Fault Branch Research Articles

A New Single-Ended Fault Location Method Based on Bergeron Model

On EHV transmission lines, the impact of distributed capacitance is necessary to be considered in case of fault location. A novel fault location method for single-phase grounded fault of transmission lines is presented based on the distributed parameter model of transmission line. In this method only the voltage and current of single end is used. The residual phase voltage at the fault point should have the same phase angle as the current through fault branch due to the pure resistive characteristics of the fault path impedance. By virtue of searching the minimum phase angle differ-ence between the phase voltage along the transmission line and the fault-component current meas-ured at the side equipped with protection, the fault distance can be located. ATP simulations are used to generate data that are supplied as inputs to the fault location algorithm.

The structure of the Sumatran Fault revealed by local seismicity

The combination of the Sunda megathrust and the (strike‐slip) Sumatran Fault (SF) represents a type example of slip‐partitioning. However, superimposed on the SF are geometrical irregularities that disrupt the local strain field. The largest such feature is in central Sumatra where the SF splits into two fault strands up to 35 km apart. A dense local network was installed along a 350 km section around this bifurcation, registering 1016 crustal events between April 2008 and February 2009. 528 of these events, with magnitudes between 1.1 and 6.0, were located using the double‐difference relative location method. These relative hypocentre locations reveal several new features about the crustal structure of the SF. Northwest and southeast of the bifurcation, where the SF has only one fault strand, seismicity is strongly focused below the surface trace, indicating a vertical fault that is seismogenic to ∼15 km depth. By contrast intense seismicity is observed within the bifurcation, displaying streaks in plan and cross‐section that indicate a complex system of faults bisecting the bifurcation. In combination with analysis of topography and focal mechanisms, we propose that the bifurcation is a strike‐slip duplex system with complex faulting between the two main fault branches.

Research of Adaptive Line Selection Leakage Protection Based on DSP in Mine

In view of the present our country coal mine high-voltage power grid widely used 6kV or 10kV cable direct power supply condition. To describe a DSP-based adaptive line selection leakage protection program of high-voltage power grid. It adopts under-compensation, adaptive random tuning and phase-sensitive comparison to judge the fault branch and achieve selective leakage protection, and make the protection system more perfect and reliable.

A Fault Steady State Component-Based Wide Area Backup Protection Algorithm

A novel wide area backup protection algorithm to identify fault branch based on the fault steady state component is proposed. Under normal conditions of the power system, subsets of buses called protection correlation regions (PCRs) are formed on the basis of the network topology and phasor measurement unit (PMU) placement. After the fault occurs, by analyzing the fault steady state component of differential current in each PCR, the fault correlation region is confirmed and then a fault correlation factor (FCF), is calculated in real time to locate the fault branch. The simulation results for the 10-generator 39-bus system verify that this method is able to easily identify fault branch with limited measurement points.

Features of the fault system and its relationship with migration and accumulation of hydrocarbon in Liaodong Bay

The fault system of Liaodong Bay developed extensively under the control of the Tanlu Fault. The fault system can be grouped into strike-slip faults of grade I, trunk faults of grade II and branch faults (induced faults) of grade III respectively based on its developmental scale. The faults of grade I and II were deep, early and large while the faults of grade III were shallow, late and small. The formation, evolution and distribution features played a significant role in controlling the migration of oil and gas in both horizontal and vertical directions. The fluid transfer in the fault system occurred in the process of faulting. The strike-slip and trunk faults moved actively forming predominant pathways for oil and gas migration. The branch faults, with weak activity, generally controlled the development of traps and were beneficial for the accumulation and preservation of oil and gas. The faults of grade I and II formed the major migration pathways for oil and gas, but their fault activity rates appeared to vary along their strikes. The zones with a relatively low fault activity rate might be favorable for oil and gas accumulation. When the activities of strike-slip, trunk, and branch faults came to a halt, the fault seal behavior had a vitally important effect on the accumulation of oil and gas. The controlling role of the fault over fluid distribution was further analyzed by calculating the fault activity quantitatively.

