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TitleThe age of sensitive clay landslides along the Gatineau Valley, southern Quebec, and their relationship to paleoseismicity in the West Quebec Seismic Zone
AuthorBrooks, G R
SourceEastern Section Seismological Society of America, 2014 Annual Meeting, abstracts; 2014 p. 1
LinksOnline - En ligne
Alt SeriesEarth Sciences Sector, Contribution Series 20140186
PublisherNatural Resources Canada
MeetingEastern Section Seismological Society of America, 2014 Annual Meeting; Charleston; US; November 2-4, 2014
Mediapaper; on-line; digital
File formatpdf
NTS31F/08; 31F/09; 31G/05; 31G/12
AreaGatineau Valley; West Quebec Seismic Zone
Lat/Long WENS -76.5000 -75.5000 45.7500 45.2500
Subjectsgeochronology; landslides; LEDA; clays; glaciomarine deposits; radiocarbon dates; paleogeography; earthquakes; Stag Creek; Daly Creek; Mullin Creek
ProgramWestern Canada Geohazards Project, Public Safety Geoscience
AbstractMajor landslide areas are present along Stag, Daly and Mullin creeks, tributaries of the Gatineau River, southwestern Quebec (near Ottawa, Ontario), where the creeks are incised into thick sensitive clay glaciomarine deposits. Along the Stag Creek landslide area (~7.2 km2), buried organic materials (outer rings of logs, small branches, other terrestrial plant remains) collected from three valley side exposures and radiocarbon dated, are relevant to the ages of three landslide deposits. Seven dated samples from two of the exposures are interpreted to indicate that the main debris field aggraded between 5070 and 5430 cal BP. Two sets of ages (790 to 920 and 980 to 1070 cal BP based on four and three ages from two exposures, respectively) relate to smaller-scale landslides within the landslide area. Similar materials for dating were also collected from the lower of two landslide zones along the Daly Creek landslide area (~2.4 km2). Seven dated samples from two valley side exposures indicate that main debris field aggraded between 5070 and 5440 cal BP. Three dated samples from the base of a terrace exposure indicate that a mudflow deposit aggraded within the incised creek valley between 730 and 890 cal BP. Dated wood samples provide ages for two secondary landslides within the Mullin Creek landslide area (~4.5 km2). One set was subsampled from a core, 1.42 m long, recovered from a wetland on the surface of a landslide deposit (~0.07 km2) that is superimposed on the main debris field. The deepest two samples indicate that the landslide aggraded by or shortly before 960-1180 cal BP. Three samples from a landslide inset within the main debris field reveal that this landslide is young, occurring after 300 cal BP. The ages of four of the Gatineau Valley landslides fall within the 980-1060 and 5000-5400 cal BP ranges of two age groups of 10 and 11 dated landslides that are located in the greater Ottawa area of the Ottawa Valley. The Gatineau Valley landslide ages reinforce the signatures of these two landslide age groups, which have been interpreted previously to represent the occurrence of paleoearthquakes in the West Quebec Seismic Zone. The results also increase the areal distribution of the landslides forming the 5000-5400 cal BP group, providing a revised minimum estimate of paleoearthquake magnitude of Mw 6.4.
Summary(Plain Language Summary, not published)
There are hundreds of sensitive clay landslide scars in the Ottawa Valley and the valleys of its major tributaries. Recent research has been investigating the age of large prehistoric failures to better under the mechanisms that may have triggered them. This work has identified paleoearthquakes as a major triggering mechanism. The results reported in this abstract reveal the ages of seven sensitive clay landslides in the Gatineau River valley. Four of the landslide ages correspond to the ages of two groups of landslides (980-1060 and 5000-5400 cal BP) that have been interpreted previously to have been triggered by paleoearthquakes. The Gatineau Valley results reinforce the paleoearthquake interpretations and allow a revision of the minimum magnitude of the older paleoearthquake to Mw 6.4.