A Systematic Study of Earthquake Detectability Using Sentinel-1 TOPS InSAR

Gareth J. Funning, & Astrid Garcia

Submitted August 15, 2017, SCEC Contribution #7854, 2017 SCEC Annual Meeting Poster #098

We report on our efforts to study global seismicity with Sentinel-1 TOPS data between April 2015 and December 2016. We searched the USGS/NEIC earthquake catalogue to identify earthquakes with epicenters located on land masses with deformation that was potentially detectable using InSAR. (As event detectability for a given hypocentral depth depends on event size, we select events in the following size and depth ranges: 6.0>Mw≥5.5, depth<10 km; 7.0>Mw≥6.0, depth<20 km; Mw≥7.0, depth<25 km.) Neglecting aftershocks or foreshocks that occurred within the interferogram intervals for the corresponding mainshocks, we identified 35 earthquakes that fit these criteria. Using the ISCE processing software, we then systematically processed interferograms for these events, prioritising image pairs with the shortest possible temporal baselines.

We find that we can identify deformation signals attributable to earthquakes in a little over half of the events tested (20 out of 35 events). A further 14% of events (5 out of 35) have deformation patterns that may be due to earthquakes, but require additional processing and/or modelling for verification. 29% of events (10 out of 35) could not be identified from their interferograms. The majority of failed detections were due to interferogram decorrelation. This was particularly apparent in heavily vegetated tropical areas, such as Central America or northern South America, where 24 day (and in some cases even 12 day) repeat coverage is insufficient to achieve good coherence with Sentinel’s C-band radars. Heavy decorrelation was also observed over ocean islands, where image acquisitions have been infrequent and/or SLC data can be missing from the archive, allowing only long timespan interferograms to be processed.

At present, the largest earthquake that we have not detected is a Mw7.0 event whose epicenter was located on Melampa Island, Vanuatu (28 April 2016). We suggest that this could be considered an estimate of the ‘magnitude of completeness’ (i.e. the magnitude above which all events are detected) for global earthquakes studied using Sentinel-1 data. In order to lower this magnitude to Mw6.0 or below, we suggest that more frequent acquisitions will likely be necessary over tropical continental areas and ocean islands near plate boundaries in future.


Key Words
Earthquake, InSAR, Sentinel-1

Citation
Funning, G. J., & Garcia, A. (2017, 08). A Systematic Study of Earthquake Detectability Using Sentinel-1 TOPS InSAR. Poster Presentation at 2017 SCEC Annual Meeting.


Related Projects & Working Groups
Tectonic Geodesy