Constraining the characters of the upper mantle discontinuities beneath the NE margin of the Tibetan Plateau with a dense broadband seismic array

Based on observations from a dense broadband seismic array located along the northeastern (NE) margin of the Tibetan Plateau in southeastern Gansu Province,we use receiver functions (RFs) to pick the arrival times of P-to-S converted waves and bin the traces in different grids according to the piercing points of the 410 and 660 km discontinuities in the upper mantle.The depths of the two discontinuities are estimated by the ray tracing method with the IASP91 velocity model and a 3-D tomography model.The results indicate the following:(1) The arrival times of the P410s and P660s converted phases are delayed by approximately 1 s than those predicted by the IASP91 model.The mantle transition zone (MTZ) is thicker than that in the global model.(2) The synchronous lags in the P410s and P660s arrival times are consistent with low-velocity anomalies in the upper mantle,which are believed to result mainly from the eastward migration of materials beneath the NE margin of the Tibetan Plateau.(3) Combined with previous tomography results,the depression of the'660'discontinuity and the thickened MTZ are somewhat consistent with the big mantle wedge (BMW) model.However,due to data limitations,more studies are required to explore the BMW in the future.     

Seismicity in the platform regions of Ukraine in the zones of anomalous electrical conductivity

It is established for the first time that there are several regions in Ukraine, in which the earthquakes occurring within platform territory are correlated to the anomalous conductive structures in the Earth’s crust and upper mantle. These regions are identified as (1) Donbass and the eastern part of the Dnieper-Donetsk Depression (DDD); (2) eastern margin of the Ingulets-Krivoi Rog suture zone in the area of the Krivoi Rog-Kremenchug fault zone; (3) the western part of the Cis-Azov megablock; (4) the western boundary of the Ukrainian Shield and its slope; (5) North Dobruja and Pre-Dobrujan Depression. The reconstructed tree-dimensional (3D) geoelectrical models of the Earth’s crust and upper mantle feature anomalously low values of electric resistivity. The earthquake sources in the platform areas of Ukraine are localized above the top and in the upper parts of the crustal anomalies of electrical conductivity.     

腾冲火山区的GPS形变特征

利用腾冲火山区2003和2004年2次测量所得的GPS数据,计算了59条测线的水平长度变化.对任意相邻的3个测点和3条测线组成的51个三角形,分别进行了地壳形变的反演计算,得出每个三角形的主应变和主方向,进而确定每个三角形的面膨胀量和最大剪应变.对整个测量区域作等值线图,可以看出有3个最大值的区域,分别位于马站－曲石(G05)附近;腾冲(G20)－热海(G13)附近,以及五合(G15)－团田(G18)附近.这3个区域与3个具有最大相对地热梯度的区域相一致,也与低速异常体所在的区域相一致.因此可能就是地下岩浆房存在的区域.为了确定岩浆活动性,利用Mogi模型的计算公式,对腾冲－热海附近的区域进行了反演,认为等效源的位置在腾冲的西南方向,岩浆活动量约为8×105m3/年,与以前用精密水准测量的垂直形变所反演的结果处于同样的量级.     

Enhancing the Forecasting of Monthly Streamflow in the Main Key Stations of the River Nile Basin

Predicting the streamflow of rivers can have a significant economic impact, as this can help in agricultural water management and in providing protection from water shortages and possible flood damage. In this study, two statistical models have been used; Deseasonalized Autoregressive moving average model (DARMA) and Artificial Neural Network (ANN) to predict monthly streamflow which important for reservoir operation policy using different time scale, monthly and 1/3 monthly (ten-days) flow data for River Nile basin at five key stations. The streamflow series is deseasonalized at different time scale and then an appropriate nonseasonal stochastic DARMA (p, q) models are built by using the plots of Partial Auto Correlation Function (PACF) to determine the order (p) of DARMA model. Then the deseasonalized data for key stations are used as input to ANN models with lags equals to the order (p) of DARMA model. The performance of ANN and DARMA models are compared using statistical methods. The results show that the developed model (using 1/3 monthly (ten-days) and ANN) has the best performance to predict monthly streamflow at all key stations. The results also show that the relative error in the developed model result did not exceed 9% while in the traditional models reach to 68% in the flood months in the testing period. The result also indicates that ANN has considerable potential for river flow forecasting.     

