Crustal strain rates of southeastern Tibetan Plateau derived from GPS measurements and implications to lithospheric deformation of the Shan-Thai terrane

The link between the crustal deformation and mantle kinematics in the Tibetan Plateau has been well known thanks to dense GPS measurements and the relatively detailed anisotropy structure of the lithospheric mantle.However, whether the crust deforms coherently with the upper mantle in the Shan-Thai terrane(also known as the Shan-Thai block) remains unclear.In this study, we investigate the deformation patterns through strain rate tensors in the southeastern Tibetan Plateau derived from the latest GPS measurements and find that in the Shan-Thai terrane the upper crust may be coupled with the lower crust and the upper mantle.The GPS-derived strain rate tensors are in agreement with the slipping patterns and rates of major strike-slip faults in the region.The most prominent shear zone, whose shear strain rates are larger than 100×10^(–9) a^(–1), is about 1000-km-long in the west, trending northward along Sagaing fault to the Eastern Himalayan Syntaxis in the north, with maximum rate of compressive strain up to –240×10^(–9) a^(–1).A secondary shear zone along the Anninghe-Xiaojiang Fault in the east shows segmented shear zones near several conjunctions.While the strain rate along RRF is relatively low due to the low slip rate and low seismicity there, in Lijiang and Tengchong several local shear zones are present under an extensional dominated stress regime that is related to normal faulting earthquakes and volcanism, respectively.Furthermore, by comparing GPS-derived strain rate tensors with earthquake focal mechanisms, we find that 75.8%(100 out of 132) of the earthquake T-axes are consistent with the GPS-derived strain rates.Moreover, we find that the Fast Velocity Direction(FVDs) at three depths beneath the Shan-Thai terrane are consistent with extensional strain rate with gradually increasing angular differences, which are likely resulting from the basal shear forces induced by asthenospheric flow associated with the oblique subduction of the India plate beneath the Shan-Thai terrane.Therefore, in this region the upper crust deformation may be coherent with that of the lower crust and the lithospheric mantle.

Research on present crustal deformation in the southern Tianshan (Jiashi) region by GPS geodesy

The pattern and range of present crustal movement as well as characteristic of deformation-strain play a key role in cognizing seismogenic mechanism in the Jiashi region, Xinjiang, northwestern China. Using GPS geodesy in 1994 and 1998, here we give geodetic evidence of rapid convergence of about 19 mm/a across the westem Tianshan, which is about 50% greater than the seismic moment solution (13 m/a) by assembling major enrthquake in the 20th century. The discrepancy of deformation rate between geodetic observation and seismic energy releasing indicates the possibilities that, there exists a lot of aseismic strain and strain during seismic interval in the westem Tianshan, or seismic fault slip in this century could not be enough to compensate the present deformation in the whole area. Whichever it maybe, from the view of accumulation of stress-strain, it suggests that there will be potential strong eathquakes in the western segment of Tianshan and the northeastern corner of Pamir in a long period.

Crustal Deformation Derived from GPS in the Chinese Mainland from 1991-2004

Based on GPS data from 1991- 2004 and the least-squares collocation method,we analyze the crustal deformation in the Chinese mainland. The results show that the first-order crustal deformation is unchanged in different periods in the Chinese mainland,which reflects the background of regional tectonic activity. The strain rate is much higher in Western China,especially in the Qinghai-Tibetan Plateau and Sichuan-Yunnan area. The variations in different periods are related with seismicity of strong earthquakes during the same time. The GPS data after 2004 shows the post-seismic deformation of the 2001 Kunlun Mountains M S8. 1 earthquake.

Horizontal crustal deformation in Chinese Mainland analyzed by CMONOC GPS data from 2009-2013

In this study, we analyze the regional GPS data of Crustal Movement Observation Network of China （CMONOC） observed from 2009-2013 using the BERNESE GPS software, and then the preliminary results of horizontal velocity field and strain rate field are presented, which could reflect the overall deformation features in the Chinese mainland from 2009-2013. Besides, the velocity error and the probable factors that could influence the estimate of long-term deformation are also discussed.

