SUMMARY
We describe best-fitting angular velocities and MORVEL, a new closure-enforced set of angular velocities for the geologically current motions of 25 tectonic plates that collectively occupy 97 per cent of Earth's surface. Seafloor spreading rates and fault azimuths are used to determine the motions of 19 plates bordered by mid-ocean ridges, including all the major plates. Six smaller plates with little or no connection to the mid-ocean ridges are linked to MORVEL with GPS station velocities and azimuthal data. By design, almost no kinematic information is exchanged between the geologically determined and geodetically constrained subsets of the global circuit—MORVEL thus averages motion over geological intervals for all the major plates. Plate geometry changes relative to NUVEL-1A include the incorporation of Nubia, Lwandle and Somalia plates for the former Africa plate, Capricorn, Australia and Macquarie plates for the former Australia plate, and Sur and South America plates for the former South America plate. MORVEL also includes Amur, Philippine Sea, Sundaland and Yangtze plates, making it more useful than NUVEL-1A for studies of deformation in Asia and the western Pacific. Seafloor spreading rates are estimated over the past 0.78 Myr for intermediate and fast spreading centres and since 3.16 Ma for slow and ultraslow spreading centres. Rates are adjusted downward by 0.6–2.6 mm yr−1 to compensate for the several kilometre width of magnetic reversal zones. Nearly all the NUVEL-1A angular velocities differ significantly from the MORVEL angular velocities. The many new data, revised plate geometries, and correction for outward displacement thus significantly modify our knowledge of geologically current plate motions. MORVEL indicates significantly slower 0.78-Myr-average motion across the Nazca–Antarctic and Nazca–Pacific boundaries than does NUVEL-1A, consistent with a progressive slowdown in the eastward component of Nazca plate motion since 3.16 Ma. It also indicates that motions across the Caribbean–North America and Caribbean–South America plate boundaries are twice as fast as given by NUVEL-1A. Summed, least-squares differences between angular velocities estimated from GPS and those for MORVEL, NUVEL-1 and NUVEL-1A are, respectively, 260 per cent larger for NUVEL-1 and 50 per cent larger for NUVEL-1A than for MORVEL, suggesting that MORVEL more accurately describes historically current plate motions. Significant differences between geological and GPS estimates of Nazca plate motion and Arabia–Eurasia and India–Eurasia motion are reduced but not eliminated when using MORVEL instead of NUVEL-1A, possibly indicating that changes have occurred in those plate motions since 3.16 Ma. The MORVEL and GPS estimates of Pacific–North America plate motion in western North America differ by only 2.6 ± 1.7 mm yr−1, ≈25 per cent smaller than for NUVEL-1A. The remaining difference for this plate pair, assuming there are no unrecognized systematic errors and no measurable change in Pacific–North America motion over the past 1–3 Myr, indicates deformation of one or more plates in the global circuit. Tests for closure of six three-plate circuits indicate that two, Pacific–Cocos–Nazca and Sur–Nubia–Antarctic, fail closure, with respective linear velocities of non-closure of 14 ± 5 and 3 ± 1 mm yr−1 (95 per cent confidence limits) at their triple junctions. We conclude that the rigid plate approximation continues to be tremendously useful, but—absent any unrecognized systematic errors—the plates deform measurably, possibly by thermal contraction and wide plate boundaries with deformation rates near or beneath the level of noise in plate kinematic data.

Geologically current plate motions

Global positioning system velocities from 553 control points within the Tibetan Plateau and on its margins show that the present-day tectonics in the plateau is best described as deformation of a continuous medium, at least when averaged over distances of .;100 km. Deformation occurs throughout the plateau interior by ESE-WNW extension and slightly slower NNE-SSW shortening. Relative to Eurasia, material within the plateau interior moves roughly eastward with speeds that increase toward the east, and then flows southward around the eastern end of the Himalaya. Crustal thickening on the northeast- ern and eastern margins of the plateau occurs over a zone ;400 km wide and cannot be the result of elastic strain on a single major thrust fault. Shortening there accommodates much of India's penetration into Eurasia. A description in terms of movements of rigid blocks with elastic strain associated with slip on faults between them cannot match the velocity field.

