Five parameters for the evaluation of the soil nonlinearity during the Ms8.0 Wenchuan Earthquake using the HVSR method

• Published in: Earth, planets, and space Vol. 69; no. 1; p. 1
• Main Authors: Ren, Yefei, Wen, Ruizhi, Yao, Xinxin, Ji, Kun
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 22.08.2017; Springer Nature B.V
• Subjects: 4. Seismology; Case studies; Correlation; Earth and Environmental Science; Earth Sciences; Earthquakes; Effect of Surface Geology on Seismic Motion: Challenges of Applying Ground Motion Simulation to Seismology and Earthquake Engineering; Geology; Geophysics/Geodesy; Nonlinearity; Parameter identification; Seismic activity; Soil investigations; Soils; Studies; Velocity; Wave velocity; Soil nonlinearity; DNL; Wenchuan Earthquake; PGA; Site response; PGV; HVSR method
• ISSN: 1880-5981; 1880-5981
• DOI: 10.1186/s40623-017-0702-7

The consideration of soil nonlinearity is important for the accurate estimation of the site response. To evaluate the soil nonlinearity during the 2008 Ms8.0 Wenchuan Earthquake, 33 strong-motion records obtained from the main shock and 890 records from 157 aftershocks were collected for this study. The horizontal-to-vertical spectral ratio (HVSR) method was used to calculate five parameters: the ratio of predominant frequency (RF p ), degree of nonlinearity (DNL), absolute degree of nonlinearity (ADNL), frequency of nonlinearity (fNL), and percentage of nonlinearity (PNL). The purpose of this study was to evaluate the soil nonlinearity level of 33 strong-motion stations and to investigate the characteristics, performance, and effective usage of these five parameters. Their correlations with the peak ground acceleration (PGA), peak ground velocity (PGV), average uppermost 30-m shear-wave velocity ( V S30 ), and maximum amplitude of HVSR ( A max ) were investigated. The results showed that all five parameters correlate well with PGA and PGV. The DNL, ADNL, and PNL also show a good correlation with A max , which means that the degree of soil nonlinearity not only depends on the ground-motion amplitude (e.g., PGA and PGV) but also on the site condition. The fNL correlates with PGA and PGV but shows no correlation with either A max or V S30 , implying that the frequency width affected by the soil nonlinearity predominantly depends on the ground-motion amplitude rather than the site condition. At 16 of the 33 stations analyzed in this study, the site response showed evident (i.e., strong and medium) nonlinearity during the main shock of the Wenchuan Earthquake, where the ground-motion level was almost beyond the threshold of PGA > 200 cm/s 2 or PGV > 15 cm/s. The site response showed weak and no nonlinearity at the other 14 and 3 stations. These results also confirm that RF p , DNL, ADNL, and PNL are effective in identifying the soil nonlinearity behavior. The identification results vary for different parameters because each parameter has individual features. The performance of the PNL was better than that of DNL and ADNL in this case study. The thresholds of ADNL and PNL are proposed to be 2.0 and 7%, respectively. Graphical Abstract .