ISSN:0954-4879    

DOI:10.1111/j.1365-3121.1993.tb00279.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Recent progress in a new field of mechanics of diluted solids is reviewed ‐ the fractal mechanics of geomaterials. It has become clear that the mechanics of geomaterials should take into consideration the influence of the fracture delocalization process on fundamental fracture characteristics such as the strength, the fractal dimension of a network of cracks, the surface energy of fracture and the elastic properties of fragmented media.The percolation model of fracture proposed by this author in 1979, in accordance with experimental data, treats the destruction process as a sequence of nucleation and coalescence of microcracks caused by their interaction. This approach enables the mathematical description of the entire process of fracturing. Many aspects of the fracture of heterogeneous solids ‐ the magnitude‐frequency distribution of seismic activity and acoustic emission, the high‐surface energy of fracture in composite materials and rocks, the geometrical peculiarities of a crack network, the appearance of forerunners of mechanical collapse, and the intermittency of the fracture process in the time domain ‐ find quantitative explanation in the percolation model. The process of determining the elasticity of fractured media, which is the object of the elastic percolation theory, also reveals some unusual features that can affect the process of geophysical interpretation. For example, the elastic modulusMand the velocity of elastic wavesvbecome scale‐dependent in the fractal regime. It is shown that the fractal dimension of the elastic modulus of a depleted solid differs significantly for ‘refilled’ and ‘hollow’ voids.Several implications of fractal mechanics for seismology are considered, namely the generalized form of the magnitude‐frequency relationship, the phenomenon of anomalous tensosensitivity, the scale‐dependence of the elastic moduli of massively faulted rocks and the possibility of appa

ISSN:0954-4879    

DOI:10.1111/j.1365-3121.1993.tb00280.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Sedimentary cycles in an upper Miocene succession of hemipelagic sediments (marls) and laminites (sapropels) were deposited in an outerarc basin and are related to the astronomical cycles of precession and eccentricity. Individual marl‐laminite couplets correspond with the cycle of precession which has a periodicity of about 22 kyr. The lower part of the succession contains a turbidite interval comprising a number of distinct turbidite sequences. The turbidite sequences occur within or substitute entirely the laminite beds, so that turbidite deposition is similarly precession punctuated.The turbidite facies is characteristic for small, prograding fan lobes fed by small‐volume turbidites. The abundant plant remains, the local palaeogeographic setting and the association with laminites (related to wet climate) suggest a river‐fed submarine fan‐lobe, where the timing of sediment transport is largely controlled by river floods during periods of high precipitation and continental run‐off. The onset and ending of the turbidite interval is most likely linked with either autocyclic processes or by tectonic steepening of the hinterland relief. Sea‐level changes seem least important for the triggering of turbidites, which is in contrast with curr

ISSN:0954-4879    

DOI:10.1111/j.1365-3121.1993.tb00281.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

The Menderes Massif, in western Anatolia, has been described as a lithological succession comprising a basal ‘Precambrian gneissic core of sedimentary origin’ overlain in sequence by ‘Palaeozoic schist’ and ‘Mesozoic‐Cenozoic marble’ forming the envelope. The boundary between core and schist envelope was interpreted as a major unconformity, the ‘Supra‐Pan‐African unconformity’. By contrast, our field observations and geochemical data show that around the southern side of Besparmak Mountain, north of Selimiye (Milas), the protoliths of highly deformed, mylonitized augen gneisses are granitoid rocks intrusive into the adjacent Palaeozoic metasedimentary schists. The field relationships indicate the age of intrusion to be younger than late Permian and there is no evidence for the existence of either an exposed Precambrian basement or the ‘Supra‐Pan‐African unconformity’ in this

ISSN:0954-4879    

DOI:10.1111/j.1365-3121.1993.tb00282.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

The source of hotspot volcanism lies in metasomatized regions of the continental mantle proximal to ancient sutures and failed rifts. Such regions are prone to melting under hotcell conditions on continental rifting, and to erosion into the deeper mantle by asthenospheric flow. In opening basins, rifting parallel to such sutures or failed rifts delaminates and cycles continental mantle into the MORB source. Rifting at some angle to a suture or failed rift generates a hotspot track by preferential melting of the metasomatized mantle as it is cycled toward the rift axis. Continental mantle eroded into the asthenosphere becomes displaced from the continent by net westward drift of the lithosphere relative to the deep mantle to give rise to hotspot volcanism in long‐lived ocean basin

ISSN:0954-4879    

DOI:10.1111/j.1365-3121.1993.tb00283.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

ISSN:0954-4879    

DOI:10.1111/j.1365-3121.1993.tb00284.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

This paper tackles the problems connected with the use of macroseismic scales, with particular attention to MSK. Intensity estimates are in principle affected by uncertainties which are seldom quantified in practice. In the case of two localities (Scisciano and Orciano) damaged by two Italian earthquakes (1741, Fabriano and 1846, Orciano), which have a good historical documentation, the difficulties of obtaining the data necessary for MSK evaluation have been analysed. In order to assess the maximum range of uncertainty the data have been analysed in two extreme scenarios. Finally a comparison between intensity assigned using the MSK and MCS scales is analysed.

ISSN:0954-4879    

DOI:10.1111/j.1365-3121.1993.tb00285.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

During 1770–1820 Northeastern Italy was hit by a series of high intensity earthquakes affecting the Piedmont area of Friuli from Maniago to Tolmezzo. Greater knowledge of these events, which seem to be extremely circumscribed and to have damaged only a small number of localities (1776, 1789, 1794: Tramonti; 1788, 1790: Tolmezzo; 1812: Cavasso), could make a significant contribution towards defining better the potential seismic hazard in Northern Friuli. A review of these shocks has been undertaken within the framework of activities organized by the macroseismic working group of the National Group for Protection against Earthquakes (GNDT). The critical revision of the information gathered by the programme ‘analysis through the compilations’, has stressed the need for a new interpretative method and for great caution to be exercised when assessing reliable intensity degrees, to avoid possible inconsistencies in their values. This preliminary investigation allowed us to identify both doubtful and some misestimated shocks. A rough macroseismic intensity distribution pattern of each event, showing that the earthquakes were felt over an area (including Italian, Slovene and Austrian territories) coherent with the epicentre intensity, has been also delin

ISSN:0954-4879    

DOI:10.1111/j.1365-3121.1993.tb00286.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

A first report on the historical seismicity of Tunisia was read at the Joint EGS‐ESC‐CEC Symposium (Bologna, 1988). Subsequently, further research has revealed new information and confirmed previous doubts. Careful discussion of sources definitely throws out the famous 408 Utica earthquake and increasingly the effects of the 306–310 and 365 events seem dubious. On the other hand, several sequences (981, 1735, 1835, 1872, 1881, 1887) are better known, although the location of most epicentres still remains vague. While catalogues underestimate the frequency of events in northern as well as in southern Tunisia (where there is azelzellegend), they continue to overestimate the intensities of modern earthq

ISSN:0954-4879    

DOI:10.1111/j.1365-3121.1993.tb00287.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY

摘要:

Earthquake swarm activity at Comrie, Perthshire was particularly marked in the period 1839–1846. It served as a focus for early scientific interest in earthquakes in the UK, chiefly under the aegis of the British Association for the Advancement of Science. The work done included both macroseismic and instrumental investigations, and saw the first use of the inverted pendulum in seismology, as well as the first seismometer network anywhere in the worl

ISSN:0954-4879    

DOI:10.1111/j.1365-3121.1993.tb00288.x

出版商:Blackwell Publishing Ltd    

年代:1993

数据来源: WILEY