A study of northeastern North American spectral moments, magnitudes, and intensities

Thirty-two earthquakes in northeastern North America ranging in seismic moments of 1.5E19 to 6.0E26 (dyne-cm) are used to develop relationships between spectral moment, magnitudes (mbLg and MS), and intensity. It is shown that northeastern North American events are readily characterized by a well-behaved, steadily increasing stress drop relative to increasing magnitude. As a result, the relationship between the regional mbLg and MS as implied by the spectral results is m b L g = M s + 1.2 ( 1.8 ≦ m b L g ≦ 4.4 ) and m b L g = 0 . 6 1 M s + 2.33 ( 4.4 ≦ m b L g ≦ 6.8 ) . Published relationships between the mbLg magnitude, the log10 of the area within the intensity IV isoseismal contour, and the falloff of the intensity technique described by Nuttli (1973b) are checked for suitability. The results are as follows m b L g = 1.13 log 10 ( A I V ) − 0.32 A I V ≧ 10 , 000 k m 2 and m b L g = 0.97 m b ( b a s e d o n f a l l o f f ) + 0.22 , with regression coefficients of 0.94 and 0.99 respectively.