Hurricane Irma is so strong it's showing up on seismometers — equipment designed to measure earthquakes.
"What we’re seeing in the seismogram are low-pitched hums that gradually become stronger as the hurricane gets closer to the seismometer on the island of Guadeloupe," said Stephen Hicks, a seismologist at the University of Southampton in the United Kingdom.
The noise is likely caused by high winds — which cause tiny motions in the ground — and also by trees swaying in the wind, which also transfers energy into the ground, he said. The seismometer is located close to the ocean, so waves crashing along the coastline reverberate around the island, also generating seismic energy, Hicks added.
The hurricane isn’t creating earthquakes, he said. "Earthquakes occur tens of (miles) deep inside Earth’s crust, a long way from the influence of weather events, and there is no evidence to suggest that hurricanes and storms directly cause earthquakes," Hicks said.
It's not unusual for large storms to register on seismometers for hours to days as they pass over.
"We saw this for Hurricane Harvey on seismometers located close to Houston," he said. In the U.K., wintertime storms can sometimes make it hard for seismologists to see small earthquakes because the noise level generated by storms is so high.
As Irma approaches seismic sensors, "we will see a dramatic increase in the amplitude of the seismic recordings," Hicks said.