Fault Branch Research Articles

Trichonis basin, western central Greece: is it an immature basin in the Corinth Rift or a pull-apart in a sinistral rift–trench link?

The 35 km long east–west-trending Trichonis basin in western central Greece is located between the Kephalonia Transform Fault and the east–west-trending Corinth Rift, exhibiting analogous, but smaller scale, morphotectonic features to the Corinth Rift. The final cooling and exhumation of the area started after at c. 10 Ma, after the burial owing to the emplacement of the Pindos thrust ( c. 30–20 Ma). The deformation includes (1) an Early–Middle Miocene transpression (T 1 ) during the waning stage of collision between Apulia and Eurasia, and (2) a Late Miocene–Pliocene radial extension (T 2 ), which relates to the separation of the Hellenic subduction zone from the Apulia (Adria)–Eurasia collision plate boundary through the Kephalonia Transform Fault. Two extensional stress tensors, T 3 and T 4 , with σ 3 in NNE (023°), and NNW (157°) directions, respectively, describe the modern stress regime in the Trichonis basin. This spatial stress partitioning is due to competition between back-arc stresses associated with Hellenic subduction-zone retreat and stresses of the post-collisional collapse of the Hellenic orogen. The Trichonis basin is not a pull-apart basin in a sinistral rift–trench link, but is an immature basin in the Corinth Rift along the Trichonis Fault. The later stands as a right-stepping fault branch to the main faults of the Corinth Rift.

Holocene paleoearthquakes on the Tianqiaogou-Huangyangchuan fault in the northeastern boundary fault system of the Tibetan Plateau

Rupture behavior, one of the quantitative features of active fault, is fundamental for understanding crustal deformation mechanisms and assessing regional seismic risk. The 120-km-long Tianqiaogou-Huangyangchuan Fault (THF) is an important branch fault of the Qilian-Haiyuan Fault System (QHFS), the main boundary fault zone at the emerging northeastern margin of the Tibetan Plateau. Mismatching with the fast strike-slip rate, there is no M ≥ 5 earthquake recorded along the THF. To obtain more precise information of the rupture behaviors along the boundary structure, we conducted a 1:50,000 active fault mapping and paleoearthquake trenching on the THF. Two trenches respectively illustrates at least 3 rupture events combining the radiocarbon dating and the OxCal modeling. According to the overlap of their age ranges and the analysis on completeness of the sedimentary records, it is determined at least 5 paleoearthquakes occurred along the THF in the Holocene with respective age ranges of 485 ± 675 BCE, 2085 ± 295 BCE, 5590 ± 1090 BCE, 7910 ± 970 BCE, and 9975 ± 955 BCE and moment magnitudes estimated to be 7.3–7.4. Meanwhile, the detailed investigations on paleoseismology and tectonic geomorphology show the THF was not involved into the seismogenic structure of the nearby 1927 Gulang M8 earthquake. The Monte Carlo statistical analysis of these paleoearthquakes yields a mean recurrence interval of 2.4 ± 0.3 ka, illustrating a strong activity of the THF that accords with its slip rates and an important role as a tectonic boundary accommodating the eastward extruding of the northeastern Tibet relative to the Gobi Alashan block. Moreover, based on its strong activity and long elapsed time of at least 1.7 ka, we propose the THF is another seismic gap with a potential of M ≥ 7 earthquakes similar to the Tianzhu gap near the triple junction in the QHFS, showing a high seismic risk along the THF and in this region.

A Novel Analytical Method of Inductance Identification for Direct Drive PMSM with a Stator Winding Fault Considering Spatial Position of the Shorted Turns

This paper presents a novel analytical method (NAM) of inductance identification for a direct drive permanent magnet synchronous motor (DDPMSM) with a stator winding fault (SWF), which considers the spatial position of the shorted turns. First, the structure of the DDPMSM is introduced and its key parameters are reported. Second, the NAM on the inductance identification is elaborated. The inductance analytical expressions of the faulty coil are derived in detail, in which the inductances of the faulty coil and the fault branch can be quickly calculated according to the spatial position coordinates of fault turns. Then, the model of DDPMSM with SWF is established. Finally, using the NAM, finite-element method (FEM), and the simplified analytical method (SAM), the inductances of the faulty coil and the branch are calculated under different fault conditions. Additionally, the fault current of the faulty coil is also studied, where the value of the fault current reflects the fault severity. The comparisons among the FEM, NAM, and SAM show that the accuracy of the NAM is higher than that of the SAM.