Crustal Deformation Revealed by GPS in Kumaun Himalaya,India

The foremost Global Positioning System(GPS) derived measurements in the Kumaun Himalaya indicate that most of the crustal motion of the Indian plate is accommodating towards the base as well as on the hanging wall of Main Central Thrust(MCT).Deformation pattern within the Kumaun Himalaya varies from south to north and indicates maximum deformation rate near MCT.Our study,based on the campaign mode GPS survey during 2003- 2006,reveals that the area between north of North Almora Thrust(NAT) and at the base of Great Himalaya registers maximum strain rate,which is lowered towards the Trans Himadri Fault(THF).The GAMIT-GLOBK processed campaign data of the area show that currently,the Himalayan Frontal Fault(HFF) and Main Boundary Thrust(MBT) are locked with the Indian plate,and a 6.7 ± 2.5 mm/yr of horizontal shortening is taking place between the Lesser Himalaya and Peninsular India.

Present-day crustal deformation revealed active tectonics in Yogyakarta,Indonesia inferred from GPS observations

We investigated the active crustal structure in Yogyakarta,Indonesia,using new and denser Global Positioning System(GPS)data.Deformation rate estimated from five years(2013-2018)of observations on 22 campaign might record broad deformation after the 2006 Mw7.8 Java tsunami earthquake and postseismic transient due to the 2006 Mw6.3 Yogyakarta earthquake.We conducted a decomposition method to obtain a short wavelength feature by removing those postseismic deformations from the observation data.The short wavelength pattern revealed active tectonics indicating a combination of E-W dip-slip motion and N-S left-lateral structure.A large maximum shear strain rate(>0.1 microstrain/yr)was estimated along the Opak fault while a large dilatation rate(<-0.1 microstrain/yr)was estimated around the Bantul Graben.The analysis result indicates important implications for crustal dynamics and assessing future seismic hazards potential in the Yogyakarta region.

Computing Crustal Strain Using Repeated GPS Survey

A method for computing crustal horizontal velocities and strain-rates using repeated GPS survey and other crustal deformation measurement was presented in detail. Based on the data taken from the Crustal Deformation Monitoring-Networks with GPS in the whole country and North China, we derived the average horizontal velocities of the points of the networks and simulated the horizontal velocity and strain-rate fields in the corresponding areas. From these results, we can conclude: (1) GPS can effectively detect current crustal motion and deformation, and (2) the method presented in the paper is valid, and through its use, calculated results can provide more information about current crustal motion and deformation than direct observation data.

The present-day kinematics of the Tianshan orogenic belt constrained by GPS velocities

Since the late Cenozoic,the reactivated Tianshan orogenic belt has accommodated crustal shortening exceeding 200 km,primarily due to the far-field effects of the India-Eurasia plate collision.However,the details of the strain partitioning in the Tianshan Mountain range remain elusive.We interpret a new compilation of GPS velocities covering the whole Tianshan range with a classic elastic block model.Compared to previous studies with a block modeling approach,the Tianshan orogenic belt is further subdivided into several blocks based on geological fault traces and a clustering analysis approach.In addition to obvious crustal shortening on the bounding thrust faults of the Tianshan,our inverted fault slip rates also reveal that faults within the Tianshan orogenic belt,such as the Nalati Fault and the southern margin of the Issyk-Kul Lake Fault,which plays a crucial role in accommodating the tectonic crustal shortening.In the 72°E-78°E region,the internal shortening rate within the mountain is approximately 5-7 mm/yr.Besides crustal shortening,strike-slip motion occurs on faults in the interior of the mountain range as well as in the foreland fold-and-thrust belts,especially in the southern margin of the Tianshan.These findings suggest that the crustal deformation in the Tianshan Mountain range is more complex than previously thought,and the oblique convergence between the Tarim Basin and the Tianshan probably results in both strike-slip and thrust motion.

Crustal deformation measurements by global positioning system(GPS)along NSL,western India

The Narmada Son Lineament(NSL)is a major palaeo-rift system and seismically active intra-plate region.In this paper,we processed and analyzed the GPS data from 2009 to 2016 to study the geodynamic characteristics of NSL.The velocities derived from GPS were used to calculate the associated deformation and crustal strain,while the slip deficit was estimated using the horizontal motion of GPS sites.The investigation reveals that the maximum deformation of western NSL is 1.6 mm per year,and the upper bound of the seismic moment(M;)is 2.0×10;dyn/cm,corresponding to an earthquake of about 6.0 magnitude.The study highlights the significance of Aravalli and Satpura mobile belts.The estimated strain of 0.03μstrain/yr is low but comparable to the stable continental region,and a close association of factors(the fragility,crustal conductors,and compressive tectonics)is considered responsible for seismogenic activities in western NSL.

