中国大陆地震低活动异常及其在中期预测中的效能研究

Low Seismicity Anomaly and its Efficiency in Mid-term Earthquake Forecasting in Chinese Mainland

在对中国大陆地震活动的分析研究中发现,在某些大地震发生前的一、两年中,中国大陆往往出现地震活动显著平静的低活动异常。本文应用最近100 a(1918—2017年)间5级以上地震资料,分析地震低活动异常与未来一、两年中国大陆地震活动的关系。从M≥5.0地震的年频度、年度最大地震震级、 6级以上地震的平静等方面建立了地震低活动异常的判据指标,并从概率增益指数β、预测效能比α、地震预测R值评分等方面对地震低活动异常与未来大震关系作了多参数检验。初步研究结果显示,地震低活动异常与未来一、两年中国大陆地震活动有一定的关系,主要表现为其与8级左右(M≥7.8)巨大地震具有一定的相关性,但其关联度较低,概率增益指数β与预测效能比α为3左右,R值评分为0.2左右。对于M<7.5的地震,地震低活动异常未显示,其概率增益β,R值评分接近于0,似呈现为近于随机关系。M7.5是开始显示地震低活动异常与其有一定相关性的转折点。

From the study of seismicity in Chinese mainland,we found that obvious low seismicity anomalies occur 1~2 years before some strong earthquakes.Using M≥5.0 seismic data in recent 100 years,in this paper the relations between low seismicity anomaly and future seismicity of Chinese mainland were analyzed.We established low seismicity indicator from annual frequency of M≥5.0 earthquakes,the maximum earthquake magnitude,and M≥6.0 seismic quiescence.Furthermore,the relations between low seismicity anomaly and future strong earthquakes were checked through probabilistic gain indexβ,predicting efficiency ratioαand R value for earthquake forecasting efficiency testing.Preliminary results indicate that some coefficients exist between low seismicity anomaly and future seismicity in Chinese mainland,mainly reflected in M≥7.8 huge earthquakes.However,the coefficients of M≥7.8 huge earthquakes are limited,and probabilistic gain indexβand predicting efficiency ratioαare about 3,R value for earthquake forecasting efficiency testing is about 0.2.For M<7.5 earthquakes,low seismicity anomaly is not exhibited,its probabilistic gain indexβand predicting efficiency ratioαare near 0,which appear as random relations.The turning point at which some relations with low seismicity anomaly show is M7.5.