Characteristics Of Crustal Deformation Research Articles

Present-day crustal movement and seismic moment balance on major active faults around the easternmost segment of the Kunlun fault, Tibetan Plateau, China

After the 2021 Ms 7.4 Madoi, China earthquake located south of the eastern Kunlun fault, the coseismic Coulomb stress changes show that the earthquake potential is enhanced towards the easternmost segment of the Kunlun fault. Before the 2008 Mw 7.9 Wenchuan, China earthquake, the easternmost segment of the Kunlun fault is considered to being a region with the highest frequency occurrence of moderate-to-strong earthquakes in mainland China, where there are still at least three seismic gaps at present, indicating an urgent earthquake hazard. The tectonic deformation pattern is closely related to the development and occurrence of earthquakes. In this study, we collect all the available GPS data to obtain a crustal movement velocity field with high precision and high resolution by removing nontectonic effects within the study area. The GPS velocity profile and two-dimensional strain rates are then derived from the updated GPS velocities to analysis the characteristics of crustal deformation. Our results demonstrate that the Longriba fault zone slips predominantly right-laterally with the rate of 5.2 ± 0.5 mm/yr and the crustal shortening rate is ∼0.5 mm/yr across the Longriba and Longmenshan faults. Along with notable crustal extension and contraction, the principal strain rate field is distributed in a wide area on the northwest part of the Longmenshan fault, and decreases southwestward along the Longmenshan fault zone. In addition, we provide the time series of 8 campaign GPS stations which have never been published before. Moreover, the moment deficit estimate is a well-established way of assessing the earthquake hazard at a specific fault. Accompanying with the inverted slip rates and locking depth, we estimate the rates of moment accumulation on major faults and compare them with the seismic moment released on each fault derived from the Chinese historical earthquake catalog which extends for more than 2000 years in many regions. We find that the moment deficit is mainly concentrated on the Longriba fault with a value of 4.18 × 1017 Nm/yr. The Longriba fault have accumulated enough seismic energy to generate one Mw > 7.7 earthquake on it, or two Mw > 7.5 earthquakes on its two branches in the future. This study is an essential indicator for understanding the present-day tectonic deformation pattern in the Tibetan Plateau and is also helpful for seismic hazard assessment.

Analysis of seasonal crustal deformation characteristics in Dali, Yunnan using GPS observations

Analysis of seasonal crustal deformation characteristics in Dali, Yunnan using GPS observations

Geodetic constraints on contemporary three-dimensional crustal deformation in the Laji Shan–Jishi Shan tectonic belt

The Laji Shan–Jishi Shan tectonic belt (LJTB), located in the southern part of the northeastern Tibetan Plateau (NETP), is a tectonic window to reveal regional tectonic deformation in the NETP. However, its kinematics in the Holocene remains controversial. We obtain the latest and dense horizontal velocity field based on data collected from our newly constructed and existing GNSS stations. Combined with fault kinematics from geologic observations, we analyze the crustal deformation characteristics along the LJTB. The results show that: (1) The Laji Shan fault (LJF) is inactive, and the northwest-oriented Jishi Shan fault (JSF) exhibits a significant dextral and thrust slip. (2) The transpression along the arc-shaped LJTB accommodates deformation transformation between the dextral Riyue Shan fault and the sinistral west Qinling fault. (3) With the continuous pushing of the Indian plate, internal strains in the Tibetan Plateau are continuously transferred in the northeast via the LJTB as they are gradually dissipated near the LJTB and translated into significant crustal uplift in these regions.

