In order to acquire changes of physicai nature around the focus, this paper has proposed a new physical quantity VFP which was used to study attenuation ratio of train waves before and after 4 great earthquakes.

• 为了从地震记录图中获取大震前后震源物理性质的变化情况，本文给出了新的物理量VFP，利用该物理量研究了四个大池震前后地震波列的衰减速率变化。