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

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 N3E, N91E, and N75E, 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.