Spheroidal oscillations of the Earth stimulated by the Sumatra-Andaman earthquake with CDSN data     

万永革盛书中  周公威郭燕平 尚丹 《地震学报(英文版)》2007,20(4):392-404

The 0S2~0S54 spheroidal modes of Earth’s free oscillations, triggered by the great Sumatra-Andaman earthquake of 26 December 2004 are retrieved from VHZ data recorded by seven upgraded stations of China Digital Seismograph Network (CDSN). We compare these spheroidal modes with theoretical free oscillation spectra calculated from the Preliminary Reference Earth Model (PREM) and find a coincidence between their periods. Spectral splitting phenomenon is observed obviously in 0S2, 0S3, 0S4, 2S1 and 1S2 free oscillation modes. What is most noticeable is that the oscillation mode 2S1 is reported for the second time (the first time by Rosat et al) without any data stacking. We simulated the split singlet of 0S2 mode on seven CDSN stations based on general focal mechanism and seismic moment of the earthquake. The result shows that seismic moment of the earthquake can reach 1023 N.m. We also find that the recording of Earth’s free oscillations carries abundant information of source mechanism and earthquake location, which is applicable to the detailed study of source rupture parameters.  相似文献   

Fhe application of electromagnetic-induction on the measurement of sea ice thickness in the Antarctic     

Guo Jingxue Sun Bo Tian Gang 《应用地球物理》2007,4(3):214-220

As an important component of the cryosphere, sea ice is very sensitive to climate change. The study of sea ice physics needs accurate sea ice thickness. This paper presents an electromagnetic induction （EM） technique which can be used to measure the sea ice thickness distribution efficiently and its successful application in the Antarctic Neila Fjord. Based on the electrical properties of sea ice and seawater and the application of electromagnetic field theory, this technique can accurately detect the distance between the EM instrument and the ice/water interface to measure the sea ice thickness. Analyzing the apparent conductivity data obtained by the electromagnetic induction technique and drill-hole measurements at same location allows the construction of a transform equation for the apparent conductivity and sea ice thickness. The verification of the calculated sea ice thickness using this equation indicates that the electromagnetic induction technique is able to determine reliable sea ice thickness with an average relative error of only 5.5%. The ice thickness profiles show the sea ice distribution in Neila Fjord is basically level with a thickness of 0.8 - 1.4 m.  相似文献   

Geochemistry and spatial distribution of OIB and MORB in A’nyemaqen ophiolite zone: Evidence of Majixueshan ancient ridge-centered hotspot   总被引：2，自引：0，他引：2  

Guo AnLin  Zhang GuoWei  Sun YanGui  Zheng JianKang  Liu Ye  Wang JianQi 《中国科学D辑(英文版)》2007,50(2):197-208

The mafic volcanic association is made up of OIB, E-MORB and N-MORB in the A'nyemaqen Paleozoic ophiolites. Compared with the same type rocks in the world, the mafic rocks generally display lower Nb/U and Ce/Pb ratios and some have Nb depletion and Pb enrichment. The OIB are LREE-enriched with (La/Yb)N =5―20, N-MORB are LREE-depleted with (La/Yb)N = 0.41―0.5. The OIB are featured by incompatible element enrichment and the N-MORB are obviously depleted with some metasomatic effect, and E-MORB are geochemically intermediated. These rocks are distributed around the Majixueshan OIB and gabbros in a thickness greater than a thousand meters and transitionally change along the ophiolite extension in a west-east direction, showing a symmetric distribution pattern as centered by the Majixueshan OIB, that is, from N-MORB, OIB and E-MORB association in the Dur'ngoi area to OIB in the Majixueshan area and then to N-MORB, OIB and E-MORB assemblage again in the Buqingshan area. By consideration of the rock association, the rock spatial distribution and the thickness of the mafic rocks in the Majixueshan, coupled with the metasomatic relationship between the OIB and MORB sources, it can be argued that the Majixueshan probably corresponds to an ancient hotspot or an ocean island formed by mantle plume on the A'nyemaqeh ocean ridge, that is the ridge-centered hotspot, tectonically similar to the present-day Iceland hotspot.  相似文献   

Tidal effects on estuarine circulation and outflow plume in the Chesapeake Bay     

Xinyu Guo  Arnoldo Valle-Levinson 《Continental Shelf Research》2007

The response of the Chesapeake Bay to river discharge under the influence and absence of tide is simulated with a numerical model. Four numerical experiments are examined: (1) response to river discharge only; (2) response to river discharge plus an ambient coastal current along the shelf outside the bay; (3) response to river discharge and tidal forcing; and (4) response to river discharge, tidal forcing, and ambient coastal current. The general salinity distribution in the four cases is similar to observations inside the bay. Observed features, such as low salinity in the western side of the bay, are consistent in model results. Also, a typical estuarine circulation with seaward current in the upper layer and landward current in the lower layer is obtained in the four cases. The two cases without tide produce stronger subtidal currents than the cases with tide owing to greater frictional effects in the cases with tide. Differences in salinity distributions among the four cases appear mostly outside the bay in terms of the outflow plume structure. The two cases without tide produce an upstream (as in a Kelvin wave sense) or northward branch of the outflow plume, while the cases with tide produce an expected downstream or southward plume. Increased friction in the cases with tide changes the vertical structure of outflow at the entrance to the bay and induces large horizontal variations in the exchange flow. Consequently, the outflow from the bay is more influenced by the bottom than in the cases without tide. Therefore, a tendency for a bottom-advected plume appears in the cases with tide, rather than a surface-advected plume, which develops in the cases without tide. Further analysis shows that the tidal current favors a salt balance between the horizontal and vertical advection of salinity around the plume and hinders the upstream expansion of the plume outside the bay.  相似文献   

