Body force,body couple and heat source equivalents for seismic dislocations     

Enzo Boschi 《Pure and Applied Geophysics》1973,111(1):2147-2157

Summary An explicit expression is derived for the body force, body couple and heat source to be applied in the absence of a seismic dislocation, which produces a thermodynamical behaviour equivalent to that produced by the dislocation.  相似文献   

Quasi-static crack models and the frictional stress threshold criterion for slip arrest     

M. Bonafede  M. Dragoni  E. Boschi 《Geophysical Journal International》1985,83(3):615-635

Summary. Two-dimensional crack problems in elastic homogeneous isotropic media are considered which describe rupture over a fault surface characterized by non-uniform stress drop. Solutions can be found in which the stress field is finite at the crack tips and the rupture surface is not assigned a priori , but is part of the solution. These crack models are found to be consistent with the frictional stress threshold criterion for slip arrest over pre-existing fault surfaces. A crack is found to stop when its contribution to the stress field is opposite to the stress drop at the crack tips. The quasi-static propagation of a crack up to the arrest configuration is studied in terms of the minimum energy principle. The crack spontaneously propagates in such a way as to make the value of the stress intensity factor at one tip equal to the value at the other tip. Furthermore a tip propagating in a region with higher friction is found to move more slowly than the other tip propagating in a region with lower friction. Simple criteria for fracture arrest are derived, in terms of a properly averaged stress drop. Piecewise constant stress drop profiles are explicitly considered yielding a variety of solutions which can be applied to modelling asperities or barriers over a fault plane. The evaluation of the amount of the energy released during the quasi-static crack propagation shows that stopping phases cannot be efficiently radiated if the crack comes to rest in a low friction region.  相似文献   

Multiple resolution surface wave tomography: the Mediterranean basin     

L. Boschi  G. Ekström  B. Kustowski 《Geophysical Journal International》2004,157(1):293-304

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Seismic deformation in the Mediterranean area estimated by moment tensor summation   总被引：2，自引：0，他引：2  

S. Pondrelli  A. Morelli  E. Boschi 《Geophysical Journal International》1995,122(3):938-952

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Heat diffusion and size reduction of a spherical magma chamber     

M. Bonafede  M. Dragoni  E. Boschi 《Bulletin of Volcanology》1984,47(2):343-347

An analytical solution is derived for the size reduction of a spherical magma chamber cooling by conduction. The use of moving boundary conditions and the constraint of a spherical symmetry allow one to ignore the details of the heat redistribution processes which take place within the magma chamber. The dependence of the solution on the initial conditions is investigated. A simple solution is found for short time, which is shown to be valid for times long enough to make it useful in the volcanological context. Moreover, the general solution confirms that the hydrothermal contribution to heat transfer in Phlegraean Fields cannot be extremely important.  相似文献   

The dynamical equations of polar wander and the global characteristics of the lithosphere as extracted from rotational data     

David A. Yuen  Roberto Sabadini  Enzo Boschi 《Physics of the Earth and Planetary Interiors》1983,33(3):226-242

The initial value problem describing the linear responses of the spin axis of a layered viscoelastic planet from surface loading is studied by means of Laplace transform techniques. A complete solution of polar motion requires the usage of two classes of eigenspectra: one arising from viscoelastic relaxation of the mantle due to surface forcing, the other involving the gradual readjustment of the spin axis as a consequence of mantle viscoelasticity. Our analytical 4-layer model comprising an elastic lithosphere, a two-layer, adiabatically stratified, viscoelastic mantle and an inviscid core has been incorporated into this formalism in which rotational deformation and isostatic relaxation are taken into account for all times. From employing both sets of rotational data, polar variations from the 70 years of data from the International Latitude Service (I.L.S.) and the non-tidal deceleration of the length of the day (l.o.d.) an estimate of the globally averaged lithosphere of between 130 and 200 km is obtained from the long wavelength flexural mode due to the degree-two harmonic. This range of values may have strong implications on the mode of continental evolution.  相似文献   

Using the Post–Widder formula to compute the Earth's viscoelastic Love numbers     

G. Spada  L. Boschi 《Geophysical Journal International》2006,166(1):309-321

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Fault slip beyond a barrier on a transform plate boundary     

M. Bonafede  E. Boschi  M. Dragoni 《Geophysical Journal International》1983,75(1):143-153

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High Resolution Electrical Resistivity Tomography (ERT) in a Transition Zone Environment: Application for Detailed Internal Architecture and Infilling Processes Study of a Rhône River Paleo-channel     

Grégoire M. Maillet  Enzo Rizzo  André Revil  Claude Vella 《Marine Geophysical Researches》2005,26(2-4):317-328

