Ground response and liquefaction evaluations for the 2017 Pohang, Korea, earthquake based on shear wave velocity profiles estimated by microtremor array measurements

The 2017 Pohang earthquake, with a moment magnitude (M) of 5.5, caused severe building damage and widespread liquefaction. In this study, we evaluate the applicability of ground response and liquefaction triggering analyses for the Pohang earthquake using deep shear wave velocity (VS) profiles. The VS profiles are obtained at Handong University and the Songdo Pine Forest by inverting the Rayleigh wave dispersion curves based on microtremor array measurements (MAM) and multi-channel analysis of surface waves (MASW). In onedimensional effective stress analyses for the two sites, we consider the uncertainty of the nonlinear soil properties for three cases and use 118 rock outcrop motions. At Handong University, the spectral accelerations of surface ground motions are larger than those of the current Korean design spectra with a return period of 500 years at the natural period of the damaged buildings. At the Songdo Pine Forest, for the Case 2, numerous ground motions result in the maximum pore water pressure ratio of 1 (i.e., liquefaction occurrence). Furthermore, we calculate the liquefaction potential index (LPI) values using the VS-based simplified method. To compute the cyclic stress ratio for depths, we utilize the peak ground accelerations estimated by ground response analyses and estimated by stress reduction factor (rd), respectively. The LPI values, based on the ground response analyses, range from 0 to 4, indicating minor or no damage, while the LPI value using the rd is zero. The results of the ground response and liquefaction triggering analyses are similar to the actual damage cases.