Planar Seismic Wavefront Modeling for Estimating Rotational Ground Motions: Case of 2D P-SV Line Source

Abstract

At large hypocentral distances, it is convenient to approximate curved transient seismic wavefronts as planar to estimate rotational ground motions from the single-station recordings of translational ground motions. This paper investigates whether and when this approximation, referred to as the plane-wave approximation, can be considered to be adequate close to the source. A simplistic source model comprising a two-dimensional (2D) kinematic shear dislocation P-SV line source buried in a homogenous, elastic half-space is considered to model the finite fault. The plane-wave rotational motion is then synthesized from the exact translational motion corresponding to the assumed model and compared with the exact rotational motion. The comparison of the two sets of rotational amplitudes in the frequency domain suggests that the plane-wave approximation may lead to significant underestimation of the Fourier amplitudes when the incidence angles of the seismic waves are small or when the wavelengths are appreciably longer than the hypocentral distance. For short wavelengths and other incidence angles, the adequacy of the plane-wave approximation depends critically on the source dip angle.