SEISMIC HAZARD ASSESSMENT IN FLORENCE CITY ITALY

A seismic hazard analysis of Florence city was performed in the frame of a project concerning the dynamic behaviour of cable-stayed bridges. Both a probabilistic approach and a methodology based on the use of a local macroseismic catalogue were applied. A local catalogue was expressly compiled for this purpose, to collect the macroseismic intensities actually observed at the site as a result of past earthquakes. This sort of catalogue is an independent tool to verify the assumptions of the probabilistic approach (seismic zoning, earthquake recurrence relation, attenuation model), though it can supply results in terms of macroseismic intensity only and reflects the effective seismic history at the site, without taking into account any variability. The Cornell' methodology was used to assess probabilistic hazard in terms of macroseismic intensity, peak ground acceleration, peak ground velocity, and pseudovelocity uniform response spectra. The local catalogue points out level VII of the Mercalli-Cancani-Sieberg scale (MCS) as the maximum intensity historically observed in Florence. The probabilistic approach leads to the consideration of intensity VIII MCS as the maximum credible for the city. The probabilistic analysis in terms of ground motion was performed using attenuation relations estimated for alluvium sites, since the geology of Florence area is represented by fluvial and lacustrine deposits of various thickness. Peak ground acceleration values with 90% non exceedence probability in 50 and 500 years are respectively 145 and 219 cm/s's for a shallow alluvium site, and 95 and 157 cm/s's for a deep alluvium site; the corresponding peak ground velocity values for sites located on alluvium are 6.41 and 11.76 cm/s. Uniform response spectra are provided for shallow and deep alluvium sites, according to frequency-dependent attenuation relations estimated from strong Italian earthquakes.     

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.     

MODELLING OF THE GROUND MOTION AT RUSSE SITE (NE BULGARIA) DUE TO THE VRANCEA EARTHQUAKES

An approach, capable of synthesising strong ground motion from a basic understanding of fault mechanism and of seismic wave propagation in the Earth, is applied to model the seismic input at a set of 25 sites along a chosen profile at Russe, NE Bulgaria, due to two intermediate-depth Vrancea events (August 30, 1986, M _ω=7.2, and May 30, 1990, M _ω=6.9). Accordingly to our results, once a strong ground motion parameter has been selected to characterise the ground motion, it is necessary to investigate the relationships between its values and the features of the earthquake source, the path to the site and the nature of the site. Therefore, a proper seismic hazard assessment requires an appro-priate parametric study to define the different ground shaking scenarios corresponding to the relevant seismogenic zones affecting the given site. Site response assessment is provided simultaneously in frequency and space domains, and thus the applied procedure differs from the traditional engineering approach that discusses the site as a single point. The applied procedure can be efficiently used to estimate the ground motion for different purposes like microzonation, urban planning, retrofitting or insurance of the built environment.     

Seismic Hazard Analysis Using Discrete Faults in Northwestern Pakistan: Part II – Results of Seismic Hazard Analysis

This article is the second of two companion articles that evaluate seismic hazard in northwestern (NW) Pakistan. Using the properties and characteristics of discrete faults in NW Pakistan described in the first article, probabilistic and deterministic seismic hazard analyses for 11 major cities in NW Pakistan were conducted. The results from both probabilistic and deterministic seismic hazard analyses exhibit good agreement. Median deterministic spectra compare favorably with uniform hazard spectra (UHS) for 475- or 975-year return periods, while the 84^th-percentile deterministic spectra compare favorably with the UHS for a 2475-year return period. Peak ground accelerations (PGAs) for 2475-year return periods exceed 1.0 g for the cities of Kaghan and Muzaffarabad, which are surrounded by major faults. The PGAs for a 475-year return period for these cities are approximately 0.6g — 3 to 4 times greater than estimates by previous studies using diffuse areal source zones. The PGAs for some cities located farther from faults (including Astor, Malakand, Mangla, Peshawar, and Talagang) are similar to those predicted using diffuse areal source zones. Seismic hazard maps for PGA and spectral accelerations at periods of 0.2 s and 1.0 s corresponding to three return period (2475, 975, and 475 years) were produced. Based on deaggregation results, a discussion of the conditional mean spectra for engineering applications is presented.     

