The configuration of sensors is determined based on the intent of the observation. Typical sensor configurations for the ground are illustrated in the figure below. If earthquake motions on the ground surface are the target, a sensor is usually placed on the rigid foundation on the free field. Or a borehole sensor is buried shallowly in the ground. For the purpose of the investigation into the effect of surface geology, borehole sensors are necessary. The deepest borehole sensor is normally set up in a hard layer, like the bedrock.
The figure below shows typical sensor configurations for building structures. For investigating seismic response of a building structure, at least two sensors are required at the base and the top of the building. According to the dimensions of a building, some additional sensors are arranged in the building. Sensors placed on intermediate floors are useful to discuss higher natural modes of a tall building. For a building with a wide shape, two or more sensors are configured on the top floor.
The soil-structure interaction effect is one of the important topics for estimating seismic force to building structures. Therefore it is to be desired that the combined sensor configuration in buildings and in the ground.