Assessing Earthquake Forecast Performance Based on b Value in Yunnan Province, China.

Rui Wang,Hongyan Chen,Zhiyi Zeng,Youjin Su,Miao Miao,Haixia Shi,Danning Li,Lifang Liu,Peng Han,Ying Chang

doi:10.3390/e23060730

Abstract

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 (January 2000–December 2004, January 2005–December 2009, January 2010–December 2014, and January 2015–December 2019). The spatial b values are calculated for each 5-year 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 (HIST-PPM) proposed by Ogata are utilized to estimate spatial b values in this study. The forecast performance is tested by Molchan error diagram (MED) and the efficiency is quantified by probability gain (PG) and probability difference (PD). 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.

Highlights

The Gutenberg–Richter (G–R) law describes the magnitude–frequency relationship of earthquakes, which is lgN = a − bM [1,2]
It can be found that the spatial b value changes in different time periods and moderate–large earthquakes are more likely to occur in areas with low b values, for earthquakes with M ≥ 5.5
The HIST-PPM method is applied to the earthquake catalogs during the past two decades to reveal the spatial–temporal distributions of the b value in Yunnan Province, China

Summary

Introduction

The b value could be an indicator of the stress level underground and may have potential value in earthquake risk assessments. Due to the self-similarity of the earthquake source, recently, it has been documented in several publications of natural time analysis of earthquake catalogues that the entropy concept is of key importance in order to achieve an earthquake risk assessment [8,9,10] since it was revealed that a decrease in the b value before large earthquakes reflects an increase in the order parameter fluctuations upon approaching the critical point (mainshock) stemming from both origins of self-similarity [11], i.e., the process increments infinite variance and/or process memory [12]. It was reported that large earthquakes tend to occur in areas with low b values [25,26], and the temporal variations of b values in epicenter regions show a decrease trend before major earthquakes [24,25,26,32], such as the 2011 Mw9.0

Results

Discussion

Conclusion