Collaborative Research: Recent Kinematic Evolution of the Northern Eastern California Shear Zone from Geologic Data

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Plate circuit calculations indicate that motion of the Pacific plate relative to North American plate changed from westerly to NW at ~8 Ma. This observation corresponds extremely well with geologic data which indicates that motion of the Sierran-Great Valley block relative to the Colorado Plateau changed from westerly to NW at ~8-10 Ma. Geologic studies indicate that the rate of right lateral shear at ~8 Ma within the Eastern California Shear Zone north of the Garlock fault was ~15 mm/yr accounting for ~30%of relative plate motion. Geodetic studies indicate a present-day dextral shear rate of 10-12 mm/yr, providing clear evidence that the Eastern California Shear Zone is still an important component of deformation within the Pacific-North America plate boundary zone. In spite of its tectonic importance, the space-time evolution of much of the Eastern California Shear Zone is only broadly understood. This proposal requests support for investigating the kinematics of a system of intraplate dextral faults in the northern part of the Eastern California Shear Zone using an integrated approach of field mapping, tectonic geomorphology, paleoseismology, and geochronology. The proposed research is motivated by ongoing geodetic investigations on present-day magnitude of strain accumulation and spatial distribution across the Eastern California Shear Zone. In light of these geodetic constraints on strain accumulation, it is timely to improve the understanding of the spatial and temporal patterns of strain release during the late Neogene and Quaternary. The two data sets will provide important constraints on geodynamic hypotheses proposed for the evolution of the Eastern California Shear Zone. An accurate characterization of the spatial and temporal patterns of strain release within the Eastern California Shear Zone is crucial for understanding tectonic processes over a much broader area of intraplate deformation associated with the interaction of the Pacific and North American plates.