Seasonal changes in the sediment flux on steep hillslopes in a humid diurnal frost environment          下载免费PDF全文

Fumitoshi Imaizumi  Osamu Suzuki  Asako Togari‐Ohta 《地球表面变化过程与地形》2017,42(3):389-398

  相似文献   

Devonian–Carboniferous slivers within the basement area of north-east Oscar II Land, Spitsbergen     

Yoshihide Ohta  Claude Lepvrier  Friedhelm Thiedig 《Polar research》2000,19(2):217-226

Formed during an early compressional period in the opening of North Atlantic Ocean, a Tertiary fold-thrust belt extends along the mid-to- southern part of the western coast of Spitsbergen. Complex thrust structures involve the basement (Caledonian and older) and many shallow dipping thrust faults dissect the overlying cover rocks (Devonian and younger) in Oscar II Land in the northern part of the belt. Some of these faults occur within the basement rocks with slivers or fault blocks of the cover rocks from south-western Brøggerhalvøya to innermost St. Jonsfjorden in north-eastern Oscar II Land. Six of the slivers contain Carboniferous rocks and one is a fault-bounded block with Devonian rocks. These steeply west-dipping faults form a complex fault system- EOFC (Engelskbukta-Osbornbreen Fault Complex) - within the basement area. The lithological units of the basement are separated by faults within the EOFC, which is structurally continuous with the Brøggerhalvøya fold-thrust zone to the north and is thought to continue to the fold-thrust zone on the south-eastern coast of St. Jonsfjorden. Some previous authors considered that the two lithologically contrasting Vendian diamictites and intervening Moefjellet Formation are stratigraphically continuous and defined two separate tilloid successions in the present area. This interpretation has been extended over the whole of western Spitsbergen. However, the present study indicates that these two tilloid formations and the Moefjellet Formation are separated by the faults, probably thrusts, within the EOFC and are not in a continuous stratigraphic relation. Therefore, the two-stage history of Vendian glaciation seems questionable.  相似文献   

Overview of the 1990–1995 eruption at Unzen Volcano     

Setsuya Nakada  Hiroshi Shimizu  Kazuya Ohta 《Journal of Volcanology and Geothermal Research》1999,89(1-4)

Following 198 years of dormancy, a small phreatic eruption started at the summit of Unzen Volcano (Mt. Fugen) in November 1990. A swarm of volcano-tectonic (VT) earthquakes had begun below the western flank of the volcano a year before this eruption, and isolated tremor occurred below the summit shortly before it. The focus of VT events had migrated eastward to the summit and became shallower. Following a period of phreatic activity, phreatomagmatic eruptions began in February 1991, became larger with time, and developed into a dacite dome eruption in May 1991 that lasted approximately 4 years. The emergence of the dome followed inflation, demagnetization and a swarm of high-frequency (HF) earthquakes in the crater area. After the dome appeared, activity of the VT earthquakes and the summit HF events was replaced largely by low-frequency (LF) earthquakes. Magma was discharged nearly continuously through the period of dome growth, and the rate decreased roughly with time. The lava dome grew in an unstable form on the shoulder of Mt. Fugen, with repeating partial collapses. The growth was exogenous when the lava effusion rate was high, and endogenous when low. A total of 13 lobes grew as a result of exogenous growth. Vigorous swarms of LF earthquakes occurred just prior to each lobe extrusion. Endogenous growth was accompanied by strong deformation of the crater floor and HF and LF earthquakes. By repeated exogenous and endogenous growth, a large dome was formed over the crater. Pyroclastic flows frequently descended to the northeast, east, and southeast, and their deposits extensively covered the eastern slope and flank of Mt. Fugen. Major pyroclastic flows took place when the lava effusion rate was high. Small vulcanian explosions were limited in the initial stage of dome growth. One of them occurred following collapse of the dome. The total volume of magma erupted was 2.1×10⁸ m³ (dense-rock-equivalent); about a half of this volume remained as a lava dome at the summit (1.2 km long, 0.8 km wide and 230–540 m high). The eruption finished with extrusion of a spine at the endogenous dome top. Several monitoring results convinced us that the eruption had come to an end: the minimal levels of both seismicity and rockfalls, no discharge of magma, the minimal SO₂ flux, and cessation of subsidence of the western flank of the volcano. The dome started slow deformation and cooling after the halt of magma effusion in February 1995.  相似文献   

Estimation of spectral refractive index of colloidal sulfur at 20°C     

Tsuyoshi Samukawa  Masamitsu Onitsuka  Kazuyuki Ohta  Mamoru Tominaga  Hidenori Yoshiyama 《Journal of Oceanography》1992,48(2):129-138

