Earthquake Jolts SW China
WASHINGTON, May 19 (Xinhua) -- After last week's
deadly earthquake in southwest China's Sichuan province, quake prediction has
become an issue of intense public concern. However, accurate predictions in the
short term are indeed "very difficult," said Lucile Jones, a seismologist at the
U.S. Geological Survey (USGS),in a recent interview with Xinhua.
When asked what factors affect
the prediction of earthquakes, she said: "This depends on what you mean by
Rescuers search for buried people at a
rubble in Yingxiu Township, one of the worst-hit areas in the
quake-devastated Wenchuan County, southwest China's Sichuan Province, May
18, 2008.(Xinhua Photo)
On the spatial distribution, that is, indicating the
location of likely earthquakes, "we (seismologists) do an excellent job," said
However, when it comes to the time and magnitude,
prediction becomes difficult.
Magnitude is determined only during the earthquake,
by measuring how far the rupture that starts at the epicenter moves down the
fault, she said.
If the rupture travels 100 meters, it will be about
magnitude 4. If it travels 300 km, the quake will be close to magnitude 8, said
But what stops the earthquake may not be connected to
what makes it start and so information about the size may not be discernible
before the earthquake begins.
"Short-term (prediction) is difficult unless the
earthquake has a foreshock," she said.
Smaller earthquakes occurring near the first one are
Only about 5 percent of the time
is the triggered earthquake bigger than the first one. The first one is then
called a foreshock and the triggered event the main shock.
Rescuers search for buried people at the
rubble in the quake-devastated Beichuan County, southwest China's Sichuan
Province, May 18, 2008. (Xinhua Photo)
She said after the first quake happens, the
probability of another event is much higher than it usually is, and therefore
the likelihood of successful prediction of the triggered event is relatively
In California, the USGS has a website that shows the
real-time probability of aftershocks all over the whole state, said Jones, who
is USGS' Chief Scientist of Multi Hazards Demonstration Project for Southern
Compared to the short term, long-term prediction of
earthquakes is fairly mature and usually based on fault history. Governments can
set up building codes according to the long-term prediction results in specific
In China and other countries, people can sometimes
predict earthquakes or other natural disasters when some unusual events such as
unusual behavior among animals or strange astronomical phenomena occur,
suggested Jones, while clarifying that there is currently no scientific evidence
or research to support this.
"Every effort to prove these has shown there is no
solid signal," she said.
Maybe the most important action for earthquake
prediction would be for governments all over the world to inject more funds into
earthquake research, Jones suggested.
"The whole earthquake monitoring and research program
in the United States is funded at 50 million U.S. dollars for the whole country
-- the same value (not adjusted for inflation) that we had in 1990," said Jones.