Fault Branch Research Articles

Shallow crustal velocity structures revealed by active source tomography and fault activities of the Mianning-Xichang segment of the Anninghe fault zone, SW China

The Anninghe fault is a large left-lateral strike-slip fault in southwestern China. It has controlled deposition and magmatic activities since the Proterozoic, and seismic activity occurs frequently. The Mianning−Xichang segment of the Anninghe fault is a seismic gap that has been locked by high stress. Many studies suggest that this segment has great potential for large earthquakes (magnitude &gt;7). We obtained three vertical velocity profiles of the Anninghe fault (between Mianning and Xichang) based on the inversion of P-wave first arrival times. The travel time data were picked from seismograms generated by methane gaseous sources and recorded by three linearly distributed across-fault dense arrays. The inversion results show that the P-wave velocity structures at depths of 0−2 km corresponds well with the local lithology. The Quaternary sediments have low seismic velocities, whereas the igneous rocks, metamorphic rocks, and bedrock have high seismic velocities. We then further discuss the fault activities of the two fault branches of the Anninghe fault in the study region based on small earthquakes (magnitudes between <inline-formula><tex-math id="M1">\begin{document}$ {M}_{L} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="RA282-shaoxihui_M1.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="RA282-shaoxihui_M1.png"/></alternatives></inline-formula> 0.5 and <inline-formula><tex-math id="M3">\begin{document}$ {M}_{L} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="RA282-shaoxihui_M3.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="RA282-shaoxihui_M3.png"/></alternatives></inline-formula> 2.5) detected by the Xichang array. The eastern fault branch is more active than the western branch and that the fault activities in the eastern branch are different in the northern and southern segments at the border of 28°21′N. The high-resolution models obtained are essential for future earthquake rupture simulations and hazard assessments of the Anninghe fault zone. Future studies of velocity models at greater depths may further explain the complex fault activities in the study region.

T-Shaped Transmission Line Fault Location Based on Phase-Angle Jump燙hecking

In order to effectively solve the dead-zone and low-precision of T-shaped transmission line fault location, a new T-shaped transmission line fault location algorithm based on phase-angle jump checking is proposed in this paper. Firstly, the 3-terminal synchronous fundamental positive sequence voltage and current phasors are extracted and substituted into the fault branch distance function to realize the selection of fault branch when the fault occurs; Secondly, use the condition of the fundamental positive sequence voltage phasor at the fault point is equal to calculate all roots (including real root and virtual roots); Finally, the phase-angle jump check function is used for checking calculation, and then the only real root can be determined as the actual fault distance, thereby achieving the purpose of high-precision fault location. MATLAB simulation results show that the proposed new algorithm is feasible and effective with high fault location accuracy and good versatility.

High-resolution teleseismic tomographic crustal imaging for potential seismogenic segment of the central Tan-Lu Fault Zone, East China

The Tan-Lu Fault Zone (TLFZ) is the largest strike-slip system in East Asia. The central TLFZ has four main branch faults across a width of 20– 40 km, and both the great 1668 Tancheng Earthquake (M8.5) and the Anqiu Earthquake (M7.0) occurred on its two eastern branch faults. Due to the lack of recent earthquakes and stations around a seismic-quiescent segment of the TLFZ centered near the 70 BCE Anqiu Earthquake, previous tomographic images have resolutions coarser than 20 km in the middle and lower crust, unable to show how the crust is faulted along the TLFZ. To improve the resolution, we deployed a 70-km-long W-E-trending seismic array with 38 portable seismographs across the TLFZ at 36.1°N. Using one month of teleseismic records and a newly developed multiscale teleseismic tomography method, our P-wave velocity profile has achieved a resolution of 5 km × 5 km in shallow crust, and 10 km × 10 km in deep crust, as shown by the resolution tests. The profile's velocity variation correlates well with surface geology and crustal electrical resistivity profiles. The new profile provides clues for the depth distribution of major TLFZ branches, and indicates the two eastern TLFZ branch faults cut through the crust along a column-shaped low-velocity anomaly. This low-velocity column is associated with low-resistivity anomalies in the upper and lower crust, indicating a likely presence of fluids in the faulted rocks. This crustal faulting interpretation is consistent with the Moho geometry of previous receiver function studies, with an alignment between a receiver function Moho dome and a large low-velocity anomaly. Though seismicity is sparse near the profile, our interpreted crust-cutting location is in line with a linear cluster of recent TLFZ earthquakes about 20 km south of the profile, indicating that this quiescent segment could be a 150 km seismic gap along the central TLFZ.

