They're not detectives, strictly speaking, but Tony Kittner and Henri Mulder are definitely searching for clues -- clues hidden beneath the surface of the earth.
The evidence they and other scientists ultimately find will help determine the fate of two of Kern County's most important structures: the main and auxiliary dams at Isabella Lake.
Mulder, a geotechnical engineer, and Kittner, a geologist, for the U.S. Army Corps of Engineers, are gathering data from a series of 15-foot-deep trenches and much deeper bore holes. Most of the trenches have been cut across a gash in the earth called the Kern Canyon Fault.
The fault, which generally runs in a north-south direction, snakes directly under the western edge of the auxiliary dam and beneath the length of Kern's largest reservoir. Once thought to be inactive, the Kern Canyon Fault is now believed to be capable of causing a 7.5 magnitude earthquake, large enough to rupture the auxiliary dam, say engineers with the Army Corps.
Before you decide to sell your house and move to higher ground, it should be understood that the last earthquake on the 88-mile-long fault happened roughly around the reign of King Tut.
"We know the fault moved 3,300 years ago," Kittner said. "But we don't know if it will ever move again -- or if it'll take another 3,300 years."
But there are other faults in the area.
"It is important to note that the Kern Canyon Fault is only one part of the seismic problem. There are multiple seismic sources that could cause strong ground shaking at the dam," said Ronn S. Rose, a geologist and dam safety program manager for the Army Corps.
While the Kern Canyon Fault does have the potential to cause a rupture of the dam, reinforcing the earthen embankment through the use of various design additions can solve the problem, Rose said.
But first, the job is to identify and quantify all possible problems, including the seismic issues and the water seepage that was detected in 2006. Once that is done, the designers and structural experts will likely go to work on a solution.
"Many dams, even recently constructed dams throughout the world, are located on active faults," Rose said. "So there is quite a lot of experience in designing dams to withstand rupture (caused by) faults underneath the dam itself."
HOW BIG IS THE PROBLEM?
On a recent morning, Kittner and Mulder walked along the edge of a 520-foot long trench dug on the dry side of the auxiliary dam. Several men wearing hard hats were down inside the 15-foot-deep trench painstakingly examining the dirt sides, looking for clues to the geology and seismic history of the area.
At one point about eight feet below the surface, the jagged sides of the trench indicated the presence of an ancient stream bed, long ago buried by the forces of earth and time.
No clues to seismic activity have yet been found in the trench, Kittner said. But the length of the ditch will eventually double, so there will soon be more to see and document.
"We look at past movement and try to date the material," Kittner said. "In geology, the past and present are the key to the future."
The long trench is just one of several that have been excavated up and down the length of the Kern Canyon Fault (see map). At each of those trenches, or investigation sites, scientists look for evidence of past earthquakes, or fault movement. If they find it, they try to locate associated organic materials that can be carbon-dated, thereby giving geologists and seismologists a clue as to when the seismic event occurred.
If two investigation sites, miles apart, reveal fault movement that happened at the same time, scientists may rightly conclude that it was the very same earthquake occurring on the same fault. And for a Sherlock Holmes-type like Kittner, an even more fascinating scenario may be detected.
When evidence of fault movement is found at two locations on the fault, and dating indicates a single event, the distance between the two locations becomes of paramount interest.
"The farther apart the sites are, the higher the magnitude of the movement," Kittner said.
SOLID ROCK VS. CRUMBLING GRANITE
Inside a storage container near Isabella Dam, the Army Corps keeps several long wooden boxes packed with cylinder-shaped core samples taken from beneath the main dam and the auxiliary dam.
When you compare the two, the differences are mind-blowing. Beneath the main dam, drillers soon encounter a massive layer of bedrock: hard, solid, stable. The rock is so hard, Kittner and Mulder can barely scratch it with a knifepoint.
"This is what the engineers like to see," Kittner said.
"Clean fractures, excellent rock material," Mulder echoes in clear praise.
But when they turn to the core sample pulled from beneath the auxiliary dam, the love is gone.
"A concrete dam, a 300-year dam, could not be built on this material," Kittner said.
"The auxiliary dam sits on 100 feet of soil," Mulder said. "Below that is weathered rock."
Kittner reaches down and picks up a piece of the bedrock pulled from under the auxiliary dam. It breaks in his hands with little effort, eventually crumbling to pieces like a stale coffee cake.
Kittner is passionate about keeping people downstream safe from catastrophe. He comes by it naturally.
As a child growing up in West Virginia, he saw first-hand the suffering caused by Hurricane Camille in 1969. Houses were washed away like twigs in a creek after 39 inches of rain fell during the massive storm.
"That experience drives me to investigate this thing as thoroughly as we can," he said. "We want nothing more than to keep people safe downstream."
Currently, the lake level at Isabella is quite low -- about 18 percent of capacity -- due to California's ongoing drought. With less than 10 feet of water pushing against the more problematic auxiliary dam (vs. about 80 feet at the main dam) the chance of disaster is miniscule, Corps. officials say. Even if the Sierra experience high precipitation this winter, the Corps has placed a limit on the amount of water that may be stored in Isabella. That limit stands at about 63 percent of the total capacity of the reservoir.
David C. Serafini, the technical lead engineer for the Isabella Dam project, said a preliminary screening of alternative solutions is scheduled to take place in December, using information from the field investigations.
"Several measures will likely be evaluated to strengthen the auxiliary dam for seismic and seepage concerns," he said.
Solutions could include the installation of filters or drains, foundation improvement and possibly replacement of portions of the embankment, Serafini said.
No one was prepared to predict when the efforts will be completed and the lake allowed to once again reach capacity, weather willing.