RESOLVING THE TSUNAMI WAVE: INTERPRETING PALAEOTSUNAMI DEPOSITS BY INTEGRATING NUMERICAL MODELLING AND SEDIMENTOLOGY

The 8.15 ka Storegga submarine slide was a large, tsunamigenic slide off the coast of Norway. The resulting tsunami had estimated run-up heights of around 10-20m on the Norwegian coast, over 20m in Shetland, 3-6 metres on the Scottish mainland coast and reached as far as Greenland. Run-up height can be estimated in certain locations via tsunami deposits, but these are not preserved everywhere. Moreover, the estimation of wave height and run-up depend on accurate knowledge of past sea-level. So far numerical modelling of the wave has focused on the regional wave, with large scale, low resolution models that do not incorporate inundation and hence can only estimate the wave run up using offshore wave heights.

New core data were taken from the Ythan valley in NE Scotland. High resolution sedimentary analysis of these data show signatures of multiple waves. We test this hypothesis by creating a very high resolution model (metre-scale) of the wave inundation, coupled to a previous regional model. The new model uses Thetis, a finite element shallow water solver that is capable of running on many cores utilising multi-scale resolution.The inundation model confirms that multiple waves did pass over the site. We explore the sensitivity of the model to a number of parameters, such as sea level and coastal geomorphology.

Combining sedimentological data with high resolution inundation modelling is a powerful tool in enhancing the sedimentary record of extreme coastal events. Together, they can help interpret the sedimentary record, extending the history of extreme events and hence improve risk knowledge.