Utilizing dense magnetotelluric array to analyze deep seismogenic environment in the Huaibei plain fold belt

The Huaibei Plain Fold Belt, located on the southeastern margin of the North China Plate, lies adjacent to the Tancheng-Lujiang fault zone—one of the most active fault zones in eastern China—characterized by complex tectonic activity. Using a 3D dense magnetotelluric (MT) array, we obtained high-quality MT data through fine time-series processing technology. Dimensionality and structural characteristics were analyzed using phase tensor analysis and statistical imaging of the impedance tensor. A fine and reliable 3D resistivity structure was constructed through nonlinear inversion, combining impedance data with a multiple iterative reconstruction technique. The results reveal that the high-resistivity and low-resistivity areas at shallow depths correspond to the Xuhuai arcuate tectonic structure and the Suzhou-Haogou Basin, respectively, with prominent low-resistivity anomalies present in the middle and lower crust. Beneath the Suzhou-Haogou Basin, blind low-resistivity faults are embedded within high-resistivity media and appear to be connected to deeper low-resistivity anomalies. These low-resistivity features are interpreted as the result of intense tectonic deformation and the presence of crustal fluids. There is no evidence of mantle-derived thermal upwelling, suggesting that deep mantle processes have limited influence on current tectonic deformation. Our findings indicate that the Huaibei Plain Fold Belt hosts a deep structural setting capable of generating strong earthquakes, with deformation primarily driven by horizontal tectonic forces. However, the underlying mechanism driving this deformation requires further investigation.