10 feet by 1964. In order to increase production, waterflooding operations were commenced in 1954 and expanded in 1955 and 1961. These injection operations increased pore pressure in portions of the oil field from 50 psi to over 850 psi by 1963 (Hamilton and Meehan, 1971). Injection depths were as shallow as 1,200 feet.
The dam structure failed due to subsurface leakage of reservoir water beneath the floor of the impoundment and under the foundation of the dam itself. The subsurface leakage was caused by a cracked seal extending across the floor of the reservoir in line with the breach in the dam (Jansen, 1988). Movement of the geologic faults crossing the floor of the reservoir with downward displacement of 2 to 7 inches on the western side of several faults caused cracking in the asphalt membrane seal and allowed water to enter the porous soil beneath the dam. Later excavations of the bottom of the reservoir indicated that leakage had occurred for an appreciable amount of time before the dam failure. The slow movement of the faults beneath the reservoir has been attributed to (1) natural causes inherent in the geologic setting, (2) subsidence of the ground surface caused by oil and gas operations or by the filling of the reservoir with water, or (3) pressure injection of water in the Inglewood Field at shallow depths for oil and gas operations and in the presence of a fault system.
Hamilton, D.H., and R.L. Meehan. 1971. Ground rupture in the Baldwin Hills. Science 172(3981):326-406.
Jansen, R.B. 1988. Advanced Dam Engineering for Design, Construction, and Rehabilitation. New York: Springer.