The 2011 Tohoku-Oki earthquake: displacement reaching the trench axis

We detected and measured coseismic displacement caused by the 11 March 2011 Tohoku-Oki earthquake [moment magnitude (M(W)) 9.0] by using multibeam bathymetric surveys. The difference between bathymetric data acquired before and after the earthquake revealed that the displacement extended out to the axis of the Japan Trench, suggesting that the fault rupture reached the trench axis. The sea floor on the outermost landward area moved about 50 meters horizontally east-southeast and ~10 meters upward. The large horizontal displacement lifted the sea floor by up to 16 meters on the landward slope in addition to the vertical displacement.     

Kodiak seamount not flat-topped

Earlier surveys in the Aleutian Trench southeast of Kodiak Island, Alaska, indicated that Kodiak Seamount had a flat top and was a tablemount or guyot. This seamount is of special significance because it has been supposed that its surface was eroded at the same time as those of a line of guyots to the southeast. If so, its present position in the axis of the Aleutian Trench indicates that the line of guyots was formed before the trench. A two-part survey in 1965 showed that Kodiak Seamount is not flat-topped, and should be eliminated from the category of guyots. Reflection profiling records indicate that the seamount was formed before the adjacent sediments were deposited, and that the small trough, or moat, on the south side is a depositional feature probably formed by a scouring effect or by the acceleration of turbidity currents around the base of the mount.     

Tectonic movement in the chile trench

An acoustic reflection profile across the Chile Trench off Valparaiso shows the trench floor to have a substantial sediment accumulation that is far from flat-lying. The morphology is transitional between the flat-lying sediment fill to the south (labeled a type I trench) and the bare V-notch character farther north (labeled type II). A sharp seaward slope break, downbowed reflectors, and a landward downthrown normal fault suggest that the oceanic lithosphere is failing in shear. This mode of failutre is more consistent with the observed features of trenches and Benioff zones than is the concept of bending and underthrusting.     

喷射式海底挖沟机试验研究

为研究影响喷射式挖沟机挖沟能力的因素,设计物理模型,并选择合适的泥沙作为试验底质,开展了室内模型试验。通过测量冲沟断面和水中泥沙质量分数的变化,研究了流速和挖沟机行进速度对挖沟效果的影响,并分析了冲沟沟型从刚开挖至平衡状态的历时变化过程和变化原因。试验结果表明:流速对冲沟深度的影响是有一定限度的;挖沟机行进速度的变化对沟宽的影响明显大于对沟深的影响;冲沟断面历时变化的前一阶段,沟深变浅的同时沟宽增大,这是因发生冲沟塌方、滑坡以及沟内泥沙的落淤而造成的,而后一阶段沟深变浅但沟宽没有明显增大的原因主要与泥沙的密实度有关。     

Seismic structure of the southern East pacific rise

Seismic data from the ultrafast-spreading (150 to 162 millimeters per year) southern East Pacific Rise show that the rise axis is underlain by a thin (less than 200 meters thick) extrusive volcanic layer (seismic layer 2A) that thickens rapidly off axis. Also beneath the rise axis is a narrow (less than 1 kilometer wide) melt sill that is in some places less than 1000 meters below the sea floor. The small dimensions of this molten body indicate that magma chamber size does not depend strongly on spreading rate as predicted by many ridge-crest thermal models. However, the shallow depth of this body is consistent with an inverse correlation between magma chamber depth and spreading rate. These observations indicate that the paradigm of ridge crest magma chambers as small, sill-like, midcrustal bodies is applicable to a wide range of intermediate- and fast-spreading ridges.     

Spreading of the ocean floor: undeformed sediments in the peru-chile trench

None of the expected stratigraphic and structural effects of a spreading sea floor have been imposed on the sedimentary fill of the Peru-Chile Trench. During at least the last several million years, and perhaps during much of the Cenozoic, the trench has not been affected by an oceanic crust thrusting under the continent.     

A kuroko-type polymetallic sulfide deposit in a submarine silicic caldera

Manned submersible studies have delineated a large and actively growing Kuroko-type volcanogenic massive sulfide deposit 400 kilometers south of Tokyo in Myojin Knoll submarine caldera. The sulfide body is located on the caldera floor at a depth of 1210 to 1360 meters, has an area of 400 by 400 by 30 meters, and is notably rich in gold and silver. The discovery of a large Kuroko-type polymetallic sulfide deposit in this arc-front caldera raises the possibility that the numerous unexplored submarine silicic calderas elsewhere might have similar deposits.     

