SEISMIC COUPLING AND OUTER RISE EARTHQUAKES
SEISMIC COUPLING AND OUTER RISE EARTHQUAKES
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DOI：
10.1029/jb093ib11p13421
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发表时间：
1988-11-10
期刊：
影响因子：
--
通讯作者：
RUFF, LJ
中科院分区：
文献类型：
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作者：
CHRISTENSEN, DH;RUFF, LJ
俯冲带板间地震耦合的变化是控制最大俯冲事件规模的主要因素。这种变化对俯冲带附近的区域板内应力也有深刻的影响。外隆地震活动与板间耦合的变化密切相关，反映了板间耦合带的应力状态。利用200多个已知震源机制的外隆地震，研究了外隆应力与板间地震耦合的关系。这些事件发生在下行（即，这些板块在测深海沟轴附近具有不同的（大洋）板块，一般属于张性（正常）或压缩性（逆冲）板块，其张性或压缩应力轴大致水平并垂直于海沟。在不耦合的俯冲带中，只发生张性外隆地震，这表明外隆主要由与板块弯曲和/或板拉力相关的张应力控制。在强耦合俯冲带中，既有张性的外隆事件，也有压性的外隆事件，这些事件在时间和空间上都与大的俯冲地震的分布有关，因而是地震周期的一个组成部分。在强耦合区域，张性外部隆起事件跟随大的俯冲事件，因为外部隆起由于俯冲运动而暂时处于张性状态。挤压性外隆事件发生时，挤压应力缓慢积累向海洋锁定部分的板间带。在四个实例中，挤压性外隆地震之后发生了大型下冲事件，这些事件发生在相关的外隆事件之后的2年、4年、7年和19年。其余的挤压性外部隆起事件位于已知地震空区或地震潜力未知的区域。挤压性外隆地震的发生表明，挤压应力正在邻近的板间区域积聚，该区域未来有可能发生大规模的俯冲事件。在中南美洲、千岛群岛、汤加和克马德克群岛、新赫布里底群岛弧和所罗门群岛地区的海沟段，已经发现了30个挤压性外隆事件。在南部堪察加半岛和北方新赫布里底群岛地区的外隆地震活动表明，在外隆的应力状态已随时间从张性，以前的大型俯冲事件，压缩目前。因此，存在从俯冲到张性外隆体制到挤压性外隆体制的三个阶段的循环，仅需要下一次俯冲事件的发生来完成该循环。挤压性外隆事件的发生对于在中等时间尺度上评估一个地区的地震潜力是有用的。
Variation of interplate seismic coupling at subduction zones is a major factor controlling the size of the largest underthrusting events. This variation also has a profound effect on the regional intraplate stresses in the vicinity of the subduction zone. Outer rise seismicity is strongly correlated with variations in interplate coupling, reflecting the stress state of the interplate coupled zone. Over 200 outer rise earthquakes with known focal mechanisms are used to investigate the relationship between stresses in the outer rise and interplate seismic coupling. These events occur within the downgoing (i.e., oceanic) plate near the bathymetric trench axes and generally fall into the categories of tensional (normal) or compressional (thrust) with their tensional or compressional stress axes oriented approximately horizontal and perpendicular to the trench. In uncoupled subduction zones, only tensional outer rise earthquakes occur, which indicates that the outer rise is dominated by tensional stresses associated with plate bending and/or slab pull forces. In strongly coupled subduction zones, both tensional and compressional outer rise events are found. These events are related both spatially and temporally to the distribution of large underthrusting earthquakes and are thus an integral part of the earthquake cycle. In the strongly coupled regions, tensional outer rise events follow large underthrusting events as the outer rise is temporarily in tension due to the underthrusting motion. Compressional outer rise events take place as compressional stress slowly accumulates oceanward of locked sections of the interplate zone. In four instances, compressional outer rise earthquakes have been followed by large underthrusting events which have occurred 2, 4, 7, and 19 years after the associated outer rise event. The remaining compressional outer rise events are located in regions that are either known seismic gaps or in regions where the seismic potential is unknown. The occurrence of compressional outer rise earthquakes suggests that compressional stress is accumulating in the adjacent interplate region and that there is the potential for a future large underthrusting event in the region. Thirty compressional outer rise events have been located in trench segments of Middle and South America, the Kurile Islands, the Tonga and Kermadec islands, the New Hebrides Arc, and the Solomon Islands regions. In both the southern Kamchatka and northern New Hebrides regions the outer rise seismicity indicates that the stress regimes in the outer rise have changed with time from tensional, following a previous large underthrusting event, to compressional at present. Thus three stages of the cycle from underthrusting to tensional outer rise regime to compressional outer rise regime are present, requiring only the occurrence of the next underthrusting event to complete the cycle. The occurrence of compressional outer rise events is useful for assessing the seismic potential of a region on an intermediate time scale.