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特大地震(≥8.0级的地震)一般都含有构造板块之间边界岩体的突然滑动。这种板间的破裂通常出现在俯冲带特大逆冲事件的海沟斜坡区,会产生动态及静态应力变化,从而激活周边的板内余震(Christensen and Ruff,1988;Dmowskaetal,1988;Layetal,1989;Ammonetal,2008)。本文研究的地震序列展示一少见的例子———特大海沟斜坡的一次板内地震触发了广泛的板间断层活动,颠倒了典型的活动模式,从而广泛地扩大了地震和海啸灾害。2009年9月29日,在汤加俯冲带北端的外海沟斜坡发生矩震级8.1的正断层地震事件,该震开始破裂后的2分钟内,发生了总地震矩等于矩震级8.0级的第二个特大地震,它由两次(矩震级均为7.8级)板间下插逆冲大地震组成,导致了周边俯冲带巨型逆断层的破裂。联合的断层作用引发了海啸,局部地区抬升约12m,导致萨摩亚、美属萨摩亚和汤加192人死亡。地震信号的重叠掩盖了这样的事实:相隔约50km的性质不同的断层发生了不同几何形状的破裂,这些被触发的逆冲断层滑动只有通过详细的地震波分析才能揭示出来。在汤加北部俯冲带的大部分区域内,激活了广泛的板间和板内余震活动。
Very large earthquakes (≥ 8.0 earthquakes) generally contain sudden slippage of the boundary mass between the tectonic plates. The rupture between the plates usually occurs in the trench slopes of the super-thrust event of the subduction zone, resulting in dynamic and static stress changes, thus activating the surrounding intraplate aftershocks (Christensen and Ruff, 1988; Dmowska et al., 1988; Layetal, 1989; Ammonetal, 2008). The seismological sequence studied in this paper shows a rare example - an intraplate earthquake that triggered a wide range of plate-faulting events on a very large trench slope, reversing the typical pattern of activity and thus widening the earthquake and tsunami disasters. On September 29, 2009, a normal-fault seismic event with a moment magnitude of 8.1 occurred at the outer trench slope at the northern end of the Tonga subduction zone. Within 2 minutes after the earthquake started to burst, a second It consists of two large earthquakes with intercalation thrusts of magnitude 7.8 with moment magnitudes, resulting in the rupture of the giant reverse faults in the peripheral subduction zone. The joint fault triggered a tsunami that raised some 12 m in some areas, resulting in 192 deaths in Samoa, American Samoa and Tonga. The overlap of the seismic signals obscures the fact that fractures of different geometries of different nature about 50 km apart are fractured in different geometries and that triggered trigonometric thrust slip can only be revealed by detailed seismic wave analysis. In most of the subduction zone in northern Tonga, extensive slab and inboard aftershock activity was activated.