Since the 2004 Indian Ocean tsunami, we have built a ~8000-year seismic and tsunami history for the 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. W
e 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 2020 is to locate buried sand sheets in coastal deposits along the entire Acehnese stretch of the Sumatran coastline. We aim to find buried tsunami sands in two regions of the Sumatran coastline. The first study region comprises three wetland sites near Meudhen, Lho Kruet and Kuede Panga villages. These villages fall between the coastal cave in the north explored in previous years by EOS and Meoulaboh in the south where Monecke et al. (2008) found tsunami deposits in beach ridge sequences. All of these areas were inundated by the 2004 Indian Ocean tsunami. Our second study region consists of wetland sites near the villages/towns of Sikandang, Koeala Batèe, Kotafajar and Kuta Padang. These are located to the south of the southern-most extent of the 2004 tsunami inundation. Our goal is to see if we can find buried tsunami sands further south of the 2004 zone and rupture patch. Together, these investigations will allow us to better understand the recurrence of past tsunamis within the 2004 zone and establish proof of concept for future paleo-tsunami studies further south along the Sumatran coast.
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 coseismic 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 coseismic 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 coseismic 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.
- Earth Observatory of Singapore
2020, 2021, 2022
Professor Benjamin Horton (second from left) during a field trip to Aceh, Indonesia (Source: Rachel Siao)