Duzce Earthquake Research Articles

Evaluation of November 23, 2022, Duzce Earthquake data with Ground Motion Prediction Equations

An earthquake with a magnitude of 5.9 Mw occurred in Düzce (Gölyaka) on November 23, 2022. A rupture occurred on the Karadere Segment, which is a section of the North Anatolian Fault zone. According to the investigations, an 8 km section that was not broken in the 1999 Gölcük Earthquake was broken by this earthquake and caused the earthquake. Station number 8105, one of the stations of the Disaster and Emergency Presidency, measured the maximum ground acceleration of the earthquake as 0.6g. This value is above the PGA value taken from the hazard map of the region. This earthquake in the Marmara region attracts the attention of researchers both because it is close to the 1999 Gölcük Earthquake and because there is an earthquake expectation in Istanbul and its surroundings. Ground motion prediction equations are created by researchers to predict the effects of future earthquakes. The aim of this study is to compare the earthquake data considered in the study with 5 of the ground motion equations developed for Turkey. PGA data were collected and compared with the 5 attenuation relations used from the stations taking measurements from the earthquake, and the compatibility of the earthquake with the 5 existing models was examined. As a result of the study, it was determined that among these attenuation relations, the attenuation relations prepared using the data in the region where the earthquake occurred showed a higher fit. In addition, it has been observed that low pga values at stations farther from the epicenter of the earthquake fit better with the curves obtained from the attenuation relations. The number of data sets used in attenuation relations and the study area increase the possibility of estimating earthquake parameters. The data set used in the AR4 attenuation relationship used in the study and the fact that the region taken into consideration is the region where the earthquake occurred increased the data-model compatibility. It was concluded that existing attenuation relationships should be updated in order to better predict future earthquakes and their effects.

A review of 20 years (1999–2019) of Turkish–French collaboration in marine geoscience research in the Sea of Marmara

This paper retraces the history and main achievements of the ongoing Turkish–French collaboration in marine geoscience research in the Sea of Marmara, which was initiated in the aftermath of the 1999, Izmit and Duzce earthquakes. The collaboration resulted in nine large oceanographic cruises along with six recovery operations involving diverse vessels, and in the participation in two major EU-funded programmes (ESONET-NoE and MARSITE) and to one bilateral project, e.g. the MAREGAMI Project, co-funded by TUBITAK and ANR (the Turkish and French national funding agencies for research, respectively). In this paper, we review the major scientific contributions on the tectonic evolution of the North-Anatolian Fault in the Marmara Region; on the relationships between faulting, seismicity, fluids and ecosystems; and on paleo-seismology and paleo-oceanography in the Sea of Marmara.

Discrimination of the natural and artificial quakes in the Eastern Marmara Region, Turkey

The aim of this study is to determine the source of seismic quakes is whether natural or artificial in the Eastern Marmara Region which is also included two branches of western part of the North Anatolian Fault Zone. It is known as one of the most seismically hazardous region in Turkey and 1999 Izmit and Duzce Earthquakes were occurred inside this area. In addition, it has geothermal springs, lots of mining areas, tunnel, bridge and road construction points. Under these conditions, it is seismologically important to make a study about the discrimination of the natural and artificial events. 611 seismic events with Ml ≤ 2.5 which has occurred between 2017 and 2019, recorded by 11 seismic stations that are being operated by Republic of Turkey Prime Ministry Disaster and Emergency Management Authority Presidential of Earthquake Department were analyzed. Amplitude ratio, complexity and continuous wavelet transform (CWT) methods were performed; linear and quadratic discriminant functions (LDF, QDF) were used for statistical processes to all waveforms and their results. All waveforms were identified by significant manual investigation that P wave first motion polarity, no or low amplitude S wave recording, the vision of coda wave decay and Rg phase detection and it called as a first determination. The results were compared to first determination and the final decisions were gained with the combination of their all. Besides with the all methods, CWT analyze could give more reliable results than the others and amplitude ratio method can serve better results than complexity. Otherwise, LDF could classify the events better than QDF. Through the final decision, 395 earthquake and 182 blast recordings were clearly discriminated with the accuracy of 94.44% and the source types of 34 seismic events could not be identified. The obtained discriminant functions for each station are useful to determine the source types of the events and they could clarify the contaminated earthquake catalogues. Increasing the reliability of the final results would be related with using these methods together.

