Scientists Record Two Biggest-to-Date Quakes on Mars, Most Powerful Since Observation Began

NASA's InSight lander's seismometer on Mars has recorded two of the planet's largest seismic occurrences to date: a magnitude 4.2 and a magnitude 4.1 marsquake, a new paper published in The Seismic Record revealed.

According to the Seismological Society of America's press release upon the findings, the two events are the first to be recorded on the planet's far side from the lander, and they are five times more powerful than the previous biggest event.

Researchers from InSight's Marsquake Service (MQS) reported that seismic wave data from the events could help researchers understand more about Mars' inner layers, notably its core-mantle boundary.

The University of Bristol's Anna Horleston and colleagues were reportedly able to identify reflected PP and SS waves from the magnitude 4.2 event known as S0976a and pinpoint its location in the Valles Marineris, a massive canyon network that is one of Mars' most distinctive geological features and one of the Solar System's largest graben systems.

Mars surface relief map showing InSight’s location (orange triangle), other located marsquakes (purple dots) that cluster around 30° distance, close to Cerberus Fossae, and S0976a, located within Valles Marineris just north of Sollis Planum. S1000a’s location is predicted to be somewhere within the shaded region between 107° and 147° from InSight.

The location had previously been suspected of being seismically active based on orbital photos of cross-cutting faults and landslides, but the latest event represents the first documented seismic activity there.

"Recording events within the core shadow zone is a real steppingstone for our understanding of Mars. Prior to these two events the majority of the seismicity was within about 40 degrees distance of InSight," Savas Ceylan, a co-author from ETH Zurich, is quoted as saying. "Being within the core shadow, the energy traverses parts of Mars we have never been able to seismologically sample before."

According to the report, reflected PP and SS waves, as well as Pdiff waves, small amplitude waves that crossed the core-mantle boundary, were all present in S1000a, a magnitude 4.1 event that occurred 24 days later.

The InSight mission has discovered Pdiff waves for the first time. S1000a, like S0976a, originated on Mars' far side, but the researchers were unable to pinpoint its exact position. With a duration of 94 minutes, the seismic energy from S1000a is likewise the longest yet recorded on Mars.

Both marsquakes occurred in the core shadow zone, an area where the core stops or bends P and S waves, preventing them from reaching InSight's seismometer, according to the publication. PP and SS waves do not travel directly to the seismometer; instead, they are reflected at least once at the surface before reaching it.

And researchers say that there are some significant differences between the two marsquakes. S0976a, like many of the quakes discovered so far on the planet, is characterized by low frequency energy, but S1000a has a relatively broad frequency spectrum.

"[S1000a] is a clear outlier in our catalog and will be key to our further understanding of Martian seismology," Horleston said, while adding that she believes S0976a has a far deeper genesis than S1000a.

According to her, the latter seismic 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," the scientist added.

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The two new far-side quakes are true outliers when compared to the remainder of the seismic activity identified by InSight, according to the researchers.

"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," Horleston said.

According to earlier studies, Valles Marineris, a 4,000 km long canyon system, is thought to represent the relic of an old Martian strike-slip fault. Even if it was once an active fault, it's unclear whether it's still active or has "frozen" into place.