Convergence, Block Rotation, and Structural Interference Across the Peninsular-Transverse Ranges Boundary, Eastern Santa Monica Mountains, California

Andrew J. Meigs, & Michael E. Oskin

Published September 2002, SCEC Contribution #410

Active deformation in southern California occurs in two discrete structural provinces. To the south of ~34°N latitude, the Peninsular Ranges structural province is characterized by northwest-trending strike-slip faulting, northwest motion of crustal blocks relative to stable North America, and negligible vertical-axis block rotation. In contrast, the Transverse Ranges province to the north of ~34°N latitude is characterized by west-trending oblique-slip faulting and a significant component of north-south crustal shortening contemporaneous with northwestward motion and vertical-axis block rotation relative to stable North America. A structurally complex transition zone between N33°45’ and N34°15’ latitude defines the boundary separating these two provinces. Bedrock and geomorphic relationships in the eastern<br>Santa Monica Mountains document the sequential development of this boundary region. At the longitude of downtown Los Angeles, the Malibu Coast-Santa Monica-Hollywood fault system and the Elysian Park fault systems have accommodated the bulk of the differential motion in the boundary zone between the two provinces over the last 2.5- to 5 m.y.. Structural evolution of the boundary zone was dictated by the progressive increase in displacement and lateral propagation of each fault system, differential vertical-axis rotation of the Transverse Ranges block relative to the Peninsular Ranges block, and a decrease in the obliquity of convergence with time. This interaction transferred a portion of the Elysian Park anticline, an anticline developed in association with the Elysian Park fault system, to the hanging wall of the Hollywood fault. Net slip across the boundary zone north of downtown Los Angeles is limited to 1.7 - 2.5 km of dip-slip, to 1.5 km of strike- slip, and 2.3 - 2.9 km of oblique-slip during the past 2.5 to 5 m.y. These low values imply that the southern boundary of the Transverse Ranges has remained largely coupled to the adjacent Peninsular Ranges structural province during compression. Using a 5 Ma age for initiation of growth of the Santa Monica Mountains and Elysian Park anticlines enables minimum rates of 0.3 - 0.5 mm/yr, 0.3 mm/yr, and 0.5 - 0.6 mm/yr for the dip-slip, strike-slip, and oblique-slip components of motion, respectively. A 2.5 Ma age of initiation of the Elysian Park anticline would double these rates. A new tectonic model for the structural evolution of the boundary zone based on the sequence of structural over-printing reconciles apparently discrepant geologic, paleoseismic, and geodetic data, data suggesting that the boundary zone is dominated by long-term strike-slip, intermediate-term oblique-slip, and short-term dip-slip displacement.

Meigs, A. J., & Oskin, M. E. (2002). Convergence, Block Rotation, and Structural Interference Across the Peninsular-Transverse Ranges Boundary, Eastern Santa Monica Mountains, California. In Meigs, A. J. (Eds.), GSA Special Paper, (Contributions to the Crustal Evolution of the SW US, pp. 279-293) , : Geological Society of America doi: 10.1130/0-8137-2365-5.279.