Numerical simulation of the variations in the total electron content of the ionosphere observed before the Haiti earthquake of January 12, 2010

We present the results of a study of the abnormal variations in the total electron content (TEC) of the ionosphere observed before the earthquake of January 12, 2010, in Haiti. Global and regional maps of TEC relative (%) deviations from the quite background state are built for January 9–12, 2010. Using the UAM (Upper Atmosphere Model) global numerical model of the upper atmosphere of the Earth, the variations in the electric potential in the ionosphere and TEC are calculated using external seismic current above faults between the Earth and the ionosphere as a lower boundary condition. The numerical simulation results are compared with observations. It is shown that the simulated variations in the TEC at a specified current density of about 1 × 10^?8 A/m² on an area of 200 km (latitude) × 4000 km (longitude) above the focus represent all main features of the observations: prevalence of increased TEC values (positive disturbances), neighboring negative disturbances of lower magnitudes, localization, magnetic conjugacy of high-intensity effects in the Southern Hemisphere, and disappearance of disturbances around midday. Methodological recommendations are given to reveal variations in the TEC related to the preparation of seismic events.     

On the variability of the flow along the Meso-American Barrier Reef system: a numerical model study of the influence of the Caribbean current and eddies

A high resolution (3–8 km grid), 3D numerical ocean model of the West Caribbean Sea (WCS) is used to investigate the variability and the forcing of flows near the Meso-American Barrier Reef System (MBRS) which runs along the coasts of Mexico, Belize, Guatemala and Honduras. Mesoscale variations in velocity and temperature along the reef were found in seasonal model simulations and in observations; these variations are associated with meandering of the Caribbean current (CC) and the propagation of Caribbean eddies. Diagnostic calculations and a simple assimilation technique are combined to infer the dynamically adjusted flow associated with particular eddies. The results demonstrate that when a cyclonic eddy (negative sea surface height anomaly (SSHA)) is found near the MBRS the CC shifts offshore, the cyclonic circulation in the Gulf of Honduras (GOH) intensifies, and a strong southward flow results along the reef. However, when an anticyclonic eddy (positive SSHA) is found near the reef, the CC moves onshore and the flow is predominantly westward across the reef. The model results help to explain how drifters are able to propagate in a direction opposite to the mean circulation when eddies cause a reversal of the coastal circulation. The effect of including the Meso-American Lagoon west of the Belize Reef in the model topography was also investigated, to show the importance of having accurate coastal topography in determining the variations of transports across the MBRS. The variations found in transports across the MBRS (on seasonal and mesoscale time scales) may have important consequences for biological activities along the reef such as spawning aggregations; better understanding the nature of these variations will help ongoing efforts in coral reef conservation and maintaining the health of the ecosystem in the region.     

The significance of tectonic-related tertiary remagnetization along the margins of the Valencia trough

The paleomagnetic data from the margins of the Valencia Trough are derived from Mesozoic and Tertiary rocks from the Balearic Islands, Catalan Coastal Ranges and Eastern Iberian Chain. These rocks are affected by a complex structural evolution consisting of an initial compressive stage followed by one of extension. Cenozoic paleomagnetic data indicate that rotations occurred during the Paleogene compression and before the extension started (Lower Miocene) in the Catalan Coastal Ranges. In contrast, in the Balearic Islands the rotations are synchronous to both compressional (Late Oligocene-Middle Miocene) and extensional tectonics (post-Middle Miocene). In both areas the Mesozoic limestones are remagnetized. In the Catalan Coastal Ranges they display the same direction as the Paleogene syn-compressive deposits whereas in the Balearic Islands they conform with Lower Miocene (Burdigalian) syncompressive rocks. It is concluded that the processes of remagnetization that affected eastern Iberia are related to a compressive rather than an extensional tectonics regime     

基于Copula函数的东江流域3大水库丰枯遭遇分析

东江流域在广东省政治、经济和社会中占有重要地位,域内新丰江、枫树坝和白盆珠3大水库的来水量直接影响区域生产生活供水.面对水库群联合调度新要求,本文利用Copula函数构建了3大水库入库流量的二维和三维联合分布,分析其丰枯遭遇概率,主要结论如下:(1)3大水库两两间丰枯同步的概率大于丰枯异步的概率,非汛期丰枯同步的概率大于汛期.其中,白盆珠与新丰江、枫树坝丰枯异步的概率相对较大,这为其与另两个水库丰枯互补提供了可能;(2)三维联合分布显示,3大水库丰枯同步的概率在全年、汛期和非汛期均较大,依次为42.29%、41.74%和51.99%,其中同丰和同枯的概率远大于同平的概率.枫树坝与新丰江对下游具有补偿能力的概率分别为29.81%和23.03%,不具有补偿能力的概率分别为32.75%和22.32%;(3)利用3大水库的联合分布,可获得各水库不同入库流量遭遇的概率以及特定概率下各水库入库流量的可能组合,对3大水库联合优化调度具有重要的理论与实践价值.     

