Dynamics of seismogenerating structures in the frontal zone of the Kolyma–Omolon superterrane

To develop a model for the dynamics of seismogenerating structures in the frontal zone of the Kolyma–Omolon superterrane (Chersky seismotectonic zone), the following aspects are analyzed: structural–tectonic position, deep structure parameters, active faults, and fields of tectonic stresses as revealed from solutions of focal mechanisms of strong earthquakes and kinematic types of Late Cenozoic fold deformations and faults. It is found that a certain dynamic setting under transpressional conditions takes place and it was caused by the interaction between structures of the Eurasian, North American, and Okhotsk lithospheric plates within regional segments of the Chersky zone (Yana–Indigirka and Indigirka–Kolyma). These conditions are possible if the Kolyma–Omolon block located in the frontal zone of the North American Plate was an indenter. Due to this, some terranes of different geodynamic origin underwent horizontal shortening, under which particular blocks of segments were pushed out laterally along the orogenic belt, on a system of conjugated strike-slip faults of different directions and hierarchical series, in the northwest and southeast directions, respectively, to form the main seismogenerating reverse-fault and thrust structures with the maximum seismic potential (M ≥ 6.5).     

Gravity models of two-level collision of lithospheric plates in northeastern Asia

Structural forms of emplacement of crustal and mantle rigid sheets in collision zones of lithospheric plates in northeastern Asia are analyzed using formalized gravity models reflecting the rheological properties of geological media. Splitting of the lithosphere of moving plates into crustal and mantle constituents is the main feature of collision zones, which is repeated in the structural units irrespective of their location, rank, and age. Formal signs of crustal sheet thrusting over convergent plate boundaries and subduction of the lithospheric mantle beneath these boundaries have been revealed. The deep boundaries and thickness of lithospheric plates and asthenospheric lenses have been traced. A similarity in the deep structure of collision zones of second-order marginal-sea buffer plates differing in age is displayed at the boundaries with the Eurasian, North American, and Pacific plates of the first order. Collision of oceanic crustal segments with the Mesozoic continental margin in the Sikhote-Alin is characterized, as well as collision of the oceanic lithosphere with the Kamchatka composite island arc. A spatiotemporal series of deep-seated Middle Mesozoic, Late Mesosoic, and Cenozoic collision tectonic units having similar structure is displayed in the transitional zone from the Asian continent to the Pacific plate.     

中国东部NWW向活动断裂带构造特征:以张家口-蓬莱断裂带为例

中国东部新构造期活动强烈,前人对该时期NE向构造已有很多研究,但NWW向构造研究程度较低.本文以张家口-蓬莱断裂带为例,从几何学、运动学、动力学及地震活动性四个方面对中国东部的NWW向活动断裂带进行了分析.结果表明,中国东部的NWW向活动断裂带具有左行走滑的运动性质,并控制了第四纪盆地左阶雁列的展布样式;NWW向活动断裂带是孕震断裂,诱发了多次地震活动.在动力学上,这些断裂带是扳缘的不同段落变形在板内不同块体间响应调节的产物,且在周边板块的联合作用下,华北和华南南部NWW向断裂可能印度-欧亚板块碰撞的影响占主导,而东北和华南东部NWW向断裂可能太平洋板块俯冲的影响占主导.     

GPS-based modeling of the interaction between the lithospheric plates in Sakhalin

The recent geodynamics of Sakhalin are determined by the convergence between the Eurasian and North American lithospheric plates, which is reflected in the high seismicity of the island. The method of inversion of the horizontal velocities of the island surface with account for the geological features of the region is used to analyze the different models of the convergence between the plates. This made it possible to estimate the depth of the mechanical contact between the plates and the velocities of their convergence for the southern, central, and northern segments of the island.     

