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Earthquake Swarms Could Signal Bigger Trouble in Tahoe

Since April, small to moderate earthquakes have shaken the Lake Tahoe region. Some scientists believe the swarms may indicate a larger, more devastating temblor is imminent.

SOUTH LAKE TAHOE, Calif. (CN) --- Lynn Thomas lives in her family’s cabin along the west shore of Lake Tahoe and is no stranger to feeling a temblor or two capable of shaking the foundations of the house and rattling the dishes. 

But something a little bigger hit the area during the morning hours of May 28. 

“That was the largest earthquake I’ve ever felt up here,” Thomas said. 

That morning, a magnitude 4.2 quake struck in the middle of the lake on an otherwise nondescript Friday. It shook some buildings around the basin but did not cause so much as a single report of a dish shattering.

But it was the culmination of a series of smaller temblors that began occurring in April. And while innocuous, it could bode ill for a region that remains particularly susceptible to the damaging effects of even a moderate earthquake. 

In fact, geologists are warning those earthquakes could portend a shaker large enough to create a tsunami capable of causing untold damage in the Lake Tahoe Basin.

“It’s a real concern,” said Gorden Seitz, a geologist with the California Geological Survey. “Although these earthquakes along the Tahoe faults are rare and may not happen, larger earthquakes have occurred and if you get a magnitude 7 earthquake, it is enough to displace the ground surface by 10, maybe 20 feet.”

Such a displacement would cause an initial tsunami wave as high as 30 feet, according to some studies. While the tsunami could cause significant damage to life and property, because of the enclosed nature of the Lake Tahoe Basin the initial tsunami wave would be followed by a series of seiche waves --- a series of standing waves in a partially or fully enclosed body of water, like a lake --- moving back and forth from lakeshore to lakeshore.

“The waves would essentially slosh back and forth and the entire lakeshore would be threatened,” Seitz said. 

To create such a scenario, there would need to be an earthquake of at least magnitude 6.0, something that has occurred repeatedly near the fault lines that run underneath Lake Tahoe in the California Geological Society’s recorded history. 

“The larger the displacement in the ground surface in the lake, the larger the tsunami wave,” Seitz said. For concerned residents, a tsunami would require at least a magnitude 6 quake if not a 7.

“The last time an earthquake that large happened in Lake Tahoe was 5,000 years ago,” said Seitz, who studied the geological record in the area to determine earthquake frequency. 

But Graham Kent, the director of the Nevada Seismological Laboratory, is one of several scientists who thinks the recent spate of earthquakes could presage an alarming prospect --- the Big One is on the way. 

Kent told the Sierra Sun this month that the series of earthquakes could very well be foreshocks, harbingers of a larger unsettling along the fault lines under the lake. 

“There’s always a little bit of concern that we are starting to have earthquakes of significant enough size that we worry about it,” Kent said. 

Seitz also points out that the series of smaller earthquakes that were detected in the Lake Tahoe Basin in April --- none above magnitude 3.0 --- might be connected to larger earthquakes along the eastern side of the Sierra Nevada.

In 2019, a series of earthquakes rocked the Searles Valley near the town of Ridgecrest in the southern Sierra, the largest of which registered 7.1 on the Richter scale. Then in April 2020, a magnitude 5.2 temblor struck between Mono Lake and Mammoth Lakes on the eastern side of the Sierra, part of a swarm of earthquakes that included more than 500 mostly tiny quakes. 

But Seitz believes it’s all part of a pattern that may include the smaller earthquakes experienced in Lake Tahoe during the past couple of months. 

“It’s almost as if the tectonic plates are unzipping as you run south to north along the east side of the Sierra Nevada,” Seitz said. “One earthquake advances the chance of the next earthquake.”

Part of the reason this is so concerning to Tahoe residents and everyone living in towns in the eastern Sierra, is because many of the largest earthquakes on record have not occurred on the San Andreas Fault, which everyone knows and recognizes, but along the Walker Lane --- a long fault that runs on California’s eastern flank near the Nevada border. 

In 1872, one of California’s largest earthquakes on record, the Lone Pine earthquake, struck in the Owens River Valley, The magnitude 7.4 quake was similar in size to the famed 1906 earthquake that destroyed large swaths of San Francisco and the East Bay. 

The Lone Pine quake and its six major aftershocks killed 27 people. 

Other more recent quakes on the Walker Lane Fault --- which runs from Death Valley north to Lassen Volcanic National Park --- include the magnitude 7.1 Hector Mine earthquake of 1999 and the magnitude 7.3 Landers quake in 1992 which killed three people and caused $90 million in damage. 

While Lake Tahoe and it’s faults are not directly connected to Walker Lane, there are undoubtedly some associations between the fault lines, Seitz says. 

“Think of it like dominos,” he said. “Slippage along one fault causes strain on the neighboring faults and that advances when the next earthquake could occur.”

In Lake Tahoe, there are three faults running north to south and have varying degrees of susceptibility to earthquakes. 

“The West Tahoe Fault is the most active,” Seitz said. 

That fault runs parallel to the west shore of Lake Tahoe, beginning roughly around Emerald Bay in the south and running toward Tahoe City in the north. In the middle of the lake, the North Tahoe or Stateline Fault runs north to south. The swarm of smaller earthquakes in the lake occurred at the southern end of this central fault line

Meanwhile the Incline Village Fault, which runs parallel to the east shore of Lake Tahoe, spurred the largest earthquake in recent history some 500 years ago. 

“West Tahoe is most active, then the Stateline and finally Incline Village,” Seitz said. 

Because the Incline Village Fault is the least active and boasts the most recent large earthquakes, scientists believe it is likely the West Tahoe Fault or the Stateline Fault that will create the next big shaker. 

“It would be a lot less surprising to see a major earthquake along West Tahoe,” Seitz said. 

However, such earthquakes are rare and residents of Tahoe may not see a major earthquake in their lifetime. In fact, the odds are they won’t. But the possibility remains. 

“If you are near the lake, especially on the beach, and you feel some shaking, that means it’s time to run for high ground,” Seitz said.  

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