Long-term slow slip events along the Nankai trough subduction zone after the 2011 Tohoku earthquake in Japan

Abstract

The global navigation satellite system (GNSS) network in Japan has detected transient crustal deformation in regions along the Nankai trough subduction zone in southwest Japan from approximately 2013, after the 2011 Tohoku earthquake. Using the GNSS data, we estimated the spatiotemporal evolution of long-term aseismic slip along the Nankai trough. The result indicates that aseismic slip has occurred on the plate interface in the Bungo, northern Miyazaki, and southern Miyazaki regions, southwest Japan. The estimated time evolution between October 2013 and April 2015 shows the simultaneous occurrence of northern and southern Miyazaki slow slips with different durations followed by a Bungo slow slip in 2014. A southern Miyazaki slow slip occurred from approximately July 2015, which was followed by a northern Miyazaki slow slip and a Bungo slow slip in 2016. The 2016 Bungo slow slip occurred in a shallow area that did not slip at the time of the 2014 Bungo slow slip. The two different rupture processes from 2013 to 2015 and from 2015 to 2016 may be an important clue toward understanding subduction tectonics in southwest Japan. These interplate slow slip events are changing the stress state in favor of the occurrence of Nankai and Hyuga-nada earthquakes together with Tokai and Kii channel slow slips, which have been occurring since approximately 2013 and 2014, respectively.Graphical abstractWe investigated aseismic slip in Shikoku and Kyushu islands using GNSS data and found out that Bungo, northern Miyazaki, and southern Miyazaki slow slips were occurring. The top figure shows the estimated aseismic slips with arrows indicating aseismic slip vectors. The two different rupture processes from 2013 to 2015 and from 2015 to 2016 may be an important clue toward understanding subduction tectonics in southwest Japan.