September 1, 2005 With a new online map, scientists can better forecast when and where aftershocks may happen. The maps calculate information based on historical earthquake patterns and known behavior of aftershocks. The color-coded map, freely available to the public, gives a more accurate picture than previously available of what to expect in the days and weeks following a major quake.
PASADENA, Calif.--Earthquakes are unpredictable, but one thing seismologists know for certain is the occurrence of one earthquake makes another one more likely. The unexpected and violent nature of earthquakes keeps a lot of people on edge, but now, they have a new tool for figuring out when and where aftershocks could occur.
"We are all scared after big earthquakes," says Lucy Jones, lead scientist of the USGS Earthquake Hazards Team at the U.S. Geological Survey in Pasadena, Calif. Now with a new online map at pasadena.wr.usgs.gov/step, scientists can better forecast when and where aftershocks may happen. Jones says, "We aren't trying to predict every earthquake, but what we are doing is looking at earthquake clustering and providing information about aftershocks." The map calculates information based on historical earthquake patterns and known behavior of aftershocks.
Seismologists at the U.S.G.S. closely monitor earthquake activity. Seismologist Matt Gerstenberger, says, "Information from the events can all be received within a matter of a minute."
"The probabilities of increased activity cover quite a large area, but the really high probabilities are really focused in on a small area around where the event occurred," Gerstenberger says. According to him the color-coded map gives a more accurate picture of what to expect in the days and weeks following a major quake.
But the map isn't just for seismologists: The public can freely access the real-time, earthquake-forecasting tool. Jones says, "It'll show the places where that really are having the aftershocks and the places that aren't." Logging onto this map following an earthquake can relieve anxiety for some and help others be better prepared.
BACKGROUND: The U.S. Geological Survey has devised the best tool yet for forecasting when and where earthquake aftershocks could occur: an online map, available to the public, that displays the probability of the ground shaking significantly over the next 24 hours for any 50-kilometer-square area of California after an earthquake.
HOW IT WORKS: The online map updates itself hourly. But it doesn't predict a primary earthquake. Instead, the map uses patterns in the initial aftershocks that follow big quakes to forecast when and where more will strike. It won't forecast the first of a series of quakes.
WHAT CAUSES EARTHQUAKES: Most earthquakes are caused by faulting: a sudden movement of rock along a rupture in the earth's surface. This surface is in constant slow motion, called plate tectonics, because deeper in the earth, hot rock continually flows. The plates cover the entire surface of the globe and can rub against each other in certain spots, sliding above or below each other. But if the motion isn't smooth, strain builds up until the "fault" ruptures, slipping to new position to relieve the strain. An earthquake is the resulting shaking that radiates out from the breaking rock.
WHAT ARE AFTERSHOCKS: Aftershocks are smaller quakes that occur after the main quake. They happen because the newly moved rock must re-settle in its new formation. Bigger earthquakes have more and larger aftershocks. Because they are so unpredictable, an aftershock can be as damaging as the initial quake, especially if building structures were weakened but not destroyed the first time around.
The U.S. Geological Survey, the Incorporated Research Institutions for Seismology, Inc., and the American Geophysical Union contributed to the information contained in the TV portion of this report.