Study on wide-area protection algorithm based on composite impedance directional principle

Wide-area differential protection uses the wide-area multiple-information to quickly identify faults. It is not affected by factors such as grounding resistance and distributed capacitance. As the wide-area measurement requires the high synchronization of wide-area information, its protection sensitivity is reduced by the accumulative errors. A novel wide-area protection (WAP) algorithm is proposed in this paper to solve these problems. Firstly, the information of the single-terminal voltage phasor and the differential current phasors of the transmission line are used to construct the protection criteria based on the composite impedance. Then, the criteria of the fault identification and fault branch are established based on the information of the wide-area branch direction and regional direction. The advantages of the wide-area differential protection are retained in the proposed algorithm. The high dependence on the synchronization of wide-area information is overcome and it is not affected by the high grounding resistance and the load current. The validity of the proposed algorithm is verified by simulation tests of the IEEE 10-generator 39-bus system.

The Bisri dam project: A dam on the seismogenic Roum fault, Lebanon

The Roum fault is a fault branch of the Dead Sea Transform Fault within the Lebanese Restraining Bend. It is an active seismogenic fault that was associated with the 1 January 1837 (Ms 7.1) earthquake, and whose extent has been the subject of great controversy within the restraining bend. In this paper, the Roum fault is revisited after a dam project (the Bisri dam) has been planned in one of the fault's most critical locations, i.e. in the Bisri valley that hosted the epicenter of the 16 March 1956 (ML 5.8) earthquake. The fault and its associated structures in the proposed dam area are discussed, and highlights on the dam site are made as a geologically complex and tectonically active area. The future water body behind the planned Bisri dam will overlie an active fault, with huge potential for fault movement underneath the dam footprint, liquefaction around the dam foundations, mass movements near the dam site, and direct effect on inducing seismicity on a delicate fault system that can potentially trigger a major earthquake that can affect the whole Lebanon and its surroundings. This requires special attention and in-depth considerations especially of the potential of reservoir-induced/triggered seismicity on the seismogenic Roum fault, and makes of the Bisri area a very unfavorable site for the proposed Bisri dam in Lebanon.

Rupture Branching Structure of the 2014 Mw 6.0 South Napa, California, Earthquake Inferred from Explosion‐Generated Fault‐Zone Trapped Waves

AbstractWe present evidence for multiple fault branches of the West Napa fault zone (WNFZ) based on fault‐zone trapped waves (FZTWs) generated by two explosions that were detonated within the main surface rupture zone produced by the 24 August 2014 Mw 6.0 South Napa earthquake. The FZTWs were recorded by a 15‐kilometer‐long dense (100 m spacing) linear seismic array consisting of 155 4.5‐hertz three‐component seismometers that were deployed across the surface ruptures and adjacent faults in Napa Valley in the summer of 2016. The two explosions were located ∼3.5 km north and ∼5 km south of the 2016 recording array. Prominent FZTWs, with large amplitudes and long wavetrains following the P and S waves, are observed on the seismograms. We analyzed FZTW waveforms in both time and frequency domains to characterize the branching structure of subsurface rupture zones along the WNFZ. The 2014 surface rupture zone was ∼12 km in length along the main trace of the WNFZ, which appears to form an ∼400–600‐meter‐wide low‐velocity waveguide to depths in excess of 5–7 km. Seismic velocities within the main rupture are reduced by 40%–50% relative to the surrounding‐rock velocities. Within 1.5 km of the main trace of the WNFZ, there are at least two subordinate fault traces that formed 3‐ to 6‐kilometer‐long surface breaks during the 2014 mainshock. Our modeling suggests that these subordinate fault traces are also low‐velocity waveguides that connect with the main rupture at depths of ∼2–3 km, forming a flower structure. FZTWs were also recorded at seismic stations across the Carneros fault (CF), which is ∼1 km west of the WNFZ; this suggests that the CF connects with the WNFZ at shallow depths, even though the CF did not experience surface rupture during the 2014 Mw 6.0 mainshock. 3D finite‐difference simulations of recorded FZTWs imply a branching structure along multiple fault strands associated with the WNFZ.

