A three‐dimensional P wave velocity model for the Charlevoix seismic zone, Quebec, Canada

Abstract

A three‐dimensional P wave velocity model has been developed for the Charlevoix seismic zone (CSZ). The CSZ is located along the St. Lawrence River ∼100 km northeast of Quebec City, Canada, and is one of the most active seismic zones in eastern North America. Five earthquakes with magnitudes equal to or exceeding 6.0 have occurred in the CSZ in historic time, and around 200 earthquakes occur annually. Hypocenters are located in Precambrian basement rocks. Basement rocks have been affected by numerous tectonic events including Grenvillian collision, Iapetan rifting, and meteor impact. We performed a sequential, tomographic inversion for P wave velocity structure based upon 3093 P wave arrivals from 489 earthquakes recorded by 12 stations. High velocity is associated with the center of the impact crater. The region of high velocity is surrounded by low velocities interpreted to be highly disrupted rocks. An elongated, high‐velocity region is present at midcrustal depths that trends parallel to the St. Lawrence River. Earthquakes avoid the high‐velocity body and separate into two bands, one on either side of the feature. Larger earthquakes (magnitude ≥ 4) have occurred along the northern edges of the high‐velocity region.