Some SH-wave seismic reflections from depths of less than three metres     

Gian Piero Deidda  Gaetano Ranieri 《Geophysical Prospecting》2001,49(5):499-508

Shallow SH-wave reflections are far from routine, although their study can provide insights into important properties of near-surface materials that cannot be inferred from P-wave data alone. Difficulties in separating SH-wave reflections from Love waves are generally considered the major obstacle to progress in shallow SH-wave seismic reflection. This may be the case in surveys undertaken at great depths, but it is not necessarily true for reflection data gathered at shallow and ultra-shallow depths. This paper shows that when SH-wave data possess wavelengths greater than the thickness of the superficial layer, Love waves are not greatly dispersed. In this case, misinterpretation between parts of reflection hyperbolae and waveguide arrivals is sufficiently limited. In a one-layer model earth, which well approximates typical situations of the near-surface underground, the most energetic modes (the lowermost modes) of the dispersed surface waves have a dominant frequency band that falls below the wavelet spectrum of the shallow reflections; therefore, they can be filtered out in the frequency domain. Higher modes, although their spectral content overlaps that of the reflections, exhibit small amplitudes on seismograms and leave strong reflections unaffected.We present field examples from three different sites where we were able to obtain ultra-shallow reflections (< 3 m) in unconsolidated sediments. The high level of resolution (vertical resolution up to 15 cm) suggests that SH-wave reflection imaging has the potential to complement other high-resolution techniques, such as P-wave reflection and ground-penetrating radar (GPR) imaging, allowing a better and more complete characterization of the near-surface environments.  相似文献   

A Systematic Study of the Stability of Symmetric Periodic Orbits in the Planar, Circular, Restricted Three-Body Problem     

Alessandra Celletti  Andrea Chessa  John Hadjidemetriou  Giovanni Battista Valsecchi 《Celestial Mechanics and Dynamical Astronomy》2002,83(1-4):239-255

We investigate symmetric periodic orbits in the framework of the planar, circular, restricted, three-body problem. Having fixed the mass of the primary equal to that of Jupiter, we determine the linear stability of a number of periodic orbits for different values of the eccentricity. A systematic study of internal resonances, with frequency p/q with 2p 9, 1 q 5 and 4/3 p/q 5, offers an overall picture of the stability character of inner orbits. For each resonance we compute the stability of the two possible periodic orbits. A similar analysis is performed for some external periodic orbits.Furthermore, we let the mass of the primary vary and we study the linear stability of the main resonances as a function of the eccentricity and of the mass of the primary. These results lead to interesting conclusions about the stability of exosolar planetary systems. In particular, we study the stability of Earth-like planets in the planetary systems HD168746, GI86, 47UMa,b and HD10697.  相似文献   

Seismic tomography imaging of an unstable embankment     

Gian Piero Deidda  Gaetano Ranieri 《Engineering Geology》2005,82(1):32-42

Seismic tomography imaging was employed to make a diagnosis and choose a remedy for an embankment supported by a retaining wall showing clear evidence of structural instability. The geometry and structural characteristics of the wall, the inside geometry of cracks, and the physical parameters of the underground materials were the primary objectives of the geophysical survey. Seismic data were acquired along two vertical sections each one delimited by the lines of the sources within an inclined borehole and of the receivers lying on the ground. For each section, a total of 744 travel times were inverted to obtain compressional-wave velocities on a regular rectangular grid of squared cells (1 m × 1 m) using an inversion algorithm which is based on the simultaneous iterative reconstruction technique (SIRT). Ultrasonic tests carried out in laboratory on intact specimens, together with other supplemental site information, improved tomography resolution, allowing global and node constraints that forced the solution of the inverse problem to match known boundary values. Tomography imaged two high-velocity zones separated by a curved-shape low-velocity zone. The first ones were found to be compatible with the concrete retaining wall and with the schist materials, ranging from highly weathered to intact schist, while the low-velocity zone was interpreted as filling materials and/or completely decomposed rock schist. The combination of seismic tomography and laboratory measurements allowed extrapolation of important parameters over a large volume of rock mass, otherwise only representative of small rock samples near boreholes. It also enabled engineering characterization of subsurface rock mass, providing useful and accurate information to design a remedy for the embankment.  相似文献   

