Seismic hazard evaluation for dams in northern Colorado, U.S.A. |
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| Authors: | Ute R Vetter Jon P Ake Roland C Laforge |
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| Institution: | (1) Seismotectonics and Geophysics Group, U.S. Bureau of Reclamation, DS 8330, Denver Federal Center, 80225 Denver, CO, U.S.A. |
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| Abstract: | A seismic hazard evaluation for three dams in the Rocky Mountains of northern Colorado is based on a study of the historical seismicity. To model earthquake occurrence as a random process utilizing a maximum likelihood method, the catalog must exhibit random space-time characteristics. This was achieved using a declustering procedure and correction for completeness of recording. On the basis of the resulting a- and b-values, probabilistic epicentral distances for a 2 × 10–5 annual probability were calculated. For a random earthquake of magnitude M
L
6.0–6.5, this distance is 15 km. Suggested ground motion parameters were estimated using a probabilistic seismic hazard analysis. Critical peak horizontal accelerations at the dams are 0.22g if median values are assumed and 0.39g if variable attenuation and seismicity rates are taken into account. For structural analysis of the dams, synthetic acceleration time series were calculated to match the empirical response spectra. In addition, existing horizontal strong motion records from two Mammoth Lakes, California earthquakes were selected and scaled to fit the target horizontal acceleration response spectra. |
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| Keywords: | Colorado dams earthquake recurrence probabilistic distances probabilistic seismic hazard analysis peak horizontal acceleration acceleration response spectra |
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