Environmental Sciences Research Institute

Tsunami Risk in the Indian Ocean from Threatened M>8 Event Under Mentawai Islands

Funded by NERC

Despite the occurrence of two very large earthquakes (December 2004 and March 2005) in the Sumatra region, the seismic hazard in the area remains extremely high. Specifically, the Dec. and March events increased stress on the Sumatra fault, which runs down the centre of the island, and on the Sunda Trench south of the March rupture. The latter region, beneath the Mentawai Islands, is of particular concern because the last large earthquakes in the area were in 1797 near Siberut Island and in 1833 farther south. The 1833 earthquake is known to have caused a devastating tsunami.

The aim of this project is to model the range of possible tsunamis that could be generated by a large earthquake on the Sunda Trench beneath the Mentawai Islands. Because neither the rupture length or slip distribution of this forthcoming event can be known in advance, we will create a range of possible synthetic earthquakes constrained by the best current understanding of the past earthquake history of the region. For each synthetic earthquake, we will calculate the seafloor displacement caused by it; this, in turn, will allow us to compute expected wave heights and energies. Based on these calculations, we will produce maps of likely, and worst case, tsunamis in the Indian Ocean

Fig. 3. The full modelling process for a 630 km earthquake rupture. Colour scales shown here are used throughout the rest of the paper. A. Slip distribution projected vertically upward from the inclined megathrust-plane to the surface. B Vertical coseismic seafloor displacements calculated for the event. C. Maximum waveheights predicted at 5 km intervals along the west coast of Sumatra. D. Maximum wave heights predicted for the Indian Ocean with synthetic mareograms predicted for some indicative coastal locations. The scales of all synthetic mareograms are identical.