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Abstract Relative relocation techniques are widely used to improve the resolution of earthquake hypocenter positions. Here, we present GrowClust3D.jl—an open-source software package written in the programming language Julia that builds and improves upon the original GrowClust algorithm, an established relative relocation technique based on cluster analysis instead of a more traditional matrix inversion approach. The adoption of Julia’s modern programming environment allows for greater flexibility in GrowClust3D.jl’s algorithm design and its computational implementation. Notable additions to the GrowClust3D.jl package include (1) several parallel processing options to improve efficiency in uncertainty quantification routines, (2) incorporation of geographic map projections and station elevations during the relocation process, and (3) the ability to use travel-time tables derived from 3D velocity models. We demonstrate the new features of the software package on relocation problems of different scales in Nevada, California, Texas, and New Zealand, where in the latter two cases the use of a 3D velocity model helps resolve structures that remain obscure with earlier versions of GrowClust. We expect that the new GrowClust3D.jl software package will become a valuable public resource for the earthquake science community. 

Climate change is increasingly predisposing polar regions to large landslides. Tsunamigenic landslides have occurred recently in Greenland (Kalaallit Nunaat), but none have been reported from the eastern fjords. In September 2023, we detected the start of a 9-day-long, global 10.88-millihertz (92-second) monochromatic very-long-period (VLP) seismic signal, originating from East Greenland. In this study, we demonstrate how this event started with a glacial thinning–induced rock-ice avalanche of 25 × 10⁶cubic meters plunging into Dickson Fjord, triggering a 200-meter-high tsunami. Simulations show that the tsunami stabilized into a 7-meter-high long-duration seiche with a frequency (11.45 millihertz) and slow amplitude decay that were nearly identical to the seismic signal. An oscillating, fjord-transverse single force with a maximum amplitude of 5 × 10¹¹newtons reproduced the seismic amplitudes and their radiation pattern relative to the fjord, demonstrating how a seiche directly caused the 9-day-long seismic signal. Our findings highlight how climate change is causing cascading, hazardous feedbacks between the cryosphere, hydrosphere, and lithosphere.