Gravity inversion constrained by OBS receiver function reveals crustal structure in Ryukyu Trench

The Ryukyu Trench is located in the northern Philippine Sea. The subduction of the Philippine Sea Plate to the Eurasia Plate along the Ryukyu Trench in the NNW direction leads to extremely complex tectonic processes such as subduction, collision, accretion, and back-arc expansion. It is of great significance to obtain the crustal structure of the Ryukyu Trench for understanding the crustal deformation characteristics, subduction direction and the scale of the Philippine Sea Plate. The ocean bottom seismometer (OBS) could provide important information on the deep structure of the oceanic area, and the wide coverage of gravity anomaly can provide more constraints for the regional crustal structure. In this study, we put the time-delay term of the sedimentary layer into the H-κ stacking formula, which eliminates the influence of the sedimentary layer in traditional H-κ stacking. Based on the accurate crustal thickness at OBS locations, a gravity inversion method is proposed to solve the problem of non-uniqueness in gravity data and limited distribution of OBSs. By using this method, we obtain a crustal structure with higher resolution than Crust1.0 model in Ryukyu Trench. The results show that the crustal thickness in the Ryukyu Trench region thickens along the NNW subduction direction, revealing that the Philippine Plate’s subduction direction towards the Eurasian Plate is in the NNW direction.

Geodetic and seismic constraints on contemporary deformation on the northeastern Tibetan plateau: Velocity and strain rate tensor analysis

The study of the velocity and strain rate of the northeastern Tibetan Plateau can explain its crustal deformation characteristics. Previous investigations have relied on mathematical interpolation in GPS velocity to obtain a continuous strain field; these approaches can be applied well to regions where the deformation is relatively smooth and are not entirely suitable for the northeastern Tibetan Plateau that is cut by several large strike-slip faults. Thus, this study incorporates seismic constraints into the GNSS velocity and strain analysis to obtain a more realistic deformation field and compares it with the uplift rate and the stress results in depth, it will provide a comprehensive view of contemporary deformation on the northeastern Tibetan Plateau. It shows that there are two prominent deforming zones localized on the middle segments of the Haiyuan and East Kunlun faults, which may result from the different strengths in fault segmentation. The velocity and strain rate in the four profiles show that the convergence strain obviously decay from ∼15.5 mm/yr and ∼ 15.48 nstrain/yr in the western Qilian Mountains to ∼5.73 mm/yr and ∼ 5.76 nstrain/yr in the eastern Long Zhong Basin, respectively. The comparison between the vertical uplift rate, SKS result, and strain rate field indicates that the northeastern Tibetan Plateau is not only dominated by crustal shortening corresponding to the topography and surface fault geometry, but also by the strain transfer of motion along these significant strike-slip faults accounting for the extrusion and growth of the Tibetan Plateau. Combined with recent seismological results, our results indicate that the deformation of the study region resembles that of the Tibetan Plateau and can be viewed as a combined process linking both NE- or NEE-directed crustal shortening, vertical uplift, lateral extrusion along strike-slip faults and partial melting or mantle upwelling at depth.

Fine divided method of active tectonic blocks based on adaptive density peak clustering and improved Euler model, revealed by GNSS velocities in Southwest Japan

The rational division of active tectonic blocks is an important premise for distinguishing active faults, discovering hidden faults, and an in-depth understanding of regional crustal deformation characteristics, seismicity, and tectonic dynamics. In recent years, clustering algorithms have been widely used in active block division owing to their high efficiency and reliability. However, the classical clustering algorithm sensitivity to the block boundary under different conditions is inconsistent. Additionally, the Euler model constraint (EMC) process involved in the classical clustering algorithm ignores the influence of the boundary points and gross error points of the active block. Therefore, in this study, a new active block division method based on adaptive density peak clustering (ADPC) and an improved Euler model constraint (IEMC) is proposed. The simulation test results show that compared with the traditional clustering algorithm, the mean error rate of the new method can be reduced by up to 40% in the simple single-fault model and by 10% in the complex three-segment model. The new method was further applied to an actual case of an active block division in southwest Japan. The results further show that the new method is less affected by the regional environmental conditions. Compared with previous results in southwest Japan, the proposed method has higher accuracy and higher reliability of the active block division results. The new method for active block division proposed in this study can be used to accurately explore the location and quantity of block boundaries.

