Last Thursday, a 6.4-magnitude earthquake hit California near the city of Ridgecrest, about 240 kilometers (150 miles) North-East of Los Angeles. The quake happened at a depth of roughly 11 kilometers (7 miles). This sizable tremor turned out to be a foreshock.
The following day at 8:19pm local time, a 7.1-magnitude quake hit roughly in the same area but at a much shallower depth (only 0.9 kilometers/0.56 miles). This was the strongest earthquake in California in the last 20 years, and was also felt in the neighboring state of Nevada and all the way down to Mexico. Houses and roads were damaged, with some “minor to moderate” level injuries but no fatalities.
Scientists at the United States Geological Survey (USGS) have estimated that there’s less than a 1 percent chance that one or more of the aftershocks will be equal to or more powerful than the 7.1-magnitude quake. Around 55 to 120 aftershocks higher than magnitude 3 are likely to be felt near Ridgecrest over the following week.
When the forecast was published during the weekend, the USGS had registered 359 tremors magnitude 3 or higher. Five of them were higher than magnitude 5, which are powerful enough to damage buildings and infrastructure.
Since the original quake, almost 5,000 additional tremors have been registered in the area, and while the vast majority of them can only be detected with seismometers, scientists and locals are keeping an eye out for anything that might be bigger and more dangerous. By the end of the seismic swarm, six times more tremors might be registered.
“No one can predict the exact time or place of an earthquake, including aftershocks. Our earthquake forecasts give us an understanding of the chances of having more earthquakes within a given time period in the affected area. We calculate this earthquake forecast using a statistical analysis based on past earthquakes,” the USGS wrote on their website.
California is located on many different systems of faults, with the biggest one being the San Andreas Fault that stretches for 1,200 kilometers (745 miles) across the state. Many expect that a devastating earthquake, significantly more powerful than the one last week, will eventually hit the state. However, the July 5th earthquake was not a prelude to the Big One or connected to the San Andreas Fault. Instead, it happened on a different, distant fault system.
[H/T: BBC News]