Paradoxes of the comparative analysis of ground-based and satellite geodetic measurements in recent geodynamics

The comparative analysis of the Earth’s surface deformations measured by ground-based and satellite geodetic methods on the regional and zonal measurement scales is carried out. The displacement velocities and strain rates are compared in the active regions such as Turkmenian–Iranian zone of interaction of the Arabian and Eurasian lithospheric plates and the Kamchatka segment of the subduction of the Pacific Plate beneath the Okotsk Plate. The comparison yields a paradoxical result. With the qualitatively identical kinematics of the motion, the quantitative characteristics of the displacement velocities and rates of strain revealed by the observations using the global navigational satellite system (GNSS) are by 1–2 orders of magnitude higher than those estimated by the more accurate methods of ground-based geodesy. For resolving the revealed paradoxes, it is required to set up special studies on the joint analysis of ground-based and satellite geodetic data from the combined observation sites.     

The topical problems of identifying the results of the observations in recent geodynamics

The paper addresses the problems of identifying the results of deformational observations on the Earth, which arise from the new measurement technologies and lead to the ambiguity relationships such as the “spatial size of the anomaly—density of the observation sites” and the “duration of the anomalies—degree of temporal detail of the measurements.” It is found that many “paradoxical” conclusions concerning the rates and scales of the recent geodynamical processes are removed if the parameters of the measurement system match the properties of the studied object and if the relative character of the observational means is taken into account. It is shown that the time variation in the uniaxial deviatoric stress leads to the variation in the volumetric strain and, consequently, to the variation in gravity. The ambiguity in determining the ground displacement vectors by SAR interferometry is demonstrated. It is concluded that the autonomous use of the interferometry data leads to the significant distortions of the results, and these data should be necessarily used in combination with the ground-based geodetic observations.     

Isotope geodynamics

The observational sciences have long been considered to be the archaic precursors of the experimental sciences. Scientific progress over the last part of this century has led us to reconsider the reality of this proposed evolution. Will Astronomy ever become an experimental science? Yet pulsars and cosmic rays do constitute topics of scientific studies. Are Ecology and Meteorology archaic? Do they not contribute to the renewal of the studies of instabilities and of strange attractors?These observational sciences, once considered in decline but actually in full development with the creation of modern techniques of observation, analytical measurements and computation, have been granted a worldwide recognition by Anna-Greta and Holger Crafoord and the Swedish Royal Academy of Sciences by the creation of the Crafoord Prize to be awarded to a range of non-experimental sciences. Hence, I would like to thank Mrs. Crafoord, the Swedish Royal Academy and His Majesty the King who placed this Fund under their high Patronage.To this gathering of renewed observational sciences, Geosciences do not arrive with their hands empty. Among the various disciplines which have contributed to this development this year, you have identified Isotopic Geology for recognition. As the recipient of the prize representing this field, I will try to present my personal views of the field, its development and future.     

Lithospheric structure and continental geodynamics

This paper briefly reviews main progress in the research on lithospheric structure and continental geodynamics made by Chinese geophysicists during last 4 years since 22nd IUGG general assembly in July 1999. The research mainly covers the following fields: investigations on regional lithospheric structure, DSS survey of crust and upper mantle velocity structure, study on present-day inner movement and deformation of Chinese mainland by analyz-ing GPS observations, geodynamics of Qingzang plateau, geophysical survey of the Dabie-Sulu ultra-high pressure metamorphic belt and probing into its formation mechanism, geophysical observations in sedimentary basins and study on their evolution process, and plate dynamics, etc.     

Wave moment geodynamics

The work presents a review of natural-science representations on the rotary motion of matter and its piecewise structure. Development of dense GPS-networks allowed to experimentally confirm the concept of block structures of the geophysical environment and to prove rotary character of block movement. An analysis of both the migration of earthquake sources and the movement of sections of tectonic plates’ borders has allowed to reveal general properties of such movements and to prove their wave nature. It is shown that within the limits of rotational model, blocks and plates are interconnected among themselves by the elastic long-range fields forming a uniform planetary geodynamic field. It is offered to use the geodynamic solutions of rotational model in the one class of phenomena as a basis at the construction of a new geological paradigm — wave moment geodynamics.     

