Tectonic geomorphology of the Ottawa-Bonnechere Graben, Eastern Canada: implications for regional uplift and intraplate seismicity

In intraplate areas where regional tectonic strain is accommodated by reactivation of pre-existing structures, the level of seismic hazard associated with faults in may be underestimated due to the poor surface expression of faults, scattered earthquake distribution, and long earthquake recurrence intervals. The cause of seismicity in eastern Canada remains unresolved. This is partially because surface expression of faults have been eroded during glacial and deglacial periods and in many cases are undetectable until a seismic event. Morphotectonic analysis has been widely applied to assess relative tectonic activity in various geological settings. To establish whether active uplift is occurring and to investigate the spatial distribution of uplift rates, 131 bedrock drainage basins in the Ottawa-Bonnechere Graben (OBG) were analysed. The aim of this was to: 1) test the applicability of geomorphic indices for quantifying active deformation, 2) quantify the spatiotemporal distribution of relative uplift rates, and 3) explore the implications for faulting mechanisms, deformation styles, and ultimately regional seismic hazard. We measured valley floor width-to-height ratio (Vf), basin elongation ratio (Re), basin hypsometric integral (HI), and normalized channel steepness index (ksn). The results demonstrate that high relative uplift rates occur in all six bedrock escarpment sections studied and suggests that are possibly associated with regional broad wavelength uplift (epeirogeny) resulting from a likely complex interaction between far field tectonic stress and glacial isostatic adjustment (GIA). Our analysis showed that Vf, Re, and ksn reveals no considerable spatial differences in high relative uplift rates, consistent with the Canadian base network GPS uplift rates.