Automatic estimation of earthquake high-frequency strong-motion spectral decay in south Iceland

• Published in: Soil Dynamics and Earthquake Engineering
• Main Authors: Sonnemann, Tim, Halldorsson, Benedikt, Jonsson, Sigurjon
• Other Authors: Crustal Deformation and InSAR Group, Earth Science and Engineering, Earth Science and Engineering Program, Physical Science and Engineering (PSE) Division, Earthquake Engineering Research Centre and Faculty of Civil and Environmental Engineering, School of Engineering and Natural Sciences, University of Iceland, Austurvegur 2a, 800, Selfoss, Iceland, Division of Processing and Research, Icelandic Meteorological Office, Bustadavegur 7-9, 108, Reykjavik, Iceland
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Elsevier BV 2019
• Subjects: Near-surface attenuation; Strong ground motion; High frequency amplitude decay; Kappa; Iceland
• Online Access: http://hdl.handle.net/10754/656287; https://doi.org/10.1016/j.soildyn.2019.05.015

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” (κ) 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 κ¯=37.2±13.6 ms on rock. The data did not allow the robust determination of linear distance dependence, nor a distinction of κ between the two site classes due to the generally large scatter of κ 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 κ values in South Iceland, and that a formal inclusion of source contributions to the parametrization and analysis of the spectral decay is needed. This study was supported by the Icelandic Centre for Research (Grant of Excellence No. 141261-051/052/053) and the Research Fund of the University of Iceland. The authors gratefully acknowledge Dr. Símon Ólafsson that provided the dataset, also available at the Internet Site for European Strong-motion Data (http://www.isesd.hi.is). The manuscript was benefitted greatly from discussions with Prof. Apostolos S. Papageorgiou at the University of Patras.