Area Of Seismic Activity Research Articles

Ductile crack growth of high-graded pipeline steels in the presence of Lüders plateau

Strain-based engineering critical assessment methods allows certain amount of plastic strain during installation and in service, for pipelines crossing seismically-active areas. Most strain-based engineering critical assessment methods are established for materials with smooth stress-strain relationship, leaving the so-called Lüders plateau influence on ductile fracture response seldomly explored. This work studied the effect of the Lüders plateau on mode I ductile crack growth with the modified boundary layer (MBL) model under plane strain conditions. The “up-down-up” constitutive model was implemented and the Gurson damage model was selected to simulate crack propagation. Factors including the plateau length and softening modulus in the “up-down-up” constitutive model, strain hardening of the matrix material and the initial void volume fraction parameter were analyzed. Numerical results show that the Lüders plateau modifies the crack tip constraint and the damage evolution, and the plateau length plays the dominant role on ductile crack growth behaviour in the presence of Lüders plateau.

Detecting DC Electrical Resistivity Changes in Seismic Active Areas: State-of-the-Art and Future Directions

In this paper, a critical review of the geoelectrical monitoring activities carried out in seismically active areas is presented and discussed. The electrical resistivity of rocks is one of the geophysical parameters of greatest interest in the study of possible seismic precursors, and it is strongly influenced by the presence of highly fractured zones with high permeability and fluid levels. The analysis in the present study was carried out on results obtained over the last 50 years in seismic zones in China, Japan, the USA and Russia. These past works made it possible to classify the different monitoring strategies, analyze the theoretical models for interpreting possible correlations between anomalies in resistivity signals and local seismicity, and identify the main scientific and technological gaps in the literature. In addition, great attention has been paid to some recent works on the study of the correlations between focal mechanisms and the shapes of anomalous patterns in resistivity time series. Finally, some future scenarios for the development of new activities in this field have been identified.

Tensile strength of girth weld joint of linepipe with softened HAZ

In seismic-active area, the buried pipeline is subjected to the axial tensile load exceeding the yield stress of pipe material due to the lateral flow induced by soil liquefaction. Designing a girth weld joint that does not fracture at girth weld but base metal which has high elongation capacity is feasible to ensure adequate ground displacement absorbing capacity of the girth weld joint. However, as for fine grain steel, the heataffected zone (HAZ) is softened by welding heat input, and then, the zone of softened HAZ can be the origin of fracture under tensile load. The apparent strength of softened HAZ is affected by the plastic constraint from the surrounding weld metal and base metal during tensile loading, and the fracture location depends on the apparent strength of HAZ. This study investigates the tensile strength and fracture location of girth weld joints with softened HAZ in the static tensile test. The effect of geometric and mechanical heterogeneity of HAZ, strength overmatching of weld metal, and the width-thickness ratio of tensile test specimen on tensile strength are elucidated using parametric finite element analysis. Subsequently, an equation is proposed to predict the tensile strength and fracture location of the welded joint. Using the proposed equation, the condition of geometric and mechanical heterogeneity of the weld to confirm the girth weld joints that fracture at base metal under tensile load is clarified. The proposed equation can be used to design a girth weld joint with liquefaction earthquake resistance.

Time history comparative analyses of a thin-walled cold-formed steel structure considering P-D effect

The paper presents a comparative time history analysis based on the 1D-beam Finite Element Method (FEM) for a thin-walled cold-formed steel structure previously investigated both theoretically and experimentally. The recent earthquake which occurred in Turkey with 7.8Mw and a Peak Ground Acceleration (PGA) of almost 0.5g showed numerous collapses of different types of buildings. Romania has an active seismic area located in the Vrancea region where, in 1977 a 7.5Mw earthquake also occurred. In this context, this paper presents a comparative analysis with time history accelerograms of the recorded earthquake in North – South and East - West directions. The structural model was analyzed in Robot Structural Analysis software in two scenarios of the time history accelerograms considering also the P-Δ effect. The finite elements of the structure were defined as 1-D beam elements with hinged joints and limited axial stiffness previously obtained in past studies. The results showed a substantial increase in terms of displacements and stresses.