Deformation caused by the 2011 eastern Japan great earthquake monitored using the GPS single-epoch precise point positioning technique

Crustal deformation can provide constraints for studying earthquake rupture and shock wave transmission for the Mw9.0 eastern Japan great earthquake. Using the single- epoch precise point positioning （PPP） method and the appropriate positioning flow, we process GPS data from six IGS （International GNSS Service） sites （e.g., MIZU, TSK2, USUD, MTKA, AIRA and KSMV） located in Japan and obtain the positioning results with centimeter scale precision. The displacement time series of the six sites are analyzed using the least squares spectral analysis method to estimate deformations caused by the Mw9.0 mainshock and the Mw7.9 aftershock, and the cumulative displacements after 1 day. Mainshock displacements at station MIZU, the nearest site to the mainshock in the North （N）, East （E）, and Up （U） directions, are -1.202 m, 2.180 m and -0.104 m, respectively, and the cumulative deformations after 1 day are -1.117 m, 2.071 m and -0.072 m, respectively. The displacements at station KSMV, the nearest site to the Mw7.9 aftershock in the N, E and U directions, are -0.032 m, 0.742 m and -0.345 m, respectively. The other sites obviously experienced eastern movements and subsidence. The deformation vectors indicate that the horizontal displacements caused by the earthquake point to the epicenter and rupture. Elastic bounds evidently took place at all sites. The results indicate that the crustal movements and earthquake were part of a megathrust caused by the Pacific Plate sinking under the North American Plate to the northeast of Japan island arc.

Characteristics of regional crustal deformation before 2016 Menyuan Ms6.4 earthquake

On January 21, 2016, a strong earthquake with a magnitude of Ms6.4 happened at Menyuan, Qinghai Province of China. In almost the same place, there was another strong earthquake happened in 1986, with similar magnitude and focal mechanism. In this paper, we analyze the characteristics of regional crustal deformation before the 2016 Menyuan Ms6.4 earth- quake by using the data from 10 continuous Global Positioning System （GPS） stations and 74 campaign-mode GPS stations within 200 km of this event： （a） Based on the velocity field from over ten years GPS observations, a regional strain rate field is calculated. The results indicate that the crustal strain rate and seismic moment accumulation rate of the Qilian- Haiyuan active fault, which is the seismogenic tectonics of the event, are significantly higher than the surrounding regions. In a 20 km~ 20 km area around the seismogenic region, the maximum and minimum principal strain rates are 21.5 nanostrain/a （NW-SE extension） and -46.6 nanostrain/a （NE-SW compression）, respectively, and the seismic moment accumulation rates is 17.4 Nm/a. The direction of principal compression is consistent with the focal mechanism of this event. （b） Based on the position time series of the continuous GPS stations for a time-span of about 6 years before the event, we calculate the strain time series. The results show that the dilatation of the seismogenic region is continuously reduced with a ＂non-linear＂ trend since 2010, which means the seismogenic region has been in a state of compression. However, about 2-3 months before the event, both the dilatation and maximum shear strain show significant inverse trends. These abnormal changes of crustal deformation may reflect the non-linear adjustment of the stress-strain accumulation of the seismogenic region, when the accumulation is approaching the critical value of rupture.

