Accounting for receiver perturbations in seismic wavefield gradiometry

Abstract

Spatial wavefield gradient data can be estimated from dense receiver arrays using a finitedifference approximation. Array-derived spatial wavefield gradient data to estimate, for example, strain and rotation components of the wavefield usually suffer from receiver perturbations, such as varying sensor coupling and/or differences in the instrument channel responses. We present a novel methodology to compute spatial seismic wavefield gradient data in the presence of receiver specific perturbation effects. We simultaneously invert the seismic wavefield recorded with an array consisting of closely spaced sensors for the spatial wavefield derivatives and station specific frequency-dependent calibration filters that remove the local receiver perturbations. Using synthetic and field data, we demonstrate that our scheme has the potential to significantly improve gradient estimation results for arrays with a low number of stations suitable, for instance, for land seismic exploration. The extracted calibration filters do not only correct for receiver perturbations but also partly compensate for the truncation error of the Taylor series expansion about the central (master) station of the array. The application of the calibration filters results in gradient estimates that are more accurate compared to conventional approaches. Multiple source recordings are used for reducing the trade-off between the extracted receiver perturbation filters and the spatial wavefield derivatives in the proposed inversion scheme.

Seismological Processing of Six Degree-of-Freedom Ground-Motion Data

“…However, the Taylor series approximation is only reasonable under the assumption that the subsurface is homogeneous and deformation varies linearly over the array area. In addition, array-based spatial wavefield gradient data is prone to noise caused by measurement uncertainties, such as varying receiver-to-ground coupling, differences in the instrument response, or sensor orientation [137][138][139][140][141]. Further issues with array-derived rotation estimates can be caused by strain-rotation coupling, a site-effect describing the conversion of strains on a large scale (seismic wavelength) to rotations on a local scale due to near-receiver heterogeneity [142].…”