Horizontal Slip Research Articles

Late Pleistocene-Holocene characteristics of the North Anatolian Fault at Adapazarı Basin: evidence from the age and geometry of the fluvial terrace staircases

The Late Pleistocene-Holocene evolution of the Adapazarı Basin was investigated using the stratigraphy, geometry, and absoluteluminescence dating of the 4-step fluvial terrace staircases of the Sakarya River. The results revealed that the fluvial cycle was primarily related to relative sea level changes of the Black Sea. The initiation of deposition and the abandonment ages of the terraces indicated relative high stands during marine isotope stage (MIS) 5a (~84-72 ka), 3 (40-30 ka), and 1 (9 ka-recent). The erosional periods in between the terrace steps reflected the response of the Sakarya River to the significantly low stands of the sea. The spatiotemporal position of the high terraces (T4 and T3) yielded an average of 0.78 ± 0.03 mm/year, and uniform and aseismic rock uplift rate for the NW part of the Anatolian Plate bounded by the North Anatolian Fault, which ruptured during the 1999 İzmit earthquake. The lower terrace (T1) was previously used to determine the horizontal slip rate of the Sapanca-Akyazı segment of the earthquake rupture and reported as 16.7 + 3.6/-2.5 mm/year. Further displacement measurements from the surfaces of T2 and T1 yielded a vertical slip rate of 1.49 ± 0.2 mm/year, calculated for the Late Holocene. Extrapolation of these 2 vertical rates to the south and north of the fault zone, in time and space, used in conjunction with the stratigraphy and geometry of the Adapazarı Basin, provided an estimation constraining the timing of the initiation of the fault to 450 ± 50 ka and the total thickness of the basin to ~1100 m.

Experimental and CFD modelling of a Progressive Cavity Pump using overset unstructured mesh

A Progressive Cavity Pump (PCP) is widely used in industry as an artificial lift method because of its high efficiency during the pumping of high viscosity fluids and two-phase liquid-gas flow slurries. However, modelling PCP through Computational Fluid Dynamics (CFD) is quite complicated since it requires a meshing algorithm and is computationally expensive. Therefore, this study's main objective is to develop a CFD model capable of predicting a progressive cavity pump's behavior by implementing the Overset Mesh, which includes the relative motion between the rotor and the stator. Overset meshes are used to discretize a computational domain with several different meshes that arbitrarily overlap each other. They are most useful because the rotor geometry can be enclosed in a fluid (background) region and set to different positions. The PCP analyzed in this study is a GRP 4.0-4000 208 TSL 1-2 mono-lobe, which contains an API J55 stainless steel rotor and stator handling four Newtonian fluids (water, oil API 11, oil API 22, and oil API 31) at three rotational speeds (100 rpm, 150 rpm, and 200 rpm). The experimental data presented in this paper was collected in the PCP experimental facility of the SLACOL BCP Group (Tenjo, Colombia). All the measurements were made using the CILA2S controller for artificial lifting in the underground and on the surface to determine the operational curves of flowrate, volumetric efficiency, torque, and power consumed. The CFD model implementation was developed on Star- CCM+ version 15.02-R8 of 2020 for laminar and turbulent regimens. The results obtained through this study show that it is unnecessary to program a structured mesh to capture a progressive cavity pump's performance since the operational parameters evaluated to have an accuracy of 10% concerning the experimental data.Similarly, capturing the viscous effect near the wall and the transversal y horizontal slip inside the cavities is possible. The flow rate obtained for higher viscosity oils is more significant for the same pressure differences for water with average volumetric efficiencies of 85%. Finally, the pressure increase per stage is homogeneous along the pump's entire length for all fluids evaluated

The Lavic Lake Fault: A Long-Term Cumulative Slip Analysis via Combined Field Work and Thermal Infrared Hyperspectral Airborne Remote Sensing

