Journal of Seismology and Earthquake Engineering
http://www.jsee.ir/
Journal of Seismology and Earthquake Engineeringendaily1Tue, 01 Aug 2023 00:00:00 +0430Tue, 01 Aug 2023 00:00:00 +0430The role of tear faults on the morphology and seismic activity of the Ashkhaneh fault zone, Kopeh-Dagh, NE Iran
http://www.jsee.ir/article_706067.html
The Kopeh-Dagh zone of NE Iran is dominated by active strike-slip and thrust faults that accommodate a part of the convergence between the Arabian and Eurasian Plates. The Ashkhaneh thrust fault zone with approximately 80 km long is one of the main accommodative structures which has been dissected by a number of strike-slip tear faults. Tectonic geomorphology, satellite-based Global Positioning System (GPS), and seismic data imply that the development of tear faults is one of the main controlling factors in structural deformation and related seismic activity along the Ashkhaneh thrust fault zone. The tectonic activity of the Ashkhaneh fault zone is mainly due to the E-W trending range-parallel reverse faults and NE-SW to ENE-WSW trending range-crossing left-lateral strike-slip tear faults coming from two stages. In the first stage, the major E-W trending Ashkhaneh thrust fault zone has been developed in response to the collision of Central Iran with the South Caspian Basin. In the second stage, the progressive N-S shortening resulted in mountain curvature in eastern Alborz and the formation of strike-slip tear faults in response to the differential shortening along the Ashkhaneh fault zone. The sense of slip and geometry of the tear faults and the Ashkhaneh thrust fault seems to provide insights into faults interaction, so that the likely movement along one of these faults may cause reactivation of the other fault(s); similar to the earthquake occurrences on the Shalgun-Yelimsi tear fault (2019/11/07, Mw 5.9) and South Bozgush thrust fault (2019/11/10, Mw 4.4) in northwestern Iran.Analysis of Bearing Capacity of Shallow Foundations Located on the Reinforced Sandy Soils by Limit Analysis Method
http://www.jsee.ir/article_708336.html
Considering the high seismicity of Iran, the study of seismic force's effects on the foundations' bearing capacity is always of interest to researchers. The current study investigated the bearing capacity of a shallow foundation reinforced with geogrid using the limit analysis method in static and seismic modes. The Optum G2 software is used for this purpose. An attempt has been made to calculate the static and seismic bearing capacity of the foundation by conducting a parametric study on the geogrid length (1B, 2B, 3B, 4B and 5B), geogrid burial depth (0.1B, 0.2B, 0.5B, 0.7B, 0.9B, 1.1B and 1.8B), geogrid layers distance (0.1B, 0.2B, 0.4B, 0.6B and 0.8B) and the number of geogrid layers (1, 2, 3 and 4). Also, these analyses were performed on different internal friction angles of sandy soil (25, 30, 35 and 40 degrees) and various foundation depths (0, 0.3B and 0.5B). The results show that the effective length of geogrid is estimated to be between 2B and 3B. Also, the geogrid's maximum effective depth is between 0.7B and 1.1B. The optimal distance of geogrid layers was estimated between 0.2B and 0.6B. Also, the optimal number of geogrid layers varies from 2 to 4, depending on the soil's internal friction angle and the foundation's burial depth. The seismic bearing capacity of the foundation estimated to be less than the static condition, and the percentage decrease of the seismic bearing capacity of the foundation compared to the static mode was varied between 7% and 20%.Numerical Modeling of a New Mitigation Measure for Reverse Surface Fault Rupture Hazards Effects on Buildings
http://www.jsee.ir/article_707341.html
Surface fault rupture can lead to significant harm to engineered structures and facilities due to differential displacement in the ground. With the growing demand for land use, it might become essential to implement strategies to protect structures against hazards arising from fault rupture propagation. This study examines a novel mitigation approach utilizing an underpinning technique. To lessen foundation rotation during a fault rupture, a pile similar to the underpinning technique is employed beneath the foundation. This pile is not used to reinforce the main foundation; rather, it serves as a structural element to reduce hazards during a fault rupture with the removed support between the foundation and the pile. The effectiveness of this pile in the soil under the structure is evaluated through a series of numerical models. The findings suggest that while this pile is effective in mitigating the dangers of surface fault rupture, such as building rotation, its application should be guided by comprehensive geotechnical investigation given the complex nature of fault-foundation interaction issues.Performance Evaluation of Natural Gas Transmission Pipelines in Landslides
http://www.jsee.ir/article_708160.html
