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.
NASA’s InSight( Interior Exploration using Seismic Investigations, Geodesy, and Heat Transport) lander is a Mars lander designed to give the Red Planet its first thorough checkup since it formed 4.5 billion years ago. It is the first outer space robotic explorer to study in-depth the “inner space” of Mars: its crust, mantle, and core.
Till October 2021, InSight recorded 951 seismic events, and all were lying within a radius of 100° of InSight.
Now, as reported in a New study, the seismometer placed on Mars by NASA’s InSight lander has recorded its two largest seismic events to date: a magnitude 4.2 and a magnitude 4.1 marsquake. The pair are the first recorded events to occur on the planet’s far side from the lander and are five times stronger than the previous largest event recorded. Two distant events that occurred within days of each other give the first glimpse into Mars’ core shadow zone.
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.
Anna Horleston of the University of Bristol and colleagues were able to identify reflected PP and SS waves from the magnitude 4.2 event, called S0976a on 25 August 2021, and located its origin in the Valles Marineris,146° ± 7° from InSight.
It is a massive canyon network that is one of Mars’ most distinguishing geological features and one of the largest graben systems in the Solar System.
Earlier orbital images of cross-cutting faults and landslides suggested the area would be seismically active, but the new event is the first confirmed seismic activity there.
S1000a, the magnitude 4.1 event recorded 24 days later on 18 September 2021, was characterized by reflected PP and SS waves as well as Pdiff waves. These small amplitude waves have traversed the core-mantle boundary. This is the first time the InSight mission has spotted Pdiff waves. The researchers could not definitively pinpoint S1000a’s location, but like S0976a, it originated on Mars’ far side. Researchers estimated this event is at a distance between 107° and 147° from InSight.The seismic energy from S1000a also holds the distinction of being the longest recorded on Mars, lasting 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.
“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.”
Two events, Two different stories:
The two marsquakes differ in some important ways. S0976a is characterized by only low-frequency energy, like many of the quakes identified so far on the planet, while S1000a 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,” Horleston said.
S0976a is likely to have a much deeper origin than S1000a, she noted. “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.”
The researchers said that compared to the rest of the seismic activity detected by InSight, the two new far-side quakes are true outliers.
“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.
Futuristic view of the study
S0976a and S1000a are remarkable events in the Martian seismic catalog, and they will be instrumental in furthering understanding of the red planet.
- Anna C. Horleston; John F. Clinton; Savas Ceylan; Domenico Giardini; Constantinos Charalambous; Jessica C. E. Irving; Philippe Lognonné; Simon C. Stähler; Géraldine Zenhäusern; Nikolaj L. Dahmen; Cecilia Duran; Taichi Kawamura; Amir Khan; Doyeon Kim; Matthieu Plasman; Fabian Euchner; Caroline Beghein; Éric Beucler; Quancheng Huang; Martin Knapmeyer; Brigitte Knapmeyer‐Endrun; Vedran Lekić; Jiaqi Li; Clément Perrin; Martin Schimmel; Nicholas C. Schmerr; Alexander E. Stott; Eléonore Stutzmann; Nicholas A. Teanby; Zongbo Xu; Mark Panning; William B. Banerdt. The Far Side of Mars: Two Distant Marsquakes Detected by InSight. The Seismic Record (2022) 2 (2): 88–99. DOI: 10.1785/0320220007