龙日坝断裂带位于青藏高原最东缘,呈北东—南西向延伸,平行于其东侧的龙门山断裂带,二者大约相距150 km.与龙门山断裂带不同的是,龙日坝断裂带在青藏高原东缘相关GPS测量中表现为一明显的速度梯度带,说明龙日坝断裂带可能具有很重要的构造属性.然而有关龙日坝断裂带的地表结构构造延伸问题一直悬而未决,目前还存在许多的争议,这在一定程度上也阻碍了我们对青藏高原东缘相对于印度—欧亚板块碰撞地球动力学响应的了解.在本次研究中,我们将首次采用ALOS-PALSAR卫星数据,并结合地表地质和前人的地球物理学研究成果,来监测与龙日坝断裂带的构造活动相关的细微地表形变,并由此控制龙日坝断裂带的延伸范围.研究结果表明,龙日坝断裂带与其西南侧的抚边河断裂带相交且近乎垂直,而非前人研究所认为的龙日坝断裂带延伸至其西缘的鲜水河断裂带.综合研究结果也为了解龙日坝断裂带的大地构造属性提供了数据支持.

Most previous studies of the Tibetan Plateau have focused on the processes of crustal thickening and subsequent outward growth. However, lithospheric structure across the tectonic boundaries of the plateau has not yet been fully imaged, and therefore, how geological structures evolved in association with the lateral expansion of the margins remains unclear. Here together with interpretation of regional aeromagnetic anomalies, we employ a recently acquired 165km long deep seismic reflection image that crosses the northeastern flank of the Tibetan Plateau. The resulting crustal architecture suggests that crustal shortening is a primary driver for plateau uplift of northeastern Tibet and that the Xiaoguan Shan to the east of the Liupan Shan belt marks the easternmost edge of the strata that has been affected by the northeastward growth of the plateau. In addition, decoupled crustal deformation owing to differential structural integrity has been accommodated during the subsequent northeastward growth of the plateau.

The regional crustal and uppermost mantle structure of the Rio Grande rift and adjacent provinces has been determined from Rayleigh wave group and phase velocity measurements and published seismic refraction data. These data clearly demonstrate thinning of the crust under the Rio Grande rift. The Colorado Plateau is characterized by a crustal thickness of ∼ 45km and an Sn velocity of ∼ 4.5 km/sec (Pn, 7.8 km/sec); the southern Great Plains are characterized by a crustal thickness of ∼ 50km and an Sn velocity of ∼ 4.6 km/sec (Pn, 8.9 km/sec); the Rio Grande rift is characterized by a crustal thickness of ∼ 35km and an Sn velocity of ∼ 4.4 km/sec (Pn, 7.7 km/sec).

The Solonker suture zone is one of the most important tectonic boundaries in the southeastern part of the Central Asian Orogenic Belt (CAOB). An ~630km-long reflection seismic profile across this suture was recently completed by the Chinese SinoProbe Project. The processed seismic data show clear crustal structures and provide new constraints on the tectonic and crustal evolution models. The Moho is delineated as a relatively flat boundary between a strongly reflective lower crust and a transparent mantle at a depth of ~40–45km (~14.5s two-way travel time), which is in agreement with the refraction data recorded along the same profile. In a broad view, the profile images an orogen that appears bivergent with, and approximately centered on, the Solonker suture zone. The southern portion of this profile is dominated by a crustal-scale, cratonward propagating fold-and-thrust system that formed during the late Permian and Triassic through collision and subsequent convergence in a post-collisional stage. The major thrust faults are truncated by Mesozoic granitoid plutons in the upper crust and by the Moho at the base of the crust. This geometry suggests that the Moho was formed after the thrusting event. The northern portion of the profile, although partially obliterated by post-collisional magmatic bodies, shows major south-dipping folding and thrusting. Bands of layered reflectors immediately overlying the Moho are interpreted as basaltic sills derived from the mantle. Episodic mafic underplating may have occurred in this region, giving rise to post-collisional magmatic events and renewal of the Moho. A few mantle reflectors are also visible. The overall geometry of these mantle reflectors supports the tectonic models that the southern orogen (Manchurides) experienced south-directed subduction and the northern orogen (Altaids) underwent north-directed subduction prior to collision along the Solonker suture zone.