Determination of Peak Impact Force for Buildings Exposed to Structural Pounding during Earthquakes

Structural pounding between adjacent, insufficiently separated buildings, or bridge segments, has been repeatedly observed during seismic excitations. Such earthquake-induced collisions may cause severe structural damage or even lead to the collapse of colliding structures. The aim of the present paper was to show the results of the study focused on determination of peak impact forces during collisions between buildings exposed to different seismic excitations. A set of different ground motion records, with various peak ground acceleration (PGA) values and frequency contents, were considered. First, pounding-involved numerical analysis was conducted for the basic parameters of colliding buildings. Then, the parametric study was carried out for different structural natural periods, structural damping ratios, gap sizes between buildings and coefficients of restitution. The results of the analysis conducted for the basic structural parameters indicate that the largest response of the analysed buildings was observed for the Duzce earthquake. The parametric study showed that the pounding-involved structural response depended substantially on all parameters considered in the analysis, and the largest response was observed for different ground motions. The results of the study presented in this paper indicate that the value of the peak impact force expected during the time of the earthquake does not depend on the PGA value of ground motion, but rather on the frequency contents of excitation and pounding scenario. It is therefore recommended that the peak impact force for buildings exposed to structural pounding during earthquakes should be determined individually for the specific structural configuration taking into account the design ground motion.

Broadband Ground Motion Simulation Within the City of Düzce (Turkey) and Building Response Simulation

In areas with significant seismic activity and insufficient seismic networks, simulated ground motions are required for both seismic hazard and engineering analyses. One important task is evaluating the efficiency of the simulated records in building response estimation. In this study, a hybrid ground motion simulation framework is presented to obtain broadband ground motion time histories of a past major earthquake in Duzce (Turkey). The hybrid ground motion simulation framework presented herein is a combination of a discrete-wavenumber finite element method for simulating low frequencies and a stochastic finite-fault method for the higher frequencies. The proposed technique is first validated by the simulation of the 12 November 1999 Duzce earthquake (\(M_{\text{w}}\) = 7.1), which occurred in the North Anatolian Fault Zone, Turkey. Peak simulated ground motions at selected nodes are then compared against ground motion prediction equations derived with global and local data sets. Next, the spatial distribution of simulated peak ground motion intensities are obtained in the region and compared with the observed damage distribution. Results demonstrate that the earthquake is simulated effectively despite the limitations in number of stations and velocity models. Finally, to evaluate the simulated records in building response estimation, nonlinear time history analyses of three reinforced-concrete multi-degree-of-freedom structures are performed with real and simulated records of the 1999 Duzce earthquake in the OpenSees platform. The results reveal that reasonable predictions can be made regarding the dynamic response of structures using the records simulated with the approach presented herein.

Analysis of the first urban regeneration area in Kocaeli after Gölcük earthquake by using zoning plans

Rapidly growing cities following The Industrial Revolution remained insufficient to fulfill today’s necessities. Also, natural disasters such as earthquakes, floods or unsound structures have affected the development of cities adversely. Although natural disasters can be unpredictable, the issue of preparing cities for natural disasters, planning cities and regulating laws accordingly are becoming increasingly crucial. Urban regeneration activities are one of these preventions taken in this purpose. It is observed that countries such as Turkey, faced with natural disasters intensively, suffer from serious physical, financial and moral losses. Therefore, urban renewal activities have gained importance in Turkey after The Golcuk Earthquake (7.4Mw) and The Duzce Earthquake (7.2Mw) in 1999. The first urban regeneration project in Kocaeli where was one of the cities experiencing hard collapses of these earthquakes is about to be completed. Research of the principles of urban sustainability and resiliency in urban regeneration practices, which are priority issues due to natural disaster risks, has come into prominence. It is important not only to make urban areas more resistant to disasters but also to design according to social, economic and ecological criteria to make more livable. In this study, social, health, green, transportation and educational areas of the first urban regeneration area in Kocaeli were examined in terms of the basic needs of the city. For this purpose, pre and postproject zoning plans are analyzed and transferred to the GIS. The areal changes in the above-mentioned needs are evaluated for changing population density and their sufficiencies are compared.

