Inversion of Multiple Traveltime Datasets for Crust and Upper Mantle Structure in Southeast Australia

Abstract:

The inversion of seismic traveltimes for 2-D or 3-D velocity structure still represents the most common form of seismic tomography in use today. Studies generally focus on a particular class of data, such as teleseismic arrival time residuals, local earthquake arrival times, refraction and wide-angle reflection traveltimes or the traveltimes of regional or global phases. Group or phase traveltimes extracted from dispersion analysis of surface waves can also be inverted for velocity structure. A much smaller number of studies attempt to combine multiple data types in a single inversion; this can be of benefit when the datasets provide overlapping coverage. For instance, local earthquake and teleseismic datasets are often complementary, because while they can both sample the crust and upper mantle, there are many situations in which the teleseisms offer poor constraint on crustal structure, and local earthquakes do not constrain upper mantle structure particularly well. A joint inversion can therefore provide good recovery throughout the crust and mantle lithosphere. In this study, an updated version of the FMTOMO package will be used to jointly invert refraction, wide-angle reflection, teleseismic and local earthquake traveltime datasets for crustal, Moho and upper mantle structure beneath southeast Australia. The main target region is Tasmania, which lies at the southeastern tip of the Australian continent and represents the southern-most expression of the Tasmanides, a large Paleozoic fold belt that abuts the Pre-Cambrian shield region of central and western Australia. Broadside refraction and wide-angle reflection coverage is provided by off-shore airguns recorded by on-shore stations, and several passive seismic arrays supply teleseismic and local earthquake data. The combined dataset is able to resolve the trade-off between velocity and interface structure in the neighbourhood of the Moho, which results in a detailed picture of the Tasmanian lithosphere.