Relations between normal-fault geometry,tilting and vertical motions in extensional terrains: an example from the southern Gulf of Suez

Earthquakes and data from subsurface oil exploration suggest that large active normal faults in the southern Gulf of Suez are approximately planar, with dips of 30–40°, from the surface to around 10 km depth. These faults, and the blocks they bound, appear to rotate about a horizontal axis as they move, causing tilting. This tilting is seen both in young vertical movements of the coastline, such as raised beaches and marshlands, and in the distribution of Middle Miocene marine rocks, which are uplifted to elevations of 400–500 m in footwalls of faults and found at depths of around 3500 m in the adjacent grabens. The absolute amplitude of the observed vertical motions can be approximately modelled by planar rotating normal faults that impose a saw-tooth topography on a regional subsidence caused by crustal and lithospheric thinning. The observations required for this simple model are: the present day fault dip, the amount of tilting and the width of the rotating blocks. The virtues of the model are its simplicity and its compatibility with our knowledge of how large active normal faults move elsewhere on the continents.     

Active faulting at the Eurasian, North American and Pacific plates junction

The active faults known and inferred in the area where the major Pacific, North American and Eurasian plates come together group into two belts. One of them comprises the faults striking roughly parallel to the Pacific ocean margin. The extreme members of the belt are the longitudinal faults of islands arcs, in its oceanic flank, and the faults along the continental margins of marginal seas, in its continental flank. The available data show that all these faults move with some strike-slip component, which is always right-lateral. We suggest that characteristic right-lateral, either partially or dominantly, kinematics of the fault movements has its source in oblique convergence of the Pacific plate with continental Eurasian and North American plates. The second belt of active faults transverses the extreme northeast Asia as a continental extension of the active mid-Arctic spreading ridge. The two active fault belts do not cross but come close to each other at the northern margin of the Sea of Okhotsk marking thus the point where the Pacific, North American and Eurasian plates meet.     

Vector analysis of fault bends and intersecting faults

An analogy is drawn between intersecting faults or shear zones and triple junctions of lithospheric plates. Vector analysis shows that fault intersections are always unstable for rigid fault blocks but can be stabilized by the presence of zones of kinking or volume change within the fault blocks.The method allows rapid assessment of the likely location and orientation of wall-rock strains for any fault geometry and should be used to test kinematic models erected to account for field data.     

Shear Tectonic Fabric in the Atlantic Ocean and Its Relation to the Geodynamic Condition of the Upper Mantle and Intraplate Deformations

The tectogenesis of the Atlantic Ocean segments is complicated by the axial difference in spreading half-velocities, which causes additional shear displacements between the lithospheric blocks along the transform faults. The intensity of these processes and density of the fault zones iis related to the presence of “cold” sublithospheric lenses along the MAR at a depth of 500 km.     

Model of the formation of marginal seas in the western Pacific Ocean

A geodynamic model for the formation and movement of marginal seas in the Pacific Ocean during lateral interaction between the Eurasian and Pacific lithospheric plates is proposed. In a transition strike-slip megazone, the continental and oceanic plates disintegrate into blocks, which are involved in rotation, thus causing formation of mantle plumes and tectonospheric funnels (ascending and descending lithospheric vortexes). The implications of the model are formulated. Three scenarios of the evolution of the marginal sea basins depending on the direction of motion of the Pacific plate are discussed.     

