With the recent availability of dense seismological array data there is the opportunity to reconstruct 2D wavefields of propagating seismic energy. Such a reconstruction allows seismic data to be viewed as wavefields rather than as single station traces. Reconstruction of such wavefields within an array will improve our understanding of complex wave propagation effects and, hence, the underlying Earth structure beneath the array. We propose an algorithm applicable for teleseismic waves that is based on wavefield expansion by cubic B-splines. Application to the high-density array in Southern California shows that we can identify basin resonances and wavefront shifts; such wavefield shifts could be caused by local structure or travel path structure, as waves pass through major structural contrasts.