Modeling of seismic hazard for Turkey using the recent neotectonic data

Recent developments in the neotectonic framework of Turkey introduced new tectonic elements necessitating the reconstruction of Turkey's seismic hazard map. In this regard, 14 seismic source zones were delineated. Maximum earthquake magnitudes for each seismic zones were determined using the fault rupture length approximation. Regression coefficients of the earthquake magnitude–frequency relationships for the seismic zones were compiled mostly from earlier works. Along with these data, a strong ground motion attenuation relationship developed by Joyner and Boore [Joyner, W.B., Boore, D.M., 1988. Measurement, characterization, and prediction of strong ground motion. Earthquake Engineering and Soil Dynamics, 2. Recent Advances Ground Motion Evaluation, pp. 43–102.] was utilized to model the seismic hazard for Turkey using the probabilistic approach. For the modeling, the “earthquake location uncertainty” concept was employed. A grid of 5106 points with 0.2° intervals was constituted for the area encompassed by the 25–46°E longitudes and 35–43°N latitudes. For the return periods of 100 and 475 years, the peak horizontal ground acceleration (pga) in bedrock was computed for each grid point. Isoacceleration maps for the return periods of 100 and 475 years were constructed by contouring the pga values at each node.     

Analysis of soil effects and distribution of damage from the Pyrgos 1993 (Greece) earthquake

Summary On 26 March, 1993, a moderate magnitude earthquake (M _s=5.5) occurred at 3 km epicentral distance from the town of Pyrgos, in Southern Greece, causing extensive damage to masonry houses. To explain the variability of seismic intensity over the town and to propose measures against future seismic activity, a microzonation study was undertaken which combined geological, geophysical and geotechnical investigations, site specific analyses of seismic ground response and detailed recording of structural damage. The analytical predictions of ground response are correlated to soil conditions and then used to identify (micro-)zones of sites with similar seismic response. Furthermore, they are compared to quantitative estimates of damage distribution over the town. It is concluded that the peak ground acceleration, normalized against the input peak seismic acceleration, is a function of the local soil conditions as well as the seismic excitation characteristics. Hence, it cannot be defined uniquely at a site, without reference to the seismic excitation. However, the normalized peak ground velocity and the acceleration response spectra are mainly functions of the soil conditions and can be used as criteria for the practical definition of (micro-)zones. The distribution of damage in various parts of the town is at least partially attributable to local soil effects. The small epicentral distance of the earthquake, connected with the direction of the fault rupture, as well as the quality and techniques of construction, are additional factors that may have influenced the extent and distribution of damage.     

A newly developed seismic microzonation model of Erbaa (Tokat, Turkey) located on seismically active eastern segment of the North Anatolian Fault Zone (NAFZ)

A methodology to model seismic microzonation maps is required in the hazard mitigation decision plans of the earthquake prone areas. The stage of disaster preparedness for new residential places is of great importance for detailed seismic microzonation models. The effects of local geological and geotechnical site conditions were considered in order to establish site characterization as the initial stage of the models in this study. Dynamic soil properties based on the empirical correlations between shear wave velocity (V _s) and standard penetration test blow counts were taken into account in order to define representative soil profiles extending down to the engineering bedrock. One-dimensional site response analyses were performed to analyze earthquake characteristics on the ground surface. The layers for soil classification, geology, depth to groundwater level, amplification, distance to fault, slope and aspect, and liquefaction-induced ground deformation potential of the study area were prepared in seismic microzonation models. The study area, Erbaa, is placed along the seismically active North Anatolian Fault Zone. Final seismic microzonation map of the study area was evaluated applying different GIS-based Multi-Criteria Decision Analysis (MCDA) techniques. Two of the MCDA techniques, simple additive weighting and analytical hierarchical process (AHP), are considered during the evaluation step of the final seismic microzonation map. The comparison is made in order to distinguish two different maps based on these MCDA techniques. Eventually, AHP-based seismic microzonation map is more preferable for the seismic design purposes in this study.     

