Climate-controlled sensitivity of lake sediments to record earthquake-related mass wasting in tropical Lake Towuti during the past 40 kyr

Abstract

Located at the triple junction of the Pacific, Eurasian and Sunda plates, the Island of Sulawesi in Indonesia is one of the most tectonically active places on Earth. This is highlighted by the recurrence of devastating earthquakes such as the 2018 Mw 7.5 earthquake that damaged the city of Palu and caused several thousand fatalities in central Sulawesi. The majority of large-magnitude earthquakes on Sulawesi are related to stress release along major strike-slip faults such as the Palu-Koro Fault and its southern extensions, the Matano and Lawanopo Faults. To date, information on the frequency and magnitude of past major events on these faults is limited to instrumental records and historical sources restricted to the last century, whereas information from natural archives is completely lacking. Lake-sediment records can fill this gap, but a detailed assessment of the various factors that influence the sensitivity of sediment successions to past earthquakes is required to evaluate their suitability. Lake Towuti, situated in Eastern Sulawesi, is known for its paleoclimate record and also promises to be a key site to generate a paleoseismology record for Sulawesi. The lake lies close to the highly active Matano and Lawanopo strike-slip faults and thereby is an ideal archive for past earthquakes that have occurred in the surrounding area. Here we combine high-resolution chirp seismic data with lithostratigraphic and petrophysical data of sediment piston cores to assess the recurrence of seismically generated mass-transport and turbidite deposits. Three major seismic-stratigraphic units are distinguished in the upper ∼10 m of the sediment succession and linked to differences in the frequency of mass-wasting during the past 60 kyrs. The evidence of a more turbidite-prone period between 12 and 40 ka is roughly coincident with a dry phase and associated lake-level lowstand during the last glacial period at Lake Towuti. Hence, we suggest that climate strongly influences the sensitivity of slopes to fail during seismic shaking in this tropical setting as a consequence of lowstand-forced sediment redeposition from the shelves onto the slopes and into the basins. As climate significantly impacts the sensitivity of the lacustrine sediments to record earthquake-related mass wasting deposits, we suggest that the frequency of mass-transport deposits can additionally be employed as a quantitative indicator for past changes in hydroclimate in these tropical settings.