A massive 7.1 magnitude earthquake has rattled parts of Southern California with its biggest tremor in 20 years. The quake struck at the depth of 0.6 miles (0.9km) near the state’s city of Ridgecrest, north-east of Los Angeles. Saturday’s terrifying event came just two days after the same area was hit by a 6.4 magnitude earthquake on Thursday.
Seismologist Dr Lucy Jones said the quakes could continue and warned “preparations” for the Big One should be in place.
Dr Jones said: “One should always be preparing for a big one. This does not make it less likely.
“There is about a one in 20 chance that this location will be having an even bigger earthquake within the next few days that we have not yet seen the biggest earthquake of the sequence.
“It is certain that this area is going to be shaken a lot today and some of those aftershocks will probably exceed magnitude five.”
READ MORE: Was Ridgecrest CA quake on San Andreas fault line?
What is the ‘Big One’?
The Big One is a hypothetical earthquake of magnitude 7.5 or greater that is expected to happen along the San Andreas Fault.
The San Andreas Fault is a continental transform fault that extends roughly 745 miles (1,200km) through California.
It forms the tectonic boundary between the Pacific Plate and the North American Plate and is divided into three segments, each with different characteristics and a different degree of earthquake risk.
Such a powerful quake would produce devastation to human civilisation within about 50 to 100 miles from it’s epicentre.
Urban areas at risk include Los Angeles, San Francisco and Palm Springs.
Californians are on permanent alert for the Big One, which seismologists say is well overdue.
The latest US Geological Survey (USGS) quake data estimates that 1906-type earthquakes occur at intervals of about every 200 years.
This is based on the long-term rate of slip on the San Andreas fault and the amount of offset that occurred on the fault in 1906.
But it remains difficult for scientists to predict when the next mega-quake will hit.
The USGS says its models suggest “there is a small chance (about two percent) that [a 7.9 magnitude quake] could happen in the next 30 years”.
But the agency points out “this does not mean that the San Francisco Bay region will not experience damaging earthquakes in the next hundred years.”