The 1999 Hector Mine earthquake ruptured to the surface in eastern California, with >5 m peak right-lateral slip on the Lavic Lake fault. The cumulative offset and geologic slip rate of this fault are not well defined, which inhibits tectonic reconstructions and risk assessment of the Eastern California Shear Zone (ECSZ). With thermal infrared hyperspectral airborne imagery, field data, and auxiliary information from legacy geologic maps, we created lithologic maps of the area using supervised and unsupervised classifications of the remote sensing imagery. We optimized a data processing sequence for supervised classifications, resulting in lithologic maps over a test area with an overall accuracy of 71 ± 1% with respect to ground-truth geologic mapping. Using all of the data and maps, we identified offset bedrock features that yield piercing points along the main Lavic Lake fault and indicate a 1036 +27/−26 m net slip, with 1008 +14/−17 m horizontal and 241 +51/−47 m vertical components. For the contribution from distributed shear, modern off-fault deformation values from another study imply a larger horizontal slip component of 1276 +18/−22 m. Within the constraints, we estimate a geologic slip rate of <4 mm/yr, which does not increase the sum geologic Mojave ECSZ rate to current geodetic values. Our result supports previous suggestions that transient tectonic activity in this area may be responsible for the discrepancy between long-term geologic and present-day geodetic rates.

The Late Quaternary dip–slip characteristics of the left-lateral strike-slip Yuanmou fault, the southwestern margin of the north–south seismic belt of China

The North–South Seismic Belt distributed along the eastern margin of the Tibetan Plateau is a regional-scale seismically active zone. The Yuanmou Fault, located at the junction of the North–South Seismic Belt and the Central Yunnan Sub-Block, is an important boundary of earthquakes distribution and topography. Therefore, the studying of the Late Quaternary activity of the Yuanmou Fault is of great significance to understand the regional geodynamic mechanism and its efforts on the regional tectonic activities, seismic distribution and future risk. Based on field observations and analysis of earthquake geology and tectonic geomorphology and the dating results of Quaternary chronology, together with the previous studies, revealed that: (1) the fluvial terrace T1 was cut by the Yuanmou fault on the northern section of Jiangbian, and the most recent earthquake event happened about 7 ka B.P. age on the Jiangbian–Luochuan segment. (2) Based on the offset measurement and dating results of deformed terraces, the horizontal and vertical average slip rate of the Yuanmou fault were determined to be ~ 1.0 mm/year and ~ 0.1 mm/year, respectively. (3) Moreover, the latest activity time of the southern segment of the Yuanmou Fault is late Pleistocene, indicating the segmentation between the northern and southern segments of the Yuanmou Fault. (4) The differential activity intensity and activity ways of the Yuanmou Fault on different segments is probably associated with the change of local stress. Therefore, these findings concerning with seismic activities and activity segmentation of the Yuanmou Fault reveal the complexity of the regional dynamic mechanisms and provide a new insight for exploring regional differences in the tectonic deformation mechanisms of the southeastern margin of the Tibetan Plateau during the Late Cenozoic.

Constraining Late Quaternary Crustal Shortening in the Eastern Qilian Shan From Deformed River Terraces

AbstractThe Qilian Shan, located in the northeastern Tibet, is under strong tectonic activity and earthquake motion due to the propagation of the plateau. At the mountain front of the eastern Qilian Shan, the Tongziba River, in the southern Zhangye Basin, flows northward and successively cuts the Minle‐Damaying Fault and the Yonggu Anticline, two parallel structures within the Frontal Thrust system of the Qilian Shan. Here we present a detailed record of seven strath terraces of this river that documents the history of active deformation of the two structures. Based on the estimated crustal shortening distance from the deformed terraces and the terrace formation age constrained by AMS14C and optically stimulated luminescence (OSL) dating, a horizontal slip rate of 1.4 ± 0.5 mm/year of the Minle‐Damaying Fault is constrained since 16.7 ± 1.8 kyr, and a shortening rate of 1.3 ± 0.4 mm/year across the Yonggu Anticline has been estimated in a similar time frame, respectively. In total, the shortening rate across the mountain front is estimated to be 2.7 ± 0.6 mm/year. GPS data show a similar modern shortening rate in this area, which indicates the rate of crustal shortening may be comparable in the modern and 104‐year scales. Our study supports a higher crustal shortening rate along the mountain front of the eastern Qilian Shan than that of the western Qilian Shan since the Late Quaternary.

