Constraining Wave Velocities for Shallow Depths on Mars

Interior Exploration using Seismic Investigations, Geodesy, and Heat Transport (InSight) landed on Mars on the Elysium Planitia. The InSight had a Seismic Experiment for Internal Structure (SEIS), which contained seismometers that recorded numerous marsquake seismograms. In this study, we propose shear (S)-wave velocity (VS) and compression (P)-wave velocity (VP) profiles at the InSight landing site on Mars by analyzing the initial portions of P-wave seismograms and incidence angles of the six marsquakes. High-quality, low-frequency seismograms are collected. Using the P-wave seismogram method, which is validated for various regions on Earth, we estimate VS values up to a depth of 3400 m. In addition, we compute the incidence angle of the P-wave for the top layer based on the ratio of the initial P-wave amplitude in the radial direction to that in the vertical direction. By hypothesizing the VP profile, we estimate the incidence angles of the P-wave for the other layers, as well as the epicentral distances. Finally, we propose a VP profile up to a depth of 3400 m that minimizes the misfit between the estimated and known epicentral distances. We confirm that the proposed VS and VP profiles agree with those of previous studies.