During the last decade, a series of controlled source seismic experiments brought new insight into the crustal and lithospheric structure of the Eastern Alps and their adjacent tectonic provinces. A fragmentation of the lithosphere into three blocks, Europe (EU), Adria (AD), and the new Pannonian fragment (PA), was interpreted and a triple junction was inferred. The goal of this study has been to relate these deep crustal structures to active tectonics. We used elastic plate modeling to reconsider the Moho fragmentation. We interpret subduction of EU below AD and PA from north to south and underthusting of AD mantle below PA from southwest to northeast. The Moho fragmentation correlates well with major upper crustal structures and is supported by gravity, seismic, and geodetic data. An analysis of crustal thickening suggests that active convergence is associated with continued thrusting and lateral extrusion in the central Eastern Alps and thickening of the Adriatic indenter under the Southern Alps. According to the velocity relations at the triple junction, PA moves relative to EU and AD along ENE and SE striking faults, mainly by strike slip. An eastward directed extensional component is compensated by the lateral extrusion of the central Eastern Alps. The Periadriatic (Insubric) line east of the triple junction and the mid-Hungarian fault zone have relatively recently lost their role as first-order active structures. We favor the idea that the Pannonian fragment and the TISZA blockmerged to a "soft" microplate surrounded by the Eastern and Southern Alpine, Carpathian, and Dinaric orogens. Citation: Bruckl, E., M. Behm, K. Decker, M. Grad, A. Guterch, G. R. Keller, and H. Thybo (2010), Crustal structure and active tectonics in the Eastern Alps, Tectonics, 29, TC2011, doi: 10.1029/2009TC002491.

Beginning in 1997, Central Europe between the Baltic and Adriatic Seas was covered by an unprecedented network of seismic refraction experiments (POLONAISE’97, CELEBRATION 2000, ALP 2002, and SUDETES 2003) that were only possible due to a massive international consortium consisting of more than 30 institutions from 16 countries in Europe and North America. The biggest experiment (CELEBRATION 2000) included 147 shots recorded by 1230 seismic stations forming, during three deployments, an array of ∼8900 km of profiles. The total length of seismic profiles in all these experiments is ∼20 000 km. During these four experiments, 295 large explosions provided the seismic sources. The majority of recording instruments were provided by the IRIS/PASSCAL Instrument Center and the University of Texas at El Paso (USA). The main results of these experiments are delineation of the deep structure of the southwestern margin of the East European craton (southern Baltica) and its relationship to younger terranes; delineation of the major terranes and crustal blocks in the Trans-European Suture Zone (TESZ); determination of the nature and extent of thrust faulting along the northern front of the Carpathians; improved understanding of the origin and structural framework of the Pannonian basin; improved knowledge of deep structure of the Eastern Alps; determination of the structural relationships between the structural elements of the Bohemian massif and adjacent features; development of three-dimensional models of the crustal structure; and development of new geodynamic models for the tectonic evolution of the Central Europe.

Potential fi eld data along the Texas portion of the Gulf of Mexico indicate a large-amplitude coast-parallel magnetic maximum and a smaller Bouguer gravity high. Models constrained by seismic-refraction data indicate that these maxima manifest a deeply buried volcanic rifted passive margin or other magnetic high in the outer transitional crust. Buried 12‐15 km, the source is 220 km wide, similar to the Voring Plateau in Norway and the U.S. East Coast. This margin, which formed during the opening of the Gulf of Mexico, differs in origin from the transform boundary of the northeast Mexico margin (Tehuantepec transform), and we infer a Jurassic triple junction related to the Borderland rift system, which is traceable as far as southeast California.

