Earthquakes occur in California on a daily basis, but most of the time they aren’t even noticed. That wasn’t the case late in the morning of July 29th, 2008, when every Californian from Santa Barbara to San Diego felt the earth move below them.
Seismic Activity and Active Faults in California
The entire state of California is riddled with faults, varying in length from a few miles to hundreds of miles, such as the famous San Andreas Fault. Earthquakes throughout California and even Nevada are very common and scars from recent earthquakes can be seen on the dessert floor.
The July 29th earthquake epicenter was located about 3 miles west of Chino, California and about 28 miles east of Los Angeles at a depth of 8.5 miles underground. The depth of the epicenter helped to lessen the actual magnitude of the earthquake as felt by people at the surface. What's more, not much building destruction was reported since the areas hardest hit are more recently developed, and newer structures are built to withstand these types of quakes.
It is not yet clear to the U.S. Geological Survey which fault exactly was responsible for this seismic activity, but it was located about halfway between the Whittier and Chino faults. With so many active faults in the area, it may take some more time and data collection before geologists can pinpoint the responsible fault exactly.
"Did You Feel It?" Reports
Reports to the USGS “Did You Feel It?” website show that those located right above the epicenter, such as people in Chino, California, felt strong to very strong shaking and experienced light to moderate structural damage. People in farther away cities such as Los Angeles and San Bernadino reported moderate to light shaking with very little to no damage to structures.
Earthquakes along coastal regions such as California have the potential to create tsunamis. Whenever an earthquake such as this is reported, agencies like the West Coast and Alaska Tsunami Warning Center issue statements to warn the public about the potential for tsunamis. In this case, the magnitude of the earthquake was such that a tsunami was not expected.
When's the Next Big Earthquake?
About 30 aftershocks were recorded within two hours after the main event. A probability report published by Cal Tech and the USGS shows that the possibility of a strong and possibly damaging aftershock in the next week is 30 percent. There is also a 5 to 10 percent chance that there will be an earthquake stronger than or equal to the July 29th event in the next week.
These probabilities are based solely on statistical observations of historical earthquakes and are not exact predictions, as stated by the USGS. But they do serve as a reminder to everyone that more earthquakes have happened in the past following an event such as the July 29th quake.
Geologists also use earthquake statistics to determine probabilities for larger earthquakes that can be more devastating. Based on historical records of seismic activity in California, scientists have determined that there is a 99 percent chance of an earthquake with a magnitude 6.7 or larger in the next 30 years.
Sources:
US Geological Survey Earthquake Hazards Program
West Coast and Alaska Tsunami Warning Center
Alexandra Matiella Novak - With a PhD in Geology and expertise in science education, Alexandra is passionate about increasing the public's Earth science literacy.
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