Reply to “Comment on ‘Mechanics of tidally driven fractures in Europa's ice shell’ ”     

Sunwoong Lee  Nicholas C. Makris 《Icarus》2007,189(2):598-599

Both Lee et al. and Qin et al. consider propagation of a surface initiated tensile crack oriented vertically in an ice sheet of finite thickness with gravitational overburden. Lee et al. assume the crack walls are always in contact and bear normal stress from overburden. In this closed crack scenario, overburden stress increases linearly with depth just as in an ice half-space. Crack walls cannot sustain tension, so the effect of far field tension is concentrated in the material below the crack walls. This leads to the deep crack penetrations of Lee et al. Qin et al., however, assume an open crack scenario. They inappropriately apply normal stress to open crack walls which are exposed to vacuum and so physically cannot sustain a normal stress [Timoshenko, S.P., Goodier, J.N., 1970. Theory of Elasticity, third ed. McGraw-Hill, New York, p. 191]. Since this inappropriate normal stress is horizontally oriented it has the effect of artificially concentrating compressive stress in the material below the open crack. The severely limited crack propagation depths of Qin et al. result from this inappropriate boundary condition on an open crack wall.  相似文献   

Seismic refraction profiles between Cyprus and Israel and their interpretation   总被引：3，自引：0，他引：3  

J. Makris  Z. Ben Abraham  A. Behle  A. Ginzburg  P. Giese  L. Steinmetz  R. B. Whitmarsh  S. Eleftheriou 《Geophysical Journal International》1983,75(3):575-591

Summary. A long seismic refraction profile was carried out between southern Israel and Cyprus. The seismic energy was generated by 33 sea shots each of 0.8 t explosives and was recorded by land stations in Israel and Cyprus and by ocean bottom seismographs deployed along the profile.
The results showed that the continental crust of southern Israel thins towards the Mediterranean underneath a northward thickening sedimentary cover. Cyprus is underlain by a 35 km thick continental crust thinning south-wards and extending to Mt Eratosthenes. Between Mt Eratosthenes and the Israel continental shelf the crystalline crust is composed of high velocity (6.5 km s^-1)material and is about 8 km thick. It is covered by 12–14 km of sediments and may represent a fossil oceanic crust.  相似文献   

Low Cost Digital Rectification on A PC     

A. Georgopoulos  G. N. Makris 《The Photogrammetric Record》1997,15(89):703-714

Digital photogrammetric techniques have opened fresh horizons and have enabled photogrammetry to become a more user friendly tool for a wide range of applications. However cost remains a critical issue, because new digital photogrammetric workstations and their related software are considered expensive. This paper examines the problem of digital rectification and presents low cost solutions involving the use of commercial off the shelf software packages, which include graphics and painting software, image processing tools and a CAD system. Additionally, specially developed software performing vector rectification is described and discussed. All the packages have been used for rectifying digital images and the results are presented. An attempt is also made to assess the accuracy and reliability of the results. Finally, several alternative digital products are presented, mainly concerning the use of the methods described in the restitution of cultural monuments.  相似文献   

Dynamic pile-soil-pile interaction. Part II: Lateral and seismic response     

Nicos Makris  George Gazetas 《地震工程与结构动力学》1992,21(2):145-162

A simplified three-step procedure is proposed for estimating the dynamic interaction between two vertical piles, subjected either to lateral pile-head loading or to vertically-propagating seismic S-waves. The starting point is the determination of the deflection profile of a solitary pile using any of the established methods available. Physically-motivated approximations are then introduced for the wave field radiating from an oscillating pile and for the effect of this field on an adjacent pile. The procedure is applied in this paper to a flexible pile embedded in a homogeneous stratum. To obtain analytical closed-form results for both pile-head and seismic-type loading pile-soil and soil-pile interaction are accounted for through a single dynamic Winkler model, with realistic frequency-dependent ‘springs’ and ‘dashpots’. Final- and intermediate-step results of the procedure compare favourably with those obtained using rigorous formulations for several pile group configurations. It is shown that, for a homogeneous stratum, pile-to-pile interaction effects are far more significant under head loading than under seismic excitation.  相似文献   

Soil–pile interaction during the passage of rayleigh waves: An analytical solution     

Nicos Makris 《地震工程与结构动力学》1994,23(2):153-167

A simple analytical solution is presented to calculate the single-pile response when excited by the passage of Rayleigh seismic waves. Closed-form expressions for the horizontal and vertical displacement distributions are presented for piles with finite or infinite length. The analytical results for both free-head and fixed-head piles are obtained through a dynamic Winkler model, with realistic frequency-dependent ‘springs’ and ‘dashpots’. The results of the presented method are in excellent agreement with results of a rigorous solution. It is shown that in vertical motion, the differences between pile and soil displacements are far more significant than in horizontal motion, and therefore, further work is needed to investigate the importance of pile-soil-pile interaction (group effects), because of the vertical component of Rayleigh seismic waves.  相似文献   

