Decomposition and migration for multicomponent seismic data

Decomposition of multicomponent seismic data into primary compressional (P) and shear (S) wave responses and migration of these decomposed wavefields are two main procedures for the multicomponent data processing. In this work, first we derive the decomposition formula from elastic wave equation to separate out the displacement vector with coupled P- and SV-waves into scalar upgoing P- and SV-waves. Pure P-wave can be decomposed by revising the vertical component with the correction of horizontal component, which can enhance P-wave but eliminate SV-wave in vertical component. Similarly, pure SV-wave can be decomposed by revising the horizontal component with the use of vertical component. Such a decomposition process requires only the knowledge of elastic parameters near the surface. Two kinds of migration schemes are then proposed to reconstruct the subsurface image by performing downward extrapolation of the separated scalar upgoing P- and SV-wave fields. For common shot gathers, the P-SV subsurface can be imaged with the correlation of forward extrapolation from the source for downgoing waves and inverse extrapolation for the upgoing P- or SV-waves with the respective P- or SV-wave velocity. The screen propagators can be used effectively in this case. For common offset sections, we modify the travel time equation of P-SV point scatterer and derive the corresponding migration equation. Results from synthetic data of one two-component record show that the P- and SV-waves are decomposed completely and the subsurface image for P-P waves is consistent with that of P-SV waves.