Persistent termini of 2004- and 2005-like ruptures of the Sunda megathrust
To gain insight into the longevity of subduction zone segmentation, we use coral microatolls to examine an 1100-year record of large earthquakes across the boundary of the great 2004 and 2005 Sunda megathrust ruptures. Simeulue, a 100-km-long island off the west coast of northern Sumatra, Indonesia, straddles this boundary: northern Simeulue was uplifted in the 2004 earthquake, whereas southern Simeulue rose in 2005. Northern Simeulue corals reveal that predecessors of the 2004 earthquake occurred in the 10th century AD, in AD 1394 ± 2, and in AD 1450 ± 3. Corals from southern Simeulue indicate that none of the major uplifts inferred on northern Simeulue in the past 1100 years extended to southern Simeulue. The two largest uplifts recognized at a south-central Simeulue site—around AD 1422 and in 2005—involved little or no uplift of northern Simeulue. The distribution of uplift and strong shaking during a historical earthquake in 1861 suggests the 1861 rupture area was also restricted to south of central Simeulue, as in 2005. The strikingly different histories of the two adjacent patches demonstrate that this boundary has persisted as an impediment to rupture through at least seven earthquakes in the past 1100 years. This implies that the rupture lengths, and hence sizes, of at least some future great earthquakes and tsunamis can be forecast. These microatolls also provide insight into megathrust behavior between earthquakes, revealing sudden and substantial changes in interseismic strain accumulation rates.
Additional Information© 2012. American Geophysical Union. Received 22 September 2011; accepted 21 February 2012; published 17 April 2012. We thank D. Prayudi, I. Suprihanto, and J. Galetzka for field support; M. Simons and J.-P. Avouac for helpful discussions; and R. Bürgmann, R. Gold, J. Freymueller, and H. Kelsey for insightful reviews that led to substantial improvements in the manuscript. This work has been supported by NSF grant EAR-0538333 (to K.S.); by NSC grants 98-2661-M-002-012, 99-2611-M-002-006, and 99-2628-M-002-012 (to C.C.S.); by the Indonesian Institute of Sciences (LIPI) and International Joint Research Program of the Indonesian Ministry of Research and Technology (RUTI); by the Gordon and Betty Moore Foundation; and by the Earth Observatory of Singapore. This is Caltech Tectonics Observatory contribution 167 and Earth Observatory of Singapore contribution 30. An annotated high-resolution X-ray mosaic of each of the BUN-A coral cross sections is provided in the electronic supplement of A. Meltzner's Ph.D. thesis [Meltzner, 2010], along with a selection of field photos from the site. We are forever grateful to Caltech geology librarian Jim O'Donnell for all his assistance on this project and over the years; Jim passed away the week this paper was accepted, and he will be sorely missed.
Published - Meltzner2012p18077J_Geophys_Res-Sol_Ea.pdf
Supplemental Material - 2011jb008888-txts01.pdf