That rumbling outgoing U.S. Senate Majority Leader Harry Reid felt wasn’t just the election-night results. Hundreds of small earthquakes have been gaining in strength in northwestern Nevada with the strongest yet, a magnitude-4.6 temblor, shaking things up Tuesday.

Although the earthquake swarm appears to be gaining strength, it doesn’t necessarily mean a big one is on the way. “There is a slightly elevated risk of a larger earthquake while the swarm is active,” Ian Madin, a seismologist with the Oregon Department of Geology and Mineral Industries, told CNN.

CBS SF Bay Area reported the Nevada region bordering California and Oregon was hit by 18 quakes in less than 24 hours, with magnitudes measuring from 2.7 to 4.5.

The swarm around the sparsely populated Sheldon National Wildlife Refuge began July 12. The Nevada Seismological Laboratory at the University of Nevada at Reno reported 550 quakes of magnitude 2 or higher have been recorded, with 42 registering more than magnitude 3. The last time Nevada was hit by an earthquake swarm was 2008 near Reno. That swarm ended with a magnitude-5 tremor.

“Whether a larger event will occur in the northwest Nevada swarm cannot be predicted or forecast. However, large earthquakes can happen anywhere in Nevada,” the seismological lab said on its website.