Reservoir Induced Seismicity:

1. Reservoir Induced Seismicity: Just Another Dam Argument • Douglas Luken • Geo361: Hydrology 3 Gorges Dam, China

2. A Rose By Any Other Name… Many state there is a difference between “Triggered” and “Induced” Induced : Is the significant change in load stress and/or pore pressure, causing a substantial change in the crust Triggered: If the crust is previously close to a fault failure due to natural processes, and only required a minor change in load or pore pressure In this presentation we will assume they are one in the same.

3. What Is RIS? “…earthquakes occurring in the vicinity of artificial water reservoirs as a consequence of impounding.” (Gupta, Harsh K., 2002.) Depth of the water is the most significant factor (Volume is also a sig. factor) One characteristic of RIS 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 (USGS, 2006) RIS can be immediately noticed during filling periods of reservoirs, and can also occur later in the life of the reservoir. Also occurs after a rapid change in reservoir water level.

4. RIS Influenced by..

5. Increased Impounding Through this pore pressure is increased and additional fractures are formed

6. Oscillating Pore Pressure. Monthly variation in reservoir water depth and seismic activity as recorded by an analogue station near the dam wall

7. Original and Relocated EQ Hypocentres Original locations with error bars, shown (a) in map view and (b) in cross section. Relocated EQs, with their much reduced error bars, (c) in map form and (d) in cross section. The shaded area of the map is the Au Reservoir.

8. A Quick History Lesson: Hoover Dam • Completed in 1935 • 100’s of Earthquakes occurred as the water rose to its peak height of 475ft in 1939 Konya, India • Completed in 1963 • M ≥6.3 Earthquake in 1967 Three Gorges Dam • Main Body Completed 2006 • 7661ft long • 1045km² surface area

9. Reported Cases of RIS with M ≥ 4.0 *Source T.Valdut, Enviromental Aspects of Reservoir Induced Seismicity, May 1993

10. Worldwide… • Up to 2008, there were 96 large dam sites that had reported RIS • 5 sites with a M ≥ 6.0 ~ These include China, Zambia, India and Greece • 10 with M 5.0 – 5.9 • 28 with M 4.0 – 4.9 • 53 with M < 4.0 Others reported but not included, due to lack of proper equipment primarily in 3rd world countries

11. What We Can Do… RIS is a under-funded and often neglected field of research. The increase in government support for monitoring stations and research for dams worldwide. Earthquake hazard assessments done as part of the dam design process Better monitoring of seismic activity during impoundment, change or possible reverse filling procedures done if RIS is detected, and model the changes to pore pressure and mechanics underground. Open disclosure of RIS occurrences during the initial impounding

12. Beyond Reasonable Doubt There is resistance in the engineering community globally to accept the significant or even existence of RIS. Some of them believe: There is no correlation to properly demonstrate between earthquakes and reservoirs If the natural seismicity is low, the danger of RIS is low as well. No dam has yet to fail disastrously due to RIS, and the dangers are being over exaggerated

13. Sources: