Ground Motion Characteristics Research Articles

Dynamic Rupture Models of the 2016 ML 5.8 Gyeongju, South Korea, Earthquake, Constrained by a Kinematic Rupture Model and Seismic Waveform Data

ABSTRACT The ML 5.8 earthquake that jolted Gyeongju in southeastern Korea in 2016 was the country’s largest inland event since instrumental seismic monitoring began in 1978. We developed dynamic rupture models of the Gyeongju event constrained by near-source ground-motion data using full 3D spontaneous dynamic rupture modeling with the slip-weakening friction law. Based on our results, we propose two simple dynamic rupture models with constant strength excess (SE) and slip-weakening distance (Dc) that produce near-source ground-motion waveforms compatible with recorded ones in the low-frequency band. Both dynamic models exhibit relatively large stress-drop values, consistent with previous estimates constrained by source spectrum analyses. The fracture energy estimates were also larger than those predicted by a scaling relationship with the seismic moment. The dynamic features constrained in this study by spontaneous rupture modeling and waveform comparison may help understand the source and ground-motion characteristics of future large events in southeastern Korea and thus the seismic hazard of the region.

Rapid damage state classification for underground box tunnels using machine learning

This study develops and compares the performance of eight machine learning (ML) models to rapidly predict the seismic damage state of underground box tunnels. Nonlinear time history analyses of 24 soil-tunnel configurations subject to 85 ground motions were performed to generate the dataset for the ML models. The aspect ratio, buried depth, flexibility ratio, and 23 ground motion intensity measures (IMs) are employed as input variables of ML models. The output variables are four damage states, namely ‘none’, ‘minor’, ‘moderate’, and ‘extensive’. Among the eight ML models, LightGBM is found to yield the most favorable prediction of the damage states, resulting in an accuracy of 91%. The effects of earthquake IMs were also examined. Results show that the spectral acceleration () and spectral displacement () at the fundamental period of the site (T 1) have the strongest correlation with the damage prediction. Finally, the effect of reducing the input variables to two groups (i.e. combinations of soil-tunnel configuration parameters with top five and top ten ranked IMs) on the model prediction capability was investigated. Accordingly, ), acceleration spectrum intensity, spectral velocity, and velocity spectrum intensity were identified as the key parameters representing the ground-motion characteristics needed for the predictive model.

Analysis of Peak Ground Acceleration and Seismogenic Fault Characteristics of the Mw7.8 Earthquake in Turkey

A Mw7.8 earthquake struck Turkey on 6 February 2023, causing severe casualties and economic losses. This paper investigates the characteristics of strong ground motion and seismogenic fault of the earthquake. We collected and processed the strong ground motion records of 379 stations using Matlab, SeismoSignal, and Surfer software: Matlab (Version R2016a), SeismoSignal (Version 5.1.0), and Surfer (Version 23.0.15), and obtained the peak ground acceleration (PGA) contour map. We analyzed the near-fault effect, the fault locking segment effect, and the trampoline effect of the earthquake based on the spatial distribution of PGA, the fault geometry, and slip distribution. We found that the earthquake generated a very strong ground motion concentration effect in the near-fault area, with the maximum PGA exceeding 2000 cm/s2. However, the presence of fault locking segments influenced the spatial distribution of ground motion, resulting in four significant PGA high-value concentration areas at a local dislocation, a turning point, and the end of the East Anatolian Fault. We also revealed for the first time the typical manifestation of the trampoline effect in this earthquake, which was characterized by a large vertical acceleration with a positive direction significantly larger than the negative direction. This paper provides an important reference for understanding the seismogenic mechanism, damage mode, characteristics, and strong earthquake law of the Turkey earthquake.

Fragility curves accounting for uncertainties in material parameters and ground motion characteristics using a data driven surrogate model

This study uses a statistical surrogate model to develop fragility curves for an infilled reinforced concrete frame building, considering uncertainties in both material properties and ground motion parameters. The focal point of this study is a school building in Nepal damaged during the 2015 Gorkha earthquake. The school was instrumented, and its seismic response was simulated using a nonlinear numerical model. The model, developed following a recently proposed framework and extensively validated with the field data, is used in a parametric study conducted to identify the most influential material parameters (MPs). The model is then used in incremental dynamic analyses conducted to provide data for the calibration of a surrogate model. The three-staged least square statistical modeling approach is adopted to relate the influential MPs and ground motion intensity measures with important response quantities related to the peak and residual first-story drift ratios. The surrogate model is employed to generate fragility curves accounting for the two sources of uncertainty. The results indicate that accounting for uncertainties associated with the MPs can alter the fragility curves, causing a shift in the prediction of the median and dispersion of intensity measures.

The constant damage inelastic displacement ratio for performance design of self-centering systems under far-field earthquake ground motions

In this research paper, the inelastic displacement ratio known as maximum nonlinear displacement to maximum elastic displacement is determined at different periods of vibration and constant damage indices based on the Park-Ang model for fully self-centering structures under 216 far-field earthquake ground motions. The effect of ground motion characteristics, including soil classification, magnitude, and source-to-site distance, are evaluated at different period ranges. Moreover, the influence of structural parameters is investigated, including the ultimate ductility of the structural system, the β factor related to the damage model, the stiffness-hardening ratio, and the dissipative-energy factor corresponding to the flag-shaped hysteresis behavior of the self-centering system. Then, a simple equation based on nonlinear regression analysis is proposed to estimate the constant damage inelastic displacement ratio. It is worth mentioning that the bias and standard deviation of the error in the suggested equation are presented for better understanding. Finally, the proposed equation is compared with the nonlinear responses obtained from the direct time history analysis in self-centering flag-shaped models under thirty earthquake records selected corresponding to desired seismic hazard level. The statistical analysis illustrates that the effect of ground motion characteristics on constant inelastic displacement ratio is not prominent, while the influence of some structural parameters like ultimate ductility and dissipative-energy factor is remarkable in higher damage levels.The verification analysis showed that the suggested equation could estimate the target displacement of the self-centering structural systems with a lower than 10% error.

Influence of frozen soil site conditions on ground motion characteristics in cold regions

It is necessary to understand the site seismic response for seismic design and post-earthquake damage assessment of structures in seismically active regions. In cold regions, the presence of layered frozen soil not only affects the ground motion characteristics but also influences the seismic response of structures on these sites. This study aims to investigate the effect of frozen soil site conditions on ground motion characteristics in cold regions through shaking table tests using a laminar shear box equipped with a soil freezing system. The seismic acceleration response, displacement response, and dynamic shear stress-strain relation were analyzed for both unfrozen and frozen soil sites under various seismic waves with different intensities. The existence of the frozen soil layer has been observed to mitigate ground motion during earthquakes, resulting in a reduced peak ground acceleration compared with the unfrozen soil site. If an earthquake occurs, the high-frequency waves will be attenuated by the frozen soil layer, which possesses a dominant frequency lower than that of the unfrozen soil site. Moreover, the energy dissipation capacity of the frozen soil site is larger than that of the unfrozen soil site during earthquakes. By combining the Fourier spectral ratio curves, it can be inferred that different input ground motions have varying effects on the seismic response of both unfrozen and frozen sites. These findings serve as valuable references for seismic design of structures in cold regions.

Variability of response spectra of single-path ground-motion record pairs

To improve the accuracy of seismic hