Recent Crustal Movements Research Articles

Electrical Conductivity Structure of the Crust and Upper Mantle Along the Profile Maqên-Lanzhou-Jingbian in the Northeastern Margin of the Qinghai-Tibet Plateau

Magnetotelluric (MT) measurements have been carried out at 62 sites along the profile Maqen-Lanzhou-Jingbian in the junction zone of the northeastern margin of the Qinghai-Tibet Plateau and the Ordos block. The Robust technique was used in data processing and the Bahr's technique was used for impedance tensor decomposition to remove 3-D effect. The apparent resistivity, impedance phase curves, 2-D skewness and regional tectonic strike were analyzed. The RRI 2-D inversion technique was used for data inversion and interpretation. The results are as follows. (1) The target area is separated by Maqen, Lanzhou and Majiatan-Dashuikeng fault zones into four electric conductivity blocks, namely the Bayan Har block (I), Qinling-Qilian block (II), boundary zone (III) and Ordos block (IV). (2) The crust of blocks I, II, and IV has similar characteristics of electric conductivity structure: a high resistivity layer in the upper crust, a low resistivity layer in the upper part of lower crust, and the resistivity increasing gradually with depth from the lower crust to the upper mantle. The electric conductivity of block 3 is poorly layered and complex in structure, where the recent tectonic movement is more intense. (3) The Maqen, Haiyuan and Luoshan-Yunwushan fault zones are steep fault zones extending through the crust, while the fault zone on the northern margin of the Qinling Range is confined inside the crust.

Recent vertical movements from precise levelling in the vicinity of the city of Basel, Switzerland

The southern end of the Upper Rhine Graben is one of the zones in Switzerland where recent crustal movements can be expected because of ongoing seismotectonic processes as witnessed by seismicity clusters occurring in this region. Therefore, in 1973 a control network with levelling profiles across the eastern Rhine Graben fault was installed and measured in the vicinity of the city of Basel in order to measure relative vertical movements and investigate their relationship with seismic events. As a contribution to EUCOR-URGENT, the profiles were observed a third time in the years 2002 and 2003 and connected to the Swiss national levelling network. The results of these local measurements are discussed in terms of accuracy and significance. Furthermore, they are combined and interpreted together with the extensive data set of recent vertical movements in Switzerland (Jura Mountains, Central Plateau and the Alps). In order to be able to prove height changes with precise levelling, their values should amount to at least 3–4 mm (1σ). The present investigations, however, have not shown any significant vertical movements over the past 30 years.

Deglacial and Holocene evolution of the Vietnam shelf: stratigraphy, sediments and sea-level change

On the Vietnam Shelf more than 1000 miles of shallow high-resolution seismics were analyzed to unravel post-glacial evolution in a tropical, siliciclastic environment together with 25 sediment cores from water depths between 21 and 169 m to determine stratigraphy, distribution and style of sedimentation. Fourty-seven samples were dated with the AMS- 14C technique. The shelf was grouped into three regions: a southern part, a central part, and a northern part. On the broad Southern Shelf, sedimentation is influenced by the Mekong River, which drains into the SCS in this area. Here, incised valley fills are abundant that were cut into the late Pleistocene land surface by the Paleo-Mekong River during times of sea level lowstand. Those valleys are filled with transgressive deposits. The Holocene sedimentation rate in this low gradient accommodation-dominated depositional system is in the range of 5–10 and 25–40 cm/ky at locations sheltered from currents. The Central Shelf is narrow and the sedimentary strata are conformable. Here, numerous small mountainous rivers reach the SCS and transport large amounts of detrital sediment onto the shelf. Therefore, the Holocene sedimentation rate is high with values of 50–100 cm/ky in this supply-dominated depositional system. The broad Northern Shelf in the vicinity of the Red River Delta shows, as on the Southern Shelf, incised valleys cut into the Pleistocene land surface by paleo river channels. In this accommodation-dominated shelf area, the sedimentation rate is low with values of 5–10 cm/ky. Where applicable, we assigned the sampled deposits to different paleo-facies. The latter are related to certain intervals of water depths at their time of deposition. Comparison with the sea-level curve of [Hanebuth, T.J.J., Stattegger, K., Grootes, P., 2000. Rapid flooding of the Sunda Shelf; a lateglacial sea-level record. Science, 288: 1033–1035.] indicates subsidence on the Central Shelf, which is in agreement with the high sedimentation rates in this area. In contrast, data from the Northern Shelf suggest tectonic uplift that might be related to recent tectonic movements along the Ailao Shan–Red River Fault zone. Data from the Southern Shelf are generally in agreement with the sea-level curve mentioned above.

