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| November 2, 2005 | Wednesday | Ramzan 28, 1426 |
Kalabagh fault: Wapda’s view
LAHORE, Nov 1: Commenting on the news item “Dams plan may be reviewed” published in Dawn on October 31, a Wapda spokesperson has said a comprehensive study involving the world’s top-class consultants on seismology had been carried out on the Kalabagh Dam project. During the process, due consideration was given to the Kalabagh fault and the maximum earthquake which could be generated on it. A reservoir-induced earthquake had also been considered in the design.
According to the Kalabagh consultants, the seismic hazard at Kalabagh was lower than that of Tarbela Dam and upstream areas. As the distance of the October 8 earthquake epicentre from Kalabagh was about 200 kilometres, the intensity at Kalabagh due to this earthquake was of a low magnitude.
According to the consultants, the salt formation is considered to be associated with a low-angle-thrust plane (decollement) and it is believed to occur at a depth of more than 10,000 feet beneath the Kalabagh Dam site. No salt deposits or dome structures associated with salt diapirism occur within the reservoir area or near the dam site.
The consultants consider the possibility that the construction of the dam and reservoir could lead to further movement of the salt, causing damage to the dam and other structures in the Kalabagh, to be highly unlikely.
The dam has been designed taking into consideration the assumption that seismic activities may occur anywhere over an area within a radius of 125 miles from the dam site.
According to the consultants, the most severe condition considered for maximum credible earthquake which can occur in 10,000 years are:
Kalabagh Fault — M 7.0 at 7.5 miles (12 km) distance with a focal depth of 4.6 miles (7.5 km).
Reservoir-Induced Seismicity M 6.0 under the site at 4.5 miles (7.5 km) depth.
The spokesperson asserts that no dam is designed in the world for maximum credible earthquake (MCE). Dams are designed for operational basis earthquake (OBE) so that they continue to perform during an earthquake. In the case of Kalabagh, ample provision in the freeboard has been made for the dam to retain water in case of maximum flood and also in case of maximum credible earthquake.
During the construction of a dam, the design is always reviewed with the latest information available.
According to the spokesperson, up till now the information available shows there is no exceeding in the value of the parameters used.
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