Basin fault lines are like ‘sleeping giants’
Studying the history of fault lines in the Tahoe Basin might be a better indicator of seismicity at the lake than recent earthquake activity in Nevada.
Last month a 6.0-magnitude earthquake hit Wells, a rural town in Eastern Nevada, damaging hundreds of homes and rupturing gas and water lines.
And in late January, three earthquakes shook the Tahoe region, with the largest measuring up to magnitude 3.0. The epicenter of the activity was about seven miles from Incline Village in the Mount Rose area.
Still, these activities are not necessarily the precursors to a major Tahoe earthquake or indicative of larger earthquakes to come, said Ken Smith, associate research professor and manager of the Nevada Seismological Laboratory’s seismic network.
“It’s typical earthquake behavior for Nevada,” Smith said. “These processes have been going on for thousands of years, and we have a short window in observing these things.”
While it’s difficult for scientists to fully understand the seismic cycle of Nevada, some advancements have been made in understanding activity in the Lake Tahoe Basin, especially on the Incline Village fault line.
The Incline Village fault line runs behind the K-2 elementary school and is about 10 miles long. It is the smallest and least active of three major faults in the basin. The second largest and more active fault line is the North Shore or Stateline fault line, which runs close to the Incline Village fault and through Crystal Bay. The largest and most active fault line is on the West Shore, beginning at Dollar Point and running along the lakeshore.
Scientists think all three faults could be linked to one another deep inside the Earth, but it’s hard to test that theory until one becomes active.
“The problem with the big faults is they are completely dormant between earthquakes,” said geologist Gordon Seitz of San Diego State University. “They are like sleeping giants, and then they suddenly awaken.”
Seitz and a team of geologists and seismologists dug into the Incline Village fault in 2004 and discovered that it becomes active about every 10,000 to 15,000 years, and its last earthquake was about 500 years ago.
“The Incline Village earthquakes are relatively rare,” Seitz said.
But there is a caveat.
Because the three faults are so close to one another, they could be linked deep underground and could set off one another like dominos, Seitz said.
One piece of evidence that supports this theory is how much the fault line moved in the last earthquake, said Robert Karlin, a professor at the University of Nevada, Reno, who studies earthquake activity.
The fault moved about 13 feet 500 years ago, which is more than expected for a fault line only 10 miles long.
“We expect at least a 40-kilometer fault line to occur, and we don’t see that,” Karlin said. “Which means that the earthquake was transferred between different faults.”
The Incline Village fault could be connected to the other basin faults or could even be connected to the Mount Rose fault zone, Seitz said.
Seitz said that in upcoming years, he and a team plan to study the West Shore fault line more in-depth, since it is the most active of the three. They suspect that fault line moves every 2,000 to 4,000 years, and the last major activity was 4,000 years ago.
Still, Seitz and the other experts said it is nearly impossible to predict when the next earthquake could happen. All scientists can do is locate the area that would be most affected.
“We are not so much trying to predict when the next earthquake will happen,” Seitz said. “It’s more important to say this is the area that is in danger and this is how big the shaking will be, then people can plan.”
Another benefit to studying fault lines is that the methods can be applied elsewhere, Seitz said.
“Because we have a deep lake, it’s almost like an ocean,” Seitz said. “We’re using it to create a method to assess offshore faults.”
Seitz said those methods can be used to study fault lines off the coast of California and other areas.