Horizontal crustal movement in Chinese mainland from 1999 to 2001

The paper introduces the horizontal crustal movement obtained from GPS observations in the regional networks (including the basic network and the fiducial network) of the Crustal Movement Observation Network of China (CMONOC) carried out in 1999 and 2001. This paper is characterized by the acquisition of the horizontal displacement velocities during the period from 1999 to 2001 at the observation stations in the regional networks with datum definition of a group of stable stations with small mutual displacements in east China. Based on the most detailed map of horizontal crustal movement in Chinese mainland, the division of blocks, their displacements and deformations are studied. An approach to analysis of the intensity of the horizontal crustal deformation is proposed. The general characteristics of the recent horizontal crustal movement in Chinese mainland and that before the Kunlunshan earthquake of M=8.1 on November 14, 2001 are analyzed.

Submerged tidal notches in the Rijeka Bay NE Adriatic Sea: indicators of relative sea-level change and of recent tectonic movements

The Rijeka Bay coast is formed predominately in carbonate rocks. Due to relatively sheltered position, processes of bioerosion dominate, while mechanical wave action has low impact. Biological zone limits in Rijeka Bay are well expressed, and they reflect the local biological mean sea level (BMSL). Therefore, they were used as referent levels for measurement of submerged tidal notch position. These in situ biological indicators could be more useful than sea-level mareograph data. Well developed tidal notches are permanently submerged and quite ubiquitous in the whole Rijeka Bay area; that is, they are situated in the infralittoral zone. They have elongated, asymmetric shape. Inasmuch as the roof top of the notches is well preserved, they were correlated with well defined biological zone limit [upper limit of white (WE) zone; sensu Schneider, J., 1976. Biological and inorganic factor in the destruction of limestone coast. Contributions to Sedimentology 6, 1–11]. Results of survey showed that, in most of the area, tidal notches are located 50–60 cm below BMSL. However, within the Bakar Bay, notches are from 103 to 115 cm below BMSL. Regional occurrence of well preserved tidal notches at 0.5–0.6 m below BMSL indicates their possible coseismic origin (rapid tectonic subsidence). Deeper positions of tidal notches in the northeastern part of Rijeka Bay and within Bakar Bay indicate enhanced subsidence of that zone which is assumed to be the most seismotectonicaly active.

Channel profiles through the active thrust front of the southern Barbados prism

AbstractSubmarine channels of the Orinoco River were analyzed using high-quality, dense- coverage bathymetric and seismic data provided by a recent marine survey on the southern Barbados prism. Analysis of the syntectonic sediments on seismic profiles shows that the four to five frontmost structures show evidence of recent tectonic movement. Slope analysis of the major channels was performed. From their headwaters to domains of little or no active tectonics, the channels display <0.2% slope and form levees. Slope and incision increase gradually in domains of moderate tectonics, but deep canyons with ∼2% mean slope form where the channels cross the active frontal folds of the prism. Detailed correlation between the active structures, their geometry, and canyon slope suggest that systematic variations in channel gradient highlight variations in substrate uplift rate. Steep slopes induced by uplift accelerate sediment flow and enhance incision. Nonetheless, such slope analysis is subject to complications introduced by variations in sediment flux and transient erosional conditions.

