Posted on June 1, 2011 by Probe International
A study by seismologists at the China Earthquake Administration
(formerly known as the China Seismological Bureau) indicates that the
massive Three Gorges dam on the Yangtze River "significantly increased"
seismic activity along the dam's reservoir.
A study by seismologists at the China Earthquake Administration, a
government agency, has confirmed that the massive Three Gorges dam on
the Yangtze River has "significantly increased" seismic activity along
the dam's reservoir. The study, recently obtained by Toronto-based Probe
International, supports Chinese press reports and anecdotal evidence
from Chinese citizens living in the vicinity of the Three Gorges Dam,
and helps to explain the numerous landslides that have caused havoc in
the region, necessitating the evacuation of 300,000 people. Part of the
study in Probe International's possession had earlier been published in
a Chinese journal.
According to the Chinese study, which Probe International scientists
have translated, seismic monitors around the reservoir and in Hubei
Province registered 3,429 earthquakes between June of 2003 (when
inundation of the reservoir began) and December 31, 2009.
"This represents a 30-fold increase in frequency over the pre-dam
period," according to Patricia Adams, executive director of
Toronto-based Probe International and English editor of the translated
study. "The earthquake activity especially increases when the dam
operators rapidly increase or decrease the level of water in the reservoir."
Most of the quakes fell under 2.9 magnitude on the Richter scale,
classifying them as "microseismic" tremors. One earthquake reached
magnitude 4.1 on the Richter scale. It occurred as the dam authorities
were attempting to fill the reservoir to its maximum height of 175
metres above sea level. Fan Xiao, chief engineer of the Sichuan Geology
and Mineral Bureau, warns that "strong earthquakes could occur in the
future as the reservoir fills because the microfractures, caused by the
large number of microearthquakes, could make the area dangerously prone
to a strong earthquake."
Large reservoirs are known to trigger earthquakes in a phenomenon called
"Reservoir-induced Seismicity (RIS)." In a report of 19 dams in China
that have suffered from RIS, 15 have geological conditions similar to
Interest in RIS has grown since geoscientists began suggesting that the
Zipingpu dam in Sichuan province may have triggered the deadly 2008
earthquake that killed close to 90,000 people. Researchers and citizens
alike are now alert to the risk of Three Gorges, the world's largest
dam, triggering an earthquake that could topple buildings. In a
worst-case scenario, an earthquake could also damage the dam itself,
with catastrophic consequence for the millions of people who live
downstream of the project.
Chinese authorities have long dismissed such concerns, saying that a
low-level seismic response to filling the reservoir is to be expected.
Because the Three Gorges area is only moderately seismic, the largest
earthquake that might occur would not cause harm, they say. This
official position may be under revision, however. The Chinese State
Council, the country's federal cabinet, acknowledged last month that
preventing geological disasters is one of the problems with the dam that
"should be solved urgently."
For more information and copies of the official report, contact:
Patricia Adams, Executive Director, Probe International
tel: 1-416-964-9223 (ext 227)
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