The Listafjorden–Drangedal Fault Complex of the Agder–Telemark Lineament Zone, southern Norway. A structural analysis based on remote sensing and potential field data

ABSTRACTThe Listafjord–Drangedal Fault Complex is a central structure in the NE-SW-trending Agder–Telemark Lineament Zone that dominates the structural grain and topography of southernmost tip of Norway. The fault can be followed for a distance of more than 170 km from the shelf area off Listafjorden–Fedafjorden in Vest Agder county to Drangedal in Telemark county. It has been analyzed by the use of digital topographic, remote sensing and potential field data, supported by field investigations. At least seven separate left-stepping fault segments have been identified. These are characterized by numerous internal fault lenses, separate fault strands and fault splays, partly displaying contrasting fault attitude and style of deformation. The northeastern termination of the Listafjord–Drangedal Fault Complex consists of fanning fault branches (horse-tailing), whereas its southwestern termination is buried below sediments in the continental shelf and remains obscure. The fault rocks of the various fault segments include cataclasites and mylonites that in places are interlayered with zones of fault gouge. By tentative correlation to the Hunnedalen dyke system in Rogaland, the age of initiation for the Listafjord–Drangedal Fault Complex is suggested to be Late Proterozoic. Parts of the fault complex were affected by at least two stages of faulting including (dextral?) shear and top-to-the-SE extension. The latter stage is assumed to be of post-Caledonian age, and recent seismic activity suggests that this ancient structural grain is still seismically active.

Sources and ore-forming fluid pathways of carbonate-hosted Pb–Zn deposits in Southwest China: implications of Pb–Zn–S–Cd isotopic compositions

The Sichuan–Yunnan–Guizhou metallogenic province of Southwest China contains more than 200 Mt of Pb–Zn ore in carbonate-hosted Pb–Zn deposits, representing ~ 27% of the total Pb and Zn resources of China. Sources of metals and pathways of ore-forming fluids were elucidated through a study of the Pb–Zn–S–Cd isotopic compositions of sphalerite from the Tianbaoshan, Fusheng, Maozu, Jinshachang, and Daliangzi carbonate-hosted Pb–Zn deposits. δ34S values indicate that S in the deposits is derived mainly from evaporites in Cambrian to Triassic sedimentary strata, sulfates coexisting with sulfides, and Meso–Neoproterozoic folded basement. δ66Zn values and Pb isotopic ratios indicate that these metals originate mainly from Sinian to lower Permian sedimentary rocks and Proterozoic basement. There is a trend towards isotopically heavier Cd and Zn compositions of sphalerite from Maozu to Daliangzi, Jinshachang, and Tianbaoshan, which are all hosted in the upper Sinian Dengying Formation. Previous studies showed that there would be a trend of enrichment in heavier Zn and Cd isotopes following the migration of fluids and precipitation of minerals. The above observations suggest that the ore-forming fluids of these deposits are probably derived from the same hydrothermal fluid system. The fluids most likely flowed through Maozu first, migrating along the Xiaojiang and Anninghe fault belts and their branch faults to Daliangzi, Jinshachang, and Tianbaoshan, respectively. Zn and Cd isotopes could be useful tools in tracing the pathways of ore-forming fluids in this district, and heavier Zn and Cd isotopic compositions could provide a geochemical fingerprint for detecting remote orebodies in large hydrothermal fluid systems.

Role of transverse structures in paleoseismicity and drainage rearrangement in rift systems: the case of the Valdecebro fault zone (Teruel graben, eastern Spain)

The E–W trending, nearly pure extensional Valdecebro fault zone is a transverse structure at the central sector of the N–S Teruel graben. It was activated by the Late Ruscinian (Early Pliocene, ca. 3.7 Ma), giving rise to structural rearrangement of the graben margin. Until the Late Pleistocene, it has accommodated a net slip ca. 205 m, with slip rate of 0.055 mm/a. Paleoseismicity has been analysed in a 29-m-long, 5-m-deep trench excavated through a fault branch that offsets a Pleistocene pediment surface. The paleoseismic succession includes a minimum of 6–7 events occurred since ca. 142 ka BP, although a model with 12 events could be more realistic. The following paleoseismic parameters have been inferred, assuming a minimum of 6 and a maximum of 12 events: average coseismic slip = 58–117 cm; recurrence period = 8.4–28.4 ka; potential moment magnitude Mw = 5.8–5.9. The recorded displacement since ca. 142 ka BP totalizes 7.0 m, with slip rate of 0.05–0.07 mm/a. Slip on the transverse Valdecebro fault zone has critically contributed to bulk deformation under a prevailing ‘multidirectional’ extensional regime. Drainage patterns have been rearranged, recurrently switching between westward and southward directions as a consequence of diverse slip episodes at the Valdecebro fault zone (E–W) and the neighbouring La Hita (N–S) and Concud (NW–SE) faults. The ultimate westward drainage of the Valdecebro depression incised and dismantled a southward-sloping Pleistocene pediment sourced at the Valdecebro mountain front, representing a capture by the Alfambra river occurred between 124 and 22 ka BP.

