The fault has been quiet for far too long.
For years, we have been hearing that the US West coast is long overdue for a major earthquake — the proverbial “Big One.” An event that will level older buildings, disrupt roads, damage water and electrical systems, and result in numerous human injuries.
During the annual National Earthquake Conference in Long Beach this week, a leading geoscientist announced that California’s San Andreas fault has been quiet for far too long and that the state should prepare for a potential earthquake as strong as a magnitude 8.0.
"The springs on the San Andreas system have been wound very, very tight. And the southern San Andreas fault, in particular, looks like it’s locked, loaded and ready to go," said Thomas Jordan, director of the Southern California Earthquake Center, reported the Los Angeles Times.
Earthquakes usually occur at the boundaries of tectonic plates — composed of Earth’s crust and the uppermost portion of the mantle — where one plate dips below another (normal fault), is pushed upward (reverse fault), or where plates run alongside each other (strike-slip fault).
The San Andreas fault is a strike-slip fault, and Jordan is worried because the Pacific Plate moves northwest relative to the Northern American Plate at a rate of around 5 meters (16 feet) every 100 years, but right now most of the plate is stuck. California experienced a magnitude 7.9 earthquake back in 1857, but some sections of the plate have remained locked in place since the late 1600s.
So centuries of pressure and tension have been building up underneath the state of California just waiting to be released. Last year, Jordan’s team found that there’s a 7 percent chance the state will experience a magnitude 8.0 quake in the next three decades.
The strength of an earthquake is measured on the Richter scale, and the magnitudes are based on a logarithmic scale. What this means is that for every whole number you go up on the magnitude scale, the intensity of ground shaking goes up 10 times. Think of it this way: a magnitude 1.0 earthquake releases as much energy as 6 ounces of TNT, whereas a magnitude 8.0 can release as much energy as detonating 6 million tons of TNT.
Back in 2008, a US Geological Survey report found that a magnitude 7.8 earthquake on the southern San Andreas fault could cause more than 1,800 deaths, 50,000 injuries, six months of compromised sewer systems, ongoing wildfires, and $200 billion in damage.
According to Jordan’s model, a magnitude 8.0 earthquake would result in 2 minutes of shaking, with the strongest activity in the Coachella Valley, Inland Empire, and Antelope Valley. However, even though Los Angeles is not on the fault, it is still at a high risk because it is built over a sedimentary (accumulation of sediments) basin, and seismic waves spread and get trapped in that material, which causes more extreme and longer-lasting shaking.
You can see for yourself in the simulation below:
Luckily, LA has been retrofitting buildings to better earthquake-proof them. But Jordan warns that the rest of the state needs to prepare for the big one by making residents more aware of ways to stay safe during an earthquake, and when and how to evacuate.
"We are fortunate that seismic activity in California has been relatively low over the past century," Jordan explained to Reuters. "But we know that tectonic forces are continually tightening the springs of the San Andreas fault system, making big quakes inevitable."
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