摘 要：  In this paper,the following assumptions are made:1) seismic source is a point one;2) the nearfieid.seismic waves are body ones:3) the medium of the earth is a halfspace which is homogeneous and elastic.Yccording to the abovementioned assumptions,this paper obtains a theoretical formula to estimate Swave incident angle by using the record of strong ground motion.During the process of calculations,the paper also presents a method of getting inplane and intiplane motions from the record of strong ground motion.By making use of 214 records of strong ground motion in the western America,this paper gives a statistical relation among Swave incident angle,epicentral distance and frequency.The results show that the average value of Swave incident angle is about 57,and has little to do with the epicentral distance.
