Two enormous "marsquakes" have been detected on the Red Planet

NASA's InSight probe has detected two huge quakes on Mars.
Christopher McFadden

In recent Mars news, NASA detected several large "marsquakes" on the Red Planet. Reaching magnitudes of 4.1 and 4.2 on the Richter Scale, these are the largest yet recorded on the planet. 

This stunning news was just reported in the journal the Seismic Record

The tremors were registered using two seismometers on the InSight lander. The quakes are significant, but they also represent the first-ever registered with their epicenters on the far side of the planet (relative to the lander) and are five times larger than any "marsquakes" ever detected. 

Seismic wave data from the events could help researchers learn more about the interior layers of Mars, particularly its core-mantle boundary, researchers from InSight’s Marsquake Service (MQS) report in The Seismic Record.

What is the cause of the marsquakes?

Like on Earth, various geological features and convection currents within the planet's layers below the surface contribute to quake formation. Over time, things like faults or sediment buildup will stress and strain before failing and moving. 

This releases a large amount of energy over a short period of time, creating vibrations in the planet's crust.  

The research team was also able to identify reflected PP and SS waves from the magnitude 4.2 event. Dubbed S0976a, the marsquake appears to have its origin in the Valles Marineris, a massive canyon network that is one of Mars’ most distinguishing geological features and one of the largest graben systems in the Solar System.

The "smaller" quake, S1000a, was recorded about 24 days later, as characterized by reflected PP and SS waves as well as, for the first time, Pdiff waves. These are small-amplitude waves that have traversed the core-mantle boundary.

The researchers are yet to pinpoint S1000a’s exact location, but like S0976a it originated on Mars’ far side. The seismic energy from S1000a is also distinguished as the most prolonged quake recorded on Mars and lasted 94 minutes.

Both marsquakes occurred in the "core shadow zone" a region where P and S waves can’t travel directly to InSight’s seismometer because they are stopped or bent by the core. PP and SS waves don’t follow a direct path, but rather are reflected at least once at the surface before traveling to the seismometer, a bit like vibrations on a ringing gong.

marsquakes detected
Mars surface relief map showing InSight’s location and the plotted sources of both marsquakes. Source:  Horelston et al. 2022

“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,” said Savas Ceylan, a co-author from ETH Zürich. “Being within the core shadow, the energy traverses parts of Mars we have never been able to seismologically sample before.”

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How are marsquakes different from earthquakes?

The mechanisms behind the formation of marsquakes and earthquakes are very similar, except for some very major differences. 

The moonquakes, for example, tend to be concentrated at great depth—between 600 km and 1000 km—which is deeper than earthquakes. The difference in distribution and magnitude of seismic energy release on the earth and the moon is probably related to fundamental differences in internal dynamics.

All very interesting, but the two recently detected marsquakes also differ in other interesting ways. S0976a, for example, is characterized by only low-frequency energy, like many of the quakes identified so far on the planet. S1000a, on the other hand,  has a very broad frequency spectrum.

“[S1000a] is a clear outlier in our catalog and will be key to our further understanding of Martian seismology,” Anna Horleston of the University of Bristol, from the research team said.

S0976a is likely to have a much deeper origin than S1000a, she noted and added, “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.”

According to the team, the two new far-side quakes are true outliers compared to the rest of the seismic activity detected by InSight. 

“Not only are they the largest and most distant events by a considerable margin, but S1000a also has a spectrum and duration unlike any other event previously observed. They truly are remarkable events in the Martian seismic catalog,” Horleston added.

Study abstract:

"For over three Earth years the Marsquake Service has been analyzing the data sent back from the Seismic Experiment for Interior Structure—the seismometer placed on the surface of Mars by NASA’s InSight lander. Although by October 2021, the Mars seismic catalog included 951 events, until recently all these events have been assessed as lying within a radius of 100° of InSight. Here we report two distant events that occurred within days of each other, located on the far side of Mars, giving us our first glimpse into Mars’ core shadow zone. The first event, recorded on 25 August 2021 (InSight sol 976), shows clear polarized arrivals that we interpret to be PP and SS phases at low frequencies and locates in Valles Marineris, 146° ± 7° from InSight. The second event, occurring on 18 September 2021 (sol 1000), has significantly more broadband energy with emergent PP and SS arrivals, and a weak phase arriving before PP that we interpret as PdiffPdiff⁠. Considering uncertain pick times and poorly constrained travel times for PdiffPdiff⁠, we estimate this event is at a distance between 107° and 147° from InSight. With magnitudes of MMawMwMa 4.2 and 4.1, respectively, these are the largest seismic events recorded so far on Mars."

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