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TitleThe Application of a Seismo- and Chronostratigraphic Approach to Investigating Evidence of Paleoseismicity in Eastern Canada
AuthorBrooks, G R
SourceNuclear Waste Management Organization, Technical Report TR-2017-03, 2017, 37 pages
Alt SeriesNatural Resources Canada, Contribution Series 20170136
PublisherNuclear Waste Management Organization
RelatedThis publication is related to the following publications
AreaLac Dasserat
Lat/Long WENS -79.5000 -79.2500 48.2500 48.0000
Subjectsgeophysics; tectonics; surficial geology/geomorphology; chronostratigraphy; seismicity; varves; glaciolacustrine deposits; deglaciation; isostatic rebound; glacial lakes; paleogeography; earthquakes; Ojibway
Illustrationstables; location maps; profiles; core logs
ProgramAssessing Earthquake Geohazards, Public Safety Geoscience
AbstractAn integrated seismo- and chronostratigraphic investigation at Lac Dasserat, northwestern Quebec, identified 74 separate failures within eight event horizons. Horizons E and B, and H and G have strong or moderately-strong multi-landslide signatures, respectively, composed of 11 to 23 failures, while horizons F, D, C, and A have minor landslide signatures consisting of a single or pair of deposit(s). Cores collected at six sites recovered glacial Lake Ojibway varve contained varved deposits that are interbedded with the event horizons. The correlation of the varves tot the regional Timiskaming varve series allowed varve ages or ranges of varve ages to be determined for the event horizons. Horizons H, G, E, and B are interpreted to be evidence of paleoearthquakes with differing levels of interpretative confidence, based on the relative strength of the multi-landslide signatures, the correlation to other disturbed deposits of similar age in the region, and the lack or possibility of alternative aseismic mechanisms. The four interpreted paleoearthquakes occurred between 9770 ± 200 and 8470 ± 200 cal yr BP, when glacial Lake Ojibway was impounded behind the Laurentide Ice Sheet during deglaciation. If correct, the interpreted paleoearthquakes identified in this study represent a Canadian example of elevated seismicity, associated with relatively rapid crustal unloading during deglaciation that occurred within an area of low historical seismicity.
Summary(Plain Language Summary, not published)
Mapping at Lac Dasserat, Quebec, revealed that the deposits of a large number of ancient landslides are buried at multiple levels within the lake bed. All of the mapped landslide deposits occur within the glaciolacustrine deposits or at the interface between the glaciolacustrine deposits and overlying lacustrine deposits. This indicates that the landslide deposits are old, and were deposited when or immediately after a large glacial lake (known as glacial Lake Ojibway) occupied the region over 8000 years ago. Most of the landslides occur within one of four distinct levels within the lake bed, which implies that the landslides within each group happened synchronously and by a common trigger. It is interpreted that each group of landslides was triggered by shaking from an ancient earthquake. These earthquakes likely represent a period of elevated seismic activity that was caused by rapid regional crustal uplift which occurred as the Laurentide Ice Sheet retreated from the area.