GRSG Conference 2022: Orbit to Outcrop

Poster Title: Monitoring post-seismic hillslope deformation using InSAR

Author: Kun He


Strong earthquakes not only induce co-seismic mass wasting but also exacerbates the shear strength of hillslope materials and cause higher landslide susceptibility in the subsequent years following the earthquake. Previous studies have investigated post-seismic landslide activity mainly by using landslide inventories.

However, landslide inventories do not provide information on deformation given by ground shaking and limit our observations with only failed hillslopes. As a consequence, we lack comprehensive, quantitative analysis revealing how hillslopes behave in post- seismic periods. Satellite-based synthetic aperture radar interferometry (InSAR) could fill this gap and provide millimeter-scale measurements of ground surface displacements that can be used to monitor hillslope deformation.

Here we use the Persistent Scatterer Interferometry technique to monitor pre- and post- seismic hillslope deformation for the area affected by the Mw 6.9 Nyingchi, China earthquake that occurred on the 18th of November 2017 in addition to several other moderate to strong ones (Mw>5) occurred after the Nyingchi earthquake.

We use Copernicus Sentinel-1 satellite data acquired between 2016 and 2022 to examine hillslope deformations and generate deformation time series for five time windows representing three intra-seismic windows as well as pre- and post- seismic periods associated with those earthquakes that hit the same area under consideration.

Based on these five different deformation time series, we identify actively deforming and stable hillslopes over the study area and monitor their evolution through the 6-year time window. Results show that hillslopes gain elevated deformation rates following the Mw 6.9 Nyingchi earthquake compared to its pre-seismic counterpart and then 1.7 years after the earthquake, surface deformations decrease again.

Although several other earthquakes of magnitude between 5 and 5.1 occurred in 2019, 2020 and 2021, none of them influences hillslope deformations as significant as the main earthquake does. Overall, our results show that after a series of earthquakes occurred in the last five years in the study area, the deformation rates have not been returned to the pre-seismic level yet.