The Seismotectonics of the Po Plain (Northern Italy): Tectonic Diversity in a Blind Faulting Domain     

Paola?VannoliEmail author  Pierfrancesco?Burrato  Gianluca?Valensise 《Pure and Applied Geophysics》2015,172(5):1105-1142

We present a systematic and updated overview of a seismotectonic model for the Po Plain (northern Italy). This flat and apparently quiet tectonic domain is, in fact, rather active as it comprises the shortened foreland and foredeep of both the Southern Alps and the Northern Apennines. Assessing its seismic hazard is crucial due to the concentration of population, industrial activities, and critical infrastructures, but it is also complicated because (a) the region is geologically very diverse, and (b) nearly all potential seismogenic faults are buried beneath a thick blanket of Pliocene–Pleistocene sediments, and thus can be investigated only indirectly. Identifying and parameterizing the potential seismogenic faults of the Po Plain requires proper consideration of their depth, geometry, kinematics, earthquake potential and location with respect to the two confronting orogens. To this end, we subdivided them into four main, homogeneous groups. Over the past 15 years we developed new strategies for coping with this diversity, resorting to different data and modeling approaches as required by each individual fault group. The most significant faults occur beneath the thrust fronts of the Ferrara-Romagna and Emilia arcs, which correspond to the most advanced and buried portions of the Northern Apennines and were the locus of the destructive May 2012 earthquake sequence. The largest known Po Plain earthquake, however, occurred on an elusive reactivated fault cutting the Alpine foreland south of Verona. Significant earthquakes are expected to be generated also by a set of transverse structures segmenting the thrust system, and by the deeper ramps of the Apennines thrusts. The new dataset is intended to be included in the next version of the Database of Individual Seismogenic Sources (DISS; http://diss.rm.ingv.it/diss/, version 3.2.0, developed and maintained by INGV) to improve completeness of potential sources for seismic hazard assessment.  相似文献   

Large Earthquakes at the Ibero-Maghrebian Region: Basis for an EEWS     

Elisa?BufornEmail author  Agustín?Udías  Carmen?Pro 《Pure and Applied Geophysics》2015,172(9):2387-2396

Large earthquakes (M_w > 6, I_max > VIII) occur at the Ibero-Maghrebian region, extending from a point (12ºW) southwest of Cape St. Vincent to Tunisia, with different characteristics depending on their location, which cause considerable damage and casualties. Seismic activity at this region is associated with the boundary between the lithospheric plates of Eurasia and Africa, which extends from the Azores Islands to Tunisia. The boundary at Cape St. Vincent, which has a clear oceanic nature in the westernmost part, experiences a transition from an oceanic to a continental boundary, with the interaction of the southern border of the Iberian Peninsula, the northern border of Africa, and the Alboran basin between them, corresponding to a wide area of deformation. Further to the east, the plate boundary recovers its oceanic nature following the northern coast of Algeria and Tunisia. The region has been divided into four zones with different seismic characteristics. From west to east, large earthquake occurrence, focal depth, total seismic moment tensor, and average seismic slip velocities for each zone along the region show the differences in seismic release of deformation. This must be taken into account in developing an EEWS for the region.  相似文献   

Intensity measures for probabilistic assessment of non‐structural components acceleration demand          下载免费PDF全文

Marco De Biasio  Stephane Grange  Frederic Dufour  Frederic Allain  Ilie Petre‐Lazar 《地震工程与结构动力学》2015,44(13):2261-2280

A fundamental issue in the framework of seismic probabilistic risk analysis is the choice of ground motion intensity measures (IMs). Based on the floor response spectrum method, the present contribution focuses on the ability of IMs to predict non‐structural components (NSCs) horizontal acceleration demand. A large panel of IMs is examined and a new IM, namely equipment relative average spectral acceleration (E‐ASA_R), is proposed for the purpose of NSCs acceleration demand prediction. The IMs efficiency and sufficiency comparisons are based on (i) the use of a large dataset of recorded earthquake ground motions; (ii) numerical analyses performed on three‐dimensional numerical models, representing actual structural wall and frame buildings; and (iii) systematic statistical analysis of the results. From the comparative study, the herein introduced E‐ASA_R shows high efficiency with respect to the estimation of maximum floor response spectra ordinates. Such efficiency is particularly remarkable in the case of structural wall buildings. Besides, the sufficiency and the simple formulation allowing the use of existing ground motion prediction models make the E‐ASA_R a promising IMs for seismic probabilistic risk assessment. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Towards a predictive model to assess the natural position of the Posidonia oceanica seagrass meadows upper limit     

Matteo Vacchi  Monica Montefalcone  Chiara F. Schiaffino  Valeriano Parravicini  Carlo Nike Bianchi  Carla Morri  Marco Ferrari 《Marine pollution bulletin》2014