Numerical comparisons of the damping of internal gravity waves in stratified fluids

Summary Comparisons are made of the attenuation of progressive internal waves in stratified fluids consisting of (a) a representation of a single thermocline, (b) a weak exponential density distribution and (c) a two-layer system. Effects of the earth's rotation are neglected, as also are heat and salt diffusion. Significant differences are found in the decay characteristics of the three density structures. Internal waves are most strongly damped in the layered system (c) whilst the calculated attenuation rates are least for the thermoclinic structure (a). All the internal modes investigated are, however, shown to be more strongly damped than the associated surface wave.     

Manifestations of the ray structure of the coronal streamer belt in the form of sharp peaks of the solar wind plasma density in the Earth’s orbit

White corona images are analyzed based on the calibrated data of the LASCO-C2/SOHO instrument (processing level 1) and the solar wind (SW) parameters with hourly and minute resolutions on the Wind spacecraft. The quasistationary events, excluding coronal mass ejections and their manifestations in SW are studied. It has been indicated that the angular dimensions and relative variations in the density of the streamer belt segments remain almost unchanged over the entire distance from the Sun to the Earth’s orbit. In the Earth’s orbit, the ray structure of the belt streamer manifests itself as sharp (with steep fronts lasting several minutes and less) peaks (of several hours in duration) of the solar wind plasma density with maximal values N _max > 10 cm^?3.     

汶川地震近场加速度基本参数的方向性特征

以2008年5月12日的Ms8.0级汶川地震强震记录为基础,根据场地条件和断层距,选取198组三分量近场加速度记录,按照台站相对于破裂传播方向的位置将其划分为破裂前方和破裂后方两类场点.为了考虑破裂传播的方向性和地震辐射图对地震动不同分量的影响,将每组地震动的两个正交水平分量旋转成为垂直断层走向和平行断层走向的分量,然...     

青藏高原东南缘南段现今变形特征研究

本文以青藏高原东南缘南段1999—2017年的GPS速度场为主,结合小震分布、历史地震和活断层探测等资料,首先,基于Okada断层位错模型反演了研究区域主要活断层的滑动速率;其次,以断层滑动速率和GPS速度场观测资料作为约束,利用DEFNODE负位错方法反演了研究区域的块体内部变形及主要活断层的闭锁程度和滑动亏损;最后,计算研究区域现今应变率场,并结合Pms和XKS剪切波分裂结果,探讨分析了青藏高原东南缘的动力学特征.研究结果表明:(1)红河断裂带现今滑动速率明显低于南华—楚雄—建水断裂和无量山断裂;(2)红河断裂带的元江—元阳段、鹤庆—洱源段和小江断裂带北段处于强闭锁状态,南华—楚雄—建水断裂带和无量山断裂带中—北段的闭锁程度强于南段;(3)青藏高原东南缘南段现今地壳变形表现为近E-W向的拉张和近N-S向的挤压,最大剪切方向与Pms和XKS剪切波分裂的快波方向呈一定角度,表明地壳与地幔处于完全解耦状态,而中-下地壳低速层可能是壳幔解耦的主要原因之一;(4)青藏高原东南缘的整体变形受控于印度板块的推挤、印缅俯冲带的深源俯冲以及缅甸微板块与巽他板块的后撤/回退的共同作用.     

Changes and variation in the discharge regime of the Upper Suriname River Basin and its relationship with the tropical Pacific and Atlantic SST anomalies

Long‐term changes and variability in river flows in the tropical Upper Suriname River Basin in Suriname (2–6°N, 54–58°W) are analysed, including the relation to sea surface temperatures (SSTs) in the tropical Atlantic and Pacific Ocean. To analyse variability, lag correlation and statistical properties of the data series are used. Long‐term changes are analysed using parametric and non‐parametric statistical techniques. The analyses are performed for the period 1952–1985. The results show that both river discharge series at Semoisie and Pokigron are non‐stationary and have a negative trend. The negative rainfall trend in the centre of Suriname may be responsible for the negative trend in the annual river discharges in the basin. The highest correlation (Pearson's coefficient c) is obtained when the Tropical North Atlantic (TNA) SSTs lags the monthly discharges at Pokigron by 3–4 months (c = 0·7) and when the Tropical South Atlantic (TSA) SSTs lags the discharges by 4 months (c = ? 0·7). It also follows that the high (low) monthly flows, from April–August (September–March) are associated with increasing (decreasing) SSTs in the TNA and with decreasing (increasing) SSTs in the TSA. The results also reveal that years with low (high) discharges are more related to warmer (colder) SSTs during the year in the TNA region and a southward displacement of the Inter‐Tropical Convergence Zone (ITCZ). However, the Pacific El Niño (La Niña) events may also be responsible for low (high) flow years in this basin. Copyright © 2007 John Wiley & Sons, Ltd.     

