Publication Date:
2007-08-01
Description:
A dataset comprising some 1200 weak- and strong-motion records from 84 earthquakes is compiled to develop a regional ground-motion model for southeastern Australia (SEA). Events were recorded from 1993 to 2004 and range in size from moment magnitude 2.0〈 or =M〈 or =4.7. The decay of vertical-component Fourier spectral amplitudes is modeled by trilinear geometrical spreading. The decay of low- frequency spectral amplitudes can be approximated by the coefficient of R (super -1.3) (where R is hypocentral distance) within 90 km of the seismic source. From approximately 90 to 160 km, we observe a transition zone in which the seismic coda are affected by postcritical reflections from midcrustal and Moho discontinuities. In this hypocentral distance range, geometrical spreading is approximately R (super +0.1) . Beyond 160 km, low-frequency seismic energy attenuates rapidly with source-receiver distance, having a geometrical spreading coefficient of R (super -1.6) . The associated regional seismic-quality factor can be expressed by the polynomial: log Q(f) = 3.66-1.44 log f+0.768 (log f) (super 2) +0.058 (log f) (super 3) for frequencies 0.78〈 or =f〈 or =19.9 Hz. Fourier spectral amplitudes, corrected for geometrical spreading and anelastic attenuation, are regressed with M to obtain quadratic source scaling coefficients. Modeled vertical-component displacement spectra fit the observed data well. Amplitude residuals are, on average, relatively small and do not vary with hypocentral distance. Predicted source spectra (i.e., at R = 1 km) are consistent with eastern North American (ENA) models at low frequencies (f less than approximately 2 Hz) indicating that moment magnitudes calculated for SEA earthquakes are consistent with moment magnitude scales used in ENA over the observed magnitude range. The models presented represent the first spectral ground-motion prediction equations developed for the southeastern Australian region. This work provides a useful framework for the development of regional ground-motion relations for earthquake hazard and risk assessment in SEA.
Print ISSN:
0037-1106
Electronic ISSN:
1943-3573
Topics:
Geosciences
,
Physics
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