Improved Constraints on Martian Crustal Velocity Structure of InSight lander

Impact-generated marsquakes with accurate positions are important to Mars seismic investigations. To better constrain the Martian crustal velocity structure, we repicked first-arrival P- and S-wave of three impacts (S0981c, S0986c and S1034a) near InSight lander and analyzed their possible ray paths. We significantly reduced body-wave arrival uncertainties by applying polarization filters and filter-bank methods. To verify that the detected energy originates from the corresponding events, the azimuth of each candidate arrival was calculated and compared with the true event azimuth. Then we derived the incidence angles from particle motion to constrain the ray path.

We find that for events at shorter epicentral distances (S0986c and S1034a), the first-arrival ray paths are typically confined to the uppermost crust. In contrast, first-arrival ray path from more distant event (S0981c) usually sample the mid-lower crust or the crust-mantle boundary. Furthermore, we detected later-arrival P-waves from S0981c. By combining these body-wave arrivals with incidence angles from three impacts, we inverted for the one-dimensional Martian crustal velocity structure beneath the InSight lander using a Markov Chain Monte Carlo (MCMC) method.

More refined processing techniques enable us to extract more information from marsquake signals, helping us understand Martian inner velocity structure better. In this study, we simultaneously incorporated body-wave travel times and incident angles into the inversion. This approach can lead to better constraints on the Martian crustal velocity structure and even constrict the Vp/Vs ratio at each crustal layer.