PSHA for Broad-Band Strong Ground-Motion Hazards in the Saronikos Gulf,Greece, from Potential Earthquake with Synthetic Ground Motions

We perform a probabilistic seismic hazard analysis (PSHA) for broad-band strong ground motion within the Saronikos Gulf region, Greece, from potential earthquakes along the 30 km long Aigina fault in the northern part of the Gulf. We perform the PSHA utilizing empirical Green’s functions (EGFs) merged with synthetic Green’s functions (SGFs) along with models of finite rupture in place of standard “attenuation relations.” Our approach considers all significant magnitudes for PSHA and full broadband ground motion simulations. Calculations are source and site specific, and could reduce uncertainties in estimating standard engineering parameters. We use a range of rupture scenarios for all significant magnitude earthquakes along the fault. The hazard calculation is for frequencies 0.0– 15.0 Hz. Recordings of small earthquakes from an onshore/offshore local seismic array were used as EGFs for frequencies of 1.5–15.0 Hz, the finite difference code E3D was utilized to synthesize SGFs for frequencies 0.0–1.5 Hz, and an algorithm for merging the EGFs with SGFs was developed. The full-waveform calculations are important for non-linear dynamic analysis of structures in the coastal zone and potential hazard to long period structures. Results of proposed PSHA identify 2%, 10%, and 50% hazard at the selected sites of Saronikos Gulf.

Finally, we compare our PSHA results to those obtained by standard practice which involves prediction equations (GMPEs) recently developed in the Next Generation Attenuation (NGA) project and empirical predictive attenuation relations proposed for Greece. We believe that differences with the NGA results are due to site- and source-specific information utilized in this study, and incorporation of this information may significantly reduce the uncertainty in seismic hazard calculations.     

SEISMIC HAZARD IN GREECE BASED ON DIFFERENT STRONG GROUND MOTION PARAMETERS

The available Greek strong ground motion records to date are used in order to study the duration of strong-motion in Greece, covering magnitudes between 4.5 and 6.9 and distances from 1 km to 128 km. An attenuation relation of strong-motion duration is calculated and compared to earlier existing similar relations proposed for Greece and Japan. Furthermore, the seismic hazard for the area of Greece is assessed, using the strong-motion parameters of duration and peak ground acceleration. The results are presented in the form of a map according to which Greece is classified in four different categories of equal seismic hazard.     

An Applied Method for General Regional Seismic Loss Assessment—With A Case Study in Los Angeles County

We describe the formulation and application of an integrated general regional seismic loss assessment (RSLA) method for buildings in seismic regions. An efficient method for RSLA is valuable for engineers involved in city planning, risk management, and insurance dealings. In contrast to previously reported methods, the framework presented herein is hazard-based and utilizes a regional rapid seismic hazard deaggregation tool that allows regional assessment to be conducted more efficiently. The proposed technique is implemented as an example to assess general regional seismic loss in Los Angeles County for a ground motion hazard with 10% probability of exceedance in 50 years.     

GROUND MOTION ANALYSIS IN THE ANCHORAGE BASIN: 1-D APPROACH

Understanding the dynamic behaviour of soil in the Anchorage basin in southcentral Alaska is essential for seismic hazard assessment of this highly seismically active region. The analysis of site responses for 40 sites from weak-motion and strong-motion data with amplitudes less than 0.1 g showed a strong influence of subsurface geological conditions on the characteristics of ground motion. Particularly, the sites in the central part of the city, including the downtown area, showed prominent resonance peaks around 1 Hz with amplification values up to about 4. The numerical analysis, based on one-dimensional multi-layer soil models shows that site response characteristics, and especially aforementioned peaks, are largely related to the thick, soft layer of Quaternary deposits, particularly cohesive fades of Bootlegger Cove Formation. The computed transfer functions for soil profiles of six representative sites are in accord with the site responses in the frequency range from 1 to 5 Hz. There is no significant change in amplification values below 2 Hz corresponding to large-amplitude (up to 0.38 g) ground motions; however, above 2-3 Hz the amplification values are greatly reduced in this case.     

Technical Note: Practical Challenges Facing the Selection of Conditional Spectrum-Compatible Accelerograms

There are various possibilities for the selection and scaling of ground motions for advanced seismic assessment of buildings using nonlinear response-history analyses. As part of an on-going project looking at building-specific loss assessment in Italy, this article highlights a number of challenges currently facing the use of conditional spectra for ground motion selection in practice, essentially related to the limited amount of seismic hazard information that is publicly available. To illustrate the points being made, the challenges faced when trying to develop conditional spectra and select spectrum-compatible accelerograms for a rock site in Napoli, Italy, are described and the seismic assessment results obtained for a number of reinforced concrete wall structures are presented. Aside from providing practitioners with an appreciation of the potential difficulty associated with using conditional spectra for record selection, this technical note should also motivate national authorities to provide more background information on national seismic hazard data and detailed guidance for record selection.     

