Active deformation across the western Kunlun range, from NW Tibet to the SW Tarim Basin (China), using Sentinel-1 InSAR data

The western Kunlun (WK) region is characterized by weak to moderate seismicity. However the recent Pishan earthquake (Mw 6.4), which ruptured in 2015 a blind thrust of the Pishan anticline at the front of the WK range, points out the potential for larger earthquakes in this region. Previous studies highlighted the existence of a major thrust sheet, connected at depth to the fault segment that likely ruptured in 2015, spanning ~ 150-180 km, between the western Kunlun front of the chain and another active deformation front further north within the Tarim basin (Mazar Tagh ridge). This active thrust sheet has a probable slip-rate of ~ 0.5-2.5 mm/yr as derived from geological and morphotectonic indicators. Would this structure be fully locked during the interseismic period, it could lead to earthquakes of Mw ~ 8 given the rupture width under consideration.

 

The present work aims at studying slip partitioning and interseismic loading in this area. GPS data within the Tarim basin lack constraints due to relatively high uncertainties and to a sparse spatial distribution. We present here an InSAR time-series analysis which provides a high space and time resolution to monitor the main active structures. This analysis is however challenging due to sand dunes and vegetation, which alter the coherence of the signal, and to topographic gradients inducing atmospheric phase delays where tectonic deformation is expected. We thus rely for this study on the ForM@Ter LArge-scale multi-Temporal Sentinel-1 InterferoMetry (FLATSIM) service (Thollard et al., 2021) to process the 5 ascending and 5 descending tracks covering our area. We compare parametric signal decompositions and principal/independent components analysis in order to separate tectonic from non-tectonic signals. We finally derive a regional linear velocity map representative of tectonic motions, masking unwrapping errors, atmospheric residuals, and remaining non-tectonic signals.

 

These first InSAR-based velocity results obtained along the WK-Tarim area allow to discuss the potential locking of the wide thrust sheet, in the context of known moderate ruptures. It also brings new insights into the possible connections between compressive structures and large strike-slip fault systems from the WK front to northwestern Tibet. In the complex junction area of the Western Kunlun, Altyn Tagh and Karakorum faults, several strike-slip and normal faults could be identified as active over the observation period (2015-2021), with slip rates consistent with the ones derived from morphotectonic studies (~ 4-5 mm/yr), and some faults likely showing creep (Longmu-Gozha Co fault system). These results may contribute to better understand the occurrence of normal faulting earthquakes in-between the identified strike-slip segments, such as the 2020 Mw 6.3 Yutian earthquake.