What site class designation is assigned to hard rock?

The designation of Site Class A is assigned to hard rock, which is characterized by its high shear wave velocity, typically above 1500 m/s. This classification is important in the context of seismic design and engineering geology, as it indicates that the ground has a high capacity to withstand seismic waves, making it less prone to amplification of seismic motion during an earthquake.

Hard rock generally includes materials such as granite and other crystalline rocks, which possess rigid properties and limited susceptibility to deformation. This strength and stability are crucial factors considered in engineering applications, particularly when assessing the potential hazards associated with seismic activity.

In contrast, the other site classes are designed for softer soils (Site Class B, C, and D), which can have lower shear wave velocities and are more susceptible to seismic amplification and ground failure during an earthquake. Each class reflects different geological conditions and anticipated responses to seismic events, making the correct identification of site class critical for safe and effective engineering practices.