Complex-parameter kelvin model for elastic foundations     

Nicos Makris 《地震工程与结构动力学》1994,23(3):251-264

A new rigorous approach in modelling mechanical behaviour is developed. The dynamic response of a rigid disc resting on an elastic half-space is approximated by a macroscopic force-displacement relationship, where not only the coefficients but also the order of time derivatives are complex valued. It is shown that comlex-parameter constitutive models are not simply an elegant alternative in modelling mechanical behaviour, but are the outcome of rigorous non-linear regression analysis on complex-valued functions, like the dynamic stiffness of dissipative systems. Complex-parameter constitutive models are very attractive since a minimum number of parameters is required to obtain a satisfactory fit of the ‘exact’ response. A two-parameter generalized Kelvin model reproduces closely the ‘exact’ dynamic stiffness of the disc for all three vertical, horizontal and rocking modes studied herein. Frequency- and time-domain algorithms to solve complex-order differential equations are developed, validated and used to calculate the foundation–response under earthquake excitation. It is the excellent agreement of results and the economy in number of parameters that make complex-parameter models so attractive in constitutive modelling.  相似文献   

Gravity study of the Djibouti area     

J. Makris  J. Zimmermann  A. Balan  A. Lebras 《Tectonophysics》1975,27(2):177-185

In March and April 1972, 380 gravity stations were established in the T.F.A.I. The data were reduced to Bouguer anomalies of 5 mGal isolines. Qualitative and quantitative interpretation based on the gravity map, on seismic data and on the magnetics and physiography of the area revealed that: The crust of the Gulf of Tadjura and the central part of the T.F.A.I. is strongly oceanized and is the direct continuation of the Sheba Ridge.To the north of the Gulf, at the Dankali Mountains, the crust increases in thickness and most probably contains sialic fragments, indicating the continuation of the Danakil Chains in the T.F.A.I.To the south, the structure is bordered by a continental block, the Aysha Horst. The oceanization is concentrated only in the area of deep injections, marked by gravity maxima, whereas the rest of the area is to be described as sub-continental. The crust is attenuated from south (Aysha Horst) to north (Red Sea), from 30 to 15 km in thickness.The pattern of the gravity anomalies shows clearly liniations only along the coasts of the Gulf of Tadjura and the Straits of Bab el Mandeb. Inland the field breaks up into relative minima and maxima, indicating the fragmentation of the crust and the ‘triple junction’ nature of the area.The tectonic process is that of extension, with normal faults having maximum displacements at the northern border of the Gulf of Tadjura.The uppermost mantle has low velocity and density values due to thermal processes in the expanding zone. The state of the upper-mantle material must be that of partial melting due to high temperatures of the order of 800° to 1,000° C at about 15 km depth.  相似文献   

Power aspects of a horizontal ring mill pulverizer under continuous comminution of olivine     

M. Founti  G. Zannis  P. Makris 《International Journal of Mineral Processing》2008

The work presents a theoretical and experimental assessment of the mechanical power absorption by a prototype horizontal ring mill, during the continuous comminution of olivine with feed rates for a wide range of operating conditions. The forces acting on a ring element of a prototype ring mill under continuous operating conditions have been theoretically calculated and it has been experimentally confirmed that they are proportional to the square of the rotational speed. A linear variation of power with feed rate has been established and a functional relationship between consumed power and rotational speed is also proposed. Results demonstrate that there exists a feed rate for which the value of the friction coefficient between the rings and the powdered material is minimized, independently of the rotational speed. It was further found that the product size depends on the absorbed mechanical power and it decreases with increasing power values.  相似文献   

Implementation of a real-time portable automatic seismological station     

D. A. Il’inskii  I. M. Aleshin  S. S. Burguchev  V. N. Koryagin  K. I. Kholodkov  J. Makris  J. Papoulia  A. Tsambas 《Seismic Instruments》2012,48(1):34-44

The paper describes the structure and organization of operation of a portable telemetric seismological station, as well as its use for both terrestrial and marine observations. The main attention is paid to the implementation of the scheme of data transmission by a real-time protocol, as well as to the feature of operation by this protocol while using a cellular communication channel. Using a standard protocol and a cellular network, in conjunction with low power consumption, relatively small cost of equipment, and ease of installation and maintenance make our solution attractive for the rapid deployment of a network of such stations. This is topical for regular monitoring of an object (or a region) to assess seismic hazards, tsunami warning, as well as in areas of aftershock activity following large earthquakes. Through the use of standard real-time protocols, data is transmitted to data processing centers and do not require additional configuration of mathematical support and an expensive procedure to organize processing of new data streams.  相似文献   

Experimental and analytical studies on the response of 1/4-scale models of freestanding laboratory equipment subjected to strong earthquake shaking     

Dimitrios Konstantinidis  Nicos Makris 《Bulletin of Earthquake Engineering》2010,8(6):1457-1477

This paper investigates the seismic response of freestanding equipment when subjected to strong earthquake motions (2% probability of being exceeded in 50 years). A two-step approach is followed because the displacement limitations of the shake table do not permit full-scale experiments. First, shake table tests are conducted on quarter-scale wooden block models of the equipment. The results are used to validate the commercially available dynamic simulation software Working Model 2D. Working Model is then used to compute the response of the full-scale freestanding equipment when subjected to strong, 2% in 50 years hazard motions. The response is dominated by sliding, with sliding displacements reaching up to 70 cm. A physically motivated dimensionless intensity measure and the associated engineering demand parameter are identified with the help of dimensional analysis, and the results of the numerical simulations are used to obtain a relationship between the two that leads to ready-to-use fragility curves.  相似文献