Seismology concerns waves. The epicenter of an earthquake is like a stone thrown into a pond. The disturbance spreads outward along the earth’s crust. This movement results in a change in pressure in the air just above the ground. This produces infrasound waves (long, slow sound waves so low that humans cannot hear them) that pass through the atmosphere both directly from the epicenter (epicentral waves) and above the seismic waves as they pass. move along the earth (surface waves).
On Earth, a network of earthquake ground stations use sensors to detect these waves and to identify the epicenter and strength of earthquakes. The new study shows how a balloon equipped with sensors can do the same from the air. An on-board barometer that captures only epicentral or terrestrial infrasound waves can provide insight into the location and strength of an earthquake. Whoever captures the two could tell what a planet’s crust looks like. This could prove useful in determining the area of a planet that we cannot actually see.
(Seismological data also works for those we can to see. The earthquake readings from the InSight lander have been invaluable in map the Martian crust.)
To prove that it was possible to study the seismology of Venus from the air, the team planned a campaign of flights to Oklahoma – where earthquakes are common, probably due to hydraulic fracturing – to test if they could hear the infrasound of Earth rumbling from high in the atmosphere. . But when the Ridgecrest series of earthquakes struck near the original JPL base in Los Angeles in 2019, triggering thousands of small aftershocks, senior program director James Cutts, research technologist Siddharth Krishnamoorthy and d other team members sensed an opportunity. “It had to be done quickly, because the later it was, the weaker and more numerous the aftershocks,” explains Krishnamoorthy.
Problem: They didn’t have any balloons yet. For 16 frenzied days, they struggled to build four ultralights “heliotropic, Simple balloons about 20 feet in diameter and 12 feet high, made from plastic sheeting and duct tape. The heliotropes, named Tortoise, Hare, Hare 2, and CrazyCat, soared into the stratosphere as the sun heated the air inside their charcoal-covered plastic balloon “envelopes”. They floated freely with the breeze, each with a set of barometric sensors hanging from a tether below, listening to the very faint sounds of an aftershock.
On July 22, 2019, the ground shook with this aftershock. As it passed under the balloons, it produced disturbance of surface infrasound waves that traveled 4.8 kilometers upward and struck the Tortoise barometer, recording a series of tiny pressure changes. These changes were so minimal that it took Krishnamoorthy months of post-flight data analysis to see them. But they were there: tiny wave profiles that perfectly matched earthquake readings from four ground-based seismic stations in the area near the balloons. They also matched computer models of the infrasound propagation of the aftershock. Turtle had heard the earthquake.
But could a balloon capture seismic infrasound by floating in the atmosphere of Venus? There, the balloon would fly much, much higher, about 50 kilometers instead of 5. At this altitude, the acid clouds of Venus could attenuate infrasound waves, which makes them slightly more difficult to detect. (What does Venus look like? This is what Bach could look like on Earth, Titan, Venus, and Mars, due to different sound wave attenuation factors.)
However, other factors would work in favor of the ball. Although Venusian winds regularly blow over 200 miles per hour, a balloon at a stable altitude should remain relatively “silent” when in flight. (Imagine the stillness of being on a hot air balloon, which travels at the same speed as the wind.) Due to Venus’ super thick atmosphere, Byrne writes, the surface of Venus is coupled to this atmosphere about 60 times more efficiently. than The Earth is, which means that the energy of an earthquake will be much more easily transmitted through the atmosphere on Venus, making it a prime location to float a seismometer.