Determination of Regional Pn Velocity in Eastern Canada

Session: Seismicity and Tectonics of Stable Continental Interiors [Poster]
Type: Poster
Date: 4/30/2020
Time: 08:00 AM
Room: Ballroom
Description: 

Our study aimed at calculating Pn velocities in subareas of eastern Canada. Generally, the Pn velocity is assumed to be 8.20 km/s for eastern Canada. We used the time-term method of Kayal and De (1987) to infer Pn velocity from the arrival time difference between a reference station and another station further away. Our data set consisted of Pn arrival times measured on recordings of the Canadian National Seismic Network (CNSN) for more than sixteen magnitude 3.8 to 5.7 earthquakes that occurred at regional distances between 2000 and 2019. Using only impulsive Pn arrivals for stations within 10° in respect to the epicenter, we obtained more than 200 transects with Pn velocity uncertainties estimated at less than ± 0.05 km/s. These transects cover three geological provinces of Canada (Superior, Grenville and Appalachians) plus the St. Lawrence Rift System (SLRS). Due to the locations of earthquakes and of stations, most transects are parallel to the axis of the SLRS. Our calculated Pn velocities appear to correlate with the geological provinces, with the SLRS as a major boundary. We found higher Pn velocities, in the 8.3 to 8.4 km/s range, north of the SLRS in the Grenville and Superior provinces. Along the SLRS, velocities are close to 8.2 km/s. Lower Pn velocities are also found south of the SLRS; the Appalachians Province has an average velocity of 8.2 km/. A notable exception is found across the Gulf of St. Lawrence to eastern Newfoundland, where Pn velocities are lower than other regions (8.0 km/s). Variations in these average values, some of them along certain paths, others related to specific stations, have to be examined further before firmer conclusions can be drawn.

Presenting Author: Maurice Lamontagne

Authors