<br>伊朗西北地下的地壳和上地幔结构：表面波和重力数据的综合分析,Geophysical Journal International

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伊朗西北地下的地壳和上地幔结构：表面波和重力数据的综合分析
Geophysical Journal International ( IF 2.8 ) Pub Date : 2024-08-28 , DOI: 10.1093/gji/ggae306
Taghi Shirzad ₁ , Shaghayegh VahidRavesh ₂ , Gholamreza Mortezanejad ₃ , Somayeh Abdollahi _{4,

5} , Mohsen Kazemnia Kakhki ₆ , Mojtaba Naghavi ₂ , Habib Rahimi ₂ , Mohammad Reza Hatami ₂

Affiliation

摘要了解构造活跃地区的地壳地震特征对于地震危险性评估至关重要。在伊朗西北部进行的研究利用表面波断层扫描、径向各向异性和密度信息来分析该地区复杂的地壳结构，该结构因其不同的构造特征、沉积盆地和火山形成而非常出色。研究人员从 3500 多次 M > 4 地震中选择了 1243 个事件的数据集，并采用严格的数据选择标准（如 SNR、M 和 Δ），使用高斯多重滤波器和相位匹配滤波计算了 Rayleigh 和 Love 波群速度色散曲线。通过排除残差为 > 2σ 的数据来启动断层扫描程序，以提高稳定性。然后对局部 Rayleigh 和 Love 波色散测量进行单独反演，以获得 1-D VSV 和 VSH 模型。径向各向异性和 VSiso 分别通过获得的 VSH 和 VSV 的差异和平均来确定。重力建模与表面波分析一起用于了解该地区的复杂地质，揭示对上-中-下地壳边界、地下结构和 Moho 深度的见解。根据提供的结果，该研究的速度图揭示了与不同地区的地质单元和构造特征相关的重要发现。南里海盆地（SCB）和库拉洼地（KD）地区的低速度归因于大量的沉积层，而伊朗西北部和东安纳托利亚增生杂岩体（EAAC）地区的低速度和 VS 深度表明上部和中部地壳中存在部分熔融物质。 Sanandaj-Sirjan 区（SSZ）区域在 VS 的较长周期和更深处表现出低速异常，周围环绕着正常到高速的异常，表明中间地壳很厚。分析径向各向异性和 VSiso 剖面可以深入了解上-中-下地壳边界、地下结构和 Moho 深度，突出 SSZ 下方的中地壳增厚和下地壳变薄。该研究证实了 SCB 海洋状下地壳在 Talesh （TAL）地区伊朗西北部下方的平缓俯冲，具有坚硬的中间地壳。此外，横截面揭示了火山区板下的火成湖岩，VSiso 为 3.7 km s-1。通过减去两个相邻深度的速度模型，结合参数测试结果观察到的差异表明，萨汉德火山系统是清晰可辨的，而细微俯冲对深达 30 公里的萨巴兰火山的影响仍然不那么明显。Sahand 下方的岩浆室位于 18 至 25 公里的深度。

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The crustal and upper-mantle structure beneath NW Iran: an integrated analysis of surface waves and gravity data

SUMMARY Understanding the crustal seismic characteristics of tectonically active regions is crucial for seismic hazard assessment. The study conducted in NW Iran utilized surface wave tomography, radial anisotropy and density information to analyse the complex crustal structure of the region, which is outstanding because of diverse tectonic features, sedimentary basins and volcanic formations. By selecting a data set of 1243 events out of over 3500 earthquakes with M > 4, and employing strict data selection criteria (such as SNR, M and Δ), the researchers calculated Rayleigh and Love wave group velocity dispersion curves using Gaussian multiple filters and phase-matched filtering. The tomographic procedure was initiated by excluding data with residuals > 2σ for enhanced stability. Individual inversions were then carried out for local Rayleigh and Love wave dispersion measurements to obtain 1-D VSV and VSH models. Radial anisotropy and VSiso were determined through a discrepancy and averaging of the obtained VSH and VSV, respectively. Gravity modelling was also employed alongside surface wave analysis to understand the region's complex geology, revealing insights into upper-middle-lower crust boundaries, subsurface structures and Moho depths. The study's velocity maps reveal significant findings related to geological units and tectonic features in various regions based on the provided results. Low velocities in the South Caspian Basin (SCB) and Kura Depression (KD) regions are attributed to substantial sedimentary layers, while low velocities, and depth of VS in NW Iran and Eastern Anatolian Accretionary Complex (EAAC) regions suggest the presence of partially molten materials in the upper and middle crust. The Sanandaj–Sirjan Zone (SSZ) region shows a low-velocity anomaly in longer periods and greater depths of VS, surrounded by normal to high velocities, indicating a thick middle crust. Analysing radial anisotropy and VSiso profiles offers insights into upper-middle-lower crust boundaries, subsurface structures and Moho depths, highlighting middle crust thickening and lower crust thinning beneath the SSZ. The study confirms the gentle subduction of the SCB oceanic-like lower crust beneath NW Iran in the Talesh (TAL) region, with a rigid middle crust. Additionally, cross-sections reveal igneous laccoliths underplate with a VSiso of 3.7 km s−1 in the volcanic region. The difference observed by subtracting the velocity models at two adjacent depths, combined with parametric test results, indicates that the Sahand volcanic system is clearly identifiable, while the influence of subtle subduction on the Sabalan volcano at depths up to 30 km remains less distinct. The magma chamber beneath Sahand is situated at depths ranging from 18 to 25 km.

更新日期：2024-08-28

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