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The Pamir and Hindu Kush are examples of a puzzling collision system where a complex junction of colliding lithospheric plates coexists with intermediate depth seismicity at 300 km. In this study, we constructed a new tomography model using travel time data from local events recorded by the TIPAGE (Tien Shan--Pamir Geodynamic program) network. In addition to the P- and S-wave velocities down to 200 km, we derived the azimuthal anisotropy. The velocity anomalies were consistent with the results of previous studies. In the crust, the velocity structure and anisotropy directions were mainly oriented along major suture zones. At depths of 80-120 km, a narrow low-velocity anomaly coinciding with the distribution of deep seismicity was interpreted as a trace of entrained crustal material by the dipping lithosphere. The anisotropy directions at these depths were mainly oriented northwest-southeast and were interpreted as indicating the direction of the motion of colliding plates. The difference in the magnitude of anisotropy south and north of the Pamir seismic zone suggests that the lithosphere coming from the south possesses less anisotropy than that of the Asian plate. The local tomography model was supplemented by previously computed regional tomography that expanded the area both laterally and axially. Beneath the Pamir, both continental plates coming from the north and south form a drop-shaped anomaly that will possibly delaminate in time. Beneath the Hindu Kush, we could clearly trace a continuous almost vertical subduction of the Katawaz block from the south. Thus, the continental collision beneath the Pamir and subduction beneath the Hindu Kush are separate processes with different rates and directions of plate movement. Key words: Pamir, Hindu Kush, seismic tomography, anisotropy, continental collision, subduction. Le Pamiretl'Hindu Kush sont des exemples d'un systeme enigmatiquedecollision dans lequel coexistent une jonction complexe de plaques lithospheriques convergentes et une sismicite de profondeur intermediaire, a 300 km. Nous avons construit un nouveau modele tomographique en utilisant des donnees de temps de trajets d'evenements locaux enregistres par le reseau TIPAGE (programme geodynamique Tien Shan-Pamir).En plusdevitesses des ondesP etSjusqu'a 200 kmde profondeur, nous avons determine l'anisotropie azimutale. Les anomalies de vitesse concordent avec les resultats d'etudes anterieures. Dans la croute, la structure de vitesses et les directions d'anisotropie sont principalement orientees parallelement a des zones de suture majeures. A des profondeurs de 80-120 km, une etroite anomalie de faible vitesse coincidant avec la repartition de la sismicite profonde est interpretee comme representant la trace de materiau crustal entraine par la lithosphere plongeante. Les directions d'anisotropie a ces profondeurs sont principalement nord-ouest-sud-est et indiqueraient la direction de deplacement de plaques convergentes. La difference de magnitude de l'anisotropie au sud et au nord de la zone sismique du Pamir donne a penser que la lithosphere venant du sud presente une moins grande anisotropie que la plaque asiatique. Au modele tomographique local s'ajoutent des donnees de tomographie regionale obtenues anterieurement qui elargissent la region tant lateralement qu'axialement. Sous le Pamir, les deux plaques continentales venant du nord et du sud forment une anomalie en forme de larme qui pourrait se delaminer a l'avenir. Sous l'Hindu Kush, nous pouvons clairement suivre la subduction continue quasi verticale du bloc de Katawaz en provenance du sud. Ainsi, la collision continentale sous le Pamir et la subduction sous l'Hindu Kush sont des processus distincts caracterises par des vitesses et directions de deplacement des plaques differentes. [Traduit par la Redaction] Mots-cles : Pamir, Hindu Kush, tomographie sismique, anisotropie, collision continentale, subduction., Introduction Continental collision isa geodynamic process that leads to complex geological and geophysical signatures in the crust and upper mantle. Convergent displacements of large continental plates are responsible for the [...]

Rotation of rigid blocks within continental interiors far from the plate convergence boundary is an unusual process, the dynamics of which is not clear. The Tarim block, as a rigid Precambrian block in central Asia, is surrounded by the Tibetan–Pamir plateau to the south and Tian Shan mountains to the north. Numerous geophysical data suggested that the Tarim block experienced significant clockwise rotation in the Cenozoic. Meanwhile, contrasting deformation patterns and associated topographic responses were observed between the western–central and eastern Tian Shan. The relationship among the India–Asia collision, Tarim rotation, and Tian Shan responses are poorly constrained. Here, a series of large-scale, high-resolution 3-D numerical models were constructed. The model results reveal that the collision of the indenting Indian lithosphere with the southwestern rim of the Tarim block triggers clockwise rotation of the Tarim block. Further on, the Tarim rotation produces differential deformation responses along the strike of Tian Shan, that is convergence-induced higher compression and strong uplifting in central Tian Shan but divergence-induced less compression and moderate uplifting in eastern Tian Shan. Thus, the Tarim rotation serves as an indispensable linkage between the Tibetan plateau evolution and the far-field Tian Shan activation. [ABSTRACT FROM AUTHOR]

A sequence of three strong (M W7.2, 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 foreshock, main shock 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, that is 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 main shock areas but the initial one exhibited foreshock activity, which was not modulated by the occurrence of the earlier earthquakes. Modelling of the static Coulomb stress changes indicates that aftershock triggering occurred over distances of ≤90 km on favourably 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 main shock may have increased nearby fault permeability, and facilitated fluid migration into the mature fault zones, eventually triggering the later large earthquakes. [ABSTRACT FROM AUTHOR]