Bright seismic reflections and fluid movement by porous flow in the lower crust

Abstract

The origin of high-amplitude lower crustal bright seismic reflections in a Phanerozoic area is investigated by modeling a distribution of metamorphic fluid flow through pores as a possible explanation. A numerical model of metamorphic fluid flow in a viscous, porous medium is developed. A model is applied to a tectonically active area such as the Basin and Range, where viscous behavior of the lower crust is suggested. Calculations show that the characteristic vertical dimension of relative volumetric flow variations corresponds to the thickness of seismic lamellae as determined from reflection frequency spectra for the Basin and Range. This result shows that a dynamic effect, which was produced by fluid pressure and viscous matrix resistance, could be responsible for the origin of the seismic lamellae in the lower crust in an area of active tectonics.