Evolution of the Puente Hills Thrust Fault

Bergen, Kristian J. and Shaw, John H.
[email protected]

This study aims to assess the evolution of the Puente Hills thrust fault (PHT) by determining its age of initiation, lateral propagation history, and changes in slip rates over time. In addition to providing structural closure for the Santa Fe Springs and Coyote Hills oil fields, the PHT presents one of the largest deterministic seismic hazards in the United States, given its location beneath downtown Los Angeles. The Los Angeles (LA) and Santa Fe Springs (SFS) segments of the PHT are characterized by growth stratigraphy where folds formed by uplift on the fault segments have been continually buried by sediment from the Los Angeles and San Gabriel rivers. The Coyote Hills (CH) segment has developed topography and is characterized by onlapping growth stratigraphy. This depositional setting gives us the opportunity to measure uplift on the LA and SFS fault segments, and minimum uplift on the CH fault segment, as the difference in sediment thicknesses across the buried folds. To constrain deformation ages from the end-Pliocene to present we utilize the sequence stratigraphic model and well picks of Ponti et al. as a basis for mapping sequence boundaries throughout our industry seismic reflection data. We utilize industry well formation picks for age constraints in the Miocene and Pliocene. The sequence and formation top picks are then used to build 3-dimensional surfaces in the modeling program Gocad. From these surfaces we measure the change in thicknesses across the folds to obtain uplift rates between each time horizon for the three segments of the PHT. Preliminary results show two distinct periods of deformation on the LA and SFS segments: an early period characterized by fault-propagation folding that terminates sometime before 2 Ma, followed by a period of activity beginning at 780 ka that involves breakthrough of these faults and fold-bend folding. Estimated slip rates for the second phase of deformation on the LA segment reach a maximum of 2.1 mm/yr from the mid-Pleistocene to present.

Ponti, D. J. et al. A 3-Dimensional Model of Water-Bearing Sequences in the Dominguez Gap Region, Long Beach, California: US Geological Survey Open-File Report 1013 (2007).

AAPG Search and Discovery Article #90162©2013 Pacific Section AAPG, SPE and SEPM Joint Technical Conference, Monterey, California, April 19-25, 2013