abstract

A spectral analysis of more than 300 Eastern Canada Telemetered Network records of the Lg wave from 103 eastern Canada earthquakes is undertaken to determine source characteristics. Both seismic moment (Mo) and corner frequency (fo) of smaller magnitude (1 ≦ M ≦ 4.2) earthquakes increase more graudally with increasing magnitude (M stands for mbLg) than do corresponding parameters for larger (4.2 < M ≦ 6.6) earthquakes. For smaller earthquakes, empirical relations are as follows: (i) log Moα0.94 M, log foα(−0.18 M), log foα(−0.18 log Mo); (ii) stress drop (Δσ) is in the range of 1 bar ≦ Δσ ≦ 10 bars and increases with increasing magnitude, a characteristic which may imply that barriers are controlling the rupture process; (iii) source dimension (2ro) is in the range 0.1 km < 2ro < 1 km; (iv) average dislocation (D) is in the range 0.1 cm < D < 1 cm; and (v) corner period (To) is in the range 0.05 sec < To < 0.5 sec. For larger earthquakes: (i) log Moα1.85 M, log foα(−0.5 M), and log foα(−0.28 log Mo); (ii) stress drop is in the range 10 bars < Δσ < 50 bars; (iii) source dimension is in the range 1 km < 2ro < 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 ≦ To < 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.

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