A long-period weak-motion inertial sensor includes a frame having a frame mounting surface, a movable mass having a movable mass mounting surface, a transducer for sensing displacements of the movable mass with respect to the frame, and a monolithic flexure element for suspending the movable mass in the frame. The monolithic flexure element includes: a stiff frame integral clamp attachable to the frame mounting surface of the frame, a stiff movable mass integral clamp attachable to the movable mass mounting surface of the movable mass, and a stiffest flexible region for operatively connecting the frame integral clamp to the movable mass integral clamp. The frame and movable mass mounting surfaces do not overlap the stiffest flexible region, thereby minimizing the generation of creep and hysteresis noise. The variation in stiffness of the monolithic flexure element is controlled by varying thickness along the length of the flexure element.