Seismic Assessment Formula for a Buried Pipeline With Local Wall Thinning

Abstract The structural strength of buried pipeline may be reduced by local wall thinning owing to corrosion in long-term operations. In seismic active area, it is necessary to ensure the integrity of buried pipeline with wall thinning against seismic motion. This study proposed a seismic assessment formula for a pipe with wall thinning subjected to cyclic axial loading assuming seismic motion. Cyclic axial loading experiments using pipes with wall thinning and finite element analysis (FEA) were conducted to study the failure behavior. The pipe with wall thinning deformed starting from the wall-thinning part, and finally plastic collapse due to elephant foot buckling or leakage at the wall thinning due to low-cycle fatigue occurred in several to ten and several cycles. Based on the deformation mechanism at wall thinning, a seismic assessment formula was proposed. The proposed formula can easily evaluate the seismic performance of the pipe with wall thinning against design seismic motion. The formula was validated by the results of experiments and FEA. In addition, based on the proposed formula, the assessment curves for an allowable wall-thinning size against design seismic motion were illustrated. The formula can be used to formulate standards and assess the safety of pipes with wall thinning that are subjected to seismic motion.

The generalized E-DVA method: a new approach for multi-modal pushover analysis under multi-component earthquakes with local variables maximization

Pushover analysis is a common nonlinear static procedure, performed to evaluate seismic response of civil structures. This approach allows considering the structural nonlinear behavior under earthquake loading in a simplified yet effective way; however, in its classic formulation, it is limited by restrictive and unrealistic assumptions. Thus, the basic method is inadequate for the accurate analysis of buildings without a vertical plane of symmetry and/or for multi-component earthquakes, where torsion effects cannot be neglected. Furthermore, standard pushover analysis only comprises one dominant mode of vibration; higher modes, and therefore their effects, are not accounted for. For all these reasons, the standard technique is generally not considered suitable for the assessment of buildings at high risk of natural-technological (NaTech) events, such as nuclear facilities in areas of high seismic activity. To overcome these limitations, a multi-modal pushover analysis procedure is here tested and validated on the data from a non-symmetric structure (the SMART case study) under multi-component earthquakes. In detail, the procedure applies a linear combination of modal load patterns, defined according to the well-established Direct Vectorial Addition (DVA) method. With respect to other existing multi-modal pushover analysis techniques, elliptical response envelopes are employed to calculate the corresponding combination factors. Innovatively, the identification of the dominant modes for the load pattern is not limited to the classic maximization of the forces at the basis of a structure but rather generalized to shear and displacement maximization at different heights and locations throughout the whole structural frame.

A multi-model probabilistic framework to evaluate seismic resilience of UHV converter stations

Ultra-high voltage converter stations are significant electric power infrastructures with a high electric energy load. To quantitatively evaluate the seismic and recovery capability of a UHV converter station, this paper proposes a multi-model probabilistic resilience assessment framework divided into four analysis modules for hierarchical evaluation. The conditional probability set of the functional state between network nodes is determined using a matrix-based approach. Taking connectivity and power transmission capacity into account, the functional reliability model was built through the improved Bayesian network. A multi-parameter quantification of the post-earthquake recovery process was carried out by constructing the stepped functional recovery function as well as the time-varying seismic resilience function. The economic loss assessment model was built from multiple aspects. Taking a typical ± 800 kV UHV converter station as a case study for seismic resilience analysis, the probabilistic resilience assessment was realized, and variation trends of the multi-parameter expected value were obtained by mathematical expectation. This article shows that taking measures to postpone the sensitive interval of the system helps to avoid the seismic active area. This avoidance of seismic activity is the objective of optimization. The proposed framework can serve as a reference for the operation and optimization of power systems.

