On September 18, 2021, NASA’s InSight lander celebrated its 1,000th Martian day by measuring one of the biggest, longest-lasting marsquakes its has ever detected; the event is estimated to be about a magnitude 4.2 and shook for nearly an hour-and-a-half; this is the third major marsquake it has detected in a month: on August 25, the lander detected two quakes of magnitudes 4.2 and 4.1.
While the September 18 marsquake is still being studied, the InSight team already knows more about the August 25 quakes.
For example, the magnitude 4.2 event occurred about 8,500 km (5,280 miles) from InSight — the most distant temblor the lander has detected so far.
The researchers are working to pinpoint the source and which direction the seismic waves traveled.
They currently know that the shaking occurred too far to have originated where InSight has detected almost all of its previous large quakes: Cerberus Fossae, a region roughly 1,609 km (1,000 miles) away where lava may have flowed within the last few million years.
One especially intriguing possibility is Valles Marineris, the epically long canyon system that scars the Martian equator. The approximate center of that canyon system is 9,700 km (6,027 miles) from InSight.
To the surprise of the scientists, the August 25 quakes were two different types, as well.
The magnitude 4.2 quake was dominated by slow, low-frequency vibrations, while fast, high-frequency vibrations characterized the magnitude 4.1 quake.
The magnitude 4.1 quake was also much closer to the lander — only about 925 km (575 miles) away.
Despite their differences, the August marquakes do have something in common other than being big: both occurred during the day, the windiest — and, to a seismometer, noisiest — time on Mars.
InSight’s seismometer usually finds marsquakes at night, when the planet cools off and winds are low.
But the signals from these quakes were large enough to rise above any noise caused by wind.