A new study suggests that it is possible to make a rough estimate of the intensity of an earthquake as soon as the shaking begins. This technology promises to provide people with valuable seconds to warn before the disaster actually strikes.
Earthquake forecasting has long been considered a challenging task. Scientists have been unable to pinpoint when a fault will rupture, whether in days, months, or even years prior to the event. However, this new method offers a brief yet accurate insight into what will happen in the next minute.
“We can determine the intensity of the earthquake just a few seconds before the first tremors and forecast ground movement from a few seconds to tens of seconds before it is felt,” said Richard Allen, a seismologist at the University of California, Berkeley.
If such an automatic warning system were implemented, children in schools would have enough time to duck under tables, and others would have sufficient time to rush out the door, Allen speculated.
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| Models of P waves, S waves, and surface waves. |
The forecasting is based on the fact that a typical earthquake generates three types of waves:
– Primary waves, or P waves, appear first. They move like a pressure wave, often causing a jolt. P waves have the least destructive power.
– Following them are the secondary waves, or S waves. These cause the ground to slip both horizontally and vertically.
– Finally, there are the surface waves, which have the strongest destructive force. They shake the ground side to side and then roll like ocean waves.
Allen and his colleagues studied seismic wave records from 71 significant earthquakes. They discovered that the frequency of P waves is related to the intensity of the surface waves that appear last.
This argument is entirely contrary to the conventional view, which holds that the intensity of an earthquake depends on a series of random events along a fault, occurring after the initial rupture.
The findings of the new study also “imply that the overall strength of a seismic shake partly depends on what happens in the first few seconds,” noted Rachel Abercrombie, an earthquake expert at Boston University who was not involved in the research.
“This type of forecasting is not a perfect system,” Allen stated. However, he also pointed out that all the strong earthquakes the research team examined during the first few seconds allowed for useful predictions. “The predicted earthquake intensity in the study varied by about 1 Richter scale unit from reality.”
Another important factor for the forecasting system is that not everyone is located right at the epicenter of the earthquake, and seismic waves travel much slower than signals transmitted at the speed of light.
For instance, if an earthquake occurs at the northern end of the 1,280 km long San Andreas Fault, the vibrations would take 80 seconds (traveling at about 3.2 miles per second) to reach San Francisco. Of course, such an event would not destroy the city by the bay. However, regardless of where the earthquake’s epicenter is, there would be a window of time to warn most potential victims.
Allen stated that it would take at least another year of testing before a real warning system could be put into operation. He envisions using the Internet to transmit information about an earthquake. A computer on the other side of the world would decode this warning for a specific area and forecast the timing and intensity of the upcoming shaking. People could also receive notifications via telephone.
T. An (according to LiveScience)
