Fault-bounded blocks and their role in localising sedimentation and deformation adjacent to the alpine fault, southern New Zealand

Continental transform boundaries in detail consist of zones of fault-bounded blocks adjacent to the principal active transform fault(s). Relative movement of these blocks in response to plate boundary motions gives rise to differential vertical displacements of the earth's crust and hence exercises a degree of control on the tectonic evolution of sedimentary basins adjacent to the transform boundary. The Cenozoic sedimentary basins of southwest New Zealand have several features in common that may be attributed directly to the movement on the adjacent plate boundary. However, their location, detailed sedimentary evolution and tectonic development may best be understood in the context of the relative displacements of a number of fault-bounded blocks, in response to the plate motions. In particular, movements of the Fiordland block, bounded by the Alpine and Moonlight fault zones, exercised a large measure of influence on the development of the basins. The tectonic model presented is consistent with plate boundary motions inferred from marine magnetic anomalies while at the same time providing an explanation for many of the more detailed features of the basins.     

Crustal deformation in northern Central America

Evaluation of the seismic moment tensor for earthquakes on plate boundary is a standard procedure to determine the relative velocity of plates, which controls the seismic deformation rate predicted from the slip on a single fault. The moment tensor is also decomposed into an isotropic and a deviatoric part to discover the relationship between the average strain rate and the relative velocity between two plates. We utilize this procedure to estimate the rates of deformation in northern Central America where plate boundaries are seismically well defined. Four different tectonic environments are considered for modelling of the plate motions. The deformation rates obtained here compare well with those predicted from the plate motions models and are in good agreement with actual observations. Deformation rates on faults are increasingly being used to estimate earthquake recurrence from information on fault slip rate and more on how we can incorporate our current understanding into seismic hazard analyses.     

大别山商城—麻城断裂带的~(40)Ar-~(39)Ar年龄及其意义

商城 麻城断裂带在大别山的构造格局中占有重要地位,但长期以来对其形成时代缺乏精细的测年研究,有鉴于此,我们采用断裂带糜棱岩中黑云母单矿物~(40)Ar-~(39)Ar年代学方法测定其变形时代。结果表明,商麻断裂带形成于226 Ma左右,是扬子和华北两大板块碰撞后期的产物,是一条垂直于造山带走向的横向平移断层。在商麻断裂带的转换调节下,其两侧地块发生差异位移、抬升和相对旋转,导致东西两侧的超高压岩石的折返出露呈现出不同的特征。     

Early Miocene stratigraphy of central west Anatolia,Turkey: implications for the tectonic evolution of the eastern Aegean area

Small‐mammalian faunas enable the discrimination and correlation of uppermost Lower Miocene lacustrine sedimentary units in central western Anatolia. On the basis of sequential stratigraphic relationships, early Early Miocene and latest Early Miocene relative ages are suggested for the older lacustrine mass‐flow deposits and younger paper shale units, respectively, which are devoid of age‐diagnostic fossils. In central western Anatolia, the sequential differences between the uppermost Lower Miocene successions delineate a deformation zone of NE–SW‐trending fault blocks separated by vertical faults. This deformation zone, inherited from Late Oligocene tectonics, underwent an early Early Miocene sinistral transtension leading to pull‐aparts that were emplaced by granitoids. Limited extension caused the late Early Miocene repetitive up‐ and down‐wards motions of the fault blocks, with variable magnitudes. This led to contrasting subsidence histories in the relevant basinal system. During the latest Early Miocene, fault blocks coalesced into a regional body characterized by uniform slow subsidence and non‐extensional deformation facies. The general trend of the above tectonic events can be explained by lateral slab segmentation and progressive asthenospheric wedging, in response to NE‐directed and decelerated palaeosubduction in the Aegean. Copyright © 2007 John Wiley & Sons, Ltd.     