Theoretical and experimental research on slip and uplift of the timber-concrete composite beam

Timber-concrete composite beams are a new type of structural element that is environmentally friendly. The structural efficiency of this kind of beam highly depends on the stiffness of the interlayer connection. The structural efficiency of the composite was evaluated by experimental and theoretical investigations performed on the relative horizontal slip and vertical uplift along the interlayer between composite’s timber and concrete slab. Differential equations were established based on a theoretical analysis of combination effects of interlayer slip and vertical uplift, by using deformation theory of elastics. Subsequently, the differential equations were solved and the magnitude of uplift force at the interlayer was obtained. It was concluded that the theoretical calculations were in good agreement with the results of experimentation.

Late Quaternary transpressional earthquakes on a long-lived intraplate fault: A case study of the Southern Yangsan Fault, SE Korea

The NNE–SSW-striking Yangsan Fault in southeastern Korea has been regarded as one of the most prominent seismogenic structures in the Korean Peninsula on the basis of instrumental and historical seismicity, and paleoseismic records along the fault zone. Its seismic behavior is, however, still uncertain due to long recurrence intervals of strong earthquakes and insufficient historical and geologic records. We conducted a detailed paleoseismic investigation, including an 8 m-deep excavation, in order to understand recent earthquake-faulting events along the Southern Yangsan Fault. Our observations indicate that at least two and possibly four dominantly strike-slip surface-faulting events have occurred along a subsidiary fault in the eastern boundary of the fault valley since the late Pleistocene. Stratigraphic features and OSL ages of the stratigraphy exposed in the trenches indicate that the most recent rupture(s) occurred after 29.2 ± 1.4 ka and the timing of earlier ruptures are constrained to between 70.0 ± 3.7 ka and 29.2 ± 1.4 ka. Using a contact of the oldest dated unit that has at least 7.5 m of vertical separation, we calculate a minimum vertical slip rate during the late Quaternary of 0.11 mm/yr. The minimum horizontal slip rate is presumed to be two times that of the vertical slip rate based on striations observed on clasts next to the fault core. We also propose that the late Quaternary earthquake-faulting kinematics along the Yangsan Fault, expressed as contractional dextral slip with east-side-up geometry, is strongly dependent on a pre-existing fault zone architecture with a strike of N10–20°E that dips to the east, and the direction of neotectonic maximum horizontal stress (ENE–WSW to E–W).

Title Paleoseismological and Neotectonic Characteristics of Çaldıran Fault Around Çaldıran District

Sağ yanal atımlı Çaldıran Fayı Türkiye’nin Doğu Anadolu bölgesindeki önemli aktif faylarındandır. Fayın 24 Kasım 1976 tarihinde ürettiği yıkıcı deprem önemli hasar ve can kaybına neden olmuş ve 50-55 km yüzey kırığı oluşturmuştur. Çaldıran ilçesi dolayında yüzey deformasyonları ve paleosismolojik kazı esasına dayalı olarak gerçekleştirilen bu çalışmada son depremde oluşan yüzey kırıklarının korunduğu kesimlerin olduğu saptanmıştır. Yüzey ve paleosismolojik çalışmalar Holosen’de bölgede yüzey kırığı oluşturan (M≥7) en az üç depremin olduğunu göstermektedir. Çaldıran dolayında, son depremde 1,5 m sağ yanal ve 30-40 cm düşey ötelenme saptanmıştır. Ayrıca,1696’da Çaldıran bölgesinde meydana gelen depremi [18] Çaldıran Fayı’nın ürettiği kabul edilerek tekrarlanma aralığının 280 yıl; kısa dönem yatay kayma hızının 5,36 mm/yıl-1 düşey kayma hızının ise 1,43 mm/yıl-1 olduğu saptanmıştır.

