Following the 25 April 2015 Nepal earthquake, Sentinel-1A radar acquisitions were used to generate a differential SAR interferogram over the affected region.
The interferogram was produced from Sentinel-1A images acquired on 17 April and 29 April 2015. This time interval includes the main earthquake on 25 April, as well as important aftershocks that occurred in the following days.
Differential SAR interferogram generated from Sentinel-1A acquisitions of 17 and 29 April 2015 over Nepal. The fringe pattern shows earthquake-induced ground deformation in the area around Kathmandu.
The interferogram shows the surface deformation caused by the earthquake. The coloured fringe pattern is produced by changes in the radar signal between the two satellite acquisitions. Each fringe corresponds to a small change in the distance between the satellite and the ground, measured along the satellite line of sight.
In this case, the deformation pattern extended over an area of approximately 100 km by 130 km, with a maximum displacement of more than 1 metre towards the satellite in an area close to Kathmandu.
ESA also reported that the maximum deformation was located only around 17 km from Kathmandu, helping to explain the strong impact of the earthquake in the area.
Why this product matters
A differential interferogram is one of the fastest ways to visualise earthquake-induced ground deformation over a large area.
It does not replace field observations or seismic analysis, but it provides an independent measurement of how the ground moved during the event. This can support:
- rapid understanding of the deformation pattern;
- comparison with earthquake source models;
- identification of uplift and subsidence areas;
- preparation of further InSAR analysis;
- communication of the spatial extent of the event.
For the Nepal earthquake, the Sentinel-1A interferogram made it possible to observe a large-scale deformation pattern around Kathmandu shortly after the event. Similar analyses are now a core part of the way satellite radar data can support geohazards response and scientific interpretation.
From interferogram to operational services
This example also shows why platforms such as GEP are useful.
Producing an interferogram requires access to suitable SAR acquisitions, processing tools, reference data and computing resources. Making the result useful also requires sharing, visualisation and interpretation.
GEP supports this type of workflow by helping users access EO data and processing services, and by providing an environment where geohazards products can be generated, shared and reused.
Image credit: Differential SAR interferogram generated from Sentinel-1A data by IREA-CNR. Contains Copernicus Sentinel data, 2015.