一个速度层的综合平均速度和均方根速度的偏差梯度或相邻两速度层均方根速度的偏差梯度，反映了岩性变化的规律和特征。本文以大安—乾安地区的实际速度的偏差和偏差梯度预测了砂岩发育带。预测结果和几个探区的已知钻井资料及地震资料基本吻合。

The gradient of deviation between the average velocity over a velocity layer and its RMS velocity or the deviation gradient of RMS velocities of two adjacent velocity layers indicates the variation law of lithology and its character. In this paper a sandprone zone is predicted from the deviation and deviation gradient of actual velocities in Daan-Qianan region. The result of prediction is basically in conformity with existent well and seismic data of some prospects.