On November 26th, NASA's Interior Exploration using Seismic Investigations, Geodesy, and Heat Transport (InSight) lander arrived on Mars. Since then, the robotic mission has been using its advanced suite of instruments to study the interior and geological activity of Mars. The main instrument of the lander was deployed on the surface of Mars less than a month after it arrived.
The mission detected a magnitude 4.2 and a magnitude 4.1 marsquake on August 25th, 2021. The previous largest event was a 3.7 marsquake that originated on the other side of the planet. The data from these events could help scientists understand the interior of Mars.
Anna Horleston, a senior research associate with the School of Earth Sciences Geophysics at the University of Bristol, conducted the research. They were able to trace where the events came from based on their body waves.
The largest of the two was traced to the largest canyon system in the Solar System. The region was suggested to be seismically active by earlier images of cross-cutting faults. This is the first time that activity has been confirmed there. The second event, S 1000a, lasted 94 minutes and was the longest on record.
The origin of S 1000a was not established by the researchers, but they did establish that it came from the far side of Mars. The results showed that it could have happened anywhere on the eastern side of the Marineris. They confirmed that both marsquakes occurred in the core shadow zone, a region that alters the path of longitudinal and compressional waves.
The waves do not reach a seismometer directly but are reflected off the core at least once before reaching the other side of the planet. Savas Ceylan explained the significance of these detections in a recent Seismological Society of America press release.
“Recording events within the core shadow zone is a real stepping stone for our understanding of Mars. Prior to these two events, the majority of the seismicity was within about 40 degrees distance of InSight. Being within the core shadow, the energy traverses parts of Mars we have never been able to seismologically sample before.”
The marsquakes differed in some key respects. S0976a was characterized by only low-frequency energy and was likely much deeper in origin. S 1000a had a broad spectrum, including low-amplitude Pdiff waves. This was the first time that InSight detected this type of energy.
Horleston said that the events are outliers and that the InSight catalog is not concerned with them.
“[S1000a] is a clear outlier in our catalog and will be key to our further understanding of Martian seismology, Not only are they the largest and most distant events by a considerable margin, S1000a has a spectrum and duration unlike any other event previously observed. They truly are remarkable events in the Martian seismic catalog.”
“The latter event has a frequency spectrum much more like a family of events that we observe that have been modeled as shallow, crustal quakes, so this event may have occurred near the surface. S0976a looks like many of the events we have located to Cerberus Fossae – an area of extensive faulting – that have depths modeled to be around 50 kilometers or more and it is likely that this event has a similar, deep, source mechanism.”
Further reading about the Seismological Society of America.
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