Continuous deformation of the Tibetan Plateau from global positioning system data

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Tibetan tectonic evolution inferred from spatial and temporal variations in post-collisional magmatism

SUMMARY A network of 27 GPS sites was implemented in Iran and northern Oman to measure displacements in this part of the Alpine‐Himalayan mountain belt. We present and interpret the results of two surveys performed in 1999 September and 2001 October. GPS sites in Oman show northward motion of the Arabian Plate relative to Eurasia slower than the NUVEL-1A estimates (e.g. 22 ± 2m m yr −1 at N8 ◦ ± 5 ◦ E instead of 30.5 mm yr −1 at N6 ◦ E at Bahrain longitude). We define a GPS Arabia‐Eurasia Euler vector of 27.9 ◦ ± 0.5 ◦ N, 19.5 ◦ ± 1.4 ◦ E, 0.41 ◦ ± 0.1 ◦ Myr −1 . The Arabia‐Eurasia convergence is accommodated differently in eastern and western Iran. East of 58 ◦ E, most of the shortening is accommodated by the Makran subduction zone (19.5 ± 2m m yr −1 ) and less by the Kopet-Dag (6.5 ± 2m m yr −1 ). West of 58 ◦ E, the deformation is distributed in separate fold and thrust belts. At the longitude of Tehran, the Zagros and the Alborz mountain ranges accommodate 6.5 ± 2m m yr −1 and 8 ± 2m m yr −1 respectively. The right-lateral displacement along the Main Recent Fault in the northern Zagros is about 3 ± 2m m yr −1 , smaller than what was generally expected. By contrast, large rightlateral displacement takes place in northwestern Iran (up to 8 ± mm yr −1 ). The Central Iranian Block is characterized by coherent plate motion (internal deformation < 2m m yr −1 ). Sites east of 61 ◦ E show very low displacements relative to Eurasia. The kinematic contrast between eastern and western Iran is accommodated by strike-slip motions along the Lut Block. To the south, the transition zone between Zagros and Makran is under transpression with right-lateral displacements of 11 ± 2m m yr −1 .

/pdf/present-day-crustal-deformation-and-plate-kinematics-in-the-4g6yjp3ie8.pdf

Present‐day crustal deformation and plate kinematics in the Middle East constrained by GPS measurements in Iran and northern Oman

[1] A high-resolution P wave tomographic model of the crust and mantle down to 1100 km depth under China and surrounding regions is determined by using about one million arrival times of P, pP, PP, and PcP waves from 19,361 earthquakes recorded by 1012 seismic stations. The subducting Pacific slab is imaged clearly as a high-velocity zone from the oceanic trenches down to about 600 km depth, and intermediate-depth and deep earthquakes are located within the slab. The Pacific slab becomes stagnant in the mantle transition zone under east China. The western edge of the stagnant slab is roughly coincident with a surface topographic boundary in east China. The active Changbai and Wudalianchi intraplate volcanoes in northeast China are underlain by significant slow anomalies in the upper mantle, above the stagnant Pacific slab. These results suggest that the active intraplate volcanoes in NE China are not hot spots but a kind of back-arc volcano associated with the deep subduction of the Pacific slab and its stagnancy in the transition zone. Under the Mariana arc, however, the Pacific slab penetrates directly down to the lower mantle. The active Tengchong volcano in southwest China is related to the eastward subduction of the Burma microplate. The subducting Indian and Philippine Sea plates are also imaged clearly. The Indian plate has subducted down to 200–300 km depth under the Tibetan Plateau with a horizontal moving distance of about 500 km. High-velocity anomalies are revealed in the upper mantle under the Tarim basin, Ordos, and Sichuan basin, which are three stable blocks in China.

High-resolution mantle tomography of China and surrounding regions

Global Positioning System (GPS) measurements in China indicate that crustal shortening accommodates most of India's penetration into Eurasia. Deformation within the Tibetan Plateau and its margins, the Himalaya, the Altyn Tagh, and the Qilian Shan, absorbs more than 90% of the relative motion between the Indian and Eurasian plates. Internal shortening of the Tibetan plateau itself accounts for more than one-third of the total convergence. However, the Tibetan plateau south of the Kunlun and Ganzi-Mani faults is moving eastward relative to both India and Eurasia. This movement is accommodated through rotation of material around the eastern Syntaxis. The North China and South China blocks, east of the Tibetan Plateau, move coherently east-southeastward at rates of 2 to 8 millimeters per year and 6 to 11 millimeters per year, respectively, with respect to the stable Eurasia.

https://science.sciencemag.org/content/sci/294/5542/574.full.pdf

Present-Day Crustal Deformation in China Constrained by Global Positioning System Measurements

