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1.
Summary This paper ties up with [5, 6] the fundamental notations of which have been adopted. The sets of Stokes' constants (harmonic coefficients) J n (k) , S n (k) were adopted from [4], and the scale factor for lengths, R0=GM/W0, from [5]. The equations for global meridional and parallel sections of the geoid surface W=W0 are formulated. The geoid sections are represented by best fitting ellipses, as regards the meridians always for the arcs between the equator and the pole. Address: Politickych vězňů 12, Praha 1-Nové Město.  相似文献   

2.
The gravity field of the seismogenic upper crust was derived from the Bouguer gravity map by applying the Butterworth high-pass filter in the wave-number domain. The cutoff wavelength of the filter was 110 km, to pass the gravity signals of structures within the 18 km thick seismogenic layer. The derived residual gravity map reveals potential stress concentrating structures, which may cause seismicity provided they lie within the existing zones of weakness. Furthermore we derived a shaded relief map of the horizontal gravity gradient, which highlighted the tectonic lines accompanied by density contrast. The directional analysis of this map shows three dominant strike directions. The most prominent one is “the Hercynian” NW-SE strike direction represented by the Franconian Line, the Gera-Jáchymov Fault Zone and the Elbe Zone. The second dominant strike is the Rhenisch NNE-SSW trending represented by the Upper Rhine Graben Zone, Rheinsberg-Heldburg Line and several Proterozoic volcanic belts in the Teplá-Barrandien Unit. The third pronounced trending of the ENE-WSW direction is represented by the Erzgebirge and Eger Graben gravity low. The N-S trending Rostock-Leipzig-Regensburg Zone (Pritzwalk-Naab Lineament) is not distinctly reflected in the derived gravity maps, although many fault segments have a meridian direction. The relative reactivation potential of some pre-existing fault systems identified in the gravity map was studied with respect to the wide range of the recent stress configuration determined in the West Bohemia/Vogtland region. The resulting diagrams show that the steep NNW-SSE to N-S faults (represented by some segments of the Mariánské Lázně Fault Zone) are oriented favourably for reactivation. On the contrary, the orientation of the ENE-WSW faults limiting the Eger Graben (Litoměřice Fault, etc.) is unfavourable for reactivation for all dip values.  相似文献   

3.
The concentration of dissolved mercury in sea water has been determined in a number of areas in the northern and southern hemispheres and an attempt has been made to correlate the values found for certain areas with natural physical phenomena. The average concentrations found ranged from 11.2 ng l?1 in the southern hemisphere to 33.5 ng l?1 for the northern hemisphere; an increase suspected to be the result of dispersion of industrial pollution by jet streams. Local effects including upwelling, volcanic action, land run-off and heavy suspended matter loads are also discussed.  相似文献   

4.
月球深部断裂是研究月球早期应力场演化和动力机制的一类重要构造.本文基于GRAIL月球重力数据计算了全月布格重力梯度，在此基础上对月球深部断裂进行了全球绘制，共识别月球深部断裂226条.计算了断裂的长度和走向等基本参数，断裂总长度达到37137 km，平均长度为164 km.统计月球深部断裂在不同范围内的分布情况，发现多数断裂分布在月球的中低纬度地区，且北半球的断裂多于南半球.此外，大型月海集中区所在的纬向带断裂分布最多，断裂经向分布最多的区域为风暴洋的西侧.从全球尺度和不同经纬度带绘制断裂走向玫瑰花图，总体上月球全球尺度上的深部断裂表现出NE-SW和NW-SE的优势走向，不同经度带断裂的优势走向变化不明显，但在纬度带上有显著的变化.南北半球的中纬度带和高纬度带具有相同的优势走向，分别为NE-SW和NW-SE、E-W，在低纬度带的优势走向有所差异，分别是南半球的NE-SW和NW-SE以及北半球的N-S.  相似文献   