The study aimed to evaluate the behavior of typical natural gas transmission pipelines in landslides and investigate the effect of various parameters such as internal pressure, pipe diameter, and soil type on their active lengths. Nonlinear Finite Element Analyses (FEA) were performed using the Winkler-type beam-on-spring model to evaluate the pipeline response in landslides. The FEA results showed that the stress and strain distribution along the pipeline were primarily positive, which indicated that the ground movement was resisted by axial tension force (membrane action) of the pipeline. The maximum axial strain occurred at the beginning and the end of the landslide zone, indicating that the pipeline would fail at these locations. The FEA results also indicated that the maximum axial forces in all cases were very close to the section capacity of the pipe, indicating that landslide-induced ground displacements resulted in very high axial force and relatively low bending moment in typical natural gas transmission pipelines.The PRCI guidelines provide an equation for estimating the anchor length of buried steel pipelines, but the results of this study indicate that the anchor lengths are much larger than those calculated by the PRCI equation. A proposed equation based on ultimate strength of the pipe section is suggested for calculating anchor length, which gives a good estimate of the anchor length with an average error of 4% relative to the analytical results. Overall, the study concluded that the internal pressure of the pipeline had no significant effect on the anchor lengths of the pipelines, and the proposed equation provides a more accurate estimate of the anchor length of typical natural gas transmission pipelines.On importance of seismic phase weighting in earthquake location problem
http://www.jsee.ir/article_707467.html
Accurate seismic source location is a critical endeavor in seismology, essential for precisely determining the origin of seismic events. Various methods are available for pinpointing seismic sources, each exhibiting varying degrees of accuracy and reliability. In this study, our objective is to assess the influence of seismic phase weighting on earthquake location by comparing the outcomes of three distinct earthquake location programs. To achieve this, we generated two synthetic earthquake catalogs employing a sophisticated 3D velocity model and a seismic network comprised of 15 stations. We intentionally introduced two synthetic faults, each with different orientations, situated to the south and north of the network. On these fault surfaces, we distributed 100 synthetic earthquakes. We then utilized the phase arrivals of these synthetic events to construct both unweighted and weighted catalogs. Weighting was assigned based on error calculations and local noise models unique to each station.Our findings reveal that the incorporation of appropriate data weighting during the phase reading stage significantly enhances the accuracy of earthquake location, resulting in reduced errors and uncertainties. Among the three programs we compared, HypoDD demonstrated the best performance, successfully determining earthquake locations with minimal localization errors. In the comparison between Hypocenter and Hypo71, the latter's robust outlier detection algorithm proved advantageous in estimating hypocentral errors, even in the presence of outliers. When examining the results obtained from the weighted catalogs, both programs yielded similar outcomes when the data was appropriately weighted, underscoring the crucial role of proper data weighting in achieving consistent performance.Design of the new rigid joint model determining panel zone deformation by both bending and shear distortion
http://www.jsee.ir/article_709271.html
Beam-to-column connection in the Moment-resisting frame plays a significant role in the seismic responses of the structure, including its ductility. Panel zone is subjected to large asymmetric anchors under seismic loads, which causes shear ductility. Therefore, an accurate estimation of the panel zone behavior during the structure's design is essential. Existing relationships have problems in estimating the behavior of the panel zone. Some relationships, such as the Krawinkler model, have good accuracy but are highly complex in the modeling process, and some of the proposed models for estimating the behavior of the panel zone, such as the scissors model, are easy to use. However, they do not have good accuracy. For this reason, engineers typically abandon panel zone modeling when using software such as SAP and ETABS to design structures, and consider the panel zone to be rigid. This method of modeling the panel zone in short-rise buildings does not have much effect on the deformation of the frame. However, with increasing the height of the structure, the effect of accurate modeling of the behavior of the panel zone on the overall behavior of the structure will increase.Given this issue, it is necessary to provide an accurate and, simultaneously, simple numerical model to predict the behavior of the panel zone. For this purpose, in this research, first, the weaknesses and strengths of the existing models were carefully studied, and then by combining these models and performing various analyzes in OpenSees software, the final model was presented. In this numerical model, a torsional spring with trilinear behavior is used to simulate the behavior of the panel zone, considering both the bending and shear effects. The relationships used in the proposed model are derived from Krawinkler relationships that have been optimized for the conditions of the new model. Using this model, the independent degree of freedom of the panel zone has been reduced by 75% compared to the Krawinkler model, and the capacity of the panel zone in the nonlinear region has been increased 6.8 times and is almost identical to the experimental results.Analysis of the prediction of earthquake locations in Anatolia and adjacent regions of 1974 in connection with the 2023 Türkiye -Syria Great Earthquakes
http://www.jsee.ir/article_709393.html