Al,Si ordering on cordierite using “magic angle spinning” NMR     

Andrew Putnis  Colin A. Fyfe  Gian C. Gobbi 《Physics and Chemistry of Minerals》1985,12(4):211-216

Silicon-29 “magic angle spinning” nuclear magnetic resonance (NMR) spectroscopy has been used to study the changes in local Si environment during Al, Si ordering in synthetic cordierite, Mg₂Al₄Si₅O₁₈. In the most disordered form, crystallized from a glass, eight distinct tetrahedral sites for silicon can be identified and assigned, while there are only two distinguishable Si sites in the well-annealed ordered form. This allows the changes in the Si site environments to be determined as a function of annealing time for the transformation from the disordered to the ordered form. The first crystallized state has a considerable degree of partitioning between T₁ and T₂ sites with the following site occupancies: T₁ ? Al:Si=0.80:0.20, T₂?Al:Si=0.27:0.73 The changes in Si environment are approximately linear with log time. The measured values of ²⁹Si isotropic chemical shift do not fit well to previously determined correlations of shift with various structural parameters.  相似文献   

The First International Workshop on Warning Criteria for Active Slides: technical issues,problems and solutions for managing early warning systems   总被引：1，自引：0，他引：1  

Catherine Cloutier  Federico Agliardi  Giovanni Battista Crosta  Paolo Frattini  Corey Froese  Michel Jaboyedoff  Jacques Locat  Clément Michoud  Hideaki Marui 《Landslides》2015,12(1):205-212

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Moment magnitude (Mw) from hydrophone records of low energy volcanic quakes     

Guardato  Sergio  Donnarumma  Gian Paolo  Riccio  Rosario  Del Pezzo  Edoardo  Iannaccone  Giovanni 《Journal of Seismology》2022,26(5):875-882

Earthquake magnitude calibration using hydrophone records has been carried out at Campi Flegrei caldera, an active area close to the highly populated area of Naples city, partly undersea. Definite integrals of the hydrophone records amplitude spectra, between the limits of 1 and 20 Hz, were calculated on a set of small volcano-tectonic earthquakes with moment magnitudes ranging from 1 to 3.3. The coefficients of a linear relationship between the logarithm of these integrals and the magnitude were obtained by linear optimization, thus defining a useful equation to calculate the moment magnitude from the hydrophone record spectra. This method could be easily exported to other volcanic areas, where submerged volcanoes are monitored by networks of hydrophones and seismic sensors on land. The proposed approach allows indeed magnitude measurements of small magnitude earthquakes occurring at sea, thus adding useful information to the seismicity of these volcanoes.

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Flash flood occurrence and magnitude assessment in an alluvial fan context: the October 2011 event in the Southern Apennines     

Santo  Antonio  Santangelo  Nicoletta  Di Crescenzo  Giuseppe  Scorpio  Vittoria  De Falco  Melania  Chirico  Giovanni Battista 《Natural Hazards》2015,78(1):417-442

Natural Hazards - This study presents the analysis of flash floods triggered by an extreme rainfall event that occurred on 7 October, 2011, over the Marzano carbonate massif (Southern Apennines)....  相似文献   

Hydrocarbon-derived imprints in olistostromes of the Early Serravallian Marnoso-arenacea Formation,Romagna Apennines (northern Italy)     

