The left-lateral Altyn Tagh Fault forms the northern boundary of the Tibetan Plateau. The strike-slip rate of the active Altyn Tagh Fault decreases northeastward and reduces close to zero as it passes north of the Qilian Shan. This geometry raises controversies on whether and how the fault terminates or extends further east. To address these controversies, wide-band magnetotelluric data were collected along four profiles across the Altyn Tagh Fault ranging from 135 to 261 km in length. All four profiles are located in the foreland of the Qilian Shan Ranges and are oriented perpendicular to the inferred fault zone that could be the continuation of Altyn Tagh Fault. Both the two-dimensional and three-dimensional electrical resistivity models derived from our magnetotelluric data show that the Hexi Corridor crust is generally of low resistivity, whereas the crust of the Huahai-Jinta basin is, in general, of high resistivity with a local and isolated low-resistivity anomaly within the mid-lower crust. The generally high-resistivity crust of the Huahai-Jinta basin may be rheologically unfavorable for the Altyn Tagh Fault passing through the basin toward the northeast. The entirely different electrical structure between the Hexi Corridor and its northern neighbors indicates the existence of a tectonic boundary that coincides with the Altyn Tagh Fault in the west and reverse faults in the east. The two-dimensional electrical conductivity models suggest that the Altyn Tagh Fault transfers from a single fault in the west to a branching set of mainly dip-slip faults in the east.

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Large restraining bends along active strike‐slip faults locally enhance the accumulation of clamping tectonic normal stresses that may limit the size of major earthquakes. In such settings, uncertain fault geometry at depth limits understanding of how effectively a bend arrests earthquake ruptures. Here we demonstrate fault imaging within a major restraining bend along the Altyn Tagh Fault of western China using the magnetotelluric (MT) method. The new MT data were collected along two profiles across the Aksay restraining double bend, which is bounded by two subparallel strands of the Altyn Tagh Fault: Northern (NATF) and Southern (SATF). Both two‐dimensional (2‐D) and three‐dimensional (3‐D) inversion models show that the Aksay bend may be the center of a positive flower structure, imaged as a high‐resistivity body extending to an ~40 km depth and bounded by subvertical resistivity discontinuities corresponding to the NATF and SATF. In the western section of the Aksay bend, both the NATF and SATF show similar low‐resistivity structure, whereas in the eastern part of the bend, the low‐resistivity anomaly below the SATF is wider and more prominent than that below the NATF. This observation indicates that the SATF shear zone may be wider and host more fluid than the NATF, lending structural support to the contention that fault slip at depth is asymmetrically focused on the SATF, even though surface slip is focused on the NATF. A south dipping, low‐resistivity interface branching upward from the SATF toward the NATF indicates a fault link between these strands at depth.

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Differences in topography and surface deformation in the northern Tibetan Plateau may reflect variable rheology in the lithosphere. Whether middle to lower crustal flow exists below the region between the eastern Kunlun Shan range and the Qaidam Basin remains debated. We provide electrical resistivity images of three new magnetotelluric (MT) profiles across the Qiman Tagh and the western Qaidam Basin. The new models reveal low‐resistivity anomalies below the Qaidam Basin in the lower crust and generally high‐resistivity crust in the Qiman Tagh range. A low‐resistivity anomaly at the uppermost‐mantle level is imaged below the Qiman Tagh range in the profile close to the Altyn Tagh Fault. This anomaly is possibly connected with partial melting in the lower portion of the thickened Songpan‐Ganzi crust close to the southern end of the study area; the minimum requirements for the low‐resistivity anomaly below the Qiman Tagh are 0.05 wt% water content or 0.02 melt fraction, which may greatly decrease the effective viscosity in the uppermost‐mantle rocks and allow flowing. Consequently, we propose that the crustal flow is not mature below the Kunlun Shan range south of the Qaidam Basin because no continuous and stable low‐resistivity anomaly was imaged at this level. The uppermost‐mantle low‐resistivity anomaly below the Qiman Tagh is a passage that allows the continuous northward transfer of materials in the interior of the plateau. This low‐resistivity channel shallows northward and reaches the lower crust of the southwestern Qaidam Basin.