Seismic-source and wave-propagation effects of Lg waves in Scandinavia

摘要: SUMMARY A set of 517 recordings Lg waves from 151 earthquakes in and around Norway has been used for determination seismic moment Mo, corner frequency fo anelastic attenuation Q(f). The data have recorded at source-receiver distances 20 to 1200 km, with ML magnitudes between 0.8 5.0, the parameters were estimated by inverting Fourier spectra all simultaneously. observed represented a source term, spreading an inversion was made assuming geometrical be known. Because non-linear behaviour spectral shape, done iteratively minimizing differences computed spectra. A standard ω-2 model inversion, supported near-field observations small-magnitude regional NORESS array. A then established investigating decay using synthetic modelled without attenuation, realistic crustal structure Moho depth 40 km. results support spherical short cylindrical longer distances, but transition distance closer 200 km than more commonly value 100 rate beyond this found close –1/2 domain, equal theoretical spreading, –3/4 time where Airy phase is –5/6. The amplitude-displacement corrected instrument response site effects, reduced (by smoothing) 64 values weighted represent equidistantly spaced points log-frequency domain. Only signal-to-noise ratios least four accepted, upper limit 10Hz, lower determined response. Mo are quite stable, exhibit linear dependency on ML. frequencies less well constrained, however, especially smaller events. In type fo∝Mo-δ we δ 3.4, indicating slightly increasing stress drop, 10 MPa cases (using Brune model). resulting Q models Q(f) = qfη yield q 440 η 0.7. This reasonably other area.