Coral Microatoll Paleogeodesy in Sumatra: Details of the 1861 Predecessor to the 2005 Nias-Simeulue Earthquake
Abstract
Coral microatolls, with their ability to provide century-long continuous records of relative sea level with high precision in both age and elevation, allow for unprecedented resolution in the reconstruction of the timing and magnitude of both paleo-sea-level change and past megathrust ruptures. Using precise 230Th-dated coral microatolls to infer uplift of Sumatra's outer arc islands, and hence slip on the underlying plate interface, we have developed paleoseismic histories at numerous sites along a 900-km stretch of the Sunda megathrust off the west coast of Sumatra. In earlier work, by comparing the records along strike, we identified two persistent barriers to earthquake rupture. Simeulue, a 100-km-long island off the west coast of northern Sumatra, straddles the boundary between the 2004 (MW 9.1) and 2005 (MW 8.6) Sunda megathrust ruptures and acted as a barrier to both. Historical and coral paleoseismic records suggest that central Simeulue has behaved as a persistent barrier for at least the past 1100 years. Farther south near the Equator, the Batu Islands patch of the megathrust has been a barrier to rupture in great earthquakes from both the south (1797, 1833) and north (1861, 2005). In this presentation, we will present new paleoseismic results from the 2005 rupture patch off the west coast of northern Sumatra. The 1861 rupture appears to be nearly identical in extent to the 2005 rupture, involving uplift of Nias, Bangkaru, and the eastern half of Simeulue. At both sites where the 1861 uplift has been well determined, it was comparable to uplift locally in 2005. In another application of paleogeodesy, coral microatolls hold details about the mid-Holocene highstand on the tectonically stable Sunda Shelf, east of Sumatra; we will offer a glimpse of our preliminary findings on the Sunda Shelf.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFM.G11C..08M
- Keywords:
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- 1211 GEODESY AND GRAVITY / Non-tectonic deformation;
- 1242 GEODESY AND GRAVITY / Seismic cycle related deformations;
- 7221 SEISMOLOGY / Paleoseismology;
- 8170 TECTONOPHYSICS / Subduction zone processes