Polycyclic aromatic hydrocarbons in the sediments of the Yalujiang Estuary,North China

Selected polycyclic aromatic hydrocarbons (PAHs) in surface sediments of the Yalujiang Estuary, North China, have been investigated by gas chromatography-mass spectrometry (GC-MS) for flood season (August, 1994) and dry season (May, 1996), respectively. PAHs concentrations from sediments range from 68 to 1500 ngg(-1) depending upon the sample locations. The most contaminated sediment samples are found in the turbidity maximum area for both dry and flood seasons. The source of PAHs is most likely pyrolytic, with minor contributions from petrogenic and diagenetic PAHs for some samples. Perylene is mainly derived from biogenic inputs, and occurs at almost stations. In the Yalujiang Estuary, both biogenic and anthropogenic hydrocarbons are primarily derived form riverine discharges and are accumulated in the mixing zone. The overall levels of PAHs in this study are low compared to other regions and reveal moderate PAHs pollution in the Yalujiang Estuary.     

Petroleum and PAH contamination of the Black Sea

Concern has been expressed regarding the extent of contamination of the Black Sea. Analyses of coastal sediments taken from throughout the region indicate, however, that levels of petroleum hydrocarbons (2-300 microg g(-1) dry wt total hydrocarbons) are generally comparable to those encountered in the Mediterranean and are lower than concentrations reported for highly contaminated areas such as the Gulf, Hong Kong, Taiwan and New York Bight. Highest concentrations of total hydrocarbons (>100 microg g(-1) dry wt) were associated with discharges from Odessa, Sochi and the River Danube. Chronic/degraded petroleum was the major contributor at these sites. Samples from the Ukrainian coastline were comparatively clean (<10 microg g(-1) dry wt total hydrocarbons). Major contributions of fresh oil (as indicated by sigma n-C14-34) occur through the River Danube. Concerning total PAH, concentrations (7-638 ng g(-1) dry wt) compare to relatively unpolluted locations in the Mediterranean and are much lower than levels reported for polluted UK estuaries (e.g. Mersey, Tyne, Thames). Both pyrolytic and petrogenic PAH are present in most samples, although petroleum derived PAH are dominant at Sochi and pyrolytic sources are prevalent in the Bosphorus region. The absence of a correlation between total hydrocarbons and PAH (R2 = 0.04) indicates different primary sources for the two.     

Ozone content of the atmosphere. 3. Statistics of extreme values of the total ozone content in the midlatitude atmosphere

The occurrence frequency of extremely large and extremely small values of the total ozone content (TOC) for Irkutsk, Berlin, and Saskatoon midlatitude stations (located near 52°N but in different climatic zones) are calculated based on the daily satellite measurements in the 1978–2005 period. The data for various seasons are presented. The interannual variability and regional differences are demonstrated. The results indicate that the TOC variability is mainly caused by natural atmospheric processes.     

A discussion of the validity of hydrodynamical equations of motions

Summary Starting from the eqts. (1) and (4) resp. (19) which are valuable for the streaming of an ideal gas in the space, where the plane resp. spheric wave is propagated adiabatically, it follows that for such a motion instead of the Euler's equation the eqts. (11) resp. (20) are valid. In the discussed cases the eqts. (1), (4) and (19) are the fundamental equations and reflect the Newton's principles of dynamics. In our two special cases the one dimensional Euler's equation follows from the fundamental eqts. (1), (4) and (19) only approximately.

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Zusammenfassung In zwei Beispielen wird gezeigt, dass die Gültigkeit der Eulerschen Bewegungsgleichungen nicht allgemein ist.

