On the origin of rock fragment mulches on Vertisols: A case study from the Ethiopian highlands   总被引：1，自引：2，他引：1  

Jan Moeyersons  Jan Nyssen  Jean Poesen  Jozef Deckers  Mitiku Haile 《Geomorphology》2006,76(3-4):411-429

Many Vertisols in Tigray, Ethiopia, typically carry a discontinuous rock fragment (RF, size 0.5–> 40 · 10^− 2 m) cover with 10 to 100 RFs m^− 2. Such RF mulches are of agricultural and environmental significance because they influence the water balance in the underlying soils and the crop yield. Natural RF concentrations are mostly considered as eolian or hydraulic lag deposits, or as the result of lateral transport over the soil surface from a rock outcrop, upslope. In cultivated areas RF mulches can develop by tillage.This paper presents the case of a natural RF mulch whose lithology indicates that the RFs are up-squeezed by the local Vertisol. The study site is located in the pass of Enda Maryam, Tigray, Northern Ethiopia (39°8′ E and 13°36′ N). A circular area of 10 m diameter, about 200 m away from the water divide in the valley has been cleared annually between 01/1999 and 05/2003. During this period, 625 RFs, 17 being > 7.5 · 10^− 2 m in size, totalling a mass of nearly 62 kg, have been collected. After correction for measurement procedures, the rate of RF up-warping by the Vertisol at Enda Maryam is assessed at 5 RFs m^− 2 in 3 years. At this rate of appearance, the formation of current RF concentrations on top of active valley Vertisols is only a matter of 10^1–2 years, provided the availability of RFs below the soil surface.Although important underground displacements were measured in the Vertisol between 01/1999 and 05/2002, the supposed link between up-squeezing of RFs and plastic deformations of ‘chimney’, ‘diapir’ or ‘intrusion’-like type in the Vertisol could not be evidenced. Instead, RFs are clearly concentrated on the soil surface as well as in depth, along the existing vertical desiccation cracks, often > 1 m deep which display polygonal configurations at the soil surface. Further, bundles of slickensides containing some RFs, have been mapped at the base of the Vertisol. The slickenside configuration suggests that the RF-bearing substrate is being scraped off.While the underground displacement of RFs along active slickensides seems normal, the process of RFs ascending in ‘upright’ position in the edge of desiccation cracks needs explanation. The closure of a desiccation crack is a peristaltic-like movement, following ascent or descent of the capillary fringe. It is hypothesized that this movement gradually pushes the RF to the surface or to another place or level in the soil profile where the crack closes in last instance.The apparent young age of the valley Vertisol mulches in Ethiopia might indicate the very recent formation of yearly recurrent desiccation cracks of Vertisols in the area. Available information confirms that most valleys in the study area used to be perennially marshy. Under these conditions no movements of RFs in the soil profile are expected to occur. Gullying, leading to pronounced seasonal desiccation of the Vertisols, started in several cases not more than 50 years ago.  相似文献   

Non-linear seismic wave propagation in anisotropic media using the flux-corrected transport technique   总被引：6，自引：0，他引：6  

Haishan Zheng  Zhongjie Zhang  Enru Liu 《Geophysical Journal International》2006,165(3):943-956

  相似文献   

Basin-related effects on ground motion for earthquake scenarios in the Lower Rhine Embayment   总被引：1，自引：0，他引：1  

Michael Ewald  Heiner Igel  Klaus-Günter Hinzen  Frank Scherbaum 《Geophysical Journal International》2006,166(1):197-212

  相似文献   

Fault plane orientations of small earthquakes of the 1997 Umbria-Marche (Italy) seismic sequence from P-wave polarities and rise times     

Marilena Filippucci  Salvatore de Lorenzo  Enzo Boschi 《Geophysical Journal International》2006,166(1):322-338

  相似文献   

Fault slip and rupture velocity inversion by isochrone backprojection     

Gaetano Festa  Aldo Zollo 《Geophysical Journal International》2006,166(2):745-756

  相似文献   

Dual simulations of fluid flow and seismic wave propagation in a fractured network: effects of pore pressure on seismic signature   总被引：1，自引：0，他引：1  

S. Vlastos  E. Liu  I. G. Main  M. Schoenberg  C. Narteau  X. Y. Li  B. Maillot 《Geophysical Journal International》2006,166(2):825-838

  相似文献   

Shear wave splitting changes associated with the 2001 volcanic eruption on Mt Etna     

Francesca Bianco  Luciano Scarf&#;  Edoardo Del Pezzo  Domenico Patanè 《Geophysical Journal International》2006,167(2):959-967

  相似文献   

Stress Green's functions for a constant slip rate on a triangular fault     

Taku Tada 《Geophysical Journal International》2006,164(3):653-669

  相似文献   

国道108线广元段公路桥梁裂缝病害及加固对策     

魏云杰  孙跃胜  许模 《中国地质灾害与防治学报》2005,16(2):129-131,153

国道108线广元段由于地质地貌条件复杂、重载作用及施工质量未能保证，桥梁裂缝病害较为普遍。文章简要介绍了沿线工程地质条件，按裂缝病害的成因将其分为3种类型：即桥台填土上部不密实引起的裂缝病害、桥台填土整体不密实引起的裂缝病害及地基土不均匀引起的裂缝病害。分别提出3种加固对策：即压浆、预应力对穿锚索锚梁及高压旋喷技术对上述病害进行治理。通过工程实例证明了这3种措施的有效性，为公路桥梁类似裂缝灾害提供了实践经验。这3种治理措施的优点为工艺简单、成本较低。但是桥梁病害的治理往往为隐蔽工程，施工难度较大、检测困难。对于压浆和高压旋喷加固工程，必须进行取芯检测，而预应力对穿锚索锚梁在施工过程中必须严格控制水平孔的倾斜度，保证施工质量。  相似文献   

亚洲赤道地区大气动能的纬向传播   总被引：7，自引：1，他引：7  

高辉  陈隆勋  何金海  陶诗言  金祖辉 《气象学报》2005,63(1):22-29

基于 1980～ 1997年 85 0hPa逐日NCEP/NCAR再分析资料讨论了亚洲赤道地区 (0°～ 5°N)大气动能的纬向传播特征。结果表明 ,在亚洲季风区内 ,赤道地区大气动能 (K)的最强中心位于 75°～ 90°E ,次强中心在索马里急流区 (5 0°E附近 )。在 0°～ 5°N ,90°E以东 ,平均的大气动能扰动和赤道上经向风扰动主要起源于西太平洋 ,并向西经南海传播到孟加拉湾。而在孟加拉湾动能中心与索马里急流区之间 ,动能传播方向比较复杂。以上事实说明赤道地区东亚季风系统确实是存在的 ,与印度季风系统中扰动的传播方向不同 ,东亚季风系统中动能和经向风扰动在东西方向上主要受西太平洋的影响。在亚洲赤道季风区 ,这两个系统的交界处约在 95°～ 10 0°E附近 ,比过去界定的偏西 5～ 10个经度。  相似文献