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.