On February 6, 2023, two devastating earthquakes occurred in the southeast of Turkey with an interval of 9 hours, which also affected the territory of Syria. The position of the epicenters of these earthquakes is discussed in connection with the forecast of M6.5+ earthquake locations for the territory of Anatolia and adjacent regions, obtained in 1974 by I.M. Gelfand, V.I. Keilis-Borok and their co-authors on the base of morphostructural zoning data employing the Cora-3 pattern recognition algorithm. It has been established that the epicenters of the earthquakes of February 6, 2023 were located in the node, which in 1974 was identified as capable of M6.5+. Since 1974, 36 M6.5+ events have been observed in the study region. The spatial distribution of these events is analyzed in relation to the seismogenic nodes recognized in 1974. It was found that the epicenters of 32 such events are located in the nodes recognized as dangerous for M6.5+ in 1974.Numerical and analytical investigation of reduced beam section with yielding damper and their comparison
http://www.jsee.ir/article_709759.html
Connections play a crucial role in structures, including steel structures, and have a significant impact on the seismic behavior of the structure. One particular type of connection commonly used in steel structures is the Reduced Beam Section (RBS). This connection reduces the moment strength of the beam near the column, which in turn results in less moment being transferred to the column at the final moment. The study involved 30 numerical analyses conducted using ABAQUS to examine two cases. The first case involved investigating a connection with a beam that had a hole in the flange area. The variables examined included the area of the flange holes and the axial force of the column. In the second case, a yield ring was utilized in the flange area of the beam. The radius of the yield ring was considered as a variable in six different cases. Equations for calculating the maximum strength moment and analyzing the linear region of a beam were presented in the study. The yielding damper must yield earlier than other members, and an equation was provided to ensure that it does. Finally, the cyclic behavior of two models was also compared. Numerical analysis revealed that if the area of the flange holes is half that of the beam flanges, the beam&#039;s strength does not significantly decrease with increasing axial force. The elastic stiffness and ductility of the SRD-equipped connection were higher than the RBS model, with the SRD model achieving 1.8 and 2.6 times greater ductility and elastic stiffness, respectively, in the most optimal state.Influence of Beam Height-Column Width Ratio on Seismic Behavior of RC Moment Resisting Frames
http://www.jsee.ir/article_710035.html
Most reputable international design codes have included provisions for achieving ductile behavior and avoiding brittle and hazardous behavior in reinforced concrete frames. These provisions aim to achieve the concept of weak beam-strong column, where plastic hinges during earthquake occur first in the beams. Analysis of frequent and repetitive failures in strong earthquakes in recent decades of reinforced concrete structures shows that the strong beam-weak column failure mode typically leads to severe damage in these structures. The frequent occurrence of this failure mode can be attributed to two main factors. Firstly, stiffer beams are often used against more flexible columns due to the absence of seismic provisions that limit the relation between beam height and column width finlay results in column severe damage on column and finally collapse of them. Secondly, the effect of the cast-in-situ slab in increasing the negative flexural strength of the beam is often underestimated or ignored, leading to the flexural strength of the columns being less than that of the beams. To assess the impact of the ratio of beam height to column width on the seismic performance of MRFs, a series of computational models were created and analyzed in a parametric study. Prior to that, the FEA performance was validated by comparing its results with experimental data. The findings emphasize the urgent need for a new seismic provision that limits the beam height to column width ratio to a maximum of 1.25.Enhancing Seismic Performance of Steel Bridge Piers with Rocking Mechanism and Friction Damper: A Finite Element Simulation Study
http://www.jsee.ir/article_711271.html
This study presents a novel rocking system for pier highway bridges that aims to minimize damage to the pier and reduce residual drift. A three-dimensional finite-element (FE) simulation was used to evaluate the proposed system. The finite element models were subjected to lateral cyclic loading to study the re-centering system, stress concentrations, and deformation. The system consists of a tubular steel column and a friction damper that absorbs energy through friction at low lateral displacements (drift less than 3%) and plasticization of the dissipator plate at large lateral displacements. The system operates on a two-level hysteresis, eliminating the need for tendons and utilizing only the gravity load for re-centering. The finite element analysis demonstrated that the re-centering of the system was achievable without the need for tendons, and the system could return to its original position (up to 5% drift) without significant damage. Although the friction damper is the only element that goes beyond the elastic state, the remaining components remain in this state.
