Crustal and mantle shear velocity structure of Costa Rica and Nicaragua from ambient noise and teleseismic Rayleigh wave tomography
Crustal and mantle shear velocity structure of Costa Rica and Nicaragua from ambient noise and teleseismic Rayleigh wave tomography
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DOI：
10.1093/gji/ggt309
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发表时间：
2013-11
影响因子：
2.8
通讯作者：
N. Harmon;M. S. D. L. Cruz;C. Rychert;G. Abers;K. Fischer
中科院分区：
文献类型：
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作者：
N. Harmon;M. S. D. L. Cruz;C. Rychert;G. Abers;K. Fischer
哥斯达黎加-尼加拉瓜俯冲带在弧化学、地质、构造和地震速度和衰减方面显示出系统的沿着走向变化，在几百公里范围内呈现出全球极值。在这项研究中，我们使用地震和环境噪声派生的面波层析成像产生的三维剪切速度模型的区域。我们使用TUCAN阵列的48个站，和多达94个事件的瑞利波反演，和18个月的连续数据的互相关估计绿色的功能，从环境噪声。在地壳浅部（0-15？公里），我们观察到低剪切速度直接下方的弧火山（40公里厚的地壳下面的哥斯达黎加弧和基律纳高地，薄地壳（？20个？km），弧后地区地壳厚度增加，与接收函数研究一致。尼加拉瓜弧下地壳变薄、地震缓慢和可能弱化的区域并不是与斜向俯冲有关的局部变形。在地幔深度（55-120？公里深度），我们观察到较低的剪切速度（高达3？per？与哥斯达黎加相比，我们的低剪切速度异常尼加拉瓜下方是在同一位置的低剪切速度异常和位移的背弧从体波层析成像中观察到的高VP/VS异常。尼加拉瓜下方较低的剪切速度可能表明地幔中较高的熔体含量，这可能是由于来自板片或较高温度的较高挥发性通量。最后，我们观察到一个线性的高速区域深度>120？与海沟平行，这与俯冲板片一致。
The Costa Rica–Nicaragua subduction zone shows systematic along strike variation in arc chemistry, geology, tectonics and seismic velocity and attenuation, presenting global extremes within a few hundred kilometres. In this study, we use teleseismic and ambient noise derived surface wave tomography to produce a 3-D shear velocity model of the region. We use the 48 stations of the TUCAN array, and up to 94 events for the teleseismic Rayleigh wave inversion, and 18 months of continuous data for cross correlation to estimate Green's functions from ambient noise. In the shallow crust (0–15?km) we observe low-shear velocities directly beneath the arc volcanoes ( 40-km-thick crust beneath the Costa Rican arc and the Nicaraguan Highlands, thinned crust (?20?km) beneath the Nicaraguan Depression, and increasing crustal thickness in the backarc region, consistent with receiver function studies. The region of thinned, seismically slow and likely weakened crust beneath the arc in Nicaragua is not localizing deformation associated with oblique subduction. At mantle depths (55–120?km depth) we observe lower shear velocities (up to 3?per?cent) beneath the Nicaraguan arc and backarc than beneath Costa Rica. Our low-shear velocity anomaly beneath Nicaragua is in the same location as a low-shear velocity anomaly and displaced towards the backarc from the high VP/VS anomaly observed in body wave tomography. The lower shear velocity beneath Nicaragua may indicate higher melt content in the mantle perhaps due to higher volatile flux from the slab or higher temperature. Finally, we observe a linear high-velocity region at depths >120?km parallel to the trench, which is consistent with the subducting slab.