Holocene activity and seismic hazard analysis of faults in Damxung, Tibet

Based on interpretation of remote sensing and geological field survey result, three secondary faults are distributed in parallel in Damxung of the southeastern piedmont fault of Nyainqentanglha mountain, which form landform profile across normal faults of graben due to cut platform margin of grade I terrace scarp formation. Through researching the displacements and the collected sediments dates, it is obtained that the horizontal slip rate is about 0.6 mm/a (millimeter per year), and the vertical slip rate is about 1.7 mm/a since 4 ka B.P. (kilo years before present). The northern margin of Damxung basin is a seismic gap, which continuously accumulated strain energy is not released in the M7.5 Damxung earthquake and the M8.0 Yangbajain earthquake. The fracture length of the seismic space can be regarded as the minimum length of potential surface rupture. The maximum moment magnitude of potential earthquakes is at least M6.8.in northern margin of Damxung basin the normal fault magnitude estimation formulas from Wells and Coppersmith (Bull Seismol Soc Am 84(4):974–1002, 1994).

Study on Bending-Shearing Separation Force of Reinforced Tenon Precast Shear Wall Joints

A new type of large-size reinforced tenon precast shear wall was proposed, which can effectively reduce the pin-key shear stress of the longitudinal connecting steel bars and improve the seismic performance of the precast shear wall. In order to study the bending-shear separation mechanism of the wall edge restraint member and the reinforcement-slotted shear, this paper first proposes the bending-shear separation mechanism of the wall edge restraint member. The concept of bending-shear separation degree was introduced, the mechanical analysis model of reinforced tenon was established, and the calculation method of horizontal relative slip of reinforced tenon interface was obtained by using Rayleigh-Ritz variational method. The relationship between horizontal relative slip of interface and shear stress of steel pin key was established, and the size of large-sized reinforced tenon to interface was studied.

Increased strength of laminated bamboo beams using a shear connector adhesive method

At this time the timber with good quality has been difficult to obtain, so the wood is increasingly rare for building construction. To reduce deforestation due to logging for construction materials, it is time to replace wood with bamboo. Laminated bamboo is an engineering building material that has a character like wood. Laminated bamboo structures can encourage the replacement of wood, steel and concrete materials so that the development of laminated bamboo technology can revolutionize the use of bamboo in construction. One of the weaknesses of the laminated bamboo beam structure is the adhesive line between the bamboo lamina. Mechanical lamination using a shear connector prevents horizontal slip between the bamboo lamina. Incising method is a method that makes the adhesive as well as the adhesive as well as the shear connector. Dendrocalamus asper research material with an average age of 4 years. The testing shear strength and tensile strength of bamboo block lamination was carried out based on ASTM D143 (2002). Experimental testing of flexural strength of laminated bamboo beams is carried out using a tool with a Multi Purpose Testing System and data logger. Changes in the structure of bamboo that are applied to lateral pressure are observed using SEM (Scaning Electron Microscopy). The use of Incising method in making laminated bamboo beams can significantly increase the strength of mechanical properties laminated beam structures.

Transient Deformation in California From Two Decades of GPS Displacements: Implications for a Three-Dimensional Kinematic Reference Frame.

Our understanding of plate boundary deformation has been enhanced by transient signals observed against the backdrop of time‐independent secular motions. We make use of a new analysis of displacement time series from about 1,000 continuous Global Positioning System (GPS) stations in California from 1999 to 2018 to distinguish tectonic and nontectonic transients from secular motion. A primary objective is to define a high‐resolution three‐dimensional reference frame (datum) for California that can be rapidly maintained with geodetic data to accommodate both secular and time‐dependent motions. To this end, we compare the displacements to those predicted by a horizontal secular fault slip model for the region and construct displacement and strain rate fields. Over the past 19 years, California has experienced 19 geodetically detectable earthquakes and widespread postseismic deformation. We observe postseismic strain rate variations as large as 1,000 nstrain/year with moment releases equivalent up to an Mw6.8 earthquake. We find significant secular differences up to 10 mm/year with the fault slip model, from the Mendocino Triple Junction to the southern Cascadia subduction zone, the northern Basin and Range, and the Santa Barbara channel. Secular vertical uplift is observed across the Transverse Ranges, Coastal Ranges, Sierra Nevada, as well as large‐scale postseismic uplift after the 1999 Mw7.1 Hector Mine and 2010 Mw7.2 El Mayor‐Cucapah earthquakes. We also identify areas of vertical land motions due to anthropogenic, natural, and magmatic processes. Finally, we demonstrate the utility of the kinematic datum by improving the accuracy of high‐spatial‐resolution 12‐day repeat‐cycle Sentinel‐1 Interferometric Synthetic Aperture Radar displacement and velocity maps.