Earthquakes and soil liquefaction in flood stories of the ancient Near East

Flood stories in the Hebrew Bible and the Koran appear to be derived from earlier flood stories like those in the Gilgamesh Epic and still earlier in the Atrahasis. All would have their source from floods of the Tigris and Euphrates rivers.

The Gilgamesh Epic magnifies the catastrophe by having the flood begin with winds, lightning, and a shattering of the earth, or earthquake. Elsewhere in Gilgamesh, an earthquake can be shown to have produced pits and chasms along with gushing of water. It is commonly observed that earthquake shaking causes water to gush from the ground and leaves pits and open fissures. The process is known as soil liquefaction. Earthquake is also a possible explanation for the verse “all the fountains of the great deep (were) broken up” that began the Flood in Genesis. Traditionally, the “great deep” was the ocean bottom. A more recent translation substitutes “burst” for “broken up” in describing the fountains, suggesting that they erupted at the ground surface and were caused by an earthquake with soil liquefaction. Another relation between soil liquefaction and the Flood is found in the Koran where the Flood starts when “water gushed forth from the oven”. Soil liquefaction observed erupting preferentially into houses during an earthquake provides a logical interpretation if the oven is seen as a tiny house. A case can be made that earthquakes with soil liquefaction are embedded in all of these flood stories.     

Engineering geologic and geotechnical analysis of paleoseismic shaking using liquefaction effects: field examples

The greatest impediments to the widespread acceptance of back-calculated ground motion characteristics from paleoliquefaction studies typically stem from three uncertainties: (1) the significance of changes in the geotechnical properties of post-liquefied sediments (e.g., “aging” and density changes), (2) the selection of appropriate geotechnical soil indices from individual paleoliquefaction sites, and (3) the methodology for integration of back-calculated results of strength of shaking from individual paleoliquefaction sites into a regional assessment of paleoseismic strength of shaking. Presented herein are two case studies that illustrate the methods outlined by Olson et al. [Engineering Geology, this issue] for addressing these uncertainties.

The first case study is for a site near Memphis, Tennessee, wherein cone penetration test data from side-by-side locations, one of liquefaction and the other of no liquefaction, are used to readily discern that the influence of post-liquefaction “aging” and density changes on the measured in situ soil indices is minimal. In the second case study, 12 sites that are at scattered locations in the Wabash Valley and that exhibit paleoliquefaction features are analyzed. The features are first provisionally attributed to the Vincennes Earthquake, which occurred around 6100 years BP, and are used to illustrate our proposed approach for selecting representative soil indices of the liquefied sediments. These indices are used in back-calculating the strength of shaking at the individual sites, the results from which are then incorporated into a regional assessment of the moment magnitude, M, of the Vincennes Earthquake. The regional assessment validated the provisional assumption that the paleoliquefaction features at the scattered sites were induced by the Vincennes Earthquake, in the main, which was determined to have M7.5. The uncertainties and assumptions used in the assessment are discussed in detail.     

中国地质科学院对5.12汶川地震的快速反应与调查研究

面对5.12汶川8级地震突发灾害,中国地质科学院组织专家,科学分析发震动力学背景,第一时间奔赴震中地区开展地表破裂变形与地震地质灾害调查,随后系统开展地震科学钻探选址、活动断裂与地震变形观测、地应力测量、地质灾害地面调查、堰塞湖与水工环综合评价。6位专家参加国家汶川地震专家委员会,编辑出版《汶川地震灾区地震—地质灾害图集》,组织召开汶川地震动力学分析研讨会,2位专家参加国土资源部抗震救灾前方指挥部工作。在第33届国际地质大会期间,组织汶川地震大型展览,应邀作汶川地震、地震科学钻、地表破裂等学术报告,受到国际同行的高度关注。组织申报汶川地震断裂带科学钻探工程,2008年11月第一口地震科学钻开工;组织落实国家专项、973课题、地质调查项目等科研任务,有效地调整了面向地质灾害的学科结构和人才布局。     

