Simulation of soil liquefaction distribution in downtown Mashiki during 2016 Kumamoto earthquake using nonlinear site response

Abstract

Several sites located between Road No.28 and Akitsu River in downtown Mashiki were liquefied during the mainshock of the 2016 Kumamoto earthquake. According to the building damage survey results, only a few buildings were damaged in areas proximate to the Akitsu River, where liquefaction occurred, however, serious building damage occurred in neighboring regions. Therefore, the effect of soil liquefaction on strong ground motions in Mashiki should be ascertained. Moreover, the distribution of visible and invisible liquefaction is required to be estimated as well. In this study, the distribution of depth of groundwater level in Mashiki was studied, which decreased from 14 to 0 m from northeast to southwest. Thereafter, the nonlinearities of the shallow layers at four borehole drilling sites were identified from the experimental data using the Ramberg–Osgood relationship. Subsequently, the dynamic nonlinear effective stress analysis of the one-dimensional soil column was performed to 592 sites in Mashiki between the seismological bedrock and ground surface to estimate the distribution of strong ground motions during the mainshock. First, the ground motions estimated by the nonlinear analysis corresponded to the ground motions observed at the Kik-net KMMH16. Second, the soil nonlinearity of shallow layers was considerably strong in the entire target area especially in the southern Mashiki, and the PGV distribution was similar to the building damage distribution after the mainshock. Furthermore, the estimated distribution of the soil liquefaction site was similar to the observed results, whereas certain invisible-liquefaction sites were estimated in the north and middle of the target area.

Application of the on-site P-wave earthquake early warning method based on site-specific ratios of S-waves to P-waves to the 2016 Kumamoto earthquake sequence, Japan

“…During the mainshock of the 2016 Kumamoto earthquake, strong ground motions with a PGA larger than 300 cm/s 2 were widely observed in and around the earthquake source fault region (Suzuki et al 2017). Nonlinearity and liquefaction of soil deposits during the mainshock of the 2016 Kumamoto earthquake were reported (e.g., Tsuno et al 2017;Wakamatsu et al 2017;Sun et al 2022). Sun et al (2022) reported that there are several sites showing the maximum shear strains greater than 1% in downtown Mashiki.…”

“…Nonlinearity and liquefaction of soil deposits during the mainshock of the 2016 Kumamoto earthquake were reported (e.g., Tsuno et al 2017;Wakamatsu et al 2017;Sun et al 2022). Sun et al (2022) reported that there are several sites showing the maximum shear strains greater than 1% in downtown Mashiki. In Fig.…”

“…In particular, the town of Mashiki, where a 7 on the Japanese seismic intensity scale was recorded, experienced heavy earthquake damage to buildings. Since the earthquake, much research on strong ground motions, nonlinear behaviors of subsurface soil, and earthquake damage has been undertaken in this area (e.g., Kawase et al 2017;Yamanaka et al 2016;Yamada et al 2017;Sun et al 2021Sun et al , 2022. Yamanaka et al (2016) installed temporary seismic stations near the earthquake source fault region immediately after the mainshock of the 2016 Kumamoto earthquake, which occurred on April 16, 2016, whereas Tsuno et al (2017) installed temporary seismic stations in Kumamoto City immediately after the foreshock, which occurred on April 14, 2016.…”