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  • 1
    Publication Date: 2014-12-05
    Description: This study explores the full 3D earthquake location for the Australian continent, exploiting the recent 3D Australian Seismological Reference Model (AuSREM). Seismic velocities from AuSREM were used as input to precompute finely spaced P - and S -travel-time grids for each station in the Australian National Seismograph Network using the multistage fast marching method. Travel times from anywhere in the grid to the corresponding station can then be computed by interpolation. The location search using these travel times is based on matching observed and computed arrival times using the neighborhood algorithm. All computations involved can be performed in practical time frames on a single processor computer. The performance of the 3D approach relative to location using the 1D global ak135 velocity model was assessed by locating a set of recent earthquakes. The arrival-time residuals for P and S arrivals are significantly smaller when using the 3D AuSREM model. The improvements over ak135 are especially large in the 10°–18° distance range, in which a distance bias is strongly reduced and for those paths where the ak135 residuals are large. A small set of six ground-truth events was used to assess to what extent the reduction in travel-time residuals leads to better absolute location accuracy. The 3D location offset from the ground-truth position is typically half that of the ak135 offset. The patterns of offsets suggest that the already fast mantle wavespeeds in western Australia need to be even faster than in AuSREM.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
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  • 2
    Publication Date: 2015-08-01
    Description: Seismic arrays have many uses for signal enhancement, from surface-wave characterization of the near surface to teleseismic detection in the context of monitoring nuclear tests. Many variants of the geometrical configuration of stations have been used with the objective of maximizing potential resolution of the incoming wavefronts direction of arrival. A versatile class of array configurations, with good resolution properties, can be constructed with multiple spiral arms. The array response is comparable with the same number of full circles, but with far fewer stations and is robust to minor position changes in emplacement. The desirable properties of the spiral-arm arrays are illustrated for a permanent array in the Precambrian Pilbara craton in northwestern Australia and for a temporary array on ancient sediments in southern Queensland, Australia. In each case, the practical array response is very good and matches the theoretical expectations. The spiral-arm configuration allows the deployment of relatively large aperture arrays with a limited number of stations, which is advantageous in a broad range of seismic applications, including near-surface characterization. Online Material: Figures illustrating the relation between spiral-arm and multiring circular arrays.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
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