ALBERT

Description: At present the Pine Island Glacier in West Antarctica is thinning and its grounding line has retreated. This work uses three ice-flow models to investigate the stability of the glacier and finds that the grounding line could retreat a further 40 km, which is equivalent to a rise in sea level of 3.5–10 mm over a 20 year period. Nature Climate Change 4 117 doi: 10.1038/nclimate2094

Description: Passive seismic interferometry is a new promising methodology for seismic exploration. Interferometry allows information about the subsurface structure to be extracted from ambient seismic noise. In this study, we apply the cross-correlation technique to approximately 25 hr of recordings of ambient seismic noise at the Ketzin experimental CO2 storage site, Germany. Common source gathers were generated from the ambient noise for all available receivers along two seismic lines by cross-correlation of noise records. This methodology isolates the interstation Green's functions that can be directly compared to active source gathers. We show that the retrieved response includes surface waves, refracted waves and reflected waves. We use the dispersive behaviour of the retrieved surface waves to infer geological properties in the shallow subsurface and perform passive seismic imaging of the subsurface structure by processing the retrieved reflected waves.

Description: We present a new 3D shear-wave velocity model and Moho map of Scandinavia, which is based on the inversion of the merged phase dispersion curves from ambient noise and earthquake-generated Rayleigh waves. A classic two step inversion scheme is used where first maps of phase velocities at different periods are derived, and then a 1D transdimensional Bayesian method is applied to determine the VSV-depth structure. We assess the question of what compensates for the unusual high Scandes mountains and aim to identify the different tectonic domains of the adjacent continental lithosphere (Baltic Shield). While the southern Scandes lacks a pronounced crustal root, we observe a crustal root below the northern Scandes that is decreasing towards the central Scandes. A ∼10 km thick high-density lower crustal layer is present below the northern Scandes and generally thickening to the east below the Baltic Shield. The lithosphere-asthenosphere boundary (LAB) below the Scandes is deepening as well from west to east with a sharp step and a strong VSV decrease with depth of 9% in the north and of 5.5% in the south. The LAB of the thinner lithosphere is at 150 km depth in the north and varies from 90 to 120 km depth in the south. Both LAB steps coincide with the mountain front. The central area shows rather smoothly varying structures (170 km LAB depth, −4% VSV with depth) towards the east and no clear spatial match with the front. We infer therefore distinct uplift mechanisms along the Scandes. The southern Scandes might sustain their topography due to dynamic support from the mantle, while the northern Scandes experience both crustal and mantle lithosphere isostasy. In both cases, we suspect a dynamic support from small-scale edge-driven convection that developed at the sharp lithospheric steps. Beneath the Archean Karelia craton in northern Finland, we find low-velocity areas below 150 km depth while a 250 km deep lithospheric keel is imaged below the Paleoproterozic southern Finland. The Norrbotten craton in northern Sweden can be identified at mantle depths as a unit different from the Karelia craton, Scandes and Paleoproterozic central Sweden.