中国岩石圈应力场与构造运动区域特征

笔者系统分析了1918—2005年间中国大陆及其周缘发生的3130个中、强地震的震源机制解,根据其特征进行了岩石圈应力场构造分区,首次得到区域应力场的压应力轴和张应力轴空间分布的统计数字结果。在此基础上研究了应力场的区域特征、探讨了其动力学来源以及构造运动特征。总体结果表明,中国大陆及其周缘岩石圈应力场和构造运动可以归结为印度洋板块、太平洋板块、菲律宾海板块与欧亚板块之间相对运动,以及大陆板内区域块体之间的相互作用的结果。印度洋板块向欧亚板块的碰撞挤压运动所产生的强烈的挤压应力,控制了喜马拉雅、青藏高原、中国西部乃至延伸到天山及其以北的广大地区。在青藏高原周缘地区和中国西部的大范围内,压应力P轴水平分量方位位于20～40°,形成了近NE方向的挤压应力场。大量逆断层型强震集中发生在青藏高原的南、北和西部周缘地区,以及天山等地区。而多数正断层型地震集中发生在青藏高原中部高海拔的地区,断层位错的水平分量位于近东西方向。表明青藏高原周缘区域发生南北向强烈挤压短缩的同时,中部高海拔地区存在着明显的近东西向的扩张运动。中国东部的华北地区受到太平洋板块向欧亚板块俯冲挤压的同时,又受到从贝加尔湖经过大华北直到琉球海沟的广阔地域里存在着的统一的、方位为170°的引张应力场的控制。华北地区大地震的震源机制解均反映出该区地震的发生大体为NEE向挤压应力和NNW向张应力的共同作用结果。台湾纵谷断层是菲律宾海板块与欧亚板块之间碰撞挤压边界。来自北西向运动的菲律宾海板块构造应力控制了从台湾纵谷、华南块体,直到中国南北地震带南段东部地域的应力场。地震的震源机制结果还表明,将中国大陆分成东、西两部分的中国南北地震带是印度洋板块、菲律宾海板块与太平洋板块在中国大陆内部影响控制范围的分界线。     

Seismogeodynamics of the Aldan-Stanovoi block

New geological-structural, seismological, seismotectonic, land geodetic, and GPS data were summirized to study the general geodynamic position of the Aldan-Stanovoi block, its recent structural-tectonic patterns, and the tendencies in the structural formation of active faults in the heterogeneous field of tectonic stresses determined by the interaction between the Eurasian and Amur lithospheric plates in southern East Siberia (Transbaikal region), southern Yakutia, and the Amur region.     

Strike-slip fault system in the Earth’s crust of the Bering Sea: A relic of boundary between the Eurasian and North American lithospheric plates

A study based on computation of D-function anomalies (method of joint gravity and magnetic data analysis) along profiles in the Bering Sea has been performed in both the Aleutian Basin with oceanic crust and the Bering continental shelf. This study revealed extended faults that affect not only the Earth’s crust but also the upper mantle. This is supported by seismic profiling. The calculated palinspastic reconstructions of the position of North America relative to “immobile” Eurasia 80, 52–50, 50–47, and 15–20 Ma ago allowed us to show that the revealed strike-slip faults are probable relics of an echeloned transform boundary between the Eurasian and North American lithospheric plates. The formation of this boundary beginning from the Late Cretaceous was apparently related to opening of the North Atalantic, which determined the large rate of displacement of North America relative to Eurasia.     

云南川西地区地震地质基本特征的探讨

云南川西地区是多震的地方(图1),从公元前116年到1974年6月,据记载共发生M≥4.75级的地震481次,其中6≤M<7的99次,7≤M<8的14次,M≥8的3次。震源深度一般小于30公里,均为浅源地震。本区强震多发生在深大断裂带上,而且都有一定的地质标志可循,与近代地壳运动、板块构造在成因上有着密切关系。     

青藏高原东南缘弧形旋扭活动构造体系及其动力学特征与机制

在系统总结前人成果资料基础上,结合最新的遥感解译与地表调查资料发现,青藏高原东南缘地壳最新的顺时针旋转运动主要受控于由川滇外弧带和滇西内弧带构成的双弧型川滇弧形旋扭活动构造体系。进一步的综合分析认为,该构造体系的弧形旋扭运动学变形模式的动力学机制及其内部块体变形的差异性与不均匀性,主要是该区边界力的作用方式、先存地质结构和现今的地壳与岩石圈结构、岩石圈物质组成及其物理性质、深部的热状态、重力势能等多种因素共同作用的结果。其中,印度板块与扬子地块之间的右旋剪切和青藏高原内部物质向东南的不均匀挤出共同产生的力偶作用和岩石圈性质与结构,可能是造成该区围绕东喜马拉雅构造结整体发生顺时针旋转运动和旋扭叠加伸展变形最重要的因素。     

