Active Bending‐Moment Faulting: Geomorphic Expression, Controlling Conditions, Accommodation of Fold Deformation

Abstract

Bending-moment faults and flexural-slip faults (FSFs), as two basic fault styles due to bending-related tangential longitudinal strain, extensively and prominently crop out as surface scarps in the Pamir-western Kunlun and southern Tian Shan regions, northwestern China. Characteristic geomorphic expression, favorable formation conditions, and the role in folding accommodation of active FSFs have been systematically summarized in our recent studies. Here we investigate similar properties for well-developed bending-moment normal fault (BMnF) scarps at four sites. Our study concludes the following: (i) BMnF scarps are relatively sinuous compared to FSF scarps and probably trend obliquely to the fold hinge. A group of BMnF scarps can delineate a single asymmetric graben or create grabens alternating with horsts. (ii) BMnF scarps primarily overlie poorly-layered conglomerates. The fold's interlimb angle can range from~160°to <40°, and the folding kinematics can vary from active-hinge migration to fixed-hinge rotation. (iii) The fault-zone width, fault spacing, and efficiency in folding accommodation significantly decrease with (a) thinner conglomerate beds, (b) a smaller interlimb angle, and (c) the transition of the hinge from migrated to fixed. (iv) Different bed lithologies and fold geometries beneath the surface account for the predominance of BMnF scarps on the western Kunlun piedmont and FSF scarps in the Pamir-Tian Shan convergent zone.(v) Presence of BMnF scarps on the western Kunlun piedmont indicates that~4 km of fault slip is transferred northward along a detachment at the base of the Cenozoic and is ultimately absorbed by the Mazatagh Thrust in the Tarim Basin.

Slip Rate of the Danghe Nan Shan Thrust Fault from 10Be Exposure Dating of Folded River Terraces: Implications for the Strain Distribution in Northern Tibet

“…At the steeper forelimb of the fold, terrace T2 dips at an angle of ∼17° to the NE (Figure 4, profiles P2, P5, and P6; Figure 5a), whereas in the backlimb, it dips 1-2° to the SW (Figure 4, profiles P2 and P6). On terrace T1 and the southwestern part of terrace T2, minor NW-SE striking faults are observed, which are presumably bending-moment normal faults (e.g., Li et al, 2018). Terrace T3 is only preserved in dome-shaped terrace patches along the crest of the anticline.…”

Neotectonic Activity in the Low-Strain Broken Foreland (Santa Bárbara System) of the North-Western Argentinean Andes (26°S)

“…The cumulative effect of this process was to produce linear fault scarps that are responsible for the formation of the observed trellis drainage patterns and diversions of fluvial channels. This scenario is reminiscent of the evolution of Quaternary flexural-slip faults in areas of flexural-slip folding in the Pamir-western Kunlun and southern Tian Shan regions of Central Asia (e.g., [86,87]).…”

Along‐Strike and Downdip Segmentation of the Pamir Frontal Thrust and Its Association With the 1985Mw6.9 Wuqia Earthquake

“…On the one hand, each along-strike segment may represent a single seismic source, as exemplified by the 1983 M w 6.5 Coalinga event in central California, USA and the 2015 M w 6.4 Pishan event at the Western Kunlun piedmont, China (Guzofski et al, 2007; T. Li et al, 2016). On the other hand, these thrust faults typically dip gently and extend downward far away from their surface traces and merge with horizontal or subhorizontal detachment horizons that then join a lower ramp rooting beneath the uplifted terrain (Figure 1; e.g., Avouac, 2015;Avouac et al, 1993;Guilbaud et al, 2017;Hubbard et al, 2010Hubbard et al, , 2016; T. Li et al, 2018;Yue et al, 2005). Consequently, the cross-section geometry of Correspondence to: T. Li,litao.410@163.com a thrust fault commonly has a wide low-angle fault plane at depth and can include multiple fault ramps and flats defined by fault bends.…”