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Article

Tectonic Deformation Analysis with ALOS-Based Digital Elevation Models in the Longshou Shan Mountains (NW China)

by
Xianghe Ji
* and
Klaus Reicherter
Institute of Neotectonics and Natural Hazards, RWTH Aachen University, Lochner Str.4-20, 52064 Aachen, Germany
*
Author to whom correspondence should be addressed.
GeoHazards 2025, 6(4), 74; https://doi.org/10.3390/geohazards6040074 (registering DOI)
Submission received: 22 August 2025 / Revised: 15 October 2025 / Accepted: 16 October 2025 / Published: 1 November 2025
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Abstract

The Longshou Shan area is located on the northeastern margin of the Tibetan Plateau in northwest China. The study area is located where the sinistral Altyn Tagh and Haiyuan Faults overlap and the Qilian Shan thrust fault systems in the northeastern Kunlun–Qaidam Block converge. This region experiences frequent seismic events, including large-magnitude earthquakes, which are significant indicators of ongoing tectonic deformation and stress accumulation in the Earth’s crust. The seismicity of Longshou Shan is not only a consequence of its tectonic setting but also a key factor in understanding the seismic hazard posed to the surrounding areas. The tectonic activity within the Longshou Shan region of NW China is a focus of our geomorphological research due to its significance in understanding the complex interactions between tectonic forces and surface processes. Situated on the northeastern edge of the Tibetan Plateau and along the eastward trace of the Altyn Tagh Fault, Longshou Shan is crucial for investigating the plateau’s northward expansion. This study leverages ALOS-based digital elevation models (DEMs) and geomorphic indices to evaluate the tectonic activity in the area, employing various indices such as mountain front sinuosity, valley floor width-to-height ratio, hypsometric curves, asymmetry factors, basin shape indices, and channel steepness index to provide a comprehensive tectonomorphological analysis. Our results indicate intense tectonic activity on both sides of Longshou Shan, making it a highly hazardous seismic area. We also highlight the importance of thrust faults and related crustal shortening in the formation and expansion of the plateau.

1. Introduction

1.1. Tectonic and Geologic Context of Longshou Shan

The Longshou Shan region is part of the broader Qilian Shan area, which marks the boundary between the Tibetan Plateau and the Alxa Block (Figure 1). The collision of the Indian and Eurasian plates formed the Tibetan Plateau [1,2,3]. The northwest boundary of the plateau is defined by the NE-trending and left-lateral-slip Altyn Tagh Fault [1]. The northeast boundary is the NW-trending North Qilian Shan Fault [4], which forms a major thrust fault (Figure 1). The ESE-trending mountain range between the two boundaries is called Qilian Shan, which is a series of middle- to upper-crustal-scale ramp anticlines controlled by a series of SW-dipping faults rooted in a broad detachment surface [5]. The propagation of the fault system rooted in detachment led to a further NE-ward propagation of the deformation front [5,6,7], documented in the North Qilian Shan (18–7 Ma) [8,9,10,11,12,13,14,15], the Laojunmiao Anticline ~3.6 Ma [11,16,17], and Yumu Shan, which became the northern boundary of the Tibetan Plateau in succession (3–4 Ma) [13,18,19]. Recent research indicates deformation across the Hexi Corridor to Jintanan Shan (1.5–1.6 Ma) [20] and Heli Shan (2 Ma) [21]. These processes are consistent with the theory of northward propagation of thrust wedges in Qilian Shan [5,22]. Continental collision is accommodated by crustal thickening dominated by thrust faulting [23,24]. Other studies suggest that the Altyn Tagh Fault extends beyond the North Qilian Shan Fault [25], dividing into at least five faults north of Longshou Shan and extending even northeast toward the Sea of Okhotsk [26]. The collision is mainly accommodated by northeastward extrusion of the Tibetan Plateau, dominated by strike-slip faults [27,28]. The theories represent two different modes of continental collision and deformation. The activities and kinematics of active structures on the edge of the plateau provide us with evidence to understand how the plateau was uplifted and formed, and provide information to verify the causal model of the plateau. As the front of the northeastward propagation of the Tibetan Plateau and the eastward trace of the Altyn Tagh Fault (Figure 1), the geomorphological features of Longshou Shan, such as its stream networks and drainage basins (Figure 2), are direct results of these tectonic processes. In arid climates, minimal erosion provides a suitable opportunity to evaluate geomorphic features [29]. The specific formation and evolution model of the plateau is still unclear. Although this study cannot construct a complete dynamic model of plateau formation, through quantitative geomorphological and structural analysis, we attempt to provide independent supporting evidence for the “crust shortening” mechanism and clarify its status and role in the evolution of the plateau.

