Estimating coseismic deformations from near source strong motion records: methods and case studies

Abstract

Digital strong-motion accelerographs have opened up the possibility of extracting ground motion characteristics at much lower frequencies than was offered by analogue instruments. High-quality digital data obtained close to the faults have tempted several efforts to retrieve permanent ground displacements after an earthquake. Such attempts have been partly successful, and somewhat subjective, the main reason being the presence of baseline offsets in the accelerometric data. We review existing methods for such applications, discuss their limitations and propose a more objective and improved scheme to make baseline adjustments and obtain permanent displacements. The proposed technique is applied to 26 digital recordings from the 29 May 2008 Ölfus Earthquake in South Iceland and 9 recordings from the 1999 Chi-Chi, Taiwan, Earthquake, and the permanent displacements obtained are compared with published results and GPS measurements from nearby stations. Our case studies show that the proposed technique, in addition to being simple and objective, is effective in making adjustments for baseline errors in accelerometric data.

Quantification of ground-motion parameters and response spectra in the near-fault region

“…Accelerograms at AQK station during the 2009 L'Aquila earthquake were obtained from the online database of the Italian accelerometric network (Luzi et al 2008). Since we are primarily concerned with forward-directivity effects in this study, permanent displacements (if any) in the ground motion records were removed by subtracting a half-sine pulse from the acceleration records, which was scaled to match permanent displacements computed by a procedure described in Rupakhety et al (2010).…”

Wavelet Domain Seismic Correction

“…The ICEARRAY yielded a useful set of data from the 11 CUSP stations, and the 33 component results for the displacements using the wavelet transform were compiled in May 2009 (Rupakhety et al 2010). We present some time series plots for the purpose of demonstrating the wavelet transform method for obtaining displacement estimates as well as the inferred tilt acceleration transients.…”

Damage to residential buildings in Hveragerði during the 2008 Ölfus Earthquake: simulated and surveyed results

“…Furthermore, distinct forward directivity pulses (see, for example, Rupakhety et al 2011) were observed in ground velocity time series. Permanent ground displacements were also observed at all of the 11 stations of ICEARRAY (Rupakhety et al 2010). Peak ground accelerations (PGA) recorded in the town was very high compared to the current design level (475 years mean return period) which is about 40 % of acceleration due to gravity.…”