STRUCTURAL INHERITANCE IN THE LITHOSPHERE FROM SEISMIC IMAGING (Invited Presentation)

The tectonic history of a region can be inferred through rock fabric mapped in surface exposures, or imaged geophysically in the subsurface via seismic anisotropy. We review a range of examples from such analysis in our recent work, contrasting a number of geological settings, and speculating on the implications for the role of structural inheritance for tectonic force transmission and lithosphere mantle coupling.

Common seismological approaches have poor depth sensitivity (shear wave splitting) or relatively low lateral resolution (surface wave inversions). We complement such approaches with anisotropy-aware receiver function analysis, which detects contrasts in rock fabric. Imaged fabric orientations in the crust and lithospheric mantle are often not easily explained with simple present-day (e.g., geodetic) deformation patterns. Instead, subsurface fabric often matches surface fault trace orientations, suggesting that both are sensitive to tectonic inheritance and strain distribution at depth.

For example, in the southern Rocky Mountains orogen-scale Proterozoic fabrics persist among NNW-SSE oriented Laramide and Rio Grande structures. At the Dead Sea transform, some features parallel recently active faults which may have been reactivated after forming in previous tectonic regimes. In the Alaskan Northern Cordillera, terranes are diffusely bounded by trends in seismicity, subsurface fabric strikes, and some mineral belts at high angles to major faults. In southern California, faults and subsurface fabrics under present-day transform deformation show geometries that appear inherited from past compressional episodes.

Overall, lithospheric rock fabric seems to not be easily overprinted after the orientations of tectonic driving forces change; fabrics complexly persist over long timescales even in tectonically active regions. This has implications for understanding present-day fault loading, intraplate geodynamics, and constraining the evolution of plate boundaries.