1.2. Overview Seismicity in Longshou Shan and Adjacent Regions

The Longshou Shan mountains are a seismically active area. The Hexi Corridor in the south of Longshou Shan and the Altyn Tagh Fault in the west have both experienced large earthquakes [37,38,39,40,41]. The earthquake in Gaotai (M 7.5) in 180 CE; Hongyazi (M 7.25) in 1609; Gulang (M 8) in 1927; Changma (M 7.6) in 1932; and Longshou Shan (M 7.25) in 1954 caused huge losses [6,39,42]. Some trench studies have also provided clear paleoearthquake records near Minle and Zhangye [43,44]. The most recent major earthquake was the M 6.9 Menyuan earthquake that occurred on the Lenglongling fault in the south of the Hexi Corridor in 2022. Fortunately, since the epicenter was in a sparsely populated mountainous area, it did not cause many casualties [45]. These earthquakes are significant indicators of the ongoing tectonic deformation and stress accumulation/release in the crust. The seismicity of Longshou Shan is not only a consequence of its tectonic setting but also a key factor in understanding the seismic hazard posed to the surrounding areas.
Figure 1b highlights the distribution of seismic events in the Longshou Shan and adjacent regions, showing the locations of historical and instrumental earthquakes with magnitudes greater than 7.0. These seismic events are concentrated along the major faults. The elevated seismic activity in this region is interpreted to be associated with the continued convergence between the Indian and Eurasian plates [6,46,47], which drives the uplift of the Tibetan Plateau and induces significant crustal deformation along its margins [1,2,3].

1.3. Seismic Sources and Fault Mechanisms

The primary sources of seismicity in the Longshou Shan region are active fault systems, including the Altyn Tagh Fault and the North Qilian Shan Fault. During the Tibetan Plateau push towards the Alxa Block in the northeast, the Longshou Shan earthquake was caused by the release of accumulated stress on the fault system [42]. As the stress accumulates, the Qilian Shan foreland thrust and fold system, where the Longshou Shan region belongs, may also be capable of causing major earthquakes [48]. The Altyn Tagh Fault accommodates significant lateral motion between the Tibetan Plateau and the Tarim Basin to the north [49].
Field observation and the stress field indicate that the fault mechanism in this region is sinistral thrusting [42,50], but a major event occurred on a dextral-normal transfer fault (M 7.25) in 1954 [42]. The interaction between the Tibetan Plateau and Alxa Block during its northeastward push contributes to the complex seismicity pattern observed in Longshou Shan [42]. The orientation and slip rates of these faults are critical factors in determining the seismic hazard in the region. Seismic moment release along these faults is indicative of the potential for large earthquakes, which could pose a significant risk to the densely populated cities around Longshou Shan, such as Zhangye, Wuwei, and Jinchang. Previous research focused on the mid-western section of Longshou Shan and delineated the danger zone in the middle section of the Longshou Shan Fault System. Two major cities are located on the east side of the mountain range. The tectonic activity of the eastern section of Longshou Shan has not yet been investigated. It is not clear whether the two cities on the east side also face the same earthquake risk as the west section. Our study revealed the risk of the eastern section by comparing the east and west sections.
In this study, we aimed to quantitatively assess the tectonic activity of the fault to verify the mechanism model of the plateau, and at the same time, we used tectonic activity to assess the seismic hazard of the region. To achieve this goal, we extracted the geomorphic indices such as Mountain front sinuosity (Smf), asymmetry factor (AF), ratio of valley floor width to valley height (Vf), hypsometric index (Hi), basin shape index (Bs), and longitudinal profile of river from the DEM, and used the species geomorphic indices to calculate the RIAT value to quantitatively assess the class of tectonic activity, and used river longitudinal profile analysis and geomorphic indices cross-validation to determine the reliability. Finally, we used activity classification to discuss the plateau mechanism model and seismic hazard.

2. Materials and Methods

2.1. Materials

Faults are developed on both the north and south sides of Longshou Shan. With the help of the Geographic Information System platform ArcGIS PRO 3.3.2, we processed and analyzed the 12.5 m digital elevation ALOS PALSAR DEM (https://search.asf.alaska.edu/ (accessed on 1 October 2023)). In addition, we also used Google Earth images to complete the determination of the mountain front line, and the regional geological map and related geological data as reference (https://geocloud.cgs.gov.cn (accessed on 5 October 2022)) [37]. The hydraulic analysis tool provided by the software divides the river system into six orders. A river section without upstream tributaries is classified as level 1. When two rivers of the same level converge, the level is +1 [51,52]. A total of 121 basins can be divided in the mountain range (Figure 2), 61 on the north side of Longshou Shan and 60 on the south side, from east to west, named N1-N61 and S1-S60, respectively.

