TOPOGRAPHIC PERTURBATIONS OF REGIONAL STRESSES AND CONSEQUENT BEDROCKFRACTURING

Stresses at Earth's surface are profoundly influenced by topography. S imple models indicate that gravitational and regional stresses are con centrated, attenuated, even reversed within landforms. Such topographi cally induced stresses are potentially manifest as bedrock fractures. Fractures reduce rock mass strength, decrease erosional resistance, an d create conduits for water. By creating fractures, topographically in duced stresses can alter processes of mass wasting, bedrock incision, and groundwater flow. We use Savage et al.'s [1985] solution for stres ses in symmetric ridges and valleys on an elastic half-space in plane strain to assess topographic effects on regional and gravity-induced s tresses. We have extended their solution to include lateral loads that vary with depth, which better approximates states of stress found in Earth's crust and allows us to examine a greater range of stress regim es. We examine the calculated stress fields to assess, in a classic Mo hr-Coulomb context, the potential for consequent fracture. This model indicates that topographic relief can cause stresses of sufficient mag nitude to break rock, creating fracture sets having a spatial distribu tion and orientation governed by landform shape and the regional state of stress. We find that in extensional tectonic regimes, topographica lly induced stresses favor surface-parallel fractures through ridges a nd steeply dipping fractures through valleys. Conversely, in compressi onal regimes, topographically induced stresses favor steeply dipping f ractures through ridges and surface-parallel fractures through valleys . Such topographic interactions with regional stresses pose consequenc es for interpretations of fracture orientation, for assessments of slo pe stability, and for processes of landscape development.