Abstract:In M area of Liaohe depression, the beggest difference of thickness in volcanic rocks can reach to 570m, in order to accurately know the wave characters of thick volcanic rocks, the paper used staggering grid finite-difference algorithm of wave equation to forward simulate the seismic response of layered volcanic rocks in M area of Liaohe depression.The analyses showed that because the volcanic rocks are characteristics of high velocity and high density,the thick volcanic rock has great influence on the precision of structural interpretation, its influence on underneath formations is not only the scattering (or shield function), but also appears the phenomenon: " depression becoming shallower and uplift becoming sag".The exact contents are as follows:(1)in comparison with the area having thin volcanic rocks (or without volcanic rock),in the area having thick volcanic rocks,the "eaten up" travel-time can reach 177ms because of high velocity in volcanic rock,among which it can lead the uplift amplitude of underneath formations to become greater and sag amplitude--smaller in seismic imaging configuration nearby the thick volcanic rocks ;(2)in the position without volcanic rock or of thin volcanic rock, it leads the uplift amplitude of underneath formations to become smaller in seismic imaging configuration; (3)if without considering the distribution of volcanic rocks in space,the volcanic rocks 500-600m thick can cause 200 -300m interpretation errors in depth for underneath formations when the time-depth conversion is implemented by using uniform time-depth template.