Crustal Velocity Variations and Constraints on Material Properties in the Charlevoix Seismic Zone, Eastern Canada

Abstract

Intraplate earthquakes occur in stable plate interiors away from tectonic plate boundaries. The typical strain rates (≤10 −10 yr −1 ) within intraplate seismic zones are two or more orders of magnitude lower than the average strain rates (≥10 −8 yr −1 ) reported for seismogenic plate boundary faults (e.g., Gordon, 1998;Mazzotti & Adams, 2005;Mazzotti & Gueydan, 2018). Consequently, intraplate fault zones produce moderate-to-large earthquakes (e.g., 2001 M 7 Bhuj earthquake, 1811-1812 ∼M 7 New Madrid earthquakes) less frequently than their plate boundary counterparts (Bendick et al., 2001;Hough et al., 2004), but their physical mechanisms remain poorly understood. Steady tectonic loading in plate interiors can be attributed to basal traction, gravitational body forces, and plate boundary forces (Liu & Stein, 2016). However, these mechanisms are not always sufficient to elevate stresses to levels that can trigger failure on intraplate faults, and are unlikely to be fully responsible for the stress budget within intraplate seismic zones. Several studies show that earthquakes within plate interiors concentrate within zones of inherited crustal weaknesses due to factors such as, tectonics, volcanism, and meteorite impacts (e.g.,

Seismic Evidence for a Weakened Thick Crust at the Beaufort Sea Continental Margin

“…We use the Local Tomography Software (LOTOS) to estimate the three‐dimensional isotropic seismic velocity structure (Koulakov, 2009). LOTOS has been successfully applied to a variety of tectonic settings (e.g., collision zones: Talebi et al., 2020; Medved et al., 2021, subduction zones: Foix et al., 2019, ocean‐continent transition zone: El Khrepy et al., 2021 and paleo‐rift system in eastern Canada: Onwuemeka et al., 2021). Starting with a 1‐D (i.e., layered) velocity model, the software calculates the travel times based on a reference table of initial event locations, and uses a grid search method to relocate all events (Koulakov & Sobolev, 2006).…”

Depth‐Dependent Crustal Stress Rotation and Strength Variation in the Charlevoix Seismic Zone (CSZ), Québec, Canada

“…Rifting associated with the Iapetus Ocean opening created the St. Lawrence valley system of normal faults that are presently under compressional stress conditions (Adams & Basham, 1991;Johnston, 1989). Seismic tomography and gravitational field modeling suggest that seismic velocity variations are dominated by the distribution of crustal fractures within the impact structure and material composition outside the impact structure (Onwuemeka et al, 2021). The crustal characteristics dictate distinctive spatial distributions of earthquake source properties, such as magnitudes, focal mechanisms, and static stress drop values (Onwuemeka et al, 2018(Onwuemeka et al, , 2021.…”

“…Seismic tomography and gravitational field modeling suggest that seismic velocity variations are dominated by the distribution of crustal fractures within the impact structure and material composition outside the impact structure (Onwuemeka et al, 2021). The crustal characteristics dictate distinctive spatial distributions of earthquake source properties, such as magnitudes, focal mechanisms, and static stress drop values (Onwuemeka et al, 2018(Onwuemeka et al, , 2021. Postglacial rebound associated with glacial retreat following the Wisconsin glaciation (85-11 kyr) superimposes perturbations to the ambient stresses conditions on critically stressed faults in the CSZ (Quinlan, 1984;Wu & Hasegawa, 1996).…”