Earthquake Disaster Risk Analysis for Mitigation Efforts in Seram and Buru Islands, Maluku

Earthquakes occur due to the sudden release of energy from within the earth causing seismic waves. Earthquake activity with a magnitude ³ 3.5 SR is grouped over 21 years from 2000-2020 to determine the level of seismicity in Seram Island, Buru Island, and surrounding areas. The area of seismic activity is clustered over three blocks. The purpose of this research is to determine the seismicity level and mitigation model in each block in the research area. The results showed that seismic activity in the study area with shallow earthquakes was mostly in Block II as many as 1195 times (40.4%) and Block III as many as 1135 times (38.4%). This block is estimated to have the potential for a tsunami to occur. Mitigation efforts to reduce the risk of earthquakes are by implementing a resilient-elastic building system and the location of settlements from the coastline > 100 m with a topography of at least 25 meters

Design charts and equations of the frictional resistance of single pipe pile under static and seismic loads

Foundations can be exposed to seismic loads in addition to static loads in seismic active areas. Thus, it might be necessary in this situation to use deep foundations rather than shallow foundations in order to prevent bearing capacity failure, improve the system’s dynamic stiffness, and/or minimize dynamic oscillations. In a seismically active area, the pile designer is expected to obtain at least the maximum earthquake-induced frictional resistance of the pile in order to achieve the necessary strength to ensure the structural integrity of the pipe pile is not compromised. However, determining the frictional resistance of the pipe pile is considered challenging. Therefore, in this study, design charts and new equations have been proposed to provide straightforward means to the designers to predict the frictional resistance of pipe piles embedded in dry and saturated cohesionless soils. The proposed charts and equations are for closed ended (CE) and open ended (OE) pipe piles. The charts have been developed based on the results of a validated three-dimensional finite element analysis. In addition, the equations were developed using regression analysis, where a high coefficient of correlation values is obtained (ranging between 0.94 and 0.98). The proposed predictive tools could assist designers in preliminary checks of the frictional capacity of pipe piles in seismic active areas.

On the issue of improving the seismic resistance of suspended buildings in areas of high seismic activity

The widespread use of high-rise buildings was caused by the growing population of cities and the lack of land. As practice shows, the structural system of high-rise buildings with a load-bearing core is one of the most reliable. A variety of such buildings are buildings with suspended structures. This structural system has found application in many high-rise buildings around the world, including in seismically active areas. At the same time, such a constructive solution is rarely found in Russia. We have no recommendations on the use of this structural system, and there is also no information about the behavior of suspended structures with high seismic activity. The greatest interest in the study of buildings with a load-bearing core occurred in the 80s – 90s of the 20th century. It is worth mentioning a number of important advantages of the considered constructive system. First of all, these structures have significant flexibility, which leads to an increase in the natural period of oscillations and a decrease in the seismic load on the load-bearing elements. In some cases, suspended structures of buildings with a load-bearing core act as dynamic absorbers. This makes it possible to ensure the stability and reliability of the entire building without the use of special devices. This article presents the results of some studies conducted to use a structural system with a load-bearing core and suspended floors in seismic construction areas.

Microseismicity clustering and mechanic properties reveal fault segmentation in southern Italy

We analyze the clustered microseismicity recorded over more than one decade in the Irpinia region, an active seismic area in Southern Italy. We studied the spatiotemporal properties of rate, source parameters and slipping mechanisms of the clustered seismicity in relationship with local medium properties and the deformation signal. Spatial pattern of both medium properties and source parameters indicates a segmentation along strike of the fault network with evidence of a high- and a low-coupling segments separated by a region with diffused microseismicity and high b-value. The high-coupling segment shows high fraction of clustered seismicity, low b-value, high relative coseismic slip, low Vp/Vs (1.7–1.75) and near-repeating earthquakes. We find that the seismicity in this high-coupling segment is triggered by non-tectonic loading, such as the recharge of a karst aquifer, suggesting a system close to critical conditions. The high-coupling segment can be identified as a potential strong motion area for future earthquakes, while the intermediate segment can mark the edges of an extensional transfer zone, which can act as a discontinuity for slip propagation. The low-coupling segment is the same where the Ms. 6.9, 1980 Irpinia earthquake nucleated. This segment shows today both relatively high b-values and high coseismic slip, but above all it shows temporal dependencies in its properties, which leads us to pay attention to it for the future spatiotemporal evolution of microseismicity in this area.

