Post contributed by Dr. A. Lucas. Research Scientist, Institut de physique du globe de Paris, France
A detailed analysis of both orbital and seismological data associated to the two largest seismic events recorded during the Nasa InSight mission to Mars (operational from the end of 2018 to the end of 2022), have been done by a team of researchers from the IPGP (Université Paris Cité / CNRS) and their colleagues. They have spotted a clear increase in the number of dust avalanches around the two epicenters of both quakes. The first seismic event was caused by an impactor hitting the Martian surface. The second seismic event was the largest marsquake ever recorded. This finding sheds light on how endogenous and exogenous processes can currently shape the surface of Mars and trigger active mass wasting.
Image 1: . Illustration of seismic waves triggering dust avalanches in an impact crater. © Nicolas Sarter for IPGP (an animation version is also available with permission to use: https://www.ipgp.fr/wp-content/uploads/2024/01/Animation_avalanche.gif, credits are © Nicolas Sarter (illustration) / Antoine Lucas (animation) )
The first seismic event under investigation, named S1000a, occurred on September 18, 2021, when a meteorite impact led to a seismic signal registering a local Martian magnitude of 4.1, resulting in the formation of a crater approximately 150 meters in diameter. A comparison of orbital images captured before and after the event reveals a massive increase in new dust avalanches within a 20 km radius of the epicenter, likely caused by intense surface acceleration and atmospheric blast. To date, this is by far the largest number of avalanches triggered by an impact that has been spotted.
The second event, named S1222a, took place on May 4, 2022, marking the most substantial marsquake ever recorded on Mars, estimated at a magnitude of 4.7. Located near the Apollinaris volcano, in proximity to the Martian crustal dichotomy (i.e., the Northern hemisphere being both younger and lower in elevation compared to the southern martian hemisphere), the epicenter is estimated to lie at a depth of less than 20 km. Despite its energy being approximately 25 times greater than the S1000a impact event, orbital data reveal more gentle number of new avalanches. Nonetheless, the comparison of orbital images since 2005 with high-resolution images post-S1222a reveals a significant rise in avalanche occurrence, from 3% to 40% in certain areas, over one Martian year (equivalent to 687 Earth days) as shown in Image 2.
Image 2: A sequence of images captured by CTX (6m/pixel) 8 months prior to S1222a, and HiRISE (downsampled to 5m/pixel at CTX resolution) ESP_074357_1745 taken shortly after the marsquake.
The evident correlation between this seismic activity and the increased avalanche frequency is underscored by the absence of storms during the observed period, as well as the lack of any discernible pattern in avalanche orientation relative to prevailing south-north winds in the region.
Building upon these findings, researchers refined the epicenter location of the S1222a seismic event using established principles from Earth sciences that associate landslide and avalanche distribution with earthquake epicenters. This refined position offers two potential interpretations of the earthquake’s mechanism. The first proposes a connection to the ancient volcano, Apollinaris Patera, although its current activity is deemed improbable. The second hypothesis posits a large geological structure — a 450 km-long ridge — as the probable seismic source, situated adjacent to the estimated epicenter location (see Image 1 and 3).
Image 3: Bird’s-eye view of the impact event s1000a where located showing the location of the epicenter (impact crater) and the resulting avalanches. Elevation is derived from the HRSC camera onboard Mars Express, the mosaic has been made by post-event HiRISE images.
These findings not only lay the groundwork for future investigations into Martian seismic activity and its influence on surface and subsurface processes but also underscore the significance of surface process analysis in elucidating the mechanisms driving the Red Planet’s seismic phenomena.
Further Reading:
A. Lucas, et al. (2024) , Possibly seismically triggered avalanches after the S1222a Marsquake and S1000a impact event, Icarus, Vol. 411, 115942.
Datasets in the IPGP Research Collection:
A. Lucas, et al. (2024) “Avalanches catalogue associated to the s1222a Marsquake”, IPGP Research Collection, V1.
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