Structural relationship between the Sea of Marmara Basin and the North Anatolian Fault Zone

The North Anatolian Fault (NAF) zone is 1500 km long, extending almost up to the Greek mainland in the west. It is a seismically active right-lateral strike-slip fault that accommodates the relative motion between the Turkish block and Black Sea plate. The Sea of Marmara lies along the western part of the NAF and shows evidence of subsidence. In this area pure strike-slip motion of the fault zone changes into extensional strike-slip movement that is responsible for the creation of the Sea of Marmara and the North Aegean basins. The northern half of the Sea of Marmara is interpreted as a large pull-apart basin. This basin is subdivided into three smaller basins separated by strike-slip fault segments of uplifted blocks NE-SW. Basinal areas are covered by horizontally layered sedimentary sequences. Uplifted blocks have undergone compressional stress. All the blocks are subsiding and are undergoing vertical motions and rotations relative to one another. The uplifted blocks exhibit positive Bouguer gravity anomalies. According to gravity interpretation, there is relative crustal thinning under the Sea of Marmara. The northern side of the Sea of Marmara is marked by a distinctive deep-rooted magnetic anomaly, which is dissected and shifted southward by strike-slip faulting. The southern shelf areas of the Sea of Marmara are dominated by short-wavelength magnetic anomalies of shallow origin.     

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。     

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。     

Active Motion of Tectonic Blocks in East Asia: Evidence from GPS Measurement

The relative Euler vectors of the Pacific, Philippine, Amurian, Okhotsk, N. Honshu and South China plates or blocks are deduced from earthquake slip vectors, transform fault azimuths and spreading rates, which are consistent with new results derived from the International Terrestrial Reference Frame ITRF2000 velocity field, the velocity field of GPS stations in China and the GPS measurement data of the GEONET network in Japan. Based on the two groups of Euler vectors, analysis and comparative study of the relative motions and deformations of the tectonic blocks in East Asia reveal the present-day motion characteristics of the blocks.     

A model with rigid rotations and slip deficits for the GPS-derived velocity field in Southwest Japan

We interpret the GPS-derived velocity field in southwest Japan by a superposition of the elastic deformation caused by fault interactions (slips or slip deficits) on the rigid motion of tectonic blocks (or plates). Based on the strain rate field and crustal seismicity, we apply a model with three blocks (Inner Arc, Outer Arc, and the northern Ryukyu block) and slip deficits along the block boundaries.Several characteristics of the synthesized contributions are found:

(1) Westward motion of the outer arc relative to the Amurian plate and the inner arc,

(2) southeastward motion of the northern Ryukyu block relative to the Amurian plate,

(3) 2−4 mm/yr deficits of left lateral slip rates along the boundary at 32°N in southern Kyushu,

(4) 0−8 mm/yr deficits of right lateral slip rates along the Median Tectonic Line and the Beppu-Shimabara Graben,

(5) slip deficit rates on the plate interface smaller than those in the case without any consideration for rigid block motions,

(6) clockwise deflection of slip deficit rate vector on the plate interface from that estimated when not taking rigid block motions into consideration.

Numerical modeling of strike-slip creeping faults and implications for the Hayward fault, California

The seismic potential of creeping faults such as the Hayward fault (San Francisco Bay Area, CA) depends on the rate at which moment (slip deficit) accumulates on the fault plane. Thus, it is important to evaluate how the creep rate observed at the surface is related to the slip on the fault plane. The surface creep rate (SCR) depends on the geometry of locked and free portions of the fault and on the interaction between the fault zone and the surrounding lithosphere. Using a viscoelastic finite element model, we investigate how fault zone geometries and physical characteristics such as frictionless or locked patches affect the observed surface creep when the system is driven by far field plate motions. These results have been applied to creep observations of the Hayward fault. This analysis differs from most previous fault creeping models in that the fault in our model is loaded by a distributed viscous flow induced by far field velocity boundary conditions instead of imposed slip beneath the major faults of the region. The far field velocity boundary conditions simulate the relative motion of the stable Pacific plate respect to the Rigid Sierra Nevada block, leaving the rheology, fault geometry, and mechanics (locked or free to creep patches), to determinate the patterns of fault creep.Our model results show that the fault geometry (e.g. length and depth of creeping) and the local rheology influence the surface creep rate (SCR) and the slip on the fault plane. In particular, we show that the viscoelastic layer beneath the elastic seismogenic zone plays a fundamental role in loading the fault. Additionally, the coupling with the surrounding lithosphere results in a smooth transition from regions free to creep to locked patches.     

