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Ansal, Atilla
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Ansal, Atilla
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- PublicationOpen AccessDetermination of shallow S-wave attenuation by down-hole waveform deconvolution: a case study in Istanbul (Turkey)(2010)
; ; ; ; ; ; ;Parolai, S.; GFZ-Potsdam ;Bindi, D.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Milano-Pavia, Milano, Italia ;Ansal, A.; 3Boğaziçi Üniversitesi, Kandilli Rasathanesi ve Deprem Araştırma Enstitüsü ;Kurtulus, A.; Boğaziçi Üniversitesi, Kandilli Rasathanesi ve Deprem Araştırma Enstitüsü ;Strollo, A.; GFZ-Potsdam ;Zscahu, J.; GFZ-Potsdam; ; ; ; ; The estimation of shear-wave velocity and attenuation in near-surface geology is of primary importance in engineering seismology. In fact, their knowledge is essential for site response studies when preparing improved seismic hazard scenarios. In this study, we propose two approaches for estimating the average shear-wave quality factor Qs by using recordings of a vertical array of accelerometers. The methods are mainly based on the deconvolution of the wavefield recorded in a borehole with that recorded at the surface. The first method requires the Fourier transform of the deconvolved wavefield to be fitted with a theoretical transfer function valid for the vertical or nearly vertical (in the case at hand up to 30° incidence angle) propagation of S-waves. The second method is based on the spectral fitting of the Fourier transform of only the acausal part of the deconvolved wavefield with a theoretical transfer function. Both methods can be applied without any prior knowledge of the subsoil structure (since they are based on empirical data analysis) and do not require a precise knowledge of the azimuthal orientation of the sensors in the boreholes (which is seldom available). First, we describe the theoretical framework of the proposed methodologies for Qs estimation, which are based on the assumption that the structure in the borehole is weakly heterogeneous in the vertical direction (that is, no large impedance contrast exists between the borehole sensor and the surface). Second, by using synthetic accelerograms, we verify that in a realistic subsoil structure, the assumption of vertical homogeneity can hold and we investigate the robustness and the suitability of the proposed methods. Finally, only the method that was shown to provide the more stable results, based on fitting the borehole-to-surface spectral ratio with a theoretical function, is applied to earthquakes signals recorded by a vertical array of accelerometers installed in Ataköy (western Istanbul). Results show that using borehole data provides a fair and robust estimate of an average Qs (of about 30, 46 and 99 for the 0-50, 0-70, 0-140 m depth ranges, respectively), that can be used for numerical simulations of ground motion.139 276 - PublicationRestrictedLoss estimation in Istanbul based on deterministic earthquake scenarios of the Marmara Sea region (Turkey)(2009-04)
; ; ; ; ; ; ; ;Ansal, A.; Bogazici University, Kandilli Observatory and Earthquake Research Institute, Istanbul, Turkey ;Akinci, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Cultrera, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Erdik, M.; Bogazici University, Kandilli Observatory and Earthquake Research Institute, Istanbul, Turkey ;Pessina, V.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Milano-Pavia, Milano, Italia ;Tönük, G.; Bogazici University, Kandilli Observatory and Earthquake Research Institute, Istanbul, Turkey ;Ameri, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Milano-Pavia, Milano, Italia; ; ; ; ; ; The rapid urban development in Istanbul has lead to an increase in the exposure levels of the urban vulnerability. Due to the steadily increasing population, with improper land-use planning, inappropriate construction techniques and inadequate infrastructure systems, associated with an existing high hazard level, Istanbul is one of the most risky cities in the Mediterranean region. Estimations of casualties and losses, expected for given earthquake scenarios, are necessary to develop sustainable rehabilitation programs and for improving preparedness. Deterministic hazard scenarios and time-dependent probabilistic hazard assessment were used as input to a GIS-based loss estimation model, to evaluate the earthquake risk for Istanbul. The deterministic ground shaking scenarios, used for loss estimation in Istanbul, were defined in terms of acceleration and velocity time series for recognized reference earthquakes caused by different rupture models along extended sources. The ground motions were calculated for the whole metropolitan area extending over a grid system of 25×100 km2. For the case of Istanbul, the representative scenario was selected by comparing the simulated peak values and response spectra with the empirical ground motion models available for the area. Simulated values are within one standard deviation of the empirical regressions. The availability of wide-ranging building inventory data allowed the application of a GIS-based loss estimation model (KoeriLoss-V2) to evaluate different loss scenarios depending on the ground shaking input, as well as to consider the implications of mitigation actions. It was found that 30% of the buildings in the metropolitan area may be in need of either strengthening or demolition to achieve an adequate degree of life safety.329 41 - PublicationOpen AccessPrediction of Ground Motion and Loss Scenarios for Selected Infrastructues Systems in European Urban Environments(2007-07)
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ;Faccioli, E.; SGI-Milano ;Callerio, A.; SGI-Milano ;Ameri, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Milano-Pavia, Milano, Italia ;Zonno, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Milano-Pavia, Milano, Italia ;Pacor, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Milano-Pavia, Milano, Italia ;Akinci, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Cultrera, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Cocco, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Franceschina, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Milano-Pavia, Milano, Italia ;Pessina, V.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Milano-Pavia, Milano, Italia ;Lombardi, A. M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Pitilakis, K.; Univerisy of Thessaloniki, Greece ;Kakderi, K.; Univerisy of Thessaloniki, Greece ;Alexaudi, M.; Univerisy of Thessaloniki, Greece ;Kim, S.; Univerisy of Thessaloniki, Greece ;Ansal, A.; Koery, Turkey ;Erdik, M.; Koery, Turkey ;Tonuk, G.; Koery, Turkey ;Dermircioglu, M.; Koery, Turkey ;Paolucci, R.; Politecnico Milano ;Scandella, L.; Politecnico Milano; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; computational tools needed for developing scenarios of earthquake ground motions and of ensuing damage to representative urban Infrastructure Systems (IS), as well as with illustrative examples of application to cities in Europe and neighbouring countries. The material illustrated is the outcome of the work carried out in LESSLOSS Sub-Project SP11, devoted to the title subject. Of main concern are the water and natural gas distribution networks and the sewage networks, because these are, with the transportation network, by far the most extensive IS in cities and, especially the first one, often the most vulnerable. Also, emphasis is placed more on the tools for achieving a scenario and on their application, rather than on the economic loss evaluation. As a partial justification of the belated development and interest in seismic IS damage, it is recalled that destructive earthquakes of recent decades in Europe did not cause large scale damage to IS. In addition to describing tools for the practical construction of damage scenarios for IS, the report also highlights some innovative research trends in the field, especially the methods leading to the estimation of pipeline damage on the basis of the peak ground strains generated by the propagation of seismic waves, which in turn needs the support of advanced 2D or 3D wave propagation modelling. The main sections of the report are devoted to: - Calculation of seismic ground motions in an area, both of advanced and simplified engineering level, with applications for Thessaloniki and Düzce (Sect 2); - Outline of the buried pipelines response during earthquakes, illustrating the chief elements at play on the side of the seismic loading effects and typical damage (Sect. 3); - Vulnerability representations for IS components, mostly those consisting of buried pipelines (Sect. 4); - Typical features of IS inventories, with examples (Sect 5); - Damage evaluation tools at urban scenario and single pipeline level (Sect. 6); - Damage scenario applications for Thessaloniki and Düzce (Sect 7); - Conclusions.292 936