Kentsel Alanlarda Zemin Büyüme Faktörlerinin Alernatif Yöntemlerle Tayini.

Amac: Bu çalışmanın temel amacı, deprem riski yüksek olan kentsel bölgelerde zeminlerin dinamik özelliklerini pratik ve gerçekçi olarak elde etmek için karma bir yöntem geliştirmektir. Bu amaçla pilot bölge olarak seçilen sahadaki zemin özellikleri literatürde varolan jeofizik ve geoteknik esaslara dayanan deneysel ve teorik yöntemlerle araştırılacak; farklı yöntemlerden elde edilen sonuçlar karşılaştırılacak ve ileride zemin büyütme analizlerinde kullanılmak üzere karma bir yaklaşım önerilecektir. Kapsam ve Yontem: Bu çalışmada öncelikli olarak Düzce ve Bolu merkezinde seçilen sahalarda sözü edilen Tübitak 1002 projesi kapsamında elde edilmiş olan mikrotremor ölçümleri üzerinde IDL ilgisayar programı tabanlı MMSPAC ters çözüm algortiması ile analiz yapılacak ve anakaya derinliklerine dek uzanan tek boyutlu S-dalgası hız profilleri elde edilecektir. Varolan diğer zemin sınıfı belirleme yöntemlerinden farklı olarak, MMSPAC yönteminin 500-1000 m derinliklere dek gerçekçi sonuç verdiği bilinmektedir. Sonuçlar literatürde bulunan diğer yöntemlerle sınanacak; sığ tabakaların dalga hızları varolan sondaj verileriyle karşılaştırılacaktır. Mikrotremör değerlendirmeleri sonucunda zemin büyütme etkisini incelemek için tek istasyonda H/V oranları hesaplanacaktır. Projenin ikinci aşamasında ise IDL tabanlı MMSPAC ters çözüm programından (Asten, 2006) yatay tabakalar halinde elde edilen S-dalga hızları SHAKE programı (Schnabel vd., 1972) ile tek boyutlu dalga yayılım prensibi kullanılarak zemin büyütme faktörleri hesaplanacaktır. Projenin üçüncü aşamasında seçilen ve MMSPAC analizi yapılmış olan yer hareketi istasyonlarında derlenen yer hareketi kayıtlarından H/V oranlama yöntemi ile büyütme faktörleri hesaplanacaktır. Son aşamada ise elde edilen tüm zemin büyütme bulguları frekans uzayında karşılaştırılacak; zemin koşullarına ve frekans aralığına bağlı olarak hangi yöntemin daha gerçekçi sonuçlar verdiği incelenecektir. Proje kapsamında, önerilen yaklaşımın uygulanması için seçilen pilot sahalar (kuvvetli yer hareketi istasyonları) Bolu ve Düzce merkezlerindedir. Sonuçları karşılaştırmak için daha önceden yapılan çalışmalarda elde edilmiş zemin etüdleri bulunan bu merkezler seçilmiş ve bu projede geliştirilmesi amaçlanan yaklaşımın bu pilot bölgelerde uygulanma ve sınanması planlanmıştır

Evaluation of Site Response with Alternative Methods A Case Study for Engineering Implications

n this paper, efficiency of alternative geophysical techniques for site response is evaluated in two sedimentary basins on the North Anatolian Fault Zone. For this purpose, fundamental frequencies of soils and corresponding amplitudes obtained from empirical horizontal-to-vertical spectral ratio curves from microtremors, weak motions and strong motions are compared with results from one-dimensional theoretical transfer functions. Theoretical transfer functions are computed using S-wave velocity profiles derived from array observations of the microtremor wavefield. Our results are consistent with studies from other regions in that the fundamental frequencies from microtremors, weak motions and theoretical transfer functions are mostly in agreement with each other although some discrepancies are observed. Even though important information about fundamental resonance frequency can be derived from horizontal-to-vertical spectral ratios, observed amplitudes do not yield consistent results with the theoretical amplification factors. Thus, the use of horizontal-to-vertical spectral ratio amplitudes is not recommended for estimation of amplification factors. Based on our observations, complementary use of alternative methods for site response is recommended. © 2017, Springer International Publishing AG

