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Quito, the capital city of Ecuador hosting ∼2 million inhabitants, lies on the hanging wall of a ∼60-km-long reverse fault offsetting the Inter-Andean Valley in the northern Andes. Such an active fault poses a significant risk, enhanced by the high density of population and overall poor building construction quality. Here, we constrain the present-day strain accumulation associated with the Quito fault with new Global Positioning System (GPS) data and Persistent Scatterer Interferometric Synthetic Aperture Radar (PS-InSAR) analysis. Far field GPS data indicate 3–5 mm yr–1 of horizontal shortening accommodated across the fault system. In the central segment of the fault, both GPS and PS-InSAR results highlight a sharp velocity gradient, which attests for creep taking place along the shallowest portion of the fault. Smoother velocity gradients observed along the other segments indicate that the amount of shallow creep decreases north and south of the central segment. 2-D elastic models using GPS horizontal velocity indicate very shallow (<1 km) locking depth for the central segment, increasing to a few kilometres south and north of it. Including InSAR results in the inversion requires locking to vary both along dip and along strike. 3-D spatially variable locking models show that shallow creep occurs along the central 20-km-long segment. North and south of the central segment, the interseismic coupling is less resolved, and data still allows significant slip deficit to accumulate. Using the interseismic moment deficit buildup resulting from our inversions and the seismicity rate, we estimate recurrence time for magnitude 6.5 + earthquake to be between 200 and 1200 yr. Finally, PS-InSAR time-series identify a 2 cm transient deformation that occurred on a secondary thrust, east of the main Quito fault between 1995 and 1997. [ABSTRACT FROM AUTHOR]

Kinematics of divergent boundaries and Rift-Rift-Rift junctions are classically studied using long-termgeodetic observations. Since significant magma-related displacements are expected, short-term deformation provides important constraints on the crustal mechanisms involved both in active rifting and in transfer of extensional deformation between spreading axes. Using InSAR and GPS data, we analyse the surface deformation in the whole Central Afar region in detail, focusing on both the extensional deformation across the Quaternary magmato-tectonic rift segments, and on the zones of deformation transfer between active segments and spreading axes. The largest deformation occurs across the two recently activated Asal-Ghoubbet (AG) and Manda Hararo-Dabbahu (MH-D) magmato-tectonic segments with very high strain rates, whereas the other Quaternary active segments do not concentrate any large strain, suggesting that these rifts are either sealed during interdyking periods or not mature enough to remain a plate boundary. Outside of these segments, the GPS horizontal velocity field shows a regular gradient following a clockwise rotation of the displacements from the Southeast to the East of Afar, with respect to Nubia. Very few shallow creeping structures can be identified as well in the InSAR data. However, using these data together with the strain rate tensor and the rotations rates deduced from GPS baselines, the present-day strain field over Central Afar is consistent with the main tectonic structures, and therefore with the long-term deformation. We investigate the current kinematics of the triple junction included in our GPS data set by building simple block models. The deformation in Central Afar can be described by adding a central microblock evolving separately from the three surrounding plates. In this model, the northern block boundary corresponds to a deep EW-trending trans-tensional dislocation, locked from the surface to 10-13 km and joining at depth the active spreading axes of the Red Sea and the Aden Ridge, from AG to MH-D rift segments. Over the long-term, this plate configuration could explain the presence of the en-échelon magmatic basins and subrifts. However, the transient behaviour of the spreading axes implies that the deformation in Central Afar evolves depending on the availability of magma supply within the well-established segments. [ABSTRACT FROM AUTHOR]

The rifting episode that occurred in Dabbahu–Manda–Hararo (Ethiopia) between 2005 and 2010 during which 14 dyke intrusions were emitted, was a unique opportunity to study interactions between tectonic deformation and magmatic processes. While magmatism has been shown to control primarily the spatial and temporal distribution of dyke intrusions during this accretion sequence, the role of faults in accommodating plate spreading in rift segments is poorly understood. During interdyking periods, transient ground deformation due to magma movement is generally observed. Investigating such a small-scale deformation and in particular the movement along faults during these periods will help understanding the factors that trigger fault movement in magmatic rifts. We analyse fault activity during three interdyking periods: 2006 December–June (d0–d1), 2007 January–July (d5–d6) and 2009 November–January (d10–d11). The time–space evolution of surface displacements along ~700 faults is derived from pairs of ascending and descending SAR interferograms. Surface slip distributions are then compared with codyking ground deformation fields. The results show that faults are mainly activated above the areas affected by magma emplacement during interdyking periods. A detailed analysis of brittle deformation during the six months following the 2005 September intrusion shows asymmetric deformation on the rift shoulders, with significant opening on faults located to the west of the dyke. We explain this feature by the activation of westward dipping pre-existing faults, with block rotations in between. In addition, we observe that the strip encompassing the activated faults narrows by 30?per?cent from co- to interdyking period. This suggests that magma keeps migrating to shallower depths after the dyke intrusion. During a rifting episode, activation of faults in a pre-existing fracture network therefore seems to be mainly controlled by deep magma processes. [ABSTRACT FROM AUTHOR]

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 (Mw ∼ 6) to large (Mw ∼ 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 Mw ∼ 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. [ABSTRACT FROM PUBLISHER]