High-Frequency Seismic Events on Mars Observed by InSight

The seismometer deployed on the surface of Mars as part of the InSight mission (Interior Exploration using Seismic Investigations, Geodesy and Heat Transport) has recorded several hundreds of marsquakes in the first 478 sols after landing. The majority of these are classified as high-frequency (HF) events in the frequency range from approximately 1 to 10 Hz on Mars' surface. All the HF events excite a resonance around 2.4 Hz and show two distinct but broad arrivals of seismic energy that are separated by up to 450 s. Based on the frequency content and vertical-to-horizontal energy ratio, the HF event family has been subdivided into three event types, two of which we show to be identical and only appear separated due to the signal-to-noise ratio. We show here that the envelope shape of the HF events is explained by guided Pg and Sg phases in the Martian crust using simple layered models with scattering. Furthermore, the relative travel times between these two arrivals can be related to the epicentral distance, which shows distinct clustering. The rate at which HF events are observed varies by an order of magnitude over the course of one year and cannot be explained by changes of the background noise only. The HF content and the absence of additional seismic phases constrain crustal attenuation and layering, and the coda shape constrains the diffusivity in the uppermost shallow layers of Mars.

Automated summary

The seismometer on Mars has detected hundreds of marsquakes, with most being high-frequency events exhibiting resonance and distinct seismic energy arrivals. These events have been classified into three types based on frequency content and energy ratio, and the travel times between arrivals are related to epicentral distance. The amplitude shape is explained by layered models with scattering.