第四系（泛指基岩顶面的松散层，下同）的厚度变化，会给重力测量带来一定影响。尤其对于第四系平均厚度较小而其变化又较大的地区，因其近地表并且与基岩的密度差大，常常使重力异常的强度和形态均遭到严重歪曲。因此，消除第四系对重 Quaternary (generally refers to the top of the bedrock loose layer, the same below) the thickness changes, will give some measure of gravity impact. Especially in the area where the average thickness of the Quaternary is smaller and its variation is larger, the intensity and morphology of gravity anomalies are often seriously distorted due to the near surface and large density difference with bedrock. Therefore, to eliminate the Quaternary counterweight