Earlier, analog instrument were usually made to record one type of ground motion like
velocity. Traditionally, seismologists prefer recording weak motion displacement or velocity,
for easy interpretation of seismic phases, while engineers use strong motion acceleration,
whose peak values are directly related to structures seismic load Today it makes less of a
difference, since due to advancement in sensor and recording systems, the weak motion
instruments can measure rather strong motions and the strong motion sensors are almost as