Morfostrukturní doklady ponásunového porušení Pavlovských vrchů, Vnější Západní Karpaty

The article presents geomorphological and structural evidences of post-thrust limestone brittle deformation in the area of Pavlov Hills on the westernmost margin of the Outer Western Carpathians, Czech Republic. Airborne LiDAR-derived digital terrain model with 1 m resolution was used for this analysis, as well as aerial photographs and fieldwork. Combining these methods, we document a distinct N-S directed fault zone that intersects or delineates the majority of the Pavlov Hills Jurassic limestone nappe outliers. Data revealed an almost continuous fault zone of the north-south direction, which ranges from Horní Věstonice in the North, to Mikulov in the South, and extends further south to Austria. The thrusted Jurassic limestone bodies are cut by the fault zone, which tectonically crushed the limestone in its core and cores of the secondary fault branches. The map pattern of the fault zone suggests directional anastomotic branching and reattaching with the production of lenticular tectonic slices. We interpret the fault as a prominent sinistral shear zone. This is indicated by block displacement on the Svatý kopeček Hill and also by the orientation of the accompanying subvertical Riedel shears with identified horizontal lineation. The activity of the fault zone onset tightly after the nappe thrusting at the final stages of the accretion wedge formation, which is suggested from the observed sinistral kinematics. The main movement along the fault is thus most probably of a late Miocene age.

Faulted landforms, slip-rate, and tectonic implications of the eastern Lenglongling fault, northeastern Tibetan Plateau

The Lenglongling fault (LLLF) is an important part of the Qilian-Haiyuan fault (QHF) zone along the NE Tibetan Plateau. The Jinqianghe fault (JQHF) branches off of the LLLF and forms a fault junction that separates middle and eastern LLLF. Currently, it is not well understood how/if strain from the LLLF is transmitted to the JQHF over geologic time scales and how seismically active the eastern section of the LLLF is. Recent studies indicate that the 1927 M8 Gulang earthquake ruptured the middle LLLF and propagated eastward onto the eastern LLLF instead of propagating onto the JQHF. To assess if this concurrent rupture of middle and eastern LLLF is (or might be) a common phenomenon, we measured the Holocene slip-rate at the Huoshaotai site, east of the LLLF – JQHF junction, to compare it with known rates from the middle LLLF. Using displaced geomorphic markers and radiocarbon dating, we determined a Holocene left-lateral slip-rate of 6.0 ± 0.8 mm/a for the eastern LLLF. This rate is only slightly below the consensus slip-rate for the middle LLLF (6.6 ± 0.3 mm/a; 6.4 ± 0.7 mm/a), suggesting a gradual strain transfer and similar seismic activity for both sections. Paleoseismic evidence further suggests that at least three preceding earthquakes may have ruptured both sections simultaneously during the Holocene, indicating that concurrent failure of both sections, as in 1927, may not be uncommon. Concurrent failure of middle LLLF and JQHF is however not reported. Hence, it appears that LLLF and JQHF act as independent seismo-tectonic entities, without substantial strain transfer or concurrent seismic activity. These observations contribute to a better understanding of the QHF zone and the potential for multi-fault rupture along it.