Recent crustal movements observed with the European VLBI network: geodetic analysis and results

Purely European geodetic Very Long Baseline Interferometry (VLBI) has been performed at regular intervals since January 1990. Meanwhile 10 VLBI sites in Europe from Sicily to Spitzbergen and the Iberian pensinsula to the Crimean peninsula contribute to the observation series. The observations are used to determine recent crustal movements in these parts of Europe. Baseline measurements are achieved with an accuracy of 2.0 mm plus an additional term depending on the baseline length of less than 1 part-per-billion. Significant horizontal crustal movements are determined with relative accuracies in the range of 10–40%, significant vertical crustal movements are determined with relative accuracies in the range of 30–40%. The determined crustal movements form thus a sound basis for interpretations in a geophysical and geological context. This article concentrates on a description of the geodetic VLBI data analysis, the analysis models used and the results for crustal movements.

Discontinuous deformation analysis and recent crustal movement

Discontinuous deformation analysis and recent crustal movement

Preliminary study on isostatic anomaly and recent tectonic stress field

On the basis of the reality of recent tectonic movement and discarding such a viewpoint that the isostatic adjustment only results from excessive or insufficient compensation, we have discussed the tectonic stress causing inequality and regarded the isostatic anomaly as a load on the earth’s interior, thus the earth’s inner stress can be calculated. The research results show that in the East China Sea and its eastern marginal seas the change of the vertical stress derived from the isostatic gravity anomaly is more marked than that of the horizontal stress. Along the Ryukyu trench there is an enhancement of vertical stress by 5 MPa, which evidently reflects the effect of plate subduction. On contrary, along the island arc to the northwest of the trench the vertical stress weakens by about 5 MPa. The horizontal stresses in eastern and western parts are obviously different, the east westward stress on the oceanic crust σxis negative (while the pressure is positive) but on the continental crust is positive. These facts indicate the effect of compression between plates.

Coastal karst springs in the Mediterranean basin : study of the mechanisms of saline pollution at the Almyros spring (Crete), observations and modelling

Variations in salinity and flow rate in the aerial, naturally salty spring of Almyros of Heraklion on Crete were monitored during two hydrological cycles. We describe the functioning of the coastal karstic system of the Almyros and show the influence of the duality of the flow in the karst (conduits and fractured matrix) on the quality of the water resource in the coastal area. A mechanism of saltwater intrusion into this highly heterogeneous system is proposed and validated with a hydraulic mathematical model, which describes the observations remarkably well.

Geodetic control on recent tectonic movements in the central Mediterranean area

During the Neogene and Quaternary, the western Mediterranean geodynamics was apparently dominated by the nearly eastward migration of the Apenninic arc and the associated opening (spreading) of the back-arc basin (Tyrrhenian Sea). However, during the last 5 My, the collision of the arc with the Apulian platform led to a dramatic change in the tectonic setting of the area. As geological processes require a long period of time to register the displacements of the different blocks, it is indispensable to take into account the present-day motion given by space geodesy data analysis in order to better constrain the geological models. Geodetic motions were derived from Global Positioning System (GPS), Satellite Laser Ranging (SLR) and Very Long Baseline Interferometry (VLBI) observations collected from different networks. All the geodetic solutions have been computed and combined at the Centre of Space Geodesy (CGS), at Matera, Italy. The geodetic results show a NNE motion of the Adriatic plate with a small component of counter-clockwise rotation, in good agreement with the geological and geophysical observations. In the southern Tyrrhenian area, the lengthening of the Matera–Cagliari baseline should imply that convergence cannot be considered as the driving mechanism for the Apenninic subduction process. The estimated motion of Noto is in quite good agreement with the estimated motion of the African plate.

Le systeme fluvio-estuarien Pleistocene moyen-superieur de Penestin (Morbihan); une paleo-Loire?

