A
Rod-type Creepmeter for Measurement of Displacement in Active Fault Zone
Jian-Cheng
Lee1,
Fu-Shu Jeng2,
Hao-Tsu Chu3,
Jacques Angelier4,
Jyr-Ching Hu5
1Institute of Earth Sciences, Academia Sinica, P.O.
Box 1-55, Nankang, Taipei, R.O.C., Taiwan
2Department of Civil Engineering, National Taiwan
University, Taipei, R.O.C., Taiwan
3Central Geological Survey, P.O. Box 968, Taipei,
R.O.C., Taiwan
4Tectonique Quantitative, Département de Géotectonique and ESA 7072, Université P.-&-M. Curie, Paris, France
5The Institute for Secondary School Teacher of
Taiwan, Taichung, R.O.C., Taiwan
(Earth,
Planets, and Space, 52, 5, 321-328,
2000)
Abstract.
A
creepmeter has been developed to monitor gradual displacements of near-surface
movement in an active fault zone. This rod-type creepmeter is a robust, low-cost
instrument that is simple to construct and install. This creepmeter consists of
two 3-m invar rods attached to anchored steel piers at each end, straddling the
surface traces of active fault. The invar rods are supported by a pair of
U-shaped solid steel girders. A mechanical dial-gauge sensor in the middle of
the creepmeter is adopted to record the displacement of fault creep, and has a
precision of 0.01mm. Because the creepmeter is installed on the surface, the
temperature effect is important. To calibrate and correct for the temperature
effect, we carried out hourly measurements over a period of 30 hours to
calculate the thermal expansion coefficients for each creepmeter. Thermal
corrections could thus be made when readings were taken. Five of these
creepmeters have been installed in the Chihshang active fault zone of eastern
Taiwan, in the present collision suture zone between the Philippine Sea plate
and the Eurasian plate. Readings taken over one year have shown that this
rod-type creepmeter is effective in providing a near-continuous record of active
fault creep with a good precision.