This report is being provided to the Fire and Emergency Services Authority (FESA) as part of the Collaborative Research Agreement (CRA) with Geoscience Australia. FESA recognises the potential vulnerability of the Western Australia coastline to tsunamigenic earthquakes originating from the Sunda Arc subduction zone. There is historic evidence of such events, \cite{CB:ausgeo}, and FESA has sought to assess the relative risk of its urban and regional communities to the tsunami threat and develop detailed response plans. This report is the first in a series of studies to assess the relative risk to the tsunami threat. The methods, assumptions and results of a single tsunami source scenario is described for the Onslow area in the North West shelf region. Onslow has a population of around 800 is part of the Shire of Ashburton in the Pilbara region of Western Autralia \footnote{http://www.pdc.wa.gov.au/region/political.htm}. Onslow supports a variety of industries, including oil, gas, mining, cattle, fishing and tourism. The report will outline the methods of modelling the tsunami from its source to its impact ashore. Section \ref{sec:tsunamiscenario} provides the background to the scenario used for this study. Whilst the return period of this scenario is unknown, it can be be classed as a plausible event. Future studies will present a series of scenarios for a range of periods to assist FESA in developing appropriate plans for a range of event impacts. The modelling technique to develop the impact ashore will be discussed in Section \ref{sec:anuga} with data inputs discussed in Section \ref{sec:data}. Inundation results shown in Section \ref{sec:results} and impact modelling results shown in Section \ref{sec:impact}. The report concludes with a summary of the results detailing issues regarding data and further model development.