[PPS05-09] Seismic wave propagation on asteroid Ryugu induced by the impact experiment of the Hayabusa2 mission
Keywords:Hayabusa2, asteroid, seismology, surface evolution, Ryugu
Using a fast modelling code for 3D seismic wave propagation, AxiSEM3D, we numerically simulate seismic shaking on asteroids, changing rigidities, quality factors and seismic efficiencies (the conversion ratio of impactor’s kinetic energy to seismic wave energy). Following previous studies, an isotropic seismic moment tensor of explosion form is assumed. Through the comparison between simulations and observations, we find that quality factor smaller than 0.5 or seismic efficiency smaller than 10-7 are required. However, such an extremely low quality factor seems unrealistic because anelastic heat generation and scattering in anhydrous asteroid regolith are expected to be too small to reduce wave energies rapidly. Thus, we consider very low seismic efficiency more plausible. The reason for such a low seismic efficiency can be resulted from the powdery behavior of regolith. Seismic waves propagate through powdery materials only if the elastic stress is lower than its yield strength. Assuming that the yield strength of regolith is 1 kPa as laboratory experiments, calculated boulder’s lateral movement would be always smaller than 1 m. This hypothesis may account for the absence of regolith lateral movement observed in the SCI operation during the Hayabusa2 mission and indicate that the low yield strength of regolith possibly limits the seismic wave propagation on asteroids, making the apparent seismic efficiency small.