Balloon fleet senses a 7.3 magnitude earthquake from the stratosphere

Researchers plan on applying the new technique on Venus to reveal its internal structure.
Deniz Yildiran
A balloon hangs above the mountains, waiting for waves of infrasound generated by an earthquake to hit. Here, those waves are approximately visualized by the gray dots.Credit: CNES/Raphael Garcia.
  • Four Strateole-2 balloons sensed a 7.3 magnitude earthquake in Indonesia from the stratosphere in a world first.
  • Excited about the event, scientists hope to detect quakes on Venus to know more about the planet's internal structure.
  • The fleet could also be used in hard-to-reach places on Earth.

In a world first, a fleet of giant balloons equipped with a network of sensors detected a large earthquake from the stratosphere.

The event is especially exciting for the scientific community, as the technique could one day be applied on Venus, whose hot and dense atmosphere prevents current technologies from detecting quakes occurring on the planet.

Humanity cannot possibly observe seismic activity on all planets through ground-based sensors, which could provide great clues about how their structures look on the inside. Therefore, planetary scientists turn to benefit from the atmosphere.

Balloons and sensors floating through the stratosphere detect infrasound released into the atmosphere when an earthquake hits. Balloons, 11 meters (36 feet) in diameter and weighing 30 kilograms (66 pounds), can support up to four instruments.

Stratosphere is new to the seismology game; the balloons are mostly helpful with atmospheric activities, which can pick up small, local quakes. However, a fleet of balloons had recently set the bar high by detecting a 7.3 magnitude earthquake in Indonesia.

“We are very, very happy because it was not only a single balloon that detected the earthquake, it was sensed on multiple balloons,” says Raphael Garcia, lead author of the new study and a planetary scientist at the Institut Supérieur de l’Aéronatique et de l’Espace of the University of Toulouse.

On December 14, 2021, the large earthquake mentioned above has been detected by four of IASE’s Strateole-2 balloons within 10 minutes. They detected the emitted infrasound within a 3,000-kilometer (1,860-mile) radius at a 20-kilometer (12-mile) altitude.

The data helped the research team accurately calculate the magnitude and various parameters about both the quake and planetary structure.

Next stop: Venus

The study is considered a great leap toward possibly finding what's inside Venus, though the balloons have only been tested on Earth.

“The search for detecting a big quake on stratospheric balloons, it’s a bit competitive,” Garcia says. “But it’s a nice competition because, in the end, we’re working to demonstrate the same concept.”

“The story for our interest in Venus is that we know nothing of its interior,” Garcia says. “We don’t know how it’s made inside, and on Earth, seismology is one of the best tools to figure that out.”

Venus draws the attention of planet enthusiasts as its interactions between tectonics and atmosphere remain quite mysterious, which makes it inhabitable, unlike its sister planet, Earth. In the early 2030s, three missions to Venus are being planned, which excites scientists to call the next ten years “the decade of Venus.”

The findings have been published in the journal Geophysical Research Letters.

Abstract:

The ground movements induced by seismic waves create acoustic waves propagating upward in the atmosphere, thus providing a practical solution to perform remote sensing of planetary interiors. However, a terrestrial demonstration of a seismic network based on balloon-carried pressure sensors has not been provided. Here we present the first detection of seismic infrasound from a large magnitude quake on a balloon network. We demonstrate that quake's properties and planet's internal structure can be probed from balloon-borne pressure records alone because these are generated by the ground movements at the planet surface below the balloon. Various seismic waves are identified, thus allowing us to infer the quake magnitude and location, as well as planetary internal structure. The mechanical resonances of balloon system are also observed. This study demonstrates the interest of planetary geophysical mission concepts based on seismic remote sensing with balloon platforms, and their interest to complement terrestrial seismic networks.

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