The extent of the Variscan deformation front is one of the key problems of the regional geology of the Central European Permian Basin system, particularly in its Polish part. Conventional reflection seismics usually fails to produce a satisfactory image of the pre-Permian strata due to the shielding effect of Zechstein (Upper Permian) evaporites. Thus we used a novel seismic acquisition technique to study the base of the Permian complex and its Variscan basement. In the GRUNDY 2003 experiment we combined wide-angle reflection-refraction measurements with the near-vertical reflection seismics by the use of the constant geophone array with dense (100 m) receiver spacing occupying 50-km long profile. 3D design of the experiment, covering 50 x 10 km area, helped in eliminating the effect of out-of-plane propagations and local inhomogeneities. An effective integration of traveltime tomography, CDP reflection processing and prestack depth migration of wide-angle reflections applied to our data, allowed us to present the model in which we deduced the contact zone of the Variscan overthrust structure (Variscan front) with its molasse-filled foredeep. The latter might be a gas-generation zone, which is of a great importance for hydrocarbons prospecting in this area. (c) 2007 Elsevier B.V All rights reserved.

An analysis of gravity data collected during the 2003 Ethiopia-Afar Geoscientific Lithospheric Experiment (EAGLE) and previously available data is used in conjunction with EAGLE seismic results to determine a preliminary crustal structure model of the main Ethiopian rift (MER). The Bouguer gravity anomaly is dominated by a regional gravity anomaly that increases in amplitude from the central MER to the southern Afar region, while the residual gravity anomaly indicates gravity maxima occur over magmatic segments that occur within the MER. Gravity modeling using the EAGLE controlled-source axial seismic model as a constraint indicates that the crust thins from ∼40km over the central MER to ∼30km over the southern Afar region. However, to model the large amplitude gravity gradient in the Nazreth region, a denser lower crust and less dense upper mantle were needed over the southern Afar region. The denser lower crust is interpreted to be caused by mafic material formed during extensional tectonics, while the less dense upper mantle is indicative of a hotter thermal regime. The presence of a thinned crust and higher density lower crust is characteristic of volcanic rifted margins and implies that the southern Afar region may be developing into a continental margin. The gravity maxima occurring over the magmatic segments were modeled as dense, mafic bodies caused by intrusion into the lower and upper crust with tops between 7 and 10km. These bodies add constraints to recently obtained three-dimensional seismic tomographic models suggest that the lower to lower–upper crust is in a ductile regime and the upper 7km of the upper crust is in a brittle regime.

The origin of regional sedimentary basins is being investigated by the ESTRID project (Explosion Seismic Transects around a Rift In Denmark). This project investigates the mechanisms of the formation of wide, regional basins and their interrelation to previous rifting processes in the Danish-Norwegian Basin in the North Sea region. In May 2004 a 143 kin long refraction seismic profile was acquired along the strike direction of a suspected major rnafic intrusion in the crust in central Denmark. The data confirms the presence of a body with high seismic velocity (> 6.5 km/s) extending from a depth of similar to 10-12 km depth into the lower crust. There is a remarkable Moho relief between 27 and 34 kin depth along this new along-strike profile as based on ray-tracing modelling of PmP reflections. The lack of PmP reflections at a zone of very high velocity in the lowest crust (7.3-7.5 km/s) suggests a possible location of a feeder channel to the batholith. The presence of volcanic rocks of Carboniferous-Permian age above the intrusion (mafic batholith) suggests a similar age of the intrusion. An older obliquely crossing profile and two new fan profiles deployed perpendicular to the main ESTRID profile, show that the batholith is about 30-40 km wide. The existence of this large mafic batholith supports the hypothesis that the origin of the Danish-Norwegian Basin is related to cooling and contraction after intrusion of large amounts of mafic melts into the crust during the late Carboniferous and early Permian. The data and interpretations from project ESTRID will form the basis for subsidence modelling. Tentatively, we interpret the formation of the Danish-Norwegian Basin as a thermal subsidence basin, which developed after widespread rifting of the region. (c) 2006 Elsevier B.V. All rights reserved.

