Ground surface displacements appeared after The Iwate-Miyagi Nairiku Earthquake in 2008 at the right bank of Aratozawa Dam. We investigated their properties by trenching, surface reconnaissance, and groundwater monitoring. As a result, we concluded that these displacements may be caused by strain concentration and deformation near the unconformity which divides rigid Kuzumine Formation and soft Onomatsuzawa Formation. Also, it is confirmed that these displacements do not affect the storage capability and safety of Aratozawa Dam.