Three Gorges Dam and Earthquakes
May 29th 2006 01:01
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Contining from Friday’s post…
Earthquakes:
There are two significant fault lines in the region of the Three Gorges Dam area. Tremors resulting from either of these two fault lines are expected to have effects on the Three Gorges Dam. The two fault lines are the Jiuwanxi Fault and the Zigui-Badong Fault. The Jiuwanxi Fault is located 17 kms upstream of the reserviour and the Zigui-Badong, 80 kms upstream. The Zigui-Badong Fault has produced seismic activity measuring 5 to 6 on the Ricter Scale. Other seismic activity can result from the collapse of local limestone caves produced from mining activity. The tremors produced by collapsing limestone caves are less sever and more localized compared to deeper geological activity associated with the fault lines, however, a localized minor tremor has the same potential and possibly detrimental effects if it strikes in a vulnerable area. The collapse of local limestone caves is associated with the filling of the reserviour. The water pressure fills the cave and the weight of the water causes void regions to collapse.
As part of the feasibility study for the Three Gorges Dam project, earth movements were predicted to assess the impact of earthquakes on the Three Gorges Dam. Geologists predicted that the worst case scenario would be an earthquake measuring 6 on the Richter Scale in a region between the two fault lines. What these predictions did not take into account were the localized reservoir induced quakes. Filling the dam to full capacity may potentially lead to the collapse of more limestone caves and of a greater magnitude than those recorded so far. Furthermore, large freakish earthquakes strike at random and can occur with little warning.
“In the case of Tangshan in northeast China, no significant tremors had previously been recorded there until a massive quake measuring 7.8 on the Richter scale occurred in 1976 [killing more than 242,000 people, according to the official toll].”
It is very difficult to accurately predict the magnitude of likely earthquakes in the area. As there are two fault lines in the region, earth movements are to be expected. Scientists have fleshed out a likely scenario but this is not necessarily the upper limit of potential earthquake activity.
Earthquakes:
There are two significant fault lines in the region of the Three Gorges Dam area. Tremors resulting from either of these two fault lines are expected to have effects on the Three Gorges Dam. The two fault lines are the Jiuwanxi Fault and the Zigui-Badong Fault. The Jiuwanxi Fault is located 17 kms upstream of the reserviour and the Zigui-Badong, 80 kms upstream. The Zigui-Badong Fault has produced seismic activity measuring 5 to 6 on the Ricter Scale. Other seismic activity can result from the collapse of local limestone caves produced from mining activity. The tremors produced by collapsing limestone caves are less sever and more localized compared to deeper geological activity associated with the fault lines, however, a localized minor tremor has the same potential and possibly detrimental effects if it strikes in a vulnerable area. The collapse of local limestone caves is associated with the filling of the reserviour. The water pressure fills the cave and the weight of the water causes void regions to collapse.
As part of the feasibility study for the Three Gorges Dam project, earth movements were predicted to assess the impact of earthquakes on the Three Gorges Dam. Geologists predicted that the worst case scenario would be an earthquake measuring 6 on the Richter Scale in a region between the two fault lines. What these predictions did not take into account were the localized reservoir induced quakes. Filling the dam to full capacity may potentially lead to the collapse of more limestone caves and of a greater magnitude than those recorded so far. Furthermore, large freakish earthquakes strike at random and can occur with little warning.
“In the case of Tangshan in northeast China, no significant tremors had previously been recorded there until a massive quake measuring 7.8 on the Richter scale occurred in 1976 [killing more than 242,000 people, according to the official toll].”
It is very difficult to accurately predict the magnitude of likely earthquakes in the area. As there are two fault lines in the region, earth movements are to be expected. Scientists have fleshed out a likely scenario but this is not necessarily the upper limit of potential earthquake activity.
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