3D crustal-scale fault structure

3D model of fault structure beneath northern Owens Valley based on clustering of earthquake hypocenters.

The 1986 Chalfant Valley Earthquake

sequence lit up the northern Owens Valley. We map out hypocenter distributions and cluster them together with focal mechanisms to resolve subsurface fault architecture.

The 1986 Chalfant Valley EQ Sequence

There were over 20,000 hypocenters assoiated with this earthquake, and they have been double-difference relocated, quite precisely due to the dense seismic network there near the Long Valley Caldera.

I have used this dense array of points to identify the diversity of fault structures that were activated during the protracted EQ.

The results show a unique arrangement of faults and fault intersections. Please see the figures below from preliminary work that is driving new 3D visualization tools for looking at dynamic stress and EQ triggering.

3D modeling

reveals that the extensional basin lies in the upper plate of a listric low-angle fault.
Beneath this fault lies a complicated suite of intersecting faults that together accommodate NW-directed transtension.

Complex, juvenile fault systems such as this pose significant seismic risk. Some faults become super-critically stressed due to the diversly-oriented, interconnected faults, which serve to lock one another up. When rupture occurs, typically on a “Keystone fault” (Fletcher et al., 2016, Nature Geoscience), the ruptures can propagate from one fault plane to the next, leading to a complex and sometimes long-lasting earthquake sequence.

Gravity models and focal mechanisms

were combined with the hypocenter clusters to build a complex 3D fault structural framework that spans the entire upper crust (~14 km depth).

Cross sections

Showing the extensional basin, the hypocenter distributions, and the intersections with modeled 3D fault mesh surfaces.
They just don’t do justice.

3D structure of faults in the northern Basin and Range

Animated view showing 3D structural model of the Wassuk Fault

Preliminary 3D structure of range-bounding faults of the northern Basin and Range. This work incorporates a comprehensive dataset of published geologic maps, cross setions, seismic lines, earthquake hypocenters, focal mechanisms, and gravity inversion models.