The Koyna earthquake of December 11, 1967 is an event of considerable engineering significance especially because it was centered in the vicinity of Koyna Dam. Koyna Dam is a straight gravity structure made of rubble concrete except for a 6 ft. thick zone of conventional concrete at the upstream face of all monoliths. It is about 2800 ft. long and 338 feet high above the deepest foundation, constructed in 50 ft. wide monoliths, and has a 300 ft. long overflow portion.