[M-IS10] Interdisciplinary studies on pre-earthquake processes

[MIS10-03] Assessing Earthquake Forecast Performance Based on b Value in Yunnan Province, China

*Rui Wang¹、Peng Han¹、Ying Chang²、Miao Miao¹、Zhiyi Zeng¹、Hongyan Chen¹、Haixia Shi³、Danning Li⁴、Lifang Liu⁴、Youjin Su⁴ (1.Southern University of Science and Technology, Shenzhen, China 、2.Institute of Mining Engineering, BGRIMM Technology Group, Beijing, China、3.China Earthquake Networks Center, Beijing, China、4.Earthquake Administration of Yunnan Province, Kunming, China)

キーワード： b value, Molchan error diagram, earthquake forecast, Yunnan, China

Many studies have shown that b values tend to decrease prior to large earthquakes. To evaluate the forecast information in b value variations, we conduct a systematic assessment in Yunnan Province, China, where the seismicity is intense and moderate large earthquakes occur frequently. The catalog in the past two decades is divided into four time periods. The spatial b values are calculated for each 5 years span and then are used to forecast moderate large earthquakes (M≥5.0) in the subsequent period. As the fault systems in Yunnan Province are complex, to avoid possible biases in b value computation caused by different faulting regimes when using the grid search, the hierarchical space time point process models proposed by Ogata are utilized to estimate spatial b values in this study. The forecast performance is tested by Molchan error diagram and the efficiency is quantified by probability gain and probability difference . It is found that moderate large earthquakes are more likely to occur in low b regions. The MED analysis shows that there is considerable precursory information in spatial b values and the forecast efficiency increases with magnitude in the Yunnan Province. These results suggest that the b value might be useful in middle and long term earthquake forecasts in the study area. After the end of this study, 21 May 2021, the Ms6.4 Yangbi earthquake preceded with a Ms5.6 earthquake occured on the area predicted to be high risk of moderate earthquake. The temporal b value before and after Yangbi earthquake indicates the difference between foreshocks and background earthquakes. These results suggest that the b value might be useful in short term earthquake forecasts in foreshock mainshock and aftershock sequence.