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    音频大地电磁法在复杂构造带调查中的应用:以藏东信本断裂带八美段为例

    Application of audio magnetotelluric method in the investigation of complex structural zone:A case study of the Bamei section of Xinben fault zone in eastern Xizang

    • 摘要: 信本断裂带为一条发育于青藏高原东部伯舒拉岭岩浆弧内北西—南东向叠加多期构造活动的区域性断裂带,带内地质结构复杂、构造类型多样,前人通过地质调查认为其发育规模仅数百米,在断裂带构造性质上也存在压扭性和逆冲推覆的争议。本文应用音频大地电磁法(audio magnetotelluric method, AMT)在信本断裂带八美段对其开展调查,对所采集数据开展时频域去噪、静态校正、极化模式识别系列精细处理后,采用非线性共轭梯度(nonlinear conjugate gradient, NLCG)反演技术获得高精度二维电性剖面,开展了地质–地球物理综合解译并建立测深剖面地质模型。结合测深剖面电性结构、区域构造背景和浅部构造现象综合查明信本断裂带八美段发育宽度7.2 km,为一条压性走滑构造性质的断裂带,带内发育有系列韧性剪切带、高角度走滑断层,具有早期深部韧性剪切叠加后期浅表层次挤压左行走滑的构造特征。

       

      Abstract: The Xinben fault zone is a regional fault zone with a strike of northwest-southeast direction in the Boshura Ridge magmatic arc of the eastern Qingzang (Tibetan) Plateau, superimposed by multiple tectonic activity, with a complex geologic structure and a variety of tectonic types. Through geologic investigations, it was previously considered to be only a few hundred meters in size and with a controversy of fault nature over the compressive-torsional and thrust-nappe. This paper applies the audio magnetotelluric (AMT) method to investigate the Bamei section of the Xinben fault zone. After the time-frequency domain denoising, static correction, and polarization pattern recognition for the AMT data, this paper uses nonlinear conjugate gradient (NLCG) inversion technology to obtain high-precision two-dimensional electrical profiles, carries out comprehensive geologic-geophysical interpretation, and establishes a geologic model for the bathymetric profiles. Combined with the deep electrical structure of the bathymetric section, the regional tectonic background and the shallow tectonic phenomena, it was found that the fault zone in the Bamei section is a compressive strike-slip tectonic zone with a width of 7.2 km, comprised of a series of ductile shear zones and high-angle strike-slip faults. The fault zone has a tectonic characteristics of early ductile shear superimposed by the later extrusion of left strike-slip on the shallow surface.

       

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