Stratigraphic evidence for an early Holocene earthquake in Aceh, Indonesia.

TitleStratigraphic evidence for an early Holocene earthquake in Aceh, Indonesia.
Publication TypeJournal Article
Year of Publication2012
AuthorsGrand Pre CA, Horton BP, Kelsey HM, Rubin C M, Hawkes AD, Daryono MR, Rosenberg G, Culver SJ
JournalQuaternary Science Reviews
Date Published10/2012
KeywordsForaminifera, Paleoseismicity, Pollen, Relative sea level, Subsidence stratigraphy, Sumatra, Tsunami deposit

The Holocene stratigraphy of the coastal plain of the Aceh Province of Sumatra contains 6 m of sediment with three regionally consistent buried soils above pre-Quaternary bedrock or pre-Holocene unconsolidated sediment. Litho-, bio-, and chronostratigraphic analyses of the lower buried soil reveals a rapid change in relative sea-level caused by coseismic subsidence during an early Holocene megathrust earthquake. Evidence for paleoseismic subsidence is preserved as a buried mangrove soil, dominated by a pollen assemblage ofRhizophora and/or Bruguiera/Ceriops taxa. The soil is abruptly overlain by a thin tsunami sand. The sand contains mixed pollen and abraded foraminiferal assemblages of both offshore and onshore environments. The tsunami sand grades upward into mud that contains both well-preserved foraminifera of intertidal origin and individuals of the gastropodCerithidea cingulata. Radiocarbon ages from the pre- and post-seismic sedimentary sequences constrain the paleoearthquake to 6500–7000 cal. yrs. BP. We use micro-and macrofossil data to determine the local paleoenvironment before and after the earthquake. We estimate coseismic subsidence to be 0.45 ± 0.30 m, which is comparable to the 0.6 m of subsidence observed during the 2004 Aceh–Andaman earthquake on Aceh’s west coast.