Geologists around the world arrive to study famous earthen crack
Joe Nelson, Staff Writer
San Bernardino County Sun
09/24/2007
For decades, Bob Mathews' backyard in the Cajon Pass has served as a laboratory for geologists studying the San Andreas fault.
The fault extends across the floor of the canyon where Mathews' 140-acre ranch sits, forming a scarp that increases in height northwesterly across the valley. It is here where abundant sedimentary deposits, primarily peat deposits, have allowed geologists to study and document ancient earthquake and seismic activity, known as paleoseismicity.
"It's the highest probability fault for rupture in Southern California," said Gordon Seitz, who hosted a field trip for more than 80 geologists from all over the world at Mathews' ranch Monday.
It was one of five stops the group made throughout the day to geologic points of interest along the San Andreas fault in the San Bernardino Valley and San Gabriel Mountains.
Other stops included Lost Lake near Lytle Creek, Table Mountain north of Pinion Hills, Government Canyon west of Wrightwood and Pallett Creek east of Pearblossom.
Seitz and other geologists like him learned of Mathews' ranch - known as the Pitman Ranch and named after Mathews' ancestors - from maps that pinpointed the location of the fault line.
Seitz, a research geologist and radiocarbon chronologist at San Diego State University, did his dissertation on fault behavior and seismic activity from information gleaned from his studies of the Pitman Ranch and surrounding Pitman Canyon area.
Two charter buses carrying curious geologists from all over the world, from as far away as Indonesia and South Africa, traversed the narrow, winding road up to Mathews' ranch above the 15 Freeway, north of Kenwood Drive, Monday morning. They trekked up the hill behind the ranch to an 18-foot deep trench - the San Andreas fault - showing layers of seismic activity dating back more than 1,000 years.
"The main trace of the San Andreas fault passes right through here," said Harry Audell, a Dana Point engineering geologist who directed Monday's field trip. "I think the take-home message here today is learning the fault characteristics and geologic hazards as related to earthquake ground shaking such as landslides, liquefaction, ground subsistence, etc."
Audell used the proceeds from the sales of his book, "Field Guide to Crack Patterns in Buildings," to fund the field trip, sponsored by the Association of Environmental and Engineering Geologists.
Dwikorita "Rita" Karnawati traveled all the way from Indonesia for the field trip. The environmental and engineering geologist, who teaches at Gadjah Mada University, gazed into the trench on Mathews' property, gazing at nails painted fluorescent red, green and yellow and pounded into the earth. They showed the traces of the fault and where it ruptured last, in the year 1812.
"In Indonesia, we have many earthquakes and many active faults, but we have difficulty in measuring and investigating faults," Karnawati said, a tan scarf wrapped around her head and crowned with a New York Yankees cap - her son's. Her son and daughter came on the trip with her.
"I'm learning how people here investigate. I've never seen this in my country," she said.
Ray Weldon, now a professor of geology at the University of Oregon, was the first to study the fault on Mathews' property, Mathews said. He started before Mathews retired as a Los Angeles County firefighter in the 1970s.
Weldon was also a mentor of Seitz's, Mathews said.
Though Audell said the fault is capable of producing an 8.5 magnitude earthquake, Mathews said he isn't worried about the potential damage or harm it can cause him or his home, and takes life one day at a time.
Ken Neal, an engineering geologist from Olympia, Wash. who runs a private consulting firm, said he was interested in evidence of the fault's movement over the years. Pieces of paper were tacked to the earthen walls inside the trench with numbers illustrating the year that a particular section of the earth moved, from the most recent year of 1812 to as early as 1375.
"The thing that's always most interesting to me are the questions that aren't answered," Neal said. "The past is usually the key to the future."
Oliver Barker traveled all the way from Johannesburg, South Africa for Monday's field trip. He's the former president of the South African Institute of Environmental and Engineering Geologists.
He said geologists are finding relatively young faults in South Africa, and paleoseismic evidence from the San Andreas Fault, the most widely studied fault in the world, can perhaps provide valuable information that can characterize other faults around the world.
"People from all over the world learn their lessons here and take them back with them," Seitz said.
