Downhole Instrument Orientations and Near Surface Q Analysis From the SMART2 Array Data

Han-Yih Peng, Kuo-Liang Wen
1993 Terrestrial, Atmospheric and Oceanic Sciences  
Installation of the SMART2 downhole array in Da-Han Industrial School was completed in May 1992. This array contains one free surface station and three downhole accelerometers down to 200 m · depth. Thirteen events recorded by this downhole array are used to study the orientations of the downhole instruments by cross -correlation method. The results show the longitudinal direction of the instruments at SO m, 100 m, and 200 m depths of downhole accelerometers are N3°E, N91°E, and N75°E,
more » ... and N75°E, respectively. The near surface Q value is calculated by using the records of three events. The result of Q(0=9.SSf 1.o6 was obtained from the smoothed power spectrum ratios. The surface ground motions of two events are simulated from the observed downhole records and Q value we obtained by using the Haskell method. The results confirm the downhole instrument orientations and near surface Q value that we derived in this study. in the Lotung area (Shieh, 1992 ). The SMART2 array (Chiu and Yeh, 1991) is located in the Hualien area. Three downhole accelerometers are installed in the Da-Han Industrial School at depths of 50 m, 100 m, and 200 m. This downhole array gives us an opportunity to study the near surface Q value in the Hualien area. The orientations of the downhole instruments are not measured since the installation. Before doing the Q value study, we must solve the problem of the downhole instrument orientations. Several methods had been used to check the downhole instrument orientation, for example, polarization method (Vidale, 1986) and cross-correlation method (Yamazaki et al., 1992) . In this study, we used the cross-correlation method to estimate the instrument orient�tions of the downhole array. To check the estimated value of instrument orientation and Q value, we used the Haskell method to simulate surface ground motion by using the downhole record as input motion. From the similarity between the synthesiz, ed results and the observed records, we can show the exactness of the instrument orientations and near surface Q value we obtained. DOWNHOLE ARRAY AND DATA The SMART2 downhole array is located in the Da-Han Industrial School in the Hualien area. This arr ay consists of one free surface and 3 downhole accelerometers whose depths are 50 m, 100 m, and 200 m. The four FBA sensors are connected to two 6-chann el SSR-1 digital recorders. Each recorder has 16 bits resolution and the sampling rate is 200 points/sec. An Omega clock timing system provides one ms accuracy and continuously synchronizes the clock to standard time. The SMART2 downhole array began operating on May 6, 1992. From this date through
doi:10.3319/tao.1993.4.4.367(t) fatcat:gjokxjrbufh5fg7tkn4vjx2zay