East pacific rise: hot springs and geophysical experiments

Hydrothermal vents jetting out water at 380 degrees +/- 30 degrees C have been discovered on the axis of the East Pacific Rise. The hottest waters issue from mineralized chimneys and are blackened by sulfide precipitates. These hydrothermal springs are the sites of actively forming massive sulfide mineral deposits. Cooler springs are clear to milky and support exotic benthic communities of giant tube worms, clams, and crabs similar to those found at the Galápagos spreading center. Four prototype geophysical experiments were successfully conducted in and near the vent area: seismic refraction measurements with both source (thumper) and receivers on the sea floor, on-bottom gravity measurements, in situ magnetic gradiometer measurements from the submersible Alvin over a sea-floor magnetic reversal boundary, and an active electrical sounding experiment. These high-resolution determinations of crustal properties along the spreading center were made to gain knowledge of the source of new oceanic crust and marine magnetic anomalies, the nature of the axial magma chamber, and the depth of hydrothermal circulation.     

基于几何非线性动力组合地基梁模型的漏粪地板自振特性

针对农业工程中猪舍漏粪地板的动力响应问题,采用静力分析方法,对漏粪地板进行自振特性进行研究。在考虑地基的压缩和剪切刚度、梁的弯曲和剪切变形、运动的平动和转动惯性力以及轴力的二阶效应的基础上,建立了几何非线性压剪平转动Timoshenko弹性地基梁动力基本方程,并给出了动力位移和内力方程;提出了组合地基梁的自振特性分析方法,对典型猪舍漏粪地板自振周期及振型进行了计算。结果表明：组合地基梁的周期及振型规律明显异于普通梁;不同结构参数对漏粪地板自振周期的影响程度各不相同：端部缝间板条不改变振动特性;支承长度和地基刚度作用显著;剪切变形、转动惯性力和地基剪切刚度引起的偏差较小,可忽略其影响。本研究建立的几何非线性动力组合地基梁模型能够用于猪舍漏粪地板舒适性验算和动力安全性设计。     

油气管沟土石方开挖量的积分计算

随着长距离油气管道沿线地形、地貌、地质条件不断变化,管沟的开挖形状也不断变化,为此难以准确计算管沟土石方开挖量。结合油气管沟开挖的技术要求,建立了油气管沟的几何模型,并将复杂的油气管沟几何模型分解为直线型体积单元和圆曲线型体积单元两种类型,利用积分法求出两种体积单元的体积计算公式。其中,圆曲线型体积单元的计算公式较复杂,采用多条线段拟合圆弧的方法对其进行验算,结果表明:圆曲线型体积单元计算公式推导合理,可以用于计算油气管沟的土石方开挖量。(图4,表2,参20)     

基于流体压润滑理论的农用潜水泵机械密封性能的研究

[目的]探讨动压槽的槽深、槽数对农用潜水泵机械泄漏量、液膜刚度等密封性能的影响。[方法]在潜水泵机械密封的设计上应用流体动压润滑理论,通过密封端面的斜直线槽产生流体动压效应,以提高密封装置的寿命。应用CFD技术建立密封的几何模型并进行数值模拟,以确保密封具有较小的泄漏量和较大的液膜刚度为优化准则,探讨动压槽的槽深、槽数等结构参数对泄漏量、液膜刚度等最佳密封性能参数的影响。[结果]外装式内侧斜直线槽密封具有明显的流体动压效应,能产生较大刚度的液膜,可实现密封端面非接触,减少摩擦磨损,能抵抗较为剧烈的外界工况变化;内侧斜直线槽能产生上游泵送效应,密封泄漏量小,当槽数为30,槽深为5—8μm时,密封综合性能最佳。[结论]斜直线槽密封具有泄漏量小、液膜刚度大等优点。     

Propagation of slow slip leading up to the 2011 M(w) 9.0 Tohoku-Oki earthquake

Many large earthquakes are preceded by one or more foreshocks, but it is unclear how these foreshocks relate to the nucleation process of the mainshock. On the basis of an earthquake catalog created using a waveform correlation technique, we identified two distinct sequences of foreshocks migrating at rates of 2 to 10 kilometers per day along the trench axis toward the epicenter of the 2011 moment magnitude (M(w)) 9.0 Tohoku-Oki earthquake in Japan. The time history of quasi-static slip along the plate interface, based on small repeating earthquakes that were part of the migrating seismicity, suggests that two sequences involved slow-slip transients propagating toward the initial rupture point. The second sequence, which involved large slip rates, may have caused substantial stress loading, prompting the unstable dynamic rupture of the mainshock.     

The geological evolution of the Tibetan Plateau

The geological evolution of the Tibetan plateau is best viewed in a context broader than the India-Eurasia collision zone. After collision about 50 million years ago, crust was shortened in western and central Tibet, while large fragments of lithosphere moved from the collision zone toward areas of trench rollback in the western Pacific and Indonesia. Cessation of rapid Pacific trench migration ( approximately 15 to 20 million years ago) coincided with a slowing of fragment extrusion beyond the plateau and probably contributed to the onset of rapid surface uplift and crustal thickening in eastern Tibet. The latter appear to result from rapid eastward flow of the deep crust, probably within crustal channels imaged seismically beneath eastern Tibet. These events mark a transition to the modern structural system that currently accommodates deformation within Tibet.     