Seismic Isolation Systems Against Earthquake Disaster

Most of our country is located in the earthquake zone where active fault lines exist. Statistical analysis show that damaging earthquake occurs every 8 months in our country.The major devastations due to the 1999 Kocaeli and Duzce earthquakes have caused almost impossible losses to compensate for the country's economy. The health facilities damaged or destroyed in these earthquakes caused the disruption of the most needed health services after the earthquake, and hence increase of the losses. Seismic isolation can be defined as, considering the characteristics of earthquake acceleration, preventing damage to small or medium-sized earthquakes, and reducing the damage to large earthquakes by increasing the period and damping of the building. Seismic isolation is an earthquake-resistant structural design approach based on the principle of reducing the seismic force of the buildings by extending the period of the building, rather than increasing the seismic resistance capacity of the structure. The right applications of this technology allow buildings to be elastic even during major earthquakes.

The development of attenuation relationship for Northwest Anatolia region

Ground-motion attenuation relationships using the 1999 Kocaeli earthquake data were developed for the Northwest Anatolia region. This region is seismically active due to its location on Northwest Anatolia Fault Zone and was affected by the 1999 Kocaeli and Duzce earthquakes. Properties of the investigated stations and strong ground-motion data were taken from the Strong Ground Motion Database of Turkey (2017) (TR-NSMN) and Pacific Earthquake Engineering Research Center-Enhancement of Next Generation Attenuation Relationships for Western US (PEER-NGA-West2) database. SeismoSignal software was used in the evaluation of the acceleration records measured in the stations. A generated database for this study contains 369 mainshock and aftershock records, which occurred in the region of 39.39 to 41.03 North (N)/26.04 to 31.73 East (E) coordinates between the years of 1999 (Kocaeli earthquake) and 2006. In this research, peak ground acceleration is greater than 1 gal, and moment magnitude (M W ) is greater than 4.0 and Joyner-Boore distance (R JB ) is 1–344 km. These records were taken from 76 stations located in the investigation area. In addition to these data, 33 mainshock records worldwide were used for recovery of regression coefficients. Therefore, total of 402 data were used in this research. Attenuation relationships obtained from different types of ground were derived from the model generated by Boore et al. (Seismol Res Lett 68(1):128–153, 1997) for shallow earthquakes in North America. In this study, attenuation relation equations were developed by applying nonlinear regression analysis, with Statistical Package for the Social Sciences (SPSS) Statistics 20.0 software for B-C and D class soil according to the National Earthquake Hazards Reduction Program (NEHRP) classification system.

Estimation of seismic slope displacements in North Anatolian Fault Zone, Karamürsel (Kocaeli,Turkey)

The seismic stability of slopes and earthquake induced displacements should be evaluated with particular emphasis on earthquake records with site specific geological and geotechnical setting. The right lateral strike slip North Anatolian Fault (NAF) caused considerable damage on environment and residential areas of northern Turkey during the devastating 17.08.1999 Marmara and 12.11.Duzce earthquakes. Several mass movements have occurred around Karamursel, Oluklu, Ihsaniye, Hayriye and Yalakdere towns of Kocaeli within weathered/completely weathered Upper Cretaceous aged flysch, Eocene aged flysch and Pliocene soil deposits. A total of 38 instabilities were encountered and classified during the field studies. Geotechnical data were compiled from previous work and trial pits. Pseudostatic slope stability analysis were conducted along the identical slopes selected from the geological units. Peak ground acceleration values were picked up from stations, located around the study area. The static factor of safety values were calculated for slopes for each lithological unit. The critical acceleration values to cause seismic displacement were extracted from pseudostatic analyses. Variation of seismic displacements based on different amplitudes of a single scenario earthquake was calculated by double integration. Earthquake triggered seismic displacements could reach up to 46 cm based on the such scenario earthquake record of Marmara earthquake. Failed slopes and quiescent slopes might be triggered by an earthquake. This must be considered during land use planning for any single residence or agricultural purposes.

Basin Edge Effect on Seismic Ground Response: A Parametric Study for Duzce Basin Case, Turkey