Influence of material contrast on fault branching behavior

[1] Material contrasts across faults are a common occurrence, and it is important to understand if these material contrasts can influence the path of rupture propagation. Here we examine models, solved numerically, of rupture propagation through one type of geometric complexity, that of a fault branch stemming from a planar main fault on which rupture initiates. This geometry, with a material contrast across the main fault, could be representative of either a mature strike-slip fault or a subduction zone interface. We consider branches in both the compressional and extensional quadrants of the fault, and material configurations in which the branch fault is in either the stiffer or the more compliant material as well as configurations with no material contrast. We find that there are regimes in which this elastic contrast can influence the rupture behavior at a branching junction, but there are also stress states for which the branch activation will not depend on the orientation of the mismatch. For the scenarios presented here, both compressional and extensional side branches are more likely to rupture if the branch is on the side of the fault with the more compliant material versus the stiffer material. The stresses induced on the branch fault, by rupture traveling on the main fault, are different for the two orientations of material contrast. We show how the interactions between rupture on the two faults determine which faults are activated.

Discovery of a Sand Blow and Associated Fault in the Epicentral Area of the 1886 Charleston Earthquake

An earthquake-induced sand blow was discovered in a shallow trench dug on the premises of the Colonial Dorchester State Historical Site in Summerville, South Carolina. A comparison of its location with available seismicity, seismic reflection, and shallow geological and geomorphologic data suggests that the sand blow was associated with a splay of the currently active Sawmill Branch fault zone. This is the first sand blow to be directly associated with a specific fault in the Middleton Place–Summerville seismic zone, the source zone for the Charleston earthquakes. Geotechnical and vibracore data revealed that the source sand is ∼3 m thick and the top of the sand is at a depth of ∼2.5 m below the ground surface. The sand blow was associated with a pre-1886 earthquake that occurred possibly 3,500 YBP or earlier, with an estimated maximum magnitude of 5.6.

Cenozoic right-lateral wrench tectonics in the Western Pyrenees (Spain): The Ubierna Fault System

A study of macro and mesostructural deformation patterns of the southern margin of the Cantabrian area (Western Pyrenees, Spain) has revealed a complex Cenozoic tectonic framework. Right-lateral tectonics reactivated inherited WNW–ESE striking faults, which developed during Late Paleozoic and Early Triassic events, and Late Jurassic to Early Cretaceous main rifting stage. The Ubierna Fault represents the southern boundary of the Mesozoic basin. During the Oligocene (even Eocene) to present day deformation, this fault and the Ventaniella Fault located to the south in the study area acted as right-lateral slightly transpressive elements forming a 120 km long and 15 km wide overstep area, here named Ubierna Fault System, where the cumulative right-lateral displacement exceeds 15 km. The Cenozoic tectonic framework of the Ubierna Fault System includes reactivation along the WNW–ESE faults, development of negative and, mostly, positive flower structures, branch faults, strike-slip duplexes, and releasing and restraining bends. NE–SW to ENE–WSW striking reverse faults and contractional horsetail terminations, and NNW–SSE striking normal faults and joints are produced by the WNW–ESE right-lateral strike-slip motion. The extensional elements are well developed and deformation progression implied their incorporation in the strike-slip system as right-lateral faults (forming part of strike-slip duplexes). The abundance of flower structures striking WNW–ESE and paralleling the main strike-slip faults, together with the overall uplift of the overstep area, testifies for a slight compressional component. At a regional scale, the Ubierna Fault System represents the most prominent element of a Cenozoic transpressional belt, which incorporates the western portion of the Basque-Cantabrian Basin and the Asturian Massif area. Lateral transition between this transpressive belt and the dip-slip belt located to the east, occurs across an area experiencing along strike-shortening, which developed to accommodate the eastward extrusion of the transpressional belt.

