In the past decade, mounting evidence has pointed to complex, layered structure within and at the base of the mantle lithosphere of tectonically quiescent continental interiors. Sometimes referred to as negative velocity gradients or midlithospheric discontinuities (MLDs), the origin of intralithospheric layering has prompted considerable discussion, particularly as to how they may result from continent formation and/or evolution. Previous Sp receiver function analysis in Australia (Ford et al., 2010, https://doi.org/10.1016/j.epsl.2010.10.007) found evidence for complex lithospheric layering beneath permanent stations located within the North, South, and West Australian Cratons and characterized these as MLDs. This study provides an update to the original study by Ford et al. (2010, https://doi.org/10.1016/j.epsl.2010.10.007). Sp receiver function results are presented for 34 permanent, broadband stations. We observe the lithosphere–asthenosphere boundary (LAB) on the eastern margin of the continent, at depths of 75–85 km. The cratonic core of Australia has discontinuities within the lithosphere, with no observable LAB. On the western margin of the continent, we observe several stations with an ambiguous phase that may correspond to an MLD or the LAB. We also observe multiple negative phases at most stations, suggesting a complex and heterogeneous lithosphere. Australian MLDs are likely linked to the presence of hydrous minerals in the midlithosphere and may result from ancient processes such as subduction, plume interaction, or melt infiltration from the paleo‐LAB.

The Australian continent preserves some of the oldest lithosphere on Earth in the Yilgarn, Pilbara, and Gawler Cratons. In this study we present shear wave splitting and Ps receiver function results at long running stations across the continent. We use these results to constrain the seismic anisotropic structure of Australia’s cratons and younger Phanerozoic Orogens. For shear wave splitting analysis, we utilize SKS and SKKS phases at 35 broadband stations. For Ps receiver function analysis, which we use to image horizontal boundaries in anisotropy, we utilize 14 stations. Shear wave splitting results at most stations show strong variations in both orientation of the fast direction and delay time as a function of backazimuth, an indication that multiple layers of anisotropy are present. In general, observed fast directions do not appear to be the result of plate motion alone, nor do they typically follow the strike of major tectonic/geologic features at the surface, although we do point out several possible exceptions. Our Ps receiver function results show significant variations in the amplitude and polarity of receiver functions with backazimuth at most stations across Australia. In general, our results do not show evidence for distinctive boundaries in seismic anisotropy, but instead suggest heterogenous anisotropic structure potentially related to previously imaged mid-lithospheric discontinuities. Comparison of Ps receiver function and shear wave splitting results indicates the presence of laterally variable and vertically layered anisotropy within both the thicker cratonic lithosphere to the west, as well as the Phanerozoic east. Such complex seismic anisotropy and seismic layering within the lithosphere suggests that anisotropic fabrics may be preserved for billions of years and record ancient events linked to the formation, stabilization, and evolution of cratonic lithosphere in deep time.

The Crust and lithosphere Investigation of the Easternmost expression of the Laramide Orogeny was a two-year deployment of 24 broadband, compact posthole seismometers in a linear array across the eastern half of the Wyoming craton. The experiment was designed to image the crust and upper mantle of the region to better understand the evolution of the cratonic lithosphere. In this article, we describe the motivation and objectives of the experiment; summarize the station design and installation; provide a detailed accounting of data completeness and quality, including issues related to sensor orientation and ambient noise; and show examples of collected waveform data from a local earthquake, a local mine blast, and a teleseismic event. We observe a range of seasonal variations in the long-period noise on the horizontal components (15–20 dB) at some stations that likely reflect the range of soil types across the experiment. In addition, coal mining in the Powder River basin creates high levels of short-period noise at some stations. Preliminary results from Ps receiver function analysis, shear-wave splitting analysis, and averaged P-wave delay times are also included in this report, as is a brief description of education and outreach activities completed during the experiment.

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