Effects of slope gradient on runoff from bare-fallow purple soil in China under natural rainfall conditions     

Yoshitaka Komatsu  Hiroaki Kato  Bo Zhu  Tao Wang  Fan Yang  Randeep Rakwal  Yuichi Onda 《山地科学学报》2018,15(4):738-751

Purple soil is highly susceptible for overland flow and surface erosion, therefore understanding surface runoff and soil erosion processes in the purple soil region are important to mitigate flooding and erosion hazards. Slope angle is an important parameter that affects the magnitude of runoff and thus surface erosion in hilly landscapes or bare land area. However, the effect of slope on runoff generation remains unclear in many different soils including Chinese purple soil. The aim of this study was to investigate the relationship between different slope gradients and surface runoff for bare-fallow purple soil, using 5 m × 1.5 m experimental plots under natural rainfall conditions. Four experimental plots(10°, 16°, 20° and 26°) were established in theYanting Agro-ecological Experimental Station of Chinese Academy of Science in central Sichuan Basin. The plot was equipped with water storage tank to monitor water level change. Field monitoring from July 1 to October 31, 2012 observed 42 rainfall events which produced surface runoff from the experimental plots. These water level changes were converted to runoff. The representative eight rainfall events were selected for further analysis, the relationship between slope and runoff coefficient were determined using ANOVA, F-test, and z-score analysis. The results indicated a strong correlation between rainfall and runoff in cumulative amount basis. The mean value of the measured runoff coefficient for four experimental plots was around 0.1. However, no statistically significant relationship was found between slope and runoff coefficient. We reviewed the relationship between slope and runoff in many previous studiesand calculated z-score to compare with our experimental results. The results of z-score analysis indicated that both positive and negative effects of slope on runoff coefficient were obtained, however a moderate gradient(16°-20° in this study) could be a threshold of runoff generation for many different soils including the Chinese purple soil.  相似文献   

钢板桩挡墙主动土压力分布的形状效应   总被引：1，自引：0，他引：1  

刘芳  张国庆  蒋明镜  熊巨华  中山裕章 《岩土力学》2012,33(Z1):315-320

采用有限元数值试验,研究帽型钢板桩的截面形状对墙后主动土压力分布规律的影响。首先,对室内缩尺模型试验进行数值模拟,对比实测数据验证数值模型的有效性;然后,建立钢板桩挡墙数值模型,模拟该挡墙在不同位移模式下土压力变化和分布的规律,与平板挡墙计算结果进行对比,分析钢板桩截面形状对土压力分布的影响,进一步探讨形状效应的可能影响因素及机制。分析结果表明,钢板桩的截面形状影响墙后主动土压力的分布形式,影响程度与位移模式有关;墙体平动和绕墙底转动情况下,钢板桩挡墙凸出部分的主动土压力值大于凹处,但墙体绕墙顶转动情况下差异不明显;主动土压力的形状效应由土拱效应引起,截面高宽比对其影响显著,墙土摩擦角影响有限。  相似文献   

Brownish discoloration of the summit crater lake of Mt. Shinmoe-dake,Kirishima Volcano,Japan: volcanic–microbial coupled origin     

Shinji Ohsawa  Kenji Sugimori  Hiroshi Yamauchi  Tomoyuki Koeda  Hiroaki Inaba  Yoshihisa Kataoka  Tsuneomi Kagiyama 《Bulletin of Volcanology》2014,76(5):1-10

A drastic change in lake water color from blue-green to brown was observed in the summit crater lake of Mt. Shinmoe-dake, Kirishima Volcano about 8 months after its 2008 eruption. The color change lasted for about 2 months (April–June 2009). The discoloration was attributed to a brownish color suspension that had formed in the lake water. X-ray fluorescence and Fourier transform infrared analyses of a sample of the suspension identified schwertmannite (Fe₈O₈(OH)₆(SO₄)). A cultivation test of iron-oxidizing bacteria for the sampled lake water with lakebed sediment revealed that the crater lake hosts iron-oxidizing bacteria, which likely participated in schwertmannite formation. We suggest that pyrite (FeS₂) provided an energy source for the iron-oxidizing bacteria since the mineral was identified in hydrothermally altered tephra ejected by the August 2008 eruption. From consideration of these and other factors, the brownish discoloration of the summit crater lake of Mt. Shinmoe-dake was inferred to have resulted from a combined volcanic–microbial process.  相似文献   

Sudden strong current generated by an eddy in the eastern part of Wakasa Bay,Japan     

