On November 25, 1988, a magnitude 6 earthquake occurred in the province of Quebec, Canada. This earthquake triggered nine digital strong motion instruments in New York and Maine at epicentral distances of 200 to 820 km which were installed as part of an effort by the National Center for Earthquake Engineering Research (NCEER) to study ground motions and wave propagation in eastern North America. We calculate Q(f) at discrete frequencies from 0.6 to 26 Hz, assuming that geometrical spreading causes 1/r0.5 decay in spectral amplitudes.

Of the nine stations, four are in the Adirondack Mountains in New York and three are in eastern Maine. If we calculate Q(f) for these two clusters of stations separately, we obtain higher values for the Adirondack stations. The Quebec-Adirondack path is along the strike of the predominant structural trends in northeastern North America, in the Grenville Province crust, while the Quebec-Maine path is at high angle to the structural grain and crosses the boundary between the Grenville and the Appalachian provinces. We thus have instrumental data in support of earlier observations based on contours of intensity from historic earthquakes: Seismic wave propagation in northeastern North America is more efficient along the predominantly NE-SW striking geological trends. We address possible biases due to site effects. ¿ American Geophysical Union 1989