Hi Kiddo. If the report out of the University of Oregon is accurate then it looks like the area of Southern California could be in for a rough time. Take Care…Cowboy

EUGENE, Ore.—Earthquakes along the San Andreas fault appear to happen at irregular intervals, according to a team of geologists led by University of Oregon geological sciences professor Ray Weldon.

Weldon’s team has produced the most complete paleoearthquake record to date at their excavation near the town of Wrightwood, Calif., about 62 miles northeast of Los Angeles. The project is yielding long-sought answers to basic questions about the recurrence of earthquakes. Weldon will present their findings on Wednesday, April 14, during the annual meeting of the Seismological Society of America (SSA) in Palm Springs, Calif.

Weldon says one of the most important findings from Wrightwood is the discovery that much larger patterns are at work than can be seen from one or two earthquake cycles.

Weldon co-authored the study with paleoseismologists Kate Scharer of the UO Department of Geological Sciences; Tom Fumal of the U.S. Geological Survey at Menlo Park, Calif.; and Glenn Biasi of the University of Nevada at Reno.

Scharer joined the team five years ago as one of Weldon’s doctoral degree students. Among her contributions is a device she calls the "trench-o-matic" to improve digital photos taken while standing inside the narrow trenches, which measure about three feet wide by 12 feet deep.

At present, the Wrightwood record shows an all-time high amount of strain on the fault, Scharer says.

"The timing and size of earthquakes in the past shows that the high level of strain in 2004 is rare," she says. "Previously, this level of strain has been followed by a spate of earthquakes taking place over a couple of centuries."

• Ray Weldon