Attenuation in Southeastern Carpathians area: Result of upper mantle inhomogeneity   总被引：1，自引：0，他引：1  

M. Popa  M. Radulian  B. Grecu  E. Popescu  A.O. Placinta 《Tectonophysics》2005,410(1-4):235-249

The systematic analysis of seismograms recorded on the Romanian territory using Vrancea intermediate-depth earthquakes shows a strong asymmetric pattern relative to the epicentral area: on one side, in the Transylvanian Basin and the Eastern Carpathians (approximately along the inner volcanic chain), the amplitudes are reduced by a factor of 20 on average and the high frequencies are attenuated, in contrast with the other side, in the foreland platform. This pattern is explained by a significant attenuation increase caused by a strong lateral variation of the structure in the upper mantle, immediately towards NW of the Vrancea seismic active volume. This region corresponds to the most recent volcanic activity in the Persani Mountains and with the low-velocity body adjacent toward NW to the high-velocity body subducted beneath Vrancea area as indicated by seismic tomography and heat flow results. The CALIXTO'99 tomography experiment, deployed for 6 months in 1999, provides the largest number of observations for Vrancea earthquakes ever recorded on the Romanian territory. We select data from 8 earthquakes generated in this time interval in the Vrancea nest, which were recorded with signal / noise ratio greater than 5 by at least 25 stations. All of them are small- to moderate-magnitude events (3.6 ≤ M_w ≤ 4.2). The attenuation is much more important in the high-frequency range (> 1 Hz), than at low frequencies. Since the large Vrancea earthquakes can radiate significant energy in the low-frequency range (< 1 Hz), our results show that the seismic hazard level is much more uniform all over the Romanian territory in the low-frequency range than in the high-frequency range.  相似文献   

3-D upper crustal tomographic structure across the Vrancea seismic zone, Romania     

CALIXTO Group  Michael Landes  W. Fielitz  F. Hauser  M. Popa   《Tectonophysics》2004,382(1-2):85-102

The VRANCEA99 and VRANCEA2001 seismic refraction experiments are part of a multidisciplinary project to study the Eastern Carpathians in Romania. The objectives of these studies are intended to disclose a more detailed picture of the crustal and upper mantle structures above the seismically active Vrancea region. In this paper we provide additional constraints for the upper crustal structures of the area. The 1999 campaign consisted of a 320-km-long N–S profile and a 70-km-long E–W profile. The intersecting 2001 profile extended in E–W direction from the Hungarian border to the Black Sea. In order to enhance the model resolution, first arrival data from local crustal earthquakes were also included.This configuration allowed for the first time to derive a 3-D velocity model for the upper crust of the Romanian Carpathian Orogen, within a 115×235 km wide region, centred over the Vrancea seismic zone. The 3-D model reveals lateral velocity variations, which were not visible on the in-line interpretations. It allows us to distinguish between foreland platform areas, foreland basins and the Carpathian Orogen. Clear velocity differences between the foreland basins south and southeast of the Eastern Carpathians and the Focsani Basin further north indicate different pre-Miocene sedimentary compositions and geological evolutions of these foreland platforms. The involved Moesian and Scythian platforms are separated by the Trotus Fault system, which is observed as a velocity discontinuity. An upper crustal high-velocity zone, above the northern Vrancea seismic zone, could also be identified. This high-velocity zone is explained by a Middle Pliocene to Pleistocene E–W oriented out-of-sequence thrust of the crystalline basement, below the decollement of the flysch nappes.  相似文献   

Post-collisional Tertiary–Quaternary mafic alkalic magmatism in the Carpathian–Pannonian region: a review     

Ioan Seghedi  Hilary Downes  Orlando Vaselli  Alexandru Szakcs  Kadosa Balogh  Zoltn Pcskay 《Tectonophysics》2004,393(1-4):43

