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Seismic wave imaging in visco-acoustic media

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science China Mathematics 2004年第z1期47卷 146-154页

作者： WANG Huazhong ZHANG Libin MA Zaitian school of ocean and earth science Tongji University Shanghai 200092 China School of Ocean and Earth Science Tongji University Shanghai 200092 China School of Ocean and Earth Science Tongji University Shanghai 200092 China

Realistic representation of the earth may be achieved by combining the mechanical properties of elastic solids and viscousliquids. That is to say, the amplitude will be attenuated withdifferent frequency and the phase will be changed in the seismicdata acquisition. In the seismic data processing, this effect mustbe compensated. In this paper, we put forward a visco-acoustic wavepropagator which is of better calculating stability and tolerablecalculating cost (little more than an acoustic wave propagator).The quite good compensation effect is demonstrated by thenumerical test results with synthetic seismic data and real data.

关键词： seismic wave dissipation, visco-acoustic wave equation,seismic wave imaging.

A CFD simulation of wave loads on a pile-type oscillating-water-column device

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Journal of Hydrodynamics 2019年第1期31卷 41-49页

作者： Zhenhua Huang Conghao Xu Shijie Huang Department of ocean and Resources Engineering School of Ocean and Earth Science TechnologyUniversity of Hawaii at ManoaHonoluluUSA

Oscillating-water-column (OWC) devices provide a practical and convenient way to convert wave energy to *** loads on bottom-sitting WECs are important design parameters for their foundation *** study considers an OWC integrated into a bottom-sitting pile structure (an OWC pile).Results from three-dimensional numerical simulations are used to examine the wave loads on an OWC *** appears that viscous loads and lateral loads are relatively *** the inline and vertical wave forces and the resulting overturning moment are not sensitive to the variability in wave period,but increase with wave *** suitable for the wave forces and overturning moment are proposed for estimating wave loads on the OWC pile.

关键词： Numerical simulation wave energy conversion OpenFOAM foundation safety

Ionospheric polarization electric field guiding magnetopause reconnection: A conceptual model of throat aurora

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science China earth sciences 2019年第12期62卷 2099-2105页

作者： Desheng HAN State Key Laboratory of Marine Geology School of Ocean and Earth Science Tongji University

Frequently observed throat auroras have been suggested to be correspondent to indentations on the subsolar magnetopause,but how these indentations can be generated is unknown *** on analyzing the detailed observational features of throat aurora,a conceptual model for generation of throat aurora is *** model suggests that precipitation of a north-south aligned stripy diffuse aurora can lead to an ionospheric conductivity enhancement and thus produce a polarization electric field in dusk-to-dawn direction in the *** mapping to the magnetosphere along closed field lines,this electric field can guide a magnetopause reconnection to develop inward the magnetosphere and result in a throat *** this model can comprehensively explain all the observational results that have been presented up to now,we argue that the assumption of ionospheric polarization electric field affecting magnetopause reconnection should be true and be worthy of further investigations.

关键词： Throat aurora Ionospheric polarization electric field Magnetopause reconnection Magnetosphere-ionosphere coupling Cusp ionosphere

The Mid-Pleistocene Climate Transition Recorded in a 1.6 Myr-Period Lacustrine Sediment Sequence from Mazatage, Tarim Basin

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Acta Geologica Sinica(English Edition) 2015年第1期89卷 312-313页

作者： LIU Jian WU Li WANG Rujian ZHAO Yue Institute of Geomechanics CAGS school of ocean and earth science Tongji University

The mid-Pleistocene climate transition （MPT） has been widely reported in worldwide geological events. As a key issue of the Quaternary geology, it has attracted much attention from the paleoclimate community. MPT refers to a period lasting for several hundreds of thousand years, during which the dominant climate periodicity gradually extended from 41 kyr to 100 kyr （Ruddiman et al., 1989）,

关键词： Wang Tarim Basin The Mid-Pleistocene Climate Transition Recorded in a 1.6 Myr-Period Lacustrine Sediment Sequence from Mazatage

Pattern of stress change and its effect on seismicity rate caused by M_s8.0 Wenchuan earthquake

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science China earth sciences 2010年第9期53卷 1260-1270页

