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Quantitative studies and applications of active tectonics
... With the rapid development of spatial measurement technology and dating methods, active tectonic research has gradually developed from the early qualitative to the quantitative research stage [1,2]. Quantitative research on active tectonics should acquire some quantitative parameters that represent the active tectonic characteristics, for which the acquisition depends on topographic and geomorphic data with high precision and a high resolution [3][4][5][6]. ...
... This study aimed to validate the accuracy of the GF-7-extracted DEMs with or without ICESat-2-derived GCPs, and evaluate the potential of applying GF-7 DEMs to active tectonics. In particular, there were three specific objectives: (1) to verify the accuracy of GF-7 DEMs with or without GCPs; (2) to assess the ability of GF-7 DEMs to identify active faults, fault scarps, and horizontal offsets; and (3) to evaluate the potential application of GF-7 DEMs to horizontal and vertical offset measurements with or without GCPs. Ultimately, this study attempted to answer the following questions: (1) Is there any difference between the accuracies of DEMs extracted from GF-7 with and without ICESat-2 derived GCPs? (2) What horizontal and vertical offset levels can be identified on the basis of GF-7 DEMs? (3) Are there any differences in the measurement accuracies of horizontal and vertical offsets with or without the GCPs extracted from ICESat-2 data? ...
... Therefore, the fitting errors of hanging wall and footwall lines were considered ( Figure 6). h h h 1 ...
China’s first optical stereo mapping satellite with a sub-meter resolution, GaoFen-7 (GF-7), launched in November 2019, shows significant potential for providing high-resolution topographic and geomorphic data for quantitative research on active tectonics. However, no studies have evaluated the capability of the GF-7-generated digital elevation model (DEM) for quantitatively studying active tectonics. This study aimed to validate the accuracy of the DEMs extracted from GF-7 stereo imagery, with or without ground control points (GCPs), and evaluated the potential of applying GF-7 DEMs to active tectonics. First, GF-7 stereo images were processed to obtain DEMs with a spatial resolution of 2 m, utilizing three different methods, including block adjustment without GCPs, block adjustment with the aid of Google Earth images and SRTM DEM, and block adjustment with GCPs derived from the Ice, Cloud, and land Elevation Satellite-2 (ICESat-2) data. These three generated DEMs were called GF-7 DEMMethod1, GF-7 DEMMethod2, and GF-7 DEMMethod3, respectively, and were verified by the airborne LiDAR data in the Hasishan section of the Haiyuan fault. Second, the capability of the GF-7 DEMs for identifying active faults, fault scarps, and horizontal offsets was evaluated. Finally, 8 vertical and 13 horizontal offsets were measured based on three different GF-7 DEMs, and airborne LiDAR data were used to verify the measurements’ accuracies. The results indicated that the accuracy of GF-7 DEMMethod1 was the worst and that of GF-7 DEMMethod3 was superior to that of GF-7 DEMMethod2. The GF-7 DEMs could effectively identify the apparent fault scarps and horizontal offsets. The RMSE values of the vertical offsets measured based on GF-7 DEMMethod1, GF-7 DEMMethod2, and GF-7 DEMMethod3 were 0.55 m, 0.55 m, and 0.41 m, respectively. The horizontal offsets yielded RMSE values of 3.98 m, 2.52 m, and 1.37 m, respectively. These findings demonstrated that vertical and horizontal offsets could be accurately measured using the DEMs generated from GF-7 stereo images. Meanwhile, our study indicated that the GCPs derived from ICESat-2 data could be utilized to improve the accuracies of the GF-7 DEM, and the measurements of vertical and horizontal offsets.
... The results of a growing number of paleoseismic trenches on active faults show that the recurrence of strong earthquakes on the faults is periodic [23][24][25][26], such as the Red River Fault in southwest China [27]. In addition, the more active the fault is, the shorter the T RP . ...
Coseismic surface displacement can cause major damage to buildings located on faults. Therefore, it is important to quantitatively evaluate the future surface displacement of active faults. The commonly used deterministic evaluation methods often tend to overestimate surface displacement values, so researchers are working toward probabilistic fault displacement hazard analysis (PFDHA). However, the PFDHA assumes that earthquakes occur equally in time, which is not consistent with the physical mechanism of earthquake occurrence. Elastic rebound theory and paleoseismic research results show that the accumulation and release of energy in the crustal medium have cyclical characteristics. In this study, using two parameters, the strong earthquake recurrence period (TRP) and strong earthquake elapsed time (tet), of active faults, the displacements of active faults with different TRP and tet under different exceedance probabilities are obtained. The calculation results indicate that the surface displacement hazard of the weakly active and extremely weakly active faults in the Holocene does not need to be considered; for the moderately and strongly active faults in the Holocene, the surface displacement result is lower than that provided by the deterministic method. According to the importance of the project, the calculation results of the PFDHA-td method under different exceedance probabilities are selected.
... To determine the latest activity age, slip rate, and palaeoearthquake sequence of the Caimashui fault, 14 C samples were collected from the trench. By analyzing the relationship between the depositional age of the stratigraphy, paleoseismic identification markers (e.g., colluvial wedge and fault scarp), and the time of earthquake events, we collected samples from corresponding locations to constrain the time of paleoearthquakes [70][71][72]. The 14 C samples were tested at Beta Laboratories in the United States. ...
The Sichuan-Yunnan block is a tectonically active region in China, with frequent large earthquakes occurring in and around it. Despite most earthquakes being concentrated along boundary faults, intraplate faults also have the potential to generate damaging earthquakes. Remote sensing makes it possible to identify these potential earthquake source faults. During an active fault investigation in the Liangshan area, a distinct lithological boundary named Caimashui fault was found. The geometric distribution and kinematic parameter of the fault is crucial for assessing seismic hazards and understanding the deformation pattern within the Sichuan-Yunnan block. The Caimashui fault is mapped with remote sensing interpretation, a field survey, and UAV measurement. Through trenching and Quaternary dating, the Late Quaternary active characteristics of the fault are studied. The fault is a Holocene active dextral strike-slip fault with a reverse component, exhibiting a dextral strike-slip rate of ~0.70 ± 0.11 mm/a. Paleoseismic investigation shows that the last surface rupture event of the Caimashui fault occurred later than 4150 ± 30a BP, with a magnitude of M ≥ 7.0. The fault may act as a secondary splitting fault, absorbing the deformation caused by various sinistral strike-slip rates of the boundary faults and the potential energy from the counterclockwise rotation of the Central Yunnan micro-block.
... The fault slip rate refers to the average velocity of a fault dislocation during a specific period (Wallace 1987;Deng et al. 2004). This parameter can reflect the accumulation rate of strain energy for a fault and can be used to quantitatively compare the relative activities of different faults or one fault during different periods. ...
Quantitative analysis of the slip rate of active faults and their seismic parameters is important for seismic hazard analysis. In this study, we first construct an elastic block model to obtain the slip rate of boundary faults based on the distribution characteristics of active faults, seismicity, and global navigation satellite system (GNSS) observations in Sichuan–Yunnan, China. Then, the long-term seismic risks of the boundary faults are quantitatively evaluated based on the principle of seismic moment balance. The Sichuan–Yunnan region can be divided into 17 relatively independent and stable subblocks. There is clear zoning in the distribution and mechanisms of boundary fault movement and deformation. The boundary faults exhibit an alternating dextral–sinistral–dextral–sinistral strike-slip pattern from northeast to southwest. Among these boundary faults, the Xianshuihe–Xiaojiang fault zone has a high sinistral strike-slip rate, and the Jinshajiang fault plays an important role in accommodating the movement and deformation of the subblocks in the Chuandian block. The dextral strike-slip rate is approximately 10 mm/yr, which is diffusely transferred to the secondary boundary faults in the Chuandian block. Comparison of the rates of moment accumulation and release reveals that the southern segment of the Xiaojiang fault, the Longriba fault, the Daliangshan fault, and the Yuanmou fault exhibit significant moment deficits, with corresponding moment magnitudes exceeding Mw 7.5. More attention should be given to the strong earthquake risks of these faults. The Xianshuihe–Xiaojiang, Jiali–Lancangjiang, and Red River faults, which are arc shaped, dominate the regional deformation and determine the motion and deformation model of the subblocks and secondary boundary faults within the Chuandian block and the area southwest of the Red River fault.
... Geomorphic features and shallow geometry of active faults are crucial for understanding and analyzing the fault's kinematics and characteristics aimed at reducing the potential losses of economic and human lives [1][2][3]. The geometry, activity and seismogenic potential of the fault were revealed by evidence recorded in the geomorphic expression and stratigraphic units [4][5][6][7][8][9][10]. Therefore, high-precision geomorphic features and shallow geometry of active faults are fundamental for understanding the fault kinematics and characteristics. ...
