SDG&E; Scientists Find Evidence of Activity on Rose Canyon Fault

Seismologists working for San Diego Gas & Electric Co. announced Wednesday that they have discovered new evidence that proves the Rose Canyon earthquake fault line is active, possibly settling an ongoing debate among scientists and public officials.

Their findings, if borne out by further testing, would establish the only active fault line in the city of San Diego and could bring into play a variety of complex state and municipal regulations regarding development in potential earthquake areas.

An earthquake “could happen tomorrow or 200 years from now. We don’t know yet,” said Scott Lindvall, a geologist with Lindvall, Richter & Associates. “It’s something that has the potential to move.”

The Lindvall firm, in conjunction with San Diego State University Prof. Tom Rockwell, discovered the new evidence while conducting research on the fault line in a trench dug in a parking lot at an SDG&E; operations center on Santa Fe Avenue. SDG&E; officials hired the seismologists two years ago to identify possible hazards to natural gas lines.

Disruptions in soil patterns indicated that a number of earthquakes have occurred in the area--east of Interstate 5 and north of Interstate 8--over the past 11,000 years.

City planning officials contacted Wednesday said they were unsure what impact a reclassification of the area might have on commercial and residential developments.

“The results are less than 24 hours old,” said Robert Hawk, senior geologist with the city’s Building Inspection Department. “I haven’t had a chance to look over the evidence, so I’m not going to say whether (the fault) is or isn’t active.”

The city currently classifies the fault line as “potentially active” under guidelines established by the state’s mines division. The city requires geologic surveys for development within 500 feet of potentially active fault lines.

“There are no active faults in the city of San Diego,” Hawk said. “We still don’t have an active one until we see the evidence. . . . Long Beach has one of the most active faults around, and they’ve done just fine.”

Regulations regarding development near active fault lines are substantially more stringent. For example, specially reinforced foundations are required and some lots in the area might be off-limits to any development, one official said.

The trench was dug Monday and the seismologists made their discovery the same day. They were working on a branch of the Rose Canyon Fault, which stretches from Mount Soledad through La Jolla Canyon west to the ocean. The branch follows a roughly north-south line east of I-5.

“It’s a complex zone,” Lindvall said. “It’s not something where you’ve got a nice, straight line.”

Lindvall said it is not clear what hazards the fault line might pose.

“Since it’s broken once, it could happen again,” he said.

The group found indications that breaks have occurred since the topsoil in the area was formed about 11,000 years ago, he said.

“We know that since that soil formed, the fault has moved,” he said. “The topsoil is very indicative of that.”

Another study is needed to determine the size of the fault line and the potential frequency and scope of future earthquakes, he said. In the meantime, charcoal samples from the dig will be tested to verify the group’s findings, a process that could take many months, Lindvall said.

Branches of the fault run through many expensive residential and commercial areas. Because the area has been so widely developed, the SDG&E; parking lot was one of the few undisturbed areas that could be studied.

Lindvall downplayed the threat to the public and emphasized the importance of the settlement of the debate about the fault line. While many scientists have contended that the Rose Canyon Fault is active, no proof has been produced to meet state requirements.

“It’s a really exciting find for the geologic community,” Lindvall said.