Calibration of the local magnitude scale (Ml) for Central Southern Africa

The Central Southern Africa is an area of moderate seismic activity generally caused by the presence of the East Africa Rift System. To improve the quantification of seismicity in this region, we propose a local magnitude scale (Ml), based on the original Richter definition to be used by the Zimbabwe and Botswana national networks. The magnitude scale is developed using 621 seismic events that occurred between 1997–2000 and 2013–2018. These events were recorded by 61 broadband seismic stations located in Botswana, Zimbabwe, and South Africa. We evaluated 5306 traces of zero to peak maximum amplitude, recorded on the horizontal channel from simulated Wood-Anderson seismograms. All 5306 maximum amplitude measurements were inverted simultaneously to determine the attenuation constants. The resultant Ml is defined as $ M_{l} = \log _{10}A+0.80 \times \log _{10}(R)+0.00086 \times R-1.37 \pm S $ in which A is ground displacement amplitude determined from instrument corrected synthetic Wood-Anderson seismograms in nanometres, R is the epicentral distance (km), and S is the station correction. Station corrections were determined for all stations during analysis resulting in values ranging between − 0.44 and + 0.31. The range in station corrections suggests a strong influence of local site effects on the amplitude of the seismic signal. Without station correction, the overall standard deviation of the magnitude residuals using our magnitude relation is 0.32, while using station corrections, the standard deviation 0.17. A comparison of our local magnitude relation with published mblg relationships for Southern Africa shows that these two magnitude scales are almost equivalent. The Ml equation for Central Southern Africa derived in this study has good correlation with mb values reported by the ISC and NEIC and attains systematically lower magnitude values than the South African relationship.

Present-Day Crustal Velocity Field in Ecuador from cGPS Position Time Series

The present study analyzes the GNSS time series obtained between the years 2017 and 2022 for the calculation of absolute and residual rates of Ecuador in 10 stations (ABEC, CUEC, ECEC, EPEC, FOEC, GZEC, MUEC, PLEC, RIOP, SEEC, TPC) of the continuous monitoring REGME network. Considering that the latest studies refer to periods 2012-2014 and Ecuador is located in an area of high seismic activity, it is important to update the GNSS rates. The RINEX data were provided by the Military Geographic Institute of Ecuador, the governing institution of geoinformation in that country; for processing, GipsyX scientific software was used with a PPP mode, considering 24 h sessions, and high precision was achieved. For the analysis of time series, the SARI platform was used. The series was modeled using a least-squares adjustment, which delivered the velocities for each station in the three local topocentric components. The results were contrasted with other studies, obtaining interesting conclusions as the presence of abnormal post-seismic rates stands out due to the high rate of seismic occurrence in Ecuador, and reaffirms the idea of a constant update of velocities for the Ecuadorian territory and the inclusion of the stochastic factor in the analysis of GNSS time series, since it can affect the ability to obtain the final GNSS velocities.

Liquefaction Potential of Saturated Sand Reinforced by Cement-Grouted Micropiles: An Evolutionary Approach Based on Shaking Table Tests

Cement-grouted injections are increasingly employed as a countermeasure material against liquefaction in active seismic areas; however, there is no methodology to thoroughly and directly evaluate the liquefaction potential of saturated sand materials reinforced by the cement grout-injected micropiles. To this end, first, a series of 1 g shaking table model tests are conducted. Time histories of pore water pressures, excess pore water pressure ratios (ru), and the number of required cycles (Npeak) to liquefy the soil are obtained and modified lower and upper boundaries are suggested for the potential of liquefaction of both pure and grout-reinforced sand. Next, adopting genetic programming and the least square method in the framework of the evolutionary polynomial regression technique, high-accuracy predictive equations are developed for the estimation of rumax. Based on the results of a three-dimensional, graphical, multiple-variable parametric (MVP) analysis, and introducing the concept of the critical, boundary inclination angle, the inclination of micropiles is shown to be more effective in view of liquefaction resistivity for loose sands. Due to a lower critical boundary inclination angle, the applicability range for inclining micropiles is narrower for the medium-dense sands. MVP analyses show that the effects of a decreasing spacing ratio on decreasing rumax are amplified while micropiles are inclined.