Although geomorphic evidence and shallow geometry of active faults are significant for the understanding and assessing of fault activity and seismic hazards, it is challenging to acquire high-resolution topographic data and shallow geometry of the Yushu fault by conventional methods. Here, we present a case study to reconstruct the detailed surficial and subsurface geometry of the Yushu fault using terrestrial laser scanning (TLS), multi-frequency ground penetrating radar (GPR) and trenching. TLS was suitable for measuring the high-resolution three-dimensional (3D) topographic data of the fault. GPR surveys with different frequency antennas (25 MHz, 100 MHz, 250 MHz and 500 MHz) were conducted to image the shallow geometry of active faults at different depths and spatial resolutions. The typical groove landscape, parallel to surface traces of the fault, was clearly observed on the TLS-derived data. A ~40 m width narrow fault system and three faults were identified on the different frequency GPR profiles. Furthermore, faults F1 and F2 were supposed to be boundary faults but were sinistral-lateral strike-slip faults with a normal component, while fault F3 was inferred as the secondary fault. The western trench section, despite the limited investigation depth (~2 m), was well consistent with the 500 MHz GPR result, especially in the location of fault F2. Finally, a 3D surficial and subsurface model was established from the TLS-derived data and GPR data offering multi-sensor and multi-view spatial data to characterize and understand the fault’s kinematics and characteristics. In addition, the shallow geometry of the fault on the GPR results would be better interpreted with the help of the corresponding surficial data. The study results demonstrate that a combination of TLS, multi-frequency GPRs and trenching can be successfully used for reconstructing a detailed surficial and subsurface geometry of the Yushu fault. It will play an increasing role in comprehensive understanding and assessing fault behavior and seismic hazards, especially on the Tibetan Plateau and the adjacent area.
... The key problem in the study of the paleoearthquake is the selection of the excavation site, which determines the success of its paleoseismic research. The selection of the location is based on the following two factors: whether we can determine the period of earthquake events and whether enough samples are available for dating the events (Deng et al., 2004;Ran et al., 2012). ...
The Liulengshan Fault (LLSF), which lies on the northeastern edge of the Ordos Plateau, is a controlling boundary fault in the northern part of the Shanxi Rift system (SRS). The displaced landforms show that the fault has undergone strong and frequent late-Quaternary seismic activities. In 1989 and 1991, two moderate–strong earthquake swarms (Ms=6.1 and Ms=5.8) successively occurred in the LLSF, and GPS velocity shows that the areas are extending at around 1–2 mm/a. However, there is no surface-rupturing earthquake reported on the LLSF in historical records. Thus, the study of paleoseismic history and rupture behavior of paleoearthquakes in late-Quaternary on the LLSF is of fundamental importance for understanding the future seismic risk of this fault. To solve these problems, we conducted paleoseismological trench excavations at two sites on the LLSF to establish its paleoearthquake history. On the basis of the field geological survey and interpretation of high-precision topographic data, we carried out large-scale fault mapping and excavated two trenches in Xujiabao and Luofengwa across the LLSF. Then, four events in the Xujiabao trench and three events in the Luofengwa trench are identified. Finally, combined with radiocarbon dating (C14), optically stimulated luminescence (OSL) and OxCal modeling, we constrained the ages of these events. Together with the previous results of paleoseismology in Yin et al. (1997), we consider that different segments of the LLSF may rupture together at the same time. Therefore, a total of six paleoearthquake events since late-Quaternary have been finally confirmed at 44,151–30881a, 40,163-28045a, 28,233-19215a, 16,742-12915a, 12,788-8252a, and 8203–2300a BP. According to the empirical relationships between moment magnitude and rupture length, the best estimated magnitude is inferred to be in the range between Mw 6.9 and Mw 7.7. Considering the strong late-Quaternary activity and a long earthquake elapsed time, we propose that the LLSF might have a high seismic hazard potential in the near future.
... Geomorphic landforms and stratigraphic units commonly document the evidence of faulting caused by surface rupturing earthquakes. The evidence of faulting at the surface and shallow subsurface provides the useful information for constraining paleo-earthquake events, determining the fault slip rates and evaluating the seismic hazard [1][2][3][4][5][6][7]. In general, geomorphic evidence of faulting is identified and analyzed by the geomorphological markers from high-resolution topographic data, such as surface ruptures, fault scarps, fluvial terraces and so on [8][9][10][11][12][13]. ...
Abstract: High-resolution topographic and stratigraphic datasets have been increasing applied in active fault investigation and seismic hazard assessment. There is a need for the comprehensive analysis of active faults on the basis of the correlating geomorphologic features and stratigraphic data. The integration of TLS and GPR was adopted to characterize the 3D geometry of the fault on the Maoyaba segment of Litang fault. The TLS was used to obtain the high-resolution topographic data for establishing the 3D surficial model of the fault. The 2D 250 MHz and 500 MHz GPR profiles were carried out to image the shallow geometry of the fault along four survey lines. In addition, the 3D GPR survey was performed by ten 2D 500 MHz GPR profiles with 1 m spacing. From the 2D and 3D GPR results, a wedge-shaped deformation zone of the electromagnetic wave was clearly found on the GPR profiles, and it was considered to be the main fault zone with a small graben structure. Three faults were identified on the main fault zone, and fault F1 and F3 were the boundary faults, while the fault F2 was the secondary fault. The subsurface geometry of the fault on the GPR interpreted results is consistent with the geomorphologic features of the TLS-derived data, and it indicates that the Maoyaba fault is a typical, normal fault. For reducing the environmental disruption and economic losses, GPR was the most optimal method for detecting the subsurface structures of active faults in the Litang fault with a non-destructive and cost-effective fashion. The 3D surface and subsurface geometry of the fault was interpreted from the integrated data of TLS and GPR. The fusion data also offers the chance for the subsurface structures of active faults on the GPR profiles to be better understood with its corresponding superficial features. The study results demonstrate that the integration of TLS and GPR has the capability to obtain the high-resolution micro geomorphology and shallow geometry of active faults on the Maoyaba segment of the Litang fault, and it also provides a future prospect for the integration of TLS and GPR, and is valuable for active fault investigation and seismic hazard assessment, especially in the Qinghai-Tibet Plateau area.
Keywords: terrestrial laser scanner; ground penetrating radar; three-dimensional geometry; data fusion; Maoyaba fault
... The surrounding or larger scale plates may be closely related to it. This is different from the previous research Figure 7: Spatial distribution of the East Asian continental marginal deformation system (plate boundary and direction [67], compressive stress trace [38], and fault in China [68]). 13 Lithosphere ideas; in this paper, through the local extension to the surrounding fault, we analyze the activity of FNF from the perspective of larger-scale plate stress change. ...
Earthquake disasters are frequent, and the seismic intensity is large in Northeast China. Earthquake activity research is an important aspect of earthquake disaster management. We chose some unconventional means to study fault activity, to find updated activity evidence. The Ms 5.3 earthquake occurred near the Fuyu North Fault (FNF) of China on May 27, 2018. Using the Sentinel-1B descending orbit data from 2016 to 2019, the line-of-sight (LOS) surface deformation in the study area was calculated by using the small baseline subset (SBAS) method. After transforming to the horizontal EW deformation, the variance component estimation method was used for fusion reconstruction with the EW data of the surrounding GNSS stations. The polynomial least square method is used to fit the fault slip rate of three EW data on the surface trace of the FNF. The fitting results of the three regions show that the horizontal eastward distribution rate of the upper plate is significantly greater than that of the lower plate, which is left-lateral clockwise torsion. The vertical structural deformation caused by the growth strata of the upper and lower plates of the upper SYT2 seismic profile of the FNF is quantitatively calculated, and the thrust rate of the upper plate is 0.2 mm/y relative to that of the lower plate. Based on the Li Siguang chessboard structure model, we found that the compression stress in the north-south direction is gradually weakened, and the compression stress in the east-west direction is gradually enhanced. Through the Coulomb stress analysis, the three events of CMT only induced the historical focal location of the surrounding part. The events of 2017 did not induce the events of 2018, but the events of 2019 were related to the induced effects of 2017 and 2018.
... The strain partitioning pattern during the active tectonic period (c. 120-100 ka to the present day; Deng et al. 2004) is well understood. For example, the Aismaola anticline, which results from the slip of the Aismaola segment of the PFT (PFT-III in Fig. 2b), grew with a shortening rate of >0.5 mm a −1 during 130-20 ka (Thompson Jobe et al. 2017). ...