5.
关于暴时电离层电流分布的南北半球不对称性   总被引：3，自引：1，他引：3       下载免费PDF全文
采用国际上广泛认可的高层大气和电离层经验模式提供的各种参数, 通过电离层电流连续方程, 计算出强磁暴条件下6月至日和12月至日内, 磁纬±72°和磁地方时00:00～24:00之间电离层电场、电流等的分布. 计算中考虑了地磁和地理坐标间的偏离; 除中性风场感生的发电机效应外, 还包含了磁层耦合(极盖区边界的晨昏电场和二区场向电流)的驱动外源. 结果表明, 6月至日时, 磁层扰动自极光区向中低纬的穿透情况在南、北半球内基本接近, 北半球内略强; 但12月至日时, 呈现明显的不对称性, 南半球的电流穿透远强于北半球, 而电场的穿透则是在北半球更强. 无论南北半球, 在中高纬地区, 午夜至黎明时段出现较强的东向电场分量, 其[WTHX]E×B[WTBZ]的向上漂移效应, 正是解释我们以往不少研究现象中所期盼的物理机制.  相似文献   

6.
40Ar/39Ar ages and paleomagnetic correlations using characteristic remanent magnetizations (ChRM) show that two main ignimbrite sheets were deposited at 4.86 ± 0.07 Ma (La Joya Ignimbrite: LJI) and at 1.63 ± 0.07 Ma (Arequipa Airport Ignimbrite: AAI) in the Arequipa area, southern Peru. The AAI is a 20–100 m-thick ignimbrite that fills in the Arequipa depression to the west of the city of Arequipa. The AAI is made up of two cooling units: an underlying white unit and an overlying weakly consolidated pink unit. Radiometric data provide the same age for the two units. As both units record exactly the same well-defined paleomagnetic direction (16 sites in the white unit of AAI: Dec = 173.7; Inc = 31.2; α95 = 0.7; k = 2749; and 10 sites in the pink unit of AAI; Dec = 173.6; Inc = 30.3; α95 = 1.2; k = 1634), showing no evidence of secular variation, the time gap between emplacement of the two units is unlikely to exceed a few years. The >50 m thick well-consolidated white underlying unit of the Arequipa airport ignimbrite provides a very specific magnetic zonation with low magnetic susceptibilities, high coercivities and unblocking temperatures of NRM above 580°C indicating a Ti-poor titanohematite signature. The Anisotropy of Magnetic Susceptibility (AMS) is strongly enhanced in this layer with anisotropy values up to 1.25. The fabric delineated by AMS was not recognized neither in the field nor in thin sections, because most of the AAI consists in a massive and isotrope deposit with no visible textural fabric. Pumices deformation due to welding is only observed at the base of the thickest sections. AMS within the AAI ignimbrite show a very well defined pattern of apparent imbrications correlated to the paleotopography, with planes of foliation and lineation dipping often at more than 20° toward the expected vent, buried beneath the Nevado Chachani volcanic complex. In contrast with the relatively small extent of the thick AAI, the La Joya ignimbrite covers large areas from the Altipano down the Piedmont. Ti-poor titanomagnetites are the dominant magnetic carriers and AMS values are generally lower than 1.05. Magnetic foliations are sub horizontal and lineations directions are scattered in the LJI. The AMS fabrics are probably controlled by post-depositional compaction and welding of the deposit rather than transport dynamics. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.  相似文献   

7.
Summary We have studied 454 oriented samples from seven loess outcrops in the Czech Republic for comparison and correlation of the magnetic properties with those of the loess profiles in China and Central Asia. Three sections at Sedlec (Prague), Zeměchy and Dolní Věstonice cover the time span of the last glacial-interglacial cycle. Loess from the middle Pleistocene period including pedocomplexes V and VI was studied at Sedlešovice (Znojmo) and Karlštejn. Loess of uncertain — possibly lower to middle Pleistocene age — was sampled at Sedlec near Mikulov. At Červeny Kopec (Red Hill, Brno) we investigated the oldest loess near the Matuyama/Brunhes (M/B) boundary. The characteristic remanence (ChRM) determined after magnetic clearning is of normal polarity throughout all sections except at Červeny Kopec. There, two polarity changes from reversed to normal were found within two sections initially thought to represent two successive stratigraphic intervals. However, the marked similarities between lithological, susceptibility, declination and inclination profiles lead us to suggest that the two polarity changes are in fact one and the same. The two sections are therefore laterally equivalent and both have recorded the M/B field reversal. The susceptibility variations were used to mutually correlate the Czech sections and to construct a composite profile across the present day loess outcrops in the Czech Republic. They also serve as a paleoclimate proxy which can be compared and correlated with the paleoclimatic records observed in the Chinese and Central Asian loess. The origin of the low field susceptibility variations was studied by measuring the frequency dependence of susceptibility which revealed that the enhancement within the pedocomplexes is controlled by the amount of fine-grained ferromagnetic minerals present.  相似文献   

