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Lg spectra of local earthquakes recorded by the Eastern Canada Telemetered Network and spectral scaling

DIVISION OF SEISMOLOGY AND GEOMAGNETISM EARTH PHYSICS BRANCH ENERGY, MINES AND RESOURCES, OTTAWA, ONTARIO, Canada , K1A 0Y3

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 (M_o) and corner frequency (f_o) of smaller magnitude (1 M 4.2) earthquakes increase more graudally with increasing magnitude (M stands for m_bLg) than do corresponding parameters for larger (4.2 < M 6.6) earthquakes. For smaller earthquakes, empirical relations are as follows: (i) log M_o0.94 M, log f_o(–0.18 M), log f_o(–0.18 log M_o); (ii) stress drop () is in the range of 1 bar 10 bars and increases with increasing magnitude, a characteristic which may imply that barriers are controlling the rupture process; (iii) source dimension (2r_o) is in the range 0.1 km < 2r_o < 1 km; (iv) average dislocation (D) is in the range 0.1 cm < D < 1 cm; and (v) corner period (T_o) is in the range 0.05 sec < T_o < 0.5 sec. For larger earthquakes: (i) log M_o1.85 M, log f_o(–0.5 M), and log f_o(–0.28 log M_o); (ii) stress drop is in the range 10 bars < < 50 bars; (iii) source dimension is in the range 1 km < 2r_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 T_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.

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