In this study, edge effect on the spatial variation of surface ground motion was evaluated by conducting one (1D) and two-dimensional (2D) dynamic analyses on the numerical model of Duzce basin. Duzce is a province in northwestern Turkey and was hit by a devastating earthquake in November 1999. In order to estimate the seismic behavior of Duzce basin, 1D and 2D dynamic response analyses were carried out on its numerical model by using the seismic bedrock motion data derived from the deconvolution analysis of the N–S component of 1999 Duzce earthquake accelerogram. In addition, a series of different accelerograms and slope values were utilized to investigate the possible effects of change in strong ground motion intensity level and edge geometry on the dynamic response of soil layers over inclined bedrock. The finite element model for the edge section of the flat sedimentary basin was set up by using the 2D shear wave velocity profile, geotechnical and geological site conditions in Duzce. The variation of 2D/1D spectral acceleration ratios and aggravation factors with distance from basin edge was obtained for different period values. The results indicate that the aggravation factors reached their maximum values at a specific zone near basin edge and they generally converged to 1 regardless of the bedrock inclination or period values with increasing distance from the edge section. The highest aggravation factor values were calculated as 2.0–2.5 for the period interval of $$T=$$ 0.2–0.6 s. A relationship was proposed between the aggravation factor and basin edge geometry.

Assessment of Simulated Ground Motions in Earthquake Engineering Practice: A Case Study for Duzce (Turkey)

Simulated ground motions can be used in structural and earthquake engineering practice as an alternative to or to augment the real ground motion data sets. Common engineering applications of simulated motions are linear and nonlinear time history analyses of building structures, where full acceleration records are necessary. Before using simulated ground motions in such applications, it is important to assess those in terms of their frequency and amplitude content as well as their match with the corresponding real records. In this study, a framework is outlined for assessment of simulated ground motions in terms of their use in structural engineering. Misfit criteria are determined for both ground motion parameters and structural response by comparing the simulated values against the corresponding real values. For this purpose, as a case study, the 12 November 1999 Duzce earthquake is simulated using stochastic finite-fault methodology. Simulated records are employed for time history analyses of frame models of typical residential buildings. Next, the relationships between ground motion misfits and structural response misfits are studied. Results show that the seismological misfits around the fundamental period of selected buildings determine the accuracy of the simulated responses in terms of their agreement with the observed responses.

Ambient vibration testing and seismic performance of precast I beam bridges on a high-speed railway line

In this study, the seismic performance levels of four bridges are determined using finite element modeling based on ambient vibration testing. The study includes finite element modeling, analytical modal analyses, ambient vibration testing and earthquake analyses of the bridges. For the purpose, four prestressed precast I beam bridges that were constructed for the Ankara-Sivas high speed railway line are selected for analytical and experimental studies. In the study, firstly a literature review related to the dynamic behavior of bridges especially precast beam bridges is given and then the formulation part related to ambient vibration testing and structural performance according to Turkish Seismic Code (2007) is presented. Next, 3D finite element models of the bridge are described and modeled using LARSA 4D software, and analytical dynamic characteristics are obtained. Then ambient vibration testing conducted on the bridges under natural excitations and experimental natural frequencies are estimated. Lastly, time history analyses of the bridges under the 1999 Kocaeli, 1992 Erzincan, and 1999 Duzce Earthquakes are performed and seismic performance levels according to TSC2007 are determined. The results show that the damage on the bridges is all under the minimum damage limit which is in the minimum damage region under all three earthquakes.

Seismic behavior of two monumental buildings in historical Cappadocia region of Turkey

This study focuses on a displacement-based approach for the investigation of seismic behavior of two monumental buildings constructed in the historical Cappadocia region of Turkey. The first historic building is located in the town of Konakli, which is 27 km away from the city of Nigde and is situated in north-east of the city. It was built in 1844 and has served as a temple. The second building is located in the town of Fertek, 2 km from the city of Nigde. It has been used as a temple since it was built in 1835. These two buildings are seen as representative of many similar temple buildings constructed in the Cappadocia region during the same era. The seismic behavior of these two monumental buildings is investigated using dynamic analysis procedures. The buildings are subjected to ground motion records obtained during recent earthquakes in Turkey. These ground motions were recorded during the Ceyhan earthquake of 1998, which occurred close to Nigde; the Marmara earthquake of 1999 and the Duzce earthquake of 1999. Dynamic analyses are conducted for two cases with and without walls, as this helps in identification of the effect of structural walls on the seismic behaviors of these buildings. In the light of the dynamic analyses results, the expected level of damage and structural irregularities of the monumental buildings are examined. It is observed that slab discontinuities on the first floors constitute a major element in the expected structural damage for both buildings. Destructive levels of deformation are observed at Konakli in the roof domes of the building. In addition, upon application of certain ground motions, destructive levels of drift are observed, another element contributing to the expected damage.

