Age-Dependent Seismic Thickness and
Mechanical Strength of the Australian Lithosphere

Frederik J Simons and Rob D. van der Hilst

Department of Earth, Atmospheric and Planetary Sciences
Massachusetts Institute of Technology (MIT)
Cambridge MA 02139, USA

Abstract

We present constraints on the regional variations of the seismic and mechanical thickness of the Australian lithosphere. We infer the seismic thickness from a waveform tomographic model of S-wave speed, and as a proxy for the elastic thickness we use the wavelength at which the coherence of surface topography and Bouguer gravity drops below half of its long-wavelength maximum. Our results show that on scales smaller than 1000 km the relationship between the age of the crust and the thickness of the lithosphere is more complicated than longer-wavelength or global averages suggest. Recent geochemical and geodynamical evidence for small-scale secular variations of the composition and stability of continental cratons further illustrates the complexity of the age dependence of seismo-mechanical lithospheric properties on regional scales.

Figures

1. Figure 01 Wave speed anomalies beneath Australia.
   
2. Figure 02 Depth to the +1.0% velocity anomaly contour, a proxy for seismic thickness.
   
3. Figure 03 Map of transitional coherence wavelengths, an indicator of the mechanical thickness.
   
4. Figure 04 Average seismic thickness of tectonic subdomains.
   
5. Figure 05 Average transitional coherence wavelength averaged over tectonic subdomains and grouped per eon.
   
6. Figure 06 Transition wavelengths, seismic thickness, and their standard deviations, as a function of age.