Piggy-back basins are characterized by growth stratigraphic sequences bounded by growth unconformities and record the complete deformational history of the related structures. The Biertuokuoyi piggy-back basin, located in the hanging wall of the Pamir frontal thrust (PFT), provides a remarkable example documenting the geometry, kinematics and mechanism of growth unconformities. High-resolution seismic data reveal that multiple growth sequences were folded with constant-dip kink band migration and their dips are equal to the change in the fault-bend angle of the PFT, indicating their kinematic coupling. Divided by a basal Cenozoic detachment, the PFT system contains five lower thrust ramps that cut Paleozoic–Mesozoic strata and an upper thrust ramp that cuts Cenozoic strata. The growth strata and unconformities record c. 4425 m of dip-slip and six stages of episodic thrusting for the PFT. We propose a coeval thrusting style for the five lower thrust ramps. The present seismic section reveals at least 31.1 km of total shortening at the northeastern Pamir front. In particular, the latest shortening of c. 8.0 km is recorded by the Biertuokuoyi Basin and the Mushi anticline. Our results show that multiple growth sequences bounded by growth unconformities are powerful resources for documenting the evolution of deformation.
Supplementary material: Supporting figures and data, including seismic profiles and kinematic simulation results, are available at https://doi.org/10.17605/OSF.IO/DNQBS .
Thematic collection: This article is part of the Fold-and-thrust belts collection available at: https://www.lyellcollection.org/cc/fold-and-thrust-belts
... Full understanding of the behavior and history of an active fault is the key to assessing seismic hazards and reducing the impacts from earthquake disasters [1]. A reasonable seismic hazard assessment mainly depends on the integrity of seismic records [2]. ...
License (CC BY 4.0). The quantitative morphology of bedrock fault surfaces combined with aerial surveys and field identification is a useful approach to identify paleoearthquakes, obtain coseismic slips, and evaluate the seismogenic capacity of active faults in bedrock areas where traditional trenching methods are not applicable. Here, we report a case study of the Jiaocheng Fault (JCF) in the Shanxi Rift, China. Although several studies have been conducted on the JCF, its coseismic slip history and seismogenic capacity are still unclear. To address these problems, we investigated two bedrock fault surfaces, Sixicun (SXC) and Shanglanzhen (SLZ), on the JCF's northern segment using quantitative morphological analysis together with aerial and field surveys. Quantitative fractal analysis based on the isotropic empirical variogram and moving window shows that both bedrock fault surfaces have the characteristics of vertical segmentation, which is likely due to periodic earthquakes, the coseismic slip of which can be determined by the height of the segments. Three seismic events at SXC, with a coseismic vertical slip of 1.74, 1.65, and 1.99 m, and three seismic events at SLZ, with a coseismic vertical slip of 1.32, 2.35, and 1.88 m, are identified. Compared with the previous studies, these three seismic events may occur in the Holocene, but it requires absolute dating ages to support, which is also the focus of our future work. Considering the seismologic capability (M > 7:5) and the relationship between the recurrence interval of~2.6 kyr and elapsed time of more than 3 kyr, the seismic hazard of the northern and middle segments of the JCF requires immediate attention.
... The slip rates of the active faults in the Qilian-Haiyuan fault zone and nearby regions, including the Jinqianghe fault, are important quantitative parameters of the deformation velocity field in the late Quaternary and allow us to probe regional tectonic transformation patterns (Deng et al., 2004;Zhang et al., 2004;Ren et al., 2013). ...
The Qilian–Haiyuan fault zone in the northeastern Tibetan Plateau has been the source of strong earthquakes in the region. In its middle segment, the Jinqianghe fault is an important active fault within the Tianzhu seismic gap; however, little is known about its slip behavior. To present a new horizontal displacement distribution along this fault, we used WorldView‐2 stereo pairs and unmanned aerial vehicle‐based photogrammetry to construct digital elevation models to obtain a detailed tectono‐geomorphic interpretation and geomorphic offsets. The offset marker measurements yielded 135 geomorphic displacements and 8 offset clusters. Radiocarbon dating was used to establish the regional age sequence of the geomorphic units in offset fluvial terraces at four study sites. The displacements and ages linked the offset clusters with the geomorphic unit sequence; the Holocene strike‐slip rate of the Jinqianghe fault was estimated to 4.8–5.6 mm/a at ∼4–12 ka and 2.9–4.7 mm/a from ∼4 ka. Three recent earthquakes (with a recurrence interval of ∼1000 years) represent an active seismic period, revealing the potential seismic hazard along this fault because it has not ruptured in the last 1500 years.
... The fault slip rate is an important parameter to limit the intensity of tectonic deformation and related seismic risk (Deng et al., 2004). The slip rate of normal faults near the main boundary of the North-South rift zone in southern Tibet is the key to limit the strength of extensional deformation across the rift zone and constrain its dynamic mechanism (e.g., Armijo et al., 1986;England and Houseman, 1990;Harrison et al., 1992;Tapponnier, 1977, 1978;Molnar et al., 1993;Tapponnier et al., 1981Tapponnier et al., , 2001Taylor et al., 2003;Chevalier et al., 2020). ...
The Yadong-Gulu rift is the largest active rift within the southern Tibet Plateau. Although tectonic characteristics and geodynamic implications of normal faulting have been widely discussed, precise constraints on the fault slip rates and their spatial distribution are still scarce to date, hindering full exploration of the deformation mechanism of active rifts in the southern Tibet. In this study, we integrated the interpretations of high-resolution satellites and unmanned aerial vehicle (UAV)-acquired images, and topography with the results of field surveys and radiocarbon dating to demonstrate the slip distribution along the Chongba Yumtso fault (CYF) bounding the northeastern sector of the Duoqing Co graben and then discussed their implications for the seismic risk and regional deformation. Since the late Pleistocene, the vertical slip rate and extension rate across the CYF are about 1.2 ± 0.1 and 1.7 (+0.7/−0.5) mm/a, respectively, and the average extension rate across the Yadong-Gulu rift zone is about 2.1 (+0.5/−0.6). According to the activity rate, plane size, basin-mountain height difference, and sediment thickness of the grabens in the southern segment of the rift zone, it is considered that the extension of the main boundary normal fault in the southern segment of the rift has the spatial variation characteristics of decreasing from south to north. According to the comparison of the total extension rate on different time scales, it is considered that the total extension rate of the rift zone in southern Tibet is approximately stable in different time periods, which is ∼16 (+5/−4) mm/a. According to the active rate and historical seismic records of the Duoqing Co graben in the Yadong-Gulu Rift Valley, it is considered that the CYF has potential to produce earthquakes with Mw 6.6-7.4.
... 4.2 CBERS-02B [2] , , ...
... Understanding the faulting behavior and history of an active fault is the cornerstone to understanding seismic activity, assessing seismic hazards, and reducing earthquake disasters (Deng et al., 2004;Parsons et al., 2000). Paleo-earthquake research is the most effective discipline to expand the history of relatively complete seismic records (Wallace, 1981). ...
The study of bedrock fault scarps is a useful approach to identify paleo-earthquakes and acquire the faulting history in bedrock areas where traditional trench techniques are not applicable. Here, we report a study on the Luoyunshan piedmont fault (LYSPF), southwestern Shanxi Rift, China. Although several studies have analyzed the LYSPF, its faulting behavior is still under debate. For example, the tectonic geomorphology fails to determine the frequency of past slips and the elapsed time. To address these problems, we investigated two bedrock fault surfaces, Luoyuncun (northern segment) and Weicun (southern segment) using quantitative morphology analyses together with multiple Quaternary dating techniques. Quantitative morphology analysis shows that both bedrock fault surfaces have the characteristics of vertical segmentation. This kind of segmentation indicates that the fault surfaces are exhumed intermittently, likely owing to periodic faulting earthquakes. Therefore, earthquake events can be identified as morphological segments, and the corresponding co-seismic displacement can be determined by the height of these segments. According to the results from the quantitative morphology and dating techniques, four seismic events, with a co-seismic vertical displacement of 0.9 m, 0.82 m, 1.64 to 2.38 m and 2.30 to 2.54 m, on the northern segment occurred during the late Pleistocene, whereas, two seismic events, with a co-seismic vertical displacement of ~1.33 m and 1 to 1.08 m are identified on the southern segment occurred during the Holocene. Combined with the results of knickpoint series and trench techniques of the LYSPF, eight paleo-earthquake events were identified since 45 ka, with an average recurrence interval of 5.8 kyr. The more complete paleo-earthquake sequence also showed the possibility that the variation of the slip rate along the LYSPF depends on the segment, and that the displacement produced by the Linfen M 7½ earthquake of 649 CE has been recorded at the WC fault surface.
