Tsunami threat in the Indian Ocean from a future megathrust earthquake west of Sumatra

Abstract

Several independent indicators imply a high probability of a great (M N 8) earthquake rupture of the subduction megathrust under the Mentawai Islands of West Sumatra. The human consequences of such an event depend crucially on its tsunamigenic potential, which in turn depends on unpredictable details of slip distribution on the megathrust and how resulting seafloor movements and the propagating tsunami waves interact with bathymetry. Here we address the forward problem by modelling about 1000 possible complex earthquake ruptures and calculating the seafloor displacements and tsunami wave height distributions that would result from the most likely 100 or so, as judged by reference to paleogeodetic data. Additionally we carry out a systematic study of the importance of the location of maximum slip with respect to the morphology of the fore-arc complex. Our results indicate a generally smaller regional tsunami hazard than was realised in Aceh during the December 2004 event, though more than 20% of simulations result in tsunami wave heights of more than 5 m for the southern Sumatran cities of Padang and Bengkulu. The extreme events in these simulations produce results which are consistent with recent deterministic studies. The study confirms the sensitivity of predicted wave heights to the distribution of slip even for events with similar moment and reproduces Plafker's rule of thumb. Additionally we show that the maximum wave height observed at a single location scales with the magnitude though data for all magnitudes exhibit extreme variability. Finally, we show that for any coastal location in the near field of the earthquake, despite the complexity of the earthquake rupture simulations and the large range of magnitudes modelled, the timing of inundation is constant to first order and the maximum height of the modelled waves is directly proportional to the vertical coseismic displacement experienced at that point. These results may assist in developing tsunami preparedness strategies around the Indian Ocean and in particular along the coasts of western Sumatra.

Numerical experiment and a case study of sediment transport simulation of the 2004 Indian Ocean tsunami in Lhok Nga, Banda Aceh, Indonesia

“…Moreover, the subsidence along the Sumatran mainland would allow tsunami waves to penetrate further inland, causing more damage and flooding than other scenarios. These phenomena were also discussed by Borrero et al (2006) and McCloskey et al (2008).…”

The quest for wisdom: lessons from 17 tsunamis, 2004–2014

“…On the other hand, the 2006 Java and 2010 Mentawai 'tsunami earthquakes' were not, or not sufficiently, recognized as such, and turned into tragic disasters. The disparity in colours along the Sunda arc in figure 5 is of particular concern given that, to the south of the 2005 Nias rupture, the 2007 Bengkulu sequence has failed to release the full strain accumulated since the great 1833 earthquake [95], resulting in a seismic gap that is widely expected to rupture through a great earthquake in the next years to decades, bearing catastrophic tsunami hazard, especially for the city of Padang with a population of 1 million [121,122].…”

Epistemic uncertainties and natural hazard risk assessment. 1. A review of different natural hazard areas

“…For instance, location, size, shape, and amplitude of slip asperities differ significantly among inversion models for the 2011 Tōhoku earthquake , reflecting the complexity and uncertainty in imaging the rupture process for mega-thrust subduction earthquakes. Additionally, different source modelling approaches, such as surface rupture to ocean bottom, effects of horizontal deformation of steep slopes on vertical deformation, hydrodynamic response of water column, and time-dependent rupture process, slow versus fast rupture 30 propagation speed, will influence the resulting tsunami waves (Geist, 2002;McCloskey et al, 2008;Løvholt et al, 2012;Satake et al, 2013). All these factors contribute to epistemic uncertainties related to tsunami source modelling.…”