Seismicity of Elysium Planitia, Mars

Kurzfassung

At first glance the single tectonic plate setting of Mars implies that most of its deformation is characterized by an intraplate seismicity. Before the InSight mission, it was proposed that Martian seismicity could be driven by contraction of the lithosphere, due to secular cooling of the planet, leading to wide-spread seismicity of thrust style. Orbital images indeed show ubiquitous wrinkle ridges and lobate scarps, which are interpreted as buried thrust faults. However, over the last 3 years, InSight observed a large number of marsquakes and have shown rather a very localized distribution of the seismicity, mainly governed by normal faulting, centered around a relatively young graben system called Cerberus Fossae. We present a working model of seismicity in Cerberus Fossae that addresses the spatial distribution of hypocenters, as well as stress drop inferred from body wave spectra. One class of events, the stronger low frequency marsquakes, are located at 20-40 km depth, near the brittle-ductile transition zone. Associated low stress drops and low corner frequencies are consistent with a heated setting, possibly due to recent or possibly ongoing volcanic activity at depth. A second class of events with higher corner frequencies can plausibly be located at the graben flanks near the surface, possibly related to long-term release of residual stress from the initial opening.