Detecting abnormal seismic activity areas of Anatolian plate and deformation directions using Python Geospatial libraries

Various inaccurate traditional models have resulted in major ambiguities and gaps in the interpretation of Anatolian plate deformation directions. To address this issue, a GIS-based spatial statistical analysis method was used for the first time to detect the directional distribution of deformation along the Anatolian Plate in Turkey. Two strategies were used in this study: firstly, identifying the abnormally active seismic areas by detecting significant hotspot and cold spot clusters and confirming this detection using optimized hotspot analysis for earthquake events that occurred from 1900 to the end of 2019. Secondly, detecting the directional distribution of deformation using a Standard Deviational Ellipse (SDE) by calculating the standard deviation of the x and y coordinates from the mean center for each set of earthquake events in the Anaconda Python Platform and ArcGIS 10.8 software. Our improved geostatistical analysis results confirmed the existence of abnormal seismic hazard zones within the study area and three deformation directions: the east-west trend, the southeast-northwest trend, and the south-north trend.

Experimental investigation of multi-layered strong wood-frame shear walls with nonstructural Type X gypsum wallboard layers under cyclic load

A fundamental premise for the design of resilient light frame timber buildings in areas of high seismic activity consists of achieving strong shear walls while keeping nonstructural damage to a minimum, especially by preventing the brittle failure of Type X gypsum wallboard (GWB) finish layers. Under this premise, it has been commonly thought that the stronger the shear wall the lesser the structural contribution of the finishes, and therefore the effect of GWB finishes in strong timber shear walls has been typically ignored by design codes and mechanical models. In the research reported in this paper, the influence of nonstructural finishes on the structural characteristics of a strong light frame shear wall was experimentally and numerically investigated. The wall evaluated in this paper, denoted here Multi-Layered Strong Shear Wall (MLSSW), is representative of walls located at the 1st story of a 7-story building located in Chile, a country where the level of seismic activity is high. The MLSSW has a continuous rod system, double OSB sheathing, robust timber framing, closely spaced nails to attach the OSB sheathing layers to wood-frame members, and is covered at both sides by two layers of screwed Type X GWB. The characteristics of the MLSSW, particularly the quantity and type of nonstructural finishes, are different from those of typical light frame timber walls. Full-scale connection-level tests, both monotonic and cyclic, are reported first, followed by descriptions of the full-scale cyclic assembly-level tests. For comparison purposes, a bare strong wall (i.e., without the GWB layers) was tested as well. The structural response of the MLSSW was evaluated in terms of stiffness, strength, energy dissipation and plastic deformation characteristics. The applicability of the SDPWS analytical model was also evaluated, as well as the applicability of existing numerical models to predict the cyclic behavior of the MLSSW.

The design solution of the hotel in Sochi, taking into account the seismic hazard of the area

The article provides an analysis of the experience of building construction in earth-quake-prone areas. The analysis of analogues of hotel complexes built in areas with high seismic activity in different countries is carried out. The features of spatial planning, architec-tural and structural solutions of buildings, the choice of structural material, and the nodes of their connections are revealed. The article contains an analysis of the features of the urban planning situation in the city of Sochi and the relief of the construction site, as well as accept-ed design proposals for the spatial planning and architectural design of the hotel complex building. A part of the antiseismic measures used in the design of a hotel in a seismic active area in the city of Sochi is presented. During the development of the project, calculations were performed for the strength, reliability and durability of the building structures, the stages of construction and others that meet the requirements of current standards. The resultsof the calculations performed showed the reliability of the operation of the building and its struc-tures. The constructive decisions taken are clearly illustrated. It is shown due to which con-structive measures the reliability of the building operation has been achieved.

