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The seismometer, placed on Mars by NASA’s InSight lander, has recorded its two largest seismic events to date: a magnitude 4.2 earthquake and a 4.1 magnitude earthquake. The pair is the first recorded event to occur on the far side of the planet from the lander and is five times stronger than the previous largest recorded event.
Seismic data from the events could help researchers learn more about the inner layers of Mars, in particular its core-mantle boundary, researchers from the Marsquake Service (MQS) of InSight in The seismic record.
Anna Horleston of the University of Bristol and her colleagues were able to identify reflected PP and SS waves from the 4.2 magnitude event, called S0976a, and locate it in Valles Marineris, a massive canyon network that is one of the most distinctive geological characteristics of Mars. and one of the largest graben systems in the solar system. Earlier orbital images of transverse faults and landslides suggested that the area would be seismically active, but the new event is the first confirmed seismic activity there.
S1000a, the event of magnitude 4.1, recorded 24 days later, is characterized by reflected PP and SS waves, as well as Pdiff waves, low-amplitude waves that have crossed the core-mantle boundary. This is the first time Pdiff waves have been spotted by the InSight mission. Researchers have not been able to definitively determine the location of S1000a, but like S0976a, it originated on the far side of Mars. The seismic energy of S1000a also differs in that it is the longest recorded on Mars, lasting 94 minutes.
Both earthquakes occurred in the shadow core area, an area where P and S waves cannot travel directly to the InSight seismometer because they are stopped or bent by the core. PP and SS waves do not follow a direct path, but rather are reflected at least once on the surface before traveling to the seismometer.
“Recording events in the main shadow zone is a real step in our understanding of Mars. Prior to these two events, most of the seismicity was about 40 degrees away from InSight, ”said Savas Ceylan, co-author of ETH Zürich. “Being in the shadow of the nucleus, the energy passes through parts of Mars that we have never been able to take seismological samples before.
The two earthquakes differ in some important ways. S0976a is characterized only by low-frequency energy, similar to many of the earthquakes identified so far on the planet, while S1000a has a very wide frequency spectrum. “[S1000a] is a clear departure from our catalog and will be key to our further understanding of Martian seismology, ”said Horleston.
S0976a probably has a much deeper origin than S1000a, she noted. “The last event has a frequency spectrum, much more like a group of events that we observe that are modeled as shallow earthquakes, so this event may have occurred near the surface. S0976a looks like many of the events we have localized to Cerberus Fossae – an area with extensive faults – that have depths modeled at about 50 kilometers or more, and it is likely that this event has a similar, deep source mechanism.
Compared to the rest of the seismic activity discovered by InSight, the two new earthquakes from the far side are real deviations, the researchers said.
“Not only are they the biggest and most distant events with a significant difference, the S1000a has a spectrum and duration unlike any other event observed before. They are truly remarkable events in the Martian seismic catalog, “said Horleston.
The seismicity of Mars, full of surprises, in the first consecutive year of data
More information: Anna C. Horleston et al, The Far Side of Mars: Two Distant Marsquakes Detected by InSight, The seismic record (2022). DOI: 10.1785 / 0320220007 Provided by the Seismological Society of America
Citation: The two largest earthquakes ever recorded on the far side of the planet (2022, April 23), extracted on April 23, 2022 from
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