Sampling the Storegga tsunami: the impacts of sampling and model resolution on tsunami sediment interpretations

Due to their rare nature, very large tsunami events are often only known from their sedimentary deposits. However, our lack of physical understanding on precisely how the sediments are deposited means we are currently unable to fully recreate a tsunami wave that created the deposit from the deposit alone. Moreover, local environmental and topographic controls on the deposit are often overlooked due to the paucity of available data. Here, we analyse a tsunami deposit from a unique site where high resolution spatial sampling of the deposit is possible, such that we can then compare these to a very high resolution (5 metre minimum resolution) numerical model of the tsunami.  Our results demonstrate clear differences in the simulated conditions depending on both the model and topographic resolution used. Local topographic controls are shown to dictate sediment transport pathways and can explain sedimentary changes seen in the cored deposits; underscoring the need for careful consideration of both the paleao-geographic reconstructions and model resolution used. There is a clear positive relationship between deposit thickness and simulated maximum flow depth, but only when the model resolution is high. Our results show that our current understanding of tsunami depositional processes is inadequate. Reconstructing the wave is not possible using current inversion techniques which produce spurious results when compared to the forward numerical model. Ultimately, improving the ability to derive wave characteristics from sedimentary records remains critical for refining future tsunami risk assessments.