Ground motion studies for microzonation in Iran

An important step in effectively reducing seismic risk and the vulnerability of a city located in an earthquake prone area is to conduct a ground motion microzonation study for the desired return period. The International Institute of Earthquake Engineering and Seismology (IIEES) initiated a number of seismic microzonation projects for Iran. This paper presents the steps followed by IIEES in ground motion microzonation. IIEES performs both probabilistic and deterministic seismic hazard analysis. IIEES uses his own fault map for seismotectonic studies and develops modulus and damping curves for the soils in the study area. The experience of ground motion microzonation shows that in almost all cases, the estimated 475-year peak ground acceleration (PGA) values are higher than the PGA proposed by the Iranian seismic code. Although ground motion microzonation in Iran has some shortcomings, IIEES is making new improvement. This includes development in deterministic seismic hazard analysis, two-dimensional and three-dimensional modelling of basin and topographical effects, using microtremor measurements to find shear-wave velocity profiles in high-density urban areas and providing maps for spectral acceleration in the study area.     

Seismic investigation of near-surface geological structure in the Paducah, Kentucky, area: application to earthquake hazard evaluation

Seismics method were used to evaluate shallow geological conditions at 33 sites in the vicinity of Paducah, Kentucky. A combined set of P- and S-wave seismic refraction and reflection soundings were used, in addition to local borehole information, to produce structure maps of (1) a shallow (< 30 m deep) horizon believed to represent an unconformity surface at the top of the Eocene, and (2) the Paleozoic bedrock surface (< 85 to > 160 m deep). Shear-wave velocity contrasts across the shallow unconformity were generally 2-to-1 while the contrast at the top of the Paleozoic bedrock exceeds 5-to-1. These seismic boundaries have been determined to be very important in modelling and interpreting earthquake ground motion amplification in the Paducah area. The quality and accuracy of the data, and the cost effective nature of the methods, suggest that other communities in areas at risk to damage from seismic activity, with foundation conditions comparable to Paducah, might benefit from similar characterization in order (1) to identify seismically hazardous, near-surface, geological conditions, and (2) to develop geological models that could be used in computer simulations of site response.     

Utilization of underground spaces in urban areas: Urban geo-grid plan

Miyake, N. and Denda, A., 1993. Utilization of underground spaces in urban areas: Urban geo-grid plan. In: M. Langer, K. Hoshino and K. Aoki (Editors). Engineering Geology in the Utilization of Underground Space.Eng. Geol., 35: 175–181.

The Urban Geo-grid Plan aims for a systematic and better coexistence of above-ground and underground areas through the utilization of underground space presently not in use, without interfering with existing urban functions. There would be “base points” supporting regional functions which are laid out in a grid connected by “lines”. Base points would consist of “grid points” and “grid stations”, which serve as control centers for grid points, the grid points and grid stations being interconnected by tunnels to form an “underground network”. Normally, a base point would be used for multiple purposes to supplement regional functions which are inadequate, as well as urban functions, and in emergencies, such as earthquake disasters, it would demonstrate information and evacuations functions.     

成都粘土场地土体的地震反应分析

根据区域地震的特点并考虑成都粘土的裂隙特性,采用实测动力指标,应用动力有限元法对成都粘土场土体进行地震反应计算,并对反应结果作统计分析,得出部分定量指标及规律性结论,对城市地震小区划及指导本区工程抗震设防工作,具有一定的应用参考价值。     

