Research On Two-dimension Vertical Pendulum Tiltmeter

The measurement of tilt is an important method of studying earth crust deformation and earth tides, which is very valuable to Geodynamics and the observation of earthquake prognostic. The tiltmeters can be classified as long-base and short-base tiltmeters. The long-base tiltmeters are the liquid tiltmeters, they all use the free surface of a liquid to define the horizontal and most measure tilts by monitoring the motion of this surface. The short-base tiltmeters include the horizontal pendulums, simple pendulums, diamagnetic tiltmeters, bubble tiltmeters and folded pendulum. While designs for short-base tiltmeters are exceedingly diverse, they all use some form of pendulum to define the vertical.We develop a kind of two-dimension vertical pendulum tiltmeter which can measure ground tilt in orthogonal directions. In this paper, the structure of the two-dimension vertical pendulum and its dynamic characteristic is described. The response of the vertical pendulum to the crustal tilt tides is also studied. Both the construction and principle of the capacitance displacement transducer used in two-dimension vertical pendulum tiltmeter are described. The method of calibrating a vertical pendulum tiltmeter using a piezoelectric transducer (PZT) and an autocollimation is first presented and performed.The tilt tides in two directions of EW (east and west) and SN (south and north) have been observed with two-dimension vertical pendulum tiltmeter. Preliminary experimental result shows that the resolution of the vertical pendulum tiltmeter can reach in the orders of about 10-9rad.