Extending paleo-tsunami records south of the 2004 Indian Ocean Tsunami patch, Sumatra, Indonesia: 2022 update

Our team has previously built a ~7500 year tsunami history for the northern patch of the Sunda Megathrust. However, the paleo-tsunami history south of Aceh province and the 2004 rupture patch remains poorly understood. We conducted geological investigation to better define the boundaries of rupture patches along the Megathrust.

 

We utilized satellite imagery to pinpoint potential sites likely to archive evidence of paleo tsunami inundations and co-seismic land-level change. Due to the continuing Covid-19 pandemic and restrictions, our researchers from Singapore, and USA could not travel to Indonesia. However, because of the longstanding close collaboration between the Earth Observatory of Singapore and Syiah Kuala University, Banda Aceh, Indonesia, the project continued to progress. The Syiah Kuala University team investigated nearly 20 sites between Banda Aceh in the northern patch of the of Sumatra Megathrust and Padang in the south. Several sites preserved probable paleo-tsunami sediments. The paleo-tsunami sediments were identified from anomalous layers of sand in low energy environments where they would not normally occur, such as mangroves, coastal lowlands, and/or swales.

 
Here we present results of litho-, bio- and chronostratigraphical analysis from Susoh as well as preliminary information from sites along the coastline between Meulaboh and Padang. From Susoh we described stratigraphy from a series of cores to a depth of 4.75 m. The top 2.5 meters was dominated by muds typical of estuarine or tidal flat settings, but it is interrupted by three pulses of sandy muds. At 2.55 m we encountered a 0.2 m thick layer of course sand, underlain by a 0.5 m thick mangrove peat with a gradual transition into organic sandy muds and sands. Pollen analysis from the fine-grained organic layers indicate they were formed in a mangrove environment. Radiocarbon dating of the organic macrofossils from the mangrove peat indicate the tsunami event occurred post 1850 cal. yrs BP. Our research continues to improve our understanding of the Sumatran Megathrust.