Abstract
The Nyingchi Mw 6.4 earthquake on 17 November 2017 is the first large event since 1950 at the southeast end of the Jiali fault. This event was captured by interferometric synthetic aperture radar (InSAR) measurements from the European Space Agency (ESA) Sentinel-1A radar satellite, which provide the potential to determine the fault plane, as well as the co-seismic slip distribution, and understand future seismic hazards. However, due to the limited magnitude of surface displacements and the strong topography variations, InSAR-derived co-seismic signals are contaminated by strong tropospheric effects which makes it difficult (if not impossible) to determine the source parameters and co-seismic slip distribution. In this paper, we employ the Generic Atmospheric Correction Online Service for InSAR (GACOS) to generate correction maps for the co-seismic interferograms, and successfully extract co-seismic surface displacements for this large event. The phase standard deviation after correction for a seriously-contaminated interferogram reaches 0.8 cm, significantly improved from the traditional phase correlation analysis (1.13 cm) or bilinear interpolation (1.28 cm) methods. Our best model suggests that the seismogenic fault is a NW–SE striking back-thrust fault with a right-lateral strike slip component. This reflects the strain partitioning of NE shortening and eastward movement of the Eastern Tibetan plateau due to the oblique convergence between the Indian and Eurasian plates.
Highlights
On 17 November 2017, a Mw 6.4 earthquake hit the Tibetan plateau, 63 km northeast of Nyingchi, China (Figure 1)
This region has long been characterized as having weak tectonic activity [4,5,6], with a limited number of recorded historical events according to the United States Geological Survey (USGS) and the China Earthquake Administration (CEA)
Tropospheric delays are often correlated with topography, but coupled with strong turbulent signals, which makes it difficult to distinguish them from actual tectonic movements [9,12]
Summary
On 17 November 2017, a Mw 6.4 earthquake hit the Tibetan plateau, 63 km northeast of Nyingchi, China (Figure 1). A limited number of geodetic surveys have been conducted in this region and this is the first large earthquake that has been captured by one of the modern geodetic techniques, SAR interferometry, with the ESA’s Sentinel-1A radar satellite [7] These InSAR measurements provide high spatial resolution co-seismic surface displacements, which can be used to infer the source parameters of seismogenic faults, assess future seismic hazards, and better understand the activity of seismogenic structures. We attempt to correct tropospheric effects on Sentinel-1A interferograms using the Generic Atmospheric Correction Online Service for InSAR (GACOS) developed at Newcastle University, which employs the high-resolution weather model outputs from the European Centre for Medium-Range Weather Forecasts (HRES-ECMWF) to generate high-resolution tropospheric delay maps for InSAR atmospheric correction [9,23] After correction, both ascending and descending interferograms show clearer co-seismic signals than the original ones, which are used to inverse the optimal fault geometry and co-seismic slip model of the Nyingchi event. The slip model is carefully tested by Monte Carlo and checkerboard tests, after which the coulomb stress changes are calculated to assess local seismic impacts
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