Determining the Seismic Structure of a Continent
- Lessons from Australia

B.L.N. Kennett
Research School of Earth Sciences
Australian National University

The Australian continent has very few permanent high-quality seismic
stations and most of the information on the lithospheric and mantle
structure beneath the region has come from deployments of temporary
broad-band instruments since 1992.

The SKIPPY experiment from 1993-1996 provide a continent-wide
reconnaissance using sequences of deployments of a limited number of
instruments.  The configuration of a mobile array was dictated by
available funding and the high level of regional seismic meant that
good data coverage could be achieved with 5-6 months of recording at
each site. Over 65 sites were occupied across the continent with an
inter-station spacing of approximately 400 km, with some gaps due to
logistic (access) issues. Unfortunately, hardware failures increased
with time and data coverage in the west of the continent was rather
limited and had to be rectified with a further deployment in
2000-2001.  From the regional events to the north and east it is
possible to get about 300 km resolution for surface wave tomography.
The results of SKIPPY have been exploited in the design of follow-up
experiments designed to look at different aspects of the lithospheric
structure at higher resolution, e.g., the substructure of the cratons.

The concept of a mobile array worked quite well but in hindsight could
have been improved in a number of ways. It would have been desirable to
have a reasonable density of stations with long-term occupation, this 
would not only provide a basic matrix for surface wave tomography but 
would also allow better use of the infrequent events suitable for SKS
splitting studies.  There should also been some degree of overlap 
between successive deployments (e.g. between summer seasons in Antarctica).
Even in Australia we tended to underestimate the logistic difficulties of
work in remote environments, these are magnified in the Antarctic.

The pattern of broad-scale coverage of the continent with subsequent
(or parallel) concentrations of instruments for detailed studies should
provide a good basis for international collaboration across
Antarctica.  Multiple simultaneous experiments would maximise path
coverage.  Data management structures will be need to set up from the
outset to cope with delivery and exchange of data.