Method for estimating shear wave reflection data from acquired compressional wave reflection data

A method of producing shear wave reflection information from compressional wave reflection information comprising the steps of:

• (a) generating descending acoustic waves from a plurality of acoustic wave sources and receiving and recording at a plurality of receivers ascending waves produced at a subsurface interface;
• (b) gathering said recorded reflection waves into sets of different source-receiver offsets having a common reflection boundary;
• (c) correcting said gathered reflection waves for normal moveout;
• (d) measuring amplitudes of said gathered waves at selected points in time for different source-receiver offset values;
• (e) determining for each said point in time a component g.sub.det which represents the amplitude variations in the measured amplitudes of said gathered waves due to the effects of source-receiver offset;
• (f) estimating for each said point in time a component of amplitude variation with offset .delta.G which is not due to a shear wave component and is not accounted for in G.sub.det ;
• and
• (g) determining for each said point in time a shear wave reflectivity component R.sub.3 in accordance with the following:
• ##EQU11## with
• P=R.sub.po and
• Q=GR.sub.po -8T.sup.2 R.sub.so +(2T.sup.2 -1/2).DELTA..rho./.rho.,
• where,
• R.sub.po =normal incident compressional wave reflection coefficient
• R.sub.so =normal incident shear wave reflection coefficient
• T=average V.sub.s /V.sub.p,
• .rho.=density
• G=totality of amplitude effects caused by said variations in the amplitude of the acoustic waves with offset,
• so that the influence of said amplitude effects on said measured acoustic waves are removed in determining shear wave reflection information.