Earthquake potential of the Sichuan-Yunnan region, western China

Abstract

We estimate the seismic hazard potential in the Sichuan-Yunnan region, western China using three different approaches. Our first approach, based on the assumption that the earthquake probability is proportional to the past seismicity rate, uses a regional earthquake catalog to constrain the probability model. A retrospective test shows that the ‘forecasts’ have some predictive power for strong events occurred on fault segments with shorter earthquake recurrence time, but not for that with longer recurrence time such as the Longmenshan fault. Our second approach, based on the assumption that the earthquake probability is proportional to crustal strain rate, uses secular geodetic strain rate deduced from GPS velocity data to constrain the probability model. A retrospective test of the model with earthquake occurrence of the past 30years shows that the model ‘forecasted’ poorly. However, the model seems to ‘forecast’ spatial intensity of earthquakes for the past 500years reasonably well, suggesting that the geodetic strain rate obtained at the decadal scale may still be a good indicator of long term earthquake activity in the region, but only at a time scale of hundreds of years. Our third approach uses GPS velocity data to determine the seismic moment accumulation rates on major faults, and a historical earthquake catalog to estimate seismic moments released in the past. Comparison of the two yields estimates of present day seismic moments cumulated on major faults, and a retrospective test shows some predictive power of the method. Our result suggests that numerous faults in the Sichuan-Yunnan region have cumulated seismic moments capable of producing M>7.5 earthquakes, including the Xiaojiang, Jiali, Northern Nujiang, Nandinghe, and Red River–Puer faults, and the junction fault between the Xianshuihe and Ganzi-Yushu faults.