SEISMIC ACTIVITY LEVEL OF MARS ESTIMATED FROM 140 SOLS OF INSIGHT DATA

We present an updated estimate of the seismic activity rate of Mars after seven months of high-quality recording of the InSight SEIS instrument. The instrument has been deployed fully on Sol 60 (February 2, 2019) and has been recording with excellent performance since then. The first distant marsquake was observed on Sol 105 (March 14), the first local event on Sol 128 (April 7). From then until end of June (Sol 200), 15 likely events and another 13 candidate events have been observed. Due to a strong diurnal variation in background noise and the generally low magnitude of the activity (compared to Earth), events have been observed only in few low-noise periods of the day and the quantitative estimation of event rates and moment release currently involves extrapolation and large uncertainties. We present a statistical analysis of the global seismic activity level based on a preliminary seismic magnitude model, weighted by the temporal evolution of the ambient noise over the mission. The resulting number of events smaller magnitude 3 is roughly consistent with the pre-mission estimate of Golombek (1992) and the medium model of Knapmeyer et al. (2006), however, as of now, there is a statistically significant lack of events above magnitude 3. This hints at a distribution that is skewed towards smaller events, compared to terrestrial global averages.