Abstract
Accurate measurements of seismic motions in soil are often required in earthquake studies and mine blasting operations at sites that have no outcropping rock. The present study shows that the most satisfactory method of coupling to soil is to attach the seismic detectors to a carefully embedded, precast mount whose shape is either cubic, or right-cylindrical with unit aspect ratio. Furthermore, because of the competing influences of radiation and scattering, it is shown that the optimum design for the cylindrical mount is achieved only when two criteria are met simultaneously. The first criterion is given by R < V S /(9f u ), where R is the mount radius, f u is the upper frequency required to be accurately detected, and V S is the shear-wave velocity of the soil. The second criterion is given by b = 10, where b is the mount mass factor m/(rho R 3 ) in which rho is the soil density and m is the total mass of the mount and detector array. Irrespective of the above criteria, if R < V S /(60f u ), then the ground coupling problem is negligible for all mount masses given by b < 100. All these conditions also apply to a fully embedded cubic mount of side L, provided R is replaced by 0.568L. The treatment is scale-independent and is applicable to seismic exploration as well as to earthquake and blast vibration monitoring.
