A vector from the point where a material particle initially was located, to its location after an increment of motion. Unless otherwise specified, it means translational displacement in seismology. In earthquake geology, a general term for the movement of one side of a fault relative to the other; the amount of displacement may be measured in any chosen direction, usually along the strike and the dip of the fault. In seismometry displacement is the ground motion commonly inferred from a seismogram. For example it may be calculated by doubly integration of an accelerogram or a single integration of a velocity-proportional recording with respect to time. It is expressed in units of length, such as nanometer, micrometer or millimeter. In geology, displacement is the (quasi-) permanent offset of a geological or man-made reference point along a fault or a landslide. In geodesy, movement of a point on the Earth's surface; traditionally defined in a local (east, north, up) coordinate system centered at a reference point fixed to the Earth. In space geodesy, the reference point can be attached to the inertial frame. In strong-motion seismology and earthquake engineering, it is the time-dependent position of a material particle during earthquake shaking relative its position at rest, typically obtained by doubly integrating the acceleration records. Recovering the long-period part of the displacement history accurately from velocity or acceleration sensors is difficult because of the sensitivity of translation sensors to rotational ground motions (Trifunac and Todorovska, 2001)