Paleoseismicity of the continental margin of eastern Canada: Rare regional failures and associated turbidites in Orphan Basin

Abstract

The eastern Canadian continental margin is a typical glaciated passive margin where historic earthquakes have triggered submarine landslides. This study compares seismological estimates of earthquake recurrence with the geological record over the past 85 k.y. offshore of Newfoundland to assess the reliability of the geologic record. Heinrich layers in cores provide chronology at ~3-5 k.y. resolution in high-resolution seismic-reflection profiles across headscarps and mass-transport deposits. Landslide-generated turbidites on the basin floor have distinctive petrology, sedimentology, and distribution, with ~1 k.y. chronologic resolution. Large slope failures occurred synchronously over margin lengths of 50-300 km. Since 85 ka, four failures have affected a >150-km-long sector of the slope and 18 failures were large enough to be recognized in seismic-reflection profiles and/or cores. The widespread failures were earthquake triggered; other mechanisms for triggering laterally extensive synchronous failure do not apply. A frequency-magnitude plot of length of failed slope was calibrated by the published relationship that an order-of-magnitude increase in failed slope length corresponds to two orders of magnitude of earthquake energy, together with the published estimate of M w = 8.0 for the largest earthquake on the Canadian eastern continental margin. Mean recurrence interval of M = 7 earthquakes at any point on the margin is estimated at 25-30 k.y. from both seismological models and the sediment failure record. On such a margin with modest sedimentation rates (~0.3 m/k.y.) and low seismicity, sediment failures provide a robust estimator of past seismicity.

Micropaleontological and Isotopic Perspective of Surface Water Mass Variability in the NE Atlantic from MIS 6 to 5e (188 to 115 ka)

“…These IRD records suggest that iceberg discharge was far less pronounced during MIS 6 compared to MIS 3 [5,15,48]. Further, the lack of detrital carbonate grains in the IRD/g peaks suggests a far more stable LIS during MIS 6 [42,54,55]. The presence of quartz grains and volcanic particles implies the contribution of icebergs by the Icelandic and Irish-British ice sheets at this time as well [56,57].…”

Earthquake-triggered submarine landslides in the St. Lawrence Estuary (Québec, Canada) during the last two millennia and the record of the major 1663 CE M ≥7 event

“…The irregularity of deposits and the presence of coarse material and debris in submarine landslides makes coring difficult. During the SLIDE-2020 expedition, the coring sites were determined in order to overcome this limitation by targeting sub-horizontal reflectors in the distal part of submarine landslides where they are thin enough for their underlying and overlying sediments to be dated (e.g., Piper et al, 2019). The relationship between these reflectors and the mass-transport deposits is observed in the Betsiamites area (seismic profile BET_D_2T) and the Saguenay area (seismic profile SAG_H_1T)…”

“…Submarine landslides, through erosion of the seafloor and incorporation of sediments and water, can evolve into a debris flow and a turbidity current (Bryn, 2005;Strachan, 2008). Over the last two decades, the marine turbidite record has been increasingly used as a proxy for earthquake recurrence (Lebreiro et al, 1997;Gracia et al, 2010;Goldfinger et al, 2012;St-Onge et al, 2012;Ratsov et al, 2015;Piper et al, 2019;Howarth et al, 2021). The recurrence of strong regional earthquakes and the risks they pose when associated with submarine slope failures can have major impacts on coastal environments (e.g., damage to coastal infrastructures and threats to coastal communities, risk of tsunamis, cable rupture, coastal erosion), particularly with increasing human populations along the coast.…”