Abstract In France, the basement domains are incised by large fluvial valley networks. Recent studies [Lefebvre et al., 1994; Bonnet, 1998; Lautridou et al., 1999; Antoine et al., 2000; Bonnet et al., 2000] show that these networks were cut during the Pleistocene in response to the uplift of western Europe combined with a fall of the base level [Haq et al., 1987; Shackleton, 1987]. The aim of this article is to study one of the rare Pleistocene sedimentary accumulations preserved in the Armorican Massif, the Penestin fluvial channel system in order to: (1) reconstitute the paleogeomorphological parameters and (2) discuss its relationships with recent tectonic movements. The Penestin fluvial system is localized at the top of the cliff of the Mine d'Or beach (west of Penestin, south of the Vilaine estuary, fig. 1). The paleochannel cuts through the Carboniferous micaschists which pass laterally into Tertiary paleoweathering deposits. The paleochannel is deformed by folds and/or by strike-slip faults. Three sectors are identified (fig. 2). Sector 1: a northern undeformed sub-area; sector 2: an intermediate slightly folded sub-area; sector 3 a southern folded and faulted sub-area. Three sedimentological units and seven associated facies are distinguished. Unit I (facies G), containing local matrix-dominated conglomerates characteristic of distal debris flows, suggests a proximal braided river environment, near the transition with alluvial fans [Blair and MacPherson, 1994]. Paleocurrent trends are directed toward N320 (fig. 3). Unit II (facies Sg, Sgm, Sf, Fb and T) is mainly dominated by sandy facies and corresponds to a more distal braided river flooded at the top by the sea (occurrence of inner estuarine deposits). The 2D and 3D megaripple cross-bedding structures indicate paleocurrents trending N320 (fig. 3). Unit III (facies G, Sg, Sgm and Fr) with multiple erosive channels is filled by braided river deposits (facies G, Sg and Sgm) or temporary lake sediments (facies Fr). The 2D and 3D megaripple cross-bedding structures indicate paleocurrents oriented N135 or N180 (fig. 3). Stratigraphically, these three units record two major base level cycles (fig. 6), in the sense of Wheeler [1958]. The first base level fall corresponds to the incision of the paleochannel. Unit I is amalgamated and was deposited during the beginning of the rise, while unit II corresponds to the maximal facies preservation during the maximum rate of rise. The erosion of unit II by unit III corresponds to a moderate base level fall followed by a small rise (little preservation of unit III). The basement, the weathering deposits and the Quaternary sedimentary units are folded and faulted by N050 to N070 strike-slip faults (fig. 2). Two stages of deformation can be characterized. The first stage, taking place before the incision of the paleochannel, corresponds to a southward tilting of the weathering profile. The second stage took place during the paleochannel infilling, producing thickness variations of the bedsets within unit II. The amount of deformation increased during deposition of unit III and is expressed by N050 to N070 strike-slip faults capped by unit III or by a topmost erosive surface. Fault orientation indicates a NNW-SSE compression (fig. 5) consistent with the stress field in northwestern Europe [Muller et al., 1992; Zoback, 1992]. Paleocurrent directions in units I and II seem to indicate a southerly drainage basin. Today, the Vilaine river flows southward. The units I and II do not represent a paleo-Vilaine river, but since unit III shows paleocurrents similar to those of the present Vilaine river and contains red schists in its basin. It could represent a paleo-Vilaine river. Units I and II might represent a paleo-Loire river, the present Loire river following a curve as it passes over the South Armorican shear zone which reorientates it toward the N320 (fig. 7). Tourenq and Pomerol [1995] show that the Loire river was captured many times ago by the Seine river during the Pleistocene. in this way, when the paleo-Loire river was captured, the paleo-Vilaine river deposited unit III. The Penestin paleochannel resulted from the fluviatile incision/filling of a braided river, which was temporarily overlain by estuarine deposits. The rivers filling this paleochannel first flowed out to the north (flow of a paleo-Loire river: units I and II), and then to the south (flow of a paleo-Vilaine river: unit III). The deformation is attributed to a N110 fault, to a set of N050 and N070 faults and to N050 folds.

General characteristics of the recent horizontal crustal movement in Chinese mainland

