P 162 REMOVING LOVE WAVES AND THEIR SCATTERING IN THE SHALLOW SUBSURFACE L.F. VAN ZANEN 1 , G.G. DRIJKONINGEN 1 , J. BROUWER 2 , C.P.A. WAPENAAR 1 and J.T. FOKKEMA 1 1 Section of Applied Geophysics and Petrophysics, Department of Applied Earth Sciences, Delft University of Technology, Mijnbouwstraat 120, 2628 RX Delft, The Netherlands 2 OYO Centre of Applied Geosciences B.V., Archimedesbaan 16, 3439 ME, Nieuwegein, The Netherlands Introduction SH-waves (Shear Horizontal) are often assumed to be decoupled from the other wave types (P- (Pressure) and SV- (Shear Vertical) waves) in elastic media. In air or gas filled media, P-waves are often severely scattered. Therefore seismic SH-wave experiments are more suitable for imaging the shallow subsurface. Unfortunately, the data of a seismic experiment are polluted with coherent noise. In SH-wave experiments, Love waves provide the largest contribution. Under certain circumstances, Love waves are difficult to separate from reflection data. First, they are surface waves, and therefore attenuate slowly, thus providing the most energy in a seismogram. Second, their wave velocity is almost equal to the shear wave velocity in soft soils, making it difficult to filter them with for example f-k filtering. Third, they are dispersive, meaning that their phase velocity is frequency dependent. Love waves are discussed in more detail by Aki and Richards [1]. With the help of reciprocity, a mathematical tool which can relate two states to each other, an expression can be derived, which removes Love waves from SH-wave data [2][3]. No structural subsurface model is needed for this procedure. The approach is similar to that of Van Borselen et al. [4], who used acoustic reciprocity to remove surface multiples from marine seismic data. Theory In previously published results [2][3], an expression was derived for removing Love waves from seismic SH-wave data: (1) Due to Parseval’s theorem, the terms under the integral are in the wavenumber-Laplace domain (denoted by a tilde ( )), whilst the terms outside the integral are in the place-Laplace domain (denoted by a hat ( )). In this equation, is the crossline component of the particle velocity measured in the field on the stress-free surface , is the desired particle velocity field, also measured on the “depth level” , as if no surface were present, is the shear modulus of the top layer, is the vertical wavenumber, defined as: , in which is the shear wave velocity of the top layer, is the signature wavelet of the volume source density of force, is the receiver position, is the source position, is the horizontal wave number, and finally is the Laplace parameter. Eq. (1) is an integral equation of the second kind, meaning that the unknown term ( ) is both EAGE 63rd Conference & Technical Exhibition — Amsterdam, The Netherlands, 11 - 15 June 2001