Seismic microzonation for Penang using geospatial contour mapping

Shear wave velocity (V _s) and the fundamental site period of the subsurface condition are the primary parameters that affect seismic soil amplification in particular sites. Within the topmost layer of the soil, which measures 30 m, the average shear wave velocity V _s30 is commonly used to build codes for site classification for the design of earthquake-resistant structures and to conduct microzonation studies. In this study, the development of a microzonation map for V _s30 distribution, National Earthquake Hazard Reduction Program V _s30 site classification, and a fundamental site period for Penang are presented. The multichannel analysis of surface wave (MASW) test was conducted for more than 50 sites with available borehole data to develop the microzonation maps. The ten selected V _s profiles measured by MASW show a good correlation with the data obtained using empirical correlations in a previous study. The highest V _s values were identified at the northeastern and southeastern parts of Penang Island, corresponding to the shallow bedrock and the outcrop zone. Conversely, the lowest V _s values were found in the northwestern and southwestern parts of the Penang mainland owing to the thick layer of soft clay and silt deposits. The site period map shows the variation in site periods, with the highest value of 1.03 s at the western part of the Penang mainland and the lowest value of 0.02 s at the eastern part of the Penang Island. The microzonation maps developed in this study are vital to studies on seismic hazard and earthquake mitigation programs in Malaysia.     

Additional evidence on some relationship between Seismic Electric Signals (SES) and earthquake focal mechanism

Investigating the period 1983–1994 for western Greece, a possible correlation between the selectivity characteristics of the SES (seismic electric signals of the VAN method) and earthquake parameters has been reported by Uyeda et al. [Uyeda, S., Al-Damegh, K.S., Dologlou, E., Nagao, T., 1999. Some relationship between VAN seismic electric signals (SES) and earthquake parameters, Tectonophysics, 304, 41–55.]. They found that the earthquake source mechanism changed from largely strike-slip type to thrust type at the end of 1987, and this coincided with a shift in the SES sensitive site from Pirgos (PIR) to Ioannina (IOA) VAN station. Here, we report the results for the period January 1, 2002–July 25, 2004, during which the SES sensitive site of PIR became again active, after a 10-year period of “quiescence”. This activation was followed by strike slip earthquakes (on August 14, 2003 and March 17, 2004 with magnitude 6.4 and 6.5, respectively) in the Hellenic arc, which provides additional evidence on the correlation reported by Uyeda et al. The SES activities recorded at PIR have been discriminated from “artificial” noise by employing the natural time-domain analysis introduced recently.     

Seismic microzonation of Bangalore,India

In the present study, an attempt has been made to evaluate the seismic hazard considering local site effects by carrying out detailed geotechnical and geophysical site characterization in Bangalore, India to develop microzonation maps. An area of 220 km², encompassing Bangalore Mahanagara Palike (BMP) has been chosen as the study area. Seismic hazard analysis and microzonation of Bangalore are addressed in three parts: in the first part, estimation of seismic hazard is done using seismotectonic and geological information. Second part deals with site characterization using geotechnical and shallow geophysical techniques. In the last part, local site effects are assessed by carrying out one-dimensional (1-D) ground response analysis (using the program SHAKE2000) using both standard penetration test (SPT) data and shear wave velocity data from multichannel analysis of surface wave (MASW) survey. Further, field experiments using microtremor studies have also been carried out for evaluation of predominant frequency of the soil columns. The same has been assessed using 1-D ground response analysis and compared with microtremor results. Further, the Seed and Idriss simplified approach has been adopted to evaluate the soil liquefaction susceptibility and liquefaction resistance assessment. Microzonation maps have been prepared with a scale of 1:20,000. The detailed methodology, along with experimental details, collated data, results and maps are presented in this paper.     

