GPS-derived coupling estimates for the Central America subduction zone and volcanic arc faults: El Salvador, Honduras and Nicaragua
GPS-derived coupling estimates for the Central America subduction zone and volcanic arc faults: El Salvador, Honduras and Nicaragua
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GPS 导出的中美洲俯冲带和火山弧断层的耦合估计：萨尔瓦多、洪都拉斯和尼加拉瓜
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发表时间：
2009
期刊：
影响因子：
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通讯作者：
C. Tenorio
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作者：
F. Correa;C. Demets;D. Alvarado;H. Turner;G. Mattioli;D. Hernández;C. Pullinger;M. Rodriguez;C. Tenorio
摘要我们从萨尔瓦多、洪都拉斯和尼加拉瓜的32个地点反演GPS速度，以估计这些国家近海的中美洲俯冲带以及萨尔瓦多和尼加拉瓜火山弧中的断层的长期弧前运动速度和地震间耦合的分布。用三维有限元模型来近似火山弧中俯冲界面和走滑断层的几何形状，并确定跨越这些断层的耦合的弹性响应。全球定位系统的速度最符合一个模型，即前弧移动14-16 mm yr−1，并具有85%-100%的耦合跨越火山弧中的断层，这与火山弧历史和现代地震活动的高水平相一致。我们的速度反演表明，俯冲界面潜在孕震区之间的耦合非常弱，平均不超过板块会聚速度的3%，只有两个分辨率较差的斑块，在我们模拟的550公里长的区段上，耦合可能更高。我们的弱俯冲耦合的大地测量证据与1690年发表的地震破坏分析得出的地震耦合估计值60%±10%不一致，但与另外三项从20世纪地震中推断弱俯冲耦合的地震学研究相一致。因此，萨尔瓦多和尼加拉瓜西部近海的大多数历史大地震可能是与1982年和2001年萨尔瓦多近海的MW7.3和MW7.7型地震类似的实验室内正常断层事件。或者，耦合程度可能会随时间而变化。弱耦合的证据间接支持了最近发表的一种假说，即中美前弧区的大部分正在向西或西北方向逃逸，远离哥斯达黎加的科科斯山脊碰撞带。这种假设对萨尔瓦多特别有吸引力，因为萨尔瓦多几乎没有或几乎没有会聚倾角来驱动观察到的海沟平行弧前运动。
SUMMARY We invert GPS velocities from 32 sites in El Salvador, Honduras and Nicaragua to estimate the rate of long-term forearc motion and distributions of interseismic coupling across the Middle America subduction zone offshore from these countries and faults in the Salvadoran and Nicaraguan volcanic arcs. A 3-D finite element model is used to approximate the geometries of the subduction interface and strike-slip faults in the volcanic arc and determine the elastic response to coupling across these faults. The GPS velocities are best fit by a model in which the forearc moves 14–16 mm yr −1 and has coupling of 85–100 per cent across faults in the volcanic arc, in agreement with the high level of historic and recent earthquake activity in the volcanic arc. Our velocity inversion indicates that coupling across the potentially seismogenic areas of the subduction interface is remarkably weak, averaging no more than 3 per cent of the plate convergence rate and with only two poorly resolved patches where coupling might be higher along the 550-km-long segment we modelled. Our geodetic evidence for weak subduction coupling disagrees with a seismically derived coupling estimate of 60 ± 10 per cent from a published analysis of earthquake damage back to 1690, but agrees with three other seismologic studies that infer weak subduction coupling from 20th century earthquakes. Most large historical earthquakes offshore from El Salvador and western Nicaragua may therefore have been intraslab normal faulting events similar to the M w 7.3 1982 and M w 7.7 2001 earthquakes offshore from El Salvador. Alternatively, the degree of coupling might vary with time. The evidence for weak coupling indirectly supports a recently published hypothesis that much of the Middle American forearc is escaping to the west or northwest away from the Cocos Ridge collision zone in Costa Rica. Such a hypothesis is particularly attractive for El Salvador, where there is little or no convergence obliquity to drive the observed trench-parallel forearc motion.