Crustal Deformation of the Kendeng Fault Branches Area from GNSS and InSAR Data in Surabaya City, Indonesia

Slip rates on active faults derived from the interseismic velocity field are critical to understanding seismic hazards in metropolitan cities. This study integrated the data from the Global Navigation Satellite System (GNSS) and Interferometric Synthetic Aperture Radar (InSAR) to evaluate the interseismic velocities in the second-largest city in Indonesia, Surabaya, where branches of the Kendeng fault (the Surabaya and the Waru faults) pass through. Data from 16 campaign-mode GNSS stations collected between 2017 and 2020 from previous research are reprocessed to estimate the velocity field. Horizontal velocities under the ITRF frame range between -23.8 mm/yr and 47.9 mm/yr toward the southeast. Vertical velocities generally range between -1.3 mm/yr and -112.2 mm/yr. Sentinel-1A SAR data of both ascending and descending tracks acquired between November 2014 and July 2020 were used to generate the interferograms with the InSAR Scientific Computing Environment (ISCE) software. Furthermore, cumulative displacement time series were constructed using the Small BAseline Subset (SBAS) technique within the Generic InSAR Analysis Toolbox (GIAnT). This study also carried out the detection of outlier SAR epochs to improve the precision of Line-of-sight (LOS) velocity estimates. The LOS velocities range from -14.8 to 10.8 mm/yr in the ascending track and from -12.7 to 9.5 mm/yr in the descending track. These results will facilitate the detection of coupling behaviors on the Kendeng fault branches, which can improve our understanding of seismic risks in the Surabaya area.

Real time FTTH network monitoring using binary coded fiber Bragg grating

The rise in users on the Passive Optical Network (PON) has made the architecture of this network increasingly complex with a growing point-to-multi-point (P2MP) network. Thus, network monitoring has become more crucial and should be carried out in order to monitor the transmission of signals to each optical network unit (ONU) and prolonged service can be provided to the users without problems. A monitoring signal using limited bandwidth has been combined with data signals at the optical line terminal (OLT) at the central office to monitor the status of each ONU in the network. This signal has been transmitted along the fiber and will be used to reflect the spectrum of uniform fiber Bragg grating (FBG) located before the ONU. FBG binary codes will be used as an indicator between one ONU to another ONUs by varying the wavelength used by the FBGs in the network to represent each ONU. This paper presents two techniques to monitor network health by creating FBG configuration design (FBG codes) to identify fault branches as well as simulation results and performance parameters will be analysed and compared to obtain the best techniques by considering several aspects such as economical and technical.

Structural characteristics of transtensional fault system and its implication for hydrocarbon accumulation in S Block, South Asia area

Transtensional faults are well developed in the S Block of the South Asia area, which have an important impact on the hydrocarbon accumulation. However, the transtensional fault structure is very complex. Based on drilling and seismic data interpretation results, faults are divided into three typical types in the Lower Cretaceous, which can help to understand the complex fault system. The main faults are distributed in the NNW-SSE direction and parallel arrangement with dextral strike-slip shear characteristics, which determines the development of the tectonic belt. The secondary faults are often associated with the main faults, often composed of multiple branch faults. The complexity of the fault system is further aggravated by the small interlayer faults. Based on balanced crosssection technique analysis, the fault evolution has experienced five geological periods, which is closely related to the Indo-Pakistan plate tectonics and the Indus Basin evolution. In the diagonal extension stage of the Late Cretaceous, the fault activity was very strong, which had a significant impact on the tectonic pattern of "horst-graben structures and locally complex faulted blocks" in S Block. It is found that transtensional fault assemblage patterns are regular and diverse. It consists of six kinds of plane assemblage and seven kinds of profile assemblage patterns. Plane assemblage patterns include en echelon, broom, feather, comb, horsetail and diamond shape, while profile assemblage patterns consist of horst-graben faulted type, consequent faulted type, antithetic faulted type, "Y" and reverse "Y" type, "X" type and negative flower type. Different transtensional fault assemblage patterns form various kinds of hydrocarbon trap types, including faulted block, faulted nose, faulted anticline and composite traps. Fault activity and evolution promote the hydrocarbon generation, control the formation of tectonic zones and favorable traps and play an important control role in hydrocarbon migration and accumulation. Therefore, in this study the main exploration and evaluation targets are faulted reservoirs in the study area.