2.2. Geomorphic Indices and Their Implications

To assess the tectonic activity, this study applies several geomorphic indices that are well-suited to capture the ongoing deformation in the landscape:

2.2.1. Mountain Front Sinuosity (Smf)

The mountain front is a long, persistent landform where active faults or folds vertically slip to create a marked linear mountain front at this intersection point. Rectilinear landforms are dominated by tectonic activity. As the surface erodes, the piedmont will become sinuous, which means that in the competition between tectonic activity and surface erosion, surface erosion dominates. Bull [53] used the linearity of the piedmont to quantitatively evaluate the activity of the tectonics.
Smf = Lmf/Ls
where Lmf is the length of the junction from the mountain to the piedmont, and Ls is the straight-line distance of the mountain front (Figure 3). The closer the Smf value is to 1, the more linear the mountain front is and the more active the structure is. Previous studies defined a Smf value less than 1.4 as active (1st class) [53], and a value larger than 3 as inactive (3rd class) [54].

2.2.2. Asymmetry Factor (AF)

In active tectonic areas, drainage systems have specific patterns and geometries influenced by tectonic activity. The asymmetry factors are calculated to assess the tectonic tilt in the drainage basin or larger scale [55].
AF = | (Ar/At) × 100 − 50 |
where Ar is the area on the right side of the main river (basin axis in Figure 4a) facing downstream in the drainage basins, and At is the total area of the entire drainage basin. Smaller AF values indicate that the drainage basin develops in stable conditions with less tilt. Previous studies have defined the classification boundaries of high (1st class), medium (2nd class), and low (3rd class) values as 18 and 7 [56].

2.2.3. Ratio of Valley Floor Width to Valley Height (Vf)

The valley width-to-height ratio was first defined by Bull and McFadden in 1977. Rapid incision by rivers in response to actively uplifted mountains forms narrow V-shaped valleys, while wide U-shaped valleys form in tectonically stable areas. The formula is defined as
Vf = 2 Vfw/(Eld − Esc) (Erd − Esc)
where Vfw is the valley width, Esc is the average valley elevation, and Erd and Eld are the elevations on the left and right sides of the basin (valley divide) facing downstream (Figure 3b). Values greater than 1 represent a typical shallow and wide U-shaped valley (3rd class), while values less than 0.5 represent a deep incision V-shaped valley (1st class) [54].

2.2.4. Hypsometric Index (Hi)

Hypsometric index is an index that calculates the distribution of elevation within a given drainage basin [57]. In general, it is the percentage of the uneroded area in a basin area to the volume of the entire basin area (Figure 4). The part below the curve is the uneroded part, and a higher value represents a less eroded part, indicating that the landscape may be younger and was produced by active tectonics. The simple equation for calculating the index is
Hi = (Elevationavg − Elevationmin)/(Elevatiomax − Elevationmin)
Previous studies have defined the classification boundaries of high (1st class), medium (2nd class) and low (3rd class) values as 0.5 and 0.4 [58,59] or 0.5 and 0.37 [60].

2.2.5. Basin Shape Index (Bs)

Near the front of the mountain, the energy of the river causes an incision, and the basin becomes narrower. Therefore, in the tectonically active area, the shape of the basin is elongated. After the tectonic activity decreases, the basin gradually becomes first elliptical, then circular. The basin shape index equation is
Bs = Bl/Bw
Bl is the length from the source of the basin to the outlet of the basin, Bw is the width of the basin at its widest point (Figure 4a), and a larger Bs value indicates a more elongated basin. In previous studies, the boundaries for dividing the values into high (1st class), medium (2nd class), and low (3rd class) were 4 and 3 [59], 1.76 and 1.2 [60], or 2.3 and 1.2 [56], respectively.

2.2.6. Longitudinal Profile of River

There are usually two indices that reflect the steepness of the longitudinal river profile channel. Sl index is defined as the slope of a certain section of a river multiplied by the length from the section to the source of the river [61].
SL = ΔH/ΔL × L
where ΔH and ΔL are the length and elevation of a given river section, respectively, and L is the distance from this river section to the source of the river. It is used to infer tectonic uplift in some studies [62], but because this index is sensitive to lithology [63], there are differences in lithology within our study basins (as shown in Figure 2b), so we used Ksn to explore the knickpoints in the river profile. Ksn is a river steepness index that eliminates the influence of the drainage area on the slope [64]. Some scholars have successfully used this index to compare the rock uplift rate in the northern Tibetan Plateau [65].
Ksn = S/Aθref
where S is the channel slope, A is the contributing drainage area, and θref is the reference concavity of the longitudinal profile (0.45).

