Sumatra, Indonesia

Using subsidence stratigraphy to identify paleoearthquakes

Research conducted at

Franklin & Marshall College

University of Pennsylvania

Humboldt State University

Earth Observatory of Singapore

On December 26th, 2004 a ~1,600 km segment of the Sunda megathrust ruptured, producing the 9.2 Mw Aceh-Andaman earthquake. This was the second largest earthquake in recorded history, generating a tsunami that devastated south and southeast Asia. There was no historical precedence for a >9 Mw earthquake along this portion of the Sunda Trench, where the 2004 earthquake ruptured.

We are interested in collecting litho- bio- and chronostratigraphic data from the coastal plain of the Aceh Province of Sumatra to reveal rapid changes in relative sea level caused by coseismic subsidence during Holocene megathrust earthquakes. Grand Pre et al., in press, found evidence for paleoseismic deformation preserved in regionally continuous coastal stratigraphy. Samples for radiocarbon dating collected within the pre- and postseismic sedimentary sequences constrain the paleoearthquake to 6,500-7,000 cal yrs. BP. Using pollen, foraminifera and gastropods, we determined the local paleoenvironment before and after coseismic deformation to estimate subsidence to be 0.45 ± 0.33m, which is comparable to the ~0.6 m observed during the 2004 Aceh-Andaman earthquake on Aceh’s west coast.

Other collaborators on this project include researchers from East Carolina University, Woods Hole Oceanographic Institute, Indonesian Institute of the Sciences, and the Academy of Natural Sciences in Philadelphia.