Seismic hazard assessment for Mymensingh,Bangladesh

Mymensingh municipality lies in one of the most earthquake-prone areas of Bangladesh. The town was completely destroyed during the Great Indian Earthquake of 12 June 1897, for which the surface-wave magnitude was 8.1. In this study the 1897 Great Indian Earthquake was used as a scenario event for developing seismic microzonation maps for Mymensingh. For microzonation purposes SPT data from 87 boreholes were collected from different relevant organizations. To verify those data ten boreholes of depth up to 30 m were drilled. Intensity values obtained for different events were calibrated against attenuation laws to check applicability to the study area. Vibration characteristics at diverse points of the study area were estimated by employing the one-dimensional wave-propagation software SHAKE. SHAKE discretizes the soil profile into several layers and uses an iterative technique to represent the non-linear behavior of the soil by adjusting the material properties at each iteration step. The required input information includes depth, shear wave velocity, damping factor, and unit weight of each soil layer. The liquefaction resistance factor and the resulting liquefaction potential were estimated to quantify the severity of liquefaction. Quantification of secondary site effects and the weighting scheme for combining the various seismic hazards were heuristic, based on judgment and expert opinion.     

汶川8级地震地质灾害的类型及实例

龙门山地区活动断裂右旋斜冲运动与汶川8级强烈地震存在成因联系。汶川8级地震造成了惨重的人员伤亡和巨大的财产损失,地震地质灾害主要类型有地震灾害、地震触发地质灾害和地震引发地质灾害隐患。严重地震灾害包括房屋倒塌与部分坍塌、房屋平移、房屋倾斜变形、墙体破裂与结构破坏、桥梁垮塌等。地震触发严重地质灾害包括山体滑坡、山体滑塌、岩块崩塌,局部产生泥石流与沙土液化。地震引发地质灾害隐患包括潜在滑坡、不稳定边坡与滑塌隐患、危岩体与崩塌隐患及泥石流灾害隐患。地震地质灾害分布与活动断层存在密切关系,沿北川映秀断裂地震地质灾害最为严重,沿汉旺漩口断裂、茂县汶川断裂、青川断裂地震地质灾害也比较严重。在活动断裂之间相对稳定地块远离活动断裂超过3~5 km,地震灾害和地震触发地质灾害显著减轻。     

Development of a geotechnical and geophysical database for seismic zonation of the Ankara Basin,Turkey

Engineering geological and geotechnical site characteristics were assessed and seismic hazard studies performed for the Upper Pliocene to Pleistocene fluvial and Quaternary alluvial and terrace deposits for a site west of Ankara, Turkey. Sediment conditions were determined and a soil profile was characterized by surface geophysical methods. These studies were integrated with existing in-situ characterization studies to create a seismic and geotechnical database for the site. A seismic zonation map of the site was then prepared. Site classification systems were assigned to account for site effects in relation to seismic hazard assessments. The consequences of the seismic hazards were investigated and recommendations were presented.     

A study of the seismic response of the city of Benevento (Southern Italy) through a combined analysis of seismological and geological data

A previous analysis [Improta, L., G. Di Giulio, and A. Rovelli (2005). Variations of local seismic response in Benevento (Southern Italy) using earthquakes and ambient noise recordings, J. Seism. 9, 191–210.] of small magnitude earthquakes recorded at 12 sites within the city of Benevento has stressed the significant role played by near-surface geology in causing variability of the ground motion. In this paper, we extend the study of the seismic response from 12 sites to the entire urban area. Based on inferences from the comparison at the 12 sites between earthquake and ambient vibration results, we have collected ambient noise at about 100 sites within the city, intensifying measurements across the main shallow geological variations. We use borehole data to interpret ambient noise H/V spectral ratios in terms of near-surface geology comparing H/V curves to theoretical transfer functions of 1D models along five well-constrained profiles.

On the basis of geological, geotechnical, and seismic data, we identify three main typologies of seismic response in the city. Each type of response is associated to zones sharing common soil conditions and similar soil classes according to building codes for seismic design. Moreover, we find that the spatial variation of the seismic response in the ancient town area is consistent with the damage pattern produced by a very destructive, well-documented historical earthquake that struck the city in 1688, causing MCS intensity of IX–X in Benevento.

