Rescue workers walk past damaged buildings in the town of Hanwang, in Sichuan province.
Photo Courtesy Associated Foreign Press.
Just 40 minutes before an earthquake measuring 7.9 on the Richter scale struck the
Sichuan province in Central China on May 12, a Texas Tech University professor of
geosciences arrived in Beijing, only 960 miles away.
Hua-wei Zhou, professor of petroleum geophysics and seismology, was about to start work for the
National Natural Science Foundation of China to monitor smaller earthquakes near the Three Gorges Reservoir, 250 miles east of
the Sichuan earthquake epicenter.
Now Zhou is leading a team of six graduate students to deploy 60 seismometers near
the
Three Gorges Dam, 350 miles east of the quake's epicenter. The team hopes to record aftershocks that
will help reveal the structure of the Earth’s crust in this area. Though there is
no reported damage to the hydroelectric dam in Three Gorges by the killer earthquake
in Sichuan, Zhou said it is imperative to study the safety of the dam during an earthquake.
Failure of the dam could result in a disaster of massive proportions , as more than
75 million people live downstream of the dam and the floodplain surrounding the Yangtze
River is used for growing much of the country’s food.
Zhou said the destructive Sichuan earthquake occurred on the Longmenshan fault. The
fault, translated literally as Dragon Gate, has produced many historic earthquakes
greater than magnitude 7. The last one occurred in 1933 and killed more than 9,300.
The earthquake on May 12 was roughly the same magnitude as the 1906 San Francisco
quake that destroyed more than 500 city blocks.
“While the Sichuan earthquake is a major human tragedy, the situation could have
been much worse considering the city of Chengdu, with a population of 4 million,
is just 60 miles away from the epicenter,” said Zhou.
“First, Chengdu is on the footwall side of the northeast-trending Longmenshan fault,
and that side usually has less damage than the hanging wall side. Second, the northeast-trending
fault and northeast rupture direction put most rupture energy away from the city
of Chengdu and its population.
Map of active faults in and surrounding the Sichuan-Yunnan faulted-block of southwestern
China. Click to Enlarge.
“However, the region near and to the northeast side of the fault will suffer a lot,
though that region has a smaller population density than Chengdu.”
Another large earthquake occurred in 1973 on the nearby Xianshuihe fault to the southwest,
he said.
“In 1986 I spent two months in the field studying that fault with several colleagues.
The main driving force of all these earthquakes is the collision of the Indian and
Eurasian plates that pushes the mountains against the Sichuan basin.”
