change in the fluid flow pattern as a result of such permeability changes within the mound.