Strong Motion Data
Strong motion data consist of recordings of those earthquake ground motions capable of damaging buildings or of weakening soils or embankments under or near buildings.
Strong motion recorders are placed in areas likely to be shaken, in order to maximize the opportunity for gaining new information when earthquakes occur. The recorders are placed on or near the surface of the ground to obtain the effects uninfluenced by buildings. In addition, many recorders are placed at strategic locations within buildings to obtain information on how the ground motion affects the buildings. Occasionally, some recorders are placed deep in the soils to obtain, together with surface recorders, the effect of the soil column on ground motion. The soil column will amplify the ground motion in different ways depending upon the depth of the soil column and the contrast between the seismic velocity of the soil column and bedrock.
Thus, three important characteristics are derived from strong motion data:
- How much the ground motion increases at a given distance as the magnitude increases.
- How much the ground motion decreases at a given magnitude as the distance increases.
- How much the soil column amplifies the ground motion.