... Usually, seismic hazards are assessed based on strong earthquake records, including both historical and instrumental earthquake records, and slip rates of active faults (e.g., Deng et al., 2004). Active faults that have produced striking earthquakes in history or slip at high rates are thought to be in high seismic hazards, while active faults that slip at relatively low slip rates with no historical earthquake record are considered to pose low seismic hazards and thus have attracted little attention for long time. ...
Assessing the seismic hazard of a fault is usually based on its record of strong earthquakes. Earthquake records with long periods of quiescence for active faults can lead to underestimates of seismic hazards, such as for the Longmenshan fault zone which produced the unanticipated 2008 Mw 7.9 Wenchuan earthquake. The Daliangshan fault zone has a low slip rate and has not produced any strong earthquakes in history. As a result, little is known about its paleoearthquake history, including the behavior of any strong earthquakes it might produce and the seismic hazards posed by the Daliangshan fault zone. To solve this problem, we excavated four trenches across the Jiaojihe and Butuo faults along the southern segment of the Daliangshan fault zone. The paleoseismic investigations revealed six paleoearthquakes on the Jiaojihe fault in ~20,000 years and determined another seven rupturing events on the Butuo fault in ~42,000 years. The strong earthquake history of the Jiaojihe fault has evidence of temporal clustering, while the Butuo fault exhibits a relatively periodic recurrence pattern with intervals of 1,710–2,460 years. Based on its surface rupture length and the magnitude of observed displacement, the southern segment of the Daliangshan fault zone is capable of producing M > 6.5 earthquakes. Furthermore, based on their respective slip rates and the elapsed times since the most recent events along the Jiaojihe and Butuo faults, they have accumulated seismic energy equivalent to M ~ 7.6, suggesting they pose a significant seismic hazard to the southeastern Tibetan Plateau.
... With the development of active tectonic studies (Wallace, 1970;Sieh and Jahns, 1984;Deng et al., 2004), the research on the influence of active tectonics on landform and geomorphology goes also deeply. On the other hand, the regional landforms and its related sediments provide a good time and space framework for constraining important parameters of active tectonics, such as properties, rates, strong earthquake activity records, and the latest activity times and so on. ...
The authors surveyed the longitudinal profiles of 28 gullies across the Luoyunshan Piedmont fault (LPF) by differential GPS and dating of sediments well preserved in the typical terraces and obtained 6-level knickpoint series of the gullies along the Luoyunshan Piedmont. The authors compared it with previous studies on the paleo-earthquakes of the LPF revealed by trenches and found that the paleo-earthquake events from knickpoint and trench studies are in good agreement in terms of the time of occurrence and vertical displacement of the fault. It shows studying the paleo-earthquake events of the fault by knickpoint series is feasible. At last, the authors established a more complete paleo-earthquake sequence of the LPF supported by geomorphologic and sedimentary evidence, i.e., six paleo-earthquake events happened on the LPF from about 28,000 years ago; the LPF has the characteristic of quasi-periodic recurrence and the average recurrence interval is 4585 years. The vertical displacement of the paleo-earthquake events is 2.4–3.0 m; according to the empirical equations between co-seismic displacement and earthquake magnitude the magnitude of these events is Ms 7.0–7.5. This study aims to complement and improve the traditional trenching method, provide theoretical and methodological support for the research of active tectonics, and contribute important information for the seismic hazard assessment of the densely populated Linfen area.
... Paleoseismology is the study of prehistoric earthquakes and supplements instrumental and historical records of seismicity by extending space and over time periods of thousands or tens of thousands of years, and through multiple-period geological documentation of earthquake events we can explore a long-term seismic behavior of active faults and estimate future risk on large earthquakes. The key technique on paleoseismology is based on trenching to reveal evidence of surface deformation produced by large earthquakes, so choosing a better trench site is critical to achieve the complete and effective dating on paleoseismic events for a reliable earthquake hazard assessment [1][2][3][4][5][6][7][8][9][10]. ...
Trenching is a primary technique on paleoseismology to reveal evidence of surface deformation produced by large earthquakes. A good trenching site requires completeness of geologic recording on paleoseismic events and corresponding reliable dating from radiocarbon samples. Based on three-dimension trenching, we show a structure of a small triangular pull-apart basin at the Daqingliangzi section on the Zemuhe fault, then explore interrelation between paleoseismic surface rupturing and evolution of the pull-apart basin, and give a corresponding identification model. Sedimentary boundary of the pull-apart basin is tightly bounded by two branch faults, which produced multiple paleoseismic events with deformation of some large fissures in sequence. Strata are thinner at north of the pull-apart basin, however thicker at south. These above characteristics show that evolution of the pull-apart basin is a continuous sedimentation process accompanying extensional deformation produced by multiple paleoseismic events. Small pull-apart basins are favorable sites for trenching and paleoseismic study on active strike-slip faults.
... Slip rate is an important parameter for an active structure [51]. Average vertical slip rates are calculated by using shallow penetrated seismic data in the paper. ...
The Tan-Lu Fault zone (TLFZ) is a significant fractural zone in eastern China and also a seismicity belt in North China. Based
on total 4000-km-long shallow penetrated single seismic data with high-resolution, structural deformation and fault activity
of the TLFZ in the Bohai Sea since the late Pleistocene are discussed in detail. The results show that the TLFZ with a discontinuous
distribution and a general NNE-trending consists of 14 active subfaults with an NNE or NE strike in the Bohai Sea. Seismic
data reveal that deformation zones along the subfaults in the central Bohai Sea and the Laizhou Bay are wider and more complex
than those in the Liaodong Gulf. Related folds and lots of secondary normal faults which are characterized by nearly vertical
fault planes and a same or reverse dip construct the fractural zone in the Laizhou Bay and the central Bohai Sea. Usually,
micro symmetrical grabens develop on the top of anticlines. In the Liaodong Gulf, subfault fractural zones usually consist
of secondary normal faults with the same inclination or opposite inclination. Ages of seismic sequences and cutting relation
between subfaults and seismic sequences suggest that the latest faulting age of the TLFZ is the end of the late Pleistocene
in the Liaodong Gulf and the early Holocene in the Laizhou Bay and the central Bohai Sea. There is a good match between distribution
of earthquakes and that of the subfaults in the Laizhou Bay and the central Bohai. Statistical result shows that total vertical
offset of the TLFZ since the late Pleistocene ranges from 6 to 11 m. On the basis of offsets of the subfaults, the vertical
slip rate is calculated and results show that average vertical slip rates in the central Bohai Sea are larger than those in
the Liaodong Gulf and the Laizhou Bay. Slip rates more than 0.06 mm/a during 23-10 ka B.P. and 85-65 ka B.P. are larger than
those in other stages. The TLFZ was mainly dominated by tensional normal component since the late Pleistocene. Synthesizing
shallow deformation, activity and distribution of earthquakes, the TLFZ in the Bohai Sea can be divided into three segments:
the Laizhou-Bay segment, the Bozhong segment, and the Liaodong-Gulf segment.
