The 5.2 magnitude earthquake near Ladysmith, Quebec, 17 May 2013: implications for the seismotectonics of the Ottawa–Bonnechere Graben

Abstract

On 17 May 2013 at 1343 hours UTC, a magnitude m N = 5.2 earthquake occurred ϳ4 km from the town of Ladysmith, Quebec, within the Western Quebec Seismic Zone (WQSZ). This event produced limited damage but represents the largest earthquake to occur along the southwest margin of the WQSZ since 1935, and provides important seismotectonic constraints of the intra-cratonic Ottawa-Bonnechere Graben (OBG). We performed a number of analyses of the main shock and aftershocks to determine source properties and obtain structural information. First, a moment tensor inversion of the main shock revealed a moment magnitude of M W = 4.7, with a reverse-sense rupture on a high dip fault, typical of earthquakes within the WQSZ. Dispersion curves for well-recorded Rayleigh waves were then used to estimate a crustal velocity model, which was used to relocate the four largest aftershocks. Hypocenters of relocated aftershocks indicate that the main rupture occurred on a northeast-dipping fault, antithetic to the main graben faults. A comparison of source parameters and aftershock statistics between the 2010 (M W = 5.0) Val-des-Bois earthquake and the 2013 (M W = 4.7) Ladysmith earthquake reveals a larger aftershock moment released by the 2013 event. Together, these results suggest that high-angle faults of the OBG can be reactivated in the current compressive stress regime despite their unfavourable orientation.Résumé : Le 17 mai 2013, à 13 h 43 UTC, un séisme de magnitude m N = 5,2 a eu lieu à environ 4 km de la municipalité de Ladysmith, Québec, dans la zone sismique de l'Ouest du Québec (WQU). Cet événement a engendré peu de dommages mais il représente le plus grand séisme à se produire de long de la bordure sud-ouest de la zone WQU depuis 1935 et il permet d'obtenir des restrictions sismotectoniques au graben intracratonique d'Ottawa-Bonnechère. Nous avons effectué plusieurs analyses de la secousse principale afin de déterminer les propriétés de la source et d'obtenir de l'information sur les structures géologiques. Tout d'abord, une inversion du tenseur des moments de la secousse principale a révélé un moment de magnitude M W = 4,7 avec une rupture en sens inverse sur une faille à pendage élevé, ce qui est typique des séismes dans la zone WQU. Les courbes de dispersion pour des ondes bien enregistrées de Rayleigh ont alors servi à estimer un modèle de vitesse de la croûte, lequel a servi à relocaliser les quatre plus importantes répliques. Les hypocentres des répliques relocalisées indiquent que la rupture principale a eu lieu sur une faille à pendage nord-est, antithétique aux principales failles du graben. Une comparaison des paramètres de la source et des statistiques des répliques entre le séisme de 2010 à Val-des-Bois (M W = 5,0) et celui de 2013 à Ladysmith (M W = 4,7) révèle que l'événement de 2013 a relâché un moment de réplique plus significatif. Pris ensemble, ces résultats indiquent que les failles à angle élevé du graben Ottawa-Bonnechère pourraient être réactivées dans le régime de contraintes compressives actuelles, ...

Reactivation Potential of Intraplate Faults in the Western Quebec Seismic Zone, Eastern Canada

“…The location, NW‐SE strike, and reverse faulting kinematics determined from detailed analysis of the source mechanism for this earthquake by Bent (1996) are consistent with fault reactivation along the NW‐SE‐striking Timiskaming graben. Conversely, some recent earthquakes, such as the 2010 M W 5.2 Val des Bois (Atkinson & Assatourians, 2010; Ma & Motazedian, 2012) and 2013 M W 4.7 Ladysmith earthquakes (Ma & Audet, 2014), are associated with well‐defined source mechanisms and locations, but have yet to be associated with their causative faults. Eastern Canada, including the WQSZ, is currently lacking a comprehensive, reliable assessment of seismic hazards, due to the scarcity of detailed earthquake source models, typically from a combination of seismic, geologic, and/or geodetic data (Morell et al., 2020).…”

Tectono-Geomorphic Analysis in Low Relief, Low Tectonic Activity Areas: Case Study of the Temiskaming Region in the Western Quebec Seismic Zone (WQSZ), Eastern Canada

“…Selected knickpoints are in yellow. Knickpoint n 1 was found coincident with hand mapped linear feature; Figure S5: River profile analysis of subset area 5 (see Figure 5 in the paper, for location of the knickpoints and river profile analysis for knickpoints 6,7,8). At this site, the knickpoints found coincident with hand mapped linear features were knickpoints n 1, 2, 7; Figure S6: Map of knickpoints for Subset area 6 and longitudinal profile of selected knickpoints.…”

“…This location therefore warrants further study. In subset 3 (Figure 10c), a promising set of knickpoints (8)(9)(10)(11)(12) were aligned N-S along newly mapped lineaments. Targets in the other three areas are less promising given that they are not as concentrated and do not show good alignment with each other or mapped lineaments or faults.…”

“…Eastern Canada is an intracratonic area that, despite generally moderate to low seismic activity, has been struck by earthquakes with a magnitude of ~6 in the last century (Mw 5.9, 1988 Saguenay earthquake, and Mw 6.2, 1935 Temiskaming earthquake) [1,2], gaining the attention of the scientific community [3][4][5][6][7][8]. Within the vast territory of Eastern Canada, the Western Quebec Seismic Zone (WQSZ [9,10]) is of particular interest to the earthquake science community.…”