Apparent Vertical Moho Offsets under Continental Strike-Slip Faults from Lithology Contrasts in the Seismogenic Crust

We demonstrate that observed contrasts of upper crustal structures across large continental strike-slip faults are sufficient to produce artificial vertical Moho offsets of several kilometers in studies using laterally homogenous models. This can have significant impact on efforts to understand how the observed surface displacement is accommodated in the deep crust. An existing hypothesis that continental strike-slip faults extend as discrete narrow features through the entire crust rests partly on inferred vertical Moho offsets across the faults based on teleseismic converted wave (receiver function) studies. However, such studies typically do not account for the juxtaposition of different structures across the faults, which can lead to significant (e. g., 10%) contrasts of seismic velocities in the upper crust. Observed profiles of velocity contrasts across faults can bias images of the deep structure to the extent where a large (>5 km) Moho offset can be purely apparent rather than real. Constraining the existence and size of true vertical Moho offsets below continental strike-slip faults thus require calculations that account for the across-fault lithology contrasts. Accurate results on the geometry of Moho across faults can have important implications for lithospheric deformation, crustal tomography, strain localization and partitioning in the crust, continental rheology, and geodynamics.