Use of recycled tires for seismic protection of embankment dams

Earth dams are currently the main type of retaining structures designed and built in areas of high seismic activity. One of the constructive measures to improve the seismic resistance of earth dams is a solution based on the use of the principle of seismic isolation. In the course of the work, structures of embankment dams were developed with a seismic isolation layer located between the body of the dam and its soil base. The seismic isolation layer is formed using recycled metal-cord tires filled with gumbrine. The use of these new designs allows, due to the unique technical properties of the waste (tires and gumbrin), to achieve increased damping and diffraction. Soil reinforcement is one of the constructive measures used on dams of small and medium height to increase their seismic resistance. The paper presents new structures of earthquake-resistant embankment dams with reinforcing elements. These reinforcing elements are made from recycled tires of heavy vehicles and concrete blocks. When seismic forces act on the dam, the reinforcing elements take on excess tensile forces due to adhesion to the dam soil. The deformability of the soil is limited and regulated by elastic tires and reinforced concrete beams in the reinforcing elements, which, with the help of tubular connections, work as one whole system. A new design of an earthquake-resistant group dam with reinforcing elements using recycled steel cord tires of two sizes has been developed. The reinforcing element consists of concrete blocks made of two paired concrete discs. The disks of larger diameter are located below the disks of smaller diameter. Recycled tires act as a fixed formwork in the manufacture of concrete discs.

Vrancea intermediate-depth focal mechanism catalog: a useful instrument for local and regional stress field estimation

The Vrancea seismic zone, located in the bend region of the South-Eastern Carpathians, is a unique area with both crustal and intermediate-depth seismic activity and is known as one of the most active seismic area in Europe. Moderate crustal seismicity is recorded all over the Carpathian region, but the far more intense activity occurs in a small subcrustal seismogenic volume beneath the SE‐bend of the Carpathian arc with about 20 × 50 km lateral and 110 km vertical extent (70–180 km depth). A unique slab geometry, likely preserved until the present, causes stress localization due to the slab bending and subsequent stress release resulting in large mantle earthquakes in the region. The main focus of this study is to determine the focal mechanisms for events with a magnitude larger than 2.7, between 2005 and 2020 and evaluate the current stress field along the Vrancea subcrustal region, from the derived fault plane solutions. The main style of faulting for Vrancea subcrustal events presents a predominant reverse one, with two main earthquakes categories: the first one with the nodal planes, oriented NE–SW parallel with the Carpathian Arc and the second one with the nodal planes, oriented NW–SE perpendicular on the Carpathian Arc. The results of stress inversion indicate a dominant thrust faulting style, with an average stress regime index of 2.87. The stress pattern shows similar partitioning with vertical extension in the slab and no preferred orientation in the overlying crust, showing a transition regime from the extensional regime in the Moesian Platform to the compressional regime in the Vrancea subcrustal zone.

Mechanical mechanism of in situ stress ratio limit and its evolution simulation

In situ stress is a natural phenomenon. According to the Mohr–Coulomb criterion, it is found that when the ratio of principal stress (the ratio of maximum principal stress to minimum principal stress) of crustal rock mass in a certain environment exceeds the critical value, the rock mass will change from an elastic state to a plastic state. This critical value is the extreme limit of the principal stress ratio, which is related to the cohesion and internal friction angle of rock mass, and the limit of the principal stress ratio in the shallow part is discrete. Although the principal stress of deep rock mass is large, the ratio limit is mainly related to the internal friction angle. The calculation results show that the principal stress ratio of deep rock mass is stable in a small range. By comparing and analyzing 574 groups of measured data, it is found that all the measured principal stress ratios are within the limit range of the theoretical ratio, which also shows the characteristics of shallow dispersion and deep stability, indicating that the theoretical analysis and the measured results are consistent with each other. In order to show the change process of in situ stress, a numerical model fitting plate motion is established, and the limits of the principal stress ratio in five periods in the past 500,000 years are compared. The results show that the maximum principal stress at measuring points at different depths shows a change law of “first increasing and then stabilizing.” In areas close to or exceeding the principal stress ratio, high shear strain zones appear in the rock mass, and the stress is released in the form of plastic failure or shear dislocation, making the main stress ratio finally stable between 6.0 and 8.0. Therefore, it is easy to judge the stability of regional strata by using the ratio of principal stress; the area with a small ratio of principal stress belongs to the area with good stability, and when the ratio of principal stress is close to the limit of the ratio, it is an unstable area. The measured data show that the area with a high ratio of principal stress is often the recent seismic activity area; therefore, the ratio of in situ stress may become a possible index for earthquake prediction.