Abstract
Extensional earthquakes in the Tibetan Plateau play an important role in the plateau’s orogenic evolution and cause heavy seismic hazard, yet their mechanisms remain poorly known, in particular in harsh northern Tibet. On 25 June 2020, a Mw 6.2 earthquake struck Yutian, Xinjiang, offering us a rare chance to gain insights into its mechanism and implications in the Tibetan extension. We used both descending and ascending Sentinel-1 images to generate coseismic deformation associated with this event, which indicates a typical extensional mechanism with a maximum subsidence displacement of 25 cm and minor uplift. The causative fault constrained with interferometric synthetic aperture radar (InSAR) data based on a finite fault model suggests that the fault plane has a strike of 186.4° and westward dip of 64.8°, and the main rupture is concentrated at a depth of 3.6–10.8 km with a peak slip of 0.85 m. Our source model indicates that the 2020 Yutian event ruptured an unknown high-angle blind normal fault with N–S striking. The total released geodetic moment yields 2.69 × 1018 N·m, equivalent to Mw 6.23. We used dense interseismic global positioning system (GPS) measurements to reveal an approximate 7 mm/yr extensional motion in the Yutian region, but it still does not seem large enough to support high local seismicity for normal events within 12 years, i.e., Mw 7.1 in 2008, Mw 6.2 in 2012, and this event in 2020. Combined with Coulomb stress change modeling, we speculate that the seismicity in Yutian is related to the lower lithospheric dynamics.
Highlights
The Tibetan Plateau, with an average altitude of 5000 m over a lateral area of thousands of kilometers, exhibits complex large-scale intercontinental deformation and serves as a prototype for intracontinental orogenic process on the Earth (e.g., [1,2,3], Figure 1)
Two pairs of terrain observation with progressive scans (TOPS) images from the C-band Sentinel-1 radar satellite, operated by the European Space Agency (ESA), were employed to derive the coseismic displacement associated with the Yutian event
To refine the quality of interferograms, we considered the atmospheric error corrected by the Generic Atmospheric Correction Online Service (GACOS) for interferometric synthetic aperture radar (InSAR) [35]
Summary
The Tibetan Plateau, with an average altitude of 5000 m over a lateral area of thousands of kilometers, exhibits complex large-scale intercontinental deformation and serves as a prototype for intracontinental orogenic process on the Earth (e.g., [1,2,3], Figure 1). On 25 June 2020 at 21:05 UTC (13:05 local time), a Mw 6.3 earthquake (Ms 6.4 according to the China Earthquake Networks Center (CENC]) struck Yutian County, Xinjiang Province, China recorded by the US Geological Survey (USGS) earthquake catalogue This event occurred in a junction area of the Altyn Tagh, Karakax, and Kunlun fault systems in northwestern Tibet, 164 km south of Yutian County. Note that this junction region has suffered high-level seismicity in recent times, consisting of one strike-slip event (Mw 6.9 in 2014) and three normal-faulting events (Mw 7.1 in 2008, Mw 6.2 in 2012, and Mw 6.2 in 2020) reported from the GCMT archive (Figure 1). We carry out Coulomb stress change modeling to explore the seismic behavior in northern Tibet
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