Searching for a Seismic Signature in the Landscape of the Western Quebec Seismic Zone, Canada

The Western Quebec Seismic Zone (WQSZ) in Eastern Canada has experienced over 9500 earthquakes since the Canadian National Seismograph Network started monitoring it in 1985, with paleoseismic studies revealing over 15 M5+ historic earthquakes. The WQSZ hosts several large population centers nested in glacial and fluvial sediment, posing a risk to over 3 million people, which calls for a thorough study of the causes and characteristics of local seismicity. Several hypotheses have been proposed to associate the seismicity with the reactivation of Early Paleozoic normal faults within a failed rift arm, lithological strength contrasts resulting from the Great Meteor hotspot track, magmatic underplating, or a restraining bend in the Paleozoic rift. Recent efforts have focused on understanding the source properties of seismicity in the WQSZ, using spectral analysis and focal mechanism solutions, yet the controls of seismicity in the area remain poorly established.

To help clarify the cause of seismicity in the WQSZ through detecting and characterizing deformation in the landscape, we combine morphotectonic analysis, topographic anisotropy plots, and earthquake hypocenter relocation. We focus our analysis on drainages and basins within the WQSZ, assessing channel steepness, drainage density and geometry, drainage basin symmetry, basin shape and orientation, basin area, hypsometry curves, Strahler channel order, and relief. We then quantify topographic anisotropy (directional dependence of landforms) throughout the WQSZ at different spatial resolutions. Last, using data recorded by the CNSN and USArray Transportable Array, we relocate over 1000 earthquakes between 2000 and 2018. Preliminary results show steep hypsometry curves and longitudinal profiles of channels that reveal a juvenile landscape in disequilibrium, plausibly related to the transition from glacially to fluvially dominated post LGM. However, a stronger, independent deformation signal is present in areas of clustered seismicity and is captured by asymmetric drainages in basins that reveal tilting, and even steeper channels and hypsometry curves. The topographic anisotropy plots show epicenters are located perpendicular to the failed rift, which appears as the dominant structure in the region in these plots.