BRIGHT SEISMIC REFLECTIONS AND FLUID MOVEMENT BY POROUS FLOW IN THE LOWER CRUST

The origin of high-amplitude lower crustal bright seismic reflections in a Phanerozoic area is investigated by modeling a distribution of me tamorphic fluid flow through pores as a possible explanation. A numeri cal model of metamorphic fluid flow in a viscous, porous medium is dev eloped. A model is applied to a tectonically active area such as the B asin and Range, where viscous behavior of the lower crust is suggested . Calculations show that the characteristic vertical dimension of rela tive volumetric flow variations corresponds to the thickness of seismi c lamellae as determined from reflection frequency spectra for the Bas in and Range. This result shows that a dynamic effect, which was produ ced by fluid pressure and viscous matrix resistance, could be responsi ble for the origin of the seismic lamellae in the lower crust in an ar ea of active tectonics.