Lithospheric plate motions — One of the factors controlling distribution of ore deposits in some mineral belts

Determination of paleolatitudes of ore deposits, based on the reconstruction of lithospheric plate motions and the absolute ages of deposits, provides a basis for a new kind of space-time analysis of structural control of ore deposition. Such analysis shows that the formation of two ore deposits of different ages, each occurring at a different latitude along a north-south trend within a mineral belt, may be controlled by the same transversal fracture zone in the substratum underlying the lithospheric plate if rotation of the plate took place in the time-span between the formation of the two ore deposits (Fig. 3). This mechanism controlling ore deposition has been elucidated using a model which assumes horizontal movement of lithospheric plates on a mobile layer that originated within solid basement that is penetrated by a system of fracture zones. The distribution of porphyry copper deposits of the Andes mineral belt is used to study this process.     

Is northern Honshu a microplate?

Seismic slip vectors along the Japan Trench, the eastern margin of the Japan Sea and the Sagami Trough are compared with global relative plate motions (RM2, Minster and Jordan, 1978) to test a new hypothesis that northern Honshu, Japan, is part of the North American plate. This hypothesis also claims that the eastern margin of the Japan Sea is a nascent convergent plate boundary (Kobayashi, 1983; Nakamura, 1983).Seismic slip vectors along the Japan Trench are more parallel to the direction of the Pacific-North American relative motion than that of the Pacific-Eurasian relative motion. However, the difference in calculated relative motions is too small avoid to the possibility that a systematic bias in seismic slip vectors due to anomalous velocity structure beneath island arcs causes this apparent coincidence. Seismic slip vectors and rates of shortening along the eastern margin of the Japan Sea for the past 400 years are also consistent with the relative motion between the North American and Eurasian plates calculated there. Seismic slip vectors and horizontal crustal strain patterns revealed by geodetic surveys in south Kanto, beneath which the Philippine Sea plate is subducting, indicate two major directions; one is the relative motion between the North American and Philippine Sea plates, and the other that between the Eurasian and Philippine Sea plates.One possible interpretation of this is that the eastern margin of the Japan Sea may be in an embryonic stage of plate convergence and the jump of the North American-Eurasian plate boundary from Sakhalin-central Hokkaido to the eastern margin of the Japan Sea has not yet been accomplished. In this case northern Honshu is a microplate which does not have a driving force itself and its motion is affected by the surrounding major plates, behaving as part of either the Eurasian or North American plate. Another possibility is that the seismic slip vectors and crustal deformations in south Kanto do not correctly represent the relative motion between plates but represent the stresses due to non-rigid behaviors of part of northern Honshu.     

Geodynamics and seismicity of the eastern part of Central Asia

Study of the geodynamics of the eastern part of Central Asia shows that the present-day tectonic activity of this territory is connected with its division into blocks limited by active faults and with the interaction among these blocks and with the neighboring lithospheric plates. The North China and South China platforms occupy most of this territory. The western boundary of the South China platform with Tibetan blocks is the most active. The energy volume increases up to 10¹⁰–10¹² J, and the earthquake magnitudes go up to 8–9 within this boundary. The interaction of Tibetan blocks with the Southeast China Block causes detachment and a clockwise turn of the upper layers of the Earth’s crust under the influence of the Hindustan indenter pressure.

