Journal Article

Locating the Largest Event Observed on Mars With Multi‐Orbit Surface Waves

Zenhäusern, G., Ceylan, S., Davis, P., Khan, A., Giardini, D., Knapmeyer‐Endrun, B., Lognonné, P., Banerdt, W. B., Beghein, C., Clinton, J. F., Stähler, S. C., Panning, M. P., Drilleau, M., Carrasco, S., Kim, D., Li, J.

2023

Overview

Prior to the 2018 landing of the InSight mission, the InSight science team proposed locating Marsquakes using multiple orbit surface waves, independent of seismic velocity models, for events larger than MW4.6. The S1222a MW4.7 of 4 May 2022 is the largest Marsquake recorded and the first large enough for this method. Group arrivals of the first three orbits of Rayleigh waves are determined to derive the group velocity, epicentral distance, and origin time. The mean distance of 36.9 ± 0.3° agrees with the Marsquake Service (MQS) distance based on body wave measurements of 37.0 ± 1.6°. The origin time from surface waves is systematically later than the MQS origin time by 20 s. Backazimuth estimation is similar to body wave estimations from MQS although suggesting a shift to the south. Backazimuth estimates from R2 and R3 are more scattered, but do show clear elliptical motion. Plain Language Summary Waves that move along the surface all the way around the planet of Mars can be used to figure out where a Marsquake occurred without knowing in advance how fast the waves move through the planet, because we know how big the planet is. Before InSight got to Mars, we predicted that we would be able to see these waves if an event was big enough, and on 4 May 2022, we finally saw a Marsquake large enough to test this approach. Based on the timing of the arrivals of these waves, we were able to figure out the distance and timing of the Marsquake. The results agreed well with the approach we had been using for smaller events, giving us additional confidence in our tools for figuring out where Marsquakes have happened. Key Points The MW 4.7 S1222a event is the first Marsquake large enough for multi‐orbit surface wave location independent of a priori seismic velocity Using measurements of R1, R2, and R3 Rayleigh waves, we determine an epicentral distance consistent with that estimated from body waves Elliptical particle motion is observed for Rayleigh wave arrivals broadly consistent with the backazimuth identified from body waves

• Publisher: John Wiley & Sons, Inc,American Geophysical Union,Wiley
• Subject: Arrivals / Distance / Earth Sciences / Geophysics / Group velocity / Locating / Mars / Mars surface / Planetology / Planets / Rayleigh waves / Sciences of the Universe / Seismic velocities / Seismic waves / Surface waves / Wave measurement