A fourth earthquake has hit the west of the United States this week, just off the northern California coast line. The huge tremor measures 6.6 magnitude and struck at approximately 22.30PST Thursday evening (06.30 GMT Friday), just 220km (125 miles) from the west coast of Eureka.

Earthquake experts are attempting to establish whether the quake was an aftershock of the 7.2 magnitude earthquake that hit on Tuesday, which resulted in an emergency tsunami alert being given across the entire West Coast.

The latest quake, as of yet, has not resulted in any reported injuries or deaths.

A geophysicist at the USGS National Earthquake Information Centre in Colorado reported that it may have been an aftershock, and said to Reuters, "It's south of and farther out to sea than the 7.2 quake."

East of Los Angeles on Tuesday, near the city of Yucaipa, and 4.9 magnitude earthquake struck and tremors were felt from Los Angeles all the way to San Diego.

In addition, a 5.2 earthquake was measured in Riverside County in southern California on Sunday.

Seismologists have attempted to ease fears of a further larger, more devastating earthquake hitting, and have commented simple that California is an "active zone" and that earthquakes in the region are likely to occur at short intervals.

Also, late on Monday, eleven people died in Chile as an earthquake hit the South American continent. Following this a 6.8 magnitude earthquake was recorded in the Aleutian Islands, which lie off of Alaska on Tuesday.