The upper portion of the meadows of the protected Mediterranean seagrass Posidonia oceanica occurs in the region of the seafloor mostly affected by surf-related effects. Evaluation of its status is part of monitoring programs, but proper conclusions are difficult to draw due to the lack of definite reference conditions. Comparing the position of the meadow upper limit with the beach morphodynamics (i.e. the distinctive type of beach produced by topography and wave climate) provided evidence that the natural landwards extension of meadows can be predicted. An innovative model was therefore developed in order to locate the region of the seafloor where the meadow upper limit should lie in natural conditions (i.e. those governed only by hydrodynamics, in absence of significant anthropogenic impact). This predictive model was validated in additional sites, which showed perfect agreement between predictions and observations. This makes the model a valuable tool for coastal management.  相似文献   

An Overview of the 28 October 2012 M<Subscript>w</Subscript> 7.7 Earthquake in Haida Gwaii,Canada: A Tsunamigenic Thrust Event Along a Predominantly Strike-Slip Margin     

John?F.?CassidyEmail author  Garry?C.?Rogers  Roy?D.?Hyndman 《Pure and Applied Geophysics》2014,171(12):3457-3465

The boundary between the Pacific and North America plates along Canada’s west coast is one of the most seismically active regions of Canada, and is where Canada’s two largest instrumentally recorded earthquakes have occurred. Although this is a predominantly strike-slip transform fault boundary, there is a component of oblique convergence between the Pacific and North America plates off Haida Gwaii. The 2012 M_w 7.7 Haida Gwaii earthquake was a thrust event that generated a tsunami with significant run up of over 7 m in several inlets on the west coast of Moresby Island (several over 6 m, with a maximum of 13 m). Damage from this earthquake and tsunami was minor due to the lack of population and vulnerable structures on this coast.  相似文献   

Impact of Three-Parameter Weibull Models in Probabilistic Assessment of Earthquake Hazards     

Sumanta?PasariEmail author  Onkar?Dikshit 《Pure and Applied Geophysics》2014,171(7):1251-1281

This paper investigates the suitability of a three-parameter (scale, shape, and location) Weibull distribution in probabilistic assessment of earthquake hazards. The performance is also compared with two other popular models from same Weibull family, namely the two-parameter Weibull model and the inverse Weibull model. A complete and homogeneous earthquake catalog (Yadav et al. in Pure Appl Geophys 167:1331–1342, 2010) of 20 events (M ≥ 7.0), spanning the period 1846 to 1995 from north–east India and its surrounding region (20°–32°N and 87°–100°E), is used to perform this study. The model parameters are initially estimated from graphical plots and later confirmed from statistical estimations such as maximum likelihood estimation (MLE) and method of moments (MoM). The asymptotic variance–covariance matrix for the MLE estimated parameters is further calculated on the basis of the Fisher information matrix (FIM). The model suitability is appraised using different statistical goodness-of-fit tests. For the study area, the estimated conditional probability for an earthquake within a decade comes out to be very high (≥0.90) for an elapsed time of 18 years (i.e., 2013). The study also reveals that the use of location parameter provides more flexibility to the three-parameter Weibull model in comparison to the two-parameter Weibull model. Therefore, it is suggested that three-parameter Weibull model has high importance in empirical modeling of earthquake recurrence and seismic hazard assessment.  相似文献   

Volcanological evolution of the Rivi–Capo Volcanic Complex at Salina,Aeolian Islands: magma storage processes and ascent dynamics     

Eugenio Nicotra  Marco Viccaro  Rosanna De Rosa  Marco Sapienza 《Bulletin of Volcanology》2014,76(8):1-24

Critical to understanding explosive eruptions is establishing how accurately representative pyroclasts are of processes during magma vesiculation and fragmentation. Here, we present data on densities, and vesicle size and number characteristics, for representative pyroclasts from six silicic eruptions of contrasting size and style from Raoul volcano (Kermadec arc). We use these data to evaluate histories of bubble nucleation, coalescence, and growth in explosive eruptions and to provide comparisons with pumiceous dome carapace material. Density/vesicularity distributions show a scarcity of pyroclasts with ～65–75 % vesicularity; however, pyroclasts closest to this vesicularity range have the highest bubble number density (BND) values regardless of eruptive intensity or style. Clasts with vesicularities greater than this 65–75 % “pivotal” vesicularity range have decreasing BNDs with increasing vesicularities, interpreted to reflect continuing bubble growth and coalescence. Clasts with vesicularities less than the pivotal range have BNDs that decrease with decreasing vesicularity and preserve textures indicative of processes such as stalling and open system degassing prior to vesiculation in a microlite-rich magma, or vesiculation during slow ascent of degassing magma. Bubble size distributions (BSDs) and BNDs show variations consistent with 65–75 % representing the vesicularity at which vesiculating magma is most likely to undergo fragmentation, consistent with the closest packing of spheres. We consider that the observed vesicularity range may reflect the development of permeability in the magma through shearing as it flows through the conduit. These processes can act in concert with multiple nucleation events, generating a situation of heterogeneous bubble populations that permit some regions of the magma to expand and bubbles to coalesce with other regions in which permeable networks are formed. Fragmentation preserves the range in vesicularity seen as well as any post-fragmentation/pre-quenching expansion which may have occurred. We demonstrate that differing density pyroclasts from a single eruption interval can have widely varying BND values corresponding to the degree of bubble maturation that has occurred. The modal density clasts (the usual targets for vesicularity studies) have likely undergone some degree of bubble maturation and are therefore may not be representative of the magma at the onset of fragmentation.  相似文献   