A Ground Motion Record Selection Approach Based on Multiobjective Optimization

The evaluation of the seismic safety and reliability of buildings and building contents within a probabilistic framework often requires response history analyses using site-specific ground motion records. The ground motion selection method proposed in this paper addresses this issue by a stochastic search procedure in which record sets are selected such that first- and second-order statistics (median and dispersion) satisfy predefined ground motion spectrum targets over a wide period range. Once a ground motion record set is selected, it can be used for seismic assessment of a broad class of buildings within the target period range at the given location.     

A Seismic Hazard Study through the Comparison of Ground Motion Prediction Equations Using the Weighting Factor of Logic Tree

Toward the assistance on selection of ground motion prediction models for seismic assessment, this article presents a seismic hazard study (compared to the viewpoint of attenuation equations), using a recent tool based on engineering judgment, called “weighting factor,” through a procedure similar to logic tree. For this purpose, the weighting factors were incorporated with a Venn diagram of attenuation models regarding experimenter’s concern and expert’s knowledge. It is found that the attenuation equations of the newer and intersection ones could be considered to estimate plausible and reasonable accelerations. The results indicate that the weighting factors could beneficially assist for suitability of attenuation models. This work is a novel for the region (Gaziantep, Turkey), thus it could complement expert’s knowledge about the attenuation models for future studies.     

SEISMIC HAZARD ASSESSMENT OF UNITED ARAB EMIRATES AND ITS SURROUNDINGS

This paper presents the seismic hazard assessment and seismic zoning of the United Arab Emirates (UAE) and its surroundings based on the probabilistic approach. The area that has been studied lies between 50°E-60°E and 20°N-30°N and spans several Gulf countries. First, the tectonics of the area and its surroundings is reviewed. An updated catalogue, containing both historical and instrumental events is used. Seismic source regions are modelled and relationships between earthquake magnitude and earthquake frequency is established. A modified attenuation relation for Zagros region is adopted. Seismic hazard assessment is then carried out for 20 km interval grid points. Seismic hazard maps of the studied area based on probable Peak Ground Acceleration (PGA) for 10% probability of exceedance for time-spans of 50, 100 and 200 years are shown. A seismic zone map is also shown for a 475-year return period. Although the results of the seismic hazard assessment indicated that UAE has moderate to low seismic hazard levels, nevertheless high seismic activities in the northern part of UAE warrant attention. The northern Emirates region is the most seismically active part of UAE. The PGA on bedrock in this region ranges between 0.22 g for a return period of 475 years to 0.38 g for a return period of 1900 years. This magnitude of PGA, together with amplification from local site effect, can cause structural damage to key structures and lifeline systems.     

MICROZONATION OF THE EXPECTED SEISMIC SITE EFFECTS ACROSS PORT VILA,VANUATU

The city of Port Vila, Vanuatu, is located in one of the most active seismic regions on earth. Earthquakes are felt frequently and, due to very rapid plate convergence rates, return period of large earthquakes (M>6) in the New Hebrides Benioff zone can be less than 10 years. Even though Port Vila does not lie on an identified seismic fault zone, strong motions by nearby earthquakes have to be expected due to the city's geographical location close to the plate boundary of New Hebrides convergence zone. An accurate estimation of the seismic ground motion across the city is of prime importance for urban developments and mitigation of earthquake risk. Following many examples of monitored strong earthquakes in the current century, it is evident that the local site effects may have a dominant contribution to the intensity of damage and destruction. In this study we focussed on the first stage of associating site effects and seismic hazard by preparing a microzonation map for Port Vila. The seismic microzonation of the city has been carried out to provide a detailed map of the zones that exhibit site effects in terms of resonance frequencies and approximated amplification of the ground shaking. Having in mind that these data will be used in improving building design to sustain strong ground motions, our analysis is limited to the frequency band of 1–10 Hz, corresponding to the expected resonance of different types of buildings in Port Vila. The Nakamura technique has been used to estimate site amplification effects from single station noise recordings. Interestingly, excluding one site located on an old dump zone, the amplification factors at about the 100 sites surveyed in Port Vila remain below 3 with an average well below 2 in the 1 to 10 Hz frequency band. These results suggest that there is no significant Vs velocity change in consequently layered material and that the uppermost sedimentary layers in the surveyed down town area are relatively thin. These observations are in agreement with the mapping of limestone terraces throughout Port Vila area. However, both the surface geology and results from seismic zonation indicate a thicker (up to several tens of meters) sedimentary cover around the Bauerfield airport and in the Mele terrace zone. Low resonance frequencies (around and below 1 Hz) and amplification factor of the order of 5 were observed over this large area, immediately outside Port Vila. Any building development in this area should take these results into account.     

