Surface wave study of earthquakes near northwestern Hudson Bay, Canada

Source parameters of an earthquake in northwestern Hudson Bay that occurred on October 2, 1971, with magnitude mb = 5.0 were determined primarily by using surface waves. An estimate of focal depth of 21 km, which in this particular case was insensitive to minor variation in azimuth and focal mechanism, was determined mainly by the Rayleigh wave amplitude spectrums at periods between 7 and 20 s. The focal mechanism solution determined from Love and Rayleigh wave amplitude and phase spectrums in conjunction with P initial motions suggests a thrust fault type with maximum compressional direction nearly NE-SE. The maximum possible fault length was estimated to be 7 km by examining the Rayleigh amplitude spectral variation with azimuth at periods less than 20 s. Another earthquake in the same region, mb = 4.5, on May 14, 1964, was estimated to have a similar focal mechanism with a focal depth of possibly about 17 km. An implied tectonic map of eastern North America is given in Figure 15. High Q values for periods between 7 and 20 s for Rayleigh waves were found also from Hudson Bay earthquakes, in agreement with a similar result for Love waves from earthquakes on Baffin Island.