3D Numerical Simulations of Magnetar Crustquakes

Abstract Crustquakes are frequently invoked as a mechanism to trigger sudden transients in the magnetospheres of magnetars. In this picture, a mechanical failure of the crust excites seismic motions of the magnetar surface that launch force-free waves into the magnetosphere. We first investigate this problem analytically and then perform 3D numerical simulations. Our simulations follow the propagation of high-frequency magnetoelastic waves in the entire crust and include magnetic coupling to the dipolar magnetosphere and liquid core through simplified radiation boundary conditions. We observe seismic waves bouncing between the crust–core interface and the surface with a characteristic frequency ∼1 kHz, which could appear as a modulation of the magnetospheric radiation. Both the starquake and its associated magnetospheric wave emission are strongly damped on a timescale ∼10 ms by magnetic coupling to the liquid core. Since the seismic waves are significantly damped before they can spread laterally around the crust, magnetospheric wave emission occurs primarily near the initial epicenter of the quake. Our simulations suggest that nonaxisymmetric quakes will launch a mixture of Alfvén and fast magnetosonic waves into the magnetosphere. The results will be important for interpreting magnetar bursts and understanding the possible trigger mechanisms of fast radio bursts.