Multiple suppression by a wave-equation extrapolation method

The wave-equation-based multiple suppression method, unlike predictive deconvolution and stacking, makes no assumptions on periodicity or moveout patterns of multiples, and can cope with complex sea-bottom and sea-surface variations. It entails multiple prediction by wave equation extrapolation of the seismic data and then multiple subtraction from the recorded seismograms. In general, the multiple subtraction method requires the calculation of a subtraction scalar (a reflection coefficient function), which is a function of the ratio of the original data to the extrapolated multiple model traces. The success of the method depends on establishing the correct scalar. However, it is difficult to get a good subtraction scalar when the wavelet of the original data is different from that of the multiple model traces. This occurs for the long offset traces because of geophone ghosting, and changes of amplitude and phase in the reflection waveform beyond the critical angle. In this paper, we develop a superior alternative scheme, based on a simple 2-D Butterworth-type gain function, calculated from the original data and the (extrapolated) multiple model data. This gain function will attenuate the multiples and preserve the primaries. A simple synthetic example is used to demonstrate the efficacy of the method in multiple suppression.