印尼苏门答腊9.0级地震前地震活动图像异常特征研究

Characteristics of Seismic Activity before the Devastating Earthquake with MW9.0 off the West Coast of Nrothern Sumatra

通过对2004年12月26日印尼苏门答腊9.0级大震前不同时空尺度地震活动性异常特征分析发现:①大震前10年,澳大利亚板块北部边界带深源地震活动显著增强,表现为频度增多、强度增大、震源深度增加等,特别是震源深度分布的非均匀性增大(即地震集中分布在500～689km深度间);同期,苏门答腊岛及其附近M≥7.0浅震活动也异常显著,形成长约1000km、宽300km的集中区。②震前1年全球M≥7.0地震活动出现明显的平静-密集现象,且在密集阶段强震沿澳大利亚板块北部边界带呈带状展布;这时主震震源区附近出现5级地震空区。③震前半年澳大利亚板块北部边界带的东、西两端先后发生2次7级以上深震,其中1次发生在罕有深震活动的苏门答腊岛。④震前3天,澳大利亚板块北部边界带上4级以上地震呈带状展布。⑤震前4年澳大利亚板块北部边界带火山活动增强,特别是震前1年火山活动异常显著。

Characteristics of seismic activity in different time-spatial domain before the Mw 9.0 earthquake was studied. The results are as follows： ①The activity of the deep earthquakes in north boundary zone of the Australian plate had evidently strengthened since 1994. It is obviously that the deep earthquake frequency has increased, the strength is stronger and the earthquake depth is deeper, especially the distribution of the earthquake depth became heterogeneous （ Namely with the earthquakes mainly occurred in a depth between 500km and 689km）. Meanwhile, the shallow earthquakes with M≥7.0 in the Sumatra island and its vicinity had obviously strengthened too, and formed a strengthening area with about 1000km long and 300km width.②The time distribution of global strong earthquakes with M≥ 7.0 show the characteristics of anomalous seismic quiescence-activity one year before the Mw9.0 earthquake and during the active period, the strong earthquakes formed a seismic belt with NWW strike direction. At the same time, there is a seismic gap formed by earthquakes with M≥ 5.0 in the epicenteral area and its neighboring. ③Two deep earthquakes of M ≥ 7.0 occurred in the west and the east of the north boundary zone of the Australian plate 6 months ago. It is notable that one of them occurred in the Sumatra island where there was no M≥ 6.0 deep earthquake during the last thirty years. ④The space distribution of the moderate shocks occurred three days ago exhibited a NWW strike seismic belt along the north boundary zone of the Australian plate. ⑤The activity of volcanoes distributed in the north boundary zone of the Autralian plate had been obviously strengthened 4 years before, especially in several months before the Mw 9.0 earthquake.