Seismic imaging of the Earth's interior.

Contributor: Malcolm Sambridge, RSES Australian National University, Malcolm.Sambridge@anu.edu.au.


Project Description

Tomographic imaging of the Earth’s internal structure has been a major pursuit of seismologists for more than 35 years. Using information from many recordings of earthquakes images are reconstructed of variations of Earth’s seismic properties as a function of position within the globe. Figure 1 shows variations of seismic shear wavespeed throughout the Earth’s mantle produced by inversion of a large number of multiple-frequency long period travel times from globally distributed earthquakes to surface receivers. Blue regions represents rocks with faster than average wavespeeds and orange represent slower than average wavespeeds. Through such inversions information is produced on the present day internal structure of Earth which in turn places constraints on mantle dynamics and composition.


3-D Global S-wave multiple-frequency tomography of the Earth’s mantle.
Figure 1. 3-D Global S-wave multiple-frequency tomography
of the Earth’s mantle.

Our group at ANU, in collaboration with colleagues around the world, develop new approaches to seismic imaging and apply them to the ever increasing database of local, regional and global recordings of earthquake waveforms. A focus of the ANU group is in imaging regional structure of the Australian continental lithosphere (0-300km depth) collected by deploying seismic stations across the continent. Figure 2 shows a recent result using local recordings of distant earthquakes.


Inversion results for seismic structure beneath S. E. Australia derived from teleseismic traveltime tomography
Figure 2. Inversion results for seismic structure beneath S. E. Australia
derived from teleseismic traveltime tomography

Inversion problems of this type usually reduce to the solving of a large system of linear (or linearized ) equations simultaneously. A large body of work exists on methods of solution and seismologists use different techniques depending on the number of data and whether the mathematical relationship between data and unknowns is linear or nonlinear. We are constantly trying to improve these methodologies as well as extending our data.

Collaborators: Christophe Zaroli (Universite de Strasbourg), Eric Debayle (Universite de Lyon), Nick Rawlinson (ANU), Brian Kennett (ANU) plus entire ANU Seismology and Mathematical Geophysics group.


Publications

Frequency-dependent effects on global S-wave travel times: wavefront-healing, scattering and attenuation,
Zaroli, C., Debayle, E. and Sambridge, M, Geophys. J. Int., in press, 2010.

The transition between the Delamerian and Lachlan orogens at upper mantle depths from simultaneous inversion of multiple teleseismic datasets,
Rawlinson, N., Kennett, B. L. N., Vanacore, E., Glen, R. A. and Fishwick, S. Gondwana Research, submitted, 2010.

New insight into Cainozoic sedimentary basins and Palaeozoic suture zones in southeast Australia from ambient noise surface wave tomography,
P. Arroucau, N. Rawlinson, and M. Sambridge, GRL, vol 37, L07303, 2010.