Present-day orogenic processes in the western Kalpin nappe explored by interseismic GNSS measurements and coseismic InSAR observations of the 2020 Mw 6.1 Kalpin event

As the largest and most active intracontinental orogenic belt on Earth, the Tien Shan (TS) is a natural laboratory for understanding the Cenozoic orogenic processes driven by the India-Asia collision. On 19 January 2020, a M-w 6.1 event stuck the Kalpin region, where the southern frontal TS interacts with the Tarim basin. To probe the local ongoing orogenic processes and potential seismic hazard in the Kalpin region, both interseismic and instantaneous deformation derived from geodetic observations are used in this study. With the constraint of interseismic global navigation satellite system (GNSS) velocities, we estimate the decollement plane parameters of the western Kalpin nappe based on a 2-D dislocation model, and the results suggest that the decollement plane is nearly subhorizontal with a dip of similar to 3 degrees at a depth of 24 km. Then, we collect both Sentinel-1 and ALOS-2 satellite images to capture the coseismic displacements caused by the 2020 Kalpin event, and the interferometric synthetic aperture radar (InSAR) images show a maximum displacement of 7 cm in the line of sight near the epicentral region. With these coseismic displacement measurements, we invert the source parameters of this event using a finite-fault model. We determine the optimal source mechanism in which the fault geometry is dominated by thrust faulting with an E-W strike of 275 degrees and a northward dip of 11.2 degrees, and the main rupture slip is concentrated within an area 28.0 km in length and 10.3 km in width, with a maximum slip of 0.3 m at a depth of 6-8 km. The total released moment of our preferred distributed slip model yields a geodetic moment of 1.59 x 10(18) N.m, equivalent to M-w 6.1. The contrast of the decollement plane depth from interseismic GNSS and the rupture depth from coseismic InSAR suggests that a compression still exists in the Kalpin nappe forefront, which is prone to frequent moderate events and may be at risk of a much more dangerous earthquake.

Automated summary

The Tien Shan is the largest and most active intracontinental orogenic belt on Earth, providing a natural laboratory for understanding Cenozoic orogenic processes driven by the India-Asia collision. A Mw 6.1 earthquake that struck the Kalpin region on January 19, 2020 has highlighted the ongoing orogenic processes and potential seismic hazard in the area. Analysis of geodetic observations has revealed a nearly subhorizontal decollement plane in the region, indicating a risk of frequent moderate earthquakes in the future.