3. Results

The North Longshou Shan Fault has a total length of approximately 140 km. The dip direction of the eastern section of the fault surface is southwest, while the dip direction of the western section is northeast, with a dip angle of 50–70° [37]. The South Longshou Shan Fault extends from Shandan to its eastern end, with a length of approximately 160 km. It dips northeast at an angle of about 60–70°. Westward from Shandan, the fault system can extend 110 km to Gaotai, but there are no signs of activity in the late Quaternary sediments [37]. Therefore, we will only discuss the section east of Shandan.
According to the characteristics of the faults and drainage basins, combined with existing research, we divided 121 drainage basins on the north and south sides of Longshou Shan into several sections, with the north and south sides divided into 6 and 5 parts, respectively. There is a 4th-order basin (N21) on the north side. Due to the different fault inclinations on the east and west sides, we divided it into six sections. The three sections on the east side have the same inclination and, except for N21, the other basins are all 1st and 2nd order. Each of the three sections on the west side contains at least one 3rd-order basin. There is a 4th-order basin (S18) and a 3rd-order basin (S21) on the south side. The axes of these two basins are oblique to the mountain front. The remaining basins are all 1st- and 2nd-order basins. Usually, the water systems at the ends of faults or between segment intervals are oblique [66], so we performed segmentation at the location of S18 and S21 basins, and then the western fault was divided into two sections according to the size of the basin

3.1. Mountain Front Sinuosity (Smf)

We used Google Earth images to draw the detailed mountain–piedmont boundary as Lmf, and then calculated the Smf values. The Smf indices of the mountain front are as shown (Figure 5 and Table 1). In order to compare the value along the strike, we divided the line along the mountain front into multiple sections according to the obviousness of the landform line. The value shows that the westernmost section of the northern fault is relatively active, and the rest of the sections are active. The west half sections on the south side are relatively active, and the sections on the east side are active. The values show that the activity on the east side of Longshou Shan is slightly higher than that on the west side.

3.2. Asymmetric Factor (AF)

In order to evaluate the activity of faults, we used the absolute value of the Af indices minus 50 as the result value to reflect the relative activity, and used the depth of color in the figure to reflect the relative activity (Figure 5). According to the classification of previous researchers [56], 36 basins in the Longshou Shan area are classified as 1st class, 61 basins are 2nd class, and 24 basins are 3rd class.

3.3. Ratio of Valley Floor Width to Valley Height (Vf)

Many rivers did not erode deep into the mountains, and there was not enough river length to select enough profile locations, so we selected only profile locations at intervals of about 200–500 m for several longer rivers, and then calculated the ratio for each profile and the average Vf value for each river. We also observed that the upstream values are generally smaller than the downstream values in the basin (Figure 6).

3.4. Hypsometric Index (Hi)

Regarding the Hi index, according to the classification method of previous studies [58,59,60], all the basins in this study area belong to the inactive type, classified as 3rd class. In order to show the spatial range and distribution, we used different colors to indicate the relative values (Figure 6).

3.5. Basin Shape Index (Bs)

For these indices, considering that the Longshou Shan basin has a wide distribution range and the maximum value reaches up to 5.45 (N37), we refer to previous studies [56,59,60] and define the high, medium and low scores as 2.5 and 1.2. In total, 59 and 55 basins are in a relatively active state of class 1 and 2, respectively, and 7 basins are inactive (Figure 7).

3.6. Longitudinal Profile of River

The mountains in the study area are occupied by drainage basins. In front of the mountains are sedimentary alluvial fans and endorheic basins. The seasonal river channels in the arid and low dip angle area are not obvious, and the measured slope is unreliable [67], so we focused on the hillslope area. We extracted Ksn data from the drainage basins on the north and south sides of Longshou Shan and divided the data into five sections at equal intervals. The maximum value in the northern watershed is 679, and the maximum value point occurs near the outlet of the N21 basin, close to the main fault in front of the mountain. High values also occur in the upper reaches of this basin. High values occur in the middle reaches of the largest S18 basin on the south side. We believe that the high Ksn values in these basins with large drainage areas are a response to fault activities, while other smaller basins may not be reflected because the knickpoint migration rate of smaller basins in arid areas is unstable and more susceptible to extreme events [68,69].

3.7. Discussion on Relative Index of Tectonic Activity (RIAT)

Our study area spans almost the entire Longshou Shan range from east to west, covering more than 120 drainage basins. Using existing geomorphic indices and combining the geological characteristics of the Longshou Shan area, we calculated RIAT for different basins.
According to previous studies [58], basins can be divided into four categories based on RIAT values: extremely high (1–1.5), high (1.51–2.0), medium (2.01–2.5), and low (>2.5). In the Longshou Shan area, the number of basins in these four categories is 7 (5.79%), 87 (72%), 27 (22.3%), and 0 (Table 2), respectively. For the north side, 6, 45 and 10 basins are categorized as extremely high, high, and medium, respectively. For the south side, 1, 42 and 17 basins are categorized as extremely high, high, and medium, respectively. The values indicate that the comparable tectonic rates for both north and south Longshou Shan Faults are relatively high. In order to compare the tectonic activity along the strike, we divided the RIAT index into 12 groups (10 or 11 data points each group), representing the different segments of the north and south sides, and tried to determine the spatial differences in tectonic activity (Figure 8). Average values from east to west are 1.99, 1.90, 1.87, 1.97, 1.85, 1.99 on the north side and 1.77, 2.16, 2.07, 2.07, 1.99, 1.91 on the south side. The numerical values show that all segments of Longshou Shan are in a highly active state, and the activity level in the central segments of the south is slightly lower than that in other parts. This is consistent with the spatial distribution of RIAT (Figure 8). The basins in the central part of the south are all in a highly or moderately active state, and there is no extremely active basin.

