Both seismic moment (M (sub o) ) and corner frequency (f (sub o) ) of smaller magnitude (1 〈 or = M 〈 or = 4.2) earthquakes increase more gradually with increasing magnitude (M stands for m (sub bLg) ) than for larger (4.2 〈 M 〈 or = 6.6) earthquakes. For smaller earthquakes, empirical relations are as follows: (i) log M (sub o) alpha 0.94 M, log f (sub o) alpha (-0.18 M), log f (sub o) alpha (-0.18 log M (sub o) ); (ii) stress drop (Delta sigma ) is in the range of 1 bar 〈 or = Delta sigma 〈 or = 10 bars and increases with increasing magnitude, a characteristic which may imply that barriers are controlling the rupture process; (iii) source dimension (2r (sub o) ) is in the range 0.1 km 〈 2r (sub o) 〈 1 km; (iv) average dislocation (D) is in the range 0.1 cm 〈 D 〈 1 cm; and (v) corner period (T (sub o) ) is in the range 0.05 sec 〈 T (sub o) 〈 0.5 sec. For larger earthquakes: (i) log M (sub o) alpha 1.85 M, log f (sub o) alpha (-0.5 M), and log f (sub o) alpha (-0.28 log M (sub o) ); (ii) stress drop is in the range 10 bars 〈 Delta sigma 〈 50 bars; (iii) source dimension is in the range 1 km 〈 2r (sub o) 〈 20 km; (iv) average dislocation is in the range 1 cm 〈 D 〈 100 cm; and (v) corner period is in the range 0.5 sec 〈 or = T (sub o) 〈 10 sec. Small earthquakes in eastern Canada tend to manifest slightly different source characteristics than those in the central and northeastern United States, namely a higher stress drop, a lower corner period, and a smaller extent of source. The lack of an adequate data base at larger magnitudes precludes a similar comparison.--Modified journal abstract.