• ISSN 2097-1893
  • CN 10-1855/P

Moho反射波噪声干涉方法及其在青藏高原东北缘地壳结构成像的应用初探

Preliminary study on Moho reflection wave based on noise interference method and its application in crustal structure imaging of the northeastern margin of the Qinghai–Xizang Plateau

  • 摘要: 基于南北地震带北段布设的密集流动地震台阵的连续波形记录,采用台阵噪声干涉技术获得了青藏高原东北缘Moho面PmP反射波,利用已有的区域三维地壳速度模型,采用沉积层校正方法建立研究区域的三维地壳初始模型,进而对噪声互相关函数进行基准面校正,然后采用共中心点叠加方法获得了研究区的地壳厚度分布. 结果显示,青藏高原东北缘及周边不同块体地壳厚度差异显著,沿青藏高原北东向的扩展方向,地壳厚度逐渐变薄. 祁连造山带中、西段地壳厚度约55~65 km,西秦岭造山带地壳厚度从西至东从53 km左右减小至42 km上下,阿拉善块体地壳厚度约50 km,鄂尔多斯块体西缘地壳厚度约40~45 km. 六盘山断裂、海原断裂与天景山断裂附近呈现局部的地壳增厚,并且出现脉冲状Moho面反射震相,表明断裂带附近可能存在速度跃变较大的Moho面结构. 祁连山北缘断裂出现叠置的反射震相,推测下地壳的逆冲形成了此类Moho结构.

     

    Abstract: Based on the continuous waveform records of the dense seismic array deployed in the northern section of the north–south seismic belt, Moho reflected PmP waves on the northeast edge of the Qinghai–Xizang Plateau were obtained using array noise interferometry technology. The existing regional 3D crustal velocity model was used to establish the initial 3D crustal model of the study area using the sedimentary layer correction method. The noise cross-correlation function was then corrected for the reference plane, and the crustal thickness distribution of the study area was obtained using the common midpoint stacking method. The results revealed a significant difference in crustal thickness between different blocks on the northeast edge and surrounding areas of the Qinghai–Xizang Plateau. The crustal thickness decreases gradually along the northeast extension direction of the plateau. The crustal thickness of the middle and western sections of the Qilian Orogenic Belt is about 55–65 km. The thickness of the western Qinling Orogenic Belt decreases from about 53 km to about 42 km from west to east. The crustal thickness of the Alxa Block is about 50 km, and the result for the western edge of the Ordos Block is between 40 and 45 km. Local crustal thickening was observed near the Liupanshan Fault, Haiyuan Fault, and Tianjingshan Fault, with pulse Moho surface reflection phases indicating the possible existence of Moho structures with significant velocity jumps near the fault zone. The overlapping reflection phases of the fault on the northern edge of the Qilian Mountains may have formed by thrust superimposition of the lower crust.

     

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