Revealing Coseismic Displacement and Displacement Partitioning at the Northern End of the 1999 Chi-Chi Earthquake, Central Taiwan, Using Digital Cadastral Data

Abstract The 1999 Chi-Chi, Taiwan, earthquake ( M w 7.6) was the largest earthquake to strike Taiwan in the twentieth century. Its surface rupture extends more than 100 km in a north–south trend. However, the northern end of this surface deformation abruptly terminates at an area between the Tachia river and the Taan river, where a broad pop-up structure with east to northeast strike (quite different from the north–south-striking main thrust) is found. This pop-up structure is composed of several regions of parallel thrusts and back thrusts and total shortening reaches about 9 m. In order to reveal the displacement field in the pop-up structure and slip vectors of branch faults, we use a digital cadastral system with about 17,000 control points to calculate coseismic displacement around the Shihkang area. The digital cadastral system was originally conceived to survey land and building boundaries. The cadastral system affords high-density control points that reach about 2800 points/km 2 , and the accuracy is to within ±11 cm. Outside of the pop-up structure, the horizontal displacements vectors are 8–9 m in about 330°–340°, changing as they pass through the surface rupture. The azimuth of horizontal displacement shows large variation with the azimuth from 360° to 315° and displacement amounts from about 4–8 m inside the pop-up structure. In addition, according to these cadastral data, we found surface ruptures that had not been observed in previous studies that could be of importance to future disaster assessment.

Probabilistic Fault Displacement Hazards for the Southern San Andreas Fault Using Scenarios and Empirical Slips

We apply a probabilistic method to develop fault displacement hazard maps and profiles for the southern San Andreas Fault. Two slip models are applied: (1) scenario slip, defined by the ShakeOut rupture model, and (2) empirical slip, calculated using regression equations relating global slip to earthquake magnitude and distance along the fault. The hazard is assessed using a range of magnitudes defined by the Uniform California Earthquake Rupture Forecast and the ShakeOut. For hazard mapping we develop a methodology to partition displacement among multiple fault branches based on geological observations. Estimated displacement hazard extends a few kilometers wide in areas of multiple mapped fault branches and poor mapping accuracy. Scenario and empirical displacement hazard differs by a factor of two or three, particularly along the southernmost section of the San Andreas Fault. We recommend the empirical slip model with site-specific geological data to constrain uncertainties for engineering applications.

Geochemical signals for determining the slip-weakening mechanism of an ancient megasplay fault in the Shimanto accretionary complex

[1] To investigate the slip behavior of a megasplay fault branching from a subduction boundary megathrust, we investigated the geochemistry of an out-of-sequence thrust that formed at 2.5–5.5 km depth. Rocks from the slip zone show major-element and fluid-immobile trace-element compositions that are consistent with disequilibrium flash melting. Distinct depletions of Li, Rb, and Cs in the slip-zone rocks indicate fluid–rock interactions at high temperatures (>350°C). These findings suggest a slip process in which high-temperature pore fluids were generated by frictional slip, but the thermally-enhanced pressure might not have reached a sufficient level to cause thermal pressurization, and the temperature continued to increase to attain melting of mica minerals. Comparison with slip zone that formed at a shallower depth (1–2 km), where only thermal pressurization occurred, suggests a transition from melt lubrication at depth to thermal pressurization at shallower depths along a megasplay faults.

Structure and Holocene evolution of an active creeping thrust fault: The Chihshang fault at Chinyuan (Taiwan)

We conducted a variety of measurements and analyses at Chihshang Active Fault Observatory in eastern Taiwan, including surface-rupture mapping, three shallow borehole core analysis and kinematic analysis of geodetic measurements. We found that the Chihshang fault exhibits a three-branch fault system in the Chinyuan alluvial fan, which is composed of at least 100 m thick gravel deposits. Outside of the Chinyuan River, the Chihshang fault shows a single fault system with a sharp lithological contact. Combining the leveling results and trench excavation, we interpret that the three fault branches are coupled with a 50−60-m-wide pop-up structure in the hangingwall. Based on the ratio between vertical and horizontal displacements, we obtained dip angles of 38°, 62° and 16° for two west-vergent thrusts and an east-vergent backthrust, respectively. This pop-up was estimated to develop at the uppermost 30–40 m unconsolidated gravels during the last few thousand years above the main fault with a dip angle of 42°. By compiling the available ages data, we obtained an uplift rate of 2.3 cm/yr of the Chihshang fault and an alluvial sedimentation rate of 1.1 cm/yr during the past thousands years. Consequently, the individual uplift rate for each fault branch at the Chihshang Observatory was slightly less than the deposition rate of the Chinyuan River. No geomorphic fault scarp can thus be observed in the three-branch fault system area.