Atsushi Kaneda  Kouta Ayukawa  Naoki Hirose  Jun Tsuzuki  Yutaka Kumaki  Tomoharu Senjyu  Yosuke Igeta  Tatsuro Watanabe 《Journal of Oceanography》2017,73(2):181-192

A sudden strong coastal current called a “kyucho” occurred in August 2013 in the eastern coastal waters of Wakasa Bay, Japan. This study examined its characteristics based on both observational data collected by intensive field investigations and the simulation results of a numerical model. The field investigations comprised moored buoy observations near the coast and voyages by a research vessels and fishing boats. The mooring observations indicated that a current speed exceeding 50 cm s^?1 occurred abruptly near the eastern coast of the bay, in association with a synchronous change in the current direction. Data collected by acoustic Doppler current profilers (ACDPs) mounted on the vessels showed that a clockwise eddy existed in the bay and that the current on the east side of the eddy generated the kyucho near the coast. Based on the results of the numerical model and the analysis of the ADCP data, it was considered that the clockwise eddy was generated by a strong current at the tip of the Tango Peninsula, in the western part of the bay. As the eddy propagated from west to east across the bay, it induced the kyucho in the coastal waters in the east of the bay.  相似文献   

Phytoplankton community structure,as derived from pigment signatures,in the Kuroshio Extension and adjacent regions in winter and spring     

Yuta Nishibe  Kazutaka Takahashi  Mitsuhide Sato  Taketoshi Kodama  Shigeho Kakehi  Hiroaki Saito  Ken Furuya 《Journal of Oceanography》2017,73(4):463-478

The relationships between the spatiotemporal variation in phytoplankton community structure and environmental variables were investigated in the Kuroshio Extension (KE) region from winter to spring by analysing biomarker pigments. In winter, when the mixed layer was deep, phytoplankton communities were characterised by low biomass and a relatively high dominance of cryptophytes, followed by chlorophytes and pelagophytes. In spring, phytoplankton biomass generally increased with shoaling of the mixed layer. In April, when nitrate was not exhausted, chlorophytes became the most dominant group throughout the KE region, followed by cryptophytes. In May, in the south of the KE, phytoplankton biomass decreased with the depletion of nitrate and cyanobacteria dominated, whereas at the northern edge of the KE, phytoplankton biomass remained high. A predominance of diatoms occurred sporadically at the northern edge of the first ridge with a shallow mixed layer and an elevated nutricline. In contrast, the contribution of diatoms was low at the northern edge of the second ridge, despite high levels of nitrate and silicic acid, suggesting that factors other than macronutrient depletion limited diatom production. In general, the contribution of diatoms to the total phytoplankton biomass in the KE region was small in both winter (2.9%) and spring (16%). This study showed that the phytoplankton communities in the KE region during the spring bloom were generally composed of non-diatom phytoplankton groups, chlorophytes, cryptophytes, and prasinophytes. It is necessary to identify the roles of non-diatoms in grazing food chains to more accurately evaluate the KE as a nursery area for pelagic fish.  相似文献   

The Mg-carbonate-Fe interaction:Implication for the fate of subducted carbonates and formation of diamond in the lower mantle     

Naira S.Martirosyan  Konstantin D.Litasov  Sergey S.Lobanov  Alexander F.Goncharov  Anton Shatskiy  Hiroaki Ohfuji  Vitali Prakapenka 《地学前缘(英文版)》2019,10(4):1449-1458

The fate of subducted carbonates in the lower mantle and at the core-mantle boundary was modelled via experiments in the MgCO3-Fe^0 system at 70-150 GPa and 800-2600 Kin a laser-heated diamond anvil cell.Using in situ synchrotro n X-ray diffraction and ex situ transmission electron microscopy we show that the reduction of Mg-carbonate can be exemplified by:6 MgCO3+19 Fe=8 FeO+10(Mg0.6Fe^0.4)O+Fe7 C3+3 C.The presented results suggest that the interaction of carbonates with Fe^0 or Fe^0-bearing rocks can produce Fe-carbide and diamond,which can accumulate in the D"region,depending on its carbon to Fe ratio.Due to the sluggish kinetics of the transformation,diamond can remain metastable at the core-mantle boundary(CMB)unless it is in a direct contact with Fe-metal.In addition,it can be remobilized by redox melting accompanying the generation of mantle plumes.  相似文献   

In situ stress measurements in a borehole close to the Nojima Fault   总被引：1，自引：0，他引：1  

