This paper analyzes the enhancement of small earthquakes before 8 earthquakes with M≥5 in inland South China since 1970, summarizes and extracts the common characteristics of the enhancement of small earthquakes before earthquakes, and gives the enhancement tracking strategy of small earthquakes before earthquakes. There has been enhancement increase of small earthquakes before 8 earthquakes with M≥5 in inland South China since 1970,the enhancement of small earthquakes can be used as an important prediction index for earthquake tracking in inland South China. Before the earthquake, the activity of small earthquakes is mainly enhanced-calm-seismogenic. From 1970 to 2010 and from 2011 to 2021,there were concentrated enhancement of earthquakes with ML≥3.0 and ML≥2.5 before the earthquakes with ML≥5.0, and at least one earthquake with ML≥4.0 occured. The dominant period for earthquakes with M≥5 in the west section of the southeastern coastal seismic belt is within 6.5 months after the end of enhancement, while that in the east section of the southeastern coastal seismic belt and the Youjiang seismic belt is within 19-33 months. The target earthquakes generally occur in the earthquake concentrated enhancement or active area and the surrounding areas. In the future, it is necessary to strengthen the tracking research and judgment of the concentrated enhancement or activity and spatio-temporal evolution of earthquakes with ML≥2.5 in inland South China.
图1 1970年以来华南及邻区M≥5.0地震分布及华南地区地震带划分[14] Fig.1 Distribution of earthquakes with M≥5.0 in South China and its adjacent areas since 1970 and division of seismic zones in South China[14]
图2 1982年云南富宁5.7级地震前小震活动图像(a)和增强区M-T图(b) Fig. 2 The seismicity image of small earthquakes before the Funing M5.7 earthquake in Yunnan in 1982(a)and the M-T map of the enhanced area(b)
图3 1982年江西龙南5.2级地震前小震活动图像(a)和增强区M-T图(b) Fig.3 The seismicity image of small earthquakes before the Longnan M5.2 earthquake in Jiangxi in 1982(a)and M-T map of the enhanced area(b)
图4 1987年江西寻乌5.5级地震前小震活动图像(a)和增强区M-T图(b) Fig. 4 The seismicity image of small earthquakes before the Xunwu M5.5 earthquake in Jiangxi in 1987(a)and the M-T map of the enhanced area(b)
图5 2016年广西苍梧5.4级地震前小震活动图像(a)和增强区M-T图(b) Fig.5 The seismicity image of small earthquakes before the Cangwu M5.4 earthquake in Guangxi in 2016(a)and the M-T map of the enhanced area(b)
图6 2019年广西靖西5.2级地震前小震活动图像(a)和增强区M-T图(b) Fig.6 The seismicity image of small earthquakes before the Jingxi M5.2 earthquake in Guangxi in 2019(a)and M-T map of the enhanced area(b)
表1 华南内陆5级以上地震前小震增强情况统计Table 1 Statistics on small earthquakes enhancement before earthquakes with M≥5.0 in inland South China