Week of quakes shake up Golden State

To endure one moderately powerful earthquake is par for the course in California - a state whose happy-go-lucky surface charm conceals more faults than the make-up of an ageing Hollywood diva.

To endure one moderately powerful earthquake is par for the course in California - a state whose happy-go-lucky surface charm conceals more faults than the make-up of an ageing Hollywood diva.

Enduring four quakes in a week, though, is another matter. From the redwood forests of the north to the Mexican border, almost everyone in the Golden State has asked themselves the question - is this a prelude to the Big One?

On Tuesday evening, a 7.2-magnitude quake off the Pacific coast was powerful enough to trigger a tsunami warning. In Crescent City, half the town left in anticipation of a big wave which did not materialise.

That was quake number two following a rumble in the desert east of Los Angeles last Sunday. A second desert quake struck on Thursday, causing several abrupt jolting across the LA area.

Then, late on Thursday night, the ocean floor rattled once more as geologists reported a quake of 6.4 magnitude on the Richter scale about 125 miles west of Eureka.

Taken separately, none of these events was cause for much concern. Nobody was actually hurt. But together, though, they were more remarkable - a reminder that the richest state in the United States happens to sit on some of the most unstable geological ground on the planet.

The Thursday afternoon earthquake was centred on a previously unknown tributary of the San Andreas fault, which runs the length of the state from San Francisco to the Mojave Desert outside LA.

Can one shudder lead to another in a chain reaction leading to a tremor of devastating impact? The government's geological experts were playing down the likelihood, saying the chances of one earthquake leading to another of magnitude 5 or greater were around 1 in 20. Hours after making that assessment, however, the quake off Eureka struck and proved that 1 in 20 is not quite as comfortable as it sounds.