Attenuation of Ground Motion Spectral Amplitudes in the Longmenshan Belt and Its Surrounding Regions in Southwestern China

Date: 4/24/2019

Time: 06:00 PM

Room: Grand Ballroom

On 12 May 2008, the magnitude 8.0 Great Wenchuan Earthquake occurred in Longmenshan belt in Southwestern China. As part of the eastern boundary of the Tibetan Plateau, this region experienced intense tectonic movements and strong seismic activity. Large amount of strong ground motion data were recorded at epicentral distances between 15 and 400 km by strong ground-motion networks installed before and after the Wenchuan earthquake. We collected horizontal-component waveforms of these strong ground-motions, and extracted shear waveforms including S, SmS, Lg, Sn phases which usually cause building damages. Considering uncertainties of the origin times and source locations, we adopted a floating group velocity window to sample shear wave phases. The noise series were picked from time windows immediately before the first arriving P waves. The Fourier spectra were calculated for both shear waves and noise. The spectral amplitudes at 11 frequencies log-evenly distributed between 0.5 and 20.0 Hz were sampled and used to construct a seismic wave attenuation model in this region. By using linear regression, we obtained a frequency-dependent Q model, geometric spreading parameters and site corrections for the studied region. The geographical distribution of site corrections show prominent differences at various tectonic divisions along the Longmenshan belt. Along the side of the Tibet Plateau and to the west of the Longmenshan belt, relatively lowerQ values are observed, whereas to the east of this belt, the Sichuan Basin is characterized by relatively higher Q values. This research was supported by the National Natural Science Foundation of China (grants 41674104, 41630210).

Presenting Author: Wang Wei-Min

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