Mihail Iancovici

Fore-Arc and Back-Arc Ground Motion Prediction Model for Vrancea Intermediate Depth Seismic Source

A next generation ground motion model for the prediction of spectral accelerations both in the fore-arc and back-arc regions of the Carpathians Mountains is developed in this research for the Vrancea intermediate depth seismic source in Romania. This ground motion prediction equation (GMPE) is an updated version of the model given in Vacareanu et al. [2014] and is applicable in both the fore-arc and the back-arc regions. The strong ground motion database from which the prediction model is derived consists of over 700 triaxial accelerograms from Vrancea subcrustal seismic events, as well as from other intermediate-depth earthquakes produced in other seismically active regions in the world. The applicability of this ground motion prediction model in both the fore-arc and the back-arc region is tested using the analysis of residuals. Moreover, the appropriateness of this GMPE for soil classes B and C defined in EN 1998-1, as well as for average soil conditions is investigated. All results suggest that this model is an improvement of the previous versions of ground motion prediction equations for Vrancea intermediate-depth seismic source and its use in both the fore-arc and the back-arc regions make it a reliable candidate for more accurate seismic hazard studies of Romania.

Spectral Characteristics of Strong Ground Motions from Intermediate‐Depth Vrancea Seismic Source

Abstract This study focuses on the investigation of spectral characteristics of ground motions recorded from intermediate‐depth Vrancea earthquakes using Newmark–Hall‐type response spectrum. The database consists of more than 700 horizontal components recorded during 10 Vrancea earthquakes. In the first step of the analysis, the component‐to‐component variability is assessed and the corresponding influence of various parameters (earthquake magnitude, peak ground acceleration, soil class, position of the seismic station, or instrument type) is evaluated. Subsequently, the correlation between the spectral acceleration and the values of the peak ground motion parameters (acceleration, velocity, and displacement) is investigated. The analyses reveal an important influence of the magnitude and a significant influence of the soil class (in the case of large magnitude earthquakes) on the results. These findings are validated through the use of the analysis of variance (ANOVA) method. The computed response amplification factors for the Newmark–Hall type spectrum are similar with those from other studies in the literature. Finally, a check of three control periods such as T B , T E , and T F of the Newmark–Hall‐type spectrum yields results somewhat different from the ones given in the Romanian seismic design code P100‐1 or in Eurocode 8.

Investigation of the variability of strong ground motions from Vrancea earthquakes

A systematic investigation of the applicability of several ground motion prediction models for Vrancea intermediate-depth seismic source is conducted in this research. Two ground motion prediction models recommended by previous evaluations (Vacareanu et al. in Bull Earthq Eng 11(6):1867–1884, 2013a; Pavel et al. in Earthq Struct 6(1):1–18, 2014), as well as two new state-of-the-art ground motion prediction equations (Vacareanu et al. in J Earthq Eng, 2013b; Earthq Struct 6(2):141–161, 2014) are tested using an increased strong ground motion database consisting of 150 recordings from Vrancea subcrustal earthquakes. The evaluation is performed by using several goodness-of-fit parameters from the literature. Moreover, the applicability of the single-station sigma method is also investigated by using the same strong ground motion database recorded in 30 seismic stations from southern and eastern Romania. The influence of the soil conditions on the numerical results obtained in this study is investigated and discussed using the results provided by the analysis of variance method. The impact of the single-station standard deviation on the levels of seismic hazard is also assessed in this study, and the results show, in the analyzed cases, significant reductions of the hazard levels.

Seismic Risk Assessment of Romania

This paper summarizes the UTCB results for the “National Risk Assessment—RO RISK” project. Within the RO-RISK project, coordinated by the General Inspectorate for Emergency Situations, the first nation-wide assessment of all types of natural risks was performed in 2016. The work was supported by collaboration of disaster reduction experts and earthquake risk modelling specialists from INFP and URBAN-INCERC. The seismic risk assessment was performed for the entire country, at the most detailed resolution available, which is the administrative-territorial unit. For each building typology, four limit states were considered in order to generate fragility curves. Each limit state is associated with a loss percentage, in order to generate vulnerability curves. The assessment shows that among the 10 analysed hazards, the seismic hazard produces the largest impact at country level, 75% of the population and 45% of the vital networks are exposed to moderate and high earthquake risk and Romania’s capital Bucharest, is highly exposed to earthquakes.

Static and Dynamic Approaches on the Low-Rise RC Frames Capacity Evaluation and Damage Quantification

The seismic capacity evaluation is a key-tool for practitioners in the standard post-design stage of building structures. This also serves as a major component for performing higher level analysis modules as seismic vulnerability analysis, risk analysis, loss estimation and resilience analysis. The seismic capacity of a structure is dependent of the applied load pattern as well as of nonlinear modelling of members. The paper examines the dependency of capacity curve parameters of typical low-rise regular reinforced concrete frames as a large proportion from actual building stock in Bucharest, using both nonlinear static and dynamic analysis approaches as well as discrete and distributed available plasticity models for reinforced concrete members. The sensitivity analysis of global seismic damage index based on the probabilistic approach using HAZUS methodology (2007) is then performed. A more accurate prediction of structural capacity in conjunction with integrated tools for the assessment of the damage states up to progressive collapse associated to various earthquake scenarios and time-domain analysis approach would truly lead implementing a real performance-based seismic design into practice.

Overview of Part IV: Seismic Evaluation and Rehabilitation. Seismic Risk Assessment

This chapter includes papers that deal with the seismic evaluation and rehabilitation of existing buildings in Romania and neighbouring countries- e.g. Republic of Moldova, using both fundamental and cutting-edge approaches.

Selecting and Scaling Strong Ground Motion Records Based on Conditional Mean Spectra. Case Study for Iasi City in Romania

The Conditional Mean Spectrum (CMS) represents one of the versatile tools for selecting and scaling the strong ground motion records for a particular site. The procedure to obtain the Conditional Mean Spectrum (CMS) presented in Baker (2011) is applied for Iasi City in N-E Romania, the second largest Romanian city in terms of seismic risk. The major seismic hazard for most of Romanian territory is dominated by the Vrancea intermediate-depth seismic source. The ground motion prediction model, proposed in Vacareanu et al. (2015) for intermediate-depth earthquakes, is used for the computation of Uniform Hazard Spectrum (UHS) and the Conditional Mean Spectrum (CMS) at a vibration period of T = 1.0 s in Iasi City. The spectral period of 1.0 s is considered to be representative for the new stock of residential and office RC buildings in Romania. Disaggregation of seismic hazard is performed in order to determine mean causal values of magnitude, source-to-site-distance and epsilon. Empirical correlations between epsilon values at different vibration periods are calculated using a set of strong ground motions recorded during ten intermediate-depth Vrancea earthquakes. Moreover, based on the empirical values of the correlation coefficients, corresponding predictive relations are developed specifically for strong ground motions generated by Vrancea intermediate-depth earthquakes. Record selection and scaling based on the criteria proposed by Baker and Cornell (2006) and Baker (2011) is performed for Iasi City using a database consisting of strong ground motions recorded during Vrancea intermediate-depth earthquakes with moment magnitude larger than 6.0.