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The calculation of horizontal accelerations from seismoscope records

Scott, Ronald F. (1973) The calculation of horizontal accelerations from seismoscope records. Bulletin of the Seismological Society of America, 63 (5). pp. 1637-1661. ISSN 0037-1106.

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The seismoscope is a simple instrument designed originally to give a largely qualitative indication of the strong ground motions produced by an earthquake. It consists of a smoked watch glass attached to a two-degree-of-freedom pendulum with a period of Formula sec and damping about 10 per cent of critical; a pen records the pendulum motions on the watch glass. One point on the displacement spectrum of the recorded ground motion at this period and damping is obtained from the measurement of the maximum pendulum excursion. An examination of the seismoscope record obtained on the east abutment of the failed Lower San Fernando dam during the 1971 San Fernando earthquake showed a high-frequency vibration superimposed on the general oscillations. It did not seem likely that this was solely an earthquake vibration component, and shaking table tests of seismoscopes revealed the presence of a seismoscope vibration mode at frequencies of 15 to 18 Hz depending on the instrument. The oscillations due to this mode on the abutment seismocope record have, therefore, been used as timing marks, to enable the seismoscope equation to be solved for the input acceleration components. The results of the calculations are presented along with analyses of the seismoscope response to indicate the range of applicability. One other record, obtained on a seismoscope alongside a strong-motion accelerograph, was also analyzed for comparison with the recorded accelerations, to demonstrate the validity of the technique. The timing vibration appears on a number of seismoscope records.

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Additional Information:© 1973 Seismological Society of America. Manuscript received February 22, 1973. The previous experience of Dr. M. D. Trifunac of the California Institute of Technology in analyzing seismoscope records was invaluable to this work. Dr. Trifunac was most helpful in many discussions of the analysis and filtering of the data and, in addition, made his seismoscope computer program available to check the results. The compilation of new computer programs and the incorporation of previous ones into the computational procedure was carried out with extreme competence by D. R. Putnick, graduate student, now at the University of Wisconsin. Dr. A. G. Brady was very patient in many explanations of digitizing and computational processes and errors. The enthusiasm and encouragement of Dr. D. E. Hudson is gratefully acknowledged. The work was carried out with the assistance of National Science Foundation Grant GI-29937.
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ID Code:49771
Deposited By: Tony Diaz
Deposited On:18 Sep 2014 03:09
Last Modified:03 Oct 2019 07:17

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