Active tectonics along the Cul-de-Sac – Enriquillo plain and seismic hazard for Port-au-Prince, Haiti

The active faults in Haiti were not well known and no detailed mapping of active fault traces was available before the 2010, M7.0 earthquake. The lack of detailed fault mapping hindered the interpretation of the event and the seismic hazard assessment. Here, using high-resolution LIDAR topography, aerial photographs, bathymetric charts, together with geological data complemented with field observations, we carried out a morphotectonic analysis at a variety of scales. We analyzed the drainage network at the northern front of the Massif de la Selle – Sierra de Bahoruco (MSB) by mapping the fans of the main rivers and their associated drainage basins. We found that the areas of all the fans were compatible with the sizes of their drainage basins, except the paleofan of Port-au-Prince. We interpret that this paleofan has been offset by 7.9±0.3km across the main strike-slip Enriquillo-Plantain Garden Fault (EPGF) and we estimate a minimum horizontal slip rate of ∼3mm/yr over the Pleistocene. Moreover, in the Cul-de-Sac – Enriquillo plain, within which the capital city of Port-au-Prince is located, we mapped numerous NW-SE to WNW-ESE-striking Quaternary folds and thrust faults. Some of the thrust faults are north-dipping and located to the southern front of the Matheux-Neiba Lower Miocene fold. Other thrusts, such as those near Ganthier, Jacquet, Nan Cadastre, and Port-au-Prince, are south-dipping and located along the northern front of the MSB Lower Miocene fold. Previously, Saint Fleur et al. (2015) showed that the 2010 Haiti earthquake activated both one of the young thrusts (Lamentin) and the EPGF, consistent with oblique convergence between the Caribbean and the North American plates.

Geodynamic importance of the strike-slip faults at the eastern part of the Anatolian Scholle: Inferences from the uplift and slip rate of the Malatya Fault (Malatya-Ovacık Fault Zone, eastern Turkey)

Controversy remains over when present-day configuration of the Anatolia boundary faults came into existence, and the issue of what are the driving forces of the Anatolian westward motion. The NW-striking dextral and NE-striking sinistral second-order strike-slip faults at the eastern part of the Anatolian Scholle play a crucial role within these long-lasting discussions, and the NE-striking sinistral Malatya–Ovacık Fault Zone (MOFZ) is particularly important in this ongoing debate. Although the MOFZ is defined as one of the intra-plate structures, it has been proposed that it was an inter-plate fault between the Anatolia and Arabian plates from the latest Miocene to mid-Pliocene and that it has been inactive during the last ca. 3.5 Ma. This study provides results from the first morphochronology-based uplift and slip rate estimates on the Malatya Fault within the southern section of the MOFZ. The cosmogenic isochron burial and cosmogenic depth burial of ages from the sinistrally offset Tohma River remnant terraces enabled us to calculate 1.0 ± 0.01 and 1.12 ± 0.01 mm/yr minimum and maximum horizontal slip rates, respectively, for the last 1.4 ± 0.1 Ma. Furthermore, we conclude that the 96 ± 11 m/Ma mean uplift has been driven by the Malatya Fault. Integrated interpretation of the findings of this study and available data on both the MOFZ and other strike-slip faults at the eastern part of the Anatolian Scholle support the hypothesis that they are plate-boundary related active deformation belts that originated from paleotectonic structures during the tectonic escape of the Anatolian Scholle.

