Current Research in EEPS: Dr. Sebastian Cardona, Colorado School of Mines
Near the Brink—Exploring Weak Layers, Creeping Landslides, and Tsunamis
Subduction zones are the locations of the greatest magnitude earthquakes and may be accompanied by tsunamis triggered by seismic shaking, submarine landslides, or a combination of both. Submarine landslides able to trigger tsunamis are known as tsunamigenic-landslides and are an existent geohazard for societies living in coastal areas—by the year 2030, about half of the world’s population will live in coastal areas exposed to flooding, storms, and tsunamis (www.un.org). Weak layers in submarine margins are often cited to explain landslide occurrence or reactivation, but little is known about the origin and evolution of weak layer. Using data and cores from International Ocean Discovery Program (IODP) Expedition 372, we identified and characterized a weak layer of a submarine landslide in the Tuaheni Landslide Complex (TLC) in the Hikurangi margin, New Zealand. This weak layer has an anomalous reduction in shear strength, porosity, and permeability that cannot be attributed to normal consolidation or composition changes. We conclude that the properties in the weak layer are the result of mechanical rearrangement of clay particles that form “clay bridges”. The measured low strength of the weak layer is approximately equal to the downslope gravitational stresses suggesting that the landslide is at or near failure- which may explain the creep-like behavior. The proposed process has global implications since these conditions can be found in other subaqueous margins around the world. The overarching goal of my research at Rice is to investigate the nature of weak layers and their role in preconditioning and/or triggering of submarine landslides by using observational, experimental, and numerical methodologies in collaboration with Professors Melodie French and Julia Morgan. The results of this research will contribute to our understanding of tsunamigenic landslides and to reducing society’s vulnerability to geohazards along the world’s coasts by potentially enabling the early identification of incipient weak layers along submarine margins.