4. Discussion

4.1. Indications for Tectonic Geomorphology

The convergence between the Tibetan plateau and Alxa Block revealed by GPS is ~5.5 mm/a [70,71], and the shortening rate across Longshou Shan is ~1 mm/a [71]. Considering the large dip angles of the south (60–70°) and north (50–70°) Longshou Shan Faults [37], it is likely that the faults have a high vertical slip rate. Our work on the Longshou Shan has shown that the fault systems are very active; in particular, the differential uplift caused by thrusting has created sharp mountain fronts that protrude significantly from the Hexi Corridor and Alxa block. The combined action of tectonic activity and surface erosion formed the current watershed landform. Our study highlights the importance of thrust faults in plateau uplift. The formation of the plateau may be due to the combined action of multiple deformation mechanisms to create the plateau’s high altitude, and even if the crust and mantle are decoupled [4,72,73], the restored cross-section can also prove the importance of crustal thickening [73]. A comprehensive uplift deformation model may remain controversial for a long time, but distributed crustal shortening should be included in the model.
As for the strike-slip component, our study cannot obtain an accurate numerical value to measure it, considering the characteristics of the regional left-lateral thrust tectonic background [42,50]. Previous GPS studies have also shown that the lateral slip rate here is as high as 2 mm/a [74], almost as large as the dip slip, and this slip may be distributed among a series of faults in the area. Perhaps a series of faults further north is also worthy of detailed study; the alluvial fan on the north side of the mountain range shows signs of tectonic activity (Figure 8). Overall, we suggest that thrust-slip faults in the upper crust that accommodate crustal shortening, supporting a model in which multiple mechanisms play a role in plateau formation and emphasizing the importance of thrusting.

4.2. Seismic Hazard Assessment in Longshou Shan and Adjacent Regions

The high activity of the fault systems is the primary contributor to the seismic hazard. The North Qilian Shan thrust system is an active thrust fold belt [75,76]. The convergence across the Qilian Shan is as high as ~5.5 mm/a [70,71], the shortening rate of the North Qilian Shan Fault at the south Zhangye segment is ~0.8 mm/a [77,78], at the Yonggu segment is ~2.7 mm/a [79], and the remaining crustal shortening is distributed on other faults in the Qilian Shan area, such as the Longshou Shan Fault. The slip rate in the central segment of Altyn Tagh Fault is ~10 mm/a [80], and the recurrence interval in the Aksay segment is ~1329 a [41]. Historical earthquake records show that both the North Qilian Shan thrust belt and the Altyn Tagh Fault have experienced large earthquakes [38,39,40]. Our results reflect the high fault activity in the Longshou Shan area; combined with previous geomorphic and seismic research, it indicates that the Longshou Shan and several nearby faults in the northern Qilian Shan are capable of causing major earthquakes [42,44,48].
Fault segmentation and fault bends often result in concentrated earthquakes [81]. According to the fault details mentioned above, our basin map shows that on the south side of Longshou Shan, the fault is divided into segments by two high-order oblique drainage systems. Previous studies have shown that there is a complex transform fault system in the area between the north and south faults [42]. Such complex fault morphology has become another source of risk. The northeastward extension of the plateau has led to stress accumulation, acting on the segmented main faults and the complex fault system between them, resulting in regional hazard risk.

4.3. Vulnerability and Risk Implications

The vulnerability of the Longshou Shan region to seismic events is influenced by several factors, including the built environment, population density, and resilience of the infrastructure. Considering the total population of several nearby cities is almost 3 M: Zhangye 1.1 M, Jinchang 430 K, and Wuwei 1.43 M; another important provincial capital, Xining, is 200 km away, with about 2.5 M people living there. The region’s proximity to active faults means that even moderate-magnitude earthquakes can have severe consequences, particularly in areas with poor building practices or inadequate seismic design.
In regions with significant seismic hazard, the resilience of infrastructure, including buildings, roads, and bridges, is paramount. Older buildings that do not comply with modern seismic codes are particularly vulnerable to collapse during an earthquake, leading to higher casualties and economic losses. Some cases show that areas with high seismically resilient buildings suffer less damage from disasters [82]. The potential for secondary hazards, such as landslides triggered by ground shaking, also poses a significant risk in the mountainous areas of Longshou Shan, with more densely populated areas near major fault lines being at greater risk. The combination of high seismic hazard and high population exposure necessitates comprehensive risk mitigation strategies, including public education, early warning systems, and emergency response planning.