KeywordsTan-Lu Fault zone-structural deformation-fault activity-late Pleistocene-Bohai Sea
In recent years, UAV (Unmanned Aerial Vehicle) SfM (Structure from Motion) technology has been widely applied as an emerging high-precision 3D topographic data acquisition technique in active tectonics research. However, existing domestic research primarily focuses on UAV platforms without RTK/PPK modules. Over the past two years, RTK and PPK technologies have gradually been introduced to UAV platforms, resulting in changes to field data collection and in-office data processing
workflows compared to traditional UAV platforms without RTK/PPK modules. The differences in topographic data quality obtained through SfM processing of aerial photographs from UAV platforms equipped and not equipped with RTK/PPK modules under the same scenes and collection conditions still require investigation. To address these questions and establish a streamlined data collection and processing workflow for different UAV platforms, a site where alluvial terraces are offset by the sinistral
Longmu Co fault, northwestern Tibetan Plateau, was surveyed using the DJI M300 RTK UAV (equipped with the Zenmuse L1 LiDAR and a 20-megapixel visible light camera) and the DJI Phantom 4 Pro UAV (equipped with a 20-megapixel visible light camera). Through processing the raw data with SfM technology, high-resolution and high-precision DEM and DOM data were obtained for the study area. Additionally, 16 ground control points (checkpoints) were uniformly distributed in the research area and their coordinates were measured using the Trimble R8 GNSS receiver in RTK mode to compare and validate the differences in data quality obtained by the two platforms. The data comparison results showed that the visible light camera and LiDAR module carried by the M300 RTK demonstrated high accuracy, with root mean square errors (RMSEs) in the centimeter to decimeter range compared to the RTK-measured ground checkpoints. Compared to SfM data collected at the same time (RMSEX=0.176, RMSEY=0.099, RMSEZ=0.180, RMSEH=0.201, RMSE3D=0.270, unit: m), the Zenmuse L1
LiDAR data exhibited slightly higher accuracy (RMSEX=0.112, RMSEY=0.076, RMSEZ=0.111, RMSEH=0.135, RMSE3D=0.174, unit: m). The uncorrected SfM data from the Phantom 4 Pro had horizontal errors of approximately 1 meter (RMSEX=1.112, RMSEY=1.295, unit: m) and a vertical error of over 200 meters (RMSEZ=249.286, unit: m). After ground control point correction, the accuracy of the Phantom 4 Pro SfM data significantly improved, with RMSE of 0.046m, 0.058m, and 0.527m in the X, Y, and Z directions, respectively. Further analysis of a topographic profile nearly perpendicular to the steep slopes of various terrace risers within the surveyed area revealed that, despite significant elevation discrepancies in the uncorrected Phantom 4 Pro SfM data, it still accurately reflected the relative topographic relief. Subtracting the profile elevation values from their corresponding RMSE, the profile shape closely matched the rest of the data. Based on the acquired DEM data, the displacement of the terrace at this location was measured using LaDicaoz software, revealing a left-lateral strike-slip
displacement of 122.5±5m and a vertical displacement of 0.8±0.2m. The study results indicate that: (1) UAV SfM method and LiDAR technology have significantly improved the resolution of DOM and DEM, enabling more detailed interpretation and analysis of active faults and related structural landforms; (2) RTK SfM technology overcomes the limitations of using ground control points, providing a higher-precision and more efficient solution for micro-landform measurements in the field of active tectonics research; (3) when absolute three-dimensional coordinates in the study area are not crucial, and only relative terrain variations are required, UAVs without RTK modules can still meet the basic requirements for geomorphic fault displacement measurements in the absence of ground control point constraints; (4) combining UAV SfM technology with traditional fault geomorphology analysis and Quaternary dating techniques in high-precision quantitative active tectonics research can offer robust technical support for analyzing fault activity patterns, seismic hazard, landform evolution, and the occurrence patterns of geological disasters. Through the aforementioned work, workflows for data collection, data processing, and geomorphic fault displacement measurement using SfM methods in active tectonics research were established for both UAV platforms equipped and not equipped with RTK/PPK modules, and the fieldwork considerations and data accuracy of UAV SfM methods were analyzed, providing a reference for selecting UAV platforms and rapidly collecting and processing data for similar studies in the future.
The development of Structure from Motion (SfM) technology makes it more convenient to obtain high precision DEM data in small and medium-sized areas quickly in the field of active tectonics research. The accuracy of DEM data is a major concern in the field of active tectonics and surveying. By comparing the SfM DEM data generated by non-RTK model UVA technology combined with ground control point (GCPs) and RTK-SfM DEM data obtained based on RTK SfM technology, this paper focuses on analyzing the vertical accuracy of DEM data obtained by SfM technology equipped with RTK module. The results of data acquisition, processing and comparison show that in the DEM data generated by non-RTK model SfM technology with the GCPs, the distortion rate is small in most areas except the distortion caused by fewer photos at the edge of the measurement area. The DEM data obtained by RTK-SfM has a smaller distortion rate, and the data generated by non-RTK SfM combined with GCPs has a system elevation error of about 0.85 m. After subtracting the system error, the point cloud comparison results show that more than 95% of the vertical errors of both are less than 0.05 m. The DEM data obtained by SfM technology equipped with RTK module has better vertical accuracy and saves time and labor cost.
Normal fault scarps, as classical topographic features and geomorphological markers along mountain range-fronts, form in consolidated bedrock due to faulting in extensional settings. They generally preserve more complete records of paleo-earthquakes than fault scarps in unconsolidated sediments. The reconstruction of paleo-seismic history from a bedrock fault scarp in terms of the times, co-seismic slips and ages by a combination of quantitative morphological analysis, TCNs dating and other physical/chemical index has been proven feasible by several previous studies. However, this success heavily relies on a suitable site selection along the bedrock fault scarp because geomorphic processes are also capable exhuming the fault surface, i.e., an erosion-origin fault surface. To distinguish between tectonic- and fault-origin fault surfaces, four bedrock fault surfaces (MJYC, NMZC, DYC and SYC) in the northern Shanxi Rift have been targeted to carry out a comparative study by combining small unmanned aerial vehicle (s-UAV) surveys and terrestrial laser scanning (TLS). The results can be classified into two groups according to their quantified morphological characteristics and exposed ways. For the NMZC and SYC group, which are in elevated areas away from gullies, the quantitative morphological analysis shows that both bedrock fault surfaces have the characteristics of vertical segmentation. This kind of segmentation indicates that the fault surfaces may be exhumed by repeated seismic events, and the corresponding co-seismic slips are determined by the height of these segments. For the MJYC and DYC group, the quantitative morphology shows a gradually-changing characteristic without segmentation. This gradually-changing characteristic indicates an erosional exposure mode from geomorphic processes, and accordingly the paleo-seismic information cannot be extracted. Thus, results from this study highlights the importance of selecting a suitable study site when conducting paleo-seismic research on bedrock faults. Based on experience obtained in this study combined with previous cases, we propose the characteristics of bedrock fault surfaces suitable for extracting paleo-seismic information and corresponding identification principles. Finally, a general workflow for paleo-earthquake history reconstruction from bedrock fault scarps is proposed to promote paleo-earthquake study in bedrock areas.
The activity of major active faults around the Ordos Block is of great interest to seismologists, as at least four M ≥ 8 earthquakes have been recorded. However, the Linhe Basin, which has the thickest Cenozoic sediments, has no record of large earthquakes. Does this basin have the structural conditions required for large earthquakes? The northern boundary fault of the Linhe Basin is composed of the NE‐striking Langshan piedmont fault (LPF), E‐W‐striking western section of the Seertengshan piedmont fault (WSPF), and NW‐striking eastern section of the Seertengshan piedmont fault (ESPF). Based on large‐scale active fault mapping, this article analyzes data from 23 trenches, using an unmanned aerial vehicle to measure the faulted landform, and combines these data with Quaternary dating methods to acquire the paleoearthquake sequences of the LPF, WSPF, and ESPF. Furthermore, this article explores their rupture modes and discusses the structural evolution of two intersection points. Through paleoseismic comparison, seven trenches revealed historical earthquakes from 7 BC, with a common magnitude of M 8.1. The trenches also revealed seven paleoseismic events since the Holocene, which conformed to the periodic model with a period of 1.37 ± 0.11 ka. The elapsed time since the latest event (2.0 ka) has exceeded the earthquake recurrence period; thus, the area is currently at risk of an M 7.4–8.0 earthquake. The NE‐striking LPF and E‐W‐striking WSPF are connected by two left‐stepping small fault segments. The E‐W‐striking WSPF and NW‐striking ESPF are connected by a large triangular relay ramp.
The Lenglongling Fault (LLLF) is located in the western section of the “Tianzhu seismic gap” along the Qilian-Haiyuan fault zone in the NE Tibetan Plateau, between the 1920 M8.5 Haiyuan and the 1927 M8.0 Gulang earthquakes. There is little information about the paleoseismic history of the LLLF and understanding the faulting history of the LLLF is important for determining the seismic hazards of both the fault and the seismic gap. Using UAV-based photogrammetry, high-resolution satellite imagery, and field investigations, we mapped the surface trace of the fault in detail and measured 192 left-lateral offsets of geomorphic markers along the fault trace. A binned cumulative offset probability density (COPD) distribution was calculated to analyze single-event and multi-event cumulative offsets. As a result, we find that the LLLF has fresh scarps along the entire ∼120 km length, indicating that the most recent event might have ruptured the full-segment of the fault. The coseismic offset of the most recent event changes along the fault trace and has an asymmetrical bell-shaped distribution. The maximum offset was ∼7 m, located in the middle-eastern section of the fault, and the offset decreases progressively towards both ends. The minimum offset, located at the western end, was ∼3.0 m, and the average coseismic offset was ∼4.8 m. The cumulative offsets of the four most recent paleoearthquakes are multiples of the coseismic offset of the most recent event, and show similar slip distributions, indicating that the fault ruptures with a characteristic slip. The fault slip distribution, estimated recurrence interval, and estimated moment magnitude imply that the LLLF releases accumulated strain energy mainly by repeatedly producing Mw 7.5–7.8 earthquakes every 1000 ± 200 years. We also show that the binned COPD technique performs well to separate single-event and multi-event cumulative offsets.
