TY  - JOUR
ID  - epos1357
UR  - http://dx.doi.org/10.1785/0120060172
IS  - 4
A1  - Allen, T. I.
A1  - Cummins, P. R.
A1  - Dhu, T.
A1  - Schneider, J. F.
Y1  - 2007/08//
N2  - A dataset comprising some 1200 weak- and strong-motion records from
84 earthquakes is compiled to develop a regional ground-motion model for south-
eastern Australia (SEA). Events were recorded from 1993 to 2004 and range in size
from moment magnitude 2.0 <= M <= 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 coef?cient of R^(-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 re?ections from midcrustal and Moho discontinuities. In this hypo-
central distance range, geometrical spreading is approximately R^0.1. Beyond
160 km, low-frequency seismic energy attenuates rapidly with source?receiver distance, having a geometrical spreading coef?cient of R^(-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)^2 + 0.058 (log f)^3
for frequencies 0.78 <= f <= 19.9 Hz.
Fourier spectral amplitudes, corrected for geometrical spreading and anelastic attenuation, are regressed with M to obtain quadratic source scaling coef?cients. Modeled vertical-component displacement spectra ?t 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 ?rst 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.
PB  - Seismological Society of America
JF  - Bulletin of the Seismological Society of America
VL  - 97
SN  - 0037-1106
TI  - Attenuation of Ground-Motion Spectral Amplitudes in Southeastern Australia
SP  - 1279
AV  - none
EP  - 1292
ER  -