【摘要】 2013-04-20四川芦山Ms7.0级强烈地震造成了极大的破坏,主震后发生了密集的余震,对其初期余震时间变化规律的认识有助于科学指导灾后重建和防灾减灾工作。根据国家地震科学数据共享中心的中国地震台网2013-04-20—05-06期间的余震时间序列数据,运用分形计盒维数的方法,研究不同震级阈值下余震序列的分形演化特征。结果表明,不同震级的芦山余震序列均表现出标度不变性和自相似特征,意味着对某震级阈值以上的余震来说,较小时间尺度内的数量与较高时间尺度内的余震数量具有相同的幂律分布规律,可以直接根据分形盒维数推算出未来某一时间尺度内高于某一震级阈值的余震的数量,这在高震级余震预测预报中有着重要的实际意义。芦山早期余震过程的分形盒维数随时间演化表现出快速衰减的趋势,这一特征与汶川余震序列有显著差异,反映出芦山地震能量释放非常快速,高震级余震在时间轴上的分布迅速地由密集变得非常稀疏;由于芦山地震能量释放很快,破坏了自组织临界条件,因此在余震后期不易累积诱发高震级的余震。但是由于主震及早期密集余震造成山体结构不稳、地表土质和岩石疏松,在本区复杂的地质构造、山地地形及独特的天气气候条件下,次生地质灾害的风险将被极大的放大,尤其要关注7—8月降雨密集期降水诱发地质灾害的风险。更多还原

【Abstract】 The strong earthquake of Ms7.0 grade in April 20,2013 in Lushan,Sichuan Province,which caused great destruction,after the main shock occurred some dense aftershocks,understanding the time variation of early aftershock contributes to the scientific guidance for post-disaster reconstruction and disaster prevention and mitigation.This paper checked the time series data of aftershocks from April 20 to May 6th,2013,according to the China Seismic Network unified earthquake catalog of National Earthquake Scientific Data Sharing Center,using the fractal box dimension method to study the fractal evolution characteristics of aftershock sequences in the different magnitude threshold.The results show that,Lushan aftershock sequence of different magnitudes have shown a characteristic of scale invariance and self-similarity,which means that,for aftershocks above the certain magnitude threshold,the number of aftershocks within the smaller time scale and the higher time scale has the same power-law distribution.,according to fractal dimension,the number of aftershocks above a certain magnitude threshold within a future time scale can be calculated directly,which has an important practical significance in the prediction of high magnitude aftershock.The fractal box dimension of early aftershocks in Lushan with time evolution showed rapid attenuation trend,this characteristic has a significant difference from the Wenchuan aftershock sequence,which reflects the rapid energy release of Lushan earthquake,and the distribution of high-magnitude aftershocks on the time axis quickly become very sparse from the dense;since the Lushan earthquake energy release soon,undermining the self-organized critical condition,therefore,it’s not easy to accumulate aftershocks which induce high-magnitude aftershocks in the late aftershocks.However,due to the main shock and early intensive aftershocks caused instability of the mountain structure and loose the surface soil and rock,in this area of complex geological structure,mountainous terrain and the unique weather and climate conditions,the risk of secondary geological disasters will be greatly amplified,particular attention should be paid to the rainfall-induced geological disasters risk of intensive rainfall during July and August.更多还原