In the marine environment, colloidal sulfurs often occur due to the redox reaction of sulfide ions and oxygen molecules. It is important to know the spectral refractive index of colloidal sulfurs for the discussion of the light scattering in the region where colloidal sulfurs are formed. We presented new methods to estimate the refractive index from the wave length of maximum absorbance (turbidity) of a nearly mono-dispersed colloidal solution. In these methods, the ripples in a first main maximum of the scattering efficiency,Q _sca , were taken into consideration. By virtue of these methods, we obtained the spectral refractive index of colloidal sulfurs,m _s (), at 20°C. The Cauchy's expression of it was given by

相似文献    115. Spatial structure within a dense bed of the brittle starOphiura sarsi (Ophiuroidea: Echinodermata) in the bathyal zone off otsuchi,Northeastern Japan      Toshihiko Fujita  Suguru Ohta 《Journal of Oceanography》1989,45(5):289-300 Photographic observations of the brittle starOphiura sarsi were conducted at a depth of approximately 280 m in the Pacific Ocean off tsuchi, northeastern Japan. Bottom photographs showed that this ophiuroid occurred in high densities, uniformly covering the sea floor and that other megafauna was rare. The mean density and biomass of ophiuroids in the dense bed were estimated to be 373 m–2 and 124 g m–2, respectively. Ophiuroids comprised 99% of all megabenthic organisms in terms of number of individuals, and megafaunal assemblage of the dense bed showed very low species diversity.O. sarsi exhibited a regular spatial pattern avoiding contact with conspecific neighbors. This regular spatial pattern was disrupted by certain other organisms, around which halo-like, bare areas were observed. The size and shape of these halo-like areas varied and were apparently related to the body size and/or motility of the organisms. In the present observation areaO. sarsi covered 96% of the sea bottom, and the remaining 4% was occupied by other organisms and their halo-like bare areas.  相似文献    116. RFLP analysis of a mitochondrial gene,cytochrome oxidase I (COI) of three species of the genusCalyptogena around Japan      Shigeaki Kojima  Takanori Kobayashi  Jun Hashimoto  Suguru Ohta 《Journal of Oceanography》1995,51(2):257-259 Phylogenetic relationship among three species of deep-sea vesicomyid bivalvesCalyptogena, i.e.,C. soyoae, C. solidissima, C. fausta and an undescribed species of the Iheya Ridge, Okinawa Trough was analyzed on the basis of the RFLP analysis of the fragment (about 1 kbp) of cytochrome oxidase I. Both the two populations ofC. soyoae (off Hatsushima and Okinoyama Bank, Sagami Bay) consisted of two haplotypes, which could be discriminated by only one restriction site (1.7% sequence divergence).Calyptogena of the Iheya Ridge could not be distinguished from one of the two haplotypes ofC. soyoae. Nucleotide substitution rates between species were calculated and dendrograms were constructed.  相似文献    117. Clinopyroxene phenocrysts (with green salite cores) in trachybasalts: implications for two magma chambers under the Kokchetav UHP massif, North Kazakhstan      Yongfeng Zhu  Yoshihide Ogasawara 《Journal of Asian Earth Sciences》2004,22(5):517 Clinopyroxene phenocrysts in the Kokchetav trachybasalts are variable in composition and textures. Two distinctive cores are recognized: diopside cores and green salite cores. The diopside cores with Mg# of 80–90 are mantled by colorless salite rims with Mg# of 70–80. The green salite cores have especially low Mg# (<70) but high Al and Ti contents. A Mg-rich band (Mg#=82–90) usually occurs between a green salite core and its rim, and/or between a colorless salite mantle and its rim. Dissolution surfaces are observed on all textural variants. Two magma chambers are needed to explain the observed clinopyroxene phenocrysts. A deep chamber at about 120 km in the upper mantle in which diopside cores crystallized, and a shallow chamber at depths of less than 40 km in which diopside cores were resorbed and overgrown by salite rims or mantles. Magma mixing in the shallow chamber is responsible for the formation of dissolution surfaces between the diopside bands and the colorless salite mantles. The dissolution surfaces on the diopside cores formed in the shallow chamber as a result of pressure decrease. This magma evolution scenario is complicated by the occurrence of the crustal-origin green salite cores in diopsides. These green cores likely represent the relics of continental materials, which were captured in the deep chamber and partially re-melted. Our observations indicate that subducted continental materials were returned to the Earth's surface as a result of magmatism. This study therefore provides direct evidence of a link between subducted continental materials (slab) and magmatism in this orogenic belt.  