     

Deformations and Manifestations of Degassing in the Sedimentary Cover of the Equatorial Segment of the West Atlantic: Implications for Lithospheric Geodynamics

Manifestations of fluids and deformations in the sedimentary cover, which are both factors of brightening (blanking anomalies) in seismoacoustic records, in the equatorial segment of the Atlantic coincide with the sublatitudinal zones of the activated passive parts of transform faults and with zones of lower gravity anomalies and higher values of remnant magnetization, which form as a result of serpentinization. The cause-and-effect sequence of intraplate phenomena includes: the contrasting geodynamic state → horizontal movements that form macrofractures → water supply to the upper mantle → serpentinization of rocks in the upper mantle → deformations associated with vertical uplift of basement and sedimentary cover blocks, coupled with fluid generation → and fluid accumulation in the sedimentary cover, accompanied by the formation of anomalies in seismoacoustic records. Based on the seismic data, we have identified imbricate-thrust deformations, diapir structures, stamp folds, and positive and negative flower structures, indicating the presence of strike-slip faults in the passive parts of transform faults. The general spatial distribution of deformation structures shows their concentration in cold mantle zones. Correlative comparison of the structural characteristics of deformations shows the direct relationship between the heights of structures and the development of serpentinization processes. As per the age of the basement, deformations range from 27–38 to 43–53 Ma; a quite thick sedimentary cover makes it possible to reveal them based on the characteristic types of seismoacoustic records. The formation of the Antilles arc ca. 10 Ma ago affected the equatorial segment of the Atlantic; it formed kink bands where lithospheric blocks underwent displacements with counterclockwise rotations, deformations related to compression and vertical uplift of crustal fragments, and local extension that favored degassing of endogenous fluids. Sublatitudinally oriented imbricate-thrust deformations with different vergences indicate irregularity and alternating strike-slip directions as blocks between fractures were laterally influenced.     

Neotectonic transpressional intraplate deformation in eastern Eurasia: Insights from active fault systems in the southeastern Korean Peninsula

Transpression occurs in response to oblique convergence across a deformation zone in intraplate regions and plate boundaries. The Korean Peninsula is located at an intraplate region of the eastern Eurasian Plate and has been deformed under the ENE–WSW maximum horizontal compression since the late Pliocene. In this study, we analyzed short-term instrumental seismic (focal mechanism) and long-term paleoseismic (Quaternary fault outcrop) data to decipher the neotectonic crustal deformation pattern in the southeastern Korean Peninsula. Available (paleo-)seismic data acquired from an NNE–SSW trending deformation zone between the Yangsan and Ulleung fault zones indicate spatial partitioning of crustal deformation by NNW–SSE to NNE–SSW striking reverse faults and NNE–SSW striking strike-slip faults, supporting a strike-slip partitioned transpression model. The instantaneous and finite neotectonic strains, estimated from the focal mechanism and Quaternary outcrop data, respectively, show discrepancies in their axes, which can be attributed to the switching between extensional and intermediate axes of finite strain during the accumulation of wrench-dominated transpression. Notably, some major faults, including the Yangsan and Ulsan fault zones, are relatively misoriented to slip under the current stress condition but, paradoxically, have more (paleo-)seismic records indicating their role in accommodating the neotectonic transpressional strain. We propose that fluids, heat flow, and lithospheric structure are potential factors affecting the reactivation of the relatively misoriented major faults. Our findings provide insights into the accommodation pattern of strain associated with the neotectonic crustal extrusion in an intraplate region of the eastern Eurasian Plate in response to the collision of the Indian Plate and the subduction of the Pacific/Philippine Sea Plates.     

Active rifting in the Japan and Okhotsk seas and the tectonic evolution of the Central Sakhalin Fault zone in the Cenozoic

Large-scale geological maps available for individual areas in the Central Sakhalin Fault zone and geological-geophysical maps of Sakhalin and surrounding sea areas were analyzed to elucidate the tectonic evolution of the fault zone determined by movements of crustal blocks due to the opening of rift basins. Changes in the direction of horizontal compression in the Sakhalin fold system from diagonal (NW-SE) to near-latitudinal resulted in the transformation of near-meridional right-lateral strike-slip faults into reversed faults in the Late Miocene. This allows Sakhalin faults to be interpreted as a zone of recent right-lateral shear between Eurasian and Sea of Okhotsk plates.