Paleoseismology Changes the San Andreas Game

An analysis of rocks drilled from deep beneath the central portion of the San Andreas fault seem to indicate a potential for larger quakes than previously thought.

IMAGE: The San Andreas Fault, on the Carrizo Plain, about 100 miles from Los Angeles. CREDIT: NASA Jet Propulsion Laboratory

A new study in the journal Geology presents an analysis of rocks drilled from a section of the San Andreas fault here in California showing that the slow creep of the faultline may be more dangerous than previously thought.

The San Andreas faultline is nearly 1300 kilometers long and runs the length of the state of California, from Baja in the south to the Mendocino Triple Junction in the north. It’s the dividing line between the Pacific Plate and the North American Plate, which are rubbing alongside each other as one moves north and the other moves south. It has been the site of several major earthquakes in the past couple of centuries, including the 1906 San Francisco earthquake, the 1989 Loma Prieta quake, and the 1994 Northridge quake. All three of these earthquakes resulted in death and destruction and were the result of a sudden, fast, and extreme slip between the two plates. Basically, they stick for a long time and then suddenly slide and cause a massive quake.

But if you know your California geography, you might have noticed something about…