User-driven science: earthquake and tsunami scenarios for the Mentawai Islands, western Sumatra

Following recovery from a large tsunami on 25-Oct-2010 that killed over 500 people, the government of the Mentawai Regency turned its attention to developing a regional disaster-risk-reduction plan. Geodetic and coral studies show that an earthquake as large as M 8.8 is likely in the coming decades on the Mentawai patch of the Sunda megathrust, yet there had not been any tsunami-inundation maps produced for the Mentawai Islands based on this scenario. By request from the Mentawai government, we will develop such tsunami-inundation maps for populated areas. Uncertainties in the source models include whether the accumulated strain on the Sunda megathrust is released in one great earthquake or in a series of large earthquakes, limited scientific understanding of the seismic potential of the Mentawai backthrust that lies inboard (east) of the islands, and whether these sources would rupture to the surface in a particular earthquake. Low-resolution bathymetry adds uncertainty to our modeled tsunami flow depths and runups. Because the Mentawai government is currently planning for disaster risk reduction, we chose to produce the inundation map now. However, we may have a communication challenge if, a few years in the future, further research leads to significant revisions of the inundation map. We will communicate the results and uncertainty to the Mentawai government and partner local NGOs through an in-person workshop. Monitoring and evaluation will inform further communication efforts. However, the remote location of the Mentawai Islands and limited internet and phone service significantly limits our ability to communicate with end-users at the community level. Since our maps are likely to be parceled out and distributed to villages in hard copy, we need to include key information for each location, including uncertainty, on a single sheet. With local partners, we will investigate the best way to frame this information in the local context.