Secular crustal deformation characteristics prior to the 2011 Tohoku-Oki earthquake detected from GNSS array, 2003–2011

In order to reveal the secular deformation evolution and strain accumulation progress along subduction zone, we focus on high-precision Global Navigation Satellite System (GNSS) data processing, GNSS time series analysis and regional spatiotemporal filtering. The GNSS position time series is modeled as a combination of the long-term plate movements, short-term noise and the frequency-dependent variations and tectonic deformation information. Common Mode Errors (CME) is removed and the deformation signals is then extracted from the residual time series by Principal Component Analysis (PCA). Combing the filtered displacement array and the dynamic regional strain array derived from GNSS baseline, a spatiotemporal tectonic evolution map is exhibited obviously. We process the data recorded by GEONET over the 2003–2011 period in middle Japan island and reveal the dynamic evolution of crustal deformation along subduction zone. The results show that the regional reference frame transformation by constraining one site location and one stable GNSS baseline direction can further improve the Signal-to-Noise Ratio (SNR) of GNSS observations. A integrated analysis combining the baseline length with azimuth change can show the crustal motion feature more comprehensively. The observed behaviors agree well with the simulation experiment results of the rock rupture in the laboratory. We divide the pre-seismic deformation into four stages, the stable linear strain accumulation stage, the formation stage of the local locked area, local decoupling stage, and strain release stage. We also give an appropriate dynamical model for the interplate coupling to explain the observed deformation characteristics. Research result provides some of the observational new evidence for inter-seismic deformation anomaly detection and the medium- to longer-term seismic hazard assessments.

Crustal deformation characteristics in the southwest segment of the Longmenshan structural belt before Lushan Mw6.6 earthquake and seismogenic structural model

Crustal deformation characteristics in the southwest segment of the Longmenshan structural belt before Lushan Mw6.6 earthquake and seismogenic structural model

Active tectonic deformation around the Tarim Basin inferred from dense GPS measurements

The surrounding area of the Tarim Basin is featured by active tectonic deformation and intense seismic activity. The study of the crustal deformation characteristics of this area will help revealing the role of the Tarim Basin in the crustal evolution. In order to accurately obtain the deformation characteristics of this area, we firstly obtained the highly detailed and accurate three-dimensional (3D) crustal deformation velocities of the Tarim Basin and its surrounding areas through high-precision processing of existing Global Positioning System (GPS) data. Thereafter, the slip rate and strain rate fields of the main faults in the region were calculated based on the updated velocity results. The strain rate of the Altyn Tagh fault is dominated by shear strain and the strike slip rate is 8–10 mm/yr. The strain rate between the Tien Shan and Tarim Basin is dominated by extrusion strain, and the extrusion rate is 4–6 mm/yr. In addition to the large shear strain, there is also a certain tensile strain in the Tibetan Plateau. Geodetic results show that the main driving force for the deformation of the Tien Shan is the northward thrust of the Tarim Basin. The relative movement mode between the Tarim Basin and Tibetan Plateau mainly comprises the strike slip movement along the strike direction of the Altyn Tagh fault, with a small extrusion deformation. Therefore, the Tarim Basin has little influence on the north–south shortening deformation of the Tibetan Plateau.

Present-Day Deformation of the Gyaring Co Fault Zone, Central Qinghai–Tibet Plateau, Determined Using Synthetic Aperture Radar Interferometry