Interpretation of the rupture history of a low slip-rate active fault by analysis of progressive displacement accumulation: an example from the Quaternary Eupcheon Fault, SE Korea

Abstract: The Eupcheon Fault, one of more than 20 identified Quaternary faults recently reported in the area around the Yangsan and Ulsan faults, SE Korean Peninsula, was discovered during the construction of a primary school in an area close to a nuclear power plant. We analysed a trench excavated across the Eupcheon Fault with the aim of understanding its movement history and kinematics. The Eupcheon Fault is a reverse fault (strike/dip: N20°E/40°SE) that records 6–7 m of displacement (3–4 m vertical separation). The fault consists of a series of branch faults, associated fault-related folds, and rotated pebbles. A previous study reported that the fault originally recorded normal slip but was reactivated during the Quaternary as a reverse fault. We identified four or five Quaternary faulting events upon the fault based on an interpretation of the trench logs including an analysis of colluvial wedges, and measurements of displacement–distance ( d – x ) relationships along the fault. We used a quantitative analysis of d – x relationships, commonly used for consolidated sedimentary rocks, to interpret the deformation history of the fault. From this we estimated the amount of slip in the range of 0.7–1.8 m for each of the five identified faulting events and the earthquake magnitude in the range of M w 5.4–7.4. We propose two ideal d – x profiles for syndepositional and post-depositional faulting, and a tectonic evolution model for the area around this fault. This approach may be applicable to analyses of earthquake hazards and studies of fault evolution elsewhere.

Surface traces of the Minnivellir, Réttarnes and Tjörvafit seismic faults in the South Iceland Seismic Zone: Segmentation, lengths and magnitude of related earthquakes

Accurate GPS mapping and field measurements have been carried out along the surface traces of three N–S right-lateral historical and prehistorical seismic strike-slip faults in the South Iceland Seismic Zone: the Minnivellir, Tjörvafit, and Réttarnes faults. We used these data and those previously collected on the Selsund and Leirubakki faults to characterise the faulting behaviour. This study illustrates a characteristic multi-scale segmentation including, from the longer to the smaller fault elements: (i) fault (corresponding to the total length of the seismic fault), (ii) fault segments, (iii) arrays of fractures and (iv) individual fractures. The most distinctive feature of such right-lateral fault is its left-stepping en-échelon arrangement at various scales, with push-up structures accommodating the motion in the relay zones. This study also highlights the role of the nature and thickness of the uppermost layer (lava flow, thin or thick grassy soil) with respect to the type and length of fractures at the surface. Our mapping reveals complex fault geometry which, however, is consistent with the general left-lateral transform behaviour of the South Iceland Seismic Zone. Some left-lateral conjugate fault branches are present along these major right-lateral faults and participate to the deformation. The estimation of the strike-slip offsets (1.3–2 m) based on the analysis of push-up structures allow to infer the total rupture lengths (45–70 km) for these faults and to estimate the magnitudes (7.0–7.2) of the related earthquakes, bringing confirmation that events significantly larger than those of June 2000 (Ms = 6.6) have occurred in the SISZ, which plays an important role for the seismic hazard assessment.