作者： XIE ChaoDi ZHU YuanQing LEI XingLin YU HaiYing HU XiongLin school of ocean&earth science Tongji UniversityShanghai 200092China Geological Survey of Japan AISTTsukuba 305-8567Japan Seismological Bureau of Shanghai Shanghai 200062China Seismological Bureau of Yunnan Kunming 650224China

We use five published source models to calculate the Coulomb failure stress changes induced by the Ms8.0 Wenchuan earthquake, and analyze the association between stress changes and the subsequent earthquakes. Based on the analysis of uncertainties resulting from source models, we determine the stress changes on nearby faults caused by the Wenchuan earthquake. Moreover, we focus on the seismicity rate change as a function of time on every fault under the influence of stress changes. The results indicate that the spatial distributions of aftershocks correlate well with the regions where stress is calculated to increase using the related models. The largest lobes of dropped stress lie in the west and east sides of source fault. The largest lobes of increased failure stress close to southern and northern ends of the source fault extend into the whole source failure plane. In addition, another region of increased stress lies in the Wenchuan-Yingxiu zone close to the southern segment of source fault, where a large number of aftershocks have occurred. And subsequent earthquakes seem to extend to even more remote distances; therefore, this area also has a high risk of seismic hazard. We find that the positive stress changes on nearby faults imposed by the Wenchuan earthquake produce an encouraging effect on seismicity rate. The effect is most significant on the Pengxian-Guanxian fault and Qingchuan fault, the value of seismicity rate maintains two times greater than the value before the mainshock for the next hundred years on these faults, and the time needed for the aftershock rate to recover to the pre-mainshock seismicity rate can reach up to 800-900 yr. The influence is not significant on the western Qinling fault, the Longquanshan fault, the Xianshuihe fault, the Yulongxi fault, the Anninghe fault, the Minjiang fault, and the Aba fault. Compared with the seismicity rate on these faults before the mainshock, the aftershock rate is raised by less than two times, and the

关键词： Wenchuan earthquake optimally oriented fault Coulomb stress change seismicity rate

Data-Domain Wave Equation Reflection Traveltime Tomography

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Journal of earth science 2015年第4期26卷 487-494页

作者： Bo Feng Huazhong Wang Wave Phenomena and Inversion Imaging Group School of Ocean and Earth ScienceTongji University

Estimation of an accurate macro velocity model plays an important role in seismic imag- ing and model parameter inversion. Full waveform inversion （FWI） is the classical data-domain inver- sion method. However, the misfit function of FWI is highly nonlinear, and the local optimization cannot prevent convergence of the misfit function toward local minima. To converge to the global minimum, FWI needs a good initial model or reliable low frequency component and long offset data. In this article, we present a wave-equation-based reflection traveltime tomography （WERTT） method, which can pro- vide a good background model （initial model） for FWI and （least-square） pre-stack depth migration （LS-PSDM）. First, the velocity model is decomposed into a low-wavenumber component （background velocity） and a high-wavenumber component （reflectivity）. Second, the primary reflection wave is pre- dicted by wave-equation demigration, and the reflection traveltime is calculated by an automatic picking method. Finally, the misfit function of the 12-norm of the reflection traveltime residuals is mini- mized by a gradient-based method. Numerical tests show that the proposed method can invert a good background model, which can be used as an initial model for LS-PSDM or FWI.

关键词： reflection traveltime tomography primary reflection wave wave equation demigration,background velocity building rough reflectivity.

Global desert variation under climatic impact during 1982-2020

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science China earth sciences 2023年第5期66卷 1062-1071页

作者： Yao CHEN Huayu LU Huijuan WU Jingjing WANG Nana LYU school of Geography and ocean science Frontiers Science Center for Critical Earth Material CyclingNanjing UniversityNanjing210023China