Free and Forced Vibration Analyses of Hyperbolic Cooling Tower Shell Using Harmonic Solid Ring Finite Elements

This paper discusses free and forced vibration responses of hyperbolic cooling tower shell which is one of the complex real life applications of axisymmetric structures. 9-noded harmonic solid ring finite element is used in the numerical model of the cooling tower. Physically a three-dimensional cooling tower problem is reduced to a two dimensional one by expressing earthquake loading in the form of Fourier series for a single harmonic with the help of harmonic elements. Therefore, the complete solution for the problem is obtained simply for a single load component that makes the model computationally much more efficient. A computer program is coded in Matlab for the purpose and the results obtained in the study are verified with the results available in the literature. A parametric study is also performed for the variations in shell curvature of the tower. The time history analysis method is used for the dynamic response of the cooling tower shell. Acceleration records of Duzce earthquake is used in the study and the results are presented in tabular and graphical formats comparatively for varying shell curvature. It can be concluded that circumferential mode number and shell curvature have significant effects on the dynamic responses of cooling towers.

Soft-Story Effects on the Behavior of Fixed-Base and LRB Base-Isolated Reinforced Concrete Buildings

In Turkey, the entry stories of reinforced concrete (RC) structures are usually used for commercial purposes because they are slightly higher than other stories. Therefore, these RC structures sometimes exhibit what is called soft-story behavior. The best examples of this behavior are observed in the severe damage or collapse of RC structures with soft stories during the 1999 Marmara and Duzce earthquakes. To prevent this type of damage, seismic isolation systems can be used in the construction of new structures. This study focuses on the soft-story behavior of RC structures with fixed-base and lead core rubber bearing (LRB) systems under different seismic loads. The superstructure is modeled using the Turkish Seismic Regulation (TEC 2007). Because there is no detailed information concerning LRB isolators in the Turkish Seismic Regulations, the Uniform Building Code (UBC 97) is used to model the substructure system under consideration. In this study, four different structural models are designed to study the effect of the soft-story behavior. The dynamic analysis of the time domain on these frame systems is conducted using Ruaumoko software, and the influences of soft-story behavior in fixed-base and LRB base-isolated systems are investigated. The period of the frame system, story accelerations, inter-story drift ratio, base shear forces, and distribution of plastic hinges and their damage conditions are evaluated.

Recent tectonic features of the central part (Bolu-Corum) of the North Anatolian Fault

North Anatolian Fault (NAF) and its share zone (NAFZ) which starts from Karliova (Bingol) the east to Saros Gulf (Aegean Sea) the west is one of the active seismic zone all over the world. Many destructive earthquakes occurred on its trace in the last century. After the 1999 Izmit and Duzce earthquakes, the earth science studies increase on the NAF to better understand mechanism and to monitor the motion of it. Monitoring such motion can be achieved by the instrumental tools or techniques like GPS, InSAR, LIDAR, creep meter, etc. Using GPS measurements in 1990’s, the rate and pole of the anticlockwise rotation of the Anatolian plate relative to Eurasia were accurately determined. The GPS observations also showed that while the NW-SE trending section of the NAF between Karliova and Vezirkopru has nearly purely strike slip mechanism, the NE-SW trending section of the NAF between Vezirkopru and Bolu has transpressive character. While the fault-parallel velocities have been estimated from just a few GPS vectors available in the region, little is known about the fault-perpendicular component of the regional velocity. The rate of conversion and how it varies along strike are not known due to the sparsely distributed GPS benchmarks in the region. At the same time, the aseismic fault creep determined using InSAR technique has needed to proof and improve by other techniques and tools. For this propose the new project has been started to determine quantitatively the rate of convergence and its variation along the NE-SW trending section/segment of the NAF between Bolu and Corum by employing a new GPS network. In this study, we discuss the tectonic phenomena on the central part (Bolu-Corum) of the NAFZ and present the first results of the project. Keywords: North Anatolian Fault; Deformation; GPS; Earthquake; Geodesy DOI: 10.17350/HJSE19030000011 Full Text:

Literature search on importance of hospital disaster plans and Earthquake ,fire and KBRN evecuaton drill administrared on a state hospital in Istanbul

In our country, with other health institutions, consideration of precautions for natural disasters in health sector and gaining speed corresponds to the period which follows Golcuk and Duzce earthquakes. After the Marmara earthquake, when disaster is mentioned, only the earthquake events were perceived. Earthquake is an important subject. However floods, terrorism, fire, industrial accidents are also in the scope of disaster medicine. If we want to reach the modern society level, we ought to have the capacity to access every aggrieved person at the areas of disaster and we must be able to resolve victimization. At the time of disaster, first reaction to it is chaos. However the intensity of this chaos can be reduced by a planned and organized approach. In cases of disaster, the health services at disaster medicine are very different than individual health services. In any unusual situation at the hospital, the emergency service is either effected or plays a big role in resolving the problem. In this study, preparation and development of a Hospital Disaster Plan which will respond to the needs by determining the disasters and crisis situations of one Government Hospital occurred until today and the course of integration of all of the hospital personnel to the consciousness of applying the Hospital Disaster Plan throughout the years will be explained.

