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The most damaging triggered earthquake of M 6.3 occurred in Koyna, India in 1967. RTS at Koyna started soon after the impoundment of the Shivaji Sagar Reservoir in 1962. Over the years the locale has hosted ~ 2 dozen M 5 and larger earthquakes and over 200 M 4 and larger earthquakes. An immense amount of field surveys and research work has been carried out at Koyna. For convenience, RTS related work at Koyna has been dealt in two chapters. This chapter deals with the period 1962 through 2004 and Chap.  7 for the period 2004 through 2024. These two chapters provide the total story of RTS at Koyna. In this chapter, the initiation of RTS at Koyna after the impoundment of the Shivaji Sagar Lake is covered. Prior to 1962, there were no earthquakes reported from the Koyna region. Earthquakes became prevalent soon after filling of the Shivaji Sagar Lake in 1962. The source parameters of this earthquake were estimated. It was found to be a multiple seismic event. Interesting rotational movements caused by the earthquake were documented. The geological and geophysical investigation carried in the region are briefly presented. A detailed study of the water levels variation and its influence on RTS is presented. Among other findings, it was discovered that a loading exceeding 40 ft/week was a necessary but not a sufficient condition for an M ≥ 5 earthquake to occur in the Koyna region. In 1985, Warna Reservoir located about 30 km south of Koyna was impounded. This provided a further impetus to RTS. An M 5.3 earthquake occurred in the immediate vicinity of the Warna Reservoir on 28 August 1993. A detailed study of earthquake focal mechanism revealed that the earthquakes occurring north of 17° 15′ latitude are basically strike-slip fault dominated, while on the south of 17° 15′, normal fault focal mechanism is prevalent. It was observed that some 400 h before the occurrence of a M 5 earthquake, foreshocks migrated from a depth of ~ 2 to 10 km. For the first time, fluctuation in the water levels in wells around the Koyna region was continuously monitored in 21 well placed wells surrounding the RTS zone. Variations of well water levels of 4–6 cm were observed associated with M ~ 4 earthquakes. The Donachiwada fault that hosted the 10 December 1967 M 6.3 and several M ~ 5 earthquakes is well delineated through the study of helium studies and drilling through the fault zone.

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Koyna, India (1962–2004)

  • 章节

  • 发表日期：

    2026年

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  • Harsh K. Gupta

摘要

The most damaging triggered earthquake of M 6.3 occurred in Koyna, India in 1967. RTS at Koyna started soon after the impoundment of the Shivaji Sagar Reservoir in 1962. Over the years the locale has hosted ~ 2 dozen M 5 and larger earthquakes and over 200 M 4 and larger earthquakes. An immense amount of field surveys and research work has been carried out at Koyna. For convenience, RTS related work at Koyna has been dealt in two chapters. This chapter deals with the period 1962 through 2004 and Chap.  7 for the period 2004 through 2024. These two chapters provide the total story of RTS at Koyna. In this chapter, the initiation of RTS at Koyna after the impoundment of the Shivaji Sagar Lake is covered. Prior to 1962, there were no earthquakes reported from the Koyna region. Earthquakes became prevalent soon after filling of the Shivaji Sagar Lake in 1962. The source parameters of this earthquake were estimated. It was found to be a multiple seismic event. Interesting rotational movements caused by the earthquake were documented. The geological and geophysical investigation carried in the region are briefly presented. A detailed study of the water levels variation and its influence on RTS is presented. Among other findings, it was discovered that a loading exceeding 40 ft/week was a necessary but not a sufficient condition for an M ≥ 5 earthquake to occur in the Koyna region. In 1985, Warna Reservoir located about 30 km south of Koyna was impounded. This provided a further impetus to RTS. An M 5.3 earthquake occurred in the immediate vicinity of the Warna Reservoir on 28 August 1993. A detailed study of earthquake focal mechanism revealed that the earthquakes occurring north of 17° 15′ latitude are basically strike-slip fault dominated, while on the south of 17° 15′, normal fault focal mechanism is prevalent. It was observed that some 400 h before the occurrence of a M 5 earthquake, foreshocks migrated from a depth of ~ 2 to 10 km. For the first time, fluctuation in the water levels in wells around the Koyna region was continuously monitored in 21 well placed wells surrounding the RTS zone. Variations of well water levels of 4–6 cm were observed associated with M ~ 4 earthquakes. The Donachiwada fault that hosted the 10 December 1967 M 6.3 and several M ~ 5 earthquakes is well delineated through the study of helium studies and drilling through the fault zone.