| Popis: |
Displacement response spectra defined up to long periods are needed for the design of large structures and to design structures according to displacement‐based methods. The spectra can theoretically be retrieved in the near field of large earthquakes from accelerations recorded by modern strong‐motion accelerometers. Difficulties exist due to instrumental limitations: long‐period noise that contaminates the acceleration time histories and record of the tilt simultaneously to the translational accelerations. Original in this work, the effect of the instrument’s permanent tilt is investigated, and the improvement of the spectra at long periods, when the residual tilt is removed from accelerations recorded by modern strong‐motion seismometers, is checked against 1 Hz Global Positioning System (GPS) measurements. Records of five strong‐motion accelerometers situated in the near field of the M w 6.8 Japanese 2007 Niigata‐ken Chuetsu‐Oki earthquake are analyzed in terms of Fourier content and displacement response spectra and are then compared to their closest 1 Hz GPS data. The results show that the uncorrected acceleration time histories, obtained by simply removing the preevent mean from the raw accelerations recorded by modern strong‐motion seismometers, provide reliable displacement response spectra at periods over 20 s. Corrected acceleration time histories, obtained by removing the permanent tilt from the uncorrected records using the Javelaud et al. (2011) method, may provide reliable response spectra at very long periods until they reach the theoretical peak ground displacement. |
