The leaning is due to ground subsidence caused by over-pumping of groundwater. In 1996, the amount of inclination surpassed 1m.
大雁塔倾斜的原因是长期超采地下水导致地面沉降，在1996年时最大倾斜超过1米。
2
The inclination and thickness of coal strata are main influencing factors of ground subsidence.
煤层的倾角、厚度等物理条件是地表沉陷的主要影响因素。
3
The effect of rate of change for semimajor axis and inclination perturbation and drift of semimajor axis and inclination on the ground-track drift was analyzed.