Variations of Shear Wave Splitting in the 2010 Yushu Ms7.1 Earthquake Region

AbstractIn this paper, variations of shear wave splitting in the 2010 Yushu Ms7.1 earthquake sequence were studied. By analyzing S‐wave particle motion of local events in the shear wave window, the polarization directions of fast shear waves and the delay times between fast and slow shear waves were derived from seismic recordings at 3 stations near the Garzê‐Yushu fault belt. The shear wave splitting results of 3 stations in the area of the fault belt reveal the NEE polarization directions of fast shear waves, which are consistent with the direction of regional principal compressive stress. Systematic changes of the time delays between two split shear waves were also observed. As for the spatial distribution, in focal region, the delay times at stations L6304 and YUS in the north branch fault of the Garzê‐Yushu fault belt are more than that of station L6303 in the south branch fault, meanwhile, the delay time at station YUS is more than that of station L6304. As for temporal changes in shear wave delay times, after the main shock, the delay times at station YUS increased rapidly, and decreased after a period of time. Seismic shear wave splitting is caused mostly by stress‐aligned microcracks in rock below the stations. The results demonstrate the changes of local stress field in the course of the main‐shock and aftershocks. After the main shock, the stress in the main‐shock region was released by the main‐shock, the crustal stress transferred to the southeastern part of the Garzê‐Yushu fault zone, and caused the delay time at station YUS to be greater than that of station L6304. The north branch fault of the Garzê‐Yushu fault belt is the causative fault of the 2010 Yushu Ms7.1 earthquake, whereas the south branch fault has a small impact on the earthquake. The stress at station YUS increased after the main‐shock, with the stress release caused by the aftershocks the stress reduced in the later stage.

Integrated Use of Time-Frequency Wavelet Decompositions for Fault Location in Distribution Networks: Theory and Experimental Validation

The paper presents a procedure for fault location in distribution networks, based on the use of the integrated time-frequency wavelet decompositions of the voltage transients associated with the fault-originated travelling waves. The proposed analysis of time-frequency wavelet decompositions has been found to improve the identification accuracy of the frequencies associated to the characteristic patterns of a fault location with respect to a sole frequency-domain wavelet analysis. Several laboratory fault tests, carried out by means of a reduced-scale model of a distribution feeder, are used to illustrate the characteristics and assess the performances of the proposed improved procedure. The paper also illustrates the application of the proposed procedure to a transient, originated by a permanent phase-to-phase fault, measured in a real distribution network in which a post-test analysis has identified the faulted branch.

Shallow low-velocity zone of the San Jacinto fault from local earthquake waveform modelling

SUMMARY We developed a method to determine the depth extent of low-velocity zone (LVZ) associated with a fault zone (FZ) using S-wave precursors from local earthquakes. The precursors are diffracted S waves around the edges of LVZ and their relative amplitudes to the direct S waves are sensitive to the LVZ depth. We applied the method to data recorded by three temporary arrays across three branches of the San Jacinto FZ. The FZ dip was constrained by differential traveltimes of P waves between stations at two side of the FZ. Other FZ parameters (width and velocity contrast) were determined by modelling waveforms of direct and FZ-reflected P and S waves. We found that the LVZ of the Buck Ridge fault branch has a width of ∼150 m with a 30–40 per cent reduction in Vp and a 50–60 per cent reduction in Vs. The fault dips 70 ± 5 ◦ to southwest and its LVZ extends only to 2 ± 1 km in depth. The LVZ of the Clark Valley fault branch has a width of ∼200 m with 40 per cent reduction in Vp and 50 per cent reduction in Vs. The Coyote Creek branch is nearly vertical and has a LVZ of ∼150 m in width and of 25 per cent reduction in Vp and 50 per cent reduction in Vs. The LVZs of these three branches are not centred at the surface fault trace but are located to their northeast, indicating asymmetric damage during earthquakes.

Landslides induced by the April 2007 Aysén Fjord earthquake, Chilean Patagonia

On the 21st of April 2007, the Aysen Fjord earthquake (Mw 6.2) in southern Chile (45.3° S, 73.0° W) triggered hundreds of landslides in the epicentral area along the fjord coast and surroundings. Some of these landslides induced large tsunami waves within the fjord causing fatalities and damaging several salmon farms, the most important economic activity of the area. The landslides included rock slides and avalanches, rock falls, shallow soil and soil–rock slides, and debris flows. The earthquake was the climax of a seismic swarm that began 3 months earlier. The seismicity is associated with tectonic activity along the Liquine–Ofqui fault zone (LOFZ), a major structural feature of the region. The earthquake-induced landslides were mapped and classified from field observations and remote sensing analysis. The landslide areas and epicentral distances are within the expected range for the earthquake magnitude according to worldwide data, while the position of landslides on the slopes strongly suggests topographic amplification effects in triggering the failures. The location of the landslides is also clearly related to some of the main fault branches of the LOFZ. The seismic event has configured a new situation of seismic and landslide hazard in the Aysen region and along the LOFZ, where the presence of towns and economic infrastructure along the coasts of several fjords constitutes a potential risk that was not considered before this seismic event.

