Resolving the seismic velocity structure of the Australian lithosphere

Marcus Haynes1, Alexei Gorbatov1, Babak Hejrani1, Rakib Hassan1, Fei Zhang1

1Geoscience Australia, Canberra, ACT

 

Tomographic inversion of seismic data enable geophysical imaging of otherwise-inaccessible regions of Earths lithosphere and mantle. Such models can provide important constrains on structure and composition with depth. For instance, the relationship between regional seismic wave-speeds and tectonics has been known for a long time. However, more recently it has been recognised that lithospheric structure can also allow spatial inferences to be made about the systems responsible for generating economic mineral deposits. Given this, high-resolution 3D seismic imaging of the Australian lithosphere has been identified as a high-priority for improving mineral exploration.

Seismic velocities in the lithosphere can be inferred by the relative travel-time between earthquakes and seismic stations. Australia’s intra-continental setting records relatively few earthquakes in comparison to the subducting oceanic slabs to the north and east, and hence passive-seismic imaging of the lithosphere requires the deployment of dense arrays of seismometers. This leads to heterogeneous data coverage across the continent and, as such, the coarseness with which we can infer lithospheric seismic velocities varies spatially.

Model resolution analysis characterises the degree to which individual model parameters can be independently predicted. We use the results of resolution analysis to directly guide the construction of an irregular grid mesh across our model domain. This effectively alters the regularisation of our inversions and allows the 3D seismic velocity structure to be inferred across a range of spatial scales corresponding to the amount of information available.


Biography:

Marcus joined Geoscience Australia in 2007 as a cadet, and has worked across the agency in various roles. He currently works as a geophysicist in the Mineral Potential section. Marcus’ role involves the geophysical imaging of the lithosphere for mineral system assessments. Marcus is also concurrently completing a PhD at the Australian National University and is in the final stages of writing up his thesis which examines the conductive flow of heat through the Australian continental crust.

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