SeisMike measures seismic surface waves travelling horizontally along the ground surface (e.g., Lamb and Rayleigh waves). When surface wave velocity exceeds air-wave velocity, its energy actively “leaks” into the air in the form of sound wave. This is called “leaky-mode” surface wave and usually possesses strong energy. The special type of surface waves generated in pavement, called Lamb wave, can leak its energy into air very effectively due to its velocity (e.g., 2000 m/s) significantly higher than air velocity (e.g., 340 m/s). In consequence, SeisMike is currently most actively used for pavement investigation.
On the other hand, if the velocity is lower than air-wave velocity (e.g., 200 m/s), fraction of its energy remains close to the ground surface with its intensity exponentially decay as it departs from it. This is called “evanescent” waves. In addition, the subsurface acoustic (P) waves (e.g., reflection, diffraction, and refraction) can always radiate into the air. SeisMike can record all these types of waves (leaky-mode, evanescent, and acoustic waves).
