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Comparison of Earthquake Source Spectra and Attenuation in Eastern North America and Southeastern Australia

¹ Risk Research Group
Geoscience Australia
GPO Box 378
Canberra, ACT 2601
Australia
 (T.I.A.)
² Department of Earth Sciences
University of Western Ontario
London, ON N6A 5B7, Canada
gmatkinson{at}aol.com
 (G.M.A.)

^* Present address: U.S. Geological Survey, Golden, Colorado 80401; tallen{at}usgs.gov.

The paucity of ground-motion data in stable continental regions (SCRs) remains a key limitation when developing relations that seek to predict effects of strong ground shaking from large damaging earthquakes. It is desirable to combine data from more than one SCR to increase database size, but this raises questions as to whether the source and attenuation properties of the SCRs are equivalent. We compare recently compiled spectral-amplitude databases from small to moderate events (moment magnitudes, 2.0 M 5.0) in both southeastern Australia and eastern North America (ENA). Both are SCRs but are widely separated, spatially and in tectonic history.

We statistically compare ground motions by plotting mean and standard deviations of spectral amplitudes for data grouped in magnitude and distance bins. These comparisons show that the source and attenuation properties of the two regions are very similar, in particular, at shorter hypocentral distances R (i.e., R < 70 km). At larger distances, regional attenuation differences are observed that may be attributed to differences in crustal structure. We conclude that it is valid to combine the Australian and ENA ground-motion datasets in the development of ground-motion prediction equations, with some limitations in frequency and distance ranges. These ground- motion relations may serve as generic functions for SCRs around the world.