Earthquake swarm hits Nevada

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Hundreds of small earthquakes have rumbled under northwestern Nevada like a seismic drumroll since midsummer, and in recent days, they have built to a crescendo.

This does not necessarily mean a big one will come, state seismologists said, but they added that it's good to be prepared, just in case.

Seismologists refer to such quake groupings as swarms, and the U.S. Geological Survey has detected them regularly. They can produce thousands of small tremors.

 The largest topped out at a magnitude 3.8 -- a strength that could be felt but was not dangerous.

In recent days -- since October 30 -- they have grown stronger, with three over magnitude 4.0.

The strongest one weighed in Tuesday at magnitude 4.6 -- approaching the threshold of a lightly damaging quake.

"There is a slightly elevated risk of a larger earthquake while the swarm is active," said seismologist Ian Madin from neighboring Oregon.

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