MINQ
Mt Isa - Northern Queensland
Passive Seismic Experiment
The MINQ experiment is being conducted by the Australian National University
and the Geological Survey of Queensland as part of the AuScope Infrastructure
program, and involves deploying an array of portable earthquake recorders on a
rectangular grid with approximately 50km spacing, beginning in the Mount Isa
area and moving progressively east towards the coast.
The instruments record seismic waves passing through the Earth from distant earthquakes in the Pacific, Indian and Southern Oceans. By comparing the signals and their arrival times at different sites it is possible to learn about the geological history of North Queensland from structures we can see deep in the crust. We can resolve these seismic velocity changes in this way down as far as 50 to 100km depth. The images are constructed from the travel times of seismic waves using ray tracing and seismic tomography.
An initial array of 25 instruments, MINQ-A, was installed in the Mount Isa area in 2009 as the first phase of the deployment. Data was successfully collected on several instrument service runs in 2009-10. Most of these instruments were pulled out and moved in September 2010 when MINQ-B, the second phase of array of 35 recorders, was installed on the gulf plains east of Cloncurry.
Seismometer sites are chosen in inconspicuous locations near an access road and usually within a few kilometres of the ideal grid position. The seismometer is buried about half a metre down, with a recorder about the size of a car tyre on the ground above it and a small timing antenna on a stake beside it. They are simply listening devices and have no effect on stock or surroundings and are not involved in petroleum or mineral exploration.
Each site installation takes a couple of hours depending on ease of access and time required to contact the property owner if we have not been able to do so beforehand. Observers return to change the batteries about every three months (except during the wet), and take them out after 6-12 months.
By tracing and timing seismic waves from distant earthquakes we can build up
a picture of structures in the crust under north Queensland using techniques
similar to medical CAT scan. Imaging these structures helps us to reconstruct
the geological history of the formation of the continent.
Data from the experiment will be publicly available as soon as they have been processed into an accessible form. In the first instance that will be a series of sections through a velocity anomaly model of the crust and lithosphere underlying the observational array. The observation array is planned to move east in annual stages following the trend of the 2007 deep seismic reflection profile across north Queensland. The results of the full experiment are intended to add an extra dimension to the cross section captured in that survey.
Questions about the MINQ experiment should be addressed to Herb McQueen (Herb.McQueen@anu.edu.au)
