Problems associated with instrument tilts during seismic events

This paper begins with a brief introduction regarding the problems associated with
instrument tilts and rotations when recording a seismic event. Most instruments are designed to
respond to translational motion along the longitudinal and vertical axes. Tilts in a gravity field
introduce a horizontal acceleration component, which is indistinguishable from horizontal
acceleration. When the seismometer frame is tilted by a small angle, a torque will be exerted around
the hinge and will cause pendulum motion relative to the frame. The effect of this torque is the same
as that produced by a horizontal acceleration and leads to baseline shifts in the recorded data. The
base line offset of the recorded seismic data makes it difficult to locate the origin. Therefore this base
line error should be corrected in order to remove the tilt component embedded in the ground
acceleration. Fourier amplitude spectra are applied to vertical and horizontal components of
acceleration to measure the difference in high frequency range; the difference is due to the residual tilt
present in the horizontal component in the N-S and E-W directions. In this paper we apply
independent component analysis (ICA) on simulated tilt data. ICA is a separation technique used in
order to recover and hence remove the tilt time series from the acceleration time histories of a near
field earthquake source.

Citation:
Thiyagu, R. and Chanerley, A.A. (2010) ‘Problems associated with instrument tilts during seismic events.’, Proceedings of Advances in Computing and Technology, (AC&T) The School of Computing and Technology 5th Annual Conference, University of East London, pp.119-126..