EXPERIMENTAL STUDY OF TOPOGRAPHIC AMPLIFICATION USING THE ISRAEL SEISMIC NETWORK

Earthquakes and microtremor records are used for estimating the site response of hard rock sites comprising four three-component seismic stations which operate as part of the Israel Seismic Network. The response functions are determined by implementing the horizontal-to-vertical component spectral ratio of earthquake shear-waves (receiver function estimates) and microtremors (Nakamura's estimate) observed simultaneously at the site. The sites of seismic stations ATZ (Mt. Atzmon), MBH (Mt. Berech) and MRNI (Mt. Meron) exhibit amplification attributed to topography effects. At ATZ, within the 1.3–2.0 Hz range, the amplification is in the order of factor 4. At MBH amplification levels of 3.0–3.5 are observed in the frequency range 1.5–4.0 Hz. Station MRNI exhibits a relatively strong amplification effect (up to 4) in the frequency range of about 2.5 to 3.5 Hz. Slight amplification around 5 Hz is observed at ATR (the proposed site for a nuclear power plant). These effects were correlated with the thickness of the weathered layer above unweathered chalk. A comparison between the amplification factor observed during earthquakes and those inferred from microtremors shows that these are, in general, in agreement. However, details of the spectral ratios from different microtremor recordings are not exactly the same. Differences appear mainly in the frequency at which the maximum amplification occurs. These observations demonstrate the usefulness of non-reference technique in estimating the topographical effects of ground shaking. These methods may be used in the process of seismic hazard assessment for ridges and mountain tops, common sites for settlements, communication relay stations, bridges, rope-drive and power transmission towers.     

Comparing expeditious procedures for the seismic vulnerability assessment on the European territorial context: reliability,feasibility, cost,and time consumption

ABSTRACT

The definition of strategies for the preservation and protection of cultural heritage is a topical issue, especially in view of the increasing relevance of the theme of seismic risk mitigation and reduction.

The prediction of the impact an earthquake could have on existing buildings requires the knowledge of their dynamic behaviour. The procedure to be adopted for this purpose is quite complex and onerous in terms of costs, time, and implementation, especially when the study concerns territorial areas rather than single buildings. The definition of methodologies aimed at respecting the principles of economic sustainability and preserving human life and architectural heritage is of paramount importance to assess seismic vulnerability using available resources. Rapid methods for the seismic vulnerability assessment, aimed at defining buildings vulnerability and intervention priority lists, must be implemented to guarantee the preservation of historical centers.

This article describes the application to some case studies of different methods aimed at creating fragility curves for the vulnerability assessment on the European territorial context. The comparison between a deterministic approach and a new probabilistic one is performed for all case studies, to define the most suitable methodology in terms of reliability and savings in cost and time.     

Predicting Probabilistic-Based Strong Ground Motion Time Series for Citadel of Arg-E-Bam (South-East of Iran)

The main objective of this article is to present a probabilistic-based strong motion compatible with the source-path and site soil condition given the probability of exceedence for citadel of Arg-e-Bam site bed rock (South-East of Iran). A Fourier amplitude spectral attenuation relation for bed rock beneath the site is proposed which permits the estimation of time-histories through a probabilistic seismic hazard analysis procedure. Due to lack of data, the two well-known simulation techniques, point source and finite fault models have been used for generating hundreds of strong motion as input data. Tens of model parameter values such as stress-drop nucleation points were used, in each specified magnitude-distance, to reduce the uncertainty effects inherently existing in seismological/geological parameters. The proposed attenuation relation is validated by comparing the estimated strong motion, in the form of Fourier amplitude spectral, using the proposed attenuation relation with those of recorded ground motion data at three stations far away from the assumed source so that the results would not be influenced by the near source problems such as directivity and fling step. The results of proposed technique is assessed by comparing the estimated response spectra, with 10% probability of exceedence and 5% damping ratio, with those of traditional uniform hazard spectra. The proposed technique is supposed to be used in retrofitting procedure of international historical adobe structures in Arg-e-Bam site, which have been damaged during the destructive Bam earthquake 2003, Iran     

Seismic Vulnerability of Historical Masonry Aggregate Buildings in Oriental Sicily