     

Development of a Lagrangian sediment model to reproduce the bathymetric evolution of the Mersey Estuary

The development and application of a Lagrangian particle-tracking model to simulate sediment transport in the Mersey Estuary (UK) is described. Each of the particles (up to a million in total) is advected horizontally by the 3-D tidal currents. Related vertical movements are: (1) downwards by settlement at a prescribed velocity w _s and (2) both upwards and downwards by a distance related to the vertical eddy diffusivity. In a novel departure from traditional practice, where initial distributions of surficial sediments are specified, all particles are introduced at the seaward boundary of the model. Provenance studies indicate surficial sediments are overwhelmingly of marine origin. For the predominant fine sediments, ‘cyclical convergence’ in suspended sediment concentrations is approximated after about two spring-neap tidal cycles. Comparisons are shown between the suspended sediment concentrations and net deposition rates computed by this model against observed values and earlier computations utilising both 1-D and 3-D Eulerian models. While all of these results are in broad agreement, the flexibility of the Lagrangian approach for simulating flocculation, consolidation and mixed sediments illustrates its future potential.     

Styles of subglacial glaciotectonic deformation within the context of the anglian ice-sheet

A substantial proportion of the glacial sediments of East Anglia, England, are chaotic and highly deformed. This has been attributed to (a) direct glaciotectonic deformation or (b) slumping of glaciomarine sediments. We show that interpretation (a) leads to a classification of subglacial glaciotectonic deposits into sites of ‘constructional deformation’, where little or no erosion of the preglacial deposits has occurred and styles of deformation are preserved moving up in the sequence, and ‘excavational deformation’, where substantial erosion of preglacial sediments has occurred and deformational styles are superimposed on each other. By using glaciological and geotechnical theory, we show that the expression of these deformational styles in East Anglia is a natural response to the stress fields imposed by the ice-sheet, and that in consequence their spatial relationships are explicable. The depth of deformation is related to the geotechnical properties of till and substrate, the stress and effective stress fields, and found to be consistent with observations.     

An outline of the geology and geochemistry,and the possible petrogenetic evolution of the volcanic rocks of the Tonga-Kermadec-New Zealand island arc

The Pleistocene-Recent volcanism of this arc extends nearly linearly NNE from northern New Zealand for some 2800 km. Along its western margin lies an active marginal basin (Lau Basin and Havre Trough) which has its southern termination in the Taupo volcanic zone (TVZ, New Zealand). The New Zealand arc segment is developed within a continental crust, whereas the Tonga-Kermadec segments are developed on a ridge system within the oceanic basin. Submarine morphology suggests that the Kermadec volcanoes represent a less advanced stage of evolution relative to those of Tonga.Magmas erupted within the TVZ are dominantly rhyolitic (≈16,000 km³) with subordinate andesites and rare high-alumina tholeiites and dacites. The Kermadec Islands are dominated by tholeiites and basaltic andesites, with subordinate andesites and dacites. The Tongan Islands are dominated by basaltic andesites, with locally developed andesites and dacites. These Tonga-Kermadec lavas are characterised by subcalcic groundmass clinopyroxenes, whereas the younger group of TVZ andesites contain groundmass hypersthene and augite.Geochemically, the TVZ andesites are systematically enriched (relative to those of Tonga-Kermadec) in “incompatible” elements (e.g. K, Rb, Cs, Ba, light REE, U, Th, Zr, Pb), are less Fe-enriched, and contain more radiogenic Sr and Pb (excepting certain ²⁰⁷Pb/²⁰⁴Pb compositions). The evidence points to crustal equilibration of the TVZ andesites prior to eruption.A complete overlap of major and trace element chemistry (including TiO₂) is observed between the Kermadec-TVZ tholeiites and basaltic andesites, and the ocean floor tholeiites of the Lau Basin. Compared to the Tongan lavas, those of the Kermadecs exhibit a greater degree of chemical variability, also reflected in the greater heterogeneity in their Pb isotopic compositions. Moreover, many of the Tonga-Kermadec basaltic andesites exhibit more depleted “incompatible” trace element abundances than the Kermadec and TVZ tholeiites.The “primary” magmas of this arc are interpreted to be of basaltic andesite type, derived from Benioff zone melting (essentially anhydrous), but extensively modified by low-pressure crystal fractionation processes. The Kermadec tholeiites are explained as products of relatively shallow upper mantle partial fusion induced during the earlier stages of diapiric rise of Benioff zone-derived magmas, which are sufficiently hot to intersect the peridotite solidus. This should result in the production and intermixing of a series of magmas extending from olivine tholeiite to basaltic andesite composition. The voluminous rhyolites of TVZ are interpreted as the products of crustal fusion involving Mesozoic sediments.