Preface     

《Coastal Engineering》2002,47(2):79-80

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Importance of active tectonics during karst formation. A Middle Eocene to Pleistocene example of the Lina Moutains (Irian Jaya,Indonesia)     

《Geodinamica Acta》1999,12(3-4):213-221

The Lina Moutains show a typical example of karst formation associated to recent and active tectonics. The limestone samples were collected from giant potholes present beneath the heavy rainforest, during speleological expeditions to the Bird's Head of Irian-Jaya. Micropalaeontological data allow us to give a Middle Pleistocene age for the most recent karst formation. A detailed stratigraphy between the Upper Lutetian and the Middle Pleistocene was recorded, with tectonic events during the Oligocene and Pleistocene. The edge of the resurgence layer was also dated. We also conclude the probable existence of a subterraneous network downhill of the karst within the most recent levels of the Kais Limestone formation. We replace this formation within the tectonic evolution of this area between the Eocene and the Middle Pleistocene, in conjunction with the oblique convergence of the Pacific plate carrying volcanic arc fragments and the Australian margin, which resulted in folding, normal faulting associated with local extension, and wrench motion, which are settings capable of creating uplift of the carbonated platform.  相似文献   

Fault-block tilting: the Gebel Zeit example,Gulf of Suez     

《Journal of Structural Geology》1988,10(1):9-19

The Gebel Zeit consists of the eroded crest of a tilted block in the southern part of the Suez rift. The Zeit block displays a typical asymmetrical geometry: it is bordered to the east by a 35–45° E-dipping normal fault with kilometric throw and has a 30° SW-dipping homoclinal flank. Part of the pre-rift sedimentary sequence has been preserved on this flank and is unconformably covered by Upper Burdigalian (NN4) Globigerina marls. In the southern part of the block crest, the complete pre-rift series has been eroded and evaporites of Langhian age (NN5) rest directly on the Precambrian basement. Field evidence indicates alternations from erosion to sedimentation at the crest of the Zeit block. In an attempt to characterize its tilting, subsidence curves were computed along a cross-section with the backstripping method. Results indicate three stages in the evolution of the block: (1) a rapid subsidence between 22 and 16 My; (2) a pause between 16 and 10 My; and (3) a slow subsidence until present time. During the tectonic quiescence, the sedimentary loading effect alone produced an increase of 8° in the tilt angle. A simple kinematic model of tilting along a circular fault is proposed to quantify the Zeit rotation. Depth of the brittle-ductile transition is estimated at 10 km to explain the tilting. Strong driving of the tilting by the listric fault induces conjugate movements between the crest and trough of the block and explains the discrepancy between the Zeit and regional tectonic subsidence.  相似文献   

Ocean surface current retrieval at Hangzhou Bay from Himawari-8 sequential satellite images     

Zhu  Zhenye  Geng  Xupu  Li  Shihui  Xie  Ting  Yan  Xiao-Hai 《中国科学:地球科学(英文版)》2020,63(7):1026-1038

Ocean surface currents play a key role in the earth's climate. They affect virtually all processes occurring in the ocean and can also directly affect many important socio-economic activities. Himawari-8 meteorological satellite has an international advanced geostationary orbit imager sensor, AHI, with high time resolution and spatial coverage, Himawari-8 can be used to observe the subtle changes in marine environments. In this study, we used Himawari-8 data received from the Joint Receiving Station for Satellite Remote Sensing of Xiamen University to retrieve coastal currents in Hangzhou Bay. Particularly, the Maximum Correlation Coefficient(MCC) and the Generalized Hough Transform(GHT) methods were used to retrieve them respectively. The retrieved sea surface currents are analyzed and verified by the numerical model data of the Taiwan Strait current forecasting system(TFOR). The results show that(1) the Himawari-8 satellite data can be used to effectively estimate the ocean current;(2) The results of the two methods are in agreement with each other, and the error in the current measured using the GHT method is smaller in the Yangtze estuary and offshore areas, where the turbidity characteristic front is stronger.  相似文献   

Can Hydraulic Conductivity of Fluvial Sediments be Informed by Spectral Reflectance?     

Yao Li  Liu  Can  Ou  Gengxin  Wang  Zhaowei  Korus  Jesse  Jiang  Ran 《Water Resources》2020,47(5):846-854

Water Resources - This study explores the statistical relationship between spectral reflectance and hydraulic conductivity (K) of fluvial sediments in two Nebraska rivers. The spectral reflectance...  相似文献   

Ice response to an underwater body moving in a frozen channel     

《Applied Ocean Research》2019

Strains in the ice cover of a frozen channel, which are caused by a body moving under the ice at a constant speed along the channel, are studied. The channel is of rectangular cross section, the fluid in the channel is inviscid and incompressible. The ice cover is modeled by a thin viscoelastic plate clamped to the channel walls. The underwater body is modeled by a three-dimensional dipole. The intensity of the dipole is related to the speed and size of the underwater body. The problem is considered within the linear theory of hydroelasticity. For small deflections of the ice cover the velocity potential of the dipole in the channel is obtained by the method of images without account for ice deflection in the leading order. The problem of a dipole moving in the channel with rigid walls provides the hydrodynamic pressure on the upper boundary of the channel, which corresponds to the ice cover. This pressure distribution does not depend on the deflection of the ice cover in the leading approximation. The deflections of ice and the strains in the ice cover are independent of time in the coordinate system moving together with the dipole. The problem is solved numerically using the Fourier transform along the channel, the method of normal modes across the channel, and the truncation method for resulting infinite systems of linear equations. It was revealed that the strains in the ice strongly depend on the speed of the dipole with respect to the critical speeds of the hydroelastic waves propagating along the frozen channel. The width of the channel matters even it is much larger than the characteristic length of the ice cover.  相似文献   