Because of the constant northward movement of the Indian plate and blockage of the Eurasian continent, the Qinghai–Tibet Plateau has been extruded by north–south compressive stresses since its formation. This has caused the plateau to escape eastward to form a large-scale east–west strike-slip fault and a north–south extensional tectonic system. The Karakorum–Jiali fault, a boundary fault between the Qiangtang and Lhasa terranes, plays an important role in the regional tectonic evolution of the Qinghai–Tibet Plateau. The Gyaring Co fault, in the middle of the Karakoram–Jiali fault zone, is a prominent tectonic component. There have been cases of strong earthquakes of magnitude 7 or greater in this fault, providing a strong earthquake occurrence background. However, current seismic activity is weak. Regional geodetic observation stations are sparsely distributed; thus, the slip rate of the Gyaring Co fault remains unknown. Based on interferometric synthetic aperture radar (InSAR) technology, we acquired current high-spatial resolution crustal deformation characteristics of the Gyaring Co fault zone. The InSAR-derived deformation features were highly consistent with Global Positioning System observational results, and the accuracy of the InSAR deformation fields was within 2 mm/y. According to InSAR results, the Gyaring Co fault controlled the regional crustal deformation pattern, and the difference in far-field deformation on both sides of the fault was 3–5 mm/y (parallel to the fault). The inversion results of the back-slip dislocation model indicated that the slip rate of the Gyaring Co fault was 3–6 mm/y, and the locking depth was ~20 km. A number of v-shaped conjugate strike-slip faults, formed along the Bangong–Nujiang suture zone in the central and southern parts of the -Tibet Plateau, played an important role in regional tectonic evolution. V-shaped conjugate shear fault systems include the Gyaring Co and Doma–Nima faults, and the future seismic risk cannot be ignored.

Present-day crustal deformation characteristics of the southeastern Tibetan Plateau and surrounding areas by using GPS analysis

The southeastern Tibetan Plateau and surrounding areas comprise a typical tectonic belt in mainland China, characterized by a complex geological background and intense tectonic activity. We study present-day crustal deformation characteristics of this region based on GPS data for the periods 1999–2007 and 2009–2011. We first analyze the variations in crustal motion and strain rate, and then discuss the 3D crustal motion and local sub-block activities, as well as the correlation between the intensity of crustal activity and the strain rate distribution. Finally, we explain the present-day geodynamic characteristics of the region. Our results indicate that the entire region shows overall clockwise motion with respect to the stable Eurasian Plate. The tectonic boundary belts between this region and the South China Block display significant compressional strain, accompanied by associated extensional strain. Relatively high maximum shear strain and the transition zones of the significant plane strain gradients are also mainly concentrated along the Ganzi–Yushu–Xianshuihe, Anninghe–Zemuhe–Xiaojiang, Lijiang–Xiaojinhe, and Red River faults, as well as the western and southern Yunnan Province. 3D crustal velocities further reflect significant differences in tectonic activity between different structural belts. We conclude that the regions showing higher shear strain and the transition zones of the significant plane strain gradients correspond to the areas with frequent earthquakes. According to the crustal deformation and strain characteristics, we infer that the present-day geodynamic setting of the region is related to the ongoing India–Eurasia collision and the associated resistance of the stable Alashan, Ordos, and South China blocks, resulting in the extrusion of the southeastern Tibetan Plateau crustal material with an overall clockwise flow around the Eastern Himalayas and significant compressional strain along the tectonic boundary belts. Furthermore, notable compressional strain and enhanced sub-block motions occurred around the Longmenshan fault area following the Wenchuan earthquake.

Crustal azimuthal anisotropy in the trans-North China orogen and adjacent regions from receiver functions

The North China Craton (NCC) is an important part of eastern China. Recent studies have shown that the eastern NCC (ENCC) has undergone significant lithospheric thinning and destruction since the late Mesozoic. Destruction of the cratonic lithosphere is necessarily accompanied by crustal deformation. Therefore, a detailed crustal deformation model can provide basic observational constraints for understanding the process and mechanisms of the destruction of the NCC. In this study, we estimated the crustal azimuthal anisotropy beneath 198 broadband stations in the NCC with a joint analysis of Ps waves converted at the Moho from radial and transverse receiver function data. We also performed a harmonic analysis to test the reliability of the measured anisotropy. We obtained robust crustal azimuthal anisotropy beneath 23 stations that are mostly located on the western margin of the Bohai Bay Basin, Yin-Yan orogenic belt, and Taihang Mountains, which reflects the crustal deformation characteristics in those regions. The crustal shear wave splitting time was found to range from 0.05 s to 0.68 s, with an average value of 0.23 s, which reveals a distinct crustal anisotropy in the Trans-North China Orogen (TNCO) and its adjacent areas. Our analysis of the results suggests that the strong NW-SE tectonic extension in the late Mesozoic and Cenozoic played an important role in crustal anisotropy in this region. In addition, the E-W trending crustal anisotropy on the margin of the Bohai Bay Basin indicates an effect of the ENE-WSW trending horizontal principal compressive stress. The crustal anisotropy in the Yin-Yan orogenic belt may be an imprint of the multiple-phase shortening of a dominant N-S direction from the early-to-middle Jurassic to the Early Cretaceous. Stations in the Taihang Mountains show large splitting times and well-aligned NW-SE fast directions that correlate with those measured from SKS splitting and that are possibly related to the lithospheric modification and magmatic underplating from the Late Mesozoic to Cenozoic in this area.

