Establishing a paleo-tsunami record along the west coast of Sumatra, Indonesia

Project Overview

Since the 2004 Indian Ocean tsunami, we have built a ~8000-year seismic and tsunami history for northern patch of the Sunda Megathrust. However, the Sunda Megathrust ruptures in patches and little is known about the paleo-tsunami activity south of the 2004 rupture patch. We will use geological field methods to extend the record of paleo-tsunami events to the entire west coast of Sumatra. The resultant dataset will be used to better define the boundaries of rupture patches along the Megathrust. This proposal will test three research hypotheses regarding megathrust behaviour and coastal response: (1) Coastal sites along the west coast of Sumatra preserve evidence of large tsunamis generated by megathrust earthquakes, including tsunami-related deposits, landforms, and archaeological records; (2) Main drivers of heterogeneity in tsunami deposits remain consistent through time; and (3) Megathrust rupture boundaries vary through time.

Our primary scientific aim for 2021 and early 2022 is to locate buried sand sheets in coastal deposits along the entire western coastline of North and West Sumatra provinces, Indonesia. We aim to find buried tsunami sands in coastal wetland sites between Singkil and Padang. This is a ~600 km stretch of the coastline where no tsunami investigations were previously conducted. Bounded to the south by a known paleotsunami site near Padang city, studied by Dura et al. (2011), where tsunami deposits were discovered in a coastal wetland.  We plan to explore 12 sites in roughly equal spacing along this coastline. Investigating these sites will allow a better understanding of the paleotsunami history over this long unstudied stretch of coastline between known paleotsunami sites. 

Our proposed research methodology consists of four tasks that address the three research hypotheses:

1. Relative sea-level (RSL) history. We will develop a RSL database and use the latest glacial isostatic adjustment models to assess the accommodation space needed for preserving co-seismic land-level change and tsunami deposits.
2. Stratigraphy, sedimentology, and geomorphology. We have used satellite imagery to identify ~12 sites that are likely to archive evidence of co-seismic land-level change and tsunami deposits. Following reconnaissance studies, we will perform detailed topographic surveys, map landforms, and conduct stratigraphic surveys to interpret evidence for co-seismic land-level changes and tsunami inundation. 
3. Identify and map local tsunami deposits. We will identify anomalous beds of sand in low-energy environments where they would not normally occur, such as mangroves and freshwater marshes, coastal lakes, and swales well landward of the beach. We will apply to the TSUFLINT inverse sediment transport model to reconstruct flow depth, speed, and sediment transport from paleo-tsunami deposits.
4. Geochronology. We will establish the timing of paleo-tsunami events and thus address whether the megathrust rupture boundaries vary through time using AMS 14C dating of plant macrofossil and charcoal.

Funding Sources

• Earth Observatory of Singapore

Project Years

2020 to 2022

Professor Benjamin Horton (second from left) during a field trip to Aceh, Indonesia (Source: Rachel Siao)