4.4. Reliability Analysis

In order to cross-validate the reliability of the data, we cross-validated two different sets of geomorphological parameters according to the previous research [83]. The correlation analysis between the Hi index and the Bs index, as well as between the Hi index and the Af index, all showed a positive weak correlation (Figure 9). This also confirms that this area has been affected by long-term tectonic activities and is still in a relatively active state.
Our data show that the Hi indices are all in an inactive state of class 3, which contrasts with the extremely active or active states shown by other geomorphological indices. On the one hand, this is because the long-term tectonic activity in the region has created today’s landscape. On the other hand, considering the lithologic differences within the basin, the upper reaches of the basin are usually the Precambrian crystalline basement that is difficult to erode, while the lower reaches of the basin are usually Cretaceous or Paleogene sedimentary rocks. The different resistance to erosion makes the lower reaches more susceptible to erosion, making the Hi index smaller. This may have led to our results being smaller, but even so, the result shows that the structure is very active. From the study of river longitudinal profiles, we can also see signs of tectonic activity, but considering that seasonal precipitation may cause some transient landforms, we only use it as a reference.

5. Conclusions

In this study, we extracted geomorphic parameters and calculated the RIAT quantitative analysis. The results showed that 7 of the 121 drainage basins in the region are extremely active and 87 are active, indicating that the faults are active and have a high seismic hazard. At the same time, quantitative data also show that there is no significant change in the fault activity along the fault direction, which means that there is no significant difference in the earthquake risk of the entire Longshou Shan area. The thrusting of the thrust faults accommodates considerable crustal shortening, which is one of the main mechanisms for the formation of the Tibetan Plateau. The formation of the Tibetan Plateau is the result of the combined action of multiple mechanisms, including the eastward intrusion of the continent and crust shortening. Although we have no way to obtain a complete model of the plateau mechanism, our quantitative data emphasize the importance of thrust faults.

Author Contributions

Conceptualization, X.J. and K.R.; methodology, X.J.; software, X.J.; validation, X.J. and K.R.; formal analysis, X.J.; investigation, X.J.; resources, X.J. and K.R.; data curation, X.J.; writing—original draft preparation, X.J.; writing—review and editing, X.J. and K.R.; visualization, X.J.; supervision, K.R.; project administration, K.R.; funding acquisition, X.J. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Data Availability Statement

The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding author.