This chapter provides an overview of the features of the West and Central African rift system(WCARS). The WCARS is a very large scale feature which is distinctive in the sense that it traverses the entire continent. Its complex history involved extension, shearing, and compression over a period extending from the early Cretaceous into the early Tertiary. Portions of its history correlate with changes in plate movements, and the basins which contained major petroleum resources. It is characterized by an unusual amount of subsidence over most of its extent which obscured many rift structures. The region is an ideal place to investigate the interaction of extension and shear during major rifting events.

This chapter deals with the capabilities and limitations of seismic methods and seismic data in studies of continental rifts. Substantial structural and velocity variations are expected, and are commonly observed, in continental rifts because of the effects of extension, magmatism, and high heat flow associated with the rifting process. The chapter describes the seismic methods that have been used in rift studies, followed by a review of seismic properties of rocks emphasizing effects of temperature. The extensive crustal velocity data available for North America, which identifies the characteristic crustal properties associated with continental rifts, are also utilized. Each method has its own capabilities and limitations in terms of the depth range of investigation, degree of resolution attainable, and the physical properties determined. At present, shear-wave velocity, anisotropy, and Poisson's ratio data from continental rift areas are relatively sparse. Similarities between the crustal velocity structures observed in North America and east Africa suggest the common characteristics of the stable continental crust, and the processes and effects of continental rifting.

In 2000, a consortium of European and North American institutions completed a huge active source seismic experiment focused on central Europe, the Central European Lithospheric Experiment Based on Refraction or CELEBRATION 2000. This experiment primarily consisted of a network of seismic refraction profiles that extended from the East European craton, along and across the Trans‐European suture zone region in Poland to the Bohemian massif, and through the Carpathians and eastern Alps to the Pannonian basin. The longest profile CEL05 (1420 km) is the focus of this paper. The resulting two‐dimensional tomographic and ray‐tracing models show strong variations in crustal and lower lithospheric structure. Clear crustal thickening from the Pannonian basin (24–25 km thick) to the Trans‐European suture zone region (∼50 km), together with the configuration of the lower lithospheric reflectors, suggests northward subduction of mantle underlying Carpathian‐Pannonian plate under the European plate. This, however, conflicts with strong geological evidence for southward subduction, and we present three tectonic models that are to not totally mutually exclusive, to explain the lithospheric structure of the area: (1) northward “old” subduction of the Pannonian lithosphere under the East European craton in the Jurassic–Lower Cretaceous, (2) a collisional zone containing a “crocodile” structure where Carpatho‐Pannonian upper crust is obducting over the crystalline crust of the East European craton and the Carpathian‐Pannonian mantle lithosphere is underthrusting cratonic lower crust, and (3) lithosphere thinning due to the effects of Neogene extension and heating with the slab associated with “young” subduction southward in the Miocene having been either detached and/or rolled back to the east. In the last case, the northwestward dipping in the lithosphere can be interpreted as being due to isotherms that could represent the lithosphere/asthenosphere boundary in the Pannonian region.

The Palaeoproterozoic crust and upper mantle in the region between the Ukrainian and Baltic shields of the East European Craton were built up finally during collision of the previously independent Fennoscandian and Sarmatian crustal segments at c. 1.8-1.7 Ga. EUROBRIDGE seismic profiling and geophysical modelling across the southwestern part of the Craton suggest that the Central Belarus Suture Zone is the junction between the two colliding segments. This junction is marked by strong deformation of the crust and the presence of a metamorphic core complex. At 1.80-1.74 Ga, major late to post-collisional extension and magmatism affected the part of Sarmatia adjoining the Central Belarus Zone and generated a high-velocity layer at the base of the crust. Other sutures separating terranes of different ages are found within Sarmatia and in the Polish-Lithuanian part of Fennoscandia. While Fennoscandia and Sarmatia were still a long distance apart, orogeny was dominantly accretionary. The accreted Palaeoproterozoic terranes in the Baltic-Belarus region of Fennoscandia are all younger than 2.0 Ga (2.0-1.9, 1.90-1.85 and 1.84-1.82 Ga), whereas those in Sarmatia have ages of c. 2.2-2.1 and 2.0-1.95 Ga. Lithospheric deformation and magmatism at c. 1.50-1.45 Ga, and Devonian rifting, are also defined by the EUROBRIDGE seismic and gravity models.

