Sizhuang Deng and Alan Levander
Plain Language Summary
The subsurface structures of Earth are imaged by the detailed analysis of seismic data recorded by thousands of stations deployed on Earth’s surface. The InSight mission landed a seismograph on Mars which was deployed at the end of 2018 to investigate the planet’s interior structure and dynamic evolution. In this study, we preprocessed the continuous vertical-component seismic data, and by autocorrelation retrieved a Rayleigh wave, one class of seismic surface wave, that orbits Mars. Rayleigh wave group velocities between 115 and 200s period were measured from the observed Mars orbiting Rayleigh waves. Synthetic seismograms were calculated using current estimates of the velocity structure of Mars for comparisons to the observation. The spherically symmetric model was updated with a Monte Carlo algorithm, an inversion method that randomly perturbs the velocity model and determines the model that best matches the Mars orbiting surface waves through trial and error. An S-wave low-velocity zone is observed to the depth of ~400km beneath the Martian surface, consistent with other InSight seismic observations and velocity models measured from geophysical modeling and high-pressure laboratory experiments.