Quake Rupture Zone Shows Signs of Wear : Seismology: Scientists studying 45-mile fissure left by Landers temblor battle erosion caused by the elements and tourists.

Rains have come, and so have scientists and sightseers, and, just three months after the event that caused it, the dramatic 45-mile-long main rupture zone of the Landers earthquake is showing signs of deterioration.

The natural and man-made erosion is complicating the job of researchers who are measuring the displacement and studying faults caused by California’s third most powerful quake this century.

A visit to the area of maximum slippage with a U.S. Geological Survey scientist last week revealed numerous tiny landslides on the escarpments that mark the cut across the Mojave Desert from just north of Yucca Valley to the remote Rodman Mountains. The surface here shifted in just 32 seconds when the magnitude 7.5 temblor hit June 28.

Rough pathways haphazardly made by scientists, bikers and occasional tourists who have come to look at the escarpments now follow the rupture.

In some places the damage is worse. Graffiti can be seen on the sheer clay surfaces that mark the rupture.

“This area has been trashed,” said seismologist Ken Hudnut of the Geological Survey as he prepared to measure the slippage along Galway Lake Road. “Some of this looks as if someone took a shovel to it.”

Hudnut visited the desert in an attempt to resolve a dispute over the width of the greatest horizontal displacement during the quake. Colleagues at the Geological Survey’s regional office in Menlo Park had challenged earlier figures, questioning whether the displacement was as great as the 22-foot estimate.

The scientist chose as his measuring point the place where Galway Lake Road crosses the rupture in a bump that used to be distinct but has been worn down by vehicles.

The road was straight before the earthquake. Now, at the point of the rupture, it jogs more than 20 feet.

When the scientist arrived at the scene at noon, the sky was almost cloudless, the air still and the temperature more than 100 degrees. By the time he left toward evening, there was lightning, the wind was picking up and a cloudburst had arrived, further obscuring the rupture zone’s features.

At best, the measuring was tedious work. It took Hudnut five hours to match bushes along the road to aerial photographs he had brought with him, calculate displacement angles, put down stakes over hundreds of feet, measure the distance between them, and take photographs to guide surveyors who may later try to confirm his work.

Most stakes were left in the ground to help the surveyors; only the ones placed in the road were pulled out.

While Hudnut did his work, no other people or vehicles ventured down the dirt road leading toward the dry lake. The only sign of life besides lizards was the occasional plane from the nearby Marine base outside Twentynine Palms.

Those who are drawn to see the rupture zone, mostly bikers, usually come on weekends. On weekdays, it is quiet.

At the end of the day, as the thunderstorm came up and a flash flood followed, Hudnut said that initial reports of a 22-foot rupture may have been a bit excessive.

“But there is no way the displacement is less than six meters (20 feet),” he said.

He said surveyors sent out by the Geological Survey may have failed to take into account the proper angle between the earthquake fault and the road used for the measurement when they questioned the rupture’s size.

Much of the survey work is done by graduate students and technical workers under the direction of scientists.

High on a nearby mountain, Hudnut pointed out the faint traces of a fault that could be thousands of years old. It remained inactive during the Landers quake.

“You can have an older fault that no longer is in a favorable orientation to slippage,” he said.

“This new slippage has occurred elsewhere. These are fault zones, not lines that last forever, and the movements that occur cut new paths when they need to.”

Away from the Landers rupture zone, Hudnut said, cracks radiate across the desert floor, in some cases for two or three miles. They could be the sites of future ruptures.