Particle motions in a physical model of shallow angle thrust faulting

A physical model of thrust faulting has been constructed out of elastic foam rubber. The thrust wedge has an angle of 25°., and is forced from the back by a steel-hydraulic system of effectively infinite rigidity, analogous to the force exerted by tectonic plates. The observed particle motions show many features different from those commonly assumed in dislocation models of subduction thrusts. Interface waves associated with fault opening propagate along the thrust plane (from the back) and temporarily decouple the overlying hanging wall plate from the foot wall. Because of the geometry of the reflecting fault boundary, and the free surface (also reflecting), energy is trapped in the wedge and, as a consequence, the particle motions and energy in the hanging wall are much greater than in the foot wall. The interface wave and the energy trapped in the upper plate propagate up the wedge and break out at the toe of the thrust with a spectacular increase in motions. If this model is analogous to the real earth, it suggests that some common assumptions in dislocation modeling may be incorrect. The model may explain apparent missing energy radiated to teleseismic distances, the anomalously low number of empirical Green’s functions needed to model teleseismicp waves, and the evidence of intense shaking on the hanging wall toe of some thrust fault earthquakes. The results support the suggestion that interface waves may explain the lack of high frictional heat generation from thrust faults, and may explain the ‘paradox of large overthrusts’. The results also suggest that the seismic hazard of great subduction thrust earthquakes and continental shallow angle thrust faults might in some cases be seriously underestimated.     

济阳盆地中生代构造特征与油气

济阳盆地中生代构造主要包括：印支期ＮＷ向压性构造（褶皱及逆断层）、消亡的ＮＷ向负反转半地垒及半地堑、燕山期ＥＮＥ向压性构造（褶皱或逆断层）、ＳＮ向地垒。印支期ＮＷ向压性构造是华北板块同扬子板块的聚敛运动的产物,而ＮＷ向负反转地垒和地堑、ＥＮＥ向压性构造及ＳＮ向地垒导源于郯庐断裂的左旋剪切作用,新生代郯庐断裂右旋剪切运动导致上述构造消亡并成为隐伏构造。中生代隐伏构造为济阳盆地深层勘探提供了潜山圈闭（     

Quaternary crustal deformation along a major branch of the San Andreas fault in central California

Deformed marine terraces and alluvial deposits record Quaternary crustal deformation along segments of a major, seismically active branch of the San Andreas fault which extends 190 km SSE roughly parallel to the California coastline from Bolinas Lagoon to the Point Sur area. Most of this complex fault zone lies offshore (mapped by others using acoustical techniques), but a 4-km segment (Seal Cove fault) near Half Moon Bay and a 26-km segment (San Gregorio fault) between San Gregorio and Point Ano Nuevo lie onshore.At Half Moon Bay, right-lateral slip and N—S horizontal compression are expressed by a broad, synclinal warp in the first (lowest: 125 ka?) and second marine terraces on the NE side of the Seal Cove fault. This structure plunges to the west at an oblique angle into the fault plane. Linear, joint0controlled stream courses draining the coastal uplands are deflected toward the topographic depression along the synclinal axis where they emerge from the hills to cross the lowest terrace. Streams crossing the downwarped part of this terrace adjacent to Half Moon Bay are depositing alluvial fans, whereas streams crossing the uplifted southern limb of the syncline southwest of the bay are deeply incised. Minimum crustal shortening across this syncline parallel to the fault is 0.7% over the past 125 ka, based on deformation of the shoreline angle of the first terrace.Between San Gregorio and Point Ano Nuevo the entire fault zone is 2.5–3.0 km wide and has three primary traces or zones of faulting consisting of numerous en-echelon and anastomozing secondary fault traces. Lateral discontinuities and variable deformation of well-preserved marine terrace sequences help define major structural blocks and document differential motions in this area and south to Santa Cruz. Vertical displacement occurs on all of the fault traces, but is small compared to horizontal displacement. Some blocks within the fault zone are intensely faulted and steeply tilted. One major block 0.8 km wide east of Point Ano Nuevo is downdropped as much as 20 m between two primary traces to form a graben presently filling with Holocene deposits. Where exposed in the sea cliff, these deposits are folded into a vertical attitude adjacent to the fault plane forming the south-west margin of the graben. Near Point Ano Nuevo sedimentary deposits and fault rubble beneath a secondary high-angle reverse fault record three and possibly six distinct offset events in the past 125 ka.The three primary fault traces offset in a right-lateral sense the shoreline angles of the two lowest terraces east of Point Ano Nuevo. The rates of displacement on the three traces are similar. The average rate of horizontal offset across the entire zone is between 0.63 and 1.30 cm/yr, based on an amino-acid age estimate of 125 ka for the first terrace, and a reasonable guess of 200–400 ka for the second terrace. Rates of this magnitude make up a significant part of the deficit between long-term relative plate motions (estimated by others to be about 6 cm/yr) and present displacement rates along other parts of the San Andreas fault system (about 3.2 cm/yr).Northwestward tilt and convergence of six marine terraces northeast of Ano Nuevo (southwest side of the fault zone) indicate continuous gentle warping associated with right-lateral displacement since early or middle Pleistocene time. Minimum local crustal shortening of this block parallel to the fault is 0.2% based on tilt of the highest terrace. Five major, evenly spaced terraces southeast of Ano Nuevo on the southwest flank of Mt. Ben Lomond (northeast side of the fault zone) rise to an elevation of 240 m, indicating relatively constant uplift (about 0.19 m/ka and southwestward tilt since Early or Middle Pleistocene time (Bradley and Griggs, 1976).     

