10:45 AM - 12:15 PM
[SSS13-P01] Three-dimensional surface displacement of the 2016 Kumamoto earthquake using differential LiDAR in Komori, Nishihara Village, Kumamoto Prefecture
Keywords:2016 Kumamoto earthquake, Nishihara Village, LiDAR, Slip partitioning
The mainshock (Mw 7.0) of the 2016 Kumamoto earthquake sequence occurred on April 16, 2016. This earthquake caused the appearance of a wide range of surface ruptures, with the Futagawa fault as the main fault (Fujiwara et al., 2016). Other active faults surrounding the Futagawa fault were activated in this earthquake (e.g., Suizenji and Idenokuchi faults). Among these, the Idenokuchi fault is considered to be involved in slip partitioning by Toda et al. (2016). Slip partitioning has been described, for example, in the Kokoxili earthquake (King et al., 2005), and is considered to be an important phenomenon for understanding the displacement hazard and tectonic geomorphology.
Recently, InSAR, LiDAR, and optical image analysis have made it possible to obtain information on coseismic displacement. In this study, we evaluate the slip partitioning quantitatively by differential LiDAR at the section where the Futagawa and Idenokuchi faults run parallel, where the slip partitioning is considered to have occurred (Toda et al., 2016).
In this study, differential LiDAR analysis (Mukoyama et al., 2011; Shinagawa et al., 2013; Ishimura et al., 2019) was applied. This analysis was performed using LiDAR data from two periods measured in January-February 2013 and May 8, 2016, to obtain the three components of displacement (vertical, east-west, and north-south) that occurred over a period of approximately three years. The analysis covered an area of about 2.5 km from east to west and 3.5 km from north to south in the eastern part of the Futagawa fault. Because the strike of the Futagawa fault in the study area is N57°E, the horizontal components were recalculated in parallel and perpendicular directions to the fault. These results are compared with those of field surveys (Kumahara et al., 2022), and slip partitioning is discussed here.
In the study area, one surface rupture is recognized along the Futagawa fault, and three surface ruptures are recognized along the Idenokuchi fault. In all of the fault locations, discontinuities in 3D displacements are consistent with those observed in the field survey. In addition, some surface ruptures that were not recognized in the field survey were also estimated to occur in the event.
Overall, 3D displacement tended to be larger than that measured in the field. Along the Futagawa fault, the 3D displacement indicates a right lateral displacement of about 2 m, compared to about 1.5 m in the field measurements. This is thought to be due to the inclusion of off-fault displacement (broad displacement) in the 3D displacement in addition to on-fault displacement (the value mainly measured in the field survey) (e.g., Scott et al., 2018). On the other hand, along the Idenokuchi fault, field measurements recorded a north-down displacement of nearly 2 m, but the 3D displacements are a little noisy due to surface failures. In a long distance, the Idenokuchi fault has a displacement of about 1 m north-down, but locally, as in the field measurements, the displacement may have been larger due to the combination of the slope movement and fault displacement.
Slip partitioning, as shown in the schematic diagram by Toda et al. (2016), was resolved on each fault, with a right lateral component on the Futagawa fault and a north-down component on the Idenokuchi fault. This means that the oblique displacement at deep is well divided into lateral and vertical components. This kind of information is important for considering the conditions under which slip partitioning occurs (subsurface fault geometry, strength, and physical properties of the faults).
Recently, InSAR, LiDAR, and optical image analysis have made it possible to obtain information on coseismic displacement. In this study, we evaluate the slip partitioning quantitatively by differential LiDAR at the section where the Futagawa and Idenokuchi faults run parallel, where the slip partitioning is considered to have occurred (Toda et al., 2016).
In this study, differential LiDAR analysis (Mukoyama et al., 2011; Shinagawa et al., 2013; Ishimura et al., 2019) was applied. This analysis was performed using LiDAR data from two periods measured in January-February 2013 and May 8, 2016, to obtain the three components of displacement (vertical, east-west, and north-south) that occurred over a period of approximately three years. The analysis covered an area of about 2.5 km from east to west and 3.5 km from north to south in the eastern part of the Futagawa fault. Because the strike of the Futagawa fault in the study area is N57°E, the horizontal components were recalculated in parallel and perpendicular directions to the fault. These results are compared with those of field surveys (Kumahara et al., 2022), and slip partitioning is discussed here.
In the study area, one surface rupture is recognized along the Futagawa fault, and three surface ruptures are recognized along the Idenokuchi fault. In all of the fault locations, discontinuities in 3D displacements are consistent with those observed in the field survey. In addition, some surface ruptures that were not recognized in the field survey were also estimated to occur in the event.
Overall, 3D displacement tended to be larger than that measured in the field. Along the Futagawa fault, the 3D displacement indicates a right lateral displacement of about 2 m, compared to about 1.5 m in the field measurements. This is thought to be due to the inclusion of off-fault displacement (broad displacement) in the 3D displacement in addition to on-fault displacement (the value mainly measured in the field survey) (e.g., Scott et al., 2018). On the other hand, along the Idenokuchi fault, field measurements recorded a north-down displacement of nearly 2 m, but the 3D displacements are a little noisy due to surface failures. In a long distance, the Idenokuchi fault has a displacement of about 1 m north-down, but locally, as in the field measurements, the displacement may have been larger due to the combination of the slope movement and fault displacement.
Slip partitioning, as shown in the schematic diagram by Toda et al. (2016), was resolved on each fault, with a right lateral component on the Futagawa fault and a north-down component on the Idenokuchi fault. This means that the oblique displacement at deep is well divided into lateral and vertical components. This kind of information is important for considering the conditions under which slip partitioning occurs (subsurface fault geometry, strength, and physical properties of the faults).