Abstract. The spatial distribution of the coseismic displacements that occurred along the Futagawa fault during the 2016 Kumamoto earthquake of M w 7.0 was estimated using airborne light detection and ranging (lidar) data. In this study, a pair of digital surface models (DSMs) obtained from the high-density lidar data before and after the mainshock on 16 April 2016 were used. A window matching search approach based on the correlation coefficient between the two DSMs was used to estimate the geodetic displacement in the near-field region. The results showed good agreements with the geodetic displacements calculated from strong-motion acceleration records and coincided with the fault line surveyed by the Geological Survey of Japan.
IntroductionOn 14 April 2016, an M w 6.2 earthquake struck Kumamoto Prefecture, Japan, at 21:26 JST. The epicenter was located at the end of the Hinagu fault at a shallow depth. After approximately 28 h (at 01:25 on 16 April 2016), another earthquake of M w 7.0 struck the Futagawa fault, which is near the Hinagu fault. The first event was designated as the foreshock and the second one as the mainshock. Both the events occurred in the town of Mashiki (with a population of approximately 33 000), which is located to the east of Kumamoto City (with a population of approximately 735 000). Many aftershocks followed these events, and as of 6 September, 4 months after the foreshock, the total number of aftershocks (larger than M w 3.5) is 272. This number is the largest among the recent inland (crustal) earthquakes in Japan (Japan Meteorological Agency, 2016). This Kumamoto earthquake sequence triggered secondary effects such as landslides and liquefaction and caused extensive damage to lifeline systems, buildings, bridges, and transportation structures. A total of 8550 buildings, mostly in Kumamoto Prefecture, were seriously damaged or collapsed, and 50 human lives were lost, mostly because of landslides or the collapse of buildings (Cabinet Office of Japan, 2016).Soon after the occurrence of the foreshock, various satellites and airborne remote sensing technologies were employed to monitor crustal movements and various damages . The Japan Aerospace Exploration Agency (JAXA) carried out extensive monitoring of the source area using the PALSAR-2 sensor on board ALOS-2 satellite. Interferometric synthetic aperture radar (InSAR) analysis using a pair of imagery data obtained from PALSAR-2 before (pre-event data) and after (postevent data) the mainshock showed the line-of-sight (LOS) displacements to the satellite direction (Geospatial Information Authority of Japan, 2016). Using the pre-event data (30 November 2015, 7 March 2016 and the co-event data (7 March, 18 April 2016) from PALSAR-2, the authors of this paper calculated the spatial coherence values (International Charter, 2016), which could highlight the extensive landslides and severe damages to buildings along the Futagawa fault line.After the Kumamoto earthquake, government agencies and aerial survey companies in Japan conducted several ...