A study on accurate fault location algorithm for parallel transmission line with a teed connection

Teed connecting parallel transmission lines frequently subject a variety of technical problems in the view of protection engineering. These problems are mainly due to the mutual coupling between lines and the multiple branch of teed connection, which requires choosing faulted branch before fault location. A new accurate fault location algorithm for parallel transmission line with a teed connection is introduced in this paper. Depending on six-sequence fault component method, the coupled transmission equations are transformed into decoupled ones. Based on the detailed analysis of peculiar characteristic of teed connection, the differential positive sequence component measurement, which is one of the six-sequence fault components, is used to implement fault location for parallel line with a teed connection. The new location algorithm makes full use of the decoupled mode and the teed structure. It is independent of source impedance, fault type, fault resistance and mutual coupling between parallel lines. The algorithm has been tested by EMTP simulations, which indicates that this location method obtains high accuracy under various fault conditions.

High-resolution spatial rupture pattern of a multiphase flower structure, Rex Hills, Nevada: New insights on scarp evolution in complex topography based on 3-D laser scanning

Fault scarps represent the most obvious expression of tectonic activity at the Earth9s surface. Studies on scarp morphology place constraints on fault kinematics and scarp-degradation processes, and were often based on geomorphic dating techniques. Fault scarps exposed in areas of simple topography facilitate data acquisition and interpretation, whereas little work had been done where fault scarps are superimposed on complex, dissected topography. Fault scarps developed in complex topography are commonly observed along flower structures and at tips of strike-slip faults. Such structures are important elements for evaluating the evolution and linking of strike-slip fault systems, and appear to be scale-independent from several meters to hundreds of kilometers. We examined the detailed meter- to hundred meter–scale structure and surface expression of a flank of one fault scarp–bounded pressure ridge (Rex Hills flower structure) by combining field mapping with high-resolution digital elevation model (DEM) analysis. Based on terrestrial laser scanning we generated a detailed DEM and extracted high-resolution topographic cross sections, which enabled us to identify fault scarps and to determine their relative ages and geometry. Our study site is located on the transpressional left-bend between the Pahrump and Amargosa segments of the dextral Stateline fault system. The topography is characterized by alternating valleys and ridges (each ∼100 m long, relief of ∼4 m). We observed the following: the southern Rex Hills slope exhibits three fault scarps related to three reverse fault branches; the basal scarp (scarp 1) is most continuous, and exhibits five segments, the upper two scarps (scarps 2 and 3) are less continuous. Furthermore, fault scarps exposed on ridge crests are more numerous (up to four to five scarps), and smaller (∼5 m high); valleys often exhibit single large (>10 m high), smoothed scarps. To easily detect differences between the scarps, we evaluated the height and slope angle of the scarps using topographic cross sections. Our analysis indicates that scarp shape is influenced by fault dip, lithology, and degradation processes resulting in large scatter and broad overlap in scarp-height–slope-angle space. The analysis further indicates that scarp degradation is stronger in the valleys, and that the preservation potential of small, individual fault scarps is therefore greater on the ridge crests. We compared our fault-scarp data with published, calibrated data yielding an age of ∼2 ka for the Rex Hills scarps consistent with an earlier finding. This suggests that the scarp shape mainly reflects progressive degradation since the most recent surface rupture. Our approach of analyzing high-resolution topographic data of closely spaced fault scarps is promising especially when combined with subsurface data as well as geochronological and paleoseismic data, and it provides a basic scheme for analyzing scarp populations in a complex topographic region. Despite the absence of subsurface data, our approach allowed the study of complex high-resolution fault-scarp morphologies across a flower structure for the first time.