Surface deformation associated with the 2015 Mw 8.3 Illapel earthquake revealed by satellite-based geodetic observations and its implications for the seismic cycle

In this study, we present inter-, co- and post-seismic displacements observed in the 2015 Illapel earthquake area by Global Positioning System (GPS) and Synthetic Aperture Radar Interferometry (InSAR). RADARSAT-2, ALOS-2 and Sentinel-1A interferograms capture the co- and post-seismic displacements due to the Illapel earthquake. Based on a layered Earth structure, we modeled both co- and post-seismic faulting behaviors on the subduction interface of central Chile. The best-fit model shows that the coseismic rupture broke a 200km×200km area with a maximum slip of 10 m at a depth of 20 km. Two distinct slip centers, likely controlled by local ramp-flat structure, are revealed. The total coseismic geodetic moment is 2.76×1021Nm, equivalent to a moment magnitude 8.3. The accumulated afterslip in the first two months after the mainshock is observed on both sides of the coseismic rupture zone with both ascending and descending Sentinel-1A interferograms. A limited overlap zone between co- and post-seismic slip models can be observed, suggesting partitioning of the frictional properties within the Illapel earthquake rupture zone. The total afterslip releases ∼5.0×1020Nm geodetic moment, which is equivalent to an earthquake of Mw 7.7. The 2010 Mw 8.8 Maule earthquake that occurred ∼400 km away from the Illapel earthquake epicenter could have exerted certain effects on the seismic cycle of the Illapel earthquake area. The seismic records from 2000 to 2015 imply that the rate of annual seismic moment release in the Illapel earthquake area dropped from 0.4 to 0.2×1019Nm/yr after the Maule earthquake. Based on the forward modeling with the best-fit slip models determined in this study, we reproduce the local surface displacements before, during and after the Illapel earthquake. A rough deformation cycle, 105±29yr, calculated by using the coseismic displacements and interseismic rate is basically identical with the revisit interval of M8 events in the adjacent areas of the Illapel earthquake, suggesting that elastic rebound theory is applicable for the long-term prediction in this region.