The Analysis of the Abnormal Characteristics of GPS Data before the 2013 Minxian-Zhangxian MS6.6 Earthquake

To study the movement characteristics of crustal deformation around the epicenter before the Ms6.6 earthquake in Minxian-Zhangxian in 2013, the paper analyzes the GPS velocity field, the baseline time series between stations and the time series of the epicentral region strain, and then discusses the characteristics of the crustal deformation before the earthquake. It is shown from the results that the Lintan-Tanchang fault and the Northern Xiqinling fault are in the inner circle of the clockwise vortex, which have obvious stress accumulation. Among the two velocity fields in 2004-2007 and 2009-2011, there are significant differences in the direction and amplitude of the movement around the Lintan-Tanchang fault, which may cause the risk of earthquake events. The baseline time series reflect the strain accumulation in NE side of Lintan-Tanchang thrust fault with NE-trending was quite high before the earthquake, and the velocity of the SW side was accelerating, which might be the main cause of the earthquake. Since 2013, the extrusion deformation of EW direction and plane shrinkage rate near the epicenter had shown an obvious weakening tendency, as well as the left-lateral shear of NW direction of the causative fault. The evidence of deformation loss before the earthquake was significant and the accumulation of strain was relatively obvious.

Crustal deformation characteristics of Sichuan-Yunnan region in China on the constraint of multi-periods of GPS velocity fields

In order to obtain deformation parameters in each block of Sichuan-Yunnan Region (SYG) in China by stages and establish a dynamic model about the variation of the strain rate fields and the surface expansion in this area, we taken the Global Positioning System (GPS) sites velocity in the region as constrained condition and taken advantage of the block strain calculation model based on spherical surface. We also analyzed the deformation of the active blocks in the whole SYG before and after the Wenchuan earthquake, and analyzed the deformation of active blocks near the epicenter of the Wenchuan earthquake in detail. The results show that, (1) Under the effects of the carving from India plate and the crimping from the potential energy of Tibetan Plateau for a long time, there is a certain periodicity in crustal deformation in SYG. And the period change and the earthquake occurrence have a good agreement. (2) The differences in GPS velocity fields relative Eurasian reference frame shows that the Wenchuan earthquake and the Ya'an earthquake mainly affect the crustal movement in the central and southern part of SYG, and the average velocity difference is about 4–8 mm/a for the Wenchuan earthquake and 2–4 mm/a for the Ya'an earthquake. (3) For the Wenchuan earthquake, the average strain changed from 10 to 20 nanostrian/a before earthquake to 40–50 nanostrian/a after the earthquake, but before and after the Ya’an earthquake, the strain value increased from about 15 nanostrian/a to about 30 nanostrian/a. (4) The Wenchuan earthquake has changed the strain parameter of each active block more or less. Especially, the Longmen block and Chengdu block near the epicenter. The research provides fundamental material for the study of the dynamic mechanism of the push extrusion from the north-east of the India plate and the crimp from Qinghai Tibet Plateau, and it also provides support for the study of crustal stress variation and earthquake prediction in Sichuan Yunnan region.

