Evolution of the Yellow River delta,China: Impacts of channel avulsion and progradation

The evolution of the Yellow River delta is characterized by heavy sediment load,rapid seaward migration,frequent avulsions,and intense anthropogenic disturbances.Evolution of the delta channel following avulsions is very complex and has not yet been thoroughly understood.In the research presented by this paper,we conducted comprehensive analyses of the changes in the water stages,slopes,longitudinal profiles,and the erosion and deposition in the Yellow River delta channels during a time period of over five decades.Results showed that,following each avulsion,channels migrated seaward at decaying rates and the slopes at the downstream of the avulsion point decreased exponentially with time and completed its major adjustment within about four to five years.A generalized geometric model was proposed to describe the changes in the longitudinal profiles of the delta channels.A calculation method to determine the characteristic water stages at the delta was proposed based on the geometric model and the delayed response model for the morphological responses of fluvial rivers to perturbations.Water stages corresponding to a discharge of 3000 m3/s at Lijin and Xihekou during 1954 through 2012 were calculated by using the proposed method.The proposed method may be used to predict the evolution of the delta channels in response to artificial avulsions at the Yellow River delta in the future.     

Assessment of Jovian synchrotron radiation with a bi-modal electron population

An explicit formula is developed to explore the mechanism of the synchrotron radiation by using a bi-modal loss-cone distribution function. The variation of the distribution function along the field line is modeled in detail and the evaluation of the total power in the synchrotron radiation is presented. The variance of synchrotron radiation with latitude depends on the electron anisotropy; for low anisotropy, synchrotron radiation increases with latitude and reaches a maximum at the particle mirror points; for high anisotropy, it decreases with latitude and maximizes at the equator. A bi-modal population is therefore suggested to explain the radiation intensity which peaks both at the equator and at high latitude.     

The Gilbert Islands (Republic of Kiribati) earthquake swarm of 1981–1983

A major swarm of intraplate earthquakes at the southeastern end of the Gilbert Islands Chain (3.5°S, 177.5°E) commenced in December 1981 and lasted through March 1983. No seismicity had been reported in the historical record in this region prior to 1981, but during the swarm 217 events with m_b ? 4.0 were located by the NEIS, with 86 events having m_b ? 5.0. The source region is quite remote, and the uniform detection level for the NEIS is for m_b ? 4.8. A b-value of 1.35 is found for the swarm using the maximum likelihood method. Four events in the sequence were large enough (m_b = 5.6?5.9) to determine focal mechanisms teleseismically using body- and surface-wave analysis. These events are found to have a range of mechanisms, from predominantly thrust with a significant oblique component, to purely strike-slip. The compression axes are consistent for all four events, with horizontal orientation trending NNE-SSW. This orientation is perpendicular to the direction of plate motion. The events are located at depths between 15 and 20 km placing them deep in the oceanic crust or in the upper mantle. No obvious bathymetric feature can be related to the fault plane orientations, though there is an offset in the island chain near the epicenters. While some characteristics of the swarm suggest a magmatic origin, the nature of the focal mechanisms, the location of the swarm, and the large accumulated moment release of the sequence favor a tectonic origin.     

Solar-wind–magnetosphere coupling,including relativistic electron energization,during high-speed streams

High geomagnetic activity occurs continuously during high-speed solar wind streams, and fluxes of relativistic electrons observed at geosynchronous orbit enhance significantly. High-speed streams are preceded by solar wind compression regions, during which time there are large losses of relativistic electrons from geosynchronous orbit. Weak to moderate geomagnetic storms often occur during the passage of these compression regions; however, we find that the phenomena that occur during the ensuing high-speed streams do not depend on whether or not a preceding storm develops. Large-amplitude Alfvén waves occur within the high-speed solar wind streams, which are expected to lead to intermittent intervals of significantly enhanced magnetospheric convection and to thus also lead to repetitive substorms due to repetitively occurring reductions in the strength of convection. We find that such repetitive substorms are clearly discernible in the LANL geosynchronous energetic particle data during high-speed stream intervals. Global auroral images are found to show unambiguously that these events are indeed classical substorms, leading us to conclude that substorms are an important contributor to the enhanced geomagnetic activity during high-speed streams. We used the onsets of these substorms as indicators of preceding periods of enhanced convection and of reductions in convection, and we have used ground-based chorus observations from the VELOX instrument at Halley station as an indicator of magnetospheric chorus intensities. These data show evidence that it is the periods of enhanced convection that precede substorm expansions, and not the expansions themselves, that lead to the enhanced dawn-side chorus wave intensity that has been postulated to cause the energization of relativistic electrons. If this inference is correct, and if it is chorus that energizes the relativistic electrons, then high-speed solar wind streams lead to relativistic electron flux enhancements because the embedded large-amplitude Alfvén waves give multi-day periods of intermittent significantly enhanced convection.     

大地震与全球地震台网

引言 地震学家经常开玩笑说,＂阻止地震的最好办法就是布设地震台站。＂为了记录地震信号或开展有针对性的有关地球结构的研究就需要布设地震仪,而地震的发生往往是变幻莫测的,在时间和空间上都绝对是非均匀的,所以安装地震仪的辛苦有时会徒劳无功。     

XUV image of the sun from eclipse observations of the ionospheric E-region

Ionospheric E-region observations from Boulder (40.0 N, 105.3 W), Grand Bahama (26.6 N, 78.2 W), Mexico City (19.3 N, 99.2 W), Vandenberg (35.6 N, 120.6 W), and Wallops Island (37.9 N, 75.5 W) during the total solar eclipse of 7 March, 1970 are used for reconstructing the distribution of the ionizing XUV radiation over the solar disk. The derived solar image compares reasonably well with the EUV and X-ray pictures of the Sun obtained from rockets.     

