Old photos, new technology help search for San Francisco quake fault

Seismologists say old photos and new technology have allowed them to confirm the exact rupture point of the fault that caused the 1906 San Francisco earthquake. The section of the San Andreas Fault that produced the deadly quake runs through the town of Portola Valley, about 40 miles south San Francisco -- but where exactly the fault trace lies has long been a mystery, they said. "The initial trace reported in 1906 was fairly accurate, but the story kept changing over the years until 100 years later, the maps and reports were no longer true to what actually happened," Ted Sayre, with the geotechnical consulting firm Cotton, Shires and Associates, said. "The story of this fault trace reminds me of that game [called 'Telephone'] we all played as kids, where one person whispers a sentence to somebody and they whisper it to the next person and by the time it goes around the circle, the sentence has completely changed," Sayre, who also served as Portola Valley's "town geologist," said. The discrepancies were born in hand-drawn maps that had been inaccurately reproduced, as well as several film negatives that had been inadvertently flipped during printing, thus producing reversed photographs, he said. The mistakes, first published in 1908 and cited by at least eight subsequent studies, placed a branching fault trace several hundred yards off the mark, he said in the journal of the Seismological Society of America. Using laser technology and closely studying original photo negatives, the researchers were able to determine the exact location of the fault, which runs through Portola Valley along a single trace.