8.
In the light of the single scattering model of coda originating from local earthquakes, and based on the aftershock coda registered respectively at the 4 short period stations installed near the foci shortly after theM7.6 Lancang andM7.2 Gengma earthquakes, this paper has tentatively calculated the rate of amplitude attenuation and theQ c-value of the coda in the Lancang and Gengma areas using a newly-founded synthetic determination method. Result of the study shows the rate of coda amplitude attenuation demonstrates remarkable regional differences respectively in the southern and northern areas. The southern area presents a faster attenuation (Q c=114), whereas the northern area shows a slower attenuation (Q c=231). The paper also discusses the reasons causing such differences. Result of the study also suggests a fairly good linear relation between the coda source factorA o(f) and the seismic moment and the magnitude. Using the earthquake scaling law, the following formulas can be derived: lgM 0=lgA 0(f)+17.6,M D=0.67lgA 0(f)+1.21 and logM 0=1.5M D+15.79. In addition, the rates of amplitude attenuationβ s andβ m are respectively calculated using the single scattering and multiple scattering models, and the ratioβ s/βm=1.20−1.50 is found for the results respectively from the two models. Finally, the mean free pathL of the S-wave scattering in the southern and northern areas are determined to be 54 km and 122 km respectively by the relations which can distinguish between the inherentQ i and scatteringQ s, testify to this areas having lowQ-values correspond to stronger scatterings. The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,14, 71–82, 1992. This study is partly supported by the Seismological Science Foundation of the State Seismological Bureau of China, and the present English version of the paper is translated from its Chinese original by Wenyi Xia, Seismological Bureau of Yunnan Province.  相似文献   

9.
Gravity anomaly reference fields, required e.g. in remove-compute-restore (RCR) geoid computation, are obtained from global geopotential models (GGM) through harmonic synthesis. Usually, the gravity anomalies are computed as point values or area mean values in spherical approximation, or point values in ellipsoidal approximation. The present study proposes a method for computation of area mean gravity anomalies in ellipsoidal approximation (‘ellipsoidal area means’) by applying a simple ellipsoidal correction to area means in spherical approximation. Ellipsoidal area means offer better consistency with GGM quasigeoid heights. The method is numerically validated with ellipsoidal area mean gravity derived from very fine grids of gravity point values in ellipsoidal approximation. Signal strengths of (i) the ellipsoidal effect (i.e., difference ellipsoidal vs. spherical approximation), (ii) the area mean effect (i.e., difference area mean vs. point gravity) and (iii) the ellipsoidal area mean effect (i.e., differences between ellipsoidal area means and point gravity in spherical approximation) are investigated in test areas in New Zealand and the Himalaya mountains. The impact of both the area mean and the ellipsoidal effect on quasigeoid heights is in the order of several centimetres. The proposed new gravity data type not only allows more accurate RCR-based geoid computation, but may also be of some value for the GGM validation using terrestrial gravity anomalies that are available as area mean values.  相似文献   

10.
There is no temperature effect in the southern Tibetan Plateau and South Asia to the south of the Tanggula Mountains. Amount effect has been observed at a few sampling stations accounting for about a half of the statistical stations. There is notable temperature effect in the middle and northern Tibetan Plateau and its adjacent Central Asia to the north of the Tanggula Mountains. Because vapor directly originates from low-latitude oceans, the relative heavy δ18O with small variation characterizes the rainfall in South Asia. A sharp depletion of the stable isotopic compositions in precipitation takes place from Kyangjin on the southern slope of the Himalayas to the Tanggula Mountains in the middle plateau. From the Tanggula Mountains to the northern Tibetan Plateau, the δ18O in precipitation increases with increasing latitude.  相似文献   

11.
地球南北半球的非对称性   总被引：12，自引：1，他引：12  
依据新的计算分析和空间观测数据,进一步论述了地球南北半球的非对称性. 全球热散失量的计算得出,南半球高出北半球33髎;南半球地幔热散失量是北半球的2倍. 比较南北半球S波速度分布,得出南半球的上地幔为低速、高温,北半球的上地幔为高速、低温. 计算地幔各层的质心位置发现,地球的质心偏于北半球. 计算地球经、纬圈长度的年变化率表明,南半球在扩张,北半球在收缩. 用空间大地测量数据的检测结果证实,南半球处于扩张状态,北半球处于压缩状态. 对地球的非对称性作了初步的动力学解释.  相似文献   