Performance evaluation of Turkish disaster relief management system in 1999 earthquakes using data envelopment analysis

This study estimates the relative efficiency of disaster relief organizations that participated in the relief activities following the Marmara and Duzce earthquakes that took place in Turkey in 1999. For this purpose, the activities in the response and relief phases of the disaster management cycle following the 1999 earthquakes are classified into four groups: “search and rescue,” “infrastructure rehabilitation and debris removal,” “health care” and “providing basic needs to the disaster victims.” Next, the unbounded data envelopment analysis (DEA) model is applied to estimate the efficiency scores and optimal input/output weights of the decision-making units (DMUs) in these groups. The efficient and inefficient units are then determined, and the target input and output values are determined for the inefficient units. However, some inputs and outputs are found to be zero or are outlier values in the unbounded model results. To eliminate this deficiency, the bounded model is applied by including additional constraints in the unbounded model. After determining a solution with this model, the optimal input/output weights, the efficiency scores of the DMUs and the efficient and inefficient units are determined. The results of the bounded version of the DEA are more accurate than those of the unbounded model. More accurate and reliable results are obtained from the unbounded model because zero and outlier values are eliminated.

A comparison of the effect of SSI on base isolation systems and fixed-base structures for soft soil

This study investigated the effect of soil-structure interaction (SSI) on the response of base-isolated buildings. Seismic isolation can significantly reduce the induced seismic loads on a relatively stiff building by introducing flexibility at its base and avoiding resonance with the predominant frequencies of common earthquakes. To provide a better understanding of the movement behavior of multi-story structures during earthquakes, this study analyzed the dynamic behavior of multi-story structures with high damping rubber bearing (HDRB) behavior base isolation systems that were built on soft soil. Various models were developed, both with and without consideration of SSI. Both the superstructure and soil were modeled linearly, but HDRB was modeled non-linearly. The behavior of the specified models under dynamic loads was analyzed using SAP2000 computer software. Erzincan, Marmara and Duzce Earthquakes were chosen as the ground motions. Following the analysis, the displacements, base shear forces, top story accelerations, base level accelerations, periods and maximum internal forces were compared in isolated and fixed-base structures with and without SSI. The results indicate that soil-structure interaction is an important factor (in terms of earthquakes) to consider in the selection of an appropriate isolator for base-isolated structures on soft soils.

Estimation of Strong Motion Experienced in the Vicinity of the Bolu Viaduct during the 1999 Duzce Earthquake: Development and Validation of a Hybrid Method

Abstract This paper revisits the 12 November 1999 earthquake in Duzce, Turkey, and attempts to derive realistic estimates of ground motions experienced near the edge of the fault‐rupture outcrop where the 2.5‐km long Bolu twin viaduct failed. The nearest accelerographic stations, in Bolu and Duzce, being neither sufficiently close to the fault nor in similar orientation with respect to the seismogenic fault, could hardly explain the observed damage when used as excitation at the exact location of the viaduct. The novelty of the research lies on the fact that the proposed ground motions are chosen on the basis of their ability to reproduce the observed rocking response of two sets of precast concrete girders temporarily stored along the highway axis at the time of the event—a case study that has hitherto received scarce attention in literature. Although lying in literally adjacent locations, all girders of the first set toppled, whereas most girders of the second set, with a different orientation than the first, remained standing. Scenarios of hybrid ground motions that account for likely near‐fault effects are devised and calibrated with nonlinear finite‐element analyses. The most likely motions identified that can simultaneously provoke toppling of the first‐site girders and not toppling of the neighboring site, are those combining a sufficiently strong forward‐rupture directivity pulse, with fault‐normal V max on the order of 100 cm/s, with a quite intense fault‐parallel direction fling‐step pulse that is compatible with a dislocation exceeding 60 cm.