Mapping of the 1994 Northridge Earthquake Fault and the Santa Susana Mountains Anticlinorium, Southern California

Thomas Davis, & Jay Namson

Published 1995, SCEC Contribution #273

The 1994 Northridge earthquake fault (Pico thrust) and Santa Susana Mountains anticlinorium have been mapped from balanced cross sections based on surface and well data. The earthquake hypocenter lies below the San Fernando Valley synclinorium which joins the Santa Monica Mountains and Santa Susana Mountains anticlinoria. We have postulated that the anticlinoria are crustal-scale fault-propagation folds underlain by active thrust faults. The Northridge earthquake occurred along the south-dipping Pico fault which builds the Santa Susana Mountains anticlinorium, and cross sectional analysis and mapping of the anticlinorium provides important information on the extend and slip of the Pico fault. The anticlinorium and fault extend eastward from the Simi Valley under the northwestern San Fernando Valley to at least the city of Glendale. The north limb of the anticlinoria is well documented by a continuous zone of steep bedding dips, 2-3 km wide and along the north side of the Santa Susana Mountains and south limb of the Merrick syncline. The Verdugo and San Rafael Mountains are the crystalline rocke core of the anticlinorium. The south limb of the anticlinoria outcrops at Laskey Mesa in the western San Fernando Valley, but much of the south limb is concealed beneath the alluvial cover of the San Fernando Valley where it is deformed by less significant faults and folds. Our mapping suggests that only the western half of the Pico fault moved in 1994 and the eastern half may pose a significant seismic hazard to the northern Los Angeles basin.

Citation
Davis, T., & Namson, J. (1995). Mapping of the 1994 Northridge Earthquake Fault and the Santa Susana Mountains Anticlinorium, Southern California. Poster Presentation at 1995 SCEC Annual Meeting.