Large water-reservoir-related induced seismicity

249 More than one hundred cases of Reservoir-Induced Seismicity (RIS) have been observed to-date all over the world and they have been grouped into three categories, namely RIS level I ( M ≧ 6.0), RIS level II ( M = 5.9 to 3.1) and RIS level III ( M ≦ 3.0) respectively exhibiting intense, moderate to mild and microlevel seismicity depending on magnitude (M) of the maximum induced earthquake. Intense level-I seismicity has been induced only in four reservoirs, namely Hsinfengchiang, China; Kariba, Zambia-Zimbabwe; Kremasta, Greece and Koyna, India. Sixty-four reservoirs have induced mild strong earthquakes of magnitudes ranging from 5.9 to 3.1 while microseismicity has been exhibited by thirty-five reservoirs. Limited evidence suggests that maximum induced earthquakes (Λί) follow high lake level and, in some cases, a high rate of change of the lake level. The largest RIS events (level I) are generally associated with reservoir depth of over one hundred meters. Significantly, the Koyna, India, and Hsinfengchiang, China, reservoirs exhibited the two strongest induced earthquakes ( M ≧ 6.0) level I as well as induced seismicity for the longest period, over two and a half decades. Worldwide, the distribution of reservoirs exhibiting induced seismicity specially in India and Japan suggests that moderate seismicity and normal and strike-slip fault environment favour RIS activities. The 6-values, large ground tilt, magnetic anomalies are some of the precursory phenomena associated with RIS.