Abstract: Based on the statistical results of 86 earthquakes with magnitude≥5.0 in the middle section of the north-south seismic belt and its surrounding regions since 1973, the types of earthquake sequences and the spatial distribution characteristics have been studied. Main conclusions are drawn as follows: 1)The sequence types of moderate and strong earthquakes in the study area are dominated by mainshock-aftershock sequence type(MAT), followed by multiple main-shock type(MMT)and least the isolated earthquake type(IET)sequence. In the same sequence type, with the increase of earthquake magnitude, the proportion of the MAT sequence increased, while the number of MMT and IET gradually decreased, M≥7 earthquakes are mainly of MAT, and there are no IET earthquakes. Among the different rupture types, the MAT earthquakes are the most in the thrust-type, while the MMT earthquakes are more likely to occur in the strike-slip and the normal-fault earthquakes. 2)There is a relatively good linear relationship between the mainshock-aftershock sequence type earthquakes and the maximum aftershock magnitude of the MAT and MMT sequences; the largest aftershock of most earthquakes mostly occurred in 15 days after the mainshock, the largest aftershock of MAT mainly occurred within 3 days after the mainshock, the largest aftershock of MMT earthquakes mainly occurred within 12 days after the mainshock, and the largest aftershock of IET earthquakes mostly occurred on the day of the earthquake. 3)The spatial distribution of seismic sequence shows that the MAT earthquake distribution range is relatively wide, the MMT earthquakes are mainly concentrated in Batang-Litang, Mabian-Zhaotong, Songpan area in Sichuan Province and Yunlong, Yao 'an, Longling and nearby areas in northwest Yunnan Province. IET earthquakes are more likely to occur in Ganzi-Yushu fault zone, the northwestern segment of Xianshuihe fault zone and in Sichuan Basin. 4)The distribution of seismic sequence types in the middle section of the north-south seismic belt and its adjacent areas may be related to the geological structure, historical seismic activity and the crustal stress in this region. The distribution of seismic sequence types also reflects the tectonic movement and dynamic environment in this region.

Key words: the middle section of the north-south seismic belt, sequence type, magnitude of maximum aftershock, spatial distribution of seismic sequence

摘要： 文中根据南北地震带中段及附近区域1973年以来86次5.0级以上的地震序列统计结果, 对地震序列类型和空间分布进行分析, 结果表明: 1)研究区域内的地震序列以主余型为主(51%), 多震型次之(29%), 孤立型最少(20%); 同一序列类型中, 随着地震震级增大, 主余型地震所占的比例增加, 多震型、 孤立型逐渐减少, 7.0级以上地震以主余型为主, 无孤立型地震; 对于不同破裂类型, 逆冲型地震中主余型最多, 多震型地震更可能为走滑和正断性质的地震。 2)主余型和多震型地震序列的主震与最大余震震级的线性关系相对较好; 绝大多数地震的最大余震多发生在震后20d内, 主余型最大余震集中在震后3d内发生, 多震型地震中次大地震集中在震后12d内发生, 孤立型地震的最大余震多发生在地震当天。 3)地震序列空间分布显示, 主余型地震分布相对较广, 多震型地震主要集中在川西巴塘—理塘、 川东马边—昭通一带、 川北松潘和滇西北云龙、 姚安、 龙陵及附近区域, 甘孜-玉树断裂带、 鲜水河断裂带NW段及四川盆地等地更易发生孤立型地震。 4)地震序列类型的空间分布可能与本区域的地质构造和历史地震活动存在一定的关系。

关键词: 南北地震带中段, 地震序列类型, 最大余震震级, 序列空间分布特征