High-precision and high-resolution topography is the basis of the quantitative study of active faults. Light detection and ranging (lidar) is currently the most popular method for obtaining such data, but its relatively high cost greatly limits its use in many geoscience applications. Recently, with the rapid development of computer vision science and the growing application of small unmanned aerial vehicles (UAVs), Structure from Motion (SfM) photogrammetry shows great potential for providing topographic information of comparable resolution and precision to lidar surveys, but at significantly lower cost. In this study, we examined the applicability of SfM photogrammetry in modelling the topography of the fault zone using images acquired with a low-cost digital camera mounted on a UAV over the Haiyuan fault. The resolution and accuracy of the SfM-derived topography were evaluated in detail using existing airborne lidar data as a benchmark. The results show that the density of the point cloud generated by SfM photogrammetry is nearly 70 times higher than that from the airborne lidar. Furthermore, considering the errors in the lidar data itself, the precision of the SfM point cloud is comparable to that of the lidar point cloud. Overall, our results demonstrate that the UAV-based SfM photogrammetry method can provide an inexpensive, effective, and flexible alternative to airborne lidar for the topography mapping of the fault zone.
Based on the result of quantitative research on active faults, analysis of regional seismicity, and especially the detailed investigation and systematic summary on paleoearthquake in Urumqi region, the recurrence mode and probability models of Xishan Faults that reflect the seismic, geological and kine-mics characteristics are established. The strong earthquake recurrence mode considers the Poisson mode and quasi-period mode and reflects the randomicity and determination with chanciness of seismicity on the fault. The probability model involves two levels of content: analyzing the paleoearthquake data and historical strong earthquake catalog on or near the faults to obtain the mean recurrence interval of surface-rupturing earthquakes (M s ≥ 6.7), and analyzing the modern instrumental earthquake catalog (1970~present, and the size of these earthquakes is in the range of 2.0~5.0) of potential seismic source zone where the active faults locate. The calculation of seismic hazard probability of active faults utilizes the expert-opinion method to assign different weights to the models such as Poisson model and BPT model, and then incorporate the weighted probability result to construct combined model, which is the core of the method. This data-processing method has two advantages: taking complexity of strong earthquake recurrence mode into consideration and reducing the possibility of overestimating the seismic hazard of active faults. The result shows that the recurrence probability of surface rupturing earthquakes is 4.0% in the coming 100 years, and 3.6% in the coming 50 years. This result is consistent with that of the method based on stress environment analysis. The maximum magnitude of Xishan Faults (belt) is M s 7.5 estimated from paleoearthquake, dimension and dip-slip rate of fault, which is consistent with the upper limit magnitude of potential seismic source zone where the faults locate. This study integrates the newest research results on regional seismology and geology, better describes the complexity of seismic process along fault to a certain extent, and assesses comprehensively seismic hazards of active faults in Urumqi. This multidisciplinary method can be applied to the region like Urumqi where complete seismogeological data are unavailable.
A reasonable and authentic estimate of surface rupture shortening amount of reverse fault is essential to a thorough understanding of the co-seismic surface deformation parameters, while we have no effective or feasible methods to deal with it, presently. The paper attempts to analyze and calcu late horizontal shortening amounts of reverse fault with trench excavation basing on the investigations of the surface ruptures of the Ms8. 0 Wenchuan earthquake. On this condition, we conclude three genesis models of fault scarp, namely, faulting, flexuring, and superposition of faulting and flexuring. The paper proposes several calculation methods about horizontal shortening amounts of reverse fault based on these fault scarp models, and also gives detailed mathematic proof and constraint factors when considering complicated phenomena. Moreover, combined with these models, we discuss how to correctly apply and interpret the reverse surface rupture information revealed by trench. Finally, we demonstrate the calculation process and results of the reverse fault's horizontal shortening amounts in the trench close to the Central School of Bailu and the trench at Quanxin village of Hanwang, which are(2. 83 ± 0.3)m and(0.61 ±0.11) m, respectively.
Slip rate of active faults is deterministic to compare active earthquake behaviors among different faults or different segments along a fault, and also it is a key parameter for seismic hazard assessment. Geologically reliable estimation on slip rate is subject to two active tectonic parameters, the cumulative displacement produced by multiple surface-rupturing seismic events and the corresponding true ages, respectively. Generally, for strike-slip faults, we carefully measure geomorphic expressions, such as deformation or offset produced by multiple faulting on river terrace, alluvial-fluvial fans or gullies, and then integrate geochronological constraint from dating on these geomorphic expressions. Based on the above two crucial parameters, we further determine slip rates along faults. However, this paper is attempted to use another deformation of geomorphic expression, a growth model for a small triangular pull-apart basin(sag pond), to constrain fault slip rate at the Daqingliangzi section of Zemuhe Fault on the southeastern margin of the Tibetan Plateau. Based on several three-dimension trench excavations, reliable radiocarbon dating at the bottom of stratigraphic unit in the triangular pull-apart basin (sag pond), detailed field investigation along the Daqingliangzi section of Zemuhe Fault and accurate RTK (GPS) survey, we suggest that Holocene average left-lateral slip rate of the Zemuhe Fault is constrained between 2.4±0.2mm/a and 3.6mm/a, which is a little smaller than those estimated by other geoscientists, however this strike-slip rate is much more accordant with paleoseismic recurrence behaviors and present velocity field obtained from GPS measurement across the Zemuhe Fault.
Haiyuan-Liupan Shan area is located in the northeastern margin of present Tibetan plateau. The study of the active structures in this area will provide constraints not only for the seismic evaluation but also for the northeastward growth of the plateau. Based on the geological survey and optically stimulated luminescence (OSL) dating, the timing of the active structures has been determined. The results indicate that active structures occurred in Late Quaternary along the Haiyuan-Liupan Shan and Xiangshan-Tianjing Shan faults, forming the structures such as angular unconformity (planation surface), fold and fault. This suggests that Haiyuan-Liupan Shan area should be considered as a focus of seismic evaluation, and also that the Tibetan plateau grew in its northeast margin in Late Quaternary.
Based on the data of shallow seismic survey and drilling geological profiles, a buried fault has been found. With eight shallow seismic profiles, it is found that the buried fault is 600 m to 1200 m apart from the front of Yuwangshan in front of Yuwangshan Mountain, cutting the floor of Daxie basin, likely extending into Quaternary strata at the basin bottom. Using OSL dating and sporo-pollen analysis, we study the Quaternary sediment in the bore holes of Qianjia village, and suggest that the Quaternary sediment is late Pleistocene stratum at western margin in Daxie basin. On the composite drilling geological section in Qianjia village, fault fracture zone is 8.5 m in width in Jurassic tuff. On the drilling geological section of Liangnan village, we find two faults in Jurassic tuff, one of which is 5 m in width. At the depth of 35 m in Liangnan DQZK6 drilling hole, fault plane obliquity is 70° in clay, with its slickenside approximately upright. In Qianjia QJZK8 bore hole, fault plane obliquity is also 70° at depth of 35 m in clay. Active rate of the fault is 0.034-0.046 mm/a in vertical direction, and it is a weak active fault in early period of late Pleistocene. From the exploration result, we obtain the depth of the upper break point of the buried fault as 35 m in the front of Yuwang Mountain. The active fault will not directly destroy buildings on ground surface along the fault zone.
Daliangshan Fault zone constitutes an important part of the eastern boundary of Sichuan-yunnan active block. The studies of slip rate along the fault is not only significant to the crust movement and deformation pattern on the southeast edge of Tibetan Plateau, but also has great value in seismic hazard assessment and mid-and long-term forecasting of earthquake of the Daliangshan region. Through detailed field work along the south segment of Daliangshan Fault zone, namely the Butuo Fault and the Jiaojihe Fault, and based on accurate RTK(GPS) survey for the alluvial fans and activity dating, we suggest that left-lateral slip rate of the south segment of the fault zone is between 2.5~4.5mm/a, and the slip rate of Jiaojihe Fault is slightly higher than that of the Butuo Fault. Due to partitioning of part of the strike-slip component on the Daliangshan Fault zone, there is an obvious deficit in the displacement and slip rate on the Anninghe-Zemuhe Fault, compared to the Xianshuihe and Xiaojiang Faults. Comparing to the slip rates between Daliangshan Fault and Anninghe-Zemuhe Fault, it is found that they have similar horizontal slip rate, indicating the seismicity level of the Daliangshan Fault will not be lower than that of Anninghe-Zemuhe Fault. As the Daliangshan Fault gradually replaces the role of Anninghe-Zemuhe Fault in the Xianshuihe-Xiaojiang Fault system, the seismicity on the Daliangshan Fault zone will increase, and the Dalianghan region will have a higher risk of earthquake damage.
