Seismometers Picked Up Hurricane Melissa’s Historic Power Like an Earthquake

Hurricane Melissa was so powerful it shook the Earth hundreds of miles away

TO Robin George Andrews edited by Andrea Thompson

Hurricane Melissa will be included in the number most powerful hurricanes in the Atlantic Oceanin doing so, the hurricane reached a strength reached by only a few storms in recorded history. Melissa was so powerful—with astonishing peak winds of 185 mph—that it literally shook the ground hundreds of miles away in Florida, where its march across the ocean was seen on seismometersinstruments designed to detect earthquakes.

Although these sensors have recorded many severe storms before, the recordings highlight the destructive power of Melissa, Category 5 it's a hurricane devastated parts of JamaicaCuba and the Bahamas. They also highlight how a tool typically used for geological purposes could improve our understanding of Earth's most ferocious weather events, particularly by opening a window into the hurricanes that raged before satellite and airborne reconnaissance was possible.

While seismic waves are easily linked to fault movements and shaking, “seismometers are used for more than just measuring earthquakes,” says seismologist and earthquake geologist Wendy Bohon, whose institutional affiliation cannot be listed at this time due to the ongoing federal government shutdown. “Seismometers detect anything that transmits energy into the ground. Taylor Swift concerts; it could be construction; it could be people walking around seismometers.” Landslides, avalanches, asteroid impacts, volcanic eruptions and secret nuclear weapons explosions are all interesting squiggles in the instrument's output, since they all generate seismic waves.

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Hurricanes and typhoons are no exception, and they rock the Earth's crust in two different ways. The first occurs “due to wind shaking trees, telegraph poles, fence posts, etc., which then connects to the ground as a seismic wave,” says Stephen Hicks, a seismologist at University College London.

The second, more important component is the storms that rock the ocean itself. “When the waves rise and fall, they drum on the ocean floor,” Bohon says. Sometimes this impact action appears on seismometers as thin peaks and troughs. Hurricane Melissa registered ominously on Jamaica's seismometers as frighteningly obvious jagged teeth in the days leading up to landfall. “It makes your heart sink a little bit because you realize the ferocity of the storm,” Bohon says.

Hurricanes and typhoons are relatively easy to track and study in real time: barometers and brave Hurricane Hunter pilots record changes in air pressure, ocean sensors track changes in temperature, and satellites can create 3D images of these eddies. Seismometers, which operate continuously and can be found around the world, can also be used to track a hurricane's path, says Andreas Fichtner, a seismologist at the Swiss Federal Institute of Technology in Zurich.

While this is useful here and now, it is especially useful for understanding hurricanes in the somewhat older past—back when aerial photography and satellite investigations were not possible. “In the pre-satellite era, we already had a seismic network on the surface of the Earth,” says Fichtner. It's not as dense as it is today, but it's still enough for hurricane researchers hoping to rewind time so they can learn where tropical cyclones used to form and where storms previously dissolved.

This long-term seismic soundtrack also shows potential for determining the intensity of past hurricanes. Seismic waves caused by storms effectively record changes in ocean wave heights. That means scientists could match the cacophony of today's hurricanes with their intensity, and then use what's preserved in old seismic catalogs to see whether the cyclones have gotten stronger over time.

As sea surface temperatures have risen sharply due to global warming, climate models predict that in the coming years hurricanes will get strongerwhich will lead to higher wind speeds, higher rainfall amounts, and stronger storm surges that will hit anyone in their path. There are some readings that this effect is already in effect. And if, as recent studies show, seismometers can determine the strength of tropical storms has been around for a long time, our understanding of this trend will undoubtedly improve.

The fact that seismometers can be used in unconventional ways to study our rapidly changing world is exciting, Bohon says. But seeing increasingly violent storms like Melissa appear on those gauges is also “frightening and heartbreaking,” she adds.

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