Destructive earthquakes shook Mexico City twice within two weeks, causing hundreds of deaths and widespread damage and increasing Southern California residents' anxiety of "The Big One" as well.
Will a much more powerful earthquake occur in Southern California at some point? Scientists at USC and elsewhere are working to improve their ability to forecast quakes and debunk myths about them.
Forecasts vs. predictions
When the magnitude 7.1 earthquake struck Mexico City on Tuesday, a siren sounded about 20 seconds before it struck. The early warning system provided local residents and the country with a few crucial seconds to avoid greater losses. The system has been operating since a 1985 earthquake led to more than 5,000 deaths.
"It is a very useful tool. How this warning system works is that communications travel a lot faster than earthquake waves so that people can take an action," said Jason Ballmann, communications manager of the Southern California Earthquake Center, or SCEC, based at USC.
The system is still in the process of being tested in the U.S., with a prototype operating in California. The U.S. Geological Survey, which operates the SCEC with the National Science Foundation, is working with scientists at Caltech, UC Berkeley, the University of Washington and University of Oregon on the system.
However, this system does not mean the earthquakes can be predicted. Ballmann distinguished the two easily confused concepts: "forecast" vs. "prediction."
"What we are trying to do is to forecast earthquakes. 'Forecasting' means we are trying to assign a probability that something will happen over time," he said. "A prediction is a certainty."
Currently scientists cannot predict an earthquake which would happen at a certain time and place. But they can try forecasting the chances of a quake, Ballmann explained. At the SCEC, scientists use a computer model called the Uniform California Earthquake Rupture Forecast.
Though people are unable to know the exact prediction of an earthquake, they can still get prepared, he said. The more people know about earthquakes, the more unlikely they are to be injured.
Earthquake weather
People tend to have strong beliefs about earthquakes and are sometimes even superstitious, Ballmann said.
"Earthquake weather," for example, is an informal expression used to describe those extreme climatic phenomena that occur along with earthquakes. Some people might misunderstand the relationship between the weather and earthquakes.
"Earthquakes have nothing to do with anything climatological at all. Earthquakes occur because one block of crust moves," Ballmann said.
Falling into the ocean
Another rumor that has pervaded for a long time is "California is going to fall into the ocean because of earthquakes," he said. The answer is no.
"The truth about that is that while we have some minor landslides that occur in the coastal areas, like the one that happened on Big Sur in the summer, not all of California is going to fall into the ocean," Ballmann said.
California is split in two by the San Andreas Fault and rests on two plates (the Pacific Plate and the Northern America Plate) that are moving in opposite directions, he said. The plates are moving past each other, but in a big quake one side is not going to fall into the Pacific.