Corps of Engineers Strong-Motion Instrumentation Program. Report 1. EarthquakeResponse Spectral Analysis of Arkabutla Dam, Mississippi

摘要

This report provides permanent documentation for and analyzes accelerograms forthe main shock (m sub b = 5.0) and aftershock (m sub b = 4.5) of the New Madrid earthquakes of 25 March 1976 obtained at the Arkabutla Dam. Both epicenters occurred in Arkansas. The main purpose of this study is to analyze the response spectra of acceleration, velocity, and displacement, the amplification factors, and the natural periods of foundation, dam, and abutment. All response spectra of longitudinal (L), vertical (Z), and transverse (T) components for the downstream (toe), crest, and abutment of Arkabutla Dam were presented individually. Five percent damped spectral amplitude-ratios of the L-component at the toe to those at the abutment and the similar crest to the abutment rates were 4.2 and 2.2, respectively, at the period of 0.35 sec or 2.9 Hz. Therefore, 0.35 sec is the natural period for both foundation and dam. Evidently, the spectral amplitude of the L-component at 0.35 sec on the crest of the dam was deamplified or reduced directly due to the dissipation (attenuation) of wave energy in the dam. The average amplification factor of the vertical component for the toe relative to the abutment is 3.22 for the period of 0.25 sec or 4 Hz; for the T-component it is 1.06 and 0.93 for 0.35 sec (2.9 Hz) and 0.40 sec (2.5 Hz), respectively.