[1] We use GPS data from 45 sites across the Tibetan Plateau surveyed between 1991 and 2001 to study the distribution of strain in that part of the India-Eurasia collision zone. The plateau is cut by a few major, rapidly slipping strike-slip fault zones, with broadly distributed strain between those zones. The GPS velocities can be fit well by a simple deforming block model that combines uniform strain with the motion of blocks separated by the major known fault zones within the plateau. The boundaries of the four blocks in this model correspond to the major, rapidly slipping faults. A rigid block model with a smaller number of blocks fits the data poorly and can be rejected. We estimate that 5.9 ± 0.7 mm/yr of extension in the N69°W direction occurs on the Yadong-Gulu rift south of the plateau; localized extension may extend as far north as the Nyainqentanglha Range. We find 7.4 ± 0.7 mm/yr of right-lateral slip on the Karakorum-Jiali fault zone, significantly slower than that previously estimated from offset geologic features. Our deforming block model and a two-dimensional single-fault screw dislocation model give lower and upper bounds of 4.4 ± 1.1 and 10.3 ± 0.4 mm/yr on the slip rate on the Kunlun fault, respectively, comparable, in its highest, to the long-term slip rate observed geologically. The distributed deformation is surprisingly uniform over the Tibetan Plateau, Qaidam Basin, and Qilian Shan and approximates a combination of pure shear and uniaxial contraction with the same axes of maximum contraction, ∼N32°E. This strain field is a combination of shortening and extension that produces little net dilatation (1% area loss per million years) at present. The broadly distributed strain most likely represents slip on many faults, each with a relatively low slip rate. Distributed conjugate strike-slip faulting is the most plausible mechanism to produce the observed strains, as supported by the record of medium to large earthquakes within the plateau. The distributed deformation is just as important in the accommodation of the total India-Eurasia convergence as is slip on the major faults. The eastward motion of central Tibet is as large as 50% of the convergence rate between India and Eurasia. However, this eastward motion is not motion of a relatively undeforming block bounded by rapidly moving strike-slip faults, as suggested by past extrusion models. Instead, much of this eastward extrusion is driven by the internal extension of the plateau. Our inference is in agreement with the model of F. Shen et al. [2001] that suggested east-west extension, north-south contraction, and eastward plateau growth dominate the present tectonics of the Tibetan Plateau.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2002JB002151

A deforming block model for the present-day tectonics of Tibet

[1] We use Global Positioning System (GPS) data and kinematic block models to study the present-day deformation of southern Tibet. GPS data from 33 sites in southern Tibet and Nepal surveyed between 1991 and 2000 reveal 13 ± 2 mm/yr of N110°E extension between Lhasa and Shiquanhe (80°E–91°E), of which 9.7 ± 3.0 mm/yr represents permanent extension of the Tibetan crust. The remaining ∼3 mm/yr results from elastic deformation from the locked, curving Main Himalayan Thrust fault. This extension is spatially nonuniform. One half to two thirds of the permanent extension is concentrated across the Yadong-Gulu rift, with an opening rate of 6.5 ± 1.5 mm/yr; most of the remainder occurs on or near the Thakkola graben, with little extension across the rifts between them. Differential velocities of sites north and south of the Yarlung-Zangbo suture in western Tibet imply that the suture or an adjacent structure may be active as a strike-slip fault. A numerical model suggests that right-lateral strike slip on the Yarlung-Zangbo suture may extend from the Karakorum Fault Zone in the west at least to the Yadong-Gulu rift in the east with ∼3 mm/yr slip rate, accommodating part of the eastward extrusion of Tibet. The convergence directions inferred from GPS are consistent with slip vectors of earthquakes; however, the rate of slip of India beneath Tibet along the Himalaya is lower than those previously estimated. We estimate a slip rate of 12.4 ± 0.4 mm/yr between longitudes 83°E and 88°E and 17 ± 1 and 19 ± 1 mm/yr in the western and eastern Himalaya, respectively. The variable slip rate correlates with the variable extension rate in southern Tibet, and we suggest that it results from variation in the deformation rate of the overriding Tibetan crust. We infer that the slower convergence rate in the central Himalaya is significant.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2002JB002350

Zhiqiang Yang

Papers

Present-Day Crustal Deformation in China Constrained by Global Positioning System Measurements

A deforming block model for the present-day tectonics of Tibet

Spatially variable extension in southern Tibet based on GPS measurements

Spatio-temporal variations of afterslip and viscoelastic relaxation following the Mw 7.8 Gorkha (Nepal) earthquake

Postseismic Deformation due to the 2012 M w 7.8 Haida Gwaii and 2013 M w 7.5 Craig Earthquakes and its Implications for Regional Rheological Structure