Electrical Resistivity Tomography (ERT) was applied in a sand-infilled paleo-channel located in the Rhône Delta, in Southern France. The detailed pattern and sedimentological evolution of the channel fill deposits – know from both historical and geological sources – made it the ideal site to test the ERT method. A geoelectrical survey was performed, using the ABEM SAS-4000 multi-electrode array system in March 2003. Very low electrical resistivity values were obtained, ranging from 0.3 to 10 Ohm m, consistent with the high salinity measured in situ (the pore water conductivity was found to range from 0.9 to 1.2 S/m at 25 °C). The electrical resistivity profiles reflect mainly salinity variations. Indeed, in this case, salinity is so high that surface conductivity associated with clay minerals can be safely neglected. ERT provided valuable high-resolution information that complemented other exiting data such as historical information, bathymetric, geological, and lithostratigraphic data, which allowed the architecture of the channel to be defined. The ERT was used to determine the infilling dynamics of the Pégoulier Channel, which opens new perspectives in terms of paleoenvironmental reconstruction and paleodynamic studies.  相似文献   

Silicic magmas from the continental Cameroon Volcanic Line (Oku, Bambouto and Ngaoundere): 40Ar-39Ar dates, petrology, Sr-Nd-O isotopes and their petrogenetic significance     

Andrea Marzoli  Paul R. Renne  Enzo M. Piccirillo  Castorina Francesca  Giuliano Bellieni  Adolpho J. Melfi  Jean B. Nyobe  Jean N'ni 《Contributions to Mineralogy and Petrology》1999,135(2-3):133-150

The intraplate Cameroon Volcanic Line (CVL) straddles the African-South Atlantic continent-ocean boundary and is composed mainly of alkaline basic volcanic rocks. Voluminous silicic volcanics characterize the continental sector of the CVL. We present here new geochemical, isotopic (Sr-Nd-O) and ⁴⁰Ar/³⁹Ar geochronological data on the main silicic volcanic centres of the Western (Mt. Oku, Sabga and Mt. Bambouto) and Eastern (Ngaoundere plateau) Cameroon Highlands. The silicic volcanism of Mt. Oku, Sabga and Mt. Bambouto occurred between 25 and 15 Ma and is represented by voluminous quartz-normative trachytes and minor rhyolitic ignimbrites. At Mt. Bambouto central volcano about 700 m of silicic volcanics erupted in less than 2.7 million years. These silicic volcanics are associated with slightly to moderately alkaline basalts and minor basanites. In general, onset of the silicic volcanism migrated from NE (Oku: 25 Ma) to SW (Sabga: 23 Ma; Bambouto: 18 Ma; and Mt. Manengouba: 12 Ma). The silicic volcanism of the Ngaoundere plateau (eastern branch of the CVL) is instead dominated by nepheline-normative trachytes which are associated with strongly alkaline basalts and basanitic rocks. These Ne-trachytes are younger (11-9 Ma) than the Q-trachytes of the Western Highlands. The least differentiated silicic volcanics are isotopically similar (⁸⁷Sr/⁸⁶Sr < 0.70380; ¹⁴³Nd/¹⁴⁴Nd > 0.51278) to the associated alkaline basalts suggesting differentiation processes without appreciable interaction with crustal materials. Such interactions may, however, have played some role in the genesis of the most evolved silicic volcanics which have ⁸⁷Sr/⁸⁶Sr as high as 0.705–0.714. Fractional crystallization is the preferred mechanism for genesis of the silicic melts of both Western and Eastern Highlands, as shown by modeling major and trace element variations. The genesis of the least evolved Q-trachytes from the Western Highlands, starting from slightly to moderately alkaline basalts, is compatible with fractionation of dominantly plagioclase, clinopyroxene and magnetite. Crystal fractionation may have occurred at low pressure and at QFM buffer f _O2conditions. Parental magmas of the Ngaoundere Ne-trachytes are likely instead to have been strongly alkaline basalts which evolved through crystal fractionation at higher P (6-2 kbar) and f _O2 (QFM + 2). The migration (25 to 12 Ma) of the silicic volcanism from NE to SW in the continental sector of the CVL is reminiscent of that (31-5 Ma) of the onset of the basic volcanism in the oceanic sector (Principe to Pagalu islands) of the CVL. These ages, and that (11-9 Ma) of the silicic volcanism of the Ngaoundere plateau, indicate that the Cameroon Volcanic Line as a whole may not be easily interpreted as the surface expression of hot-spot magmatism. Received: 24 February 1998 / Accepted: 22 September 1998  相似文献