Principal stress analysis of rock fracture data from the Long Beach oil field, Los Angeles basin, California

Twelve electric borehole-image logs from oil wells located in the Long Beach oil field were used to conduct a fracture analysis of principal stress orientations associated with the Newport-Inglewood Fault Zone. The fractures analyzed are located in the Puente, Repetto, Pico, and San Pedro formations. Fractures were grouped based on fracture type, orientation, and formation. In-situ SHmax orientation was interpreted to range between 320° to 40°. Variations form the in-situ stress were observed across every formation and interpreted as paleo-stress. The SHmax orientation begins to change from NW to N-NW in the Pico Formation, which may signal the onset of the dextral movement of the Newport-Inglewood Fault 2.5 million years ago or later. The NE SHmax orientation in the San Pedro Formation may reflect stress trajectory changes as the Newport-Inglewood Fault continues to propagate in the Pleistocene. Additional SHmax orientations indicate a more complex structural evolution of stress trajectories.