12.
Particulate fluxes investigated in the central South China Sea (SCS) during 1993―1996 indicate that opal flux can be used to show primary productivity change, which provides a foundation for tracing the evolutionary relationship between the surface productivity and East Asian monsoon in the SCS during the late Quaternary glacial and interglacial periods. Based on the studies of opal % and their mass accumulation rates (MAR) at the six sites recovered from the SCS during the “Resolution” ODP Leg 184 and “Sonne” 95 cruise of the Sino-Germany cooperation, opal % and their MARs increased evidently in the northern sites since 470―900 ka, and they enhanced and reduced, respectively, during the glacial and interglacial periods. Whereas they increased obviously in the southern sites since 420―450 ka, and they augmented and declined, respectively, during the interglacial and glacial periods. The vari- ability in opal % and their MARs in the late Quaternary glacial cyclicity indicate the “seesaw” pattern of surface productivity in the SCS. The winter monsoon intensified during the glacial periods, surface productivity increased and decreased, respectively, in the northern and southern SCS. The summer monsoon strengthened during the interglacial periods, surface productivity increased and decreased, respectively, in the southern and northern SCS. The cross spectral analyses between the opal % in the northern and southern SCS during the Quaternary and global ice volume (δ 18O) and orbital forcing (ETP) indicate that the East Asian winter and summer monsoons could be ascribed to the different drive mechanisms. On the orbital time scale, the global ice volume change could be a dominant factor for the winter monsoon intension and temporal variations. As compared with the winter monsoon, the correlative summer solar radiation with the obliquity and precession in the Northern Hemisphere could be a mostly controlling factor for the summer monsoon intension and temporal variations.  相似文献   

13.
The spatial and temporal distribution of marine geophysical surveys   总被引：1，自引：0，他引：1  
We examine how bathymetric mapping coverage varies with distance from the coastline, here a proxy for the effort involved in collecting the data. Distances to the nearest coastline were evaluated on a 1′ × 1′ global grid. We evaluate the density of marine survey track lines, which falls off with increasing distance from the coastline and drops off precipitously for the most remote regions. Bathymetric coverage shows a marked asymmetry between the southern and northern hemispheres, the latter having a factor of 2–4 denser coverage. We find a rapid decrease in data acquisition for previously unexplored regions beginning in 1973–1975. This rate change may reflect a transition from serendipitous exploration to more targeted investigations as the plate tectonics hypothesis became accepted, but it could also reflect the 1970s oil shocks. Coverage of the seafloor varies logarithmically with mapping resolution. At 0.5° resolution, only ∼60% of the seafloor has been mapped; the 50% mark was reached in 1979 and coverage of unexplored seafloor has since been less rapid. For comparison, at 1′ resolution less than 10% of the seafloor has been mapped. Given rising fuel costs we predict the most remote areas will see a decline in future surveys. Better coordination of exploration among agencies and nations could mitigate this concern and improve global coverage, as could future altimetric mapping dedicated to bathymetric prediction.  相似文献   

14.
~~Global tectonics and the plate motion obtained from the ITRF97 station velocity vectors@马宗晋 @任金卫 @张进~~  相似文献   

15.
We have conducted detailed rock magnetic experiments on samples from loess unit 8 (L8) and paleosol unit 8 (S8) in Jingbian, Yichuan and Duanjiapo loess sections along an N-S transect in the Chinese Loess Plateau. Major rock magnetic results are as follows: (i) An increase of high field susceptibility (χh) in the same level of loess or paleosol from north to south is observed, suggesting an enhancement of pedogenesis. (ii) The low field susceptibility(χL) in loess unit L8 is almost the same in three sections. In contrast, the χL of paleosol unit S8 in Yichuan is highest, and the χL of Duanjiapo is lower than that in Yichuan section, suggesting that there is not correlation between the χL and the degree of pedogenesis in loess-paleosols. (iii) With the increasing of χL, both the contents of the superparamagnetic (SP) and the ferrimagnetic grains in loess-paleosol increase, however, the enhancement of magnetic susceptibility is probably dependent more on the increase of the ferrimagnetic concentration than on a change in the grain size. (iv) The content of the maghemite in loess unit 8 increases from the northern to the southern part of the Chinese Loess Plateau, and is positively correlated with the pedogenesis of the loess.  相似文献   

