<p>The 1929 Grand Banks submarine landslide was triggered by a M<sub>w</sub> 7.2 strike slip earthquake on the southwestern Grand Banks of Newfoundland. Studies following the event by several decades were the first to recognize that slope failure can cause tsunamis. These studies identified St. Pierre Slope as the main failure area and showed widespread, shallow (<25 m-thick), translational and possibly retrogressive sediment failures occurred predominately in >1700 m water depth (mwd). It seems unlikely this style of failure in deep water generated a tsunami that had >13 m of run-up along the coast of Newfoundland. The objective of this study is to identify possible alternative tsunami source mechanisms and pre-conditioning factors that may have led to sediment instability. These objectives are addressed using a comprehensive data set of multiscale 2D seismic reflection, multibeam swath bathymetry and laboratory geomechanical test data. Results show numerous reflection offsets within the Quaternary section of the slope underneath modern seafloor escarpments (750-2300 mwd).&#160; These offsets appear down to 550 m below seafloor (mbsf) and are interpreted as low angle (~17&#176;), planar-normal faults of <100 m-high vertical and ~330 m of horizontal displacement. The faults are interpreted as part of a massive (~560 km&#179;) complex slump with evidence for multiple d&#233;collements (250 mbsf & 400-550 mbsf) and slumping in at least two directions. Infinite slope stability analysis using peak ground acceleration (PGA) indicates that a combination of earthquake loading and the presence of geomechanical weak layers are needed to explain the slope failure. At St. Pierre Slope, the analysis of sediment cores shows that geomechanical weak layers form as a consequence of underconsolidation in connection with excess pore pressures that are related to: 1) high sedimentation rates, 2) instantaneous deposition of mass transport deposits (MTD&#8217;s) and sandy turbidites, and 3) the presence of gas. The d&#233;collements of the slump are associated with MTD&#8217;s and sediment waves that likely form weak layers. The layers of sediment waves are assumed to consist of sorted silts or fine sands and are therefore likely to be susceptible to excess pore pressure development during earthquake loading. Excess pore pressure development results in reduced effective stress and higher potential for instability. It is interpreted, therefore, that the 1929 earthquake triggered displacement of a 550 m-thick slump with ~100 m of vertical seafloor displacement. This instantaneous displacement of the slump in 750 mwd with a seafloor volume displacement of 70 to 130 km&#178; is likely a more effective source for tsunami generation than the translational, shallow (<25 m) failures in deeper water.</p>
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.