Numerical Modelling of a Meteorite Impact Seismic Source Using the Stress Glut Theory

Meteorite Impacts have proved to be a significant source of seismic signal on the Moon, and have now been recorded on Mars by InSight seismometers. Understanding how impacts produce seismic signal is key to the interpretation of this unique data.

Here, we use the seismic representation theorem, and particularly the stress glut theory, to model the seismic motion resulting from impact cratering. The source is described by equivalent forces exerted on an initially undeformed medium, which result from the impactor momentum transfer, and from inelastic, non-linear processes occurring in the impacted region. We condense them into a point source with a time-varying single force and moment tensor. This analytical representation bridges the gap between the complex dynamics of crater formation, and the linear point-source representation classically used by seismologists.

Using the modelling software HOSS (Hybrid Optimization Software Suite), we develop a method to compute the equivalent forces of an impact, and its point source. We verify this model by comparing two signals: (1) HOSS is coupled to SPECFEM3D to propagate the near-source signal to remote seismic stations; (2) The point-source model derived from the stress-glut theory is used to generate displacements at the same distance. The comparison shows that the point-source model is accurately simulating the low-frequency impact seismic waveform. High-frequencies discrepancies exist. We are testing if they are related to finite-source effects.