Characterization, processing, and interpretation of weak-motion records of a CFRD dam

Permanent seismic monitoring plays an essential role in the surveillance of embankment dams in seismically active regions. Weak-motion recordings collected from instruments located along the dam body and abutments provide valuable data sets to identify and characterize the dynamic response of the dam-foundation system at small strain levels. The objective of this work was to summarize the characterization and processing of the acceleration time histories recorded during the operation of an earth dam in Argentina, to identify the main features of its dynamic response. The paper first describes the seismic monitoring system of the dam; then, the records were attributed to seismic events pertaining to distinct seismogenic sources through catalogs of seismicity. It was shown that several seismogenic sources characterized by different types of faulting style, distance and magnitude may affect the dam during its operation. A number of selected records was processed in order to obtain a preliminary description of the dynamic response of the dam-foundation system at low-acceleration amplitudes. The analysis of peak acceleration ratios between the crest and mid-height recording stations revealed the significant influence of asynchronous motion. This aspect was confirmed by the analysis of Fourier’s and response spectral ratios, which yielded consistent estimates of the fundamental frequency of the dam-foundation system, notwithstanding the variability of the source mechanisms, and permitted to back-figure a realistic value of the average shear wave velocity of the gravelly soil.