California hit by fourth tremor

An undersea earthquake with a magnitude of 6.6 has struck off northern California - the fourth to hit the US West Coast this week.

The tremor struck at around 2230 on Thursday (0630 GMT Friday), some 200km (125 miles) west of Eureka.

Experts are trying to establish whether it was an aftershock of a magnitude 7.2 quake late on Tuesday, which sparked a tsunami alert for the whole West Coast.

There were no reports of injuries or damage following the latest quake.

"It's south of and farther out to sea than the 7.2 quake," Bruce Presgrave, a geophysicist at the USGS National Earthquake Information Center in Golden, Colorado, told Reuters news agency.

He added the latest episode might have been an aftershock.

'Active zone'

Earlier on Thursday, another quake with a magnitude of 4.9 struck near the town of Yucaipa, 126km (79 miles) east of Los Angeles.

Tremors were felt across a large area spanning the major cities of Los Angeles and San Diego.

Tuesday's 7.2 quake occurred under the ocean 146km (91 miles) west of Crescent City. A 5.2 quake shook Riverside County in southern California on Sunday.

But seismologists have played down the threat, saying that California is an "active zone", and therefore earthquakes can occur at short intervals without it being of particular significance.

Eleven people died when an earthquake struck northern Chile late on Monday. It had a magnitude of 7.9 and was felt in neighbouring Peru and Bolivia.

Another one, with a magnitude of 6.8, was felt in the Aleutian Islands, off Alaska, on Tuesday.

There were no reports of casualties or damage.