A NW-striking dextral strike-slip fault at the eastern end of the Altyn Tagh fault and its tectonic implications for northeastward growth of the Tibetan Plateau

The eastern end of the Altyn Tagh fault connects the western Qilian Shan thrust belt and its foreland basin, the Hexi Corridor, which contains numerous active faults with various strikes and kinematics. Although understanding of the geometry and kinematics of these active faults is increasing, the deformation pattern since the late Quaternary in the western end of the Hexi Corridor remains controversial. Studying the geometry and kinematics of these faults provides great benefit for understanding regional deformation patterns. The North Kuantan Shan fault (NKTSF) is located at the eastern end of the Altyn Tagh fault and the western end of the Hexi Corridor. Remote sensing images and field investigations suggest that the NKTSF strikes NW and acts as a right-lateral strike-slip fault with a reverse component. Optically stimulated luminescence (OSL) data combined with vertical offsets of the fault scarp imply a range of vertical slip rates of 0.015–0.093 mm/a, and cosmogenic 10Be ages and displacements of river terrace risers suggest a range of horizontal slip rates of 0.25–0.71 mm/a. The geometry and kinematics of the NKTSF enable us to estimate the deformation pattern in the western Hexi Corridor, which indicates that this area is undergoing northeastward compression related to the northern Tibetan Plateau (Qilian Shan). Active faults in the region are driven by the northeastward push of the Tibetan Plateau rather than the eastward extension of the Altyn Tagh fault.

Theoretical analysis and test verification of pull-out forces in shear connectors of composite beam under negative bending moment

A mechanical model of steel-concrete composite beams considering horizontal slip and vertical pull-out effects under negative bending moment was established based on the theory of elastic deformation. By using the principle of force equilibrium and deformation compatibility condition, the differential equation was derived and deduced using computational calculation program, in which the formula of the pull-out force in shear connectors under negative bending moment was obtained. The experiment was conducted in order to verify the reliability of theoretical results. The results show: under the same load condition, the pull-out force of a single stud increases with the increase of the stud spacing. All the theoretical results were verified by comparing with experiment results to illustrate the accuracy and reliability of the calculation method. It provides a theoretical reference for the study of the interface interaction considering horizontal slip and vertical pull-out effect in the negative bending moment region of continuous composite beams.

Three‐Dimensional Surface Deformation in the 2016 MW7.8 Kaikōura, New Zealand, Earthquake From Optical Image Correlation: Implications for Strain Localization and Long‐Term Evolution of the Pacific‐Australian Plate Boundary

AbstractWe generated dense, high‐resolution 3‐D ground displacement maps for the 2016 MW7.8 Kaikōura, New Zealand earthquake—the most geometrically and kinematically complex rupture yet recorded—from stereo WorldView optical satellite imagery using a new methodology that combines subpixel image correlation with a ray‐tracing approach. Our analysis reveals fundamental new details of near‐field displacement patterns, which cannot easily be obtained through other methods. From our detailed correlation maps, we measured fault slip in 3‐D along 19 faults at 500‐m spacing. Minimum resolvable horizontal slip is ~0.1 m, and vertical is ~0.5 m. Net slip measurements range from <1 to ~12 m. System‐level kinematic analysis shows that slip on faults north of the Hope fault was oriented primarily subparallel to the Pacific‐Australian plate motion direction. In contrast, slip on faults to the south was primarily at high angle to the plate motion and secondarily parallel to plate motion. Fault kinematics are in some locations consistent with long‐term uplift patterns, but inconsistent in others. Deformation within the Seaward Kaikōura Range may indicate an attempt by the plate boundary fault system to geometrically simplify. Comparison of published field measurements along the Kekerengu fault with our correlation‐derived measurements reveals that ~36% of surface displacement was accommodated as distributed off‐fault deformation when considering only field measurements of discrete slip. Comparatively, field measurements that project previously linear features (e.g., fence lines) into the fault over apertures >5–100 m capture nearly all (~90%) of the surface deformation.

