Exploring the impact of deglaciation on fault slip in the Sangre de Cristo Mountains, Colorado, USA

Few natural examples exist where climate’s influence on tectonics is clear. Based on a study of the Sangre de Cristo Mountains in southern Colorado, we argue that climate-driven changes in ice loads affected spatial and temporal slip patterns on the range-front normal fault. Relict glacial features enable the reconstruction of paleoglacier extents and show variable amounts of footwall ice coverage during the Last Glacial Maximum (LGM). Line load models indicate post-LGM ice melting reduced fault clamping stress by ∼20−55 kPa at seismic depths. Flexural isostatic modeling shows several meters of footwall uplift due to ice unloading with spatial patterns and magnitudes consistent with post-LGM fault throw measured from offset Holocene and late Pleistocene alluvial fans. Post-LGM fault throw rates are at least a factor of five higher than middle and early Pleistocene rates. We infer that climate-modulated ice-load changes can pace fault clamping stress and slip patterns on range-bounding normal faults.