Uplift, Subsidence, and Basin Development Along the Evolving Pacific-North American Plate Boundary

University Of California-Santa Barbara, Santa Barbara CA

Investigators

Abstract

Understanding continental structure, basin development and the dynamics of plate boundary deformation are important problems in earth science. The offshore California Continental Borderland is an ideal natural laboratory to investigate many aspects of this deformation, because it was the locus of Pacific-North America plate motion for about 70% of its displacement history, and recent GPS data suggest that up to 20% of current plate motion is still located offshore. Moreover, the Borderland is generally an area of deposition rather than erosion, suggesting that the record of plate boundary deformation is more complete, more accessible and can be better imaged in three dimensions offshore. This project will use grids of high-quality industry multichannel seismic reflection data (originally collected for hydrocarbon exploration) to investigate the crustal deformation and tectonic evolution of this offshore portion of the plate boundary. Digital fault surfaces and stratigraphic reference horizons will be produced to define active fault, fold, and basin geometry in three dimensions offshore, and to help quantify the finite strain field with time. A prime objective is to document the timing, rates, and spatial patterns of uplift, subsidence, and related volcanic activity that are most sensitive to important parameters of plate boundary processes, such as mechanical strengths, viscosities, cooling histories, plate coupling and changing plate boundary geometry. This will then help distinguish between competing tectonic models for plate boundary evolution and provide a more accurate picture of plate boundary strain accumulation. Our results will thus complement land-based studies and provide a more synoptic view of the plate boundary, including what some of the important geodynamic processes are that help drive modern basin development, and the regional pattern of uplift and subsidence along this active transform system. Evaluating the offshore structure, stratigraphy and plate boundary deformation of the Continental Borderland will help address several important fundamental questions about the evolution of continents and continental deformation, including how strain accumulates and is partitioned within plate boundaries, and what controls the crustal architecture at plate boundaries. Evaluating this deformation is important because these active offshore structures represent a largely as yet unknown hazard to many California coastal communities, and provide important analogs to active buried (less-accessible) onshore structures that may produce large, damaging earthquakes in the Los Angeles basin and other areas. Project results will thus be incorporated into regional community fault models for southern California that form the basis for estimating earthquake and tsunami hazards, for interpreting geodetic strain data, and for understanding other aspects of continental deformation, including fault interaction and fault system dynamics. The project will also provide further insight into the nature of offshore basin development that forms important reservoirs for hydrocarbon accumulation.