Deserts are important landscapes on the earth and their variations have impacts on global climate through feedback ***,there is a limited understanding of the climatic controls on the spatial and temporal variations of global ***,we use climate reanalysis datasets,global land use/land cover(LULC)products and the CMIP6(Coupled Model Intercomparison Project)model outputs to calculate the changing of global deserts during 1982-2020,and estimate future spatial trends of global *** results show that mean annual global desert area over this period is 17.64×10^(6)km^(2),accounting for 12%of the terrestrial *** areas decreased rapidly from the end of the 1980s to the 1990s in North Africa and Australia,followed by a slow expansion in early 21st century ***-temporal variations of areas of arid climate are characterized by interdecadal fluctuations,and there are clear regional differences in dynamic s of the aridity index(AI,used here as a proxy for the area of drylands)and desert *** analyses reveal that increased vegetation cover is directly related to the reduction of desert area,while potential evaporation,surface temperature and humidity are also significantly correlated with the desert *** relationship between wind speed and desert dynamics varies *** results of the CMIP6simulations suggest that global deserts will expand in the 21st century,albeit at different rates under the ssp245 and *** expansions are modelled to be greatest in Asia,Africa and Australia,while those of southern North Africa may reduce as their southern borders migrate northwards.

关键词： Global desert Dryland Spatial variations Climate factors CMIP6

Cosmogenic ^(26)Al/^(10)Be Burial Dating of the Uplift Rate of Southern Qinling Mountains since the Middle Pleistocene

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Acta Geologica Sinica(English Edition) 2018年第4期92卷 1674-1675页

作者： LU Yiming SUN Xuefeng TU Hua ZENG Qiongxuan XU Xinghua school of Geography and ocean science Nanjing University BGEG School of Earth Sciences China University of GeosciencesWuhan

Objective The Qinling Mountains （QM） in Central China is a natural harrier that corresponds to the boundary between the southern and northern climate and environment （Gong Hujun et al., 2017）. Northern QM is relatively steep, and southern QM is in contrast relatively low and gentle. Investigations have shown that the average uplift rate of northern QM since 17.8 Ma is approximately 0.19 mm/a （Yin Gongming et al., 2001）, whereas that of central QM since 0.36 Ma is approximately 0.32 mm/a （Wang Fei et al., 2004）. To date, however, few investigations have yet been conducted on the uplift rate of southern QM. Accordingly, we aim to obtain the uplift rate of southern QM by using the cosmogenic ^26A1/^10 Be burial dating method to determine the age of the highest river terrace on the southern slope of QM.

关键词： Be Burial Dating of the Uplift Rate of Southern Qinling Mountains since the Middle Pleistocene Cosmogenic QM Al

Potential role of strike-slip faults in opening up the South China Sea

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National science Review 2019年第5期6卷 891-901页

作者： Chi-Yue Huang Pinxian Wang Mengming Yu Chen-Feng You Char-Shine Liu Xixi Zhao Lei Shao Guangfa Zhong Graciano P.Yumul Jr State Key Laboratory of Marine Geology School of Ocean and Earth Science Tongji University Department of earth science Cheng Kung University Institute of oceanography Taiwan University earth and Planetary sciences University of California school of Environmental science and Management University of the Philippines Los Banos College

Radiometric dates of key rock units indicate that a remnant Late Mesozoic ocean of the Huatung Basin is still preserved today east of the South China Sea(SCS).We integrate regional geology with a Cretaceous oceanic basement in the vicinity of the Huatung Basin to reconstruct the Huatung Plate east of the Eurasian *** of geophysical investigations, four expeditions of deep-sea drilling and a renaissance of regional geology allow us to propose a hypothesis that the mechanism responsible for the SCS opening was raised from strike-slip fault on the *** hypothesis suggests that the SCS opening could highly relate to the strike-slip faults inherited from Late Mesozoic structures onshore–offshore the SE Cathaysia Block to develop rhombic-shaped extensional basins en echelon on the thinned Eurasian continental crust in the Early *** was followed by sinistral strike-slip movements along the boundary between the Eurasian Plate and the Huatung Plate driven by oblique subduction of the Huatung Plate to the northwest coupled with slab-pull force by southward subduction of the Proto-SCS to open up the triangle-shaped oceanic East Sub-basin in the Early Oligocene(33/34 Ma).The spreading ridge then propagated southwestward in the step-over segment between the Zhongnan-Lile and the Red River strike-slip fault systems to open the triangle-shaped oceanic Southwest Sub-basin by 23 *** plate boundary fault was subsequently converted into the Manila Trench when the Eocene Sierra Madre arc of the Huatung Plate had moved from the south to its present latitude by the Middle Miocene.

关键词： South China Sea Huatung Basin Eurasian continent strike-slip fault plate boundary