Mafic alkalic volcanism was widespread in the Carpathian–Pannonian region (CPR) between 11 and 0.2 Ma. It followed the Miocene continental collision of the Alcapa and Tisia blocks with the European plate, as subduction-related calc-alkaline magmatism was waning. Several groups of mafic alkalic rocks from different regions within the CPR have been distinguished on the basis of ages and/or trace-element compositions. Their trace element and Sr–Nd–Pb isotope systematics are consistent with derivation from complex mantle-source regions, which included both depleted asthenosphere and metasomatized lithosphere. The mixing of DMM-HIMU-EMII mantle components within asthenosphere-derived magmas indicates variable contamination of the shallow asthenosphere and/or thermal boundary layer of the lithosphere by a HIMU-like component prior to and following the introduction of subduction components.Various mantle sources have been identified: Lower lithospheric mantle modified by several ancient asthenospheric enrichments (source A); Young asthenospheric plumes with OIB-like trace element signatures that are either isotopically enriched (source B) or variably depleted (source C); Old upper asthenosphere heterogeneously contaminated by DM-HIMU-EMII-EMI components and slightly influenced by Miocene subduction-related enrichment (source D); Old upper asthenosphere heterogeneously contaminated by DM-HIMU-EMII components and significantly influenced by Miocene subduction-related enrichment (source E). Melt generation was initiated either by: (i) finger-like young asthenospheric plumes rising to and heating up the base of the lithosphere (below the Alcapa block), or (ii) decompressional melting of old asthenosphere upwelling to replace any lower lithosphere or heating and melting former subducted slabs (the Tisia block).  相似文献   

What Ångström—Prescott equation tells us about the cloud and clear-sky climatologies?     

Paulescu  Marius  Badescu  Viorel  Budea  Sanda  Dumitrescu  Alexandru 《Theoretical and Applied Climatology》2022,147(1-2):239-250

Theoretical and Applied Climatology - The Ångström–Prescott equation defines generically the relationship between solar energy available at ground level and sunshine duration. From...  相似文献   

Experimental testing on emulative connections for precast columns using grouted corrugated steel sleeves   总被引：1，自引：1，他引：0  

Viorel Popa  Andrei Papurcu  Dragos Cotofana  Radu Pascu 《Bulletin of Earthquake Engineering》2015,13(8):2429-2447

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Cover Image          下载免费PDF全文

Jan‐Hendrik May  He‐Qing Huang  Toshiyuki Fujioka  David Fink  Alexandru Codilean  Guo‐An Yu  Yuanxu Ma  Gerwin Wulf  Jing Gu 《地球表面变化过程与地形》2018,43(3):i-i

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Risk-targeted maps for Romania     

Radu Vacareanu  Florin Pavel  Ionut Craciun  Veronica Coliba  Cristian Arion  Alexandru Aldea  Cristian Neagu 《Journal of Seismology》2018,22(2):407-417

Romania has one of the highest seismic hazard levels in Europe. The seismic hazard is due to a combination of local crustal seismic sources, situated mainly in the western part of the country and the Vrancea intermediate-depth seismic source, which can be found at the bend of the Carpathian Mountains. Recent seismic hazard studies have shown that there are consistent differences between the slopes of the seismic hazard curves for sites situated in the fore-arc and back-arc of the Carpathian Mountains. Consequently, in this study we extend this finding to the evaluation of the probability of collapse of buildings and finally to the development of uniform risk-targeted maps. The main advantage of uniform risk approach is that the target probability of collapse will be uniform throughout the country. Finally, the results obtained are discussed in the light of a recent study with the same focus performed at European level using the hazard data from SHARE project. The analyses performed in this study have pointed out to a dominant influence of the quantile of peak ground acceleration used for anchoring the fragility function. This parameter basically alters the shape of the risk-targeted maps shifting the areas which have higher collapse probabilities from eastern Romania to western Romania, as its exceedance probability increases. Consequently, a uniform procedure for deriving risk-targeted maps appears as more than necessary.  相似文献   

Evolution of sandstone peak‐forest landscapes – insights from quantifying erosional processes with cosmogenic nuclides          下载免费PDF全文

Jan‐Hendrik May  He‐Qing Huang  Toshiyuki Fujioka  David Fink  Alexandru Codilean  Guo‐An Yu  Yuanxu Ma  Gerwin Wulf  Jing Gu 《地球表面变化过程与地形》2018,43(3):639-653

