
Tibet Earthquake: Mapping Ground Deformation with Sentinel-1
On January 7, a magnitude 7.1 earthquake struck Tibet, triggering significant ground displacement. To analyze the surface deformation, I processed Sentinel-1 SLC data from January 5 and January 17 using SNAP, generating an interferogram that reveals how the earthquake reshaped the landscape. (Figure 1).
Each fringe (the variation in color in the interferogram) represents a specific displacement along the satellite’s line-of-sight (LOS), which depends on the radar wavelength (5.546 cm for Sentinel-1 C-band) and the incidence angle of the satellite (which varies across the swath). As an approximation, each fringe corresponds to 2.8 cm of displacement along LOS.

The total ground movement is estimated by counting the number of fringes and applying the appropriate correction based on satellite geometry, which includes factors such as the incidence angle, swath position, and local topography. In the figure, we can identify three primary deformation lobes: the right lobe, spanning approximately 70 km and containing 10 fringes, which, after adjusting for the incidence angle, corresponds to a total ground movement of ~36.2 cm; the left lobe, extending for about 50 km with 11 fringes, indicating a total displacement of ~40 cm; and the lower lobe, covering 15 km and containing 5 fringes, corresponding to a displacement of approximately ~16.8 cm. At the center of the interferogram, the fringe pattern becomes highly dense and complex, making it difficult to precisely quantify the displacement.
Determining the exact displacement in centimeters is a complex task, as various factors influence the final calculation, including the satellite’s observation geometry, precise orbit, local terrain conditions, and potential noise in the interferometric signal. While the values presented may not be exact, this image provides a striking visualization of the earthquake’s impact, illustrating the significant deformation that occurred. More importantly, it highlights how the Earth is continuously shifting due to active fault systems, offering crucial insights into the ongoing tectonic activity shaping the region (Figure 2).

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Written by Giovanna Palumbo
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