COMPARATIVE STUDY BETWEEN THE CHARACTERISTICS OF SEISMIC WAVES RECORDED DOWNHOLE AND ON GROUNDSURFACE

A comparative study between the characteristics of seismic waves recorded downhole and on groundsurface in plain area is made; the travel time and the amplitude relationships of which are derived in this paper. Then the following conclusions are drown:1. Under the condition of uniform layered medium, tc, the travel time of seismic waves recorded on the ground is larger than th, the value recorded downhole. Their difference is given as follow:△t=tc-th=cosic/Vch Correspondingly, Tc, the travel time of seismic phase observed on groundsurface is greater than Th, the value observed downhole. The difference is represented by △T.2. Ahe ratio of Ac, the groundsurface amplitude to Ah, the downhole amplitude is defined as K = Ac/AhUnder specified conditions, K>1. Thus K is considered as the amplifying factor of the groundsurface amplitude relative to the downhole amplitude.The data observed downhole and on groundsurface at the Jinghai station are analysed and the results from the comparison between △T and K at a single station are obtained.