Research on Recent GPS Crustal Deformation Characteristics in the Northeastern Edge of Qinghai-Tibet Plateau

Based on the GPS data in the northeastern edge of Qinghai-Tibet Plateau, the velocity field and the extension change rate of baseline between stations are analyzed. The crustal movement characteristics and their dynamic changes in this region are discussed. The result indicates that the baseline in the regions demonstrates an overall characteristic of shrinking in the NE direction and extending in the NW direction; The extrusion of Bayan Har Block in SE direction since 2009 has amplified obviously, which leads to the enhancement of correlated movement in SE direction in the NW side of Longmenshan Fault. In addition, Tianzhu empty regions and the area near the epicenter of Menyuan Ms6.4 earthquake in 2016 are right in the boundary of this differentiated movement. Recently, a certain amount of strain energy might have been accumulated in the nearby area of the northern margin of Alkin Fault Zone, west boundary of Erdos Block and west to105°N on Northern Xiqinling Fault. The seismic risk in the west and east section of the intersecting area between Bayan Har Block and Qaidam Block is high. The west section of Northern Xiqinling Fault belongs to the inner ring of clockwise vortex and possesses medium-strong seismic risk.

Mechanism of crustal deformation in the Sichuan-Yunnan region, southeastern Tibetan Plateau: Insights from numerical modeling

The characteristics of crustal deformation and its dynamical mechanisms in the Sichuan-Yunnan region are of interest to many researchers because they can help explain the deformation pattern of the eastern Tibetan Plateau. In this paper, we employ a precise three-dimensional viscoelastic finite element model to simulate the crustal deformation in the Sichuan-Yunnan region, southeastern Tibetan Plateau. We investigate the influence of lower crustal flow and rheological variations by comparing the modeled results with GPS observations. The results demonstrate that lower crustal flow plays an important role in crustal deformation in the Sichuan-Yunnan region. The best fitting is achieved when the flow velocity of the lower crust is approximately 10–11mm/a faster than that of the upper crust. Additionally, crustal rheological properties affect regional crustal deformation. When the viscosity of the middle and lower crust in the South China block reaches 1022 and 1023Pa·s, respectively, the modeled results match observations well, especially for the magnitude of crustal motion within the South China block. Finally, our dynamic model shows that the maximum principal stress field of the Sichuan-Yunnan region exhibits clear zoning, gradually shifting from an approximately east-west orientation in the northern Bayan Har block to southeast in the South China block, southwest in the western Yunnan block, and a radially divergent distribution in the Middle Yunnan and Southern Yunnan blocks.

THE DISTRIBUTION CHARACTERISTICS OF DEFORMATION FIELD CAUSED BY THREE GREAT EARTHQUAKES IN THE QINGHAI‐TIBET PLATEAU AND ITS VICINITY SINCE 2001

AbstractBased on a viscous‐elastic crustal model with constraint conditions from GPS and seismic dislocation data and adopting the finite element method, we analyzed the crustal deformation characteristics caused by 2001 Kunlun Mountain MS8.1, 2008 Wenchuan MS8.0 and 2015 Nepal MS8.1 earthquakes, obtained the displacement and deformation field. These earthquakes have occurred in the north, east, and south margins of the Tibetan Plateau respectively. Our primary results suggest obvious differences in deformation regimes, seismogenic fault geometry and source parameters, as well as crustal deformation patters despite the substantially similar magnitudes. These differences caused by seismogenic fault nature and subsurface structures are mainly manifested by different scopes of deformed regions and different strain amplitudes. Through these simulation results, we can detect more about the distribution characteristics of stress loading and unloading area caused by large earthquakes. Moreover, it plays an important role in forecasting the earthquake possibility of seismogenic region.

PRESENT‐DAY CRUSTAL STRAIN RATE FIELD IN THE TAIWAN ACTIVE COLLISION ZONE AND ITS GEODYNAMIC MECHANISMS: INSIGHT FROM FEM SIMULATIONS

