A systematic study of earthquake detectability using Sentinel-1 Interferometric Wide-Swath data

The Sentinel-1 mission comprises two synthetic aperture radar satellites, each with a 12-d orbital repeat, orbiting 6 d apart within a narrow tube. The mission design promises the ability to respond quickly to earthquakes with InSAR, and to facilitate production of interferograms with good interferometric correlation globally. We report on our efforts to study global seismicity using Sentinel-1 Interferometric Wide-Swath data between April 2015 and December 2016. We select 35 potentially detectable terrestrial earthquakes in the range 5.5 <= M-w <= 7.8 on the basis of their locations, depths and magnitudes, and process the first post-event interferogram with the shortest possible time span for each using the ISCE software. We evaluate each interferogram for earthquake deformation signals by visual inspection. We can identify deformation signals attributable to earthquakes in 18 of these interferograms (51 per cent); a further six interferograms (17 per cent) have ambiguous interferometric phase affected by tropospheric noise. 11 events (31 per cent) could not be identified from their interferograms. The majority of these failed detections were due to interferogram decorrelation, particularly apparent for earthquakes that occurred between 15 degrees N and 15 degrees S, where climate conditions promote dense vegetation. The majority of the ambiguous interferograms are affected by tropospheric noise, suggesting that techniques to mitigate such noise could improve detection performance. The largest event we do not detect with Sentinel-1 data is a M(w)7.0 earthquake that occurred in Vanuatu in April 2016; we also fail to detect the 2016 M(w)6.2 Kurayoshi earthquake in one out of two possible 24-d interferograms. We propose these as upper and lower estimates on the magnitude of completeness for earthquakes studied with Sentinel-1 data; to lower the magnitude of completeness we suggest that more frequent (e.g. 6-d) recurrence may be necessary in low latitude areas.