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(A) Elevation distribution of the boreholes and terraces in Sertengshan; (B) elevation distribution of the boreholes and terraces in Wulashan; (C) elevation distribution of the boreholes and terraces in Daqingshan.
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The slip rate is a fundamental kinematic parameter of active faults. Traditional methods using fault scarps or trenches may produce inaccurate estimates of a fault’s vertical slip rate. A normal fault’s vertical slip rate requires constraints from the hanging wall and footwall. Here, the vertical slip rate at each measuring point along the fault wa...
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Citations
... mm/a (Liang et al., 2019); 3) the vertical slip rates of the Daqingshan Piedmont Fault were 2.5-3.88 mm/a and 1.78-2.83 mm/a since 58 and 11 ka (Xu et al., 2022); 4) the vertical slip rate of Wulashan Piedmont Fault were 2.20-2.28 mm/a and 1.12-1.34 ...
The Late Quaternary activity characteristics of secondary faults located between the main active faults at the boundaries of large basins are of great significance to the overall understanding of regional seismic hazards. The Wulashan Northern Fault (WNF) is located on the northern side of the Ordos Block, within the Northern Margin Fault Basin in North China, between the Sertengshan Piedmont Fault and Daqingshan Piedmont Fault. Current research on the geometry and kinematics of the WNF needs to be improved. In this study, we aimed to determine the shallow structural characteristics and Late Quaternary activity of the WNF using shallow seismic exploration and composite drilling geological cross-sectional analysis. The results indicate that the WNF is not a single surface fault but multiple branches with a northward-dipping stepped surface distribution. The latest activity of the F1 branch with a maximum coseismic vertical dislocation of 0.9 m occurred before 47.08 ± 3.7 ka B.P. The latest and older activities of the branch of F2 with a maximum coseismic vertical dislocation of 0.96 m and 1.15 m occurred before 73.8 ± 2.8 ka B.P. and 91.2 ± 4.4 ka B.P., respectively. According to a series of empirical relationships between length of surface rupture and magnitude, the maximum potential magnitude of the earthquake was determined to be M = 6.5–7.0. We argue that even though the Late Quaternary activity of the WNF was weaker than that of the other boundary faults of the Hetao Basin, the local urban and rural planning and land and resources construction in the Hetao Basin region should pay attention to the seismic risk of the WNF as an independent section in the future for the effect of secular tectonic loading.
... The city of Hohhot is mainly divided into two geomorphic units, with the northern Daqing Mountain and southeastern Manhan Mountain being mountainous terrains, and the southern and southwestern areas being the Tumochuan Plain, with the terrain gradually sloping from northeast to southwest. Located in the northwestern part of the North China fault block, within a radius of 320 km centered on the city, there are two active tectonic zones, Yin Mountain and northern Shanxi, which have complex geological structures and are influenced by the northeast-southeast squeezing stress field in the North China Seismic Zone [38,39]. Hohhot is an important seismic zone in North China with frequent seismic activity. ...
The subway alleviates the traffic pressure in the city but also brings the potential risk of land subsidence. The land subsidence caused by the subway is a global problem that seriously affects the safety of subway operations and surrounding buildings. Therefore, it is very important to carry out long-term deformation monitoring on the subway system. StaMPS-PS is a time-series Interferometric Synthetic Aperture Radar (InSAR) technique that serves as an effective means for monitoring urban ground subsidence. However, the accuracy of external (Digital Elevation Models) DEM will affect the accuracy of StaMPS-PS monitoring, and previous studies have mostly used SRTM-1 arc DEM (30 m) as the external DEM. In this study, to obtain a more precise measurement of surface deformation caused by the excavation of the Hohhot subway, a total of 85 scenes of Sentinel-1A data from July 2015 to October 2021, as well as two different resolution digital elevation models (DEMs) (ALOS PALSAR DEM and SRTM-1 arc DEM), were used to calculate and analyze the subsidence along the subway line in Hohhot city. The StaMPS-PS monitoring results showed the ALOS PALSAR DEM, as an external DEM, had higher accuracy, and there was regional subsidence in both the construction processes of Line 1 and Line 2 of the Hohhot subway, with a maximum subsidence rate of −21.1 mm/year. The dynamic changes in subway subsidence were fitted using the Peck formula and the long short-term memory (LSTM) model. The Peck formula results showed the width and maximum subsidence of the settlement troughs gradually expanded during the construction of the subway. The predicted values of the Root Mean Square Error (RMSE) and Mean Absolute Percentage Error (MAPE) of the LSTM model were less than 4 mm and 10%, respectively, consistent with the measured results. Furthermore, we discussed the factors that affect settlement along the subway line and the impact of two external DEMs on StaMPS-PS. The study results provide a scientific method for DEM selection and subsidence analysis calculations in the StaMPS-PS monitoring of urban subway subsidence.
... The complete Holocene vertical slip rates of the three faults in the northern margin of the Hetao Basin were calculated by using boreholes in the hanging wall and terraces in the footwall. From west to east, the vertical slip rates of the Sertengshan piedmont fault, Wulashan piedmont fault, and Daqingshan piedmont fault are 1.68 mm/a, 2.3 mm/a, and 2.45 mm/a, respectively (Xu et al., 2022). ...
... The paleoearthquake events are concentrated after 5.77 ± 0.11 ka, and certain characteristics of clustering are present; however, the COV of the Tuzuoxi and Hohhot segments is closer to 0, and its paleoearthquake event periodicity is more obvious, which is more conducive to estimating the time of the next event. Xu et al. (2022) calculated the complete vertical slip rates of the three faults in the northern margin of the Hetao Basin by considering strata inclination and using the boreholes in the hanging wall and the marker strata of the terrace in the footwall. Combining the long series and recurrence characteristics of paleoearthquakes obtained in this study, we can provide support for evaluating the seismic hazards of faults. ...
