Crustal Shear-Wave Velocity Models Retrieved from Rayleigh-Wave Dispersion Data in Northeastern North America

On 23 June 2010, a moderate earthquake with M-w 5.2 occurred near the town of Val-des-Bois, Quebec, Canada, similar to 60 km northeast of Ottawa, Ontario. The earthquake generated excellent crustal Rayleigh-wave records. We divided the 54 seismic stations that recorded clear Rayleigh-wave trains into 14 groups by station azimuth. In each group, we measured the Rayleigh-wave dispersion data station by station and formed one dispersion data file for the inversion. In this way, we obtained 14 crustal velocity models around the epicenter. We compared all 14 models and found that there are low-velocity layers in the top 10 km on the north side of the Ottawa-Bonnechere graben. Based on model similarity, we formed one model for the north side by averaging the north-side models and another model for the south side by averaging the south-side models. The separation of the north-side and south-side models appears to follow the Ottawa-Bonnechere graben. In the top 10 km, the velocities in the south model are obviously slower than those in the north model.