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Abstract: Tsunamis are frequent events in modern marine environments but evidence of their passing in subtidal ancient epicontinental sea deposits is elusive. It has been suggested that this is due to mis-identification or poor preservation potential. Herein a numerical modelling approach is used to show that tsunami propagation in one large ancient epicontinental sea was hindered by the damping effect of shallow bathymetries and reflection, refraction and diffraction from emergent landmasses. The Imperial College Ocean Model (ICOM) is used for this study and is first validated against data from the Sumatra–Andaman Tsunami of December 2004. A palaeobathymetric dataset is then presented for the Hettangian (Lower Jurassic) Laurasian Seaway with idealised tsunami sources situated on the continental shelf and within the adjacent oceanic basin. Results show that tsunamis forced from within ocean basins adjacent to the epicontinental sea are rapidly attenuated over the continental slope and fail to propagate great distances onto the shelf. Similarly, the sedimentological effect of tsunamis forced from within the epicontinental sea is also restricted. It is concluded that tsunami deposits in ancient epicontinental seas are most likely to occur in relative proximity to the source region and this must contribute to their scarcity in the geological record. [Copyright &y& Elsevier]