Acknowledgments

This work was supported by the China Scholarship Council (CSC) under Grant No. 202106180008. The authors would like to thank Vanessa Steinritz, Napoleon Njeng, and Rashid Haider for their valuable discussions and support. We thank three anonymous reviewers for their constructive comments that significantly improved the quality of the manuscript.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. (a) Map of the Tibetan Plateau and surrounding regions, showing the location of Figure 1b. (b) Earthquakes and neotectonic fault map of the Qilian Shan (northeastern Tibetan Plateau) and adjacent regions, LJM: Laojunmiao Anticline. Fault data are from [5,20,30,31,32]. Blue stars and fault plane solution of earthquake data are from USGS (https://earthquake.usgs.gov/earthquakes/search/ (accessed on 1 October 2023)) and [33] (IRIS). Purple triangles are historical earthquakes from [34,35,36].
Figure 1. (a) Map of the Tibetan Plateau and surrounding regions, showing the location of Figure 1b. (b) Earthquakes and neotectonic fault map of the Qilian Shan (northeastern Tibetan Plateau) and adjacent regions, LJM: Laojunmiao Anticline. Fault data are from [5,20,30,31,32]. Blue stars and fault plane solution of earthquake data are from USGS (https://earthquake.usgs.gov/earthquakes/search/ (accessed on 1 October 2023)) and [33] (IRIS). Purple triangles are historical earthquakes from [34,35,36].
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Figure 2. (a) Stream network and drainage basins in Longshou Shan and adjacent area. Black polygons represent different drainage basins, red solid lines represent mountain fronts, and river sections of different colors represent rivers of different river orders. (b) Geological map and main rovers of the Longshou Shan and adjacent areas from https://geocloud.cgs.gov.cn (accessed on 5 October 2022).
Figure 2. (a) Stream network and drainage basins in Longshou Shan and adjacent area. Black polygons represent different drainage basins, red solid lines represent mountain fronts, and river sections of different colors represent rivers of different river orders. (b) Geological map and main rovers of the Longshou Shan and adjacent areas from https://geocloud.cgs.gov.cn (accessed on 5 October 2022).
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Figure 3. Mountain front sinuosity Smf and valley floor width-to-height ratio Vf. (a)Valley is the location of valley Cross-section, Ls is the straight-line distance between the two points, and Lmf is the length of the red line that zigzags along the front of the mountain. (b) Cross-section of valley demonstrates the valley floor and valley height, Esc is the average valley elevation, and Erd and Eld are the elevations on the left and right sides of the basin.
Figure 3. Mountain front sinuosity Smf and valley floor width-to-height ratio Vf. (a)Valley is the location of valley Cross-section, Ls is the straight-line distance between the two points, and Lmf is the length of the red line that zigzags along the front of the mountain. (b) Cross-section of valley demonstrates the valley floor and valley height, Esc is the average valley elevation, and Erd and Eld are the elevations on the left and right sides of the basin.
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Figure 4. (a) Basin shape index, different colors represent different height. (b) hypsometric index, and (c) hypsometric curves for basins on the north side; (d) hypsometric curves for basins on the south side.
Figure 4. (a) Basin shape index, different colors represent different height. (b) hypsometric index, and (c) hypsometric curves for basins on the north side; (d) hypsometric curves for basins on the south side.
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Figure 5. Asymmetry factor and mountain front sinuosity data indicate Longshou Shan has a linear mountain front, and most basins have low symmetry.
Figure 5. Asymmetry factor and mountain front sinuosity data indicate Longshou Shan has a linear mountain front, and most basins have low symmetry.
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Figure 6. Hypsometric index value range and valley floor–valley height ratio data.
Figure 6. Hypsometric index value range and valley floor–valley height ratio data.
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Figure 7. Basin shape index data indicate that most basins are active or relatively active. ksn values indicate knickpoints in the drainage basins.
Figure 7. Basin shape index data indicate that most basins are active or relatively active. ksn values indicate knickpoints in the drainage basins.
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Figure 8. Main rivers and faults, and RIAT values distribution in Longshou Shan area. Short red lines are used to indicate the boundaries between RIAT groups (plotted on Gaofen-1 (GF-1) Satellite image). The morphology of the rivers and the oasis to the north of Longshou Shan indicates possible tectonic activity.
Figure 8. Main rivers and faults, and RIAT values distribution in Longshou Shan area. Short red lines are used to indicate the boundaries between RIAT groups (plotted on Gaofen-1 (GF-1) Satellite image). The morphology of the rivers and the oasis to the north of Longshou Shan indicates possible tectonic activity.
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Figure 9. Geomorphic correlation plots. (a) Weak positive correlation between HI and Af. (b) Weak positive correlation between HI and Bs, demonstrating the influence of tectonism on geomorphic evolution.