The main purpose of paleoseismic study is to distinguish or reveal deformation evidence of large earthquakes recorded by geologic and geomorphic features, and obtain corresponding seismic parameters such as timing, recurrence behavior, and coseismic displacement of large earthquakes. To achieve the aforementioned scientific aim, whether a trenching site preserves evidence of a complete paleoseismic sequence since late Quaternary and contains multiple measurable samples or not, and whether it can accurately identify paleoseismic events and collect well-constrained samples on events or not, all of these problems are directly responsible for reliabilities on assessment of future large earthquake hazard. Due to special displacement styles on strike-slip faults, good trenching sites are not widespread. Through comprehensive analysis on characteristics of coseismic surface ruptures and influencing factors on several trenching cases, we suggest micro-landforms such as depressions, basins, troughs, sag ponds, successive-offset channels, continuous scarp-derived deposit and multiple geomorphic surfaces are likely to be good trenching sites for paleoseismic studies on strike-slip faults. Multiple trenching or three-dimensional trenching should be the primary layout on strike-slip faults. Offsets of micro-land-form across a fault, young stratigraphic units overlying on faulted units, locally distributed scarp-derived colluvial deposits, filled fissures, abrupt increases or decreases in displacement of different strati-graphic units on a fault, warping in different degrees, and multiple periodic paleo-sag ponds accumulation, all of these deformation evidences are good indicators for identifying paleoseismic events. To narrow uncertainties of paleoseismic studies, we should base on an organized research process and make a technical proposal and sophisticatedly conduct trenching work. Conclusions need to be repeatedly checked and widespread discussed, and also we should pay much attention on details and use more evidence to support or supplement analysis.
Longling-Ruili Fault zone(LRF)is located at the boundary between China and Burma, striking in northeast direction for about 135km and controling the formation and evolution of Longling, Luxi, Zhefang and Ruili Basins. This study utilizes the high-resolution remote sensing data, such as ALOS and ASTER and SRTM digital elevation model data in combination with field work and RTK-GPS(Real Time Kinematic-Global Positioning System)to present the tectono-geomorphic features and geologic structures along the LRF. Analysis from the remote sensing data reveals that the LRF always develops along the south and north edges of the basins, and forms the NE-striking linear mountains and valleys between the basins, with a general strike in N55°E direction. In the field, many geomorphic features, including saddle-shaped landform, fault facets and shutter ridges, are developed along the LRF; While at Xintangfang and Ganlanpo, a several meters-wide shear zone crops out with fresh fault gouge. All the descriptions above demonstrate that the LRF is sinistral strike-slip fault and has been active since late Quaternary. To gain more insight into the activity of the LRF, a trench was excavated at Zhujiazhai which reveals the fresh fault plane at the base rocks and late Quaternary alluvial deposits above, but no evidence found indicating the fault offset those young deposits. Radiocarbon dating of charcoal samples from the bottom of alluvial fans indicates that there is no destructive earthquake happening along the north segment of LRF since 1150 B.P. Finally, analysis for the 1976 Longling earthquake and distribution of historical earthquake imply that the 1976 destructive earthquake may be triggered mostly by the NNW-striking newly formed fault zone rather than the NE Longling-Ruili Fault zone.
Quantitative study of active tectonics needs to get a series of deformation parameters, and fault displacement is one of the most basic active parameters. Alluvial fan and terrace around active fault zones can record the information of time and strength of fault movement. River terrace as a most common landform contains structural information. It is meaningful for quantitative tectonic movement study to ascertain river terrace. In the article we use photogrammetric software virtuoNT to extract high resolution DEM. Based on DEM, the method and program for terrace analysis are built on the platform of ARCGIS. In the light of the distribution characteristics of slope and height, we generate the slope classification map and height classification map. And by multiplication of the two maps, the terrace landform map is generated. In the Zimakua region of Sichuan province, we applied the method to extract terrace information and got its distribution. We compared the terrace extracted based on DEM with the terrace interpreted in the filed, and the result shows that they have good consistency. The terrace boundaries record the information of fault dislocation. By measuring the dislocation of terrace boundary, we get the average dislocation of secondary fault to be 85. 4m, which is in accord with the filed surveys. The results indicate that the method of terrace extraction based on DEM has the properties of high precision, high efficiency, visualization and so on.
The Yunnan-Burma block, located in the southeast margin of the Tibetan plateau, is one of the most tectonically active regions in mainland China. Since 1900, more than 10 earthquakes with magnitude over 7 occurred in this region, which account for more than a half of the great earthquakes in Yunnan. Moreover, the recent MS7.2 earthquake occurred in Mong Hpayak on March 24, 2011, and a series of MS5.5 earthquakes in the western Yunnan. If these earthquakes are not isolated, does they mean early warning of great earthquakes in the future? Therefore, for the purpose of earthquake prevention and disaster mitigation, it is urgent and necessary to carry out seismic risk assessment in this region especially along the NE-trending fault zones. The method of tectonic geomorphology was used to analyze fault activity. By measuring the deformation of the typical geomorphic or geologic units together with dating data, fault activity was estimated. The measurement was finished indoor or in the field. Remote sensing data were interpreted and geologic maps were prepared. According to the interpretation of drainage systems based on the remote sensing data, displacement of faults were determined. In the field, the rope and scale were employed for measurement (if displacement is too long, GPS equipment was used). Using dating technology, motion rates on the faults in the study area were estimated. The analysis of tectonic geomorphology along the Nanting fault zone, and drainages and channels across the fault zone shows systematically left-lateral offset. The largest offset occurs along the Nujiang River, and total displacement of the fault here is about 10 km. Moreover, offsets of rivers near the village Datianba range from 1.5 to 5.5 km and 1.8 to 2.1 km near Panhe Farm, respectively. Besides geomorphic units, geologic units are also displaced. Granite bodies west of the Yun County show obviously sinistral slip ranging from 4.1m to 5.6 km. Based on the tectonic characteristics and deep dynamic mechanism of NE-trending tectonics within the Yunnan-Myanmar block, the following conclusions are obtained. Firstly, the maximum displacement of the NE-trending left lateral strike-slip fault zone is 10 km. According to its initial age of 5 Ma, the minimum of the left lateral strike slip rate is ca. 2 mm·a-1. Secondly, the late Cenozoic tectonic deformation and seismic activity of the Yunnan-Myanmar block are mainly controlled by the East India plate subduction, and the deformation in dominated by strike slip on faults. Thirdly, based on the analysis of the scales of NE direction left-lateral faults and recurrence times of historical earthquakes, the study region including the Nantinghe, Wanding and Dayingjiang fault zones and the surrounding areas has risk of large earthquakes of magnitude 7 or greater. More attention should be paid to earthquake prevention and risk assessment of large engineering projects in this region.
Taking tectonic geomorphology of southeastern Ganzi-Yushu Fault zone as the research object, and based on remote sensing interpretation, the paper investigates the late Quaternary activity of the southeastern segment of Ganzi-Yushu Fault zone through trenching and detailed field investigation on several typical sites. We analyze the landscapes and calculate the late Quaternary slip rates along the fault zone at the sites in Shengkang township, Renguo township, Cuoa township, and Ria township, respectively. The horizontal and vertical slip rates are(7.6±0.5) mm/a and(1.1±0.1) mm/a at Shengkang township, (8.0±0.3) mm/a and (1.1±0.1) mm/a at Renguo township. And horizontal slip rate of Cuoa township is (10.3±0.4) mm/a. The horizontal and vertical slip rates of Ria township are (10.8±0.8) mm/a and (1.1±0.1) mm/a, respectively. Both trenches at Renguo township and Cuoa township have revealed several paleoearthquake events. Though there are some differences in fault tectonic styles revealed between the two trenches, the fault motion on this segment is of strike-slip with a certain amount of thrust component on the whole. Associated with the analysis of paleoearthquake events and slip rate, it is found that the southeastern Ganzi-Yushu Fault zone is subject to intensive activity since late Quaternary, especially since Holocene.
