Seismic sources of InSight marsquakes and seismotectonic context of Elysium Planitia, Mars
Résumé
Since early 2019, the InSight mission has proven that Mars is seismically active, with more than 900 seismic events recorded. Among them, several events have characteristics close to terrestrial tectonic earthquakes. Most of these events are located on the major graben system of Cerberus fossae and, a little further north, on the secondary system of Grjotá Valles. In this study, we invert the seismic moment tensors for nine of these tectonic marsquakes characterized by high quality data. Seven of them are located on Cerberus fossae/Grjotá Valles and two of them are located near the Martian dichotomy. The moment tensors allow us to interpret the nature and depth of the seismic sources at the origin of these events. In our approach, we invert the P and S body waveforms, the PP, SS, PPP and SSS secondary phase maximum amplitudes and we look for solutions with surface waves weaker than the Martian noise. From our results on moment tensors, we determine that all our events have been triggered at moderate depths of 15-36 km. We deduce that the seven events located on Cerberus fossae have geometries similar to the fractures and are generated by tectonics. This activity is supposed to result from the reactivation of previous faults and fractures, which would have been initially induced by the propagation of volcanic dikes at depth. The two dichotomy events are due to deep compressive fracturing of the Martian lowlands. They are therefore triggered by the planetary thermal contraction. Our results are in strong agreement with recent studies on the event depths and on the previous moment tensors calculated for two events.
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