ISSN 1004-4140
CN 11-3017/P

走时互易性约束壳幔速度结构的反演方法及实例

An Inversion Method for Crust-Mantle Velocity Structure Constrained by Traveltime Reciprocity: Case Study of Pamir Region

  • 摘要: 地震波传播具有走时互易性,即当震源与接收点位置互换时,其传播时间保持不变。基于此原理,本文提出一种适用于无观测台站或台站分布稀疏区域的走时互易性层析成像反演方法。该方法利用远场台站记录的地震走时数据,结合理论传播路径及传播时间的估值,反演震源区及其周边的壳幔速度结构。以帕米尔高原区域的地震事件为例,本文选取40个地震及其周边3000余公里范围内121个地震台站的观测数据,开展走时互易性层析成像反演,系统评估传播时间的不同估算方式以及研究区域边界设置对反演结果的影响。同时,将走时互易性层析成像结果与传统近震层析成像结果进行对比,进一步验证其反演精度与可靠性。测试结果表明,不同估算方式所得的速度结构特征具有高度一致性,主要结构单元在不同研究区域边界下均能被稳定反演求出,体现出良好的区域适应性。与传统近震成像结果相比,走时互易性层析成像不仅能够得到可靠的反演结果,还可以获得比震源区域稍广的壳幔结构图像,尤其适用于无台站覆盖或观测条件受限的震源区域。本研究为深部结构探测提供了有效且可行的备选途径,具有良好的应用潜力与推广前景。

     

    Abstract: Seismic wave propagation exhibits traveltime reciprocity; thus, the traveltime remains unchanged when the positions of the source and receiver are interchanged. This study proposes a traveltime reciprocity tomography method designed for regions without or with sparse seismic station coverage. Moreover, the method utilizes traveltime data recorded at distant seismic stations, combined with theoretical propagation paths and traveltime estimations, to invert the crust–mantle velocity structure within and around the earthquake source region. We selected 40 earthquakes and 121 seismic stations within a 3000-km radius in the Pamir Plateau region to perform traveltime reciprocity tomography inversion. The impacts of different traveltime estimation approaches and variations in the study area boundaries were evaluated. Furthermore, the traveltime reciprocity tomography results were compared with those obtained from traditional local earthquake tomography to verify the accuracy and reliability of the inversion. The tests demonstrated that velocity structure features derived from different estimation methods are highly consistent. In addition, major structural units can be recovered under varying study area boundaries, indicating strong regional adaptability. Compared with traditional local earthquake tomography, the traveltime reciprocity tomography produced reliable inversion results. In addition, it yielded a slightly broader crust–mantle structural image extending beyond the source region, making it suitable for seismic source zones that lack station coverage or have limited observational conditions. This study provides a practical and feasible alternative approach for deep structure imaging, with promising potential for practical applications and broader dissemination.

     

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