  The software package Volna-OP2 is a robust and efficient code capable of
simulating the complete life cycle of a tsunami whilst harnessing the latest
High Performance Computing (HPC) architectures. In this paper, a comprehensive
error analysis and scalability study of the GPU version of the code is
presented. A novel decomposition of the numerical errors into the dispersion
and dissipation components is explored. Most tsunami codes exhibit amplitude
smearing and/or phase lagging/leading, so the decomposition shown here is a new
approach and novel tool for explaining these occurrences. It is the first time
that the errors of a tsunami code have been assessed in this manner.
  To date, Volna-OP2 has been widely used by the tsunami modelling community.
In particular its computational efficiency has allowed various sensitivity
analyses and uncertainty quantification studies. Due to the number of
simulations required, there is always a trade-off between accuracy and runtime
when carrying out these statistical studies. The analysis presented in this
paper will guide the user towards an acceptable level of accuracy within a
given runtime.
