Shear Strength of Siliciclastic Sediments from Passive and Active Margins (0–100 m Below Seafloor): Insights into Seismic Strengthening

Abstract

Submarine geohazards threaten coastal communities and global economies. Submarine debris flows are the largest mass-wasting events observed on the Earth’s surface, comprising of up to 50 % of basin fill. Further insight can be gained into these important processes by understanding in-situ preconditioning factors that lead to slope destabilization. We examine two locations from the International Ocean Discovery Program data archive to determine how external effects on sediment properties compare between passive margins and active margins. We select representative passive margin (Amazon Fan) and active margin sites (Nankai Trough), and analyse peak shear strength, void ratio, and composition from the uppermost 100 m below seafloor. This depth corresponds to a depth range in which most submarine mass movements originate. However, it is not appropriate to directly compare shear strength and void ratio of samples from different settings due to differing stress histories, sedimentary composition, and consolidation properties. We focus on ideal locations on both margin types that have solely undergone one-dimensional burial, no diagenesis/cementation, and no unroofing. We find that active margin sediments exhibit an increase in shear strength when compared to their passive margin counterparts, while void ratio tends to be higher on active margins. We are currently conducting a focused lab program to better understand compositional effects and determine the intrinsic properties of each site to more definitively normalize the in-situ sediment profiles. Our results suggest a potential link between shear strength and margin seismicity.