Method and system using wave-equation for obtaining traveltime and amplitude used in Kirchhoff migration

Obtaining 2100 seismic data acquired in an area over a subsurface formation, migrating 2120 the seismic data based on a model of the subsurface formation and using a wave-equation Kirchhoff (WEK) technique for pre-defined surface locations. The WEK technique includes forward-propagating a low-frequency wavefield from a shot location among pre-defined source locations, calculating an arrival traveltime of a maximum amplitude of the low-frequency wavefield, and applying Kirchhoff migration using the arrival traveltime and the maximum amplitude. An image of the subsurface formation is outputted 2130 based on the migrated seismic data. The low-frequency wavefield may correspond to a frequency range of 10-20 Hz or it may extend up to 100 Hz. The forward propagating may include calculating a first full-wavefield propagation based on a wave equation at low frequency with a source wavelet, calculating a second full-wavefield propagation based on the wave equation at the low frequency with a Hilbert transformation of the source wavelet and applying a1D Fourier filter in depth domain to a combination of the first full-wavefield and the second full-wavefield to extract a down-going wavefield.