Postseismic fluid discharge chemically recorded in altered pseudotachylyte discovered from an ancient megasplay fault: an example from the Nobeoka Thrust in the Shimanto accretionary complex, SW Japan

Megasplay fault branching from plate boundaries of subduction zones is thought to be important sources of earthquakes and tsunamis. In this study, we performed structural and geochemical analyses on a fossilized megasplay fault (the Nobeoka Thrust of the Shimanto accretionary complex) to understand fluid-rock interaction and how the splay fault plays a role in fluid flow in the seismogenic zone. As a result of structural observations, we report that the principal slip zone (PSZ) of the Nobeoka Thrust is composed of foliated cataclasite originating from a sandstone-shale mélange and includes a thin (~ 1.5 mm thick) pseudotachylyte layer. Major and trace element composition analysis and EPMA element mapping revealed that the pseudotachylyte is enriched in Li and Cs within the PSZ, as well as in the slip zone of a minor fault in the footwall. Li and Cs enrichment in pseudotachylyte is interpreted as a result of fluid-rock interaction in the postseismic stage, because such an anomaly only results from a large fluid/rock ratio (R > 512–24 at 250–350 °C) under the influence of Li- and Cs-enriched fluids. The amount of fluid that reacted with the pseudotachylyte is estimated to be 1.78 × 100 to 7.61 × 103 m3.

МОДЕЛЬ СТРУКТУРЫ И ТЕКТОНИЧЕСКАЯ ЭВОЛЮЦИЯ СИСТЕМЫ РАЗЛОМОВ В ЮЖНОЙ ЧАСТИ РЕГИОНА ХУР, ЦЕНТРАЛЬНЫЙ ИРАН

In the southern part of the Khur area, there is faults system with predominantly North-West strike. This network of tectonic disturbances is one of the most important fault systems in Central Iran which crosses Paleozoic metamorphic rocks, Cretaceous limestones, and Eocene volcanic rocks. Interpretation of satellite imagery ETM+ (Enhanced Thematic Mapper plus, Landsat) and field observations showed the presence of left-lateral shifts along with fault system. This formed the structure of the branch faults at the northeast end of the main fault. Another feature associated with shear dislocations is the rotation of blocks in the northeastern and southwestern segments of the area under study. There are several basins and positive structures within the area such as a series of uplifts and thrusts, indicating the presence of compressional and extensional tectonics. Another part of the work is devoted to the study of the correlation between active faults and earthquakes. Processing of satellite images, field observations, records of micro-earthquakes within a radius of 17 km made it possible to analyze the earthquakes parameters and the position of tectonic disturbances, and, as a result, confirm the presence of active faults in the region. In addition, we have identified three successive stages of the Khur area tectonics: rifting, contraction, change of convergence and uplift direction.

The pattern of local stress heterogeneities along the central part of the Great Sumatran fault: A preliminary result

Based on world stress map, the in-situ stress along the Great Sumatran Fault (GSF) is assumed to be strike-slip, and the maximum principal stress is oriented N14°E. However, this estimation neglects the local impact of fault branching and material heterogeneity which might have a significant impact on the stress heterogeneity. Despite its importance, very few studies have been performed on this issue in GSF. We intend to analyze variations of the in-situ stress in GSF from the geological data and seismicity pattern. This was performed on a catalogue data set of 707 earthquakes with magnitude (Mw) >3.5 between January 1, 1970 and April 1, 2017. The preliminary results of this study highlight the stress rotation of around 30° clockwise in the central part of GSF. Geological observation also shows faults branching and bifurcation which are interpreted as the product of the stress changes. Furthermore, the seismicity analysis quantifies this issue by showing a sharp different of b-values for subduction and GSF zones, i.e. 1.0 and 0.7, respectively. Therefore, it can be concluded that the stress heterogeneity in the central part of GSF affects both the seismicity occurrence and magnitude.