Benthic respiration and stoichiometry of regenerated nutrients in lake sediments with Dreissena polymorpha     

Tomas Ruginis  Marco Bartoli  Jolita Petkuviene  Mindaugas Zilius  Irma Lubiene  Alex Laini  Arturas Razinkovas-Baziukas 《Aquatic Sciences - Research Across Boundaries》2014,76(3):405-417

The effect of patchy colonies of the invasive zebra mussel (Dreissena polymorpha) on sedimentary processes was investigated in a mesotrophic lake (Plateliai Lake, Lithuania). Benthic fluxes of O₂, TCO₂, CH₄, Mn²⁺, Fe²⁺, N₂, the inorganic forms of N, Si and P and dissolved organic C and N were quantified by dark incubations of sediments cores, with and without D. polymorpha. Individual mussels also were incubated for metabolic measurements. Sediments with D. polymorpha had significantly higher O₂ and TCO₂ fluxes and displayed higher rates of denitrification. The presence of mussels also resulted in higher regeneration of P and N (mostly as ammonium) while the effect on Si was not significant. However, likely due to the low zebra mussel biomass (57.2 ± 25.3 g_SFDW m^?2), biodeposition has not changed the ratio between anaerobic and total respiration. Methane and reduced metals fluxes were in fact similar in the presence and absence of D. polymorpha. Incubations of mussels without sediments confirmed that bivalve metabolism was the main driver of benthic respiration and nutrient recycling. Nitrate production suggested the presence of nitrifiers associated with the molluscs. The main outcome of this study was that zebra mussels alter the quantity and the stoichiometry of nutrients regenerated by the benthic compartment. The enhancement of nitrogen loss via denitrification, by a factor of 1.5, was much less pronounced than the increase in ammonium recycling rate, stimulated by a factor of 33. Negligible PO₄ ^3? fluxes in bare sediments (?3.4 ± 6.8 μmol m^?2 h^?1) increased in the presence of mussels and considerable amounts of this nutrient (69.6 ± 29.4 μmol m^?2 h^?1) were mobilized to the water column. Further research should address other nutrient sources to the lake to verify whether altered rates and stoichiometry of benthic regeneration can affect primary producer community composition and activity.  相似文献   

Urbanization effects on shoreline phytobenthos: a multiscale approach at lake extent     

Daniel Spitale  Alessia Scalfi  Marco Cantonati 《Aquatic Sciences - Research Across Boundaries》2014,76(1):17-28

To understand how littoral biota respond to anthropogenic disturbances, limnologists seek to detect the scale at which patterns and processes occur. We conducted an extensive study on the shoreline phytobenthos of Lake Garda (Italy) with the following main objectives: (i) to examine the importance of urbanization for species distribution within a set of hierarchical spatial scales (10¹–10⁴ m), and then (ii) to test the spatio-temporal interactions on a reduced set of scales (10¹–10² m, and 10¹–10² days). Results showed that most of the variation in most abundant species and habitat characteristics occurred at the spatial scale of 10¹–10² m. Species richness was positively related with microheterogeneity, but the relationship occurred only at low urbanization and not at highly-urbanized sites where artificial shores were less heterogeneous. The similarity of species assemblages was regulated by two interacting processes, one operating at a fine spatial scale (10² m), reflecting the physical-habitat requirements of the species, and the other one operating at a broader scale (10⁴ m) in relation to the N–S nitrogen gradient. Overall, time explained 73 % of the total variation of species assemblages, space 7 %, and 20 % was explained by the interaction between space and time (the patch scale, 10s of m, and area scale, 100s of m, interacted with the finest temporal scale, 10s of days). This interaction might be explained by the process of species recruitment operating at different rates at the two spatial scales. Since the largest variation in species assemblages was at the temporal scale (due to the seasonal succession of phytobenthos), we recommend collecting at least one sample per season when monitoring littoral habitats.  相似文献   

地震波在孔隙介质中低频衰减现象的粘弹性特征分析及近似（英文）     

凌云  韩立国  张益明 《应用地球物理》2014,11(4):355-363

由于介观尺度的孔隙流体流动,弹性波传播过孔隙岩层时在地震频段表现出较强的频散和衰减。Johnson理论给出了在任意孔隙形状的条件下,部分气水饱和孔隙介质的理论相速度和品质因子的解析解。本文在Johnson模型的基础上,通过对Q值曲线的低频和高频近似,推导了Q值曲线的近似公式,以及基于孔隙介质基本地球物理参数和孔隙斑块几何形态参数T和比表面积S/V的最大衰减Qmin近似公式。通过与理论值的对比,对Qmin近似公式存在的线性误差进行改正,进一步提高了精度。复杂的斑块形态对最大衰减Qmin和过渡频率ftr的都产生一定影响,且对ftr影响更大。因为数值模拟直接求解介观尺度的Biot孔隙介质方程需要极大的计算量,我们使用Zener模型建立了等效粘弹模型,有效地模拟了地震频带内的衰减和频散现象。  相似文献