Attenuation tomography in the western central Andes: A detailed insight into the structure of a magmatic arc
Attenuation tomography in the western central Andes: A detailed insight into the structure of a magmatic arc
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安第斯山脉中西部的衰减断层扫描：详细了解岩浆弧的结构
DOI：
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发表时间：
2001
期刊：
影响因子：
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通讯作者：
A. Rietbrock
中科院分区：
文献类型：
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作者：
C. Haberland;A. Rietbrock
皮斯科'94记录的1498次地方地震的高质量资料（《西方科迪勒拉山脉系统调查项目》，1994年）和ANCORP '96（安第斯大陆研究项目，1996年）临时地震台网允许详细测定安第斯山脉中西部现代岩浆弧下的三维（3-D）衰减结构（Qp-1（20°至24°S）。假设在1到30 Hz之间的频带中Qp-1与频率无关，则使用谱比和谱反演技术从P波的振幅谱估计全程衰减（t*）。阻尼最小二乘反演（层析成像）的数据揭示了一个复杂的衰减结构。弧前和俯冲板片的壳幔衰减普遍较低（Qp > 1000）。岩浆弧下的地壳和地幔表现出高衰减。最强的极低Qp异常出现在现代火山弧之下的22° ~ 23°S之间的地壳中（Qp < 100）。可以观察到南北变化：地壳衰减异常的西侧遵循火山前缘的弯曲路线。21°S以北衰减不太发达。在研究区的北方部分，低Qp带穿透到弧前地幔中，直至俯冲板片。在南部，在俯冲板块正上方的南纬23°和24°之间，有一个更深的高衰减区。地幔中的低Qp与地震群有关。强烈的地壳衰减局限于年轻的熔结凝灰岩和火山活动的分布，并解释为热弱化带部分熔融。上地幔中的衰减模式可能反映了软流圈的变化程度，并映射了地幔楔中来自板片流体的俯冲相关水化过程的变化。
High-quality data from 1498 local earthquakes recorded by the PISCO ’94 (Proyecto de Investigation Sismologica de la Cordillera Occidental, 1994) and ANCORP ’96 (Andean Continental Research Project, 1996) temporary seismological networks allowed the detailed determination of the three-dimensional (3-D) attenuation structure (Qp−1) beneath the recent magmatic arc in the western central Andes (20° to 24°S). Assuming a frequency-independent Qp−1 in a frequency band between 1 and 30 Hz, whole path attenuation (t*) was estimated from the amplitude spectra of the P waves using spectral ratios and a spectral inversion technique. The damped least squares inversion (tomography) of the data reveals a complex attenuation structure. Crust and mantle of the forearc and subducting slab are generally characterized by low attenuation (Qp > 1000). Crust and mantle beneath the magmatic arc show elevated attenuation. The strongest anomaly of extremely low Qp is found in the crust between 22° and 23°S beneath the recent volcanic arc (Qp < 100). N-S variations can be observed: The western flank of the crustal attenuation anomaly follows the curved course of the volcanic front. North of 21°S the attenuation is less developed. In the northern part of the study area the low-Qp zone penetrates in the forearc mantle down to the subducting slab. In the south a deeper zone of high attenuation is resolved between 23° and 24°S directly above the subducting slab. Low Qp in the mantle correlates with earthquake clusters. The strong crustal attenuation is confined to the distribution of young ignimbrites and silicic volcanism and is interpreted as a thermally weakened zone with partial melts. The attenuation pattern in the upper mantle might reflect the variable extent of the asthenosphere and maps variations of subduction-related hydration processes in the mantle wedge from slab-derived fluids.