A Balanced Cross Section of the 1994 Northridge Earthquake, Southern California

Thomas Davis, & Jay Namson

Published November 2002, SCEC Contribution #150

THE Northridge earthquake of 17 January 1994 was the latest in a series of very damaging, thrust-fault-generated earthquakes to strike California, following the San Fernando 1971, Coalinga 1983, and Whittier Narrows 1987 events. Like the last two of these, the Northridge event occurred along a fault that did not reach the surface and which had not been detected by traditional seismic-hazard methods. Balanced cross-sections, which flatten and remove the crustal deformation, can be used to identify and quantify the seismic hazard posed by thrust faults. Here we present a balanced cross-section through the Northridge portion of the Transverse Ranges fold-and-thrust belt, which shows that the earthquake occurred on what we call the Pico thrust. A cross-section of this sort constructed before the earthquake would have revealed the fault, although it would not have predicted the earthquake. Cross-sectional modelling of the Pico thrust yields an average slip rate of 1.4–1.7 mm yr-1 and a recurrence interval of Northridge-sized (Mw 6.7) earthquakes every 1,500–1,800 years. We show that the Pico thrust is the back thrust to the 170-km Elysian Park thrust which underlies some of the most densely urbanized portions of the Los Angeles basin.

Davis, T., & Namson, J. (2002). A Balanced Cross Section of the 1994 Northridge Earthquake, Southern California. Nature, 372(6502), 167-169. doi: 10.1038/372167a0.