Modelling ocean waves in ice-covered seas     

《Applied Ocean Research》2019

Over the past decade there has been a rapid growth of interest in wave propagation through ice covers. This paper summarizes the author’s observation of the modeling efforts on this topic. Models can be theory-based, data-driven, or a combination of the two. A pure data-driven model relies on a large amount of observations and is only becoming available recently. Theory-based models on the other hand have a long history. They are always a simplified version of the reality. As our knowledge grows, theories become more complicated. A theory for waves-in-ice that captures all possible processes does not exist. However, when integrated with observation through calibration, these combined theory + data-based models may be used with some confidence. In this paper, different models, their basic concepts, their calibration and validation are discussed. The present theory-based models do not have the correct spectral attenuation trend as observed from field or laboratory experiments. Hence, through calibration they may fit different parts of the wave spectra but not all. Pure data-driven models can reproduce the correct trend, but its dependability outside the situation where the data are collected is uncertain. In addition to offering tools to forecast waves-in-ice, these model building and validating efforts point to missing mechanisms that should be carefully studied. Despite the many challenges towards building a satisfactory general waves-in-ice model, significant progress has been made for models that work reasonably well in the marginal ice zone. We anticipate much more data will become available in the coming years to help us improve the existing models.  相似文献   

Perceived attributes of hurricane-related retrofits and their effect on household adoption     

Zou  Yilin  Stock  Alexia  Davidson  Rachel  Nozick  Linda  Trainor  Joseph  Kruse  Jamie 《Natural Hazards》2020,104(1):201-224

Natural Hazards - Understanding how homeowners make protective action decisions is important for designing policies and programs to encourage those actions and community resilience as a whole. This...  相似文献   

A time dependent approach to model X-ray and γ–ray light curves of Mrk 421 observed during the flare in February 2010     

《New Astronomy》2017

Strong X-ray and γ–ray flares have been detected in February 2010 from the high synchrotron peaked blazar Mrk 421 (z = 0.031). With the motivation of understanding the physics involved in this flaring activity, we study the variability of the source in X-ray and γ–ray energy bands during the period February 10–23, 2010 (MJD 55237–55250). We use near simultaneous X-ray data collected by MAXI, Swift-XRT and γ–ray data collected by Fermi-LAT and TACTIC along with the optical V-band observations by SPOL at Steward Observatory. We observe that the variation in the one day averaged flux from the source during the flare is characterized by fast rise and slow decay. Besides, the TeV γ–ray flux shows a strong correlation with the X-ray flux, suggesting the former to be an outcome of synchrotron self Compton emission process. To model the observed X-ray and γ–ray light curves, we numerically solve the kinetic equation describing the evolution of particle distribution in the emission region. The injection of particle distribution into the emission region, from the putative acceleration region, is assumed to be a time dependent power law. The synchrotron and synchrotron self Compton emission from the evolving particle distribution in the emission region are used to reproduce the X-ray and γ–ray flares successfully. Our study suggests that the flaring activity of Mrk 421 can be an outcome of an efficient acceleration process associated with the increase in underlying non-thermal particle distribution.  相似文献   

A pretty good sponge: Dealing with open boundaries in limited-area ocean models     

《Ocean Modelling》2008,20(3):270-292

The problem of computing within a limited domain surrounded by open boundaries is discussed within the context of the shallow-water wave equations by comparing three different treatments, all of which surround the domain by absorbing zones intended to prevent reflections of outgoing waves. The first, which has attracted a lot of attention for use in electromagnetic and aeroacoustic applications, is intended to prevent all reflections. However, it has not yet been developed to handle the second important requirement of open boundaries, namely the ability to pass information about external conditions into the domain of interest. The other two treatments, which absorb differences from a specified external solution, allow information to pass through the open boundary in both directions. One, based on the flow relaxation scheme of [Martinsen, E.A., Engedahl, H., 1987. Implementation and testing of a lateral boundary scheme as an open-boundary condition in a barotropic ocean model. Coastal Eng. 11, 603–627] and termed here the “simple sponge,” relaxes all fields toward their external counterparts. The other, a simplification and generalization of the perfectly matched layer, referred to here as the “pretty good sponge,” avoids absorbing the component of momentum parallel to the open boundary. Comparisons for a case that is dominated by outgoing waves shows the pretty good sponge to perform essentially as well as the perfectly matched layer and better than the simple sponge. In comparisons for a geostrophically balanced eddy passing through open boundaries, the pretty good sponge out-performed the simple sponge when the only external information available was about the advecting flow, but when information about the nature of the eddy in the sponge zones was also available, the simple sponge performed better. For the case of an equatorial soliton passing through the boundary and no information provided about its nature outside the open domain, again the pretty good sponge performed better. Proving useful for situations governed by nonlinear equations forced by external conditions and being easy to implement, the pretty good sponge should be considered for use with existing limited-area ocean models.  相似文献