Geochemical characteristics of gold-related granitoids in southwestern New Brunswick, Canada

Two groups of granitoids associated with gold mineralization in the Appalachian orogen of southwestern New Brunswick are recognized: a Late Silurian to Early Devonian (423–396 Ma) granodioritic to monzogranitic series (GMS), and a Late Devonian (370–360 Ma) granitic series (GS). The GMS granitoids are relatively low in silica, calc-alkaline, metaluminous to weakly peraluminous, and show characteristics of normal (oxidized) to reduced I-type granites depending on the properties of country rocks. They may have been derived from partial melting of lower crustal rocks triggered by underplated basaltic magmas; and country rocks bearing reduced organic carbon and/or graphite may have played an important role in the reduction of normal I-type intrusions to reduced I-type, which is essential in the formation of intrusion-related gold systems. In contrast, the GS granites, although calc-alkaline and metaluminous to peraluminous, are relatively rich in silica, incompatible elements, and high field strength elements. They are fractionated I-type granites, and are probably related to the coeval Mount Douglas granite in the Saint George batholith through fractional crystallization. Their parental magmas may have been derived from partial melting of quartzofeldspathic sources at relatively low temperatures. Both GMS and GS intrusions are orogenic, although some of them display the affinity of those emplaced into a within-plate environment. The origin of intrusion-related gold systems in this region appears to be controlled by several factors, including magma sources, magmatic processes, redox conditions (country-rock nature), and local structural regimes.     

Estimating explosion yield by analytical waveform comparison

Summary. The yields of 28 underground nuclear explosions at NTS (25 on Pahute Mesa) are estimated by applying a relative waveform analysis called intercorrelation to 1256 teleseismic short-period P -waves recorded at 74 WWSSN and CSN stations. Corrections for the effects of pP interference and yield-scaling of the explosion source functions are determined and applied to the waveforms, enabling analytical comparison of signals from events with different yields and burial depths. The procedure accounts for common receiver and propagation effects. Relative explosion source strengths in the 0.5–2.0 Hz frequency band are determined, with results of near-field modelling of strong ground motions establishing the absolute source spectral levels. Four events with detailed near-field models are used as master events in the intercorrelation process, and it is demonstrated that the relative source strengths are better resolved than the absolute values. Events with announced yields are used to determine empirical relations between yield and source strength, which in turn predict the yields of the other events. These yield estimates are shown to be comparable with those obtained by standard m _b and relative amplitude analysis. The analytical waveform comparisons also provide estimates of the pP parameters for each event, and criteria for identifying anomalous events, such as PIPKIN and MUENSTER, for which the waveforms differ from those of other events in the test site. Possible mechanisms affecting the anomalous events are considered. Pahute Mesa is shown to be a distinct subsite within NTS, with different teleseismic amplitude and waveform variations than observed at other subsites.     

Probable causes of late twentieth century tropospheric temperature trends

We assess the most probable causes of late twentieth century (1960–1994) tropospheric temperature changes. Optimal detection techniques are used to compare observed spatio-temporal patterns of near-surface and tropospheric temperature change with results from experiments performed with two different versions of the Hadley Centre climate model. We detect anthropogenic forcings, particularly well-mixed greenhouse-gases, with a less certain sulfate aerosol cooling influence. More limited evidence exists for a detectable volcanic influence. Our principal results do not depend upon the choice of model. Both models, but particularly HadCM3, appear to overestimate the simulated climate response to greenhouse gases (especially at the surface) and volcanoes. This result may arise, at least in part, due to errors in the forcings (especially sulfate) and technical details of our approach, which differs from previous studies. We use corrected and uncorrected versions of the radiosonde record to assess sensitivity of our detection results to observational uncertainties. We find that previous corrections applied to the radiosonde temperature record are likely to have been sub-optimal in only taking into account temporal consistency. However, the choice of corrected or uncorrected version has no systematic effect upon our main conclusions. We show that both models are potentially internally consistent explanations of observed tropospheric temperatures.     

Tectonics, global changes in sea level and their relationship to stratigraphical sequences at the US Atlantic continental margin

The principal factors that control the extent of seas through geological time are vertical movements of the lithosphere and global changes in sea level. The relative height of the sea surface determines the facies and the thickness of sediments that can accumulate in a sedimentary basin. Backstripping studies show that the primary factors affecting the subsidence of rifted sedimentary basins are thermal contraction, following heating and thinning of the lithosphere at the time of rifting, and sedimentary loading. Factors such as compaction, palaeobathymetry, erosion and global sea level changes also contribute, but their combined affects are small compared to those of thermal contraction and sedimentary loading. Simple models have been constructed which combine the effects of sedimentary loading and thermal contraction with those of compaction, sub-aerial erosion and global changes in sea level. In the models it was assumed that the lithosphere was heated and thinned by stretching at the time of rifting, sedimentary loading occurs by flexure of a lithosphere that progressively increases its flexural rigidity with age following rifting and, that sediment compaction and bathymetry change across a basin but do not vary significantly with gwological time. Furthermore, different assumptions were made on the magnitude of curves of global sea level changes and the relationship between denudation rate and regional elevation. The models show that tectonics, in the form of thermal contraction of the lithosphere and flexure and slowly varying global changes in sea level, can explain a number of the stratigraphic features of the US Atlantic continental margin. In this Paper some of the implications of these results are examined for studies of (a) sea level changes through geological time; and (b) the maturation history of continental margin basins.