Abstract
Post-earthquake analysis using radar interferometry has become a standard procedure for assessing earthquakes with significant damages. Sentinel-1 satellite provides 6-day revisiting time, and Sentinel-2 data has 5-day revisiting time and the same viewing angle that can enable the detection of changes in surface/land-cover after a major seismic event. Using Sentinel-2 alongside Sentinel-1 could bring new benefits when gathering spatial information about a post seismic event. In our study, we focused on analyzing a major earthquake, which occurred on 14 November 2016 with 7.8 magnitude near the city of Kaikōura, New Zealand, using both Sentinel-1 radar images and Sentinel-2 optical data. Hundreds of landslides were reported as a result of this earthquake. In addition, substantial land uplift was detected in some parts of the sea shore. Differential interferometry allowed us to estimate earthquake strength analyzing the distribution of absolute vertical displacement values. Sentinel-2 pre- and post-earthquake images were used in order to assess land-cover changes and automatically detect landslides, which occurred after the earthquake. Linking DInSAR results with Sentinel-2 change detection analysis helped us to get a more complex perspective on the earthquake impact, to create landslide inventory maps, and to subsequently develop workflows for quick post-event analysis.
Highlights
Earthquake impact assessment and subsequent landslide mapping have become the crucial tasks that follow a seismic event
We demonstrate how differential synthetic aperture radar interferometry (DInSAR) results derived from Sentinel-1 data and Sentinel-2 change detection analysis can be used to develop workflows for quick post-event analysis, to create landslide inventory maps, and overall, to get a complex perspective on the earthquake impacts
Changes in vegetation cover were mapped using two scenes of Sentinel-2 and, together with the vertical displacement obtained from an interferometric pair of Sentinel-1 images, served as a basis for landslide analysis triggered by the earthquake
Summary
Earthquake impact assessment and subsequent landslide mapping have become the crucial tasks that follow a seismic event. A strong earthquake can potentially trigger thousands of landslides. The spatial extent that is affected by a strong earthquake is very big. In the case of the Kaikōura earthquake, up to hundreds of square kilometers were affected, which made it hard to quickly assess landslides using traditional mapping techniques. Radar interferometry offers substantial operational advantages over optical sensors, such as weather independence. Since the introduction of the ESA’s Sentinel-1B satellite, radar data has been made freely available at 6-day revisit time. Radar data has been already successfully used to assess earthquake triggered landslides [1], usually L-band radar data (e.g., ALOS-PALSAR, JAXA) were used. L-band radar data has an advantage over C-band, as it penetrates through vegetation and can get better coherence values
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