Variations in crustal properties from teleseismic methods in the South Island, New Zealand

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Ramlakhan, Kevin
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Traditionally, H-k stacking of receiver functions has been used to measure the thickness and Vp/Vs ratio of the crust. This involves receiver-function deconvolution followed by stacking along the travel time curves of the Ps conversion and other later phases. Deconvolution of noisy, narrow banded receiver function data imposes a non-unique inverse problem, which can potentially introduce artefacts. The deconvolution step can be avoided by employing the transfer function method. The relationship between the vertical component and the radial component can be predicted by creating an array of synthetic transfer functions. Each transfer function is convolved with the vertical component to calculate a radial component and then the misfit between the calculated and real radial component is determined. The presence of a sedimentary layer can cause large outliers in apparent crustal thickness and Vp/Vs ratio from H-k stacking and result in unreliable measurements in sedimentary basins. The transfer function method allows the detection of sedimentary basins and resolves crustal thickness and Vp/Vs ratio without the influence of the sedimentary layer. In addition, transfer functions may be applied to areas where a more complex model of the crust is needed, whereas the H-k stacking method treats the crust as a single homogeneous layer. The transfer function approach is completed on 27 stations and over 2500 events and revealed variations of crustal thickness and Vp/Vs ratio from 15.2 – 25.6 km and 1.55 – 1.9 respectively. In addition, sedimentary thicknesses and lower crust thicknesses ranging from 0.1 – 4.4 and 4 - 15 km respectively, were resolved. The highest values of crustal thickness are located southwest near the Alpine Fault and the lowest values of crustal thickness are seen near the Otago Schist, southeast of the Alpine Fault.
Teleseismic research, Variations in crustal properties, Transfer function, South Island, New Zealand