MINQ
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 setting up an array of portable earthquake recorders on a rectangular grid with approximately 50km spacing, beginning in the Mount Isa area.
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 21 instruments were installed in the Mount Isa area in June 2009 as the first phase of a deployment that will move progressively to the east over several years. The network was expanded to 25 instruments when the first data was collected on an instrument service run in September. Most of these instruments will be pulled out and moved in late 2010 when the second phase of the experiment, MINQ-B, is installed on the plains east of Cloncurry.
Installation
We choose seismometer sites 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. Installation of the recorders began in June 2009. Observers will return to change the batteries about every three months, and take them out after 6-12 months.
A typical field installation is placed near a low shrub or fence and covered with some brush which also provides some protection from foraging animals. Picking a site is a compromise beween protection from disturbaces, ground suitability, sky visivility for the antenna and the danger of fires and floods.
Outcomes
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. Future plans are to extend the observation array to the 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.
Related projects
The MINQ experiment is one of a series of deep crustal studies conducted around Australia in recent years. More details of these experiments an be found at the seismology website.Questions about the MINQ experiment should be addressed to Dr Herb McQueen.