Observation of variations of long-period microseismic noise by precision laser interferometry

The results of the study of dynamic peculiarities of deformational oscillations of Earth crust with periods in the range from 10 to 300 sec by He-Ne laser dephormograph placed in underground gallery are presented. The mean square amplitude of deformational noise observed during one month is about 0.01 micrometers. It has constant components and variable one with period 24 hours. A mechanism of the deformational noise generation and a practical implementation of the laser apparatus and observed phenomenon for geodynamic and seismic monitoring are discussed.