more than 50 per cent of the slopes failed, sending soil and trees into the valleys below. Large and catastrophic failures of thick deposits of wind-blown silt (loess) have occurred repeatedly in Central Asia, such as the disaster in Kansu province China in a 1970 earthquake where some 100,000 people were killed by loess flows that came off the slopes and filled the valleys. Similar failures of loess have caused heavy damage in Tadzhikistan in the USSR. 6.2.3 Liquefaction of loose flat-lying sedimentary deposits Some deposits in flat alluvial valleys have a very loose structure that is disturbed by seismic vibration. In consequence the component particles of a f’sensitive” clay or fine sand, for example, assume a closer packing and smaller bulk volume. If the layer is initially saturated, the load from material above would not be carried by solid-to-solid grain con&t but by the interstitial water. A soil in such a condition has effectively zero shear strength,‘and thus the sediments above are free to move under gravity forces towards any free face. The whole of the material above the liquefied layer may then spread laterally and break up into smaller units. Moreover, if buildings : I - I. ./ . . 18 are founded upon a layer which is subject to liquefaction they may subside, break up, or tip over, Standard penetration tests and mechanical analysis of soils may be used as a first estimate for determining liquefaction potential. 6.2.4 Cohesive natural embankments, levees and earth dams More or less homogeneous cohesive materials may fail by slumping along curved shear surfaces under strong seismic shock, particularly if the material is saturated. Failures in the open air are generally not common or so rapid that they present a serious hazard to life although property may be destroyed. 
**Analysis**
The text appears to be discussing the effects of earthquakes on soil and land formations, specifically the failure of slopes, loess deposits, and cohesive natural embankments. The language used is technical and scientific, suggesting that the text is aimed at a specialized audience, possibly in the field of geology, engineering, or natural disaster response. The focus on the physical consequences of earthquakes, such as soil liquefaction and landslide failures, suggests that the text is more closely related to natural sciences and environmental issues rather than economic or social development.

**Category**
Natural resources and environment, Science and technology