Gang Rao

Active Normal Faulting along the Langshan Piedmont Fault, North China: Implications for Slip Partitioning in the Western Hetao Graben

The northwestern margin of the Hetao Graben, North China, is bounded by a pronounced 160-km-long Langshan Piedmont fault (LPF). The kinematics and recent tectonic activity of this rift-border fault and its accommodated extensional strain can help us better assess the seismic potentials. In this study, on the basis of high-resolution satellite images, digital elevation models acquired by small unmanned aerial vehicles using structure-for-motion techniques, field observations, and radiocarbon (14C) age dating, we demonstrate that (1) the LPF is a Holocene active normal fault with an average dip of ∼60°; the extension rate is estimated to be ∼0.4–0.7 mm/y, lower than geodetic strain rate; (2) the ongoing tectonic activity along this fault has played a significant role in controlling the present topography of the Langshan Mountains and neighboring areas; (3) slip partitioning probably occurred in the western Hetao Graben; namely, normal slip dominated the basin-bounding faults, and right-lateral slip occurred on the buried faults within the flat-lying graben. We suggest that precisely determined fault slip rates and geometry are needed with the aim of further quantifying the extensional strain distribution. The results of this study would be helpful in achieving a better understanding of fault development and evolution in actively extending regions.

Relationship between Landslides and Active Normal Faulting in the Epicentral Area of the AD 1556 M ~8.5 Huaxian Earthquake, SE Weihe Graben (Central China)

In this paper, we focus on the characteristics of the landslides developed in the epicentral area of AD 1556 M~8.5 Huaxian Earthquake, and discuss their relations to the active normal faults in the SE Weihe Graben, Central China. The results from analyzing high-resolution remote-sensing imagery and digital elevation models (DEMs), in combination with field survey, demonstrate that: (i) the landslides observed in the study area range from small-scale debris/rock falls to large-scale rock avalanches; (ii) the landslides are mostly developed upon steep slopes of ≥30°; and (iii) the step-like normalfault scarps along the range-fronts of the Huashan Mountains as well as the thick loess sediments in the Weinan area may facilitate the occurrence of large landslides. The results presented in this study would be helpful to assess the potential landslide hazards in densely-populated areas affected by active normal faulting.

Geomorphological signatures of the evolution of active normal faults along the Langshan Mountains, North China

Abstract Segmentation, propagation, and linkage of normal faults often occur in regions of active extension, and observations of the distribution and structural properties of segment boundaries can provide important insights for seismic hazard assessment. In this study, we carry out quantitative geomorphological analysis to evaluate the relative tectonic activity along the Langshan Piedmont Fault (LPF), which bounds the NW margin of the Hetao Graben, North China. On the basis of obtained morphometric indices (HI, BS, Smf, VF, SLK, and χ), tectonic knickpoint heights, footwall topography, and small unmanned aerial vehicles (sUAV)-based field observations, we demonstrate that: (i) The Langshan landscape is in a state of disequilibrium in response to active rock uplift and channel incision; (ii) The LPF consists of two major fault segments with lengths of 65 and 95 km, respectively, which likely have been linked with each other; (iii) Rupturing of the whole of one segment can generate an earthquake of M w ~7.3–7.5, and earthquake magnitude may reach M w ~7.8 if the entire fault trace of ~160 km is ruptured, posing a significant seismic risk in the western Hetao Graben. These findings would further our understanding of normal fault evolution through space and time in actively extending regions.