华北块体、胶辽朝块体与郯庐断裂

华北块体（NCB）与胶辽朝块体（JLKB）是中朝板块东部从震旦纪（680Ma)开始裂解的两个不同的构造单元。两个块体的界线称古郯庐断裂（PTLF），古郯庐断裂位置与现今郯庐断裂（TLF）相吻合，即由合肥向北延伸，过渤海，经沈阳以东呈NE走向至吉林南部。古郯庐断裂带附近震旦纪碳酸盐岩中的强地震记录及相应的辉绿岩侵位，是中朝板块内部裂解的基本地质证据，古郯庐断裂带（板内地震带）与元古超大陆Rodinia的裂解时期是一致的。两个块体上，太古宙基底岩石不同；元古宙及古生代的发展历史有别，两个块体于晚石炭世的莫斯科期重新闭合。朝鲜半岛中部的临津江带曾被认为是大别-胶南造山带的东延部分，但临津江带只是一般性断裂，胶南超高压带在朝鲜半岛并未发现，朝鲜半岛南部主体与辽东半岛古生界相似，因此，将中朝板块的南界，也是较辽朝块体的南界置于朝鲜半岛之南，它与胶南造山带以黄海转换断层（YSTF）联结。辽宁省瓦房店（旧称复县）与山东省蒙阴含金刚石的金伯利岩分布在郯庐断裂带的东，西两侧，南北方向距离的550km。两地金伯利岩年龄值在500-450Ma之间，即中奥陶世末侵位。鉴于两地金伯利岩在岩相学，矿物学与侵位年龄等某些方面的相似性，又紧邻郯庐断裂两侧，有些地质学家认为二者在侵位时可能相距颇近，属同一岩省，因而将瓦房店与蒙阴两个金伯利岩岩省之间的距离总是用郯庐断裂的巨大平移来解释。郯庐断裂为切过岩石圈的深断裂，对比瓦房店与蒙阴两地岩石圈剖面的异同，应是判断郯庐断裂有无巨大平移的重要依据。通过对金伯利岩中地幔样品的研究，揭示出了两地岩体侵位时所穿越的古岩石圈剖面是很不一致的，表明二者当时并非连接一起或相距甚近图片者结合区域地质构造研究的新认识，发现它们实际是分别侵位于中朝板块的两个不同的构造单元上，两地距离与平移无关，不支持郯庐断裂左行走滑巨大平移的观点，本文期望这种交叉学科研究所提供的材料能有助于讨论中国东部这一巨型断裂系统的性质。     

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。     

Seismic strain in the Altai-Sayan active seismic area and elements of collisional geodynamics

Seismic strain estimated from about 900 earthquake mechanisms in the Altai-Sayan area indicates that the area evolves mainly under N-S compression caused by the India-Eurasia collision. Plastic flow in the mountains of the western and central Altai-Sayan area is controlled by convergence of aseismic rigid blocks, including the Dzungarian microplate, the Minusa basin, the Tuva basin, Uvs Nuur and other basins in the region of Great Lakes in Mongolia. Earthquake rupture follows the existing fault pattern. The pattern of rigid blocks and mountain ranges correlates well with upper mantle thermal heterogeneity as imaged by seismic tomography.Earthquake mechanisms in the presence of plate convergence depend on different factors. Slip geometry depends on focal depth at a given geodynamic regime, and the latter, in terms of the seismic process, is controlled by lateral (W-E) constraint. Reverse-slip earthquakes most often originate at shallow depths in regions of constrained compression, such as the Tien Shan, and strike slip is the dominant mechanism under non-constrained and moderately constrained compression. The direction of slip is governed by the parallel component of convergence and by the fault pattern. In regions of strain shadow, slip occurs mostly on normal planes, and shallow earthquakes have strike-slip mechanisms. The crust in the collisional region is divided into systems of rigid and plastic blocks (rheological structure) and of fault blocks (fault-block structure). The two types of systems coexist and determine the generally similar but specifically different features of local mass transfer.     