MODELING OF THE 1939 ERZINCAN, TURKEY (MS~7.8)EARTHQUAKE: OBSERVATIONS ON ANTICIPATED GROUNDMOTIONS AND FELT INTENSITY DISTRIBUTION

Located within a pull-apart basin at the conjunction of three active faults (North Anatolian, North East Anatolian and Ovacik Faults), Erzincan city center is one of the most hazardous regions of the world. Combination of the seismotectonic and geological settings of the region has resulted in series of significant seismic activities including the 27 December 1939 (Ms=8.0) and the 13 March 1992 (Mw=6.6) events. The former earthquake was in the pre-instrumental era in the region with no available local seismograms. However, despite the sparse local network, the 1992 earthquake has been studied extensively. The objective of this study is to model the 1939 Erzincan earthquake using the regional seismic and geological parameters available mostly from the previous studies on the 1992 event. Despite several uncertainties involved, such an effort to quantitatively simulate the 1939 earthquake is promising, given the historical reports of extensive damage and fatalities in the area. The results are expressed in terms of anticipated spatial distribution of selected ground motion parameters and feltintensity maps in the region. These shaking maps are obtained using local correlations between intensity and peak ground motion values. Comparisons of simulated motions against empirical prediction equations and the existing damage observations indicate a reasonable modeling of the 1939 earthquake

Stochastic Strong Ground Motion Simulation of the 12 November 1999 Duzce (Turkey) Earthquake Using a Dynamic Corner Frequency Approach

On 12 November 1999, only three months after the 17 August 1999 Kocaeli earthquake (M(w) 7: 4), an earthquake of Mw 7: 1 occurred immediately to the east of the Kocaeli rupture in northwestern Turkey resulting in extensive structural damage in the city of Duzce and its surrounding area. It was reported to be a right-lateral strike slip event on the previously unbroken segment of the North Anatolian fault zone with a north-dipping fault plane. This paper presents stochastic finite-fault simulation of near-field ground motions from this earthquake at selected near-fault stations based on a dynamic corner frequency approach using the computer program EXSIM (Motazedian and Atkinson, 2005). The method requires region-specific source, path, and site characterizations as input model parameters. The source mechanism of the 1999 Duzce event and regional path effects are well constrained from previous studies of the earthquake. The local site effects at the selected stations are studied as a combination of the kappa operator and frequency-dependent soil amplification. The model parameters are validated against recordings and a stress-drop value of 100 bars is estimated for the 1999 Duzce earthquake. The validated model is then used to compute synthetic records around the fault. Distribution of peak ground-motion parameters is observed to be consistent with the building damage distribution in the near-fault region most affected by the seismic shaking. The attenuation of synthetic ground-motion parameters is compared with recent ground-motion prediction equations proposed for the region by Gulkan and Kalkan (2002), Ulusay et al. (2004), and Akkar and Bommer (2007), as well as two next generation attenuation models by Boore and Atkinson (2007) and Campbell and Bozorgnia (2007). Despite discrepancies at several stations, stochastic finite-fault modeling based on a dynamic corner frequency approach confirms to be a practical tool to reproduce the ground motions of large earthquakes

