Dynamic Stress Triggering during the Great 25 March 1998 Antarctic Plate Earthquake

Abstract

We investigate the coseismic stress redistribution during the 25 March 1998 great Antarctic plate (MW 8.1) earthquake, in which the mainshock consisted of two distinct subevents separated in time by several tens of seconds. We compute the dynamic stress time histories for the fault geometry and the rupture and slip history determined by Henry et al. (2000), using the discrete wavenumber and re- flectivity method of Cotton and Coutant (1997), both for a homogeneous and a strat- ified half-space. We first image the coseismic stress evolution caused by the first subevent on the fault plane of the second one for both the velocity models. We compute both shear and normal stress changes and a time-dependent Coulomb failure function (CFF). Our results show that the shear stress changes have larger amplitudes than the other stress components and hence are the primary control on the evolution of the CFF. The dynamic stress amplitudes are larger than the static stress pertur- bations, with the largest positive dynamic stress peak on the second subevent fault plane reaching slightly less than 0.2 MPa at 60 sec and 65 sec after the nucleation, for the layered and the homogeneous crustal models, respectively. We suggest that the dynamic stress changes caused by the first subevent promoted a nearly instan- taneous failure on the second subevent fault.