The effect of texture and porosity on seismic reflection amplitude in granular sediments: Theory and examples from a high-resolution shallow seismic experiment

Sediment properties such as grain shape, sorting, porosity, and the effective stress applied on the grains affect the elastic behavior of granular aggregates and, with it, the propagation of seismic waves. Seismic reflections from boundaries within granular sedimentary packs such as sands carry information about variation in the sediment properties. In this paper we analyze elastic contact mechanics models of granular media to show that within mineralogically uniform, homogeneously saturated sediments, the reflection strength can be theoretically related to variations in texture and porosity. The theoretical formulation indicates that in dry, mineralogically uniform sediments, seismic reflection amplitude depends strongly on changes in textures (such as angularity or sorting). In saturated sediments at low confining pressures, the reflection amplitude is primarily related to changes in porosity. Shallow seismic field data are interpreted quantitatively within the context of the theory. The field seismic data and supportive evidence from a nearby well are consistent with our interpretation of reflections arising from changes in textural properties of the sediment above the water table. This analysis can be used to quantify texture and porosity changes within sedimentary packets from measurements of seismic reflection strength and, thus, spatially map sedimentary properties in aquifers.