地球物理学及地球动力学研究与计算数学

地球物理学是20世纪,特别是在其中叶以后迅速发展起来的一门边缘科学.它以物理学、数学和信息科学为依托,并与地质学、地球化学密切结合;以研究和探索地球内部介质的属性、结构变异和深部物质与能量的交换、深层过程和动力学响应.这在促进社会与经济的发展和科学与技术的进步中占有重要地位,因为大量资源的需求和自然灾害的防范在人类生活和生存空间以及可持续发展中乃核心所在.在研究和探索这一系列的地球科学问题的进程中,首先必须通过地表进行高精度的地球物理探测、观测和高分辨率的数据采集,进而利用不同的数学方法反演计算地球内部介质的精细结构和其物理—力学过程与动力学响应.基于此,本文主要讨论了：1）地球物理学和地球动力学的发展趋势及特点;2）地球物理学的发展对计算数学的需求;3）地球动力学和数值模拟与计算地球物理学.最后对这些问题和基本导向进行了讨论.     

Recent geodynamics of dangerous faults

The analysis of the existing information concerning the present-day deformation activity of the fault zones in seismically active and aseismic regions suggests that the notions of an active fault and a dangerous fault should be distinguished. It is shown that a fault which is active for an expert in geotectonics will not be considered dangerous by an expert in geotechnical monitoring of buildings. The definition is given according to which a dangerous fault is understood as a zone of linear destruction which accommodates the contemporary short-period (a few months and years) pulsed and/or alternating motions with strain rates above 5 × 10^–5 per annum and earthquakes with M ≥ 5. A technique is developed for identifying the dangerous faults based on monitoring the recent ground surface displacements in accordance with a special protocol which ensures an increased degree of detail in time and space. Based on the idea of the probable accumulation of dangerous strains during the operating cycle of the objects, the criteria for assessing their geodynamical risks are formulated.     

Introduction to geodynamics for high- and ultrahigh-pressure metamorphism

Since the first workshop on ultrahigh-pressure (UHP) metamorphism at Stanford in 1994 and the special issue of The Island Arc `Ultrahigh-Pressure Metamorphism and Tectonics' published in December 1995, many symposia and special sessions specifically with regard to the UHP metamorphic terrane have been held. While we are still wondering how exhumation of UHP rocks from mantle depths to the surface takes place, the finding of possible records from the mantle transition zone at 300–400 km depths is astonishing. The study of the UHP regime has expanded to include input from mineral physics, experimental geochemistry and kinetics in addition to the petrochemical and tectonic study of a variety of HP–UHP rocks. It was with this theme that the second workshop for the task group III-6 `Ultrahigh-Pressure Metamorphism and Geodynamics in Collision-type Orogenic Belts' of the International Lithosphere Program was held during the International Geological Congress in Beijing, 1996. The Symposium 8–9 `Dynamic Metamorphic Rocks and High- and Ultrahigh-Pressure Metamorphism' (Cong Bolin & J. G. Liou conveners) had more than 25 presentations in two oral sessions and 70 papers in one poster session. This second special issue of The Island Arc includes nine papers from this symposium and a few related contributions to the geodynamics of HP–UHP metamorphism and tectonics. It is our hope that The Island Arc will continue to publish a special issue on this increasingly recognized subject that is essential to our understanding of continental collision, mantle dynamics and geochemical + fluid cycles.     

Energy cycle of geodynamics and the seismic process

Estimates are obtained for the energy cycle of geodynamics, namely, the contributions of the geothermal flux to the generation rate of the kinetic energy of convective motions in the mantle and the generation of stresses in the crust that are later released during earthquakes. As follows from theoretical considerations, about half of the geothermal flux is spent on the generation of motions in the mantle, and the fraction of the total geothermal flux from the Earth’s interior that is spent on the seismic process is estimated at 0.5%. This estimate is obtained with the use of data of global earthquake catalogs. For volcanic processes, this fraction is smaller by two orders of magnitude. The energies required for the formation of the Earth’s surface topography and for seismic activity are comparable.     

