Intensity Spectra Versus Response Spectra: Basic Concepts and Applications     

Horea Sandi  Ioan Sorin Borcia 《Pure and Applied Geophysics》2011,168(1-2):261-287

This paper begins with a critical assessment of the concept of macroseismic intensity, on which traditional scales, such as MSK and EMS, are based. The main shortcoming identified is the model's failure to consider the spectral features of ground motion. This omission may lead to erroneous seismic zonation, as shown in the paper. As a result, the model is of little interest to engineers who must design and build safe structures while adopting economical solutions. The paper presents a way to radically improve this situation. The starting point for this approach was the experience of the destructive Vrancea earthquake of 1977.03.04, which made it clear that intensity appears to be different for structures having natural periods pertaining to different spectral domains. The solution proposed to the shortcomings of the traditional intensity concept is postulated on a system of analytical expressions, covering definitions of global intensities, of intensities related to oscillation frequency and of intensities related to a definite spectral band. The latter definition lies at the basis of a definition of discrete intensity spectra. Illustrative applications are presented, in relation to global intensities and to discrete intensity spectra. We then analyze an illustrative case in which the use of traditional macroseismic survey techniques led to erroneous seismic zonation. Finally, some conclusions and recommendations are presented. Based on the authors?? long-term experience, we strongly recommend close interaction between seismologists and engineers in working groups and joint projects targeted on radical improvement of the basic concepts of seismic intensity and of specific analysis procedures.  相似文献   

Avalonian, Ganderian and East Cadomian terranes in South Carpathians, Romania, and Pan-African events recorded in their basement     

Ioan Balintoni  Constantin Balica 《Mineralogy and Petrology》2013,107(5):709-725

New U-Pb geochronology is used to refine the provenance and evolution of northwest Gondwana Pan-African terranes preserved in the South Carpathians of Romania. The Dr?g?an terrane of Avalonian affinity, from the Danubian domain of the South Carpathians originated in the Panthalassa Ocean and accreted to the Amazonian part of Rodinia not much before 800 Ma, when the F?ge?el orthogneiss was intruded, at around 807–810 Ma. After this event no other Neoproterozoic magmatic pulse is known in the basement of the Dr?g?an terrane. The Ganderian type Lainici-P?iu? terrane from the same domain of the South Carpathians, recorded magmatic pulses at 782 Ma, 739 Ma, 708 Ma, 639 Ma, 600–587 Ma and 574–568 Ma. The East Cadomian Sebe?-Lotru terrane from the Getic domain of the South Carpathians recorded magmatic pulses at 817 Ma, 768 Ma, 685 Ma, 620 Ma, 584 Ma and 550 Ma. Post 630 Ma the northwestern Gondwana margin evolved as an active continental margin at least until 550 Ma, but the pre-630 Ma magmatism could be associated to some island arcs docked with different pre-Gondwanan continental fragments. Independent of the tectonic setting, the post 750 Ma orogens dated in the basement of the peri-Gondwanan terranes are discussed in the frame of the Cadomian orogens, as constituents of the Pan-African orogens in a broader sense. The detrital zircon may also record magmatic pulses from Pan-African orogens other than the Cadomian ones.  相似文献   

Carpathian peri-Gondwanan terranes in the East Carpathians (Romania): A testimony of an Ordovician,North-African orogeny     

Ioan Balintoni  Constantin Balica 《Gondwana Research》2013,23(3):1053-1070

The eastern branch of the Romanian Carpathians – the East Carpathians – is essentially an Alpine thrust and fold belt made up in its median part by a Crystalline–Mesozoic zone. This, in turn, is built up by several Alpine nappes (top to bottom): the Wildflysch, Bucovinian, Subbucovinian and Infrabucovinian. In the basement of the Bucovinian and Subbucovinian nappes the following Variscan tectonic units have been identified (top to bottom): Rar?u, Putna, Pietrosu Bistri?ei and Rodna. The Infrabucovinian nappes comprise the Rar?u nappe only. The Alpine nappes have an eastward vergence, opposite to the Variscan ones (present coordinates). In terms of pre-Variscan terranes distribution, the Rar?u nappe involved the Bretila terrane basement and its late Paleozoic cover, Putna the Tulghe? terrane basement, Pietrosu Bistri?ei the Negri?oara terrane basement and Rodna the Rebra terrane basement. These terranes originated along northwestern Gondwana margin during some Ordovician thermotectonic events. They do not represent Cadomian terranes and we call them Carpathian-type terranes. Two igneous protoliths from Bretila terrane basement (i.e. Anie? orthogneiss and H?ghima? granitoid) yield U/Pb LA-ICP-MS zircon ages of 462 ± 3 Ma and 469.2 ± 6.5 Ma, respectively. An orthogneiss from Tulghe? terrane basement yield 462.6 ± 3.1 Ma; the Pietrosu porphyritic orthogneiss from Negri?oara terrane basement yield 461.1 ± 5.2 Ma; and the Nichita? orthogneiss from Rebra terrane basement yield 447.9 ± 2.8 Ma. All these ages suggest the magma crystallization time. Two paragneisses from the Rebra terrane basement show a detrital zircon age distribution characteristic of a NE-African provenance. Regarding the tectonic settings, the lithology of the Bretila terrane suggests a magmatic arc on a continental margin, while of the Tulghe? terrane suggests a back arc environment, and those of the Rebra and Negri?oara terranes suggest a passive continental margin. An Ordovician metamorphism of medium grade (staurolite–kyanite zone) affected the basements of Bretila, Negri?oara and Rebra terranes, whereas a low grade (chlorite to biotite zone) event affects the Tulghe? terrane. With regard to the Variscan orogeny, the existence of a Paleotethys suture is proposed within the metamorphic basement of the East Carpathians. In this interpretation, the Bretila terrane was the upper plate, the Rebra and Negri?oara terrane pair formed the lower plate and the Tulghe? terrane was a component of the suture. The Variscan thermotectonic events reflect isothermal decompression with andalusite + cordierite in the basement of the Rebra terrane and retrogression in the basement of the other terranes.  相似文献