High‐resolution seismic reflection profiling of neotectonic faults in Lake Timiskaming, Timiskaming Graben, Ontario‐Quebec, Canada

Abstract

The Timiskaming Graben is a 400 km long, 50 km wide north-west trending morphotectonic depression within the Canadian Shield of eastern North America and experiences frequent intraplate earthquakes. The graben extends along the border of Ontario and Quebec, connecting southward with the Nipissing and Ottawa-Bonnechere grabens and the St. Lawrence Rift System which includes a similar structure underlying the Hudson Valley of the eastern USA. Together they form a complex failed rift system related to regional extension of North American crust during the breakup of Rodinia and, later, Pangea. The Timiskaming Graben lies within a belt of heightened seismic activity (Western Quebec Seismic Zone) with frequent moderate magnitude (greater than magnitude 5) earthquakes including a magnitude 6.2 in 1935. These events threaten aging urban infrastructure built on soft glacial sediments; post-glacial landslides along the Ottawa Valley suggest earthquakes as large as magnitude 7. The inner part of the Timiskaming Graben is filled by Lake Timiskaming, a large 110 km long post-glacial successor to glacial Lake Barlow that was ponded by the Laurentide Ice Sheet 9500 years ago. The effects of frequent ground shaking on lake floor sediments was assessed by collecting more than 1000 line kilometres of high-resolution 'chirp' seismic profiles. Late glacial Lake Barlow glaciolacustrine and overlying post-glacial sediments are extensively deformed by extensional faults that define prominent horsts and grabens; multibeam bathymetry data suggest that faults influence the morphology of the modern lake floor, despite high sedimentation rates, and indicate recent neotectonic deformation. The Lake Timiskaming area provides evidence of post-glacial intracratonic faulting related to recurring earthquake activity along a weak spot within the North American plate.

Evidence of late glacial paleoseismicity from submarine landslide deposits within Lac Dasserat, northwestern Quebec, Canada

“…The basal surface is primarily conformable, but very locally is unconformable where the facies overlies apparent landslide scars. Deposits with similar acoustic facies are ubiquitous to lakes on the Canadian Shield and have been observed in many sub-bottom profiling surveys reported elsewhere (e.g., Klassen and Shilts, 1982;Shilts, 1984;Kaszycki, 1987;Lazorek et al, 2006;Doughty et al, 2010Doughty et al, , 2013Doughty et al, , 2014Brooks and Medioli, 2012;Normandeau et al, 2013). This facies represents post-glacial lacustrine deposits in Lac Dasserat.…”

Late-Quaternary glacial to postglacial sedimentation in three adjacent fjord-lakes of the Québec North Shore (eastern Canadian Shield)

“…Based on the stratigraphic position, MMDs are buried under 4-8 m of sediments of units 3 and 4. The acoustic properties are similar to those of acoustic units interpreted as MMDs in other lakes of eastern Canada (Doughty et al, 2013(Doughty et al, , 2014Normandeau et al, 2013;Lajeunesse et al, 2017;Normandeau et al, 2016bNormandeau et al, , 2017.…”

“…8; 9A; 10C), but can reach >80-thick in Lake Pentecôte. U3 shows typical acoustic characteristics of high amplitude parallel reflections observed in other formerly glaciated lake basins (Mullins and Hinchey, 1989;Eyles et al, 1990Eyles et al, , 1991Shilts and Clague, 1992;Ouellet, 1997;Turgeon et al, 2003;Lajeunesse et al, 2008Lajeunesse et al, , 2017Doughty et al, 2013;Evans, 2013;Doughty et al, 2014). The base of U3 is interpreted as glaciomarine sediments deposited during the Goldthwait Sea transgression, changing into glaciolacustrine sediments due to lake isolation induced by glacio-isostatic rebound.…”

Deglacial record of palaeoearthquakes interpreted from mass transport deposits at three lakes near Rouyn‐Noranda, north‐western Quebec, Canada

“…The seismogenic interpretation for the multi‐MTD event horizons is also consistent with those made by Doughty et al . (, ) for MTDs buried within Lake Barlow glaciolacustrine deposits in Lake Timiskaming, located 100 to 200 km to the south (Fig. A).…”