Thursday, November 1, 2012

Mega-dams in China's earthquake zones could have "disastrous consequences"

Mega-dams in China's earthquake zones could have "disastrous consequences"
By Liu Hongqiao
chinadialogue (Article was first published in Caixin's New Century Weekly.)
October 29, 2012

The row over the safety of large dam cascades in earthquake-prone
south-west China is heating up following revelations that 48% lie in
zones of high seismic hazard.

The Chinese government has approved a number of large dam cascades in
the south-west of China. But not everyone agrees that the plans are safe. 

Earlier this year, Canadian NGO Probe International published a report
called "Earthquake Hazards and Large Dams in Western China", by John
Jackson, a pseudonym. Probe International describes the author as a
"geologist with a detailed knowledge of western China who must remain
anonymous". He reportedly has four decades experience studying
earthquakes and seismic faults. 

For the report, Jackson looked at 130 sites in western China where dams
have been built, are under construction or proposed, cross-referencing
dam locations with maps of seismic hazard. The rivers affected include
the Yarlung Zangbo, Parlung Zangbo, Nu River, Lancang, Yalong, Dadu, Min
and Yellow rivers. 

He found that 48.2% of the dams were in zones of high to very high
seismic hazard, while 50.4% were in zones of moderate seismic hazard.
Only 1.4% were located in zones of low seismic hazard. The report argues
that the rapid rate of dam construction in areas of high seismic hazard
in western China could have disastrous consequences for both the economy
and the people. 

Since its publication, the report has drawn widespread academic and
industry interest in China. In August, Zhang Boting, deputy secretary of
the China Society for Hydropower Engineering, issued a written response
in which he stressed that safety precautions are taken when dams are
built in areas at risk of earthquakes. He added that reservoirs can
trigger small earthquakes, releasing energy that might otherwise build
up and cause large quakes. In other words, dams actually reduce
earthquake risks. 

Jackson and Zhang's positions couldn't be further apart.

Did a reservoir cause the Wenchuan Earthquake?

What the critics worry about is reservoir-induced seismicity (RIS):
the idea that the pressure created by the weight of the reservoir water,
and the infiltration of water into fissures can cause rockfalls,
landslides and tremors, and even set off more destructive earthquakes.
This view has been fiercely debated among scientists both inside and
outside China over the last four years, since a link was drawn between
the magnitude-eight Wenchuan earthquake in Sichuan in 2008 and the
Zipingpu reservoir.

The large Zipingpu reservoir lies on China's Min River. Between
September 2005 and the moment the earthquake struck in 2008, it was
filled three times and emptied twice. "A Human Trigger for the Great
Quake of Sichuan" was how one article published in US magazine Science
in 2009 described the filling of the Zipingpu Reservoir. 

Some experts have rejected this analysis, pointing out that water from
the reservoir could not have penetrated to the source of the Wenchuan
Earthquake, which was 14 kilometres deep, and that RIS would not be able
to trigger an earthquake of such magnitude. The most powerful RIS quake
ever recorded measured 6.3 on the Richter scale. 

In his dismissal of Jackson's research, Zhang quoted Ji Shaocheng, a
professor at Polytechnique Montreal's Department of Civil, Geological
and Mining Engineering, on the link between rock strata and earthquakes:
"Strong rock means strong quakes, weak rock means weak quakes, and soft
rock means no quakes". Zhang added that the intrusion of water under
high pressure can weaken strong rock and make weak rock soft, so filling
a reservoir is very likely to result in weaker earthquakes.

But those who blame Zipingpu for the Wenchuan disaster have their own
evidence. In December 2008, the journal Seismology and Geology published
a paper by researchers from the China Earthquake Administration's
Institute of Geology, Japan's National Institute of Advanced Industrial
Science and Technology and the Sichuan Earthquake Bureau. That study
drew the preliminary conclusion that the filling of the Zipingpu
Reservoir did have a clear effect on the Longmenshan central and
range-front faults. The paper described the possibility that this had
caused the 8.0 magnitude earthquake to occur sooner than it would have
otherwise as a "scientific question which should not be avoided and is
worth further research."

In April 2009, Hu Xianming, chief engineer at the Sichuan Earthquake
Bureau added to this evidence. He found, based on a study of 262 minor
tremors in the Zipingpu Reservoir area between August 2004 and December
2007, that the Wenchuan-Shuimo tremor cluster caused by the reservoir
and the subsequent 8.0 magnitude earthquake had the same origin. 

Then there is the risk of natural earthquakes - as opposed to those
triggered by the reservoirs - hitting the proposed dam cascades on the
Jinsha, Lancang, Yalong and Nu rivers.

China's south-west lies in the Himalayan earthquake region, the
world's most active tectonic zone. According to John Jackson, large dams
built in such high-risk areas will be at threat from naturally occurring
earthquakes, and going ahead with construction is an extraordinarily
risky experiment. 

Zhang Boting, meanwhile, says that as long as dams are kept away from
the faults themselves, the risks are negligible: "There's nothing you
can do about fault lines, and that's why dams are always built
elsewhere. To date, no dam has failed due to an earthquake anywhere in
the world." He believes that as long as the distribution of earthquakes
is known and dams are not built directly over faults, planners can
guarantee safety through earthquake-resistant construction.

But seismologist Ma Wentao points out that the maps of earthquake risk
currently used by engineers are based on historical information about
earthquakes and seismic activity. Due to inaccuracies in earthquake
monitoring and a lack of monitoring of active faults, along with a
scarcity of historical records in many regions, it is very hard to
accurately map faults and estimate earthquake risk, Ma says.

Seismic research "only just getting started"

Research into RIS in China only started in 1963. In 2004, the China
Earthquake Administration set up China's first network of digital
seismic monitoring stations designed to monitor RIS across a number of
reservoirs in the Wu River basin. The Earthquake Monitoring Regulations,
implemented the same year, specifically required that all dams capable
of inducing earthquakes of 5.0 magnitude or over - in other words dams
more than 100 metres high, or reservoirs of 500 million cubic metres in
volume - should have dedicated seismic monitoring networks. In 2007,
methodology for RIS risk evaluation was issued by the China Earthquake
Standards Technology Commission, the first of its kind.

An expert at the Institute of Geology, who did not wish to be named,
says that research on RIS in China is "only just getting started" and
mainly focuses on areas of low seismic activity; there have been no
in-depth studies in medium or high risk areas. Another geologist
familiar with the seismology field in China says that RIS in western
China only started to be taken seriously after the Wenchuan Earthquake.

Lei Xinglin, deputy director of the Tectonic Physics Laboratory at the
Institute of Geology has written that, in the right circumstances, a
reservoir may directly trigger a major quake, and "the risk is greater
with big dams of over 100 metres in height."

Jackson urges the Chinese government to commission third-party
research into the risks of building dams in earthquake-prone regions and
to consider possible changes to the current plans for cascade
development. Otherwise, he says, "in the up to 150-year life span of
these large dams, China will be plagued by the earthquake risks brought
by this highly dangerous method of developing energy. 

"And then, the only solution may be to stop using the dams, with China
paying a huge economic price."

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