Abstract
The stress tensor is an important property for upper crustal studies
such as those that involve pore fluids and earthquake hazards. At
tectonic plate scale, plate boundary forces and mantle convection are
the primary drivers of the stress field. In many local settings (10s to
100s of km and <10 km depth) in tectonic plate interiors, we
can simplify by assuming a constant background stress field that is
perturbed by local heterogeneity in density and elasticity. Local stress
orientation and sometimes magnitude can be estimated from earthquake and
borehole-based observations when available. Modeling of the local stress
field often involves interpolating sparse observations. We present a new
method to estimate the 3D stress field in the upper crust and
demonstrate it for Oklahoma. We created a 3D material model by inverting
multiple types of geophysical observations simultaneously. Integrating
surface-wave dispersion, local travel times and gravity observations
produces a model of P-wave velocity, S-wave velocity and density. The
stress field can then be modeled using finite element simulations. The
simulations are performed using our simplified view of the local stress
field as the sum of a constant background stress field that is perturbed
by local density and elasticity heterogeneity and gravitational body
forces. An orientation of N82˚E, for the maximum compressive tectonic
force, best agrees with previously observed stress orientations and
faulting types in Oklahoma. The gravitational contribution of the
horizontal stress field has a magnitude comparable to the tectonic
contribution for the upper 5 km of the subsurface.