16.
Summary A coalification data set from the first seam of the Rosice-Oslavany coal district in the Boskovice furrow was used to estimate the temperature gradient prevailing within the furrow during Autunian sedimentation. An appreciable scatter of the data reflects the complicated history of the sedimentary region. The northern part of the district displays a higher degree of coalification. The results of the evaluation suggest that the region ceased to subside in the upper Autunian, and that the extent of the post-Autunian erosion does not exceed 500 metres. This version of the burial history, which is consistent with geological data, yields a temperature paleogradient of 76 mK/m for the northern part and of 72 mK/m for the southern part of the district. The gradients estimated are higher than those prevailing during the Carboniferous sedimentation in the Central Bohemian Basin (45 – 53 mK/m), lower than values found for the Ostrava Formation in the Upper Silesian Basin during its Namurian A sedimentation (about 95 mK/m), but comparable with values evaluated for the Karviná Formation of the same basin deposited during the Namurian B - C and Westphalian A (60 – 77 mK/m).Dedicated to the Memory of Professor Karel P  相似文献   

17.
Regional gravity data from an eroded Miocene to Pliocene volcanic arc exposed in the Coromandel Peninsula, New Zealand, delineate a circular − 26-mGal, 15-km-diameter gravity anomaly. This anomaly, which has steep gradients on its northern and western margins but shallow gradients elsewhere, correlates with relatively young volcanic and volcaniclastic rocks within a broad topographic depression. Gravity modelling, using an exponentially decreasing density contrast with depth profile, requires very low-density rocks (ca. 2280 kg m− 3) in the near-surface to account for the observed anomaly, giving a total depth of ca. 2.8 km for these rocks. The northern and western margins of this body dip steeply inward at 70°, whereas the southern and eastern margins have shallow inward dips (20–30°). The western margin coincides with the regional-scale Mangakino Fault, but the northern margin, recognizable only in the geophysical data (and named here the Ohinemuri Fault), is partially buried under younger volcanic rocks. We interpret these deep and steeply bounded, low-density volcanics in terms of a trapdoor caldera, faulted on its northern and western margins, with its hinge on the southern and eastern margins. Epithermal deposits are spatially associated with the Mangakino and Ohinemuri Faults, suggesting that both structures may have influenced hydrothermal fluid flow. These deposits pre-date caldera fill, indicating that caldera development followed pre-existing regional faults. These results delineate the subsurface geometry of a trapdoor caldera and highlight the role of pre-existing, regional-scale faults in controlling such caldera location and collapse.  相似文献   

18.
 Kuju Volcano lies near Aso Caldera at the center of Kyushu Island, western Japan. After a few hundred years of dormancy, a phreatic explosion accompanied by a small ash eruption occurred on 11 October 1995. This study was undertaken to determine the subsurface seismic velocity structure associated with the active magmatic regime in the Kuju volcanic region. The three-dimensional, upper crustal, P-wave velocity structure beneath Kuju Volcano was determined using methods for the simultaneous inversion of P-wave arrival times from local earthquakes in and around the Kuju volcanic region for velocities and hypocentral parameters. Results reveal two shallower low-velocity anomalies located in the northern and southern parts of Kuju Volcano, consistent with the presence of significant negative Bouguer gravity anomalies. In addition, a high-velocity anomaly is located approximately 5 km northwest of Mt. Kuju, one of the domes in Kuju Volcano. Beneath this high-velocity anomaly, a low-velocity anomaly is present. This velocity structure suggests a magmatic regime that has a lid consisting of cooled solid material overlying a chamber of partially molten material. Received: 23 September 1997 / Accepted: 20 June 1998  相似文献   

19.
As the gravity field is the most primary and direct physical quantity reflecting the density variation of the Earth’s interior and its geodynamic properties under various environmental changes and as the knowledge of the fine structure of the Earth’s interior and its geo-dynamics has a strong impact on space research, grav-ity observations become more and more important in Earth sciences. Therefore based on a global network of superconducting gravimeters (SGs), the Global Geo-dynamic Proje…  相似文献   

20.
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