Scientists are hoping that a trench dug across the Wasatch Fault can help them date the last major earthquake to hit the area.

Davis County Geologist Mike Lowe said deposit samples taken from the trench dug in a Fruit Heights field will undergo dating tests not available 10 years ago when a previous trench was carved in the same area.Dating the last quake may help officials with planning, zoning and construction restrictions along the fault line, he said.

Scientists can't predict exact intervals between earthquakes, but they believe the average interval along the section of the fault that runs through Davis and Weber counties is about 2,000 years.

"If we discover the last surface fault rupture occurred 1,000 years ago, then our risk (for another one) is much greater than if it was, say, 500 years ago," Lowe said. "It's important to know so we know how seriously to respond to and plan for earthquakes in planning, zoning and construction."

The geologist took about 10 local mayors and county commissioners Wednesday to the trench dug on land owned by Ray Harvey just south of Vista Drive.

The trench is about 30 yards long, 3 feet wide and 15 feet deep. Scientists are using a series of hydraulic supports to help hold up the trench's sheer, vertical walls.

Its south wall is marked with a series of colored tags showing the patterns of different sediment layers that help outline places where deformation has occurred due to the fault's movement.

Lowe said evidence gleaned thus far shows the fault has vertically shifted the land surface some 90 to 100 feet over the last 12,000 years. That accounts, he said, for the 80- to 100-foot-tall hill on the trench's east end.

Davis County lies along the so-called Weber segment of the Wasatch Fault, Lowe said. It is the largest continuous segment along the fault. The segment's ends are marked by North Ogden on the north and North Salt Lake on the south.

Lowe said it may take six months to a year to get results of the dating test.