Aftershock sequence of the 2017 Mw 6.5 Jiuzhaigou, China earthquake monitored by an AsA network and its implication to fault structures and strength

SUMMARY We deployed a seismic network near the source region of the 2017 Mw 6.5 Jiuzhaigou earthquake to monitor aftershock activity and to investigate the local fault structure. An aftershock deployment of Array of small Arrays (AsA) and a Geometric Mean Envelop (GME) algorithm are adopted to enhance detection performance. We also adopt a set of association, relocation and matched-filter techniques to obtain a detailed regional catalogue. 16 742 events are detected and relocated, including 1279 aftershocks following the Mw 4.8 aftershock. We develop a joint inversion algorithm utilizing locations of event clusters and focal mechanisms to determine the geometry of planar faults. Six segments were finally determined, in which three segments are related to the Huya fault reflecting a change in fault dip direction near the main shock hypocentre, while the other segments reflect branches showing orthogonal and conjugate geometries with the Huya fault. Aftershocks were active on branching faults between the Huya and Minjiang faults indicating that the main shock may have ruptured both major faults. We also resolve a fault portion with ‘weak strength’ near the main shock hypocentre, which is characterized by limited coseismic slips, concentrated afterslip, low aftershock activities, high b-value and high sensitivity to stress changes. These phenomena can be explained by fault frictional properties at conditional stable sliding status, which may be related to the localized high pore-fluid pressure produced by the fluid intrusion.

Fiber Bragg grating-based monitoring system for fiber to the home (FTTH) passive optical network

Abstract Fiber to the home (FTTH) passive optical network is one of the cost effective and effortlessly planning systems in the current era of communication systems. However, one of the substantial limitations of this optical communication network is the monitoring operation. It is essential to locate the fault branch in the network in order to take the required action to overcome the problem. Unfortunately, since the network is all passive, it is necessary to introduce a technique that should be passive and has the capacity to locate the fault location inside the network. In this paper, a methodology to localize the fault line was introduced, where a combination of Fiber Bragg Gratings was suggested, using this approach, the fault location can be easily determined among 36-branch, distributed in eight groups. Simulation results show that the broken line can be determined through monitoring the reflected signals from all the branches in the Central Office without paying any power to locate the leakage. In other words, it is easy to recognize the fault location by monitoring the power of the reflected signals, where after comprehensive simulations and power calculations, it was possible to put a threshold for that reflected power, hence, the fault branch, for any reason, may reflect power of less than that threshold, otherwise, the branch is not considered as broken.

The Seismogenic Structure of the 2017 Mw 6.9 Milin, Tibet, Earthquake: A Possible Newly Active Fault at the Eastern Himalayan Syntaxis

AbstractOn 18 November 2017, an Mw 6.9 earthquake occurred in Milin, Tibet, with the epicenter at the top of the Namche Barwa syntaxis. This event did not produce surface ruptures, and its seismogenic structure remains unclear or controversial. Using the locations of the Milin mainshock and aftershocks, locations of regional small earthquakes and focal mechanism solutions from 2007 to 2009, this work analyzed the causative fault and tectonic setting of the Milin earthquake and assessed the regional seismic risk. The results suggest that the seismogenic structure of the Milin earthquake was a secondary fault, the southern branch of the XiXingla fault (XXLF). Within 28 hr after the mainshock, the aftershocks of the Milin event spread northeastward to the secondary north branch fault of the XXLF and the secondary south branch fault of the Palong–Pangxin fault. Across the top of the Namche Barwa syntaxis (Namche Barwa block) and the Chayu block in the southeast, an earthquake dense belt (EDB) has developed. This EDB has similar deep structures beneath the two blocks, in which several northeast-dipping structural planes exit, and different portions of the EDB imply a unified tectonic stress field. Combining these data with the foreshock–mainshock–aftershock data for the 1950 Mw 8.6 Chayu, Tibet, earthquake, we speculate that the structural planes produced by the EDB at depth in the two blocks have already been connected or tended to connect, resulting in a new fault system trending northwest and approximately 280 km long. The 2017 Mw 6.9 Milin earthquake occurred at the northwestern end of this fault system. At present, the development stage, maturity, and fine structure of this new fault system remain unclear but should receive additional attention. Based on its maximum rupture area, this new fault system is capable of generating an Mw 7.7 earthquake in the future.

