Contrasting effect of earthquakes on active margins: from lacustrine studies to seismic hazard assessment

Active margins cause the largest earthquakes and tsunamis on Earth. Due to the scarcity of such giant events, paleoseismic research on sedimentary records is crucial to reveal their recurrence patterns and estimate the probability for new events. Turbidite paleoseismology, i.e. identifying and dating remobilized deposits in ocean trenches and terminal basins, has been applied along several active margins worldwide. However, this discipline was recently subjected to substantial criticism because the processes behind earthquake-triggered sediment remobilization are poorly investigated. Moreover, repeated shaking may cause extra consolidation of marine slope sequences (“seismic strengthening”), hampering the initiation of submarine landslides. In this seminar, I will present new process understanding based on turbidite research in Chilean lakes. We found that turbidites mainly result from erosion of only a few cm of near-surface sediments, an observation that was later confirmed by several studies in the Japan Trench. Such surficial remobilization seems rather unspectacular, but has large implications for turbidite paleoseismology and the carbon cycle at active margins, topics that form the base for the upcoming IODP Expedition 386 (Japan Trench).