A fault locating method for multi-branch hybrid transmission lines in wind farm based on redundancy parameter estimation

In order to solve the problem of “abandoned” wind caused by short circuit faults in a wind farm, a wind farm fault locating method based on redundancy parameter estimation is proposed. Using the characteristics of the traveling wave, transmission equations containing the position of the fault point are constructed. Parameter estimation from statistical theory is used to solve the redundant transmission equations formed by multiple measuring points to locate the faults. In addition, the bad data error detection capability of the parameter estimation is used to determine bad data and remove them. This improves locating accuracy. A length coefficient is introduced to solve the error enlargement problem caused by a transmission line sag. The proposed fault locating method can solve the fault branch misjudgment problem caused by the short circuit faults near the data measuring nodes of the wind farm based on the proposed fault interval criterion. It also avoids the requirements to the traveling wave speed of traditional methods, thus its fault location is more accurate. Its effectiveness is verified through simulations in PSCAD/EMTDC, and the results shows that it can be used in the fault locating of hybrid transmission lines.

Shallow subsurface imaging of the Wagad active fault system (Kachchh, northwestern India) by time domain electromagnetic studies

The Kachchh rift basin (KRB) in the northwestern Indian shield is one of the most seismically active intraplate regions of the world. It has witnessed four large earthquakes in the past two centuries that leads the region most vulnerable for seismic hazard. For effective seismic hazard assessment, detailed information on faults and its subsurface geometry is essential. Recently, shallow subsurface geophysical studies, particularly electrical resistivity studies have become a successful practice in imaging of fault zones and their attribute. In the present study, we carried out the time domain electromagnetic (TDEM) investigations across the Wagad highland of eastern KRB to map shallow subsurface structure and imaging fault zones in terms of resistivity. Resistivity section obtained after combining one dimensional models of 21 sites display significant details of the fault structures and geometry of shallow basin infill down to 200 m. The shallow layer of the basin infill across the South Wagad fault (SWF) and the North Wagad fault has a wedge shape made of unconsolidated deposits with thickness of \(\sim \)15–20 m. We infer that it might be due to syntectonic sedimentation due to the footwall subsidence across a branch fault of the SWF. The section indicates a \(\sim \)60–65 and 50–55 m estimates of cumulative throws for the SWF and NWF, respectively. Across the Gedi fault, the section indicates least block displacements, which might either be due to dominate strike-slip nature of faulting or more activeness of NWF compared to GF during the recent geological past. The results from the study affirm the ongoing Holocene deformation in the region signifying active nature of these faults.

A Micro-grid Fault Section Positioning Method Based On Fault Steady State Component

After the micro-grid is connected to the distribution network, the unidirectional power flow in the original network is transformed into a bidirectional flow, and the original protection device cannot meet the current safe operation of the micro-grid. Due to the complex structure of the micro-network, it is necessary to study the fault location and identification methods in the network when a fault occurs.In this paper, in order to solve the fault section location problem, the phase-to-phase short circuit model of the micro-grid under the state of distributed power grid-connected faults was established, and the positive sequence currents amplitude at the upstream and downstream of the fault point are extracted using the symmetrical component method.The fault section is determined by the amplitude of the positive sequence current at the adjacent detection point on the fault branch. It solves the problem of increasing the difficulty of fault detection due to changes in the access of conventional power electronic devices and changes in short circuit types. The distribution network model was built by MATLAB to simulate and verify the feasibility of fault-based steady-state component section positioning method.

Computational Fault Time Difference-Based Fault Location Method for Branched Power Distribution Networks

Fault location in a power distribution network is a challenging task due to the presence of multilayer branches and short line lengths. Existing fault-location methods generally require measurements at both ends of each branch, which requires a large number of measuring points. The placement of measuring points at branch terminals is an approach that can be used to reduce the number of measuring points. Such a measuring point layout allows the existing fault-location methods for power distribution networks to determine fault points after identifying faulted branches. However, these methods fail to locate a fault if the faulted branch cannot be correctly identified. This paper proposes a traveling-wave-based fault-location method for branched power distribution networks without requiring faulted branches to be identified. In the proposed method, by using the first arrival times of the fault-generated traveling waves detected at the substation and each branch terminal, the computational fault time difference (CFTD) is defined. By calculating the value of CFTD, the fault point is directly searched out. Finally, the quartile method is used to eliminate the impact of the arrival-time error on the fault-location accuracy of the proposed method. The simulation results verify the high accuracy, traveling-wave velocity stability, and strong arrival-time error robustness of the proposed method.

