There are two kinds of people in Southern California: those who think they've experienced a major earthquake, and those of us who know we haven't.
If you were here Jan. 17, 1994, you probably put yourself in the first group. Many of us were jolted out of bed at 4:31 a.m. that day, and some of us experienced earthquake shaking that was about as bad as it gets. All of us recall the images: apartment buildings pancaked, freeway overpasses torn apart. The Northridge quake, an abrupt lurch across a patch of a fault some 10 miles square, caused 57 deaths. Those eight seconds were an emotional seismogram etched indelibly onto our central nervous systems.
So it offends sensibility that seismologists consider Northridge to be only a strong temblor, two steps below the dreaded magnitude 8 Big One. But here's the reality: A Big One on the southern San Andreas fault will be the result of a lurch along a swath of a fault. A long swath. What seismologists call the earthquake rupture will extend 10 to 15 miles deep and 200 to 250 miles long. Maybe more. It will be the size of 20 Northridge earthquakes laid end to end.
It will feel like the Ft. Tejon earthquake that struck 150 years ago, the Big One none of us remember.
On Jan. 9, 1857, the San Andreas fault unzipped from near the central California town of Parkfield down to Cajon Pass, a distance of nearly 250 miles. Stream channels crossing the fault reveal that, at least in some places, fault motion reached a staggering 30 feet, with an average sideways movement of about 15 feet. It blasted down the Carrizo Plain, past the modern mountain communities of Frazier Park and Gorman, along the edge of Palmdale, running out of steam only miles from San Bernardino. The earthquake appears to have proceeded from north to south, a freight train barreling down on San Bernardino at 6,000 mph. (Only in bad TV movies do earthquakes chase trains.) It rivaled the great 1906 San Francisco earthquake in magnitude, power and extent--every aspect that matters to a seismologist. But for Angelenos, it's a history that precedes us, a moment in time that does not define us.
