Attenuation of the LG Phase and Site Response for the Eastern Canada Telemetered Network

Abstract

Abstract Data from the Eastern Canada Telemetered Network (ECTN) contain information concerning source characteristics, regional attenuation, and site response in eastern North America (ENA). This paper presents results of multi- variate linear regression analyses of ECTN data from the Lg phase of moderate (mN 4 to 5.5) shallow (h < 15 km) ENA earthquakes, at distances of 100 to 1200 km. The regressions are performed upon the instrument-corrected Fourier amplitudes of acceleration, for frequencies from 0.5 to 10 Hz. The analysis follows the method of Joyner and Boore (1981), employing dummy variables to determine source terms for each of the earthquakes, site terms for each of the stations, and regional attenuation. The analyses indicate that attenuation of the Lg phase in southeastern Canada can be represented by geometric attenuation of R−1, with an associated quality factor of Q =1100f0.17, for distances up to 1200 km. The R−1 geometric attenuation is stronger than the theoretical R −0.5 spreading predicted for the Lg phase. The latter may be preferable on a theoretical basis, but the former has practical utility, and is apparently allowed by the scatter of the data. Earthquake source spectra for events in the magnitude range 4 to 5.5 are consistent with the Brune source model, with a stress drop of approximately 100 bars. Site response terms for all ECTN rock stations are within a factor of approximately 1.5 of unity. The soil site at Welcome, Ontario amplifies high frequencies (5 to 10 Hz) by an order of magnitude.