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TitleHunting for Quaternary faults in eastern Canada: a critical appraisal of two potential candidates
AuthorPinet, N; Lamontagne, MORCID logo; Duchesne, M JORCID logo; Brake, V I
SourceSeismological Research Letters vol. 92, issue 2, 2020 p. 1102-1111,
Alt SeriesNatural Resources Canada, Contribution Series 20200506
PublisherSeismological Society of America
Mediapaper; on-line; digital
File formatpdf; html
ProvinceQuebec; New Brunswick
NTS11L; 11M; 12E; 12L; 21I; 21J; 21K; 21L; 21M; 21N; 21O; 21P; 22A; 22B; 22C; 22D; 22E; 22F; 22G; 22H; 22I; 22J; 22K; 22L
AreaBaie-Saint-Paul; Tadoussac; St. Lawrence River; Péninsule de la Gaspésie; Anticosti Island; Sept-Îles; Gulf of St. Lawrence
Lat/Long WENS -71.5000 -63.8333 50.5000 46.6667
Subjectsgeophysics; marine geology; structural geology; tectonics; Science and Technology; Nature and Environment; Health and Safety; earthquakes; bedrock geology; structural features; faults; landforms; scarps; escarpments; geophysical surveys; seismic surveys, marine; acoustic surveys, marine; bathymetry; tectonic history; displacement; Holocene; Lower St. Lawrence Seismic Zone; St. Lawrence Fault; Phanerozoic; Cenozoic; Quaternary
Illustrationslocation maps; geoscientific sketch maps; seismic profiles; cross-sections; 3-D images
Released2020 12 23
AbstractThis study documents two potential neotectonic features in the seismically active St. Lawrence estuary and western part of the Gulf of St. Lawrence of Quebec (Canada). Historically, the region is the locus of series of damaging earthquakes, including the M 7 1663 earthquake, which suggests the occurrence of co-seismic ruptures beneath the St. Lawrence River. In the western Gulf of St. Lawrence (Lower St. Lawrence seismic zone), a potential fault scarp identified on a vintage seismic profile has been investigated through high resolution seismic and multibeam bathymetry data. On the seafloor, the scarp corresponds to a ~ 1.8 m high (maximum) feature that is located above a buried escarpment of the Paleozoic bedrock. Holocene units are draping over the escarpment on one profile, but are possibly cut on two others. The scarp meets several of the criteria generally associated with neotectonic features. However, a close look at the data indicates that the staircase geometry of the top of the bedrock and its expression at surface are linked, at least partially, with the presence of an erosion-resistant unit. This makes a neotectonic reactivation possible but not proven. In the Tadoussac area, ~ 40 km north of Charlevoix seismic zone, the offshore extension of the St-Laurent fault corresponds to a ~110 m high bathymetric escarpment with well-preserved triangular facets. Such 'fresh' morphology is unique in the St. Lawrence River Estuary and may attest to Quaternary displacements, yet other interpretations may also explain the unusual preservation of the escarpment. These two case studies illustrate the difficulty to unambiguously document Holocene fault scarps, even in the marine domain where the sedimentary succession is generally continuous.
Summary(Plain Language Summary, not published)
Documenting faults with seismic hazard is difficult, especially in continental settings with relatively low rates of large earthquakes. In this study, two faults with potential Quaternary displacements are documented in the western Gulf of St. Lawrence and in the St. Lawrence Estuary. These faults meet several criteria associated with 'recent' tectonic features, but Quaternary displacements remain hypothetical.

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