|Title||The Application of a Seismo- and Chronostratigraphic Approach to Investigating Evidence of Paleoseismicity in Eastern Canada|
|Author||Brooks, G R|
|Source||Nuclear Waste Management Organization, Technical Report TR-2017-03, 2017, 37 pages|
|Alt Series||Natural Resources Canada, Contribution Series 20170136|
|Publisher||Nuclear Waste Management Organization|
|Related||This publication is related to the following
|Lat/Long WENS|| -79.5000 -79.2500 48.2500 48.0000|
|Subjects||geophysics; tectonics; surficial geology/geomorphology; chronostratigraphy; seismicity; varves; glaciolacustrine deposits; deglaciation; isostatic rebound; glacial lakes; paleogeography; earthquakes;
|Illustrations||tables; location maps; profiles; core logs|
|Program||Assessing Earthquake Geohazards, Public Safety Geoscience|
|Abstract||An 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
|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.