Dc fault current calculation method in MMC‐HVDC grid considering current‐limiting devices

This paper proposes a DC fault current calculation method to reveal the fault current evolution mechanism of the modular multilevel converter (MMC)-based HVDC grid. The new method includes the fast switching of the current-limiting devices and the transient characteristics of the metal oxide arresters (MOA), which are not reported previously. Specifically, begin from a single-end MMC, two peak-valley points of inflection in the DC fault current curve are pointed out when switching the current-limiting devices into the fault branch with a follow-up action of MOA when the branch current reaches zero. The two points are selected as important indicators in the design of the coordinated protection scheme and switching logics. Then, the impact of the total DC reactance distribution in the DC-side reactor and the fault current-limiter (FCL) together with the initial current values on the two points of inflection are discussed. The applicability of the above approaches on HVDC grid is studied and an overall fault current calculation procedure with six steps including the tripping of the DC circuit breakers (DCCB) are proposed for HVDC gird applications. The proposed calculation method is validated by Electromagnetic Transient (EMT) simulation for pole-to-pole fault, different fault locations, and DC reactance values.

Optimized Branch Current Control of Modular Multilevel Matrix Converters Under Branch Fault Conditions

The modular multilevel matrix converter (M3C) is a promising topology for high-voltage high-power applications. It features easy scalability, high-quality input and output waveforms, superior availability, etc. This letter aims to further increase the availability of the M3C when one or more of the nine branches are lost. A general nonlinear multivariable optimization model is set up to optimize the branch current configuration after the branch lost. The proposed method reduces system power capability loss after the branch failure. It achieves a smooth transition from a full M3C to a reduced topology without shutdown of the system. A M3C prototype with 27 cells is designed, and experiment results are presented to confirm the validity of this method.

High-resolution stratigraphy and multiple luminescence dating techniques to reveal the paleoseismic history of the central Dead Sea fault (Yammouneh fault, Lebanon)

Continuous sedimentation and detailed stratigraphy are key parameters for a complete paleo-earthquake record. Here, we present a new paleoseismological study across the main strike-slip fault branch of the Dead Sea fault in Lebanon. We aim to expand the current knowledge on local paleoseismicity and seismic behavior of strike-slip plate boundary faults and to explore the limitations of paleoseismology and dating methods. The trench, dug in the Jbab el-Homr basin, reveals a succession of remarkable, very thin (0.1 to 5 cm) palustrine and lacustrine layers, ruptured by at least 17 earthquakes. Absolute ages of 4 samples are obtained from three luminescence-dating techniques targeting fine-grain minerals. Blue-green stimulated luminescence (BGSL) on quartz and post-infrared infrared-stimulated luminescence at 225 °C on polymineral aliquots led to consistent ages, while ages from infrared-stimulated luminescence at 50 °C on polymineral aliquots appeared underestimated. The quartz BGSL ages are 26.9 ± 2.3 ka at 0.50 m depth and 30.8 ± 2.9 ka at 3.65 m depth. During this time period of 3.9 ka ([0; 9.1 ka]), 14 surface-rupturing events occurred with a mean return time of 280 years ([0; 650 years]) and probable clustering. This return time is much shorter than the 1127 ± 135 years return time previously determined at the Yammouneh site, located 30 km south. Although fault segmentation and temporal variations in the earthquake cycle remain possible causes for such different records, we argue that the high-resolution stratigraphy in Jbab is the main factor, enabling us to record small deformations related to smaller-magnitude events that may have been missed in the rougher strata of Yammouneh. Indeed, focusing only on larger events of Jbab, we obtain a mean return time of 720 years ([0; 1670 years]) that is compatible with the Yammouneh record.

Geological Factors for the Formation of Xi’an Ground Fractures

Xi’an ground fractures are the most typical ground fractures in China. Fourteen fractures have nearly divided the historical city into several distinct sections. These fractures are parallel and distributed in NEE direction at the same interval, with all features exhibiting a down dropping southerly block which extends to connect with the underlying fault. The activities of fractures are primarily expressed as normal faults. The faulted strata are well defined and dislocation displacement increases with depth. Thus, fractures have the characteristics of syn-sedimentary faults, which constitute the hanging wall of the Lintong-Chang’an fault branch system. Crustal thinning caused by the uplifting of upper mantle provides a power source for extension and stretching along the fracture surface of the upper crust, which results in a series of extensional faults and the suitable conditions for forming massive ground fractures. The movement of tectonic blocks influences the normal dip-slipping tension of Lintong-Chang’an fault branches, and produces a series of secondary tectonic fractures adjacent to surface, which constitute the prototype of ground fractures. The recent regional tensile stress produced by modern mainland deformation, also profoundly influences the current activity of Xi’an ground fractures.