ABSTRACT

The seismic vulnerability assessment of historical UnReinforced Masonry (URM) buildings is a very complex task since it is strongly related to a great variety both of geometrical layouts and of masonry mechanical characteristics. In this article, some results of a Catania University research project, denomined “FIR 2014”, focused on the seismic vulnerability estimation of historical buildings, built in Catania after the 1963 earthquake, are presented. First, a detailed typological analysis of the considered urban fabric, characterized by typical residential masonry buildings, has been performed. Such analysis allowed recognizing an elementary structural modulus, which has been studied according to different geometrical layouts representative of isolated or aggregate buildings. The results of nonlinear static analyses, performed by applying an innovative macro-element approach, allowed for the assessment the seismic vulnerability of typical URM buildings coherently to the Italian seismic code. The adopted macro-element strategy for the seismic assessment of aggregate masonry buildings, although related to a specific historical center, may be applied to similar urban fabrics and can also be used for the calibration and validation of fast seismic assessment strategies, particularly useful for the evaluation of the seismic risk at urban scale.     

ATTENUATION RELATION FOR WEST EURASIA DETERMINED WITH RECENT NEAR-FAULT RECORDS FROM CALIFORNIA,JAPAN AND TURKEY

Strong ground motion close to a fault can be expected to be very large, so its estimation is essential for human safetv. Although a few strong-motion data exist for the west Eurasian region, we proposed in a previous work [Berge-Thierry et al., 2003] an attenuation relation for spectral acceleration using strong-motion data recorded in west Eurasia (mainly in Europe) and some in the western United States: this relationship was derived for the French Safety Rule, which is applied for seismic hazard assessment at nuclear power plants. In this study, we propose a constraining of the amplitude saturation term related to the proximity of the fault, and an adding of an amplitude saturation term in the regression model. We add, to the data-set previously used to derive the west Eurasian attenuation relationship strong-motions recorded during recent large earth-quakes: the 1995 Hyogo-ken Nanbu (Kobe) event in Japan and the 1999 Kocaeli (Izmit) event in Turkey. The regression analysis, adopted from Fukushima and Tanaka [1990], is non-linear, so an iterative procedure is applied. The determined regression coefficients lead to a prediction of a peak ground acceleration of about 0.7 g for soil site conditions at a fault distance of 0.5 km. The Q coefficient deduced, from the distance coefficient is in agreement with scattering Q models. The introduction of the saturation term leads to significantly lower predictions of average spectral accelerations at short distances as compared with using the Berge-Thierry et al. [2003] empirical model.     

TUNING OF SEISMIC HAZARD ESTIMATES BY MEANS OF OBSERVED SITE INTENSITIES

Probabilistic seismic hazard is usually assessed by means of computer codes using seis-mogenic sources, parametric catalogues, seismicity rates and attenuation relationships. All these ingredients are conditioned by expert judgement that influences the final results. Even the attenuation relationships, though strictly based on experimental data, are considered a weak point due to the difficulty of modelling the interaction between seismic energy radiation and site response, and because earthquakes do not usually repeat themselves according to one theoretical model. Recently, methods making wide use of site intensity data have been developed in regions such as Italy, where the observed seismic history at selected sites is quite exhaustive. We analyzed these observations to assess seismic hazard at about 600 sites. We used a probabilistic counting technique, integrating the observations (when necessary), with computed shakings obtained from a logistic-type attenuation model. The results were then compared with the estimates provided by the recent seismic hazard map of Italy, compiled according to the traditional probabilistic seismic hazard approach. The match shows significant differences for some sites. A tentative explanation which seems to point to three alternatives is provided: (1) The mismatch between the two methodologies might appear because the stationary assumption has a poor fit with reality (at least in certain areas); (2) Some sites show a response that is systematically different from the average values predicted using attenuation relationships; (3) The definition of seismogenic zones leads to a bias in the seismicity rate estimate.     

Sensitivity of the Earthquake Response of Tall Steel Moment Frame Buildings to Ground Motion Features

The seismic response of two tall steel moment frame buildings and their variants is explored through parametric nonlinear analysis using idealized sawtooth-like ground velocity waveforms, with a characteristic period (T), amplitude (peak ground velocity, PGV), and duration (number of cycles, N). Collapse-level response is induced only by long-period, moderate to large PGV ground excitation. This agrees well with a simple energy balance analysis. The collapse initiation regime expands to lower ground motion periods and amplitudes with increasing number of ground motion cycles.