Seasonal and transient surface displacements in the Kumamoto area, Japan, associated with the 2016 Kumamoto earthquake: implications for seismic-induced groundwater level change

The 2016 Kumamoto earthquake sequence on April 14 (M(w)6.2) and April 16 (M(w)7.0) altered the regional groundwater level. To better understand the relationship between groundwater level change and surface displacement, we estimated surface displacement in the Kumamoto area (Japan) using persistent scatterer interferometry from 19 ALOS/PALSAR images acquired between January 7, 2007 and March 5, 2011, 28 ALOS-2/PALSAR-2 images acquired between April 17, 2016 and December 10, 2018, and 113 Sentinel-1 images acquired between May 26, 2016 and December 30, 2018. Our estimation shows that transient surface displacement occurred following the 2016 Kumamoto earthquake sequence, together with seasonal surface displacement that was not detected from the 2007-2011 images. We suggest that a portion of the transient displacement occurred via groundwater drawdown through new ruptures that formed owing to the 2016 Kumamoto earthquake sequence and sediment compaction. Seasonal surface displacements detected after the 2016 Kumamoto earthquake sequence are linked to groundwater level variations.