Finally, we use ground motions recorded during the experiment by Improta et al. [Improta, L., G. Di Giulio, and A. Rovelli (2005). Variations of local seismic response in Benevento (Southern Italy) using earthquakes and ambient noise recordings, J. Seism. 9, 191–210.] to generate synthetic seismograms of moderate to strong (Mw 5.7, Molise 2002 and Ms 6.9, 1980 Irpinia) earthquakes. We calibrate the random summation technique by Ordaz et al. [Ordaz, M., J. Arboleda, and S.K. Singh (1995). A scheme of random summation of an Empirical Green's Function to estimate ground motions for future large earthquakes, Bull. Seism. Soc. Am. 85, 1635–1647.] using recordings of these earthquakes available in Benevento. After a satisfactory fit between observed and synthetic seismograms, we compute response spectra at different sites and speculate on effects of the geology class at large level of shaking, including soil nonlinearity. We find that large discrepancies from design spectra prescribed by seismic codes can occur for a wide sector of Benevento, especially for periods < 0.5 s.     

Assessment of potential seismic hazard and site effect in Antakya (Hatay Province), SE Turkey

Antakya city is at risk because of strong earthquakes occurring in the area, and different soil conditions that can produce variation of the ground motion amplification. Microzonation of cities provides a basis for site-specific hazard analysis in urban settlements. In particular, seismic microzonation can be provided by means of detailed seismic assessment of the area, including earthquake recordings and geological studies. In this paper, we propose a preliminary microzonation map for the city of Antakya, based on the variation of the dominant periods and shear velocities of the sediments covering the area. The periods are retrieved from microtremor measurements conducted at 69 sites, using the horizontal-to-vertical spectral ratio technique. The results of microtremor analysis were compared with data obtained from refraction microtremor (ReMi) measurements at four profiles crossing the studied area. According to the classification of dominant periods, Antakya city can be divided into five zones, probably prone to different levels of seismic hazard. The shorter natural periods are in inner Antakya and both the sides of Asi River (i.e., northern and southern parts). The eastern and western parts of Antakya have maximum dominant periods. The V _s ³⁰ values were calculated by using the ReMi method along the profiles. Antakya city has V _s ³⁰ values in the range of category C of the national earthquake hazard reduction programme site classification.     

Horizontal to vertical spectral ratio in different geological formations

A study of horizontal-to-vertical (H/V) spectral ratios with the short duration data in different geological formations with varying soil thicknesses were carried out. The study has been implemented by using the ambient seismic noise and hammer impact to determine the fundamental frequency and the corresponding amplification of soils. In addition, the average shear wave velocity (Vs³⁰) was calculated to infer the stiffness of soils. The results are correlating well with the local geology and therefore testify that the short duration data is adequate to estimate the H/V spectral ratio in site characterization and microzonation studies.     

Evaluation of local site effects on earthquake damages of Fatih Mosque

Fatih Mosque and its Kulliye (complex) are one of the most important historical monuments in Istanbul. Since it has been built between 1463 and 1470, Fatih Mosque had been subjected to nine strong earthquakes and suffered various degrees of structural damage at every case, including the latest August 17, 1999 Kocaeli Earthquake (M_w = 7.4, epicentral distance approximately 100 km). Recently, a project has been initiated first to study the possible causes of earthquake damage and then develop retrofitting and strengthening techniques to protect this invaluable monument from further damages in the future earthquakes. As part of this investigation, local site soil conditions had been determined and site behavior during earthquakes had been studied in detail. In this paper, the results of 1-D site response analysis, which included convolution and deconvolution analyses utilizing the strong ground motions recorded during the August 17, 1999 Kocaeli Earthquake are presented. The results of the analyses had demonstrated the considerable degree of site amplification, compatible with the recorded motions and the damage suffered. The expected site behavior during a probable future earthquake is also studied using a site specific simulated bedrock motion, and earthquake parameters to be used in dynamic structural analysis are estimated.