Galicia Bank sediment transport activity in response to continuous sedimentary instability dynamics: a geotechnical perspective

Abstract

The sedimentary instability dynamics occurring over time throughout the isolated Galicia Bank (Atlantic Ocean, NW Iberian Peninsula) have been studied using a sedimentological and geotechnical approach featuring a quantitative assessment of slope stability under different scenarios, including earthquake activity. The erosion of the scarps in the Galicia Bank includes the continuous development of small instabilities evacuated along gullies and channels or deposited on slopes. These deposits may be subsequently mobilized, evolving into new sedimentary gravity flows (e.g., turbidity flow). The studied sediments consist mostly of poorly to very poorly sorted sands and silts transported by turbidity currents and occasionally by debris flow processes. The sediments in the study area identified as normally consolidated and located on gently sloping areas (gradients less than 5°) may become unstable if low-magnitude seismic events occur (PGA 10° without any trigger other than oversteepening. In contrast, overconsolidated sediments may remain stable under static conditions and may become unstable on slope gradients > 10° when earthquakes occur with the maximum peak ground acceleration (PGA = 0.34). The sedimentological and geotechnical models presented herein are complementary approaches that can be utilized to understand the long-term sedimentary instability dynamics observed within the study area. Such results are critical for better understanding sedimentary models of the dismantling processes of deep seamounts located far away from continental sedimentary inputs.