SITE-SPECIFIC PROBABILISTIC SEISMIC HAZARD ASSESSMENT ANALYSES IN ZEYTINBURNU, ISTANBUL

The first step in estimation of seismic losses in urban areas is the assessment of regional seismic hazard. The source and local site parameters determine the accuracy of the hazard model. Using locally derived input parameters in site response modeling and hazard analyses, the earthquake potential of Zeytinburnu region in Istanbul is investigated in detail. In this study, two alternative source models including area and fault (line) sources are considered in the hazard computations. Analyses are initially performed using generic rock and soil conditions considering return periods of 475, 975 and 2475 years. Then, site-specific seismic hazard analyses are made using available local soil conditions. Probabilistic seismic hazard analyses with line sources and local soil models yield significantly different results than area sources and a generic soil model for all return periods. This observation points out the fact that detailed local source and site parameters should be employed in hazard analyses. In summary, numerical results obtained with locally derived input parameters indicate that Istanbul has significant potential for hazard in terms of both local earthquake occurrence and site amplifications

Full Anelastic Waveform Tomography Including Model Uncertainty

This article is concerned with the problem of seismic inversion in the presence of model uncertainty. In a recent article (Askan et al., 2007), we described an inverse adjoint anelastic wave propagation algorithm for determining the crustal velocity and attenuation properties of basins in earthquake-prone regions. We formulated the tomography problem as a constrained optimization problem where the constraints are the partial and the ordinary differential equations that govern the anelastic wave propagation from the source to the receivers. We employed a wave propagation model in which the intrinsic energy-dissipating nature of the soil medium was modeled by a set of standard linear solids. Assuming no information was initially available on the target shear-wave velocity distribution, we employed a homogeneous shear-wave velocity profile as the initial guess. In practice, some information is usually available. The purpose of the present article is to modify our nonlinear inversion method to start from an initial velocity model, and include a priori information regarding the initial model parameters in the misfit (objective) function. To represent model uncertainties, given an initial velocity model, in addition to the data misfit term in our objective function, we include an L(2)-normed weighting term, which quantifies the model estimation errors, independently of the measured data. We use total variation (TV) regularization to overcome ill posedness. We illustrate the methodology with pseudo-observed data from two-dimensional sedimentary models of the San Fernando Valley, using a source model with an antiplane slip function

Relationships between Felt Intensity and Recorded Ground-Motion Parameters for Turkey

In this paper, empirical relationships between modified Mercalli intensity (MMI) and recorded peak ground-motion parameters are developed for Turkey. Strong ground motion data from moderate-to-large earthquakes are employed along with the corresponding MMI information inferred from isoseismal maps and earthquake damage reports. Linear least-squares regression technique is used to derive the following simple relationships between MMI and peak ground acceleration (PGA), peak ground velocity (PGV), and pseudospectral acceleration (PSA): MMI = 0.132 + 3.884 x log (PGA), MMI = 2.673 + 4.340 x log(PGV), MMI = -0.247 + 3.404 x log[PSA(0.3 s)], MMI = -0: 934 + 4.119 x log[PSA(1.0 s)], and MMI = -0.313 + 4.453 x log[PSA(2.0 s)]

Hybrid-empirical ground motion models for Georgia

Ground motion prediction equations are essential for several purposes ranging from seismic design and analysis to probabilistic seismic hazard assessment. In seismically active regions without sufficient data to build empirical models, hybrid models become necessary. Georgia, despite being located in a region with moderate seismic activity, does not have sufficient strong ground motion data to build empirical ground motion models. In this study, we have applied the host-to-target method to two regions in Georgia with different source mechanisms: Javaxeti and Racha regions. According to the tectonic regime of the target areas, two different regions are been chosen as host regions. One of them is the North Anatolian Fault zone in Turkey with mostly strike-slip stress regime and the other is Tabas in Iran with mostly reverse mechanism. We performed stochastic finite-fault simulations in both host and target areas and employed the hybrid-empirical method of Campbell (2003). An initial hybrid empirical ground motion model is developed for PGA and SA at selected periods for Georgia. This model could be employed in various applications where use of ground motion prediction equations is required. An application of these coefficients for ground motion models to be used in regional PSHA in Georgia is now in progress. Potential future research includes the test and use of such hybrid-empirical models for a variety of earthquake engineering purposes