The sandstone peak‐forest landscape in Zhangjiajie UNESCO Global Geopark of Hunan Province, China, is characterized by >3000 vertical pillars and peak walls of up to 350 m height, representing a spectacular example of sandstone landform variety. Few studies have addressed the mechanisms and timescales of the longer‐term evolution of this landscape, and have focused on fluvial incision. We use in situ cosmogenic nuclides combined with GIS analysis to investigate the erosional processes contributing to the formation of pillars and peak‐forests, and discuss their relative roles in the formation and decay of the landscape. Model maximum‐limiting bedrock erosion rates are the highest along the narrow fluvial channels and valleys at the base of the sandstone pillars (~83–122 mm kyr^?1), and lowest on the peak wall tops (~2.5 mm kyr^?1). Erosion rates are highly variable and intermediate along vertical sandstone peak walls and pillars (~30 to 84 mm kyr^?1). Catchment‐wide denudation rates from river sediment vary between ~26 and 96 mm kyr^?1 and are generally consistent with vertical wall retreat rates. This highlights the importance of wall retreat for overall erosion in the sandstone peak‐forest. In combination with GIS‐derived erosional volumes, our results suggest that the peak‐forest formation in Zhangjiajie commenced in the Pliocene, and that the general evolution of the landscape followed our sequential refined model: (i) slow lowering rates following initial uplift; (ii) fast plateau dissection by headward knickpoint propagation along joints and faults followed by; (iii) increasing contribution of wall retreat in the well‐developed pillars and peak‐forests and a gradual decrease in overall denudation rates, leading to; (iv) the final consumption of pillars and peak‐forests. Our study provides an approach for quantifying the complex interplay between multiple geomorphic processes as required to assess the evolutionary pathways of other sandstone peak‐forest landscapes across the globe. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

26Al/10Be ratios reveal the source of river sediments in the Kimberley,NW Australia     

Gaël Cazes  David Fink  Alexandru T. Codilean  Réka-Hajnalka Fülöp  Toshiyuki Fujioka  Klaus M. Wilcken 《地球表面变化过程与地形》2020,45(2):424-439

We use cosmogenic ¹⁰Be and ²⁶Al in both bedrock and fluvial sediments to investigate controls on erosion rates and sediment supply to river basins at the regional scale in the Kimberley, NW Australia. The area is characterised by lithologically controlled morphologies such as cuestas, isolated mesas and extensive plateaus made of slightly dipping, extensively jointed sandstones. All sampled bedrock surfaces at plateau tops, ridgelines, and in the broader floodplain of major rivers over the region show similar slow lowering rates between 0.17 and 4.88 m.Myr^-1, with a mean value of 1.0 ± 0.6 m.Myr^-1 (n=15), whilst two bedrock samples collected directly within river-beds record rates that are one to two orders of magnitude higher (14.4 ± 1.5 and 20.9 ± 2.5 m.Myr^-1, respectively). Bedrock ²⁶Al/¹⁰Be ratios are all compatible with simple, continuous sub-aerial exposure histories. Modern river sediment yield lower ¹⁰Be and ²⁶Al concentrations, apparent ¹⁰Be basin-wide denudation rates ranging between 1.8 and 7.7 m.Myr^-1, with a median value of 2.6 m.Myr^-1, more than double the magnitude of bedrock erosion rates. ²⁶Al/¹⁰Be ratios of the sediment samples are lower than those obtained for bedrock samples. We propose that these depleted ²⁶Al/¹⁰Be ratios can largely be explained by the supply of sediment to river basins from the slab fragmentation and chemical weathering of channel gorge walls and plateau escarpments that result in diluting the cosmogenic nuclide concentration in river sediments measured at the basin outlets. The results of a mass-balance model suggest that ~60–90% of river sediment in the Kimberley results from the breakdown and chemical weathering of retreating vertical sandstone rock-walls in contrast to sediment generated by bedrock weathering and erosion on the plateau tops. This study emphasises the value of analysing two or more isotopes in basin-scale studies using cosmogenic nuclides, especially in slowly eroding post-orogenic settings. © 2019 John Wiley & Sons, Ltd.  相似文献   

Mercury’s radius change estimates revisited using MESSENGER data     

G. Di Achille  C. Popa  M. Massironi  E. Mazzotta Epifani  M. Zusi  G. Cremonese  P. Palumbo 《Icarus》2012,221(1):456-460

Mapping tectonic features using MESSENGER data mainly acquired at high Sun incidence angle (>50°) reveals previously undetected structures. The analysis of the latter features determines an upward revision of measurements of density and spatial distribution of tectonism and thus of estimates of average contractional strain and planetary radius decrease. We calculated an average surface contraction of ～0.23–0.30% (～0.28% for fault dip angle θ = 30°) within an area corresponding to 21% of the planet. This strain, extrapolated to the entire surface, corresponds to a decrease in radius of about 2.4–3.6 km (～3.0 km for θ = 30°). These values are three–four times higher with respect to previous estimates and are compatible with results from thermomechanical models.  相似文献