Late Quaternary slip rates and Holocene paleoearthquakes of the eastern Yumu Shan fault, northeast Tibet: Implications for kinematic mechanism and seismic hazard

The Yumu Shan (YMS) fault zone at the northeastern margin of the Tibetan Plateau is characterized by actively growing fault-related folds and northeast-vergent thrusts or buried faults. This fault zone is expressed by an arc-shaped fault line and can be divided into two segments: the northern and eastern YMS faults. Numerous studies indicated that the northern YMS fault is marked by reverse faulting with a left-lateral component and has undertaken two surface-rupturing events in the Holocene. But previous studies on the eastern YMS fault were conducted in the 1990s, and the limitations of dating and survey techniques led to a large uncertainty in fault slip rates and paleoseismological results. In addition, the kinematic mechanism of the arc-shaped YMS fault zone remains unknown. In this study, combining with the interpretation of high-resolution satellite imagery, real-time kinematic (RTK) GPS survey, optically stimulated luminescence (OSL) and Accelerator Mass Spectrometry (AMS) radiocarbon dating of deformed landforms and trenching, we study slip rates and paleoseismology along the eastern YMS fault. Our results show that its Late Quaternary vertical and horizontal slip rates are ∼0.3–0.4 mm/yr and ∼1.1 ± 0.1 mm/yr, respectively. At its northwest tip, the fault consists of several sub-parallel branches and becomes dominantly reverse or thrusting with a vertical rate of ∼1.1 mm/yr. Trenching data indicate that two events ruptured the eastern YMS fault occurring at 7.37–5.24 ka and 5.17–4.01 ka, respectively. The eastern YMS fault may behave synchronously or interact with the northern YMS fault. We propose that the arcuate structure under the perpendicular compression to the arch apex might illustrate the kinematic mechanism of the YMS fault zone.

Geological and geomorphic evidence for activity of the Mengzi fault along the southeastern margin of the Tibetan Plateau

Few studies have been conducted on the activity of the Mengzi fault system, which is located to the southeast of the Sichuan-Yunnan block. The Mengzi fault is distributed along the eastern margin of the Mengzi basin. However, little is known about the location, length, and activity of the fault or the occurrence of paleo-earthquakes during the late Quaternary. This paper studies the geometric distribution and activity of the fault via remote sensing imagery interpretation, fault outcrops in the area, faulted landforms and chronological analyses. The results show that the Mengzi fault extends from Nandong (Kaiyuan basin) in the north through the eastern margin of the Mengzi basin to Pingbian in the southeast, eventually intersecting with the Honghe fault. The Mengzi fault is approximately 250 km long and is characterized as a reverse strike-slip fault. We survey and calculate the offset gullies and terraces dislocated by the fault; combined with sample dating, we calculate the horizontal slip rate of the fault since 30 ka BP to be 0.91–1.56 mm/a. Three paleo-events since 30–40 ka BP are observed with a 10-ka major earthquake recurrence period. We analyze the relationships among the Mengzi fault, southern Xiaojiang fault, and Qujiang-Jianshui fault and note a slip rate loss of ≥8 mm/a from the southern Xiaojiang fault that was absorbed by reverse dextral strike-slip faulting and lateral shortening of the Qujiang-Jianshui fault and the Mengzi fault. The Mengzi fault plays an important role in the adjustment of the large slip rate reduction along the southern Xiaojiang fault. Moreover, the Mengzi fault has a similar tectonic position to the seismogenic faults of the 2008 Wenchuan earthquake, 2013 Lushan earthquake and 2014 Ludian earthquake, and the Mengzi fault and southern Xiaojiang fault both accumulate the energy generated by the southeastward movement of the Sichuan-Yunnan block. Studies on the Mengzi fault are helpful for renewing our understanding of the tectonic patterns of the southeastern Sichuan-Yunnan block and delimiting the boundary of the southeastern block margin. Furthermore, because the cities of Mengzi and Kaiyuan are located along the Mengzi fault, this study has practical significance for earthquake disaster mitigation.

