Lower crustal reflectivity patterns in wide‐angle seismic recordings

Many features of wide‐angle reflection data have been attributed to finely‐layered structure in the lower crust. Reflections with similar character, however, can be produced by small‐amplitude 2‐D random velocity variations. Finite‐difference seismograms for a lower crustal model with isotropic random velocity variations match field data recorded at the Black Forest, Germany. At source‐receiver offsets beyond about twice the target depth, waves scattered from a random zone produce the appearance of horizontal layering in wide‐angle data. Lower crustal reflectivity patterns can thus be explained by models that have lateral and vertical random fluctutations rather than fine‐scale layering.