Giant dikes and dike-induced seismicity in a weak crust underneath Cerberus Fossae, Mars

Abstract

Cerberus Fossae is a long and narrow graben system located approximately 1000 km southeast of Elysium Mons, Mars. These structures have long been thought to be dike-induced, and are the focus of renewed attention due to the detection of seismic activity in this area by InSight. Here we report that structural modeling and linear elastic fracture mechanics provide strong evidence that the Cerberus Fossae grabens are dike-related structures, and that their intrusion may have released significant amounts of seismic energy. The modeled dike apertures are between ∼175 and 750 m, and their aspect ratios are consistent with fluid-induced fractures formed in a weakened host rock. We observe densely fractured terrains in high-resolution images of the graben walls, confirming the presence of a weakened crust underneath Cerberus. We used dike geometry and plausible mechanical properties to calculate the source moment released by dike opening and inflation in two scenarios; using the present-day dike dimensions (Md) and in dikes with downscaled sizes to represent smaller intrusions (md). These yielded values between 2.7⋅1016 and 1.3 1021 Nm. From these we estimate that the Cerberus diking events may have expressed seismically through a marsquake series with cumulative moment magnitudes (Mw) between 4.6 and 7.8. InSight has so far detected seismic events with Mw magnitudes as low as 1. Therefore, these results suggest that if the emplacement of even smaller dikes than those inferred below Cerberus is currently taking place, intrusion-induced seismicity could be detected by InSight.