The proposed system achieves a self-centering ability via rocking and eliminates permanent deformations. Moreover, the system is relatively easy to construct, maintain, and retrofit, in addition to the aforementioned benefits. Therefore, this novel rocking system is a promising solution for pier highway bridges, potentially improving their seismic performance while reducing maintenance and retrofitting costs.MULTI-SECTORAL RAPID ASSESSMENT AND POST-EVALUATION IN KAHRAMANMARAS EARTHQUAKE, TURKIYE: ADDRESSING THE NEEDS OF AFFECTED PEOPLE
http://www.jsee.ir/article_712039.html
Two devastating earthquakes struck on February 6, 2023, the first with a magnitude of 7.7 at 04:17 in the Pazarcık district of Kahramanmaraş, and the second one with a magnitude of 7.6 at 13:24 in the Ekin&ouml;z&uuml; and Elbistan districts of Kahramanmaraş in eastern and southeastern Anatolia, as well as northern Syria. These two earthquakes caused vast destruction in 11 provinces and affected 15.2 million people, including 5.4 million children, living in stricken provinces (Kahramannaras and Hatay Report, Post Earthquake Assessment, 2023). The two earthquakes had a devastating impact on settlements, housing, and businesses in most of the impacted locations, with extremely high levels of damage in highly populated areas. The Nirengi, a Turkish Non-governmental Organization team&#039;s reflections on the severe impact of the two earthquakes and living conditions in several lifeline sectors, derived through field observations, data from interviewees, and partly desk research, which are presented briefly in this paper. The provided information has been gathered a few days after the earthquake and the recommendations are noted based on the findings of initial assessment following the disaster. Also results of the observations one year after the earthquake are presented to show the trend and progress in aiding the affected people.Earthquake Nowcasting: Retrospective Testing in Sarpol-e Zahab, Iran
http://www.jsee.ir/article_712050.html
Sarpol-e Zahab, in the west of Iran, is subjected to a high earthquake risk. Located in the north part of the Zagros seismic belt and is surrounded by several active faults that show some M7+ earthquake records.
Nowcasting refers to the process of determining the uncertain state of the seismicity at the present time by indirect means for the seismically active regions, where the goal is to estimate the current state of risk, the current state of the fault system, and its current level of progress through the earthquake cycle. The local catalog of earthquakes is used, using &ldquo;small&rdquo; earthquakes to determine the level of hazard from &ldquo;large&rdquo; earthquakes in the region. To evaluate the statistical distribution of the inter-event counts of small events that occur between large events, the natural time concept was used rather than clock time (Origin Time of Earthquake). This method does not involve any model other than the idea of an earthquake cycle. Rather, a specific radius and a specific large earthquake magnitude of interest are defined, ensuring that we have enough data to span at least ~10 or larger earthquake cycles in the region. We then compute the earthquake potential score (EPS) which is defined as the cumulative probability distribution P (n&lt;n(t)) for the current count n(t) for the small earthquakes in the region. The EPS was calculated as the total number of small earthquakes after the last large occurrence in the studied area. EPS is therefore the current level of hazard and assigns a number between 0% and 100% to every region so defined, thus providing a unique measure. Physically, the EPS corresponds to an estimate of the level of progress through the earthquake cycle in the defined region at the current time.
We have determined the EPS values to consider events of Mw&ge;4.4 within two different radiuses (250 and 350 km) around Sarpol-e Zahab. The EPS values for Sarpol-e Zahab at 250 km corresponding to Mw&ge;5.5 and six events were found to be almost 0.86 and 0.97, respectively, while at 350 km these values are equal to 0.73 and 0.50 for Mw&ge;5.5 and six events, respectively.