Plate kinematics and geodynamics in the Central Mediterranean

We argue that seismotectonic activity in the Central Mediterranean area and the Aegean–Balkan zone is driven by the NNE-ward motion of Africa and westward motion of Anatolia with respect to Eurasia. These boundary conditions can plausibly and coherently account for E–W shortening and roughly S–N extension in the Aegean domain, thrusting and uplift at the boundary between the Aegean–Balkan system and the Adriatic/Ionian domain (Hellenic trench, Cephalonia fault, Epirus, Albanides and Southern Dinarides), the kinematics of the Adria plate (a large block encompassing the Adriatic continental domain, the northern Ionian zone and Hyblean-Adventure block) and consequently, the complex pattern of deformation recognized at its boundaries. Furthermore, the fact that in our scheme Adria moves almost in connection with Africa is consistent with the lack of an active decoupling zone between Adria and Africa, an evidence that can hardly be reconciled with the kinematics so far proposed for these two plates. The reasons why we adopt an Africa–Eurasia relative motion different from that implied by the popular NUVEL-1 global solution are discussed in detail. Finally, we make some considerations about the possible implications of the presently available geodetic data on the long-term plate kinematics.     

Tectonic evolution and geodynamics of the Neo-Tethys Ocean

The Neo-Tethys Ocean was an eastward-gaping triangular oceanic embayment between Laurasia to the north and Gondwana to the south.The Neo-Tethys Ocean was initiated from the Early Permian with mircoblocks rifted from the northern margin of Gondwana.As the microblocks drifted northwards,the Neo-Tethys Ocean was expanded.Most of these microblocks collided with the Eurasia continent in the Late Triassic,leading to the final closure of the Paleo-Tethys Ocean,followed by oceanic subduction of the Neo-Tethys oceanic slab beneath the newly formed southern margin of the Eurasia continent.As the splitting of Gondwana continued,African-Arabian,Indian and Australian continents were separated from Gondwana and moved northwards at different rates.Collision of these blocks with the Eurasia continent occurred at different time during the Cenozoic,resulting in the closure of the Neo-Tethys Ocean and building of the most significant Alps-Zagros-Himalaya orogenic belt on Earth.The tectonic evolution of the Neo-Tethys Ocean shows different characteristics from west to east:Multi-oceanic basins expansion,bidirectional subduction and microblocks collision dominate in the Mediterranean region;northward oceanic subduction and diachronous continental collision along the Zagros suture occur in the Middle East;the Tibet and Southeast Asia are characterized by multi-block riftings from Gondwana and multi-stage collisions with the Eurasia continent.The negative buoyancy of subducting oceanic slabs can be considered as the main engine for northward drifting of Gondwana-derived blocks and subduction of the Neo-Tethys Ocean.Meanwhile,mantle convection and counterclockwise rotation of Gondwana-derived blocks and the Gondwana continent around an Euler pole in West Africa in non-free boundary conditions also controlled the evolution of the Neo-Tethys Ocean.     

Mechanical problems in geodynamics and work done in China

The subject of geodynamics concerns the dynamics of the global motion of the earth, of the motion in the earth's interior and its interaction with surface features, together with mechanical processes in the deformation and rupture of geological structures. A brief historical review is given from Sir I. Newton, Maclauwin, Jacobi, Poincaré, Poisson, Lamé, Darwin, Rayleigh, and Love, who dealt with the homogeneous sphere, to Leibenson, Takeuchi, and Meinesz, concentrating on layered spheres, and after the advent of plate tectonics, on the use of numerical simulation, to the analyses of tectonic features, earthquake mechanism, the application of nonlinear dynamics. By discussing the forward and inverse mechanical problems, and the questions facing the inverse problems of searching for the structural parameters, driving forces, etc. are raised in more detail. Thereafter, some works accomplished in China on the global and regional stress fields analyses; tectonic features' analyses, mantle flow studies; experimental studies of rocks and their constitutive relations are presented. Finally, the interdisciplinary nature of the subject is emphasized, and the main mechanical problems that need special attention are then proposed.     

数值模拟在地球动力学中的研究进展

本文主要针对有限单元法,对近10几年来数值模拟在地球动力学中的应用和发展作了回顾,分为构造应力场模拟;地幔热对流模拟;板块碰撞模拟;岩石圈流变学模拟;以及地震机制与预测模拟等部分.简单阐述了当前地球动力学数值模拟的发展趋势并论述了其面临的主要问题.     