Crustal block rotations in Chinese mainland revealed by GPS measurements

We simulate GPS horizontal velocity field in terms of rotations of crustal blocks to describe deformation behavior of the Chinese mainland and its neighboring areas. 31 crustal blocks are bounded primarily by -30 Quaternary faults with distinct geometries and variable long-term rates of 〈20 mm/a, and 1 683 GPS velocities were determined from decade-long observations mostly with an averaged uncertainty of 1-2 mm/a. We define GPS velocity at a site by the combination of motion of rigid block and elastic strain induced by the fault that is locking during a seismic cycle. Model velocities predicted from the preferable block model match well with the GPS velocities to an uncertainty of-l.7mm/a. The slip rates inferred from this model is in a range of 6-18 mm/a for the major faults in Tibet and its margins and 1-4 mm/a in eastern China, consistent with geological observations. Our numerical simulation suggests that the crustal blocks deform internally at a level of-10× 10^-9/a, quite small in comparison with significant deformation localized along fault zones of 50-100 km wide. We conclude that the pattern of continental deformation is not continuous-like but block-like, and the tenet of plate tectonics may be applicable to characterize the active deformation in Asia.

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 northesouth shortening deformation of the Tibetan Plateau.

Characteristics of crustal strain associated with M=6.4 Baotou earthquake in 1996

Based on the horizontal crustal strain derived from GPS data and the rate accumulation intensity calculated from across-fault vertical deformation, the strain characteristics in the periods of 1992~1995, 1995~1996 and 1996~1999 in Baotou-Datong area is studied in the paper. From the comparison between the crustal strains before and after the M=6.4 Baotou earthquake occurred on May 3, 1996, it is considered that the high-magnitude area with predominant compressive strain might be the seismogenic zone for a coming strong earthquake. The area with the simultaneous higher surface strain, principal compressive strain, shear strain and tendency accumulation might be the place with higher risk of strong earthquakes. Generally, the area with low strain and predominant tensile strain might have a small possibility for strong earthquake development, which belongs to a stable area. The evolution of horizontal strain obtained from GPS measurements carried out in Baotou-Datong area in the period of 1992~1999 reflects the total developing and ending processes of the seismic episode from 1996 to 1998. The area with high and predominant compressive strain and the strain gradient zone can be considered as one of the indicators for determining the strong earthquake risk area in the future.

Study of main body element of crustal strain and its relationship with moderate-strong earthquakes

In this paper, progress in strain study of blocks and faults by GPS data are discussed, and the concept that active structures between blocks are the main body of crustal strain is clarified. By energy transfer principle of elastic mechanics, the relation between strain around faults and tectonic force on fault surfaces is set up and main body element model of crustal strain is constructed. Finally, the relation between mechanical evolution of model and seismogenic process of Kunlun earthquake （Ms=8.1） is discussed by continuous GPS data of datum stations. The result suggests that the relatively relaxed change under background of strong compressing and shearing may help to trigger moderate-strong earthquakes.

Numerical analysis of contemporary hori-zontal tectonic deformation fields in China from GPS data

Assuming that the contemporary tectonic activity in China can be treated as continuous, we have simulated 1245 present-day multiple-epoch GPS velocity solutions in the range of Chinese mainland, Mongolia, Myanma, India, Nepal and Himalayas with a bi-cubic spline interpolation function to inverse the integral horizontal velocity with the fitting accuracy less than 3 mm and obtained the strain rate fields in Chinese mainland. We have also analyzed the characteristics of spatial distribution of horizontal deformation and strain rate fields in Chinese mainland. The result shows that the analysis on the continuous deformation in the large-scale and dense GPS velocity fields can reveal not only the integral tectonic characters of Chinese mainland but also the tectonic characters in local regions. Generally, the magnitude and intensity of horizontal tectonic deformation have a mutation in the South-North Seismic Belt (95°E-102°E), which is stronger in the west than the east and stronger in the south than the north. Large strain rates are found in the areas as Kunlun block, Xianshuihe fault zone and central Yunnan, and the variation of velocity is very rapid. At the same time, the tectonic activity is relatively calm on Altyn Tagh fault zone, and extensive strain is found in the eastern part of central Tianshan.

