Abstract:In the multicomponent seismograms of surface hydrocarbon seismic exploration,compressional wave usually occurs in vertical component,Vertically-polarized shear wave vs/vp).We can see from analysis that the influence of free-surface effect makes P-wave and SV-wave coexist in both vertical component and horizontal component in compacted-rock cropping area where vs/vp is high;but in loose ground area (low velocity layer where vs/vp is low,vs and vp are low),the influence of free-surface effectdd and the refraction due to low velocity layer make P-wave and SV-wave occur separately in vertical component and horizontal component.Hence one can foresee that surface elastic wave data behave as vector wave field in high vs/}P surface area (such as permafrost,limestone crop and other compacted-rock crop);but in low vs/vP area,they nearly behave as two scalar wave fields (P-wave mainly occurs in vertical component,and SV-wave in horizontal component,favouring data acquisition and processing). In addition,author makes following suggestions:.Various forward modelings of elastic waves and the physical modeling of u1trasonic waves ought to offer the result of low vs/vp surface layer so as to cope with real conditions in hydrocarbon exploration area.·All methods (such as AVO and inversion) in which prestack amplitude information is used and those methods for extracting elastic polarization parameter must consider free-surface effect so as to improve accuracy.