Deep deformation of the Longmenshan fault zone related to the 2008 Wenchuan earthquake

This paper reviews studies of the past ten year related to the crustal deformation of the Longmenshan fault zone (LMSFZ) which was struck by the M 8.0 Wenchuan earthquake on May 12, 2008. The tectonics of the LMSFZ located at the eastern margin of the Tibetan Plateau is complex, with complicated fault geometry and a heterogeneous velocity structure. The Wenchuan earthquake rupture extended for about 300 km along the middle and northern segments of the LMSFZ, with a very complicated rupture process involving multiple sub-events. The Wenchuan slip distribution is characterized by two major slip patches near Hongkou/Yingxiu and Beichuan with peak slip of 5.0–15.5 m and extended from near the surface to below 20 km depth. Prior to the Wenchuan earthquake, the LMSFZ had been seismically quiet for several centuries and there were no hints that suggested that such an M 8.0 earthquake might strike the area. The long-term geological investigations and short-term geodetic measurements before the Wenchuan earthquake generally agree that the horizontal slip rate along the LMSFZ is no more than 3 mm per year. The low slip rate observed at the surface around the LMSFZ may not reveal the real state of accumulated strain at depth where the devastating Wenchuan earthquake nucleated. Rates of aseismic slip at depth derived from seismological investigation of repeating microearthquakes were found to be approximately twice as large as the interseismic rates inferred from surface GPS and geological data. Most of the clusters of repeating microearthquakes are located at the edge of locked areas where large coseismic slips were observed during the Wenchuan earthquake, suggesting a close relationship between microearthquakes and impending large earthquakes. A two-dimensional viscoelastic finite-element model produces a depth-related slip rate pattern around the LMSFZ that is consistent with that revealed by the seismological observation of repeating earthquakes. The measured in situ deep slip rates increase with depth and vary from 3.5 to 9.6 mm/a over a depth range of 4–18 km.The seismological observations of deep slip rates and microseismicity in the three decades before the Wenchuan earthquake reveal that the LMSFZ is indeed not as “quiet” as traditionally assumed in comparison with its neighboring fault systems. Considering the deep slip rates (3.5−9.6 mm/a) from the repeating microearthquakes and coseismic peak offsets of 5.0–15.5 m, the recurrence interval of Wenchuan-like events is estimated to be about 500−4500 years. The estimated recurrence interval based on the deep slip rates is much smaller than those estimates using the same coseismic displacements divided by GPS-derived or geological slip rates. Slip rate increases with depth were also recognized in the Parkfield section of the San Andreas fault zone and in the northeastern Japan subduction zone before the ruptures of the 2004 M w6.0 Parkfield earthquake and the 2011 M w9.0 Tohoku-oki earthquake, respectively. Accelerated slip is thought to have preceded a number of recent large subduction zone earthquakes and the 2008 Wenchuan earthquake, and repeating earthquakes may document short-term precursory slip at depth. Alternatively, the rapid slip rates indicated by the repeating microearthquakes may represent transiently accelerated slip preceding the Wenchuan mainshock. We suggest that slip rates at seismogenic depths are of critical importance in seismic hazard analysis. Repeating earthquakes can be regarded as “deep creepmeters” that measure the in - situ deep slip rate on otherwise aseismically slipping faults. For less well defined and widespread faults within the continents, it is essential to reveal a fault’s or region’s seismic history over different time scale. Combining a better understanding of earthquake diversity with modern technology is the key to effective and comprehensive hazard mitigation practices. The potential earthquake hazard of locked faults with unusually high inferred deep slow slip rates should be paid more attention. The 2008 Wenchuan earthquake is the best-studied continental earthquake to date with a large number of scientific publications enabled by the vast collected data sets. The research community efforts have provided first-order information about this unexpected event regarding its coseismic slip distribution and fault geometry. However, there are many remaining questions about the basic nature of this earthquake to be further constrained with multiple data sets, including the relationship of its rupture with prior coupling and interseismic creep, the varying dynamical rupture processes with depth, the frequency dependence of seismic radiation across the fault zone, and the role of multiple postseismic deformation processes.