Southern California rocked by two earthquakes felt by millions

Southern California has been rocked by two earthquakes less than 30 minutes apart.

The quakes were felt by millions across the region after they hit on Saturday morning.

The first measured 3.5 on the Richter scale as it struck at 10.05am local time.

The epicenter was 4.3 miles southeast of Ontario, according to the U.S. Geological Survey.

The second, stronger 3.9 magnitude quake, rattled in at 10.34am, with an epicenter almost exactly in the same spot.

There have been no reports of any injuries or damage at this stage. 

So far, Californians up to 119km away from the epicenter have reported feeling the latest tremor. 

Earthquakes are not uncommon in the region, but rarely excess a magnitude of around three. 

However, 2024 has seen a record number of mini-quakes across the state.

Geophysicists now warn California could be at risk of a generation-defining massive earthquake.

2024 has had more earthquakes than any year we've seen since 1988,' Caltech geophysicist Dr Lucy Jones told reporters. 'We should expect this to continue.' 

Experts believe a major quake in Southern California- usually defined as 7.0 and up - could kill at least 1,800,leave 50,000 injured and cause more than $200 billion in damage.

Dr Jones noted that it's a common misconception that spike in mini-earthquakes relieve tension in the plate tectonics underground, leaving a region more calm and less prone to 'The Big One.' 

She warned locals that the opposite is true. 

'The most constant feature of earthquakes is the relative number of large to small,' Dr Jones told local KTLA 5 Morning News on Tuesday.

'For every magnitude seven, you have 10 magnitude sixes, 100 magnitude fives, 1,000 magnitude fours, etc.' 

'So, if your rate of [magnitude] fours goes up, your chance of having a bigger one would go up by about the same amount,' the CalTech researcher explained.

There are concerns the state is poised to be struck by the 'Big One' within the next decade - researchers believe the San Andreas Fault Line ruptures roughly every 150 years.

If the Big One did strike, 'it would be a matter of a few tens of seconds before the shaking from a San Andreas event that ruptures the segments closest to Los Angeles reach our urban areas,' Jonathan Stewart with the University of California, Los Angeles told DailyMail.com.