Stress evolution before the 2014 Ludian M6.5 earthquake: Insights from groundwater and geodetic measurement

Because the meta-instability stage before an earthquake can be found in rock-deformation experiments in the laboratory, great expectations are placed on the detection of possible precursors in earthquake forecasting and prediction. However, varietal observations are difficult to compare, and it is very difficult to distinguish to which stage the observed value belongs. The top priority is to study the relationship between the observations and the meta-instability stage in a uniform system of measurement. The 2014 Ludian M6.5 earthquake, which occurred in the southeastern region of the Qinghai-Tibet Plateau, was surrounded by 122 observatories for groundwater, electromagnetism, and surface deformation within a 300-km radius. Many data were observed before and after the Ludian earthquake, which provided a great case to study the relationship between the observations, stress evolutions, and meta-instability stage before the earthquake. We determined the detailed spatiotemporal variations in groundwater temperature, water level, chemical ion measurement, and crust deformation by strain meter and tilt meter. Following the previous study on the relationship between the observations and stress field, we simply classified all these data from 78 observatories into three groups: stress increased, stress disturbed, and uninfluenced. The results show that the stress field displayed a four-quadrant pattern around the seismogenic structure of the 2014 Ludian earthquake, which is called the Baogunao-Xiaohe Fault and is known as a buried branch fault of the Daliangshan fault. Along with the orientation of fault-block movement, the stress decreased at the back while increasing at the front. In addition, some stress perturbations were found along nearby large active faults, such as the Xianshuihe-Anninghe-Zemuhe-Xiaojiang fault zone, which is a deep-cutting active fault belt confining the Sichuan-Yunnan block. Based on the spatiotemporal evolution of the stress field and distribution of aftershocks, we simplified the seismogenic structure to a set of conjugated strike–slip faults. The nonlinear friction finite-element method was applied to simulate the stress variations before and after the extensive disengagement and slip of nodes on the fault plane. The computed stress field is consistent with the observed phenomenon and the meta-instability stage could be distinguished out from our simulation. Our research can be used to help detach earthquake precursors and determine whether the earthquake system is in the meta-instability stage.

영덕군 병곡면 해안에 형성된 단층에 대한 연구

In the southeastern part of the Korean Peninsula, the Yangsan Fault, an active fault zone, has developed. Many earthquakes occur around these faults, and the possibility of earthquakes occurring along the branch faults is being discussed. On the other hand, the Yeongdeok Fault is reported in Yeongdeok-gun, which is the northern part of the Yangsan fault. In this study, goemorphic characteristics of a set faults found on the outcrop of the gentle slope of the coast of Byeonggok-myeon were analyzed and granulometric and geochemical characteristics of sediments and other materials, including fault gouges were analyzed. The outcrop of Byeonggok-myeon is the part of the fault core and can be divided into two parts. Theses fault are formed on the upper part of the Mesozoic bedrock and the tertiary sedimentary layer of red sand-supported clasts are covered in several sedimentary units. The faults were normal fault sets, and a number of vertical cracks were developed, and glossy surfaces were observed in the fault area. It appears that these faults have occurred after alluvial deposition had been formed. In the case of samples from fault gouges, there were differences in particle size and geochemical characteristics from the surrounding area.

IDENTIFICATION OF HORST AND GRABEN STRUCTURAL PATTERNS USING GRAVITY AND SECOND VERTICAL DERIVATIVE (SVD) METHODS IN THE LUBUKSIKAPING AREA OF WEST SUMATERA

