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Automatic estimation of earthquake high-frequency strong-motion spectral decay in south Iceland
Abstract We present an adaptive automated algorithm for estimating the spectral decay of high frequency waves from recorded acceleration time histories of strong ground motion, along with a simple P- and S-phase picking algorithm to achieve complete automation. Our approach negotiates site resonance peaks and spectral corners through a spectral linearity criterion that on average provides indistinguishable results compared to manual estimates. The overall spectral decay, represented by the so-called “kappa” () parameter, is demonstrated on a dataset of accelerograms from earthquakes of magnitudes 3.7-6.5 at distances of 1–76 km recorded on site conditions classified as rock and stiff soil, respectively, in South Iceland. The automatic procedure gives an average estimate of ms on rock. The data did not allow the robust determination of linear distance dependence, nor a distinction of between the two site classes due to the generally large scatter of values. Using a subset of stations for the analysis however, a slight distance-dependence could be observed but is likely due to the influence of the quality factor being proportional to frequency. The results indicate that source and site effects drive values in South Iceland, and that a formal inclusion of source contributions to the parametrization and analysis of the spectral decay is needed.
Highlights Fully automatic spectral decay estimation algorithm approaches manual methods. Large scatter of Kappa values precludes distinction between rock and soil sites. Separation of source and site effects is unachievable from small datasets. Only weak distance dependence of Kappa found in South Iceland. Discussion on source contribution can inform future research.
Automatic estimation of earthquake high-frequency strong-motion spectral decay in south Iceland
Abstract We present an adaptive automated algorithm for estimating the spectral decay of high frequency waves from recorded acceleration time histories of strong ground motion, along with a simple P- and S-phase picking algorithm to achieve complete automation. Our approach negotiates site resonance peaks and spectral corners through a spectral linearity criterion that on average provides indistinguishable results compared to manual estimates. The overall spectral decay, represented by the so-called “kappa” () parameter, is demonstrated on a dataset of accelerograms from earthquakes of magnitudes 3.7-6.5 at distances of 1–76 km recorded on site conditions classified as rock and stiff soil, respectively, in South Iceland. The automatic procedure gives an average estimate of ms on rock. The data did not allow the robust determination of linear distance dependence, nor a distinction of between the two site classes due to the generally large scatter of values. Using a subset of stations for the analysis however, a slight distance-dependence could be observed but is likely due to the influence of the quality factor being proportional to frequency. The results indicate that source and site effects drive values in South Iceland, and that a formal inclusion of source contributions to the parametrization and analysis of the spectral decay is needed.
Highlights Fully automatic spectral decay estimation algorithm approaches manual methods. Large scatter of Kappa values precludes distinction between rock and soil sites. Separation of source and site effects is unachievable from small datasets. Only weak distance dependence of Kappa found in South Iceland. Discussion on source contribution can inform future research.
Automatic estimation of earthquake high-frequency strong-motion spectral decay in south Iceland
Sonnemann, Tim (author) / Halldorsson, Benedikt (author) / Jónsson, Sigurjón (author)
2019-05-10
Article (Journal)
Electronic Resource
English
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