J.W. Verbeek, C.S. de Leeuw, N. Parker and Th.E. Wong 2002. Characterisation and correlation of Tertiary seismostratigraphic units in the Roer Valley Graben. Netherlands Journal of Geosciences. 81, (Aug. 2002), 159-166. DOI:https://doi.org/10.1017/S0016774600022393.