Site investigations were performed on a damaged river dike, which was located in the central and southern part of Iwate prefecture. The field investigation results show that subsidence related failure probably had taken place in the dike body with low penetration resistance and high water table. Further investigations also revealed that the dike body had low liquefaction resistance and the volume change after liquefaction was rather large. Numerical investigation through two dimensional effective stress analyses show that due to main shock and aftershock, there is a likelihood of liquefaction in dike body and the re-liquefaction possibilities are high even under small ground motion.