Continue . . .
Observations from geophysics, seafloor geology, and ocean drilling accumulated over the last several decades demonstrate that a variety of both short-term as well as long-term dynamic processes acting on Earth’s lithosphere, are relevant for preconditioning submarine slopes for failure and for accumulation and release of strains that cause earthquakes – both potentially causing tsunamis. These dynamic processes are also governed by the longer term tectonic, hydrologic and geochemical evolution of the ocean floor and its subsurface, as it controls the relationships between rock physical properties, fault/slip zone architecture and composition, in situ stress/strength conditions, and fault slip/slope failure behavior. Some hypotheses suggest that pore fluid pressure and rock frictional properties may provide fundamental controls on the earthquake cycle. Earthquakes themselves have been suggested as likely ultimate trigger for initiation of slope failure. However, long-term causal factors, including tectonic oversteepening, climatic and oceanographic conditions controlling sea level, sedimentation patterns and gas hydrate stability, as well as margin hydrogeology and fluid flow regimes, exert key roles in preconditioning submarine slopes to fail.
IODP is investigating relevant processes related to submarine landslides, earthquakes and tsunamis both by single-expeditions as well as by long-term, interdisciplinary studies, including the Gulf of Mexico Hydrology and Landslides (Exp 308), Nankai Trough Submarine Landslide History (NanTroSLIDE; Exp 333) and Lesser Antilles Volcanism and Landslides (Exp 340) projects, and the Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE; IODP Expeditions 314, 315, 316, 319, 322, 332, 333), and the Costa Rica Seismogenesis Project (CRISP; IODP Expedition 334), respectively. These Ocean Drilling initiatives and experiments are expanding our understanding of the timing, size, and nature of geohazards by sampling materials, measuring properties, and monitoring subsurface conditions. Coring, logging, and sampling across faults and slope failures at depths where slip occurs, illuminates the composition and structure of tsunamigenic faults and failure surfaces. Sampling and dating of event deposits helps determine the timing and size of past geohazards, ultimately allowing determination of earthquake and landslide recurrence intervals. Downhole measurements quantify in situ conditions that control failure, including pore pressure, temperature, and stress. Borehole observatories have been installed to monitor strain, pore fluid pressure, and seismicity, to resolve processes controlling the initiation and triggering of fault slip and slope failures, to identify potential precursory phenomena, to understand the dynamics of slip and post-failure recovery, and to characterize links between submarine landslide, earthquake and tsunami hazards.
The ECORD summer school seeks to raise the awareness of young scientists for the need of such interdisciplinary approaches and prepare them for future work, which will be critical in coming decades for understanding the complex dynamics of offshore geohazards and for which IODP plays a key role in resolving Earth-system processes that influence human civilization.