New Cretaceous palaeointensity data and the constraints on geodynamics

A combined geochronologic (K-Ar) and palaeomagnetic study has been conducted on a basalt lava sequence at Yixian Formation in Liaoning Province, northeastern China. The new K-Ar age obtained from thirteen lava flows is 120.93±0.88 Ma. Detailed rock-magnetic investigations were conducted on each lava flow to determine their remanence carriers. The modified version of the Thellier-Thellier palaeointensity method with systematic partial thermoremanent magnetization (pTRM) checks was used for the palaeointensity determination. Virtual dipole moment (VDM) value is (3.66±0.10)x10²² Am². This low dipole-field intensity value is approximately forty-five percent of the today field VDM. Combined with all of the other published palaeointensity data, possible links between the earth’s interior process and its control on the variation of the earth’s magnetic field during the geological time were tentatively discussed.     

Late-alpine fault systems and geodynamics of the West Caucasus

This work describes the most general results of investigations of fault structures of various ranks in the Russian part of the West Caucasus. The investigations were based on the methods of structural-paragenetic analysis and were aimed at the determination of acting stress fields, as well as at the revealing and mapping of fault systems and zones of concentration of deformations of various geological-kinematic types. Structural parageneses of tectonic fractures and faults, most characteristic of the Russian part of the West Caucasus, are established.     

Geothermal regime and geodynamics of the North Pacific Ocean

The distribution of heat flow in the North Pacific Ocean has been examined, and a map of geothermal and geomagnetic fields for the Bering Sea as it is known today has been made. Reliable data are lacking regarding the time of origin for features of oceanic and continental genesis in the Bering Sea, which is an obstacle to the study of geodynamic processes in the North Pacific. Heat flow data were used to yield numerical estimates for the age of seafloor features in the Bering Sea: the Kamchatka Basin (21 Ma), Shirshov Ridge (95 Ma for the northern part and 33 Ma for the southern), the Aleutian Basin (70 Ma), Vitus Rise (44 Ma), Bowers Ridge (30 Ma), and Bowers Basin (40 Ma). These age estimates are corroborated by combined geological, geophysical, and plate kinematic data. A thermochemical model of global mantle convection has been developed in order to perform a numerical simulation of the thermal process involved in the generation of extended regional features in the North Pacific (the Emperor Fracture Zone, Chinook Trough, etc.). The modeling suggests a plume-tectonic origin for these features, yielding the optimal model for the tectonic evolution of the North Pacific. An integrated geological and geothermal analysis leads to the conclusion that the northern and southern parts of the Shirshov Ridge are different, not only in geologic age, but also in tectonic structure. The northern part is of imbricated-thrust terrane origin, while the southern part is of ensimatic island-arc origin, similar to that of Bowers Ridge. The seafloor of the Aleutian Basin is an outlier of the Upper Cretaceous Kula plate where, in the Vitus Rise area, backarc spreading processes originated during Eocene time. The terminating phase of activity in the Bering Sea began about 21 Ma by spreading in the older seafloor of the Kamchatka Basin. We developed plate-tectonic reconstructions of evolution for the North Pacific for the times 21, 33, 40, and 70 Ma in the hotspot system based on age estimates for the seafloor features derived from heat flow data and modeling of the thermal generation of regional faults, as well as on an analysis of geomagnetic, tectonic, and geological data.     

The Kamchatka subduction zone: Seismotectonic regionalization and geodynamics

Seismotectonic regionalization of the Kamchatka subduction zone was carried out by retrospective analysis of the temporal sequence and locations of earthquake occurrence and an examination of relationships between the earthquake hypocenters and morphostructures in the continental slope of eastern Kamchatka. Ten segments separated with earthquake-generating strike-slip faults have been identified in the overthrusting (overhanging) margin of the Sea-of-Okhotsk plate in the zone where the Pacific and the Sea-of-Okhotsk plates interact orthogonally. Two to three earthquake-generating thrust blocks have been identified within these segments. This type of subduction is consistent with the keyboard-block model of L.I. Lobkovskii and B.V. Baranov. We put forward a model involving segmentation and generation of thrust blocks due to nonuniform coupling between the subducted Pacific plate and the overhanging Sea-of-Okhotsk plate. According to this model, both segmentation and the formation of thrust blocks are caused by nonuniform plate coupling due to unevenness in the relief of the plunging plate. The thrusts have relief expression as underwater highs and terraces, which indicate that a tsunami-generating earthquake can occur at this location. The highest rate of occurrence for magnitude 7 or greater earthquakes is found at the sharp bend of the Pacific plate, where the subduction angle is 10°–12° instead of 50°–51°, corresponding to a frontal (tectonic) arc, which can be traced by a positive free-air gravity anomaly and by an isostatic anomaly.