Group B, Poster #100, Earthquake Geology

Investigating Uplift Patterns and Slip Rates in Restraining Bends along the Pacific-North American Plate Boundary in the San Francisco Bay Area, California

George E. Hilley

Poster Presentation

2024 SCEC Annual Meeting, Poster #100, SCEC Contribution #13887
Restraining bends and steps along strike-slip faults create zones of localized shortening that generate secondary structures, such as reverse faults and folds, which produce rock uplift and elevated topography. This study integrates two investigations focused on understanding the uplift patterns and slip rates along the Pacific-North American plate boundary in the San Francisco Bay Area, California.

In the Gabilan Mesa and East Bay Hills, our approach combines topographic analysis of river profiles with watershed-averaged millennial-scale erosion rates, constrained by cosmogenic radionuclide analyses. We target locations above and below knickpoints in river profiles to capture... erosion dynamics and uplift rates. These regions exhibit low-relief plateaus bordered by steep canyons, which suggest recent changes in uplift rates. In the Mount Diablo region, we are estimating slip rates along structures within the restraining step of the Concord-Greenville Fault System using cosmogenic 10-Be erosion-rate measurements. Long-river profiles in watersheds draining Mount Diablo suggest that erosion rates may approximate rock uplift rates, which are then used to infer slip rates along the Mount Diablo Thrust. These slip rates, driven by the strike-slip motion of the Concord-Greenville Faults, are modeled using boundary element methods to estimate the rate of relative plate motion driving these deformations. This project builds on our previous work in northern and central California and introduces new methodologies to combine erosion rate estimates with mechanical models to constrain rates of potential seismic moment accumulation.

While the Mount Diablo study is specific to this region, the methodologies have broader applications for understanding other restraining structures that transfer slip between strike-slip faults, such as the Hayward-Calaveras Fault System. These methods provide a framework for studying similar structures at a larger scale, contributing to a better understanding of seismic hazards and fault mechanics in tectonically active regions of central and northern California.
SHOW MORE

Citation: Hilley, G. E. (2024, 09). Investigating Uplift Patterns and Slip Rates in Restraining Bends along the Pacific-North American Plate Boundary in the San Francisco Bay Area, California. Poster Presentation at 2024 SCEC Annual Meeting.
Keywords: Restraining bends, strike-slip faults, uplift patterns, slip rates, San Andreas Fault, Concord-Greenville Fault, cosmogenic radionuclide analyses, boundary element models, seismic hazards, tectonic geomorphology
SCEC Award: 24004, 24005
Relevant SCEC Themes:
Improving Observations and Closing Data Gaps