Summary We present a new S-wave velocity tomographic model of the upper mantle beneath the Australian Plate and its boundaries that we call Aus22. It includes azimuthal anisotropy and was constrained by waveforms from 0.9 million vertical-component seismograms, with the densest data sampling in the hemisphere centred on the Australian continent, using all available data covering this hemisphere. Waveform inversion extracted structural information from surface waves, S- and multiple S-waves and constrained S- and P-wave speeds and S-wave azimuthal anisotropy of the crust and upper mantle, down to the 660-km discontinuity. The model was validated by resolution tests and, for particular locations in Australia with notable differences from previous models, by independent inter-station measurements of surface-wave phase velocities. Aus22 can be used to constrain the structure and evolution of the Australian Plate and its boundaries in fine detail at the regional scale. Thick, high-velocity (and, by inference, cold) cratonic lithosphere occupies nearly all of western and central Australia but shows substantial lateral heterogeneity. It extends up to the northern edge of the plate, where it collides with island arcs, without subducting. Diamondiferous kimberlites and lamproite deposits are underlain by cratonic lithosphere, except for the most recent diamondiferous lamproites in the King Leopold Orogen. The rugged eastern boundary of the cratonic lithosphere resolved by the model provides a lithospheric definition of the Tasman Line. Just east of the Tasman Line, an area of intermediate-thick lithosphere is observed in the southern part of the continent. The eastern part of Australia is underlain by thin, warm lithosphere, evidenced by low seismic velocities. All the sites of Cenozoic intraplate volcanism in eastern Australia are located on thin lithosphere. A low-velocity anomaly is present in the mantle transition zone (410-660 km depths) beneath the Lord Howe and Tasmanid hotspots, indicative of anomalously high temperature and consistent with a deep mantle upwelling feeding these hotspots and, possibly, also the East Australia hotspot. High seismic velocities at 200-410 km depth below New Guinea indicate the presence of slab fragments, probably linked to the subduction of the Australian Plate. High seismic velocities are observed in the transition zone below northeast Australia and indicate the presence of subducted lithospheric fragments trapped in the transition zone, possibly parts of the former northern continental margin of Australia.

Summary Instrumental timing and phase errors are a notorious problem in seismic data acquisition and processing. These can be frequency independent, for example due to clock drift, but may also be frequency dependent, for example due to imperfectly known instrument responses. A technique is presented that allows both types of errors to be recovered in a systematic fashion. The methodology relies on the time-symmetry usually inherent in time-averaged crosscorrelations of ambient seismic noise: the difference between the arrival time of the direct surface wave at positive time and the arrival time of the direct surface wave at negative time is quantified. Doing this for all eligible receiver-receiver pairs of a large-N seismic array, including one or more receivers devoid of instrumental timing errors, the instrumental timing errors of all incorrectly timed receivers can be determined uniquely. Most notably, this is accomplished by means of a weighted least-squares inversion. The weights are based on the receiver-receiver distances and decrease the adverse effect of inhomogeneities in the noise illumination pattern on the recovered instrumental timing errors. Inversion results are furthermore optimized by limiting the inversion to receiver couples that (i) exceed a specific receiver-receiver distance threshold and (ii) whose time-averaged crosscorrelations exceed a specific signal-to-noise ratio threshold. Potential frequency dependence of the timing errors is incorporated by means of an iterative, frequency-dependent approach. The proposed methodology is validated using synthetic recordings of ambient seismic surface-wave noise due to an arbitrary non-uniform illumination pattern. The methodology is successfully applied to time-averaged crosscorrelations of field recordings of ambient seismic noise on and around the Reykjanes peninsula, SW Iceland.

Abstract. An exciting research project, for example with an unusual field component, presents a unique opportunity for education and public engagement (EPE). The adventure aspect of the fieldwork and the drive and creativity of the researchers can combine to produce effective, novel EPE approaches. Engagement with schools, in particular, can have a profound impact, showing the students how science works in practice, encouraging them to study science, and broadening their career perspectives. The project SEA-SEIS (Structure, Evolution And Seismicity of the Irish offshore, https://www.sea-seis.ie, last access: 6 October 2019) kicked off in 2018 with a 3-week expedition on the research vessel (RV) Celtic Explorer in the North Atlantic. Secondary and primary school students were invited to participate and help scientists in the research project, which got the students enthusiastically engaged. In a nation-wide competition before the expedition, schools from across Ireland gave names to each of the seismometers. During the expedition, teachers were invited to sign up for live, ship-to-class video link-ups, and 18 of these were conducted. The follow-up survey showed that the engagement was not only exciting but encouraged the students' interest in science, technology, engineering, and mathematics (STEM) and STEM-related careers. With most of the lead presenting scientists on the ship being female, both girls and boys in the classrooms were presented with engaging role models. After the expedition, the programme continued with follow-up, geoscience-themed competitions (a song-and-rap one for secondary and a drawing one for primary schools). Many of the programme's best ideas came from teachers, who were its key co-creators. The activities were developed by a diverse team including scientists and engineers, teachers, a journalist, and a sound artist. The programme's success in engaging and inspiring school students illustrates the EPE potential of active research projects. The programme shows how research projects and the researchers working on them are a rich resource for EPE, highlights the importance of an EPE team with diverse backgrounds and expertise, and demonstrates the value of co-creation by the EPE team, teachers, and school students. It also provides a template for a multifaceted EPE programme that school teachers can use with flexibility, without extra strain on their teaching schedules. The outcomes of an EPE programme coupled with research projects can include both an increase in the students' interest in STEM and STEM careers and an increase in the researchers' interest and proficiency in EPE.