Scientists have known about the faults for years, but now they can actually see them better. Researchers mapped the Tahoe area using technology called LIDAR, where a small aircraft reads the landscape using laser points.
Before that, they had to use boots on the ground, says Jim Howle of the USGS.
HOWLE: "But it was very hard to trace exactly where they went, because the vegetation is so dense."
The maps suggest Tahoe has seen seismic activity over the past
10,000 years; that's more recent than scientists previously
thought.
HOWLE: "The tectonic rates that we have quantified are two to three times greater then previous estimates."
Researchers can't yet tell exactly when past quakes occurred,
or just how many might be in store -- but the new data does suggest
these fault lines have potential for a quake ranging in magnitude
from 6.3 to 6.9.