In this paper, the horizontal crustal movement obtained from GPS observations in 1998 and 2000 at basic and fiducial stations in the Crustal Movement Observation Network of China (CMONOC) is introduced. A brief introduction of the field observations, the data processing with GAMIT/GLOBK software and the accuracy of the GPS observations is given. In average the accuracy of the results for each year is about 2 mm in the horizontal components and 5 mm in the vertical component, and the average accuracy of horizontal displacements at a station is about 3 mm. The results of crustal movement during the period from early September 1998 to mid June, 2000, including the displacements at each station with datum definition of a group of stable stations of insignificant relative movements among themselves in the eastern part of China, strains in different parts of the network and rotations in some parts, are obtained. Based on the crustal movement maps which are more complete and detailed than previous ones, the general characteristics of the recent crustal movement in Chinese mainland are discussed. During the above mentioned period of observations, the crustal deformation in the eastern part of China was relatively small and quite stable. With reference to a group of stable stations with small relative movement in the eastern part of China, the northeastern China block moved northward for about 10 mm, the South China block moved southeastward for about 9 mm. In reference to the eastern part the northwestern part of China moved northward for about 26 mm, the Tibetan area in southwestern part of China moved mainly northward for about 32 mm. The area in Yunnan and east Tibet showed significant clockwise tectonic rotation of 0.0045″ or average rotational displacement of 12 mm with the rotation center at 26.5°N and 95.5°E. The North-South Seismic Belt in the middle part of China is of active and complicated deformation. The observation results show that the northward pushing by the Indian plate has still played the dominant role in the crustal movement in Chinese mainland.

Preliminary division of active block boundary in Chinese mainland based on recent vertical crustal movement

The characteristics of vertical crustal movement in Chinese mainland are studied, and the ideas and principles for dividing active blocks according to the map of recent vertical crustal deformation rate in China is proposed. As a result, Chinese mainland is divided into 2 first-grade blocks, the east and west block, 6 second-grade blocks, the Northeast China, North China, East China, Xizang (Tibet), Gansu-Qinghai-Xizang (Gan-Qing-Zang) and Xinjiang block, and 16 third-grade blocks. The boundaries of active blocks divided in this paper are generally consistent with the pattern of neotectonic movement with some local difference. It shows that the recent crustal activity in Chinese mainland inherits the neotectonic movement occurred since the Quaternary, while some new activity tendencies appear.

Recent crustal horizontal movement in the Chinese mainland

According to the results of careful re-processing of data obtained from two GPS survey campaigns of crustal movement monitoring network in Chinese mainland carried out in 1994 and 1996, the crustal horizontal movement characteristics in Chinese mainland are studied in the paper. In the analysis, a relatively consummate deformation model in which the deformation is described by the relative movement between the tectonic blocks with interior strain and the corresponding analysis method are used. The magnitude of movement along the boundary zones between the tectonic blocks is calculated. And the characters and intensities between the main boundary zones are compared.

Risk Assessment and Disaster Management for Natural and Anthropogenically Induced Geologic Hazards: Application to the Preolkhon Region, Western Lake Baikal, Siberia, Russia

In the Western Lake Baikal, recent Baikal Rift's tectonics control the topography, seismicity, climate, geomorphology, and economy. Scarps, facets, structural terraces, horsts and grabens, and trapezoid valleys can be clearly observed. They have been generated by the recent tectonic movements along the faults and represent a serious geologic hazard. The specific geological conditions predetermine a unique variety of landscapes. Thus, the main type of the economy is tourism. However, unorganized tourism leads to the degradation of the unique landscapes. It increases risk and requires disaster management. Three criteria has been used for risk assessment: (1) degree of geologic hazard; (2) degree of landscape degradation; and (3) degree of the economy's vitality. The high ecological significance and low stability to antropogeneous pressure are typical for landscapes of the Western Lake Baikal. Thus, some special activities of disaster management should be implemented based on our investigation.

Monitoring of geodynamic activity in the West Bohemia seismoactive region between 1993–1996

The western part of the Bohemian Massif is characterized by repeated earthquake swarm occurrence, juvenile carbon dioxide waters, mineral springs, mofettes, Quaternary volcanics etc. To study the geodynamic activity of the region, repeated geodetic measurements of recent crustal movements, repeated gravity measurements and continuous recording of groundwater level have supplemented the seismological investigations since the fall of 1993. The December 4–5, 1994 weak earthquake swarm, the strongest seismic sequence between 1993–96, remarkably coincided with the absolute minimum of the groundwater level and a maximum of gravity. Repeated gravimetric measurements confirmed the existence of temporal variations of gravity, characterized by a certain correlation with the local tectonic setting. The results of GPS did not prove any displacement >5 mm–a in horizontal component. Precise levelling indicated small negative changes in elevation at several points of measurements.