Subsidence history and forming mechanism of anomalous tectonic subsidence in the Bozhong depression, Bohaiwan basin   总被引：1，自引：0，他引：1  

MüLLER R. Dietmar 《中国科学D辑(英文版)》2007,50(9):1310-1318

The Bozhong depression of the Bohaiwan basin belongs to a family of extensional basins in East China, but is quite different from other parts of the basin. The Cenozoic subsidence of the depression is controlled by a combination of lithospheric thinning and polycyclic strike-slip movements. Three episodic rifts have been identified, i.e. Paleocence-early Eocene, middle-late Eocene and Oligocene age. The depression underwent syn-rift and post-rift stages, but two episodic dextral movement events of the strike-slip faults modify the subsidence of the Bozhong depression since the Oligocene. The early dextral movement of the Tan-Lu fault associated with crustal extension resulted in accelerated subsidence during the time of deposition of the Dongying Formation with a maximum thickness of 4000 m. A late reactivation of dextral movement of the Tan-Lu fault began in late Miocene (about 12 Ma), which resulted in the intense subsidence of Minghuazhen Formation and Quaternary. In addition, dynamic mantle convection-driven topography also accelerated the post-rift anomalous subsidence since the Miocene (24.6 Ma). Our results indicate that the primary control on rapid subsidence both during the rift and post-rift stages in the Bozhong depression originates from a combination of multiple episodic crustal extension and polycyclic dextral movements of strike-slip faults, and dynamic topography.  相似文献   

电磁感应技术在南极海冰厚度探测中的研究与应用   总被引：1，自引：0，他引：1  

郭井学  孙波  田钢 《应用地球物理》2007,4(3)

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Deriving Acceleration from DGPS: Toward Higher Resolution Applications of Airborne Gravimetry     

A. M. Bruton  K. P. Schwarz  S. Ferguson  M. Kern  Ming Wei 《GPS Solutions》2002,5(3):1-14

Although airborne gravimetry is now considered a fully operational technique, errors due to motion compensation using differential GPS (DGPS) continue to influence both its accuracy and the range of applications in which it can be used. In typical medium-resolution applications such as airborne geoid mapping, errors due to DGPS contribute considerably to the error budget of an airborne gravity system. At the same time, efforts to increase the resolution of such systems for demanding applications such as resource exploration remain impedded by errors in DGPS. This article has three objectives. The first one is to compare eight industrially relevant DGPS software packages for the determination of aircraft acceleration. The second objective is to analyze and quantify the effect that each relevant portion of the DGPS error budget has on the determination of acceleration. Using data sets that represent a wide range of operational conditions, this is done in the frequency domain over a range of frequencies corresponding to spatial resolution as high as 450 m. The third objective is to use that information to recommend and demonstrate approaches that optimize the estimation of aircraft acceleration for determining the geoid and for resource exploration. It is shown, for example, that the time of day in which the survey is carried out and the dynamic characteristics of the aircraft being used are two of the most crucial parameters for very high-resolution gravity field estimation. It is demonstrated that when following the above-mentioned recommendations, agreements with ground daa of better than 1.5 and 2.5 mGal can be achieved for spatial resolutions (half-wavelengths) of 2.0 and 1.4 km, respectively. ? 2002 Wiley Periodicals, Inc.  相似文献   

有限区域变分四维同化系统的设计和试验     

徐国强  沈桐立  覃丹宇 《南京气象学院学报》2002,25(6):764-771

使用共轭码技术，构造了中尺度模式的伴随模式，研究了模式侧边界条件。基于伴随模式技术的原理，设计了伴随同化和Derber同化方法两套方案；下降算法采用共轭梯度法，使用准真实资料，进行子同化数值试验和预报试验。结果表明，两套同化方案都取得了一定的同化效果，Derber同化方法比伴随同化更令人满意。证明了变分同化是提高预报准确率的一种非常有效的手段。  相似文献   

2001年台风暴雨的分析   总被引：5，自引：0，他引：5  

杨克明  王文东  张守峰  张建忠  崔绚  郭文华 《气象》2002,28(10):22-27

利用常规资料、HLAFS格点资料和GMS－5静止卫星红外云图，对2001年我国台风暴雨的天气气候特征、热带低压造成的“8.5”上海特大暴雨及0103号台风“榴莲”的强暴雨形成的物理条件进行了诊断分析研究，并探讨了动力学、热力学和大气层结稳定度等物理因子在这两次强暴雨过程中的主要作用。分析结果对实时预报业务和科研工作有一定启示意义。  相似文献   

MM5中新边界层方案的引入和对比试验   总被引：10，自引：4，他引：10       下载免费PDF全文

江勇  赵鸣 《气象科学》2002,22(3):253-263

本文介绍了一种新的边界层方案，即E－ε－1方案，并用五种层结下的通量廓线关系计算地面通量，将其引入到中尺度数值天气预报模式MM5中，并用新的边界层方案对江淮流域存季暴雨进行了短期模拟，与此同时，对新的方案和模式原有的各种边界层方案作了比较，对此得到了一些有价值的结果。  相似文献