Surficial sediment failures due to the 1929 Grand Banks Earthquake, St Pierre Slope

Abstract

A Mw 7.2 earthquake centred beneath the upper Laurentian Fan of the SW Newfoundland continental slope triggered a damaging turbidity current and tsunami on 18 November 1929. The turbidity current broke telecommunication cables, and the tsunami killed 28 people and caused major infrastructure damage along the south coast of Newfoundland. Both events are believed to have been derived from sediment mass failure as a result of the earthquake. This study aims to identify the volume and kinematics of the 1929 slope failure in order to understand the geohazard potential of this style of sediment failure. Ultra-high-resolution seismic reflection and multibeam swath bathymetry data are used to determine: (1) the dimension of the failure area; (2) the thickness and volume of failed sediment; (3) fault patterns and displacements; and (4) styles of sediment failure. The total failure area at St Pierre Slope is estimated to be 5200 km2, recognized by escarpments, debris fields and eroded zones on the seafloor. Escarpments are typically 20–100 m high, suggesting failed sediment consisted of this uppermost portion of the sediment column. Landslide deposits consist mostly of debris flows with evidence of translational, retrogressive sliding in deeper water (>1700 m) and evidence of instantaneous sediment failure along fault scarps in shallower water (730–1300 m). Two failure mechanisms therefore seem to be involved in the 1929 submarine landslide: faulting and translation. The main surficial sediment failure concentrated along the deep-water escarpments consisted of widely distributed, translational, retrogressive failure that liquefied to become a debris flow and rapidly evolved into a massive channelized turbidity current. Although most of the surficial failures occurred at these deeper head scarps, their deep-water location and retrogressive nature make them an unlikely main contributor to the tsunami generation. The localized fault scarps in shallower water are a more likely candidate for the generation of the tsunami, but further research is needed in order to address the characteristics of these fault scarps.

A Massive Slump on the St. Pierre Slope, A New Perspective on the 1929 Grand Banks Submarine Landslide

“…Option 3 is preferred over options 1 and 2, as an increase in sedimentation rate before deposition of horizon R6 is probable given the presence of glacial ice margin wedges beneath the upper slope down to horizon R3 (Table ; e.g., Piper et al, ; Skene & Piper, ; Schulten et al, ). Cohen and Gibbard () described MIS 22 (option 3, R3) as a profound cooling event within a subseries of discrete events that predate MIS 12 (R6).…”

“…The exceptions are 20‐ to 50‐m high escarpments in the western part of the slope between 1,500 and 2,000 mwd (Figure ). Ultrahigh‐resolution seismic data show an association of these escarpments with slump deposits, indicating that these headscarps resulted from shallow sediment mass failure (Schulten et al, ).…”

“…The 1929 submarine landslide was described in previous studies as a widespread, retrogressive slope failure with evidence of ~20‐m thick sediment failures along the St. Pierre Slope, the head of Eastern Valley, Western Valley and Grand Banks Valley (Mosher & Piper, ; Piper et al, , ). On St. Pierre Slope, surficial failures are observed in water depths of 750 to 2,300 m (Mosher & Piper, ; Schulten et al, ). Schulten et al () showed that only 7‐ to 11‐m thick sediment failures occurred along the escarpments in 750 to 1,300 mwd.…”

“…On St. Pierre Slope, surficial failures are observed in water depths of 750 to 2,300 m (Mosher & Piper, ; Schulten et al, ). Schulten et al () showed that only 7‐ to 11‐m thick sediment failures occurred along the escarpments in 750 to 1,300 mwd. Most of the failures at the St. Pierre Slope were previously interpreted as shallow (~20 m), translational and probably retrogressive landslides restricted to water depths of 1,700 to 2,300 m (Piper et al, ; Schulten et al, ).…”

“…The upper Laurentian Fan is the location of the 1929 earthquake, the area of the instantaneous cable breaks, and it hosts seafloor escarpments and shallow (<25‐m thick) deposits believed related to the landslide (Figure b; Piper et al, ; Mosher & Piper, ; Schulten et al, ). The area affected by surficial submarine landsliding in the 1929 event extends from the western edge of Laurentian Channel to the eastern part of Halibut Canyon (Figure b; Piper et al, ; Mosher & Piper, ).…”