Abstract Tsunami hazard maps are generated for the coastline of the Mentawai Islands, West Sumatra, Indonesia, to support evacuation and disaster response planning. A random heterogeneous slip generator is used to forward model a suite of earthquake rupture scenarios on the Mentawai Segment of the Sunda Subduction Zone. Up to 1000 rupture models that fit constraints provided by coral and geodetic records of coseismic vertical deformation from major earthquakes in 1797, 1833 and 2007 are used to model inundation and to define a maximum inundation zone that envelopes all of these scenarios. Comparison with single-scenario hazard assessments developed by experts and agreed through scientific consensus shows that there is value in modelling a suite of scenarios in order to obtain a more robust and conservative estimate of potential inundated areas. Although both the model presented here and the single-scenario models are based on assumptions about the characteristics of future events using knowledge of past events, by sampling a range of plausible outcomes we gain a more robust estimate of which areas may be inundated during a tsunami within the bounds of the assumptions applied.

The Andaman Islands are part of the Andaman-Nicobar Ridge, an accretionary complex that forms part of the outer-arc ridge of the Sunda subduction zone. The Tertiary rocks exposed on the Andaman Islands preserve a record of the tectonic evolution of the surrounding region, including the evolution and closure of the Tethys Ocean. Some of the Paleogene sediments on Andaman may represent an offscraped part of the early Bengal Fan. Through field and petrographic observations, and use of a number of isotopic tracers, new age and provenance constraints are placed on the key Paleogene formations exposed on South Andaman. A paucity of biostratigraphic data poorly define sediment depositional ages. Constraints on timing of deposition obtained by dating detrital minerals for the Mithakhari Group indicate sedimentation after 60 Ma, possibly younger than 40 Ma. A better constraint is obtained for the Andaman Flysch Formation, which was deposited between 30 and 20 Ma, based on Ar-Ar ages of the youngest detrital muscovites at ca. 30 Ma and thermal history modeling of apatite fission-track and U-Th/He data. The latter record sediment burial and inversion (uplift) at ca. 20 Ma. In terms of sediment sources the Mithakhari Group shows a predominantly arc-derived composition, with a very subordinate contribution from the continental margin to the east of the arc. The Oligocene Andaman Flysch at Corbyn's Cove is dominated by recycled orogenic sources, but it also contains a subordinate arc-derived contribution. It is likely that the sources of the Andaman Flysch included rocks from Myanmar affected by India-Asia collision. Any contribution of material from the nascent Himalayas must have been minor. Nd isotope data discount any major input from cratonic Greater India sources.

Abstract The Andaman-Nicobar Ridge and the Indo-Burman Range are composed of sediments of the Bengal and Nicobar Fans scraped off the underthrusting Indian plate at the Sunda subduction zone. The Andaman Sea and the eastern part of the central valley of Burma represent a Neogene-Quaternary extensional basin underlain by oceanic crust formed by northwestward rifting of this orogenic ridge away from continental crust of the eastern Burma highlands and the Malay Peninsula. The plate edge is defined by a north-south transform in Burma, by the Sumatran fault system longitudinally bisecting Sumatra, and by a complex system of short spreading rifts and transforms in the central basin of the Andaman Sea. Where sedimentation rates are high over the newly formed oceanic crust, no magnetic anomalies are identifiable; where sedimentation rates are low or negligible, clear magnetic anomalies have permitted dating this phase of opening at approximately 11 m.y. B.P.

Abstract The Andaman–Nicobar subduction system is the northwestern segment of the Sunda subduction system, where the Indian Plate subducts beneath the Sunda Plate in a nearly arc-parallel direction. The entire segment ruptured during the 2004 great Andaman–Sumatra earthquake ( M w =9.3). Using recently acquired high-resolution seismic reflection data, we characterize the shallow structure of the whole Andaman–Nicobar subduction system from west to east, starting from the nature of the subducting plate in the Bay of Bengal to back-arc spreading in the Andaman Sea. We find that the Ninety-East Ridge is overlain by thick continental margin sediments beneath the recent Bengal Fan sediments. The boundary between these two sedimentary units defines the plate interface. We observe evidence of re-activation of fracture zones on the subducting plate beneath the forearc, influencing the morphology of the upper plate. The forearc region, which includes the accretionary wedge, the forearc high and the forearc basin, is exceptionally wide (250 km). We observe an unusually large bathymetric depression within the forearc high. The forearc high is bounded in the east by a normal fault, whereas the forearc basin contains an active backthrust. The forearc basin is floored by the continental crust of Malayan Peninsula origin. The active sliver strike-slip fault lies in a deep basin, created during the rifting of the forearc continental crust and the Malayan Peninsula. The sliver fault connects with the Great Sumatra Fault in the south and with the Sagaing Fault in the north, via the Andaman Sea spreading centre and a large transform fault in the Andaman Sea.