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Scientist wonders if uncommon earthquakes under Tahoe could be foreshocks

Miranda Jacobson
mjacobson@tahoedailytribune.com

INCLINE VILLAGE, Nev. — A recent series of rare earthquakes centered under Lake Tahoe have scientists wondering if they could be foreshocks of bigger events.

The temblors began in April when many smaller magnitude quakes shook the region. They got stronger and a magnitude-4.2 earthquake struck right under the lake at about 8:30 a.m. on May 28.

University of Nevada, Reno Seismological Laboratory Director Dr. Graham Kent began watching the basin carefully, unsure if these quakes are isolated or if they could be the start of something much larger.



“Earthquakes that are on the fault lines below Lake Tahoe are not very common,” Kent said. “The real question is, are we having smaller but significant earthquakes and they’re just going to go away, or are they going to be a foreshock to quite larger events? Statistically, it’s unlikely that they’re going to be the foreshock or predecessor to large quakes, 7 or 8, but we don’t know that. So that’s why there’s always a little bit of concern that we are starting to have earthquakes of significant enough size that we worry about it.”

“Earthquakes that are on the fault lines below Lake Tahoe are not very common. The real question is, are we having smaller but significant earthquakes and they’re just going to go away, or are they going to be a foreshock to quite larger events? Statistically, it’s unlikely that they’re going to be the foreshock or predecessor to large quakes but we don’t know that. So that’s why there’s always a little bit of concern that we are starting to have earthquakes of significant enough size that we worry about it.” — University of Nevada, Reno Seismological Laboratory Director Dr. Graham Kent

A foreshock is a mild tremor preceding the violent shaking movements of an earthquake. The energy in the Sierra granite doesn’t dissipate in the same way, for example, broken up rocks would in the Bay Area, and the West Shore is long overdue for a rupture event, Kent said.



Lake Tahoe lies on three major fault lines in the region. The first, and biggest, spans from Emerald Bay to Dollar Point, with two more cutting through the Incline Village and Crystal Bay region. Dr. Kent said the recent earthquakes the basin experienced are happening at smaller faults that connect other larger faults. This means their rupture size is limited, but are still rubbing against the larger faults.

The Incline Village fault line runs throughout the town. The photo above shows the trench at the Incline Village Elementary School across the IV fault line. (Provided
Dr. Graham M. Kent)

“The east side of the fault drops relatively to the west side,” Kent said.

The dropping of these faults is what leads to the formation of the deepest parts of the lake, and could eventually influence a tsunami.

Kent said that it would take a large magnitude-6 to 7 earthquake to start actually seeing a tsunami at the lake, but there’s no way for them to predict if these previous quakes are related to a bigger event or isolated. While hypothesizing what could happen if there were a tsunami, Dr. Kent pointed out that one of the biggest differences lies in the season it occurs, especially during the summer.

“I think the biggest issue, other than the potential loss of life, which would be significant, is the boat issue,” Dr. Kent said.

The ‘boat issue’ is multiple vessels potentially tipping during a large wave, which could rise up to 30 feet, and potentially start fires with leaking boat fuel. Another potential issue includes the redistribution of the entire lake depending on which direction the wave goes.

Dr. Kent said that while these things could all possibly happen, those things are worse case scenarios. For now, he has some advice for those who live and vacation in the basin.

“If you feel a strong shaking,” Kent said, “Not like it’s kind of strong, but a strong, violent, shaking, move off the beach immediately. The second thing people need to know is even without the earthquake, if the water level ever changes dramatically or quickly, leave the beach because it could be a landslide. With an earthquake that could make the tsunami larger, or you could just have a landslide without the earthquake and it could be significant.”

If you feel an earthquake, you can report it on the USGS website.


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