(January 5, 2011) Reservoir-induced seismicity in connection with large hydropower dams has been well known for at least 60 years. Induced seismic activity can be divided in two categories:
* Triggered. This group of earthquakes are caused by tectonic stresses. They would probably have occurred sooner or later, but their time-space proximity to human activity indicate antropogenic activity.
* Truly induced. This group of earthquakes are purely antropogenic in that stress buildup can be traced directly to human activity.
For convenience people use the term induced for both types.
Reservoir-induced seismicity (RIS), is the triggering of earthquakes by the physical processes that accompany the impoundment of large reservoirs.
A leading scholar on this topic is Harsh K. Gupta who defines the occurrence as:“…earthquakes occurring in the vicinity of artificial water reservoirs as a consequence of impoundment.”Gupta, in his review of studies on RTS, highlights the following points:
- Globally, there are over 90 identified sites of earthquakes triggered by the filling of water reservoirs
- The largest and most damaging earthquake triggered by a man-made reservoir was in 1967 in Koyna, India. The magnitude of the earthquake was a 6.3
- Depth of the water in the reservoir is the most important factor in RTS. The volume of the water also pays a significant role in triggering an earthquake
- One characteristic of RTS is that the magnitude of the foreshock is higher than the magnitude of the aftershock and both values are generally higher than in cases of natural earthquakes (according to the USGS, some large quakes are preceded by foreshocks. The largest quake in a cluster is the mainshock, and those after it are called aftershocks. For more information, see here).
- RTS can be immediately noticed during filling periods of reservoirs
- The effect of RTS can be rapid (following the initial filling of the reservoir) or delayed (occurring later in the life of the reservoir)
- There is resistance in the engineering community globally to accept the significant or even existence of RTS. However, groups such as the US Commission on Large Dams have reported that RTS should be considered for reservoirs deeper than 80-100m.
Dr. V. P Jauhari, wrote the following about RIS in a paper prepared for the World Commission on Dams:
“The most widely accepted explanation of how dams cause earthquakes is related to the extra water pressure created in the micro-cracks and fissures in the ground under and near a reservoir. When the pressure of the water in the rocks increases, it acts to lubricate faults which are already under tectonic strain, but are prevented from slipping by the friction of the rock surfaces.” (Jauhari, 1999)
He also makes the following points:
- The scientific explanation for RIS is still not well understood and is therefore not possible to predict;
- Reservoirs can increase the frequency of earthquakes in areas with a previously low occurrence of seismic activity.
See pdf for some examples of RTS by date, location and magnitude.
Sources: Gupta, Harsh K., 2002. “A review of recent studies of triggered earthquakes by artificial water reservoirs with special emphasis on earthquakes in Koyna, India.” Earth-Science Reviews 58 279–310.
Jauhari, V.P., 1999. Prepared for Thematic Review IV.5. “Options Assessment- Large Dams in India -Operation, Monitoring and Decommissioning of Dams.”
Howard, C.D.D., 2000. Operations, Monitoring and Decommissioning of Dams, Thematic Review IV.5 prepared as an input to the World Commission on Dams, Cape Town,
Linyue Chen and Pradeep Talwani, “Reservoir-induced Seismicity in China,” Pure and Applied Geophysics, 153(1998) 133–149.
Probe International, January 5, 2011