In Northwestern South America (NWSA) the geodetic data show a consistent northeastward displacement of blocks, while the geological record shows a predominant shortening in NW-SE direction suggesting a clear pattern of strain partitioning. This type of deformation has been extensively studied in the context of two convergent plates. However, in NWSA this is complicated by the interaction of multiple tectonic elements, including the Caribbean and Farallon/Nazca plates and the accretion of the Panama-Choco Arc. In this study we integrate the plate convergence evolution with multiple lines of evidence in the geological record, to propose a tectonic reconstruction that accounts for the deformation distribution during the Cenozoic. Our results indicate that deformation was not spatially homogeneous nor did it occur continuously during the Cenozoic. The main drivers of these variations were variations of convergence obliquity of the involved plates, the presence of heterogeneous lithospheric strength zones, changes in the geometry of the subducting slabs and the transition from subduction to collisional tectonics of the Panama-Choco Arc against NWSA. The obtained relative motion of blocks reproduces a strain evolution that is consistent with the different episodes of deformation reported in the literature. The model is additionally supported by the reconstructed velocity and strain vectors, which have a good match with equivalent indicators of the recent deformation in NWSA. Furthermore, the integration of the proposed palinspastic model with existing paleoenvironmental models, allowed us to construct restored paleogeographic maps that agree well with the deformation and exhumation history of the Northern Andes.

A sequence of three strong (M W 7.2, 6.4, 6.6) earthquakes struck the Pamir of Central Asia in 2015–2017. With a local seismic network, we recorded the succession of the fore-, main-, and aftershock sequences at local distances with good azimuthal coverage. We located 11,784 seismic events and determined 33 earthquake moment tensors. The seismicity delineates the tectonic structures of the Pamir in unprecedented detail, i.e., the thrusts that absorb shortening along the Pamir’s thrust front, and the strike-slip and normal faults that dissect the Pamir Plateau into a westward extruding block and a northward advancing block. Ruptures on the kinematically dissimilar faults were activated subsequently from the initial M W 7.2 Sarez event at times and distances that follow a diffusion equation. All mainshock areas but the initial one exhibited foreshock activity, which was not modulated by the occurrence of the earlier earthquakes. Modeling of the static Coulomb stress changes indicates that aftershock triggering occurred over distances of ≤90 km on favorably oriented faults. The third event in the sequence, the M W 6.6 Muji earthquake, ruptured despite its repeated stabilization through stress transfer in the order of -10 kPa. To explain the accumulation of M W > 6 earthquakes, we reason that the initial mainshock may have increased nearby fault permeability, and facilitated fluid migration into the mature fault zones, eventually triggering the later large earthquakes.

Embedded between the Tian Shan, Pamir, and Hindu Kush, the Tajik depression is a remnant of the Mesozoic-Miocene Tajik-Tarim basin system. Since ~12 Ma, westward collapse of the north-advancing Pamir-Plateau crust inverted the Tajik basin into a thin-skinned fold-thrust belt with ~150 km of ~E-W shortening distributed between foreland- and hinterland-vergent structures. Geodetically-derived shortening rates decay westward from ~15 to 2 mm/yr. Seismicity outlines the ~east-striking dextral Ilyak fault, bounding the fold-thrust belt in the north, and distributed shortening in the central and eastern Tajik depression. We derived E-W and vertical deformation-rate maps from radar interferometric time-series, consisting of 900+ radar scenes acquired over 2.0-4.5 years, and available accurate positioning data. We confirm the westward collapse of the Pamir and the drastic shortening-rate decline across the Main Pamir Thrust at the Pamir front. In the Tajik depression, the maps unveil a combination of basin-scale tectonics, local halokinesis, and seasonal/weather-driven soil or near-surface effects. Although the Tajik-basin strata move westward with rates decreasing away from the Pamir, the most external Babatag backthrust currently absorbs the highest shortening (~6 mm/yr) as it has done in the past (>20 km). The Ilyak fault accommodates ~5-8 mm/yr, eastward-increasing slip; rates decay sharply across the fault, suggesting a locking depth of <1 km - possibly creep. At least 10 mm/yr uplift and westward motion occur across the Tajik-depression-Pamir transition, including the sinistral Darvaz fault zone, likely outlining a crustal-scale ramp. The Hoja Mumin salt fountain is spreading laterally at >300 mm/yr.

Megathrust earthquakes impose changes of differential stress and pore pressure in the lithosphere-asthenosphere system that are transiently relaxed during the postseismic period primarily due to afterslip, viscoelastic and poroelastic processes. Especially during the early postseismic phase, however, the relative contribution of these processes to the observed surface deformation is unclear. To investigate this, we use geodetic data collected in the first 48 days following the 2010 Maule earthquake and a poro-viscoelastic forward model combined with an afterslip inversion. This model approach fits the geodetic data 14% better than a pure elastic model. Particularly near the region of maximum coseismic slip, the predicted surface poroelastic uplift pattern explains well the observations. If poroelasticity is neglected, the spatial afterslip distribution is locally altered by up to ±40%. Moreover, we find that shallow crustal aftershocks mostly occur in regions of increased postseismic pore-pressure changes, indicating that both processes might be mechanically coupled