SOURCE PARAMETERS OF THE DAMAGING CORNWALL-MASSENA EARTHQUAKE OF 1944FROM REGIONAL WAVE-FORMS

The Cornwall-Massena earthquake (M(W) 5.8) of 5 September 1944 was one of the most damaging earthquakes in Canadian history. Its epicenter, near the Canada-United States border and the southern end of the Weste rn Quebec seismic zone, lies within a heavily populated region, render ing this earthquake significant for regional seismic hazard analysis. The reappearance of a seismogram collection from the 1940s previously unavailable to (recent) researchers helps provide new insight into thi s earthquake. Waveforms recorded at regional distances indicate that t his was a mid-crustal (20-km deep) oblique thrust event (strike 313 de grees, dip 70 degrees, rake 52 degrees). Either nodal plane is a plaus ible fault plane in terms of the local and regional seismotectonics-on e is more consistent with the seismicity pattern and the other with th e mapped faults. The mechanism is similar to those determined for many smaller and more recent events in the Western Quebec seismic zone and is consistent with the regional stress field. The low value of a prev iously determined m(b) (4.6) relative to the moment magnitude is at le ast partially a result of the P-wave radiation pattern and the distrib ution of stations used to calculate m(b). Previously calculated values for M(S) range from 5.1 to 5.6. While the larger number is more consi stent with the M(W) determined in this study, the reason for the large variation in M(S) values has not yet been fully explained.