Dams and Earthquacks
Earthquake is defined as a sudden and rapid shaking of the earth caused by the breaking and shifting of rock beneath the Earth’s surface and it creates seismic waves, which can result in damages and failures on man-made structures constructed on the crust of earth. Earthquake effects on dams mainly depend on dam types. Safety concerns for embankment dams subjected to earthquakes involve either the loss of stability due to a loss of strength of the embankment and foundation materials or excessive deformations such as slumping, settlement, cracking and planer or rotational slope failures.
Ground shaking from earthquakes can collapse dams. There are some important cases, which subjected to damages and failures after earthquake. Lower San Fernando Dam in USA is first example failed as a result of liquefaction phenomenon under the earthquake loading conditions. In case of the May 12, 2008 Wenchuan earthquake in China many dams and reservoirs had been subjected to strong ground shaking. So many dams and hydropower plants were damaged.
Large reservoirs can trigger earthquake. According to recent surveys, Reservoir Triggering Seismicity (RTS) has been observed at over 100 locations worldwide [4, 19, 20]. The largest and most damaging earthquake triggered by a man-made reservoir may be the 7.9-magnitude Sichuan earthquake in May 12, 2008. One of the most serious cases was in 1967 in Koyna, India. The magnitude of this earthquake was 6.3. Also significant effects have been observed Hsingfengkiang dam in China, Kariba dam in Zimbabwe and Kremasta dam in Greece.
Damages due to RTS have been in two dams: Hsinfengkiang dam, which a buttress dam having a height of 105 m in China. It was subjected to earthquake with magnitude of 6.1 in 1962.
Koyna dam, which is gravity dam having 103 m height in India. It was subjected to an earthquake with magnitude of 6.3 in 1967. Researchers state that earthquakes were caused in their reservoirs by RTS.
The small magnitude earthquakes, which occur immediately after reservoir water level fluctuations are mainly related to stress adjustments in the foundation rock, collapse of karst caves and mining pits and mass movements.