Recent crustal movements in the southern Black Forest (western Germany)

Precise levelling data are examined in the southern Black Forest massif by comparing them analytically along levelling profiles. Instead of generalizing regional vertical motion trends, the method emphasizes the current activity of accurately located individual structural elements. Measured recent crustal movement rates range from 0.2 to 1.1 mm/year for the 1930–1961 (1972) period, the inferred motions corresponding to aseismic fault creep. Based on the near infrared band image of a Landsat MSS scene, a lineament map of the study area is compared with the recent crustal movement (RCM) map. The Upper Rhine graben eastern border fault between Badenweiler and Freiburg displays the highest RCM: these displacements are consistent with the geological motion and the topographic expression of that structure. Within the massif, both the lineament map and the RCM map demonstrate the predominant role played by WNW/ESE- to NW/SE-striking structures in accommodating the deformation. Moreover, with the seismic dislocations in the southern Black Forest taking place also mainly on N120 and N20 faults, it is most probable that these active structures are deep-reaching zones of crustal weakness. To some extent, seismicity and RCM appear, however, to be mutually exclusive in their spatial distribution, the seismic Black Forest flexure and Dinkelberg block being opposed to the aseismically moving eastern and northern parts of the study area.

The influence of the San Gregorio fault on the morphology of Monterey Canyon

A side-scan sonar survey was conducted of Monterey Canyon and the San Gregorio fault zone, off shore of Monterey Bay. The acoustic character and morphology of the sonar images, enhanced by SeaBeam bathymetry, show the path of the San Gregorio fault zone across the shelf, upper slope, and Monterey Canyon. High backscatter linear features a few kilometers long and 100 to 200 m wide delineate the sea-floor expression of the fault zone on the shelf. Previous studies have shown that brachiopod pavements and carbonate crusts are the source of the lineations backscatter. In Monterey Canyon, the fault zone occurs where the path of the canyon makes a sharp bend from WNW to SSW (1800 m). Here, the fault is marked by NW–SE-trending, high reflectivity lineations that cross the canyon floor between 1850 m and 1900 m. The lineations can be traced to ridges on the northwestern canyon wall where they have ∼15 m of relief. Above the low-relief ridges, bowl-shaped features have been excavated on the canyon wall contributing to the widening of the canyon. We suggest that shear along the San Gregorio fault has led to the formation of the low-relief ridges near the canyon wall and that carbonate crusts, as along the shelf, may be the source of the high backscatter features on the canyon floor. The path of the fault zone across the upper slope is marked by elongated tributary canyons with high backscatter floors and `U'-shaped cross-sectional profiles. Linear features and stepped scarps suggestive of recent crustal movement and mass-wasting, occur on the walls and floors of these canyons. Three magnitude-4 earthquakes have occurred within the last 30 years in the vicinity of the canyons that may have contributed to the observed features. As shown by others, motion along the fault zone has juxtaposed diverse lithologies that outcrop on the canyon walls. Gully morphology and the canyon's drainage patterns have been influenced by the substrate into which the gullies have formed.

Coral reefs, Sinai, Egypt: A historical perspective

This note complements and supplements the historical perspective of a paper in which Strasser and Strohmenger (1997) related diagenesis to tectonics, sea-level, and climate. Johannes Walther (1888) studied a fossil reef at Ras Muhammed at 6 meters below sea level and suggested that it had subsided. W.F. Hume (1906) described raised coral reefs along the western shore of the Gulf of Aqaba. He suggested a Pleistocene or post-Pleistocene movement of the shoreline of the Gulf. Hume cited Walther's observations of the reef at 6 meters below sea-level as evidence for subsidence. I discovered a fossil reef (Friedman 1966) which gave a radiocarbon age of 477±140 years B.P. This reef reflects either Recent tectonic movement of the Gulf's shoreline or lowering of sea level. Like modern reefs, this fossil reef is composed of aragonite and high-magnesian calcite with subordinate low-magnesian calcite sporadically present (Fig. 1). In modern Red Sea reefs peloids of high-magnesian calcite in cryptocrystalline high-magnesian calcite cement are interpreted as calcified algal filaments.