3D MECHANICAL MODELING OF NORTHERN CALIFORNIA FAULT SYSTEM

百花草

Northern California’s tectonic is characterized by a fault system in which the main
trace of the San Andreas fault is associated to two en échelon fault systems: the
Maacama and Roger Creek, that are the northward continuations of the Calaveras and
Hayward faults in the Bay Area. Geological evidences, along with principal stresses
orientations, suggest that this fault system behaves mechanically differently than the
southern segments, and show that its frictional strength is slightly higher than in the
south. In this study we investigate the influence of thermal and rheological parameters
and the geometry of the fault system on stress orientations and long term velocities.
We model the fault system in a cross-section view, from Pt. Arena to the West to 180
km inland, assuming there is no stress or strain variation along strike in this area.
A simplified three-dimensional (3-D) model was built with a finite element code
(ADELI3D). Heat flow measurements, seismicity distribution, and surface velocities
were used to constrain the thermal structure of the crust and internal fault friction. The
rheology of the lithosphere is composed of a frictional upper crust and a viscoelastic
lower crust. Fault zones are modeled using low effective friction with respect to the
surrounding crust. The lithosphere is supported by hydrostatic pressure at its base
(representing the asthenosphere).

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