Publisher Summary This chapter discusses the Rio Grande rift, which is a part of a broad region of the western United States, including the Basin and Range province, that has undergone lithospheric thinning and crustal extension during the middle to late Cenozoic. The present extensional setting of the rift is generally related to plate boundary forces acting along the southwestern edge of the North American plate, a transform boundary along which right-lateral slip occurs. The rift follows a zone of crustal deformation formed during the Laramide and Ancestral Rocky Mountains orogenic events. Tertiary sedimentation in the rift area is characterized generally by continental basinal deposits, including interbedded epi- and pyroclastic rocks.

The Ethiopia Afar Geoscientific Lithospheric Experiment (EAGLE) was undertaken to provide a snapshot of lithospheric break-up above a mantle upwelling at the transition between continental and oceanic rifting. The focus of the project was the northern Main Ethiopian Rift (NMER) cutting across the uplifted Ethiopian plateau comprising the Eocene-Oligocene Afar flood basalt province. A major component of EAGLE was a controlled-source seismic survey involving one rift-axial and one cross-rift c. 400 km profile, and a c. 100 km diameter 2D array to provide a 3D subsurface image beneath the profiles' intersection. The resulting seismic data are interpreted in terms of a crustal and sub-Moho P-wave seismic velocity model. We identify four main results: (1) the velocity within the mid- and upper crust varies from 6.1 km s(-1) beneath the rift flanks to 6.6 km s-1 beneath overlying Quaternary axial magmatic segments, interpreted in terms of the presence of cooled gabbroic bodies arranged en echelon along the axis of the rift; (2) the existence of a high-velocity body (V-p 7.4 km s(-1)) in the lower crust beneath the northwestern rift flank, interpreted in terms of about 15 km-thick, mafic underplated/intruded layer at the base of the crust (we suggest this was emplaced during the eruption of Oligocene flood basalts and modified by more recent mafic melt during rifting); (3) the variation in crustal thickness along the NMER axis from c. 40 km in the SW to c. 26 km in the NE beneath Afar. This variation is interpreted in terms of the transition from near-continental rifting in the south to a crust in the north that could be almost entirely composed of mantle-derived mafic melt; and (4) the presence of a possibly continuous mantle reflector at a depth of about 1525 km below the base of the crust beneath both linear profiles. We suggest this results from a compositional or structural boundary, its depth apparently correlated with the amount of extension.

This chapter describes the formation of extensional stresses in the Earth's lithosphere that is a global tectonic phenomenon, occurring in all plate settings. When initiated in continental lithosphere, extension give rise to a range of tectonic features called “continental rifts.” Continental rifts preserve the most complete, and possibly the only, record of critical structures and of transient processes associated with the incipient stages of continental breakup. Continental rifts have existed at least since the Proterozoic Eon, and their effects on continental lithosphere are both short- and long term. Modification of the crust occurs through deformational processes associated directly with rifting or with post-rifting stress regimes. The timing of uplift, faulting, and magmatism, are of key importance in understanding processes of lithospheric extension.

This chapter describes the Baikal rift system, which is 1800 km to 2400 km long and is situated at the boundary between the Siberian Platform to the northwest and the Caledonian Sayan-Baikal fold belt to the southeast. This rift system has been the object of intensive study by Soviet scientists for many years. The Baikal rift system is composed of fifteen individual topographic depressions which are associated with an approximately 1500-km long domal uplift. The central portion of Baikal Rift system is almost entirely located on the relatively weak and anisotropic basement of the Sayan-Baikal fold belt. The sub-vertical crustal boundary between the Siberian Platform and the fold belt forms an abrupt western boundary for the central portion of the rift system and its domal uplift, and in particular runs along the west side of the Lake Baikal depressions.