In the case that hypocenter depth is far less than the epicenter distance without depth phases available, only the relative epicenter distribution could be obtained accurately by double difference method, the depth determined would be not stable.

• 当震源深度远小于震中距时，如果没有深度震相的参与，只能得到误差较小的震中相对分布，深度的相对位置仍有较大的误差。