Hiroaki Tsukahara  Ryuji Ikeda  Kiyohiko Yamamoto 《Island Arc》2001,10(3-4):261-265

Abstract In situ stress was measured close to the fault associated with the 1995 Kobe Earthquake (Hyogo-ken Nanbu earthquake; January 1995; M 7.2) 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.  相似文献   

准噶尔板块东北缘富铌玄武岩的发现及其地质意义   总被引：4，自引：0，他引：4       下载免费PDF全文

张海祥  牛贺才  于学元  单强  HiroakiSato  JunichiIto 《地质找矿论丛》2003,18(1):71-72

富铌玄武岩是硅过饱和,富Ｎａ2Ｏ,ＴｉＯ2,Ｐ2Ｏ5,同时富集高场强元素的一类岛弧玄武岩,这类玄武岩的ｗ(Ｎｂ)>7×10-6,(ｗ(Ｌａ)/ｗ(Ｎｂ))ＭＮ<2。它是由来源于70100ｋｍ深处、受ａｄａｋｉｔｅ熔体交代过的地幔楔橄榄岩部分熔融形成的,是大洋板块俯冲作用的产物。目前发现的富铌玄武岩大多分布在环太平洋新生代岛弧环境,与洋壳俯冲作用密切相关[1 5]。本研究在准噶尔板块东北缘富蕴县的索尔库都克附近首次发现了富铌玄武岩。它产于下泥盆统托让格库都克组中、上部。该地层自下而上的岩石组合为:玄武岩 火山凝灰角砾岩 火山集块岩 含…  相似文献   

Structural characteristics off Miyagi forearc region, the Japan Trench seismogenic zone, deduced from a wide-angle reflection and refraction study   总被引：4，自引：0，他引：4  

Seiichi Miura  Narumi Takahashi  Ayako Nakanishi  Tetsuro Tsuru  Shuichi Kodaira  Yoshiyuki Kaneda 《Tectonophysics》2005,407(3-4):165-188

The Japan Trench subduction zone, located east of NE Japan, has regional variation in seismicity. Many large earthquakes occurred in the northern part of Japan Trench, but few in the southern part. Off Miyagi region is in the middle of the Japan Trench, where the large earthquakes (M > 7) with thrust mechanisms have occurred at an interval of about 40 years in two parts: inner trench slope and near land. A seismic experiment using 36 ocean bottom seismographs (OBS) and a 12,000 cu. in. airgun array was conducted to determine a detailed, 2D velocity structure in the forearc region off Miyagi. The depth to the Moho is 21 km, at 115 km from the trench axis, and becomes progressively deeper landward. The P-wave velocity of the mantle wedge is 7.9–8.1 km/s, which is typical velocity for uppermost mantle without large serpentinization. The dip angle of oceanic crust is increased from 5–6° near the trench axis to 23° 150 km landward from the trench axis. The P-wave velocity of the oceanic uppermost mantle is as small as 7.7 km/s. This low-velocity oceanic mantle seems to be caused by not a lateral anisotropy but some subduction process. By comparison with the seismicity off Miyagi, the subduction zone can be divided into four parts: 1) Seaward of the trench axis, the seismicity is low and normal fault-type earthquakes occur associated with the destruction of oceanic lithosphere. 2) Beneath the deformed zone landward of the trench axis, the plate boundary is characterized as a stable sliding fault plain. In case of earthquakes, this zone may be tsunamigenic. 3) Below forearc crust where P-wave velocity is almost 6 km/s and larger: this zone is the seismogenic zone below inner trench slope, which is a plate boundary between the forearc and oceanic crusts. 4) Below mantle wedge: the rupture zones of thrust large earthquakes near land (e.g. 1978 off Miyagi earthquake) are located beneath the mantle wedge. The depth of the rupture zones is 30–50 km below sea level. From the comparison, the rupture zones of large earthquakes off Miyagi are limited in two parts: plate boundary between the forearc and oceanic crusts and below mantle wedge. This limitation is a rare case for subduction zone. Although the seismogenic process beneath the mantle wedge is not fully clarified, our observation suggests the two possibilities: earthquake generation at the plate boundary overridden by the mantle wedge without serpentinization or that in the subducting slab.  相似文献   

Shear-wave splitting detected by using downhole triaxial seismic detector during dilation of artificial subsurface fracture     

Hirokazu Moriya  Katsuro Tanaka  Hiroaki Niitsuma 《Geophysical Journal International》2006,164(2):401-410

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