Measurements of surface waves phase velocity with a large ring laser gyroscope and a seismometer

n recent years the development of large ring laser gyroscopes gave birth to a new discipline: the rotational seismology. This field of study is rapidly expanding and many areas of geophysics are or can be involved, from geodesy to seismology to the monitoring of critical structures. New rotational sensors based on optical interferometry and Sagnac effect has been developed in the last two decades. These sensors are called ring laser gyroscopes (RLG) and are now able to cover the range of rotations of seismological interest i.e. from 10−2 to 10−9 rad/sec. A measure of rotations in seismology is of fundamental interest for several reasons: Quantitative seismology requires a measure of all the six degrees of freedom that characterize a rigid body’s motion. Standard seismological observations are contaminated by rotations that produce a bias in the estimate of ground translation. Rotational observables provide important informations about the elastic properties of the subsoil. The extension of rotational observations to exploration seismology can improve resolution and accuracy of subsurface imaging.