Distributed lower-crustal flow beneath the central Xianshuihe-Xiaojiang Fault system: reconciling geodesy and geology

We use recently compiled GNSS velocities across the Zemuhe-Daliangshan fault zone, part of the central Xianshuihe-Xiaojiang fault system, to reconcile a long-standing mismatch between geodetic and geologic slip-rate estimates. We show that conventional elastic dislocation models yield slip rates and locking depths that conflict with seismic and geologic constraints. In contrast, models incorporating a viscoelastic rheology for the lower crust yield geologically consistent slip rates, with the Zemuhe fault slipping 7 mm/yr and the Daliangshan fault slipping 2 mm/yr, and locking depths more consistent with microseismicity (17-20 km). In contrast with major strike-slip faults worldwide, deformation in this immature system appears distributed over a broad lower-crustal region. These findings indicate that interpreting interseismic deformation with purely elastic models in fault zones that lack a mature, localized shear zone at depth can lead to misleading results; surface strain rates may correlate poorly with seismic hazard in these regions.