Fold-accommodation faults, secondary faults subordinated to the principal fold, are of much significance to accommodate strain variation in different parts of the rock during the evolution of folding. They are generally found in groups. And each of them has limited displacement and does not connect with the main detachment. After the geological survey in the East Qiulitage anticline zone, we find that the secondary faults accompanying fold scarps in this area are out-of-syncline thrusts and also give an instance of secondary faults occurring later than the folding. The fact that the secondary faults in fold scarps force the hanging wall to move upward relative to the footwall not only makes the terrace tilting and increases the slope of fold scarps, but also affects the authenticity in calculating regional shortening increment. The theoretical results show that if we do not consider the increased fold scarps height influenced by the secondary faults, the shortening increment is 51.42 m. Otherwise, the value will be 45.23 m and the difference between them is 6.19 m. Because the deviation is 13.7% of the total shortening increment, the contributions of fold-accommodation faults to the calculation should not be ignored. The fold scarps in the northern and southern flanks of the East Qiultiage anticline depend on same bedrock type and formation mechanism. But three levels of fold scarps were found in the cross section of less than 300 meters in horizontal distance. This fact indicates that the active kink band of northern part is more closed because of higher compressive stress and faster lifting, which produce a large number of secondary faults in the fold scarps only in the northern flank. Therefore, the study of secondary faults is of significance in understanding of regional tectonic evolution and interaction between folds and faults. But there still exist many problems: 1) Limited by the observing scope, discontinuous distribution of secondary faults and variations of displacement along fault, we may underestimate the influence of secondary faults and the theoretical result should be the minimum. 2) What is the quantitative relationship among the increased height of fold scarps, the transfer slip and the dip of secondary faults? 3) If secondary faults only grow in active kink band, how will they affect fold scarp? More examples of fold-accommodation faults are needed for further research. ©, 2015, Editorial Office of Seismology and Geology. All right reserved.
Nonvisibility (dieout) of fault strands occurs primarily in stratigraphic units associated with young paleoseismic events, which may cause misidentification of the young events and bring more uncertainties for seismic risk assessment. Based on previous related studies, this paper integrates case studies in mainland China to discuss the nonvisibility of fault strands and identification of young paleoseismic events. Nonvisibility of fault strands is prevailing in sandy, soil, silty, loess, and clay-sandy units, and is more possibly associated with strike-slip faults comparing with normal and reverse faults. Case studies on several trenches across surface ruptures produced by the Wenchuan earthquake and others located at different regions suggest that trench siting, excavation, and comprehensive analysis are key technical points to identify young paleoseismic events in the stratigraphic units where nonvisibility of fault strands is prone to occur. Stratigraphic units with more sequences have been suggested to be good sites for trenching to avoid misidentification produced by nonvisibility of fault strands. Multiple trenching is facilitated to lower the influence of local nonvisibility. Assumed extending of upper and lower units, grain sizes, color, and soil horizon are the basic methods to identify nonvisibility. Analysis of microstructures, grain sizes and magnetic susceptibility is one of the future studies related to identification of nonvisibility of fault strands.
Daliangshan Fault Zone (DFZ) constitutes a significant part of the eastern boundary of Sichuan-Yunnan Active Block (SYAB). Studying the activity and slip rate of this fault zone is not only of great significance in understanding the movement of tectonic blocks and crustal deformation at the southeastern margin of Tibetan plateau, but also valuable in seismic hazard assessment and mid-and long-term forecasting of earthquake in west Sichuan. Zhuma Fault is the east branch of northern segment of DFZ which consists of six branch faults. Based on the detailed field investigations and through the accurate RTK (GPS) surveying and dating of the displaced landforms, we find that Zhuma Fault has been active since Holocene with a dominant left-lateral movement pattern and constrain its slip rate to be 1.5~3.1 mm/a. Furthermore, a trench was excavated which reveals two paleoearthquakes occurring within (50.3±5.7)~30 ka BP and 30~(17.4±1.2) ka BP, respectively from the stratigraphic evidence and OSL dating data. Although the slip rate on the Zhuma Fault is a little smaller than that on the southern segment of DFZ, we suggest uniform slip rates on the DFZ in consideration of the existence of another branch faults on the northern segment. The similar slip rate on DFZ to those on Anninghe Fault Zone (AFZ) and Zemuhe Fault Zone (ZFZ) implies that DFZ possesses a comparable partitioning component of displacement of Xianshuihe-Xiaojiang Fault System (XXFS) to AFZ and ZFZ. Further, the sum of slip rates on central segment of XXFS shows a good agreement with that on northern or southern segment. Thus, it is suggested that the DFZ not only patches the gap generated by the deviation of the strikes of AFZ and ZFZ from the average strike of XXFS, thus, making it a perfect small arc on earth, but also covers the deficiency in displacement and slip rate between central segment and northern or southern segment to maintain the XXFS to be harmonious. Moreover, according to the sedimentary characteristics and dating data, it is revealed that the alluvial-proluvial fans along the Zhuma Fault are formed by the glacial melt water in the last deglaciation after the Younger Dryas cooling event and such landforms could be widely developed in this region.
Hetao fault-depression zone, the largest one of 4 fault-depression zones around the Ordos block, is characterized by intense tectonic activities. According to historical records, 2 large earthquakes, occurring in 849AD and 7BC respectively, were recognized to be located at this zone. However, there is still some dispute about the seismogenic structure of the 849AD earthquake, and there is no tangible geological evidence to support the view that the 7BC event occurred in Hetao fault-depression. In this paper, based on the image interpretation(from Google Earth), field investigation, trench excavation, and \{14C\} and single grain OSL dating, we analyzed the tectonic landform and paleoseismic events on the Daqingshan piedmont fault, Wulashan piedmont fault and Langshan piedmont fault in the Hetao fault-depression zone. Furthermore, a comparative study of the latest rupture events on the 3 active faults was carried out. In order to lower the uncertainty of paleoseismic event dating, several effective measures, such as sampling according to the stratigraphic sequence, collecting multi samples in important strata, were adopted. Combining the previous achievements, the seismogenic structures of the 849AD earthquake and the 7BC earthquake were discussed. The results support that the Daqingshan piedmont fault is the seismogenic structure of the 849AD earthquake, and the latest surface rupture event of the Langshan piedmont fault may be related to the 7BC earthquake.
The crustal structure was investigated with Deep Seismic Sounding (DSS) data obtained from wide angle reflection/refraction profiles crossing the region; its southern section is Qin-ling fold zone, the middle is Weihe rift basin, and the northern section is the southern margin of the Ordos platform. The results showed that the crust has obviously layered and laterally varying structures; the boundary between upper and lower crust is reliably determined by the relatively continuous reflection wave, P2 and P3 in the crust. The M interface of Ordos platform is the deepest in the region; the crustal thickness is up to 42 km or so and the crustal structure is relatively simple with shallow crystalline basement. The crustal thickness of Qinling Fold Belt is about 37 similar to 38 km, with shallow or even exposed crystalline basement. The Moho interface under Weihe fault basin is significantly and asymmetrically uplifted relative to both sides, and the crustal structure is complex; the abrupt Moho uplift relative to the Ordos block and the intrusion of high-speed material of the upper mantle into the lower crust are the deep tectonic background of occurrence of strong earthquakes in the area.
Chinese early aerial photo digital photographic method is fit to active fault researcher. The photographic result can meet the need of morphotectonics quantitative measurement and large scale mapping. The abundant product by using photographic technique can help the researcher to analyze fault and morphotectonics.
The paper introduces the anomalies observed by digital tiltmeter, cross-fault deformation meter, 4-component borehole strainmeter and geothermometer before May 12, 2008, Ms8.0 Wenchuan earthquake, Sichuan. The digital tiltmeter installed in the epicentral region in Shifang County recorded the tilt anomalies 15 days before the earthquake with variation amplitude of 3.7 times larger than the annual deviation of 2007. The cross-fault deformation meter installed at Zimakua station on the Xianshuihe-Anninghe fault zone detected displacement anomaly occurring since 2006 with the variation amplitude exceeding the cumulative value of the last ten years. Five borehole strainmeter stations in the Chongqing section of Three Gorges Reservoir area observed unconventional strain changes occurring in the period from May 1 through 12, 2008. Among them, the strainmeter at Wanzhou station recorded the great compression strain rate on the EW component at 14:00 o'clock of May 10, and the anomaly amplitude was so large that the instrument output exceeded its dynamic range, corresponding to a level of ∼104 nanostrains. The geothermometers installed in Xi'an, Chongqing and Xichang recorded the sudden temperature changes from November 2007 to January 2008 with the variation amplitudes several times larger than the ordinary deviation. The above phenomena and the criteria for distinguishing the anomalies from background fluctuations are discussed in this paper.
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