Figure 9. Geomorphic correlation plots. (a) Weak positive correlation between HI and Af. (b) Weak positive correlation between HI and Bs, demonstrating the influence of tectonism on geomorphic evolution.
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Table 1. Geomorphic indices value of geomorphic indices.
Table 1. Geomorphic indices value of geomorphic indices.
BasinAFHiBsSmfVfBasinAFHiBsSmfVf
N110.810.251.681.27 S115.660.181.851.19
N215.760.351.681.270.68S210.930.323.581.19
N314.630.312.591.270.43S38.650.224.271.19
N412.940.251.611.27 S417.770.312.741.19
N512.410.382.611.27 S58.160.283.221.19
N61.830.281.331.27 S624.480.272.091.390.51
N77.990.192.311.27 S718.300.262.901.390.92
N817.140.291.901.27 S817.040.272.311.39
N94.040.162.171.27 S910.400.343.211.390.67
N105.210.174.041.27 S1019.280.272.821.39
N1121.220.142.511.27 S110.490.233.111.39
N1212.430.291.321.271.04S1239.240.281.181.391.44
N137.330.302.341.27 S132.690.391.591.39
N145.620.182.751.27 S142.540.331.271.390.70
N1520.000.312.541.27 S154.150.191.151.39
N1613.040.213.531.27 S161.560.272.811.393.33
N1711.990.273.321.270.76S175.420.243.151.39
N180.610.171.571.27 S1820.160.212.211.192.01
N1910.140.192.411.27 S198.790.351.221.193.40
N207.320.221.621.27 S2011.630.241.211.191.42
N219.200.290.641.270.81S212.110.302.541.192.93
N2233.110.181.361.27 S228.260.271.231.44
N2315.590.252.151.12 S2316.050.202.481.44
N2415.220.232.781.12 S2411.600.262.831.44
N2513.920.202.181.12 S2515.620.203.291.44
N2611.470.322.581.12 S2615.070.202.901.44
N2723.980.183.791.12 S2713.290.232.811.44
N2819.250.262.561.15 S2816.340.214.211.44
N290.210.141.751.15 S2911.530.233.351.44
N306.850.272.681.15 S3013.950.154.291.44
N3125.480.250.831.15 S3116.570.183.571.44
N3218.520.391.161.15 S327.520.205.261.44
N3324.140.222.031.152.73S3324.620.162.451.44
N344.730.174.101.15 S3415.640.303.121.44
N3531.100.301.561.15 S3511.730.285.121.44
N360.310.143.931.15 S369.470.233.041.44
N373.390.185.441.15 S3717.110.222.351.44
N3814.080.172.261.15 S3818.080.312.761.44
N391.950.312.781.152.75S3914.290.212.041.44
N4023.310.232.441.15 S403.610.241.451.44
N4112.220.281.591.24 S4119.020.222.741.44
N4213.560.262.021.241.07S420.070.193.421.44
N4314.720.402.861.24 S430.260.281.631.39
N4427.850.223.331.24 S449.190.262.021.39
N457.880.191.951.24 S4511.340.293.281.39
N460.720.293.261.24 S460.930.282.421.394.68
N4721.210.152.421.24 S4719.980.221.631.3911.43
N4818.670.332.711.24 S4815.890.221.481.39
N4926.480.221.881.24 S4918.460.101.891.39
N5016.670.292.661.62 S509.140.183.091.39
N511.480.265.451.62 S5115.030.124.041.39
N5217.100.221.841.621.36S5223.780.221.671.394.43
N538.640.192.911.62 S5319.200.252.071.39
N549.400.312.641.62 S5419.370.231.691.39
N5521.190.243.481.62 S5527.480.290.851.391.32
N5622.390.253.441.62 S567.440.281.561.39
N577.980.232.521.62 S5730.450.281.981.39
N5827.630.222.251.62 S5821.080.281.501.39
N5918.380.342.391.62 S5910.200.272.441.39
N608.730.283.281.62 S6020.200.261.111.391.08
N6118.930.293.761.62
Table 2. Geomorphic indices classes and RIAT of tectonic activity.
Table 2. Geomorphic indices classes and RIAT of tectonic activity.
BasinAFHiBsSmfVfRIATBasinAFHiBsSmfVfRIAT
N12321 2S12321 2
N2232122S22311 1.75
N3231111.6S32311 1.75
N42321 2S42311 1.75
N52311 1.75S52311 1.75
N63321 2.25S6132121.8
N72321 2S7131121.6
N82321 2S82321 2
N93321 2.25S9231121.8
N103311 2S101311 1.5
N111311 1.5S113311 2
N12232132.2S12133132.2
N132321 2S133321 2.25
N143311 2S14332122.2
N151311 1.5S153331 2.5
N162311 1.75S16331132.2
N17231121.8S173311 2
N183321 2.25S18132132
N192321 2S19232132.2
N202321 2S20232122
N21233122.2S21331132.2
N221321 1.75S222322 2.25
N232321 2S232322 2.25
N242311 1.75S242312 2
N252321 2S252312 2
N262311 1.75S262312 2
N271311 1.5S272312 2
N281311 1.5S282312 2
N293321 2.25S292312 2
N303311 2S302312 2
N311331 2S312312 2
N321331 2S322312 2
N33132132S331322 2
N343311 2S342312 2
N351321 1.75S352312 2
N363311 2S362312 2
N373311 2S372322 2.25
N382321 2S381312 1.75
N39331132.2S392322 2.25
N401321 1.75S403322 2.5
N412321 2S411312 1.75
N42232132.2S423312 2.25
N432311 1.75S433321 2.25
N441311 1.5S442321 2
N452321 2S452311 1.75
N463311 2S46332132.4
N471321 1.75S47132132
N481311 1.5S482321 2
N491321 1.75S491321 1.75
N502312 2S502311 1.75
N513312 2.25S512311 1.75
N52232232.4S52132132
N532312 2S531321 1.75
N542312 2S541321 1.75
N551312 1.75S55133132.2
N561312 1.75S562321 2
N572312 2S571321 1.75
N581322 2S581321 1.75
N591322 2S592321 2
N602312 2S60133132.2
N611312 1.75
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Ji, X.; Reicherter, K. Tectonic Deformation Analysis with ALOS-Based Digital Elevation Models in the Longshou Shan Mountains (NW China). GeoHazards 2025, 6, 74. https://doi.org/10.3390/geohazards6040074

AMA Style

Ji X, Reicherter K. Tectonic Deformation Analysis with ALOS-Based Digital Elevation Models in the Longshou Shan Mountains (NW China). GeoHazards. 2025; 6(4):74. https://doi.org/10.3390/geohazards6040074

Chicago/Turabian Style

Ji, Xianghe, and Klaus Reicherter. 2025. "Tectonic Deformation Analysis with ALOS-Based Digital Elevation Models in the Longshou Shan Mountains (NW China)" GeoHazards 6, no. 4: 74. https://doi.org/10.3390/geohazards6040074

APA Style

Ji, X., & Reicherter, K. (2025). Tectonic Deformation Analysis with ALOS-Based Digital Elevation Models in the Longshou Shan Mountains (NW China). GeoHazards, 6(4), 74. https://doi.org/10.3390/geohazards6040074

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