ON THE INTERACTION OF HORIZONTAL AND VERTICAL MOTION OBSERVED IN THE STRONG EARTHQUAKE RECORDS

In the 2018 Hokkaido Eastern Iburi Earthquake (M6.7), seismic intensities as high as 7 and 6+ were observed at KiK-net Oiwake (IBUH01) and K-NET Oiwake (HKD127) stations, respectively. The large acceleration records observed at both stations are discussed based on constant-pressure cyclic direct box shear tests, microscopic studies, and elastoplastic theory. As a result, it was shown that at both observation points, downward vertical acceleration (volume expansion) occurred due to the dilatancy of the surface ground, and that the generated vertical and horizontal motions were strongly coupled.