Submergence and uplift associated with the giant 1833 Sumatran subduction earthquake: Evidence from coral microatolls

The giant Sumatran subduction earthquake of 1833 appears as a large emergen ce event in fossil coral microatolls on the reefs of Sumatra's outer-arc ri dge. Stratigraphic analysis of these and living microatolls nearby allow us to estimate that 1833 emergence increased trenchward from about 1 to 2 m. This pattern and magnitude of uplift are consistent with about 13 m of slip on the subduction interface and suggest a magnitude (M-w) of 8.8-9.2 for t he earthquake. The fossil microatolls also record rapid submergence in the decades prior to the earthquake, with rates increasing trenchward from 5 to 11 mm/yr. Living microatolls show similar rates and a similar pattern. The fossil microatolls also record at least two less extensive emergence event s in the decades prior to 1833. These observations show that coral microato lls can be useful paleoseismic and paleogeodetic instruments in convergent tectonic environments.