The NASA InSight mission landed on Mars in November 2018 and successfully deployed its seismometer SEIS in February 2019. It is dedicated to characterize the seismic activity and the internal structure of Mars. Several tens of seismic events have been detected since then. On sol 173 (May, 23rd, 2019) and sol 235 (July, 27th 2019) the two largest events of Mw ~3 have been recorded. They show clear arrivals of P and S waves with high SNR. The first estimations of their epicentral distances and azimuths have been determined by the InSight Mars Quake Service: sol 173 event probability density function (PDF) is at 28±3° distance and 91±10°N azimuth and sol 235 is at 26±3° distance and 74±10°N azimuth. The two PDF ellipsoids are centered on the region of the Cerberus Fossae fault system, the closest and largest tectonic structure (1200km long) near the landing site. It is located in the vicinity of Elysium Mons and supposed to be a dyke-induced, young and active fault system of 4 to 5 main sub-parallel grabens. We provide constraints on location of potential higher stress concentrations based on the detailed analysis of the surface geometry and morphology over the entire graben system. We computed DEMs at local scale derived from both CTX and HiRISE images. Graben widths and throws suggest that the direction of the long-term propagation of faults is towards the East. Additionally, we detect up to four scales of fault segmentation, where segments are formed by 3-4 subsegments at each scale and separated by geometrical complexities, as observed on Earth. The inter-segments and fault tips are expected to concentrate higher stresses, where marsquakes are more likely to occur. Additionally, segment lengths are related to the seismic momentum implying that smaller segments could be involved in such medium quakes, with possible local surface expression like fallen boulders or landslides. Based on our analyses, we expect the youngest parts of Cerberus Fossae major grabens being the most seismogenic. In particular, their eastern tips seem the most probable source of sol 173 and sol 235 events. To improve the epicenter location determination, these observations will be associated to recent and future high-resolution satellite acquisitions in order to monitor the collapsing of boulders and mass wasting potentially triggered by the seismic activity.