The Lubuksikaping area is located between the main fault branching of the Sumateran Fault so it can be seen that there are many quite complex structures. This research was conducted to determine the structure pattern of the high (horst) and low (graben) that formed in the sub-surface of the Lubuksikaping area, West Sumatera. This research uses gravity data which will then be carried out by spectral analysis, upward continuation, separation of regional and residual anomalies, and Second Vertical Derivative (SVD) analysis. Furthermore, 2D forward modeling is carried out to determine the correlation between the 2D subsurface forward modeling and the resulting SVD graph. Based on the analysis of the regional anomaly map, it can be seen that the measured low anomaly is due to the area in the form of a structural valley formed due to the activity of the Sumatera Fault, while the high is thought to be a structural hill (horst) that forms an elongated mountain range and separated by graben. In addition, based on the analysis of the residual anomaly map, it can be seen that the low anomaly indicates the presence of a depositor (graben), whereas, the high anomaly is indicated as the presence of rocks with high-density contrast values. and is interpreted as a horst structure. Based on the analysis of the horst and graben patterns in the residual Bouguer anomaly, it can be seen that there is an elevation zone (horst) that are northwest and northeast on the residual map and it is known that there are 3 graben structures in Lubuksikaping, namely Panyabungan Graben, Rao Graben and Sumpur Graben with relative northwest-southeast direction. The 2D models of paths A-A' and B-B' show faults that are located relatively the same as the SVD graph obtained from the residual SVD anomaly map.

Fault location of hybrid three-terminal HVDC transmission line based on improved LMD

To reduce the impact of traveling wave velocity, wave head recognition, and LMD (Local Mean Decomposition) end effect and mode mixing on location accuracy, this paper presents a fault location method based on improved LMD for hybrid three-terminal HVDC transmission lines, which is not affected by wave velocity. Firstly, the improved LMD is used to get the time when the fault traveling wave first arrives at the four measuring terminals. Then the fault branch is identified according to the ratio of the time of the fault traveling wave arriving at the measuring terminal. Finally, the equation is listed according to the principle of traveling wave location and the measurement equation which is not affected by the wave velocity is deduced. A hybrid three-terminal HVDC transmission system model is built by PSCAD to simulate various faults and output fault data under various fault conditions. MATLAB is used to process the fault data and verify the location algorithm. The simulation results show that the location method proposed in this paper is not affected by fault distances, fault types, infeed levels and transition resistances. In addition, it has higher accuracy than LMD based on CSI (Cubic Spline Interpolation) algorithm, wavelet packet location algorithm and double-ended location method of using wave velocity calculation.

Frequency Response Analysis Technique of Short Circuit Faults Detection in Photovoltaic Single-Phase Inverter Experimental Study

The work proposed in this paper concerns the study of short circuit faults in a single-phase inverter dedicated to a photovoltaic application by applying the frequency response analysis (FRA) technique on this IGBT-based inverter controlled by a 18F2550 microcontroller, a prototype inverter was designed in the laboratory to be able to apply off-line short-circuit faults using an LRC meter. The FRA technique is based on the comparison of amplitude-frequency and phase-frequency signatures of healthy cases and fault situations. The experimental results also led to the conclusion that frequency response analysis can be used as an effective tool to detect faults in power electronic devices. This method allows for efficient detection and classification of faults with ease of implementation. For fault location, the fault branch is determined according to its position relative to its healthy state.

Near-Fault Monitoring Reveals Combined Seismic and Slow Activation of a Fault Branch within the Istanbul–Marmara Seismic Gap in Northwest Turkey

Abstract Various geophysical observations show that seismic and aseismic slip on a fault may occur concurrently. We analyze microseismicity recordings from a temporary near-fault seismic network and borehole strainmeter data from the eastern Marmara region in northwest Turkey to track seismic and aseismic deformation around the hypocentral region of an Mw 4.5 earthquake in 2018. A slow transient is observed that lasted about 30 days starting at the time of the Mw 4.5 event. We study about 1200 microseismic events that occurred during 417 days after the Mw 4.5 event around the mainshock fault rupture. The seismicity reveals a strong temporal clustering, including four episodic seismic sequences, each containing more than 30 events per day. Seismicity from the first two sequences displayed typical characteristics driven by aseismic slip and/or fluids, such as the activation of a broader region around the mainshock and swarm-like topology. The third and fourth sequences correspond to typical mainshock–aftershock sequences. These observations suggest that slow slip and potentially fluid diffusion along the fault plane could have controlled the seismicity during the initial 150 days following the Mw 4.5 event. In contrast, stress redistribution and breaking of remaining asperities may have caused the activity after the initial 150 days. Our observation from a newly installed combined dense seismic and borehole strainmeter network follows an earlier observation of a slow transient occurring in conjunction with enhanced local seismic moment release in the same region. This suggests a frequent interaction of seismic and aseismic slip in the Istanbul–Marmara seismic gap.

