Scientists use seismic noise to image first hundred meters of Mars - Ars Technica

The results, combined with some nearby surface features, reveal that InSight is likely above two large lava flows, separated by layers of sediment.

But Mars lacks both of these noise sources, and its background is dominated by the wind interacting with features on Mars.

But when the data was examined at times of day when winds were generally high, the noise turned out to be dominated by frequencies that were produced by the wind interacting with the lander itself.

So the researchers focused on what was early evening, Mars time, when the winds tended to die down.

At that point, most of the seismic noise is generated by weak winds interacting with nearby geology rather than with the lander itself.

Geologists have used seismic noise to reconstruct features on Earth by comparing the horizontal and vertical components of the noise.

Closest to the surface, the regolith of Mars is formed by dust and rock fragments produced by impacts.

By three meters below the surface, there appears to be a layer of volcanic rock, formed by major eruptions in Mars' distant past.

Below that, from roughly 30 meters to 80 meters (these figures are pretty inexact), is another layer of material where seismic signals move slowly.

Since then, impacts and Mars' winds have deposited a layer of loose material on top of the volcanic layers.