Journal Article

Stratification of Heterogeneity in the Lithosphere of Mars From Envelope Modeling of Event S1222a and Near Impacts: Interpretation and Implications for Very‐High‐Frequency Events

Garcia, R., Xu, Z., Knapmeyer-Endrun, B., Margerin, L., Lognonné, P., Menina, S., Kawamura, T., Drilleau, M., Calvet, M., Carrasco, S., Stott, A., Onodera, K., Banerdt, W., Heller, G.

2023

Overview

We have modeled the high‐frequency seismogram envelopes of the large event S1222a and four recently identified near impacts recorded by the InSight mission by introducing a stratification of velocity and attenuation into a multiple‐scattering approach. We show that a simple conceptual model composed of a strongly diffusive, weakly attenuating layer overlying a transparent medium captures the essential features of the observed envelopes. The attenuation profiles reveal that the minimal extension of heterogeneities at depth is of the order of 20 km in the vicinity of InSight and 60 km on the path to S1222a. We interpret this result as an indication that the Martian crust as a whole is at the origin of the strong scattering. Our heterogeneity model suggests that the sources of a number of distant Very‐high‐Frequency seismic events are shallow and located to the south or in close vicinity of the Martian dichotomy. Plain Language Summary The seismometers deployed at the surface of Mars in the framework of the Interior Exploration using Seismic Investigations, Geodesy and Heat Transport mission have recently recorded seismic waves generated by meteorite impacts and a very large Marsquake. These exceptional data offer the opportunity to study how seismic waves propagate in the interior of Mars and more particularly how they attenuate. This is an important topic because attenuation characterizes the physical state of planetary interiors. There are two basic mechanisms at the origin of seismic attenuation: “absorption,” which is highly sensitive to the presence of fluids—such as water—in the porosity of the rocks and “scattering,” which is caused by the geological heterogeneity at length scales ranging from tens of meters to kilometers. Using advanced modeling techniques which allow for the separate quantification of the two processes, we have determined that scattering is the dominant seismic attenuation mechanism on Mars, that originates from a heterogeneous and dry crust. In the light of this result, we have revised previous interpretations of specific seismic events with a predominantly high‐frequency content and propose that they originate from the vicinity of a major geological feature known as the Martian dichotomy. Key Points Envelope modeling of event S1222a and near impacts reveals a strong stratification of scattering properties in the lithosphere of Mars The whole crust acts as a diffusive layer with a minimal thickness of 20 km below InSight and 60 km at the location of S1222a Distant Very‐high‐Frequency events are shallow quakes or impacts originating from the south or the vicinity of the Martian dichotomy

• Publisher: American Geophysical Union (AGU),John Wiley & Sons, Inc,American Geophysical Union,Wiley
• Subject: [PHYS.PHYS.PHYS-GEO-PH] Physics [physics]/Physics [physics]/Geophysics [physics.geo-ph] / [SDU]Sciences of the Universe [physics] / absorption / Attenuation / Earth Science / Earthquakes / Envelopes / Fluids / Geodesy / Geology / Geophysics. Cosmic physics / Heat transport / Heterogeneity / InSight mission / Lithosphere / Mars / Mars surface / Martian lithosphere / Meteorite collisions / Meteorite impacts / Modelling / multiple scattering / P-waves / Physical states / Planetary interiors / Porosity / QC801-809 / Scattering / Sciences of the Universe / Seismic activity / Seismic attenuation / Seismic investigations / Seismic waves / Seismograms / Seismometers / Stratification / Stratigraphy / Transparency (optical)