Abstract: A laser strainmeter has a plurality of sensor resonators, each comprising a multiple reflection interferometer having a pair of concave mirrors (8) which are secured to the inner wall of a container (1) to face each other in the diametrical direction of the container so that the optical axes of the sensor resonators extend in different directions. The laser strainmeter further has a reference resonator comprising a multiple reflection interferometer having a pair of concave mirrors (12) which are disposed in the vicinity of the sensor resonators, and which are held at a fixed distance. Laser light having the same resonance frequencies as those of the associated resonators are transmitted from laser oscillators to the resonators through optical fibers (3).

Abstract: The SH wave generating apparatus includes a driving plate (1) of increased rigidity; a fixing device (6) provided on the bottom of the driving plate for fixing the driving plate onto the earth's surface; a plurality of hydraulic actuators (2) mounted on the driving plate, which have reaction masses and act tangentially on the same circumference from the center of the driving plate; and a driving device (4,5) for reciprocating the plurality of hydraulic actuators (2) at a controlled frequency, thereby generating transverse waves. The plurality of hydraulic actuators (2) are equidistantly mounted on the driving plate (1), and each include a cylinder (2) and a piston rod extending therethrough. The said piston rod is mounted at both ends on supports (3) fixed to the driving plate (1) and the cylinder acts as a reaction mass. Alternatively, the piston rod extending through the cylinder 2 may be provided at both ends with reaction masses.