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

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.