Funded in part by
NSF grant 0538333

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Our early work (Zachariasen et al., 2000) showed that we could recover records of sea level from living coral microatoll colonies by studying their annual growth bands and morphology.  We found that many of the offshore islands of Sumatra have been slowly sinking over the past few decades.
View animations: Coral growth in response to sea level changes.
Our early work also demonstrated that sudden uplifts of about 1 to 2 meters occurred in association with a historical great earthquake in 1833 (Zachariasen et al., 1999).  Our modeling of the pattern of uplift suggested that the 1833 earthquake resulted from slip of about 12 meters on a large section of the subduction interface south of the Equator
Near the Equator, the patterns of uplift, submergence and stability have been nearly stable since the early 1960s.  Our modeling of these motions (Sieh et al., 1999) suggested that the shallow section of the subduction interface near the Equator has been locked or nearly locked for the past few decades.
More thorough investigation of modern and fossil microatolls near the Equator (Natawidjaja, 2003; Natawidjaja et al., 2004) revealed a systematic uplift, submergence and tilt associated with the major earthquake of 1935.  Our modeling of these deformations, in concert with modeling of historical seismograms (Rivera et al., 2002) showed that the earthquake was produced by slip of about 2.5 meters on a 35 by 70-km patch of the subduction interface.
Ongoing work is aimed at a more thorough characterization of the giant earthquake of 1833 and its large predecessor in 1797.  We are also extracting a record of nearly periodic ruptures of the subduction interface south of the Equator over the past seven centuries.
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