Assessing Maximum Credible Ground-Motion Parameters of Large Earthquakes at Near-Field Site

In deterministic seismic hazard analysis, the worst-case scenario or maximum credible earthquake is used to estimate the seismic ground-motion intensities, which is crucial for the seismic design of key facilities. The stochastic finite-fault method has been proven to enable reliable simulations of the near-field ground-motion parameters of large earthquakes, which can effectively synthesize Fourier amplitude spectra, response spectra, and the time history of acceleration.

The Longpan hydropower station is located in northwest Yunnan Province in the middle reaches of the Jinsha River, on the southwestern margin of the Tibetan Plateau (Figure 1a). As shown in Figure 1b, the seismic structure in the study area is very complex. The source models of the Daju–Lijiang, Xiaozhongdian–Daju, and Longpan–Qiaohou faults were established based on geological and geophysical data. To perform physics-based ground-motion simulation via the stochastic finite-fault simulation, the regional specific ground-motion characteristics can be approximately described by several critical parameters. By applying the multi-scheme stochastic finite-fault simulation method (multi-SFFSM), parameter uncertainty in ground-motion simulations and the impact of the three faults were analyzed on the PGA value and pseudo-spectral acceleration response spectra (PSA) at the target dam to determine the maximum credible ground-motion parameters. The flowchart of our study is shown in Figure 2.

Figure 1. (a) Tectonic locations of the study area. (b) Seismotectonic map of the hydropower station. F1: Changsongping–Wenming fault; F2: Xiaozhongdian–Daju fault; F3: Daju–Lijiang fault; F4: Chongjianghe fault; F5: east of Jinsha River fault; F6: Jinsha River fault; F7: Longpan–Qiaohou fault; F8: Xiaojinhe–Lijiang fault; F9: Heqing–Eryuan fault; F10: Weixi–Qiaohou fault; F11: Honghe fault.

Figure 2. Flowchart of the multi-scheme stochastic finite-fault simulation method.

The results showed that the Longpan–Qiaohou fault can generate the largest ground-motion parameters compared with the other two faults. Moreover, this result was supported by the statistical analysis of the results of six thousand simulations of these three faults. Thus, it can be concluded that the maximum credible ground-motion parameters are represented by the 84th-percentile pseudo-spectral acceleration response spectrum of the Longpan–Qiaohou fault. This finding will benefit the seismic safety design of the target dam. More importantly, this multi-scheme method can be applied to other key facilities to obtain reasonable ground-motion parameters.