Just when Southern Californians have begun to pat themselves on the backs for having the world's stiffest earthquake building codes, there now comes news of “supershears.” These are not competitors to Supercuts, but a newly discussed type of earthquake known for the incredibly high velocities by which it travels — and compacts the earth.

New Scientist writers Richard Fisher describes “one that slipped at such blistering speeds that the rip in the Earth overtook its own seismic waves. This created the earthquake equivalent of a sonic boom, capable of striking anything in its path like a hammer blow.”

According to Fisher's article, which appeared online Wednesday, evidence

shows that this little-understood phenomenon occurs more often than

previously suspected and that a “superhighway” of supershear faults

grids the planet where 60 million people live. Although a brief moment

during a 1979 Imperial Valley earthquake seemed to fit the description

of a supershear, such quakes had long been relegated to the realm of

theory — until Turkey's 1999 Izmit quake. That 7.6 earthquake was

measured as spreading five kilometers per second. (Five kilometers is about 3.1 miles. The speed of sound

is 343 meters per second.)

Fisher says that

some geologists now believe the 1906 San Francisco earthquake may have been

a supershear. More ominously, he notes that not only is California's

San Andreas Fault part of the supershear superhighway, but says that even the state's well-fortified buildings may be no match

for the “mach fronts” generated by supershears, and quotes a Caltech

scientist as noting that less-rigorously built structures five

kilometers outside of L.A. would be especially at risk.

LA Weekly