Active strike–slip faulting and macroscopically nonrigid deformation of volcanic rocks in central Japan inferred from a paleomagnetic study

Detailed paleomagnetic investigation of a pyroclastic flow deposit has clarified the deformation mode around an active fault. In central Japan, the early Quaternary Nyukawa Pyroclastic Flow Deposit is cut by the active dextral Enako fault. Activity level of the fault is evaluated on the basis of geological and geomorphological surveys. Then, paleomagnetic samples are collected from 22 sites at exposures located on a lineament that is adjoining and parallel to the Enako fault. Stable thermoremanent magnetization (TRM) of the pyroclastic deposit is isolated through progressive thermal and/or alternating field demagnetization tests. Untilted site-mean directions of the TRMs simultaneously acquired during initial cooling indicate significant clockwise vertical-axis rotation. The lineament was then activated with right-lateral motions through the early Quaternary. Together with the late Quaternary activities along the adjoining Enako fault evaluated by our study, the present result exemplifies a migration of active segments within a fault system during the Quaternary. Paleomagnetic directions on the strike–slip fault are not concordant with uniform deformation predicted by the model of rotation of rigid blocks aligned on a master fault, but suggestive of a periodic deformation as a result of intense fracturing and differential rotation of blocks bounded by nested parallel faults.     

Convection in the earth's mantle

According to the hypothesis of global plate tectonics the surface motions of the earth are now known in considerable detail, but very little is known about the three-dimensional flow in the earth and about the forces which maintain the motions. The motions at depth are difficult to study because they produce few surface effects. For instance, there is now no reason to believe that ridges are the surface evidence for rising convection currents at depth. Only the plate motions themselves and the gravity field observed by satellites must be consequences of three-dimensional flow beneath the plates. Other observations, such as the high heat flow near ridges or deep earthquakes beneath trenches, now appear to be explained by the production and destruction of plates.     

地球表层运动和变形的GPS描述

利用IERS所公布的分在全球各大构造板块上的 6 5 7个GPS、SLR和VLBI连续观测站在ITRF框架下的速度场资料 ,采用刚体板块运动 +板块整体均匀应变 +板块内局部不均匀应变的变形分析模型 ,研究了全球各主要板块的运动和变形。结果表明板块的整体变形在统计上均不显著。在一级近似上板块间表现出来的整体相对运动显著 ,根据这些运动参数定量研究了板块边界的相对运动的大小和性质。认为地球的双重不对称变形可能主要表现为南北、东西两半球所含的板块边界的运动方式不同所致。板块内的局部不均匀变形明显 ,为板块内部可能应划分成次一级的活动地块提供了佐证。由于观测点分布的密度和均匀性不足 ,本文未能就板内不均匀变形作进一步的深入讨论。     

伸展盆地复杂断块运动学平面复原--以渤海湾盆地廓坊-固安断陷为例

本文选取廊固凹陷为例,利用平面恢复方法,研究伸展盆地断块平面运动特征。根据大兴断层的分段性,将研究区分为3个区块：西南区,中区以及东北区,又根据研究区的断块旋转特征,将中区分为中北区以及中南区。每个区块的断块运动差异性很大。通过对廊固凹陷古近系的断块进行构造平面恢复,发现其平面运动具有以下特征：西南区,断块主要以顺时针旋转,位移方向为东南—西北; 中区,中南区断块主要以顺时针旋转,中北区主要以逆时针旋转,位移方向为西北—东南,中间位移量最大,向东北及西南端位移量逐渐减小; 东北区,除沙二段外,断块主要受桐柏镇断裂影响以逆时针旋转,位移方向为近似南—北。其中东北区和西南区的位移方向相似,且与中区的位移方向相反,猜测与主控断层大兴断层的分段性有关。中区的中南部断块主要以顺时针旋转,而中北部断块主要以逆时针旋转,由于中区主应力集中在凹陷中间,向两端应力逐渐减小,导致应力作用不平衡。