NASA’s InSight lander has recorded the two strongest quakes detected so far on Mars, with both measuring over magnitude 4. These seismic events came from the far side of the Red Planet, and one also clocked the record for the longest marsquake.
The epicenter of S0976a was traced to a huge network of canyons called Valles Marineris. Images taken in the past from orbit have revealed features that suggest the region is seismically active, but this is the first confirmed quake from the area. The precise origin of S1000a couldn’t be pinpointed, except to say that it also came from the far side.
An event designated S0976a was sensed on August 25, 2021, and had a magnitude of 4.2. Another designated S1000a, occurred on September 18 with a magnitude of 4.1. The second quake was also the longest recorded so far, lasting 94 minutes.
Because of their location on the other side of the world from InSight, the core of the Red Planet would have blocked the direct seismic waves, known as P and S waves, that are usually detected from closer events. Instead, the instrument detected PP and SS waves that were reflected by the surface at least once before bouncing back to the sensor. The depth of each quake can also be calculated from the frequencies of the waves.
“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 km (31 miles) or more and it is likely that this event has a similar, deep, source mechanism,” said Anna Horleston, corresponding author of the study.
S1000a, however, has a much broader spectrum of frequencies to its waves, which the team says makes it “a clear outlier in our catalog.”
These detections will help scientists comprehend the seismology of Mars.
The research was published in the journal The Seismic Record.