Coral 13C/12C records of vertical seafloor displacement during megathrust earthquakes west of Sumatra

Earth and Planetary Science Letters
By: , and 

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Abstract

The recent surge of megathrust earthquakes and tsunami disasters has highlighted the need for a comprehensive understanding of earthquake cycles along convergent plate boundaries. Space geodesy has been used to document recent crustal deformation patterns with unprecedented precision, however the production of long paleogeodetic records of vertical seafloor motion is still a major challenge. Here we show that carbon isotope ratios (View the MathML source) in the skeletons of massive Porites   corals from west Sumatra record abrupt changes in light exposure resulting from coseismic seafloor displacements. Validation of the method is based on the coral View the MathML source response to uplift (and subsidence) produced by the March 2005 Mw 8.6 Nias–Simeulue earthquake, and uplift further south around Sipora Island during a M∼8.4 megathrust earthquake in February 1797. At Nias, the average step-change in coral View the MathML source was 0.6±0.1‰/m for coseismic displacements of +1.8 m and −0.4 m in 2005. At Sipora, a distinct change in Porites  microatoll growth morphology marks coseismic uplift of 0.7 m in 1797. In this shallow water setting, with a steep light attenuation gradient, the step-change in microatoll View the MathML source is2.3‰/m, nearly four times greater than for the Nias Porites  . Considering the natural variability in coral skeletal View the MathML source, we show that the lower detection limit of the method is around 0.2 m of vertical seafloor motion. Analysis of vertical displacement for well-documented earthquakes suggests this sensitivity equates to shallow events exceedingMw∼7.2 in central megathrust and back-arc thrust fault settings. Our findings indicate that the coral View the MathML source paleogeodesy technique could be applied to convergent tectonic margins throughout the tropical western Pacific and eastern Indian oceans, which host prolific coral reefs, and some of the world's greatest earthquake catastrophes. While our focus here is the link between coral View the MathML source, light exposure and coseismic crustal deformation, the same principles could be used to characterize interseismic strain during earthquake cycles over the last several millennia.

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Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Coral 13C/12C records of vertical seafloor displacement during megathrust earthquakes west of Sumatra
Series title Earth and Planetary Science Letters
DOI 10.1016/j.epsl.2015.10.002
Volume 432
Year Published 2015
Language English
Publisher Elsevier
Contributing office(s) Geologic Hazards Science Center
Description 11 p.
First page 461
Last page 471
Country Indonesia
Online Only (Y/N) N
Additional Online Files (Y/N) N