天山地块强震活动的时空特征研究

The temporal and spatial characteristics of strong earthquakes in Tianshan block

通过对天山地块近百年地震活动时空特征分析表明:①MS≥7.0地震沿块体边界成带分布,南边界带强于北边界带,南、北边界带的西部强于东部,南天山西段是地震活动水平最高、复发周期最短、强震序列类型最复杂、地震危险性最大的地区;②地震活动在时间上显示出准周期性,表现为MS≥7.0地震具有活跃与平静的交替性及5级以上地震活动度曲线的起伏变化;最大熵谱计算地震活动度的显著周期为40年,小波分析给出40年左右周期系数的时间曲线表明,7级以上地震都发生在曲线由最高值至最低值的下降段,而上升段为强震的平静期;③在强震活跃期及平静期,中强以上地震(MS≥5.0)在块体的不同部位(地块南、北边界带及块体内部)的分布状态和活动水平存在明显的差异,在活跃期南、北边界带中强以上地震的集中性和成带性强,且彼此活动水平差异小,但与块体内部差异大;而在平静期南、北边界带的活动水平差异大,块体内部地震活动显著增强;④在活跃期,天山地块南、北边界带强震活动存在一定的呼应关系,当一个边发生强震后,另一边在数天至数年也存在发生强震的可能。

In this paper, the tempo-spatial distribution of strong earthquake since 1895 in Tianshan block has been studies. The results show that: ① All earthquakes with M_S≥7.0 occurred along the boundary zones of the Tianshan block. The seismic activity along southern boundary zone is higher than that along the northern one, and the seismicity of their west is higher than that of their east. While there exists the highest seismic activity and has complicated earthquake sequences along the western segment of the South Tianshan. ② It is obviously that the time distribution of strong earthquakes has quasi-periodic characteristics. The prominent period calculated by the maximum entropy spectral method is 40 years. The cycle coefficient of 40 years obtained by wavelet transform shows that M_S≥7.0 earthquakes occurred in the descend process of the cycle coefficient of 40 years period, and the quiet period is during the increase process of this cycle coefficient. ③ During seismic active periods and quiet periods, the space distribution of the activity of earthquakes with M_S≥5.0 is different in different parts of Tianshan block, for example, the southern boundary of the block, the northern boundary of the block and the interior of the blocks. Especially in active period, the activity difference is smaller between the Southern boundary and the Northern boundary, but the difference between boundaries and the interior of the block is obvious. On the other hand, in quiet period, their difference is small. Meanwhile the seismic activity in the interior of the blocks is very strong. ④ In the activity period, there exists a corresponding relation of seismic activity between the southern boundary zone and the northern boundary zone. That is, if a strong earthquake occurs along one boundary zone, there will occur strong earthquakes along another zone in days or several years.