Large earthquakes produce crustal deformation that can be quantified by geodetic measurements, allowing for the determination of the slip distribution on the fault. We used data from Global Positioning System (GPS) networks in Central Chile to infer the static deformation and the kinematics of the 2010 moment magnitude (M(w)) 8.8 Maule megathrust earthquake. From elastic modeling, we found a total rupture length of ~500 kilometers where slip (up to 15 meters) concentrated on two main asperities situated on both sides of the epicenter. We found that rupture reached shallow depths, probably extending up to the trench. Resolvable afterslip occurred in regions of low coseismic slip. The low-frequency hypocenter is relocated 40 kilometers southwest of initial estimates. Rupture propagated bilaterally at about 3.1 kilometers per second, with possible but not fully resolved velocity variations.

The Atacama region (between 29 • S and 25 • S) is located in the North-Central area of Chile, a tectonically complex transition area between North and Central Chile. Deformation in Atacama is due mainly to elastic loading on the subduction interface but also to diffuse shortening in the Sierras Pampeanas, Argentina. The seismicity of the subduction is complex in this region: seismic swarms often occur, moderate (M w ∼ 6) to large (M w ∼ 7) earthquakes occur repeatedly and finally, megathrust earthquakes of magnitudes significantly larger than 8 occur once in a while, the last one being in 1922-almost a century ago. We use new GPS data we collected in the Atacama region between 2008 and 2012 to complete and densify existing data we acquired since 2004 in North-Central Chile. These new data allow to quantify the motion of the Andean sliver and assess the kinematic coupling on the subduction interface at these latitudes. We find that only 7 per cent of the whole convergence motion is taken up by an eastward rotation of the rigid sliver. A large part of the remaining 93 per cent (approximately 6 cm yr −1 ) gives way to accumulation of elastic deformation in the upper plate, due to locking on the plate interface. This accumulation shows important along-strike and along-dip variations, interpreted in terms of variable coupling which we correlate with seismicity. We identify two areas of low coupling near the 'La Serena' (30 • S) and 'Baranquilla' (27.5 • S) bays. Both are correlated with the subduction of singular bathymetric features and seem to stop the propagation of large seismic ruptures. These zones are also seismic swarm prone areas, which seem to occur rather on their edges. These low coupling areas separate two seismic segments where coupling is high: the Atacama segment (∼100 km long between 29 • S and 28 • S) and the Chañaral segment (∼200 km long between 27 • S and 25 • S). Should they rupture alone, these segments are sufficiently coupled and apparently since long enough, to produce M w ∼ 8 events. However, a collective failure of both segments could generate a megathrust earthquake of magnitude close to 8.5, similar to the 1819 and 1922 complex events, which produced important tsunamis. Such giant events may occur in the area once a century.

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Characterisation of the ecosystem functioning of mudflats requires insight on the morphology and facies of these coastal features, but also on biological processes that influence mudflat geomorphology, such as crab bioturbation and the formation of benthic biofilms, as well as their heterogeneity at cm or less scales. Insight into this fine scale of ecosystem functioning is also important as far as minimizing errors in upscaling are concerned. The realisation of high-resolution ground surveys of these mudflats without perturbing their surface is a real challenge. Here, we address this challenge using UAV-supported photogrammetry based on the Structure-from-Motion (SfM) workflow. We produced a Digital Surface Model (DSM) and an orthophotograph at 1 cm and 0.5 cm pixel resolutions, respectively, of a mudflat in French Guiana, and mapped and classed into different size ranges intricate morphological features, including crab burrow apertures, tidal drainage creeks and depressions. We also determined subtle facies and elevation changes and slopes, and the footprint of different degrees of benthic biofilm development. The results generated at this scale of photogrammetric analysis also enabled us to relate macrofaunal crab burrowing activity to various parameters, including mudflat elevation, spatial distribution and sizes of creeks and depressions, benthic biofilm distribution, and flooding duration. SfM photogrammetry offers interesting new perspectives in fine-scale characterisation of the geomorphology, benthic activity and degree of biofilm development of dynamic muddy intertidal environments that are generally difficult of access. The main shortcomings highlighted in this study are a drift of accuracy of the DSM outside areas of ground control points and the deployment of which perturb the mudflat morphology and biology, the water-logged or very wet surfaces which generate reconstruction artefacts through the sun glint effect, and the time-consuming task of manual interpretation of extraction of features such as crab burrow apertures. On-going developments in UAV positioning integrating RTK/PPK GPS solutions for image-georeferencing and precise orientation with high-quality inertial measurement units will limit the difficulties inherent to ground control points, while conduction of surveys during homogeneous cloudy conditions could reduce the sun-glint effect. Manual extraction of image features could be automated in the future through the use of deep-learning algorithms.