Inversion for parameters of tensile earthquakes

Abstract

The tensile source model generalizes the shear source model by assuming that the slip vector can be arbitrarily oriented with respect to the fault and is not constrained to lie within the fault plane. The proposed inversion for the parameters of tensile sources is based on the evaluation of the isotropic (ISO), compensated linear vector dipole (CLVD), and double-couple (DC) components in seismic moment tensors. The most significant parameters inverted are the λ/μ ratio at the fault (denoted as the κ parameter) and the inclination α of the slip vector from the fault. The κ parameter is significant for discriminating noisy moment tensors of shear earthquakes from those of tensile earthquakes. The inclination α can be accurately determined from the DC component in the moment tensor because the DC component rapidly decreases with increasing α. For example, the inclination of 20° causes DC being ∼50–60% only. The inversion is applied to earthquakes which occurred in January 1997 in West Bohemia, Czech Republic. It is shown that some of these earthquakes display tensile faulting. The κ parameter is ∼0.1. The inclination of the slip from the fault attains values of up to 20°. This inclination is a result of tensile traction and reduced shear traction along the fault and high-fluid pressure in the region.