M. Berti  M. G. Cuzzani  G. B. Vai  A. Landuzzi  M. Taviani  P. Aharon 《Geo-Marine Letters》1994,14(2-3):192-200

Evidence of hydrocarbon venting within slumped bodies associated with the siliciclastic, dominantly turbiditic, Marnoso-arenacea Formation (Umbria-Romagna structural domain, Romagna Apennine, northern Italy) is documented with sedimentological, faunal, and geochemical data. Specifically,¹³C-depleted carbonate concretions and limestones and clusters of chemosynthetic clams (Vesicomyidae) have been identified in the marls of the Le Caselle Olistostrome and other slumped bodies contained within the Early Serravallian section of the Marnoso-arenacea Fm. Most of the olistostrome marls and limestones are extrabasinal and must have slid from a source area located several kilometers southwest of their present position. Thus, they presumably pertain to the Vicchio Marls Formation of the northeastern (outer) Tuscan structural domain, with possible minor contributions from the epi-Ligurian Bismantova Fm. It is suggested that venting of methane in the source area of the olistostromes permitted the establishment of exotic chemosynthetic communities and promoted the precipitation of carbonate concretions and limestones. According to the field evidence, these materials were later subjected to multistep downslope remobilization and were eventually carried into the Marnoso-arenacea basin through gravity mass transport.  相似文献   

Gravitational mode calculation of basins discretized by orthogonal curvilinear grids     

Gian Mario BeltramiRiccardo Briganti 《Ocean Engineering》2003,30(7):833-853

This paper presents a simple and straightforward method for carrying out the direct numerical solution of the eigenvalue problem associated to the homogeneous linear shallow-water equations expressed using orthogonal curvilinear coordinates, when ‘adiabatic’ boundary conditions apply. These equations, together with the boundary conditions, define a self-adjoint problem in the continuum. The method presented here, which is thought for calculating the 2-D theoretical gravity modes of both natural and artificial basins, relies on a change of basis of the dependent variable vector. This preliminary transformation makes it, in fact, possible to formulate two different numerical approaches which guarantee the self-adjoint property of the discrete form of the system consisting of the governing equations and the boundary conditions. The method is tested using a square and a fully circular domain, both of which allow comparisons with well-known analytical and numerical solutions. Discretizing the physical domain of a fully circular basin by a cylindrical coordinate grid makes it possible to show the actual efficiency of the method in calculating the theoretical gravity modes of basins discretized by a boundary-following coordinate grid which allows laterally variable resolution.  相似文献   

Role of Extratropical Cyclones in the Recently Observed Increase in Poleward Moisture Transport into the Arctic Ocean     

Gian A.VILLAMIL-OTERO  Jing ZHANG  Juanxiong HE  Xiangdong ZHANG 《大气科学进展》2018,35(1):85-94

Poleward atmospheric moisture transport(AMT) into the Arctic Ocean can change atmospheric moisture or water vapor content and cause cloud formation and redistribution, which may change downward longwave radiation and, in turn, surface energy budgets, air temperatures, and sea-ice production and melt. In this study, we found a consistently enhanced poleward AMT across 60?N since 1959 based on the NCAR–NCEP reanalysis. Regional analysis demonstrates that the poleward AMT predominantly occurs over the North Atlantic and North Pacific regions, contributing about 57% and 32%, respectively, to the total transport. To improve our understanding of the driving force for this enhanced poleward AMT, we explored the role that extratropical cyclone activity may play. Climatologically, about 207 extratropical cyclones move across 60?N into the Arctic Ocean each year, among which about 66(32% of the total) and 47(23%) originate from the North Atlantic and North Pacific Ocean, respectively. When analyzing the linear trends of the time series constructed by using a 20-year running window, we found a positive correlation of 0.70 between poleward yearly AMT and the integrated cyclone activity index(measurement of cyclone intensity, number, and duration). This shows the consistent multidecadal changes between these two parameters and may suggest cyclone activity plays a driving role in the enhanced poleward AMT. Furthermore, a composite analysis indicates that intensification and poleward extension of the Icelandic low and accompanying strengthened cyclone activity play an important role in enhancing poleward AMT over the North Atlantic region.  相似文献