Effect of Ground Motion Modification Technique on Seismic Geotechnical Engineering Analyses

Abstract

Ground motion modification (or spectral matching) has been criticized, but has many appealing characteristics and is widely used in practice. Modification of ground motions can be performed in either the time domain or the frequency domain. Depending on the choice of modification technique, modified ground motions can be significantly different from each other as well as from the original ground motion. This paper studies the impact of these differences on seismic geotechnical analyses for two different site profiles using two earthquake scenarios and a total of 20 ground motions. This study shows that the final results are influenced by many factors such as the original (seed) ground motion, the target spectrum, and the local site conditions, in addition to the ground motion modification technique used. The results also show that while both techniques can significantly modify the original ground motion, neither technique is consistently more conservative than the other. Therefore, a general conclusion that a particular technique results in ground motions that yield the largest intensity parameters cannot be made a priori.

Predictive Equations to Quantify the Impact of Spectral Matching on Ground Motion Characteristics

“…In some cases, large changes in ground motion characteristics have been observed, cautioning against the use of spectral matching in engineering practice (Naeim and Lew 1995). In other cases, the impact of spectral matching on ground motion characteristics has been found to vary from minimal to significant (Zekkos et al 2012, Gascot and Montejo 2014). Overall, the impact of spectral matching on a seed ground motion, as reported by Carlson et al (2014b), is known to be affected by (a) the relative shape and amplitude of the acceleration response spectrum of the seed ground motion to the target spectrum, (b) the seed ground motion itself and its characteristics, (c) the ground motion characteristic of interest (e.g., Arias intensity versus peak ground velocity), and (d) the technique (i.e., the mathematical manipulations) used for modification (e.g., TD versus FD).…”

“…Spectral matching is also used when three-component ground motions are needed for dynamic analyses or spectrum compatible ground motions are required by regulations. The numerous advantages of spectral matching compared to other approaches (such as scaling of motions or use of synthetic motions) have been outlined by Zekkos et al 2012.…”

Spectral Matching of Three-Component Seismic Ground Accelerations for Nuclear Power Plants

“…al., 2018). In some cases, major changes were noticed (Naeim and Lew, 1995), and in others the effect could vary from minor to significant (Zekkos et. al., 2012;Gascot and Montejo, 2016).…”

A Metric to Screen Acceptable Velocity and Displacement Time Histories of Modified Ground Motions

“…For earthquake scenarios where recorded ground motions are either not available or the spectra of the available motions do not resemble the target spectrum, ground motion modification becomes a useful alternative. Additional advantages of spectral matching over other approaches (such as scaling of motions or use of synthetic motions) have been discussed in Zekkos et al (2012).…”

“…Altering the frequency content of the seed motion during ground motion modification can significantly change its velocity and displacement time histories (Naeim and Lew 1995, Hancock et al 2006, Zekkos et al 2012). Therefore, the characteristics and time histories of the modified ground motion must be carefully examined after modification to decide if the modified motion is acceptable or has undergone an unacceptable amount of change relative to the seed ground motion.…”