Deformation and slip along the Sunda megathrust in the great 2005 Nias-Simeulue earthquake

Seismic rupture produced spectacular tectonic deformation above a 400-kilometer strip of the Sunda megathrust, offshore northern Sumatra, in March 2005. Measurements from coral microatolls and Global Positioning System stations reveal trench-parallel belts of uplift up to 3 meters high on the outer-arc islands above the rupture and a 1-meter-deep subsidence trough farther from the trench. Surface deformation reflects more than 11 meters of fault slip under the islands and a pronounced lessening of slip trenchward. A saddle in megathrust slip separates the northwestern edge of the 2005 rupture from the great 2004 Sumatra-Andaman rupture. The southeastern edge abuts a predominantly aseismic section of the megathrust near the equator.     

Recognition of paleoearthquakes on the Puente Hills blind thrust fault,California

Borehole data from young sediments folded above the Puente Hills blind thrust fault beneath Los Angeles reveal that the folding extends to the surface as a discrete zone (相似文献   

竹节水平沟对红壤坡面土壤水分的影响

在江西省泰和县老虎山小流域选择了裸露地、水保林、水保林+竹节水平沟和水保林+竹节水平沟+枯落物覆盖4个坡面样地进行了全年取样试验,分析竹节水平沟对红壤坡面土壤水分的影响。结果表明：在土壤蓄水量上,竹节水平沟沟内的蓄水量相对更大,60 cm土层为138.1～237.3 mm,水保林下水土流失区域土壤蓄水量相对最小。从土壤含水量看,水保林土壤含水量较小,所有土层各月均在16%以下;水保林+竹节水平沟的土壤含水量基本在16%以上,说明在水保林中开挖竹节水平沟具有蓄积水分的作用;水保林+竹节水平沟+枯落物覆盖在月降雨量最小的9月,其土壤含水量仍然较高。对比各处理样地,土壤含水量最低的都是水保林,最高的是水保林+竹节水平沟+枯落物覆盖沟内样地或裸露地,水保林+竹节水平沟+枯落物覆盖样地沟内的土壤含水量比水保林样地高出79%～146%;同一处理样地的沟内土壤含水量基本大于沟外。竹节水平沟能起到蓄水保水的作用,对于防汛和抗旱都具有重要意义,是南方红壤侵蚀区调控水量的治本措施之一。     

油锯人机界面的优化研究

该文通过实验研究探讨了油锯人机界面几何参数对操作者主观施力及对其身体生理负荷的影响规律 .通过对实验数据的回归得出了高把油锯和矮把油锯的人机界面几何参数与评价指标 (最大有效扭矩、力损耗因子、肌肉收缩强度 )之间存在的定量化方程 .建立了油锯的人机界面几何参数优化的目标函数 ,并求出了高把油锯和矮把油锯的最佳几何参数 .高把油锯的最佳几何参数 :把手横轴距为 5 40mm ;把手与地面垂轴距为 6 88mm ;把手与油箱后部纵轴距为 186mm ;把手直径为 30mm ;把手倾角为 33° .矮把油锯的最佳几何参数 :把手横轴距为 14mm ;把手纵轴距为 40 0mm ;把手垂轴距为 5 0mm ;把手直径为 2 8mm ;把手倾角为 2 3     

Mercury's Surface: Preliminary Description and Interpretation from Mariner 10 Pictures

The surface morphology and optical properties of Mercury resemble those of the moon in remarkable detail and record a very similar sequence of events. Chemical and mineralogical similarity of the outer layers of Mercury and the moon is implied; Mercury is probably a differentiated planet with a large iron-rich core. Differentiation is inferred to have occurred very early. No evidence of atmospheric modification of landforms has been found. Large-scale scarps and ridges unlike lunar or martian features may reflect a unique period of planetary compression near the end of heavy bombardment by small planetesimals.     

Hydrothermal germanium over the southern East pacific rise

Germanium enrichment in the oceanic water column above the southern axis of the East Pacific Rise results from hydrothermal solutions emanating from hot springs along the rise crest. This plume signature provides a new oceanic tracer of reactions between seawater and sea floor basalts during hydrothermal alteration. In contrast to the sharp plumes of (3)He and manganese, the germanium plume is broad and diffuse, suggesting the existence of pervasive venting of low-temperature solutions off the ridge axis.     

Hillslope Evolution by Bedrock Landslides

Bedrock landsliding is a dominant geomorphic process in a number of high-relief landscapes, yet is neglected in landscape evolution models. A physical model of sliding in beans is presented, in which incremental lowering of one wall simulates baselevel fall and generates slides. Frequent small slides produce irregular hillslopes, on which steep toes and head scarps persist until being cleared by infrequent large slides. These steep segments are observed on hillslopes in high-relief landscapes and have been interpreted as evidence for increases in tectonic or climatic process rates. In certain cases, they may instead reflect normal hillslope evolution by landsliding.