... Therefore, we believe that the hazard of earthquakes is high for the Wulashan piedmont fault, and the Baotou segment has a higher chance of rupturing sooner than later. The Daqingshan piedmont fault exhibits high activity and a high slip rate under the dual action of eastward migration of the sedimentary center and vertical movement of deep materials in the Hetao Basin (Xu et al., 2022). Among the five fault segments, the Baotou east and Bikeqi segments have fewer trenches, and their future seismic hazard is difficult to accurately evaluate because of incomplete paleoseismic data and a lack of slip rate data. ...
Long paleoearthquake series are crucial for understanding the recurrence patterns of active faults and evaluating the seismic hazards of faults. In this study, the first semiquantitative evaluation of paleoearthquake events from trenches was applied to normal faults, and classification criteria for identifying paleoearthquakes in trenches on normal faults are proposed to demonstrate the feasibility of semiquantitative evaluations of paleoearthquake events on normal faults. In this study, 72 paleoearthquake trench sites on normal faults around the world were analyzed, and the main indicators for identifying paleoearthquakes on normal faults include the presence of vertical offset (VO), collapse wedge (CW), fissure (FIS), buried paleosol (BP), angular unconformity (AU), upward termination (UT), and sand liquefaction (LF) features. To describe and apply this semiquantitative evaluation method for paleoearthquake events on normal faults, 33 trenches for paleoearthquakes on a fault system in the northern margin of the Hetao Basin were comprehensively analyzed to determine Holocene paleoearthquake events on the Sertengshan, Wulashan, and Daqingshan piedmont faults, and the reliability of paleoearthquake events is discussed. The integrity of the paleoearthquake events obtained was tested by the displacement limit method. The Holocene paleoearthquake recurrence on the three faults was quasiperiodic; the coefficients of variation (COVs) were 0.44, 0.58, and 0.4.
... mm/a (Yang et al., 2002(Yang et al., , 2003Zhang et al., 2017). He et al. (2020) and Xu et al. (2022) reported slip rates of 0.7-2.3 mm/a for the WPF since the late Pleistocene. ...
... mm/a for the WPF since the late Pleistocene. For the DPF, the latest results show that the Holocene vertical slip rate of the fault is~1.8-2.8 mm/a (Xu et al., 2022). However, the activity of the faults on the southern boundary of the Hetao Basin is low, and quantitative research is lacking. ...
The slip rates of normal faults on the northern margin of the Ordos Block are critical for understanding the deformation of the Ordos Block and adjacent areas. In this study, we obtain the late Pleistocene slip rate of an active normal fault, the Zhuozishan West Piedmont Fault (ZWPF), in the northwestern corner of the Ordos Block. Satellite imagery interpretation and field investigations suggest that the fault displaces late Pleistocene alluvial fans and forms west-facing fault scarps. To quantify the vertical slip rate of the ZWPF, we measured the displacements along the fault scarps using differential GPS and an unmanned aerial vehicle system and dated the displaced geomorphic surfaces using optically stimulated luminescence (OSL) dating methods. The vertical slip rate of the fault is constrained to 0.1 ± 0.02 mm/a, which suggests a horizontal extension rate of 0.05 mm/a for a dip of 65°. This rate is consistent with those on similar structures in the northwestern Ordos Block. Combining this result with published slip rates along other active faults, we infer that the NW-directed extension rate across the northwestern corner of the Ordos Block is ∼0.6–1.3 mm/a. This rate is comparable with the geodetic strain rate. Given the extension rate, we believe that extensional deformation is mainly concentrated on the western side of the basin.
... earthquakes in this area. Due to the lack of large earthquakes recorded by modern instruments in the fault depression structural area of LLA, the existing research results in this area focus on geomorphology and paleoseismology (Jia et al., 2016;Rao et al., 2016;He et al., 2017He et al., , 2018Dong et al., 2018aDong et al., , 2018bDong et al., , 2018cHe et al., 2020;Zhang et al., 2020;Li J. et al., 2021;Liang et al., 2021;Xu et al., 2022). The results obtained lack the support of deep geophysical data. ...
A series of fault depression structures have developed around the Ordos Block. The Langshan Mountain-Linhe Basin area (LLA), located on the northwest edge of the Ordos Block, is a typical, normal tension fault system. A geological survey shows that the Langshan Piedmont fault (LPF) in this area has a large slip rate and indicates risk of earthquake preparation. Broadband magnetotelluric (MT) exploration research was recently carried out across the LLA in the NW–SE direction, and the three-dimensional deep electrical structure thus obtained revealed that the LPF in the LLA is an evident electrical boundary zone on the whole crustal scale and is the main boundary fault of the primary structural block of the Alxa and Ordos Blocks. The MT results also show that the Linhe Basin and Ordos Block belong to the same tectonic basement. The Linhe and Dengkou faults belong to the internal faults of the Ordos Block. The upper crust of the Langshan Mountain on the west side of LPF is characterized by high-resistivity, the middle and lower crust have a low-resistivity layer, and the Linhe Basin on the east side has a Cenozoic low-resistivity sedimentary layer of approximately 10 km thick, which reveals that the Linhe Basin is a faulted basin with sedimentary thickness around the Ordos Block. This indicates that the LLA has experienced continuous and strong tension, normal fault depression sedimentary activities since the Cenozoic era. The current Global Positioning System velocity field shows that there is an apparent NW–SE acceleration zone in the LLA. The leveling data indicate that Linhe Basin shows a subsidence trend relative to the Ordos Block, indicating that the area is undergoing continuous NW–SE tension and faulting. It is speculated that there is a risk of earthquake preparation in the LPF.
