柯林斯詞典asthenosphere /?s?θi?n??sf??, -?θ?n-/ 1. N a thin semifluid layer of the earth (100–200 km thick), below the outer rigid lithosphere, forming part of the mantle and thought to be able to flow vertically and horizontally, enabling sections of lithosphere to subside, rise, and undergo lateral movement 軟流圈→see also isostasy 返回 asthenosphere