相似文献    118. Shear wave velocity measurement during a standard penetration test      Yutaka Ohta  Noritoshi Goto  Hiroshi Kagami  Keishi Shiono 《地震工程与结构动力学》1978,6(1):43-50 An experiment was carried out to develop a technique to measure shear wave velocity simultaneously with the standard penetration test popular in soil engineering. In the standard penetration test an impact at the bottom of a borehole is produced by weight dropping and may be expected to generate seismic waves. A three-component geophone was set on the ground surface near the borehole and the waves generated were recorded with a magnetic recorder at successive depths of the penetration test. The predominance of the SV wave obtained with this simple method was assured by measurement of the particle orbit. Signal amplitudes decrease with depth and become less than the noise level at a certain depth. Therefore records from deeper sources must be processed to disclose the shear waves. Since waveforms of SV events generated by blows of the penetration test at a given depth are very similar, the signal to noise ratio would be expected to be improved by a stack of wave trains. A paste-up of the radial component after stacking was compared with that before stacking and a refinement was clearly recognized. A vertical distribution of shear wave velocity was obtained by reading the onset time at each depth. Shear wave velocities thus obtained were compared with N values from the standard penetration test and specific resistivities from electrical logging in the same borehole. The data were mutually consistent. This experiment showed that a convenient, precise shear wave velocity measurement can be conducted during the routine work of a standard penetration test.  相似文献    119. Correlation between dissolved He concentration and Cl in groundwater at Äspö, Sweden      Yasunori Mahara  Takuma Hasegawa  Kimio Miyakawa  Tomoko Ohta 《Applied Geochemistry》2008,23(12):3305-3320 Tunnel excavation at Äspö Island, Sweden, has caused severe groundwater disturbance, gradually extending deeper into the tunnel as present-day Baltic seawater intrudes through fractures connecting to the surface. However, the paleo-hydrogeochemical conditions have remained in the deep highly saline waters that have avoided mixing. A correlation has been observed between dissolved 4He concentration and Cl− ion concentration, measured every two years from 1995 to 2001 at Äspö. Groundwater mixing conditions can be examined by the correlations between 1/Cl, 36Cl/Cl, and 3H concentrations. Subsurface production is responsible for the majority of the 36Cl and excess dissolved 4He of interstitial groundwater in fractures. The secular equilibrium ratio of 36Cl/Cl in rock was theoretically estimated to be (5.05 ± 0.82) × 10−14 based on the neutron flux intensity, a value comparable to the measured 36Cl/Cl ratio in rock and groundwater. The degassing crustal 4He flux was estimated to be 2.9 × 10−8  1.3 × 10−6 (ccSTP/cm2a) using the HTO diffusion coefficient for the Äspö diorite. The 4He accumulation rate ranges from 6.8 × 10−10 (for the in situ accumulation rate) to 7.0 × 10−9 (ccSTP/(gwater · a) considering both 4He in situ production and the degassing flux, assuming 4He is accumulated constantly in groundwater. By comparing the subsurface 36Cl increase with 4He concentrations in groundwater, the 4He accumulation rate was determined from data for groundwater arriving at the secular equilibrium of 36Cl/Cl. The 4He accumulation rate was found to be (1.83 ± 0.72) × 10−8 ccSTP/(gwater · a) without determining the magnitude of degassing 4He flux.  相似文献    120. Factors affecting rainfall interception determined by a forest simulator and numerical model      T. Toba  T. Ohta 《水文研究》2008,22(14):2634-2643 To elucidate the factors involved in interception loss, we conducted experiments in which we measured environmental variables such as rainfall intensity, forest structure, and weather conditions. An artificial forest consisting of 24 vinyl trees was used to examine the influences of forest structure and rainfall conditions on interception loss. The interception rate was higher at higher plant area index (PAI) values and wind speeds and lower with greater rainfall intensity. We confirmed the factors affecting interception loss by using an interception model based on the tank model. The artificial forest simulations provide new evidence that interception loss is influenced by the PAI, rainfall intensity, saturation deficit, and wind speed. The effect of the saturation deficit on the interception rate was unclear from the experimental results, but the single‐tank model revealed that wind speed strongly influences the effects of the saturation deficit on interception loss. Thus, whereas interception loss was not significantly affected by the saturation deficit at low wind speeds, it increased significantly with the saturation deficit under windy conditions. The model simulation also showed the sensitivity of each factor with regard to the interception rate. The sensitivity of rainfall intensity decreased as the PAI increased, and the sensitivity of the saturation deficit increased as the wind speed increased. The experiments and model calculations clarified the main elements affecting interception loss and their sensitivities. Compared with previous studies on interception loss, this study revealed a positive relationship between the PAI and interception loss, a negative exponential relationship with rainfall intensity, and the effects of the saturation deficit on interception loss. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献    [首页] « 上一页 [4] [5] [6] [7] [8] [9] [10] [11] 12 [13] 下一页 » 末  页»