Earthquake‐Spawning Faults in the Seoul Metropolitan Area and Their Seismic Implications

AbstractQuaternary faults run across the Seoul metropolitan area that is the highest population region in the Korean Peninsula. Active fault identification and seismic hazard potential assessment are crucial for public safety. Densely deployed permanent and temporal seismic stations enabled us to detect micro to small earthquakes, allowing us to identify earthquake‐spawning faults in Seoul metropolitan area. The source parameters of 455 earthquakes in 2004–2020 are refined. The Gutenberg‐Richter b value is 0.94. Dominant focal depths are 4–15 km. The focal mechanism solutions of 64 earthquakes are determined using seismic‐wave polarities and amplitude ratios. Strike‐slip earthquakes are dominant in the region. Earthquakes are clustered around the Chugaryeong fault system. The dominant strikes of fault planes range from N20°E to N45°E in the northern and southern Seoul metropolitan areas, suggesting branch fault development locally. The earthquakes in middle‐northern Seoul present N‐S directional strike‐slip motions at depths ∼7.5 km along the Chugaryeong fault, suggesting seismically active near‐vertical faults subparallel with Chugaryeong fault.

Geometric and Dynamic Patterns of the Golmud Segment in the Southern Marginal Fault of the Qaidam Basin

The southern marginal fault of the Qaidam Basin (SMQBF) is a block-bounding border fault that has played a key role in the structural evolution of the Kunlun Fault. However, its geometric and dynamic deformation patterns since the Late Pleistocene have not been clearly observed. Field investigations, combined with high-resolution imagery and shallow seismic profiles, show that the SMQBF is a thrust fault with a sinistral strike-slip component composed of several secondary faults. Its Late Quaternary deformation pattern is characterized by piggyback thrust propagation, and the frontal fault may not be exposed to the surface. Due to the flexural slip of the hanging strata of the secondary fault, sub-parallel faults with widths of thousands of meters have formed on high terraces; these are important when assessing the seismic hazard of this area. Based on high-resolution topographic data obtained using an unmanned erial vehicle and optically stimulated luminescence chronology, the slip rates of several secondary faults were obtained. The vertical and strike-slip rates of the SMQBF were determined to be 0.96 ± 0.33 mm/a and 2.66 ± 0.50 mm/a, respectively, which may be the minimum rates for the fault. Considering that the SMQBF is composed of several secondary faults, these rates possibly correspond to minimum deformation only. The evident sinistral strike-slip of the SMQBF indicates that although the sinistral slip of the Kunlun Fault system is concentrated in main fault of this system, the branch faults have a significant influence on the lateral extrusion of the Qinghai-Tibet Plateau.

Single-end fault identification scheme for multi-terminal DC grid based on amplitude similarity of injection signal

Effective fault identification scheme plays an important role in the fault isolation stage and system recovery stage of multi-terminal DC grid. Therefore, an active detection based single-end DC fault identification scheme is proposed to improve the reliability and sensitivity of fault identification. The control strategy is suggested of the generation of sinusoidal signals at different frequencies by the hybrid modular multilevel converters. Based on the blocking effect of the fault branch on the injection signal, by introducing the improved correlation discrimination algorithm, a single-end fault identification scheme is proposed by using the amplitude difference between the measured and calculated values of injection signals. The proposed scheme can be used for fault isolation and adaptive system recovery. Intensive simulation studies prove the improved sensitivity, and reliability of the proposed scheme for the full length of transmission line without relying on DC boundary. Moreover, the scheme can identify the permanent fault during the system recovery stage.