InSight detected powerful Mars quakes on the opposite side of the planet

(ORDO NEWS) — The Martian apparatus for the first time “heard” the seismic events that occurred in the shadow zone. They turned out to be five times more powerful than the largest known marsquake.

By October 2021, the Marsquake Service (MQS) , which analyzes data from the Martian InSight spacecraft , has entered 951 events into the seismic catalog of the Red Planet.

It was believed that all of them occurred within a radius of 100° from the spacecraft’s sensors. In a new paper published in The Seismic Record , scientists describe two quakes that happened on the other side of the planet.

For more than 1100 sols (Martian days), an international team of seismologists has been analyzing data from SEIS (Seismic Experiment of Internal Structure), the main scientific instrument of the first geophysical mission to another planet, the InSight mission.

All marsquakes with an established source that occurred before Sol 976 of the mission originated within 75° of the apparatus, and their magnitude did not exceed 3.8. SEIS sensors caught several events that happened next, but their foci could not be determined.

Two new described events – S0976a and S1000a – turned out to be the largest for the entire time of observations, and scientists were able to determine that their foci are in the shadow zone of Mars for InSight.

InSight detected powerful Mars quakes on the opposite side of the planet
Map of the seismic activity of Mars according to InSight data (triangle). Marsquakes with known sources are marked with pink dots. The shaded white area is the possible location of the source of the S1000a event. The dashed line indicates the most probable distance to the source S1000a (116°)

The shadow zone is a region from which seismic longitudinal (P) and transverse (S) waves cannot directly enter the seismometer sensors, because they are stopped or distorted by the planet’s core.

Nevertheless, these waves are reflected and refracted, turning into PP and SS waves. It was from them that the researchers determined the location of the foci and the parameters of new events.

Event S0976a with a magnitude of 4.2 occurred on the mission’s Sol 976, August 25, 2021. Its focus was 146° ± 7° from InSight , in the Mariner Valleys, one of Mars’ most famous geological landmarks.

This is a huge network of canyons up to 11 kilometers deep, stretching for 4,500 kilometers. From satellite images of faults and landslides, scientists understood that the region must be seismically active, but this activity was detected for the first time.

The second event – S1000a with a magnitude of 4.1 – occurred on sol 1000, September 18, 2021. In addition to PP- and SS-waves, the seismograph detected Pdiff-waves – waves of small amplitude that passed the boundary between the core and the mantle.

The quake lasted a record 94 minutes. The exact focus could not be established, but analysis of the waves showed that the event occurred at a distance of 107° to 147° from the device.

This excludes the vicinity of the extinct volcano Olympus. The quake may have originated in the “Alba grooves,” faults west of the gently sloping Alba volcano.

Thanks to these events, scientists for the first time “saw” the internal structures of the shadow side of Mars for InSight . Further analysis and data from new marsquakes will allow us to better understand the structures of the crust, mantle, and core.

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