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Backprojection has proven useful in imaging large earthquake rupture processes. The method is generally robust and requires relatively simple assumptions about the fault geometry or the Earth velocity model. It can be applied in both the time and frequency domain. Backprojection images are often obtained from records filtered in a narrow frequency band, limiting its ability to uncover the whole rupture process. Here, we develop and apply a novel frequency-difference backprojection (FDBP) technique to image large earthquakes, which imitates frequencies below the bandwidth of the signal. The new approach originates from frequency-difference beamforming, which was initially designed to locate acoustic sources. Our method stacks the phase-difference of frequency pairs, given by the autoproduct, and is less affected by scattering and -time errors from 3-D Earth structures. It can potentially locate sources more accurately, albeit with lower resolution. In this study, we first develop the FDBP algorithm and then validate it by performing synthetic tests. We further compare two stacking techniques of the FDBP method, Band Width Averaged Autoproduct and its counterpart (BWAP and non-BWAP), and their effects in the backprojection images. We then apply both the FDBP and conventional backprojection methods to the 2015 M7.8 Gorkha earthquake as a case study. The backprojection results from the two methods agree well with each other, and we find that the peak radiation loci of the FDBP non-BWAP snapshots have standard error of less than 0.33° during the rupture process. The FDBP method shows promise in resolving complex earthquake rupture processes in tectonically complex regions.

 

ABSTRACT This is a cross institution project involving four Institutes of Technology in Ireland. The objective of this project is to assess the use of technology to enhance the assessment of laboratory sessions in Science and Health. In science, health and engineering, the laboratory sessions are at the core of the learning process for skill development. These laboratory sessions focus on the skills acquisition. The Irish Institute of Technology sector, in particular, develops these skills and considers them essential for ‘professionally ready’ graduates. In terms of student progression and retention, the assessment structure has been identified as having a significant impact on student engagement. The Technology Enhanced Assessment Methods (TEAM) project led by Dundalk Institute of Technology and partnering with Institute of Technology Sligo, Athlone Institute of Technology and Institute of Technology Carlow is exploring the potential offered by digital technologies to address these concerns. It aims to develop a framework for applying the principles of effective assessment and feedback to practical assessment. The TEAM project also aims to facilitate dialogue among stakeholders about what it is we want student to learn in laboratory sessions and how our assessment can facilitate this. A peer network of discipline-specific academics and students in the Science and Health field has been established across all four Institutes. As the network focuses on authentic skills assessment in all core modules, including physics and chemistry, the best practice from this project will inform future assessment procedures across laboratory sessions and may be considered for application within a Science and Materials Engineering context. Assessing the skills acquired in this environment takes many forms. Using student and stakeholder feedback along with an extensive literature review of the area, the team identified key technologies that cut across science and health disciplines, with the potential to influence and enable the learning process. The emphasis was on developing a powerful learning environment approach to enable students to deepen their learning through engagement with the process. The areas identified are: (i) Pre-practical preparation (videos and quizzes), (ii) Electronic laboratory notebooks and ePortfolios, (iii) Digital Feedback technologies and (iv) Rubrics). This paper describes the student experience and perceptions of the adoption of digital technology in science practical assessments. It also describes the process involved in setting up the pilot structure and it presents the initial results from the student survey.