Depth of the brittle-ductile transition in a transcurrent boundary zone     

Michele Dragoni  Silvia Pondrelli 《Pure and Applied Geophysics》1991,135(3):447-461

A model is proposed which describes the boundary zone between two transcurrent plates as a viscoelastic body, with rheological properties changing with depth. In this model, the brittle-ductile transition is defined as the depth at which the time derivative of shear stress changes from positive to negative values. Variations of this depth are studied as functions of geothermal gradient, rheological parameters and strain rate, using a power law rheology with exponent ranging from 1 to 4. Stress relaxation in the ductile zone is controlled by a local characteristic time, which depends on petrology, temperature and, in the case of non-Newtonian rheology, on strain rate. The composition and the hydration degree of crustal rocks may also sensibly influence the depth of the brittle-ductile transition. The model predictions are compared with observations regarding the San Andreas, Imperial Valley and North Anatolian Faults: it is found that values ofn from 1 to 3 are more appropriate to reproduce the transition depth inferred by the seismicity distribution.  相似文献   

Persistence of benthic communities: a case study from the Valli di Comacchio, a Northern Adriatic lagoonal ecosystem (Italy)   总被引：1，自引：0，他引：1  

Mistri  Michele 《ICES Journal of Marine Science》2002,59(2):314-322

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Glacial morphology and post-glacial contourites in northern Prince Gustav Channel (NW Weddell Sea,Antarctica)     

Camerlenghi  Angelo  Domack  Eugene  Rebesco  Michele  Gilbert  Robert  Ishman  Scott  Leventer  Amy  Brachfeld  Stefanie  Drake  Allison 《Marine Geophysical Researches》2001,22(5-6):417-443

We present the results of a marine geophysical investigation of the northern Prince Gustav Channel. By comparative analysis of multibeam bathymetric data, single channel seismic reflection profiles, underway chirp sonar data, ADCP current data and sediment coring, we define the main morphological elements of the area. In particular we define the glacial morphogenesis in relation to the excavation of inner shelf basins and troughs along structural discontinuities and lithologic boundaries. We identify streamlined surfaces that testify to the grounding of ice and past ice flow directions. These glacial forms are found only on glacial tills preserved in the deepest part of the basins, while net erosion to bedrock has occurred elsewhere. Since the Last Glacial Maximum (LGM), the relict glacial morphology has been draped by hemipelagic and diatomaceous mud, and bottom currents have played a major role in focusing sedimentation within small depocentres, that we define as contouritic drifts. Based on shallow sediment architecture and supported by direct measurements, we propose that the direction of bottom water flow is from the outer shelf into the Prince Gustav channel as a result of a combination of tidal currents and ice shelf-related thermohaline circulation.  相似文献   

Larval Fishes in Relation to Water Masses of the Central North Pacific Transitional Areas, Including the Shelf Break of West-Central Alaska     

Brenda L. Norcross  Skip M. McKinnell  Michele Frandsen  David L. Musgrave  Steven R. Sweet 《Journal of Oceanography》2003,59(4):445-460

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Seismic expression of contourites and related deposits: a preface   总被引：1，自引：0，他引：1  

Rebesco  Michele  Stow  Dorrik 《Marine Geophysical Researches》2001,22(5-6):303-308

Contourites are widespread throughout the deep sea, ranging from those that build up individually distinct bodies (mounded drifts) to those that occur closely interbedded with other deep-water facies. Although seismic data should not be used to make a firm identification of contourites without supporting evidence, much progress has been made in determining the combination of seismic criteria that best represent contourite deposits. With some modifications and additions, these criteria are in broad agreement with those recently proposed by Faugères and colleagues (1999). The papers in this special issue are mainly drawn from those presented at an IGCP workshop held in Trieste, Italy (October 2000), together with selected additions. Some of the new and important topics covered include: discussion of bottom-current controlled deposits on continental shelves and in large lakes (shallow-water and lacustrine `contourites'); the unique characteristics of high-latitude contourite systems that show interaction with turbidity current, debris flow and glacigenic processes; and the importance of local slope topography, developed as a result of synsedimentary tectonics and downslope mass movement, in focussing and shaping drift deposits (infill and fault-related drifts). An introduction to the powerful use of 3D seismic data in understanding contourite systems points the way towards important future research.  相似文献   

Growth and Production of the Ark Shell Scapharca inaequlvalvis (BRUGUIÈRE) in a Lagoon of the Po River Delta     

Michele  Mistri  Remigio  Rossi Victor Ugo  Ceccherelli 《Marine Ecology》1988,9(1):35-49

Abstract. Scapharcu inuequivalvis is an Indopacific bivalve which has recently immigrated to the Adriatic Sea and has progressively replaced dominant species within some infauna communities. Density, growth, and secondary production of this Arcidae were investigated between 1984 and 1985 in a bed located in a brackish environment of the Northern Adriatic coast.  相似文献   

Tethya (Porifera,Demosponglae) Species Coexisting in a Maldivian Coral Reef Lagoon: Taxonomical,Genetic and Ecological Data     

Michele Sar  Giuseppe Corriero  Giorgio Bavestrello 《Marine Ecology》1993,14(4):341-355

Abstract. Tethya microstella, T. orphei, T. robusta, and T. seychellensis live in sympatry in a Maldivian coral reef lagoon (Gangehi Island, Ari Atoll). A morphological, morphometric, and electrophoretical study of these species show that their Maldivian populations are well separated morphologically and genetically. The genetic distances and the other data are more consistent with an immigration than with a local speciation hypothesis. Their coexistence may be explained by a differentiation in ecological requirements. The four species inhabit the shallow water biotope of the lagoon among the rubble of dead corals. Our data show that T. orphei and T. seychellensis occupy the upper rubble layer, T. microstella and T. robusta the lower one. This distinction agrees with the different morpho-functional features of the two pairs of species.  相似文献   

An Overview of the Small BAseline Subset Algorithm: a DInSAR Technique for Surface Deformation Analysis   总被引：1，自引：0，他引：1  

Riccardo Lanari  Francesco Casu  Mariarosaria Manzo  Giovanni Zeni  Paolo Berardino  Michele Manunta  Antonio Pepe 《Pure and Applied Geophysics》2007,164(4):637-661

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Detection of a significant change in the solar diameter     

Axel D. Wittmann  Edoardo Alge  Michele Bianda 《Solar physics》1993,145(1):205-206

Drift-time measurements of the solar diameter made at Izaña and Locarno in 1990–1992 show a significant increase of the observed angular semidiameter when compared to results obtained at the same two sites in 1981. The observed increase of 0.4 is not due to a systematic (or long-term) variation, but seems to reflect a more complicated behaviour with time: As both series of measurements were made around a maximum of the 11-year cycle, it seems that a variation in phase with solar activity (in the sense of the Secchi-Rosa law) can be ruled out.  相似文献   

Drought, vegetation change, and human history on Rapa Nui (Isla de Pascua, Easter Island)     

Daniel Mann  James Edwards  Warren Beck  Michele Mass  John Loret 《Quaternary Research》2008,69(1):16-28

Stratigraphic records from lake sediment cores and slope deposits on Rapa Nui document prehistoric human impacts and natural environmental changes. A hiatus in sedimentation in Rano Raraku suggests that this lake basin dried out sometime after 4090-4410 cal yr BP and refilled only decades to centuries before AD 1180-1290. Widespread ecosystem changes caused by forest clearance by Polynesian farmers began shortly after the end of this drought. Terrestrial sections show a chronology of burning and soil erosion similar to the lake cores. Although changing sediment types and shifts in the pollen rain suggest that droughts occurred earlier in the Holocene, as yet there is no evidence for droughts occurring after AD 1180-1290. The timing of the agricultural colonization of Rapa Nui now seems well established at ca. AD 1200 and it was accompanied by rapid deforestation that was probably exacerbated by the island's small size, its droughty climate, and the rarity of primeval fires. Detailed records of a large interval of Rapa Nui's ecological history remain elusive due to the drought hiatus in the Rano Raraku sediment record. We find no evidence for a “rat outbreak impact” on Rapa Nui's vegetation preceding anthropogenic forest clearance.  相似文献