The migration of the crustal deformation peak area in the eastern Himalayan Syntaxis inferred from present-day crustal deformation and morpho-tectonic markers

The present-day Global Positioning System(GPS)velocity field shows that the Indian Plate is not a complete rigid block,as its northeastern corner has been torn off and clockwise rotating relative to the main part.With the updated GPS velocity data,the Euler vector of the northeastern corner of the Indian Plate relative to the stable main plate is deduced as(89.566±0.06°E,26.131±0.05°N,1.34±0.11°/Myr).The peak area of the present-day crustal deformation is located in the Chayu deformation belt with the compressional dilation strain rate over 160 nanostrain/yr.However,the Namche-Barwa Syntaxis with the massive crustal thickening and intense surface erosion is generally considered to be the previous locus of the strongest compressional stress in the Eastern Himalayan Syntaxis over long geological timescales.Thus,there is a discrepancy between the previous and present-day crustal deformation peak areas.We argue the migration of the crustal deformation peak area with a total distance of about 120 km and ascribe it to the variation of stress conditions caused by northeast India’s clockwise rotation.

Study on the Relationship Between Recent Crustal Deformation and the Temporal-Spatial Distribution of Strong Earthquakes (M_s≥6.0) in the Sichuan-Yunnan Region

Analysis of deformation data measured across the faults, regional vertical deformation data and GPS measurements in the Sichuan-Yunnan region made since the 1980s permitted us to conclude that the crustal deformation in the region during this period of time was relatively weak and caused the occurrence of earthquakes (M S≥6.0), which were not distributed along the major boundary active faults in the region after the 1981 Dawu M S 6.9 earthquake and that the seismic activity is characterized by quasi-clockwise migration. Thus, it follows that earthquake prediction research should be focused on the central part of the Sichuan-Yunnan region in the coming years. Finally, a concept of temporal division of the region into active blocks is suggested and the preliminary result of the division is given in the paper.

Crustal Deformation Background Simulation of the Kekexili M_S8.1 Earthquake Happening in 2001

Using the GPS velocity data from 27 stations around the Eastern Kunlun fault as constraints, we first invert the slip velocities of the Eastern Kuniun fault, the north boundary fault of the Qaidam basin, the Mani-Yushu fault and the Margai Caka fault before the Kekexili Ms 8.1 earthquake with a 3-D elastic half-space dislocation model. The deformation field calculated from the slip movement of these faults can be considered the deformation background field of the earthquake. Based on the deformation background field with tectonic implications, we have obtained the strain field and earthquake moment accumulation field. The results show that there are two obvious high moment accumulation rate regions, one of which is the Dongdatan- Xidatan segment of the Eastern Kuniun fault where the Ms8.1 earthquake occurred in 2001.

Contemporary crustal tectonic movement in the southern Sichuan-Yunnan block based on dense GPS observation data

We analyzed 360 permanent and campaign GPS data from 1999 to 2017 in the southern Sichuan-Yunan block, and obtained crustal horizontal deformation in this region.Then, we derived the strain rate using a multi-scale spherical wavelet method.Results reveal a complex pattern of tectonic movement in the southern Sichuan-Yunnan block.Compared to the stable Eurasian plate, the maximum rate of the horizontal deformation in the southern Sichuan-Yunnan block is approximately 22 mm/a.The Xiaojiang fault shows a significantly lower deformation—a left-lateral strike-slip movement of 9.5 mm/a.The Honghe fault clearly shows a complex segmental deformation from the north to south.The northern Honghe fault shows 4.3 mm/a right strike-slip with 6.7 mm/a extension; the southern Honghe fault shows 1.9 mm/a right strike-slip with 1.9 mm/a extension; the junction zone in the Honghe and Lijiang–Xiaojinhe faults shows an obvious clockwise-rotation deformation.The strain calculation results reveal that the maximum shear-strain rate in this region reaches 70 nstrain/a, concentrated around the Xiaojiang fault and at the junction of the Honghe and Lijiang–Xiaojinhe faults.We note that most of the earthquakes with magnitudes of 4 and above that occurred in this region were within the high shear strain-rate zones and the strain rate gradient boundary zone, which indicates that the magnitude of strain accumulation is closely related to the seismic activities.Comparison of the fast shear-wave polarization direction of the upper-crust with the upper-mantle anisotropy and the direction of the surface principal compressive strain rate obtained from the inversion of the GPS data reveals that the direction of the surface principal compressive strain is basically consistent with the fast shear-wave polarization direction of the upper crust anisotropy, but different from the polarization direction of the upper mantle.Our results support the hypothesis that the principal elements of the deformation mechanism in the southern Sichuan-Yunnan block are decoupling between the upper and lower crust and ductile flow in the lower crust.