Spatial Wavefield Gradient Data in Seismic Exploration

Multicomponent seismic array data provide not only recordings of the 3D particle motion and direction of arrival but also important information on the spatial gradients of the seismic wavefield. Such gradient data enable numerous new possibilities to analyse land-seismic data. Benefits of seismic spatial wavefield gradient data include enhanced wavefield separation, local slowness estimation, local elastic-parameter determination, and coherent-noise attenuation. Therefore, long-standing problems in seismic exploration such as suppression of scattered surface waves, isolation of particular wave modes, and wavefield reconstruction from spatially under-sampled data can be addressed with gradient data. Interesting applications of spatial gradients arise for shear (S) wave imaging. Considering that rotational motion (curl of wavefield) is directly linked to the S-wave presence, rotational motion measurements facilitate the identification, isolation, and processing of S-waves. If placed at the Earth’s free surface, rotational rates can be estimated from three-component (3C, vector) sensor arrays. Such data enable capture of all six degrees of freedom (three components of translation and three component of rotation). It is straightforward to apply the same principles of array-derived gradients and rotations to arrays of closely-spaced vector (3C, directed forces) seismic sources, which enables the simulation of pure rotational sources and, thus, ‘pure’ S-wave sources.