Preservation of Holocene Prehistoric Earthquakes, Sungai Pinang, Western Sumatra

Two late Holocene coseismic subsidence events are preserved within the coastal sediment of western Sumatra. Each subsidence event and abrupt rise in relative sea level is preserved as a sharp contact between soil and overlying mud and records a sudden transition from an intertidal to tidal depositional environment. This is the first documentation of a subsidence stratigraphy record of great earthquakes along the Mentawai segment (0.5°- 3°S) of the Sunda megathrust. Radiocarbon dating of woody detritus and seeds constrain the times of subsidence to ~4100 yrs BP and ~3200 yrs BP. The absence of an earthquake record after ~3 ka indicates that subduction zone earthquakes are not preserved in coastal wetlands following the mid-Holocene relative sea level highstand because such records are only preserved during relative sea level rise.