AbstractThe Taiwan Island is the product of convergence and collision between the Eurasian and the Philippine Sea plates, where the geological structure is complex, seismicity is high and deformation strong. In order to quantitatively study characteristics of crustal deformation and to understand its geodynamic mechanisms of this area, we calculated the strain rate field in and around Taiwan by using the finite element method (FEM), utilizing GPS data from 1995 to 2005 as boundary constraints in simulation. The results show that contractions are predominant in central Taiwan, while extension exists in northeast and south, respectively. The largest deformation appears on the Coast Range and the adjacent waters in eastern Taiwan. The calculated slip rates on the Longitudinal Valley Fault (LVF) are 13.81∼23.48 mm/yr, meaning part of the convergence is absorbed by LVF, thus deformation to the west of LVF decays rapidly westwards and northwestwards. Moreover, the results show that the calculated velocities and GPS vectors are in good agreement, and calculated orientations of principal stresses are consistent with in‐situ stress measurements and focal mechanism solutions, demonstrating the finite element model established in this paper is reasonable. In addition, the calculated results imply that the general framework of present‐day deformation in Taiwan results from interactions by many factors such as plate collision between the Eurasian and the Philippine Sea plates, geometry of plate boundaries, faulting and rifting, opening of the Okinawa trough and retreat of the Ryukyu trench.

D-InSAR monitoring of crustal deformation in the eastern segment of the Altyn Tagh Fault

In recent years, the differential Interferometric Synthetic Aperture Radar (D-InSAR) technique has been widely used in monitoring deformation on the Earth's surface. Compared with conventional approaches (such as global positioning system (GPS) monitoring), application of the D-InSAR technique has many advantages in surface deformation monitoring. In this paper, the D-InSAR technique is applied to study the crustal deformation characteristics of the eastern segment of the Altyn Tagh Fault (ATF), which is an important boundary of crustal deformation in the north-eastern area of the Tibetan Plateau. To the north of the boundary, the deformation gradually decreases from 2.8 cm in the west to 0.8 cm in the east; to the south of the boundary, the deformation presents different characteristics at the two sides of the western part of the North Qilian Shan Fault (NQF). At the south-west side, the deformation is intense, with relatively weaker deformation of 1.6∼2.1 cm inside the Changma Basin and stronger deformation of 2.2∼6.0 cm outside the Changma Basin. At the north-east side, the deformation is smaller than that in the other side, with a decrease from 1.3 cm in the west to nearly 0 cm in the east. North-east to the western part of the NQF, there exists negative deformation. This is because when the northern margin of the Tibetan Plateau was moving to the north-east, it was blocked off by the rigid Alashan Block and was bent down close to the north-east of the Qilian Shan Orogen to form a foreland basin. This paper also shows that currently the ATF is active and has left-lateral strike-slip. The slip rate of the eastern segment of the ATF is 4.7 mm/year. For different locations, the slip rate is different.

GPS Medium-Range Kinematic Positioning for the Seafloor Geodesy of Eastern Taiwan

To realize the plate motion of the Philippine Sea Plate (PSP) and the characteristics of crustal deformation in the plate boundary zone between the PSP and Eurasia Plate, three seafloor geodetic arrays using a combination of GPS kinematic positioning and acoustic ranging techniques have been established off eastern Taiwan since 2008. Each array is composed of three transponders deployed on the ocean bottom in a triangular shape and has been observed at least two times since 2009. The GPS kinematic positioning in the relative distance ranging from 80 to 120 km off the eastern coast of Taiwan plays a main role in the whole seafloor geodetic deformation system. Seven stations from Taiwan Continuous GPS Array are taken as reference sites and three or four rover GPS units are set up on the vessel or buoy. Both on-land reference and onboard rover receivers record data in sampling rates of 1 and 5 Hz to determine the instantaneous positions of transducer onboard which transmits and receives the acoustic signal to and from seafloor transponders and the attitude of vessel or buoy in kinematic mode. We compare the results of medium-range kinematic positioning between the on-land reference stations and rovers onboard by the GrafNav and Bernese V5.0 software, respectively. In addition, we determine the attitude at all times by way of computing the inter-distance of rover receivers onboard. Hence there are two positioning results can be estimated which are direct (by short relative distances from onboard) and indirect (by medium-range kinematic mode for each GPS unit from on-land continuous stations) methods, and the difference reveals in decimeter level.