The significance of Messinian occurrences of Globorotalia margaritae and Globorotalia puncticulata in Sicily     

R.W.H. Butler  H.M. Pedle  R. Maniscalco  M. Grasso  E. McClelland  B. Finegan 《地学学报》1996,8(1):59-64

Globorotalia puncticulata and Globorotalia margaritae are critical species that define internationally recognized planktonic foraminiferal biozones in the Pliocene. These biozones are defined from stratotype sections on Sicily and their fauna are commonly considered to have been introduced to the Mediterranean after an influx of Atlantic water that terminated the late Miocene desiccation of the basin. Herein new discoveries of these species in rocks that predate the late Miocene desiccation are described. These data are supported by magneto- and lithostratigraphy that have been integrated at a single continuous section. Not only do these discoveries question the existing foraminiferal biozone stratigraphy, they also suggest new models for the dispersal of planktonic species. It is proposed that Globorotalia puncticulata and perhaps even Globorotalia margaritae evolved in the Mediterranean during earliest Messinian times (during or before chron C3Bn1n) and dispersed into the Atlantic. This suggests that a marine connection remained between the two sea areas until at least chron C3An.1n. Using the existing geomagnetic polarity time scale, these occurrences are some 2 Myr earlier than previously recorded in the Mediterranean. The distribution of G. margaritae and G. puncticulata in Mediterranean sections is likely to reflect palaeoenvironment or the preservation of deposits rather than the absolute age of the sediments.  相似文献   

Seismic signature of a phreatic explosion: hydrofracturing damage at Karthala volcano, Grande Comore Island, Indian Ocean     

Cécile Savin  Jean-Robert Grasso  Patrick Bachelery 《Bulletin of Volcanology》2005,67(8):717-731

Karthala volcano is a basaltic shield volcano with an active hydrothermal system that forms the southern two-thirds of the Grande Comore Island, off the east coat of Africa, northwest of Madagascar. Since the start of volcano monitoring by the local volcano observatory in 1988, the July 11th, 1991 phreatic eruption was the first volcanic event seismically recorded on this volcano, and a rare example of a monitored basaltic shield. From 1991 to 1995 the VT locations, 0.5<M_l<4.3, show a crack shaped pattern (3 km long, 1 km wide) within the summit caldera extending at depth from –2 km to +2 km relative to sea level. This N-S elongated pattern coincides with the direction of the regional maximum horizontal stress as deduced from regional focal mechanism solutions. This brittle signature of the damage associated with the 1991 phreatic eruption is a typical pattern of the seismicity induced by controlled fluid injections such as those applied at geothermal fields, in oil and gas recovery, or for stress measurements. It suggests the 1991 phreatic eruption was driven by hydraulic fracturing induced by forced fluid flow. We propose that the extremely high LP and VT seismicity rates, relative to other effusive volcanoes, during the climax of the 1991 phreatic explosion, are due to the activation of the whole hydrothermal system, as roughly sized by the distribution of VT hypocenters. The seismicity rate in 1995 was still higher than the pre-eruption seismicity rate, and disagrees with the time pattern of thermo-elastic stress readjustment induced by single magma intrusions at basaltic volcanoes. We propose that it corresponds to the still ongoing relaxation of pressure heterogeneity within the hydrothermal system as suggested by the few LP events that still occurred in 1995.Editorial responsibility: H Shinohara  相似文献   

The M_L 5.3 Épagny (French Alps) earthquake of 1996 July 15: a long-awaited event on the Vuache Fault     

François Thouvenot  Julien Fréchet  Paul Tapponnier  Jean-Charles Thomas  Benoît Le Brun  Gilles Ménard  Robin Lacassin  Liliane Jenatton  Jean-Robert Grasso  Olivier Coutant  Anne Paul  & Denis Hatzfeld 《Geophysical Journal International》1998,135(3):876-892

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Overview of the Late Tertiary–Recent tectonic and palaeo-environmental development of the Mediterranean region     

A.H.F. Robertson  M. Grasso 《地学学报》1995,7(2):114-127

The Late Tertiary history of the Mediterranean region exemplifies processes of ocean basin closure and continental collision, as determined from integrated land and marine evidence. During the Mesozoic–Early Tertiary, tectonic settings were dominated by evolution of Neotethys. This ocean generally widened eastwards, with a number of oceanic strands in the Eastern Mediterranean area. Great diversity of tectonic settings and palaeo-environments developed during the Tertiary closure history of these oceanic basins. In the Eastern Mediterranean region, more northerly Neotethyan strands were closed by the Mid Tertiary, while oceanic crust remained in the south in the present Eastern Mediterranean Sea area. Northwards subduction of the remaining southerly Neotethyan strand was probably active by the Early Miocene. Different areas exhibit different stages of convergence and ocean basin closure. In the east, the amalgamated Eurasian plate had collided with the Arabian margin (Africa) by the Late Miocene, while oceanic crust still persisted further west. Steady-state subduction during the Late Tertiary gave rise to the Mediterranean ridge, as a substantial mud-dominated accretionary wedge. In the Aegean area, sufficient northward subduction took place to activate arc volcanism and pervasive back arc extension, short of marginal basin opening. In the easternmost Mediterranean, only limited subduction took place, associated with supra-subduction zone extension (e.g. in Cyprus). Today, steady state-subduction continues only locally, where vestiges of Neotethys remain (e.g. Herodotus abyssal plain). In the Western Mediterranean area, suturing of the African and Eurasian plates initially took place in the Betic region (Early–Mid Tertiary), where the Neotethys had existed only as a narrow connection with the Central North Atlantic. In the Central Mediterranean region, where the Western Neotethys was wider, northward subduction was active, apparently as early as the Late Cretaceous. In a widely accepted interpretation, an Andean-type magmatic arc developed along the southern margin of Europe and was then rifted off in the Late Oligocene-Early Miocene, to form the Corsica-Sardinia Block, opening the North Balearic marginal basin in its wake. The migrating subduction zone and microcontinent then collided diachronously with North Africa-related continental units (North Africa and Apulia) from Late Oligocene-Early Miocene, giving rise to collisional thrust belts in the Northern and Southern Apennines and along the North African continental margin (i.e. the Maghrebian chain) to the Betic-Rif area. From the Early Miocene onwards, a separate subduction system became active, related to removal of Neotethyan oceanic crust to the southeast (Ionian Sea), fueling suprasubduction zone extension and opening of the Tyrrhenian Sea. ‘Orogenic collapse’ is an alternative mechanism of such extension, and is widely believed to have caused divergent thrusting in the Betic and Rif regions of the westernmost Mediterranean, at the same time as crustal extension and subsidence of the Alboran Sea.  相似文献   

Origin and role of major strike-slip transfers during plate collision in the central Mediterranean     

Claus-Dieter Reuther  Zvi Ben-Avraham  Mario Grasso 《地学学报》1993,5(3):249-257

Variations in the crustal structure along the northern African plate margin have caused different modes of collision with Eurasia. Lateral density variations along the central Mediterranean collision zone are expressed in a change of the angle of the downbending African Plate and lead to the formation of strike-slip transfers in these transition zones that are roughly perpendicular to the trend of the collisional zone. In some cases these transfer zones are developed into hinge faults, while in others they can be developed into transform faults. This process governs the segmentation of the collision zone in the central Mediterranean region south of the Maghrebian thrust belt in Tunisia and Sicily through the Calabrian Arc to the northeastern Hellenic Arc, extending further to the Cyprian Arc and to the Taurus-Zagros chain.  相似文献   

Lichens as bioindicators in volcanic areas: Mt. Etna and Vulcano Island (Italy)     

M. F. Grasso  R. Clocchiatti  F. Carrot  C. Deschamps  F. Vurro 《Environmental Geology》1999,37(3):207-217

 The aim of this paper is to verify whether lichens have the capacity to accumulate atmospheric contaminators linked to volcanic activity. About 100 lichens were collected in 1994 and 1995 from two active volcanic areas in Italy: Mount Etna and Vulcano Island. Twenty-seven elements were analyzed for each individual lichen using Instrumental Neutronic Activation Analysis and Inductively Coupled Plasma-Mass Spectrometry. Lichen composition reflects the contribution of the volcanic particulate material, and the two areas investigated can be distinguished on the basis of the concentration of some lithophile elements. Moreover, the distribution in lichens of the elements (As, Sb, Br, Pb) – derived from gas emissions (plume, fumaroles) – also shows different geochemical trends on Mt. Etna and Vulcano. Received: 20 April 1998 · Accepted: 4 July 1998  相似文献   

Reservoir construction from the Newberry Volcano EGS Demonstration     

Trenton T Cladouhos  Susan Petty  Yini Nordin  Michael Moore  Kyla Grasso  Matt Uddenberg  Michael W Swyer 《地下水科学与工程》2014,2(3):1-7

The Newberry Volcano EGS Demonstration in central Oregon tests recent technological advances designed to reduce the cost of power generated by EGS in a hot, dry well (NWG 55-29) drilled in 2008. An EGS reservoir was created by injecting large volumes of cold water, causing existing fractures to slip in shear (known as hydroshearing) generating the seismic waves that can be used to map fracture location and size. At the Newberry Demonstration the final injectivity ranged between 1.4 and 1.7 L/s/MPa a ~6x improvement over the initial injectivity of the well. The injectivity improvement and seismic analysis indicate that previously impermeable fractures were enhanced during the NWG 55-29 stimulation.  相似文献   

Numerical modelling of mixed-sediment consolidation     

Florent Grasso  Pierre Le Hir  Philippe Bassoullet 《Ocean Dynamics》2015,65(4):607-616

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Mechanical behaviour of deep rock core samples from a seismically active gas field     

D. Fabre  J. -R. Grasso  Y. Orengo 《Pure and Applied Geophysics》1991,137(3):201-219

This study concerns the laboratory testing of core samples from massive sedimentary rocks from an oil and gas field. The depth of extraction of the samples analysed varies between 1000 and 5000 metres. In all, 65 tests were performed, most of which included systematic measurement of acoustic activity during loading. The aim of the testing was to determine which types of fracture could occur in the rock matrix under field-stress conditions by examining in particular the relationship between confining pressure and the transition from brittle to ductile behaviour. The results of the laboratory tests are used to predict the occurrence of seismic activity resulting from the depletion of the gas reservoir which has been monitored during the last twenty years.  相似文献   

Relation between seismic source parameters and mechanical properties of rocks: A case study     

Bruno Feignier  Jean-Robert Grasso 《Pure and Applied Geophysics》1991,137(3):175-199

This study attempts to determine the relation between source parameters and mechanical properties of the rock matrix in which the microseismic events occur. For this purpose, accurate geological, mechanical and seismological data were acquired on a gas field experiencing induced seismicity due to its reservoir pressure drop. More than 30 deep boreholes (depth greater than 4 km) are concentrated in a 10×10×5 km volume, providing core samples for both geological and mechanical assessment. In this study, we focus on induced seismic events recorded by the local seismic network, over a three-year-long period. Characteristics of the seismic sources were obtained using spectral analysis and a dynamic model of failure. Results point out correlation between physical parameters of the seismic sources and the geomechanical properties of the rocks involved. Maximal static stress drops are found to be associated with the mechanical strength of the geological strata where the rupture occurs. The fracture size, using a circular model of failure, is also found to be dependent on the geomechanical setting. It is found that the size of the seismic fractures is dependent on the layer thickness and the prefracturation of the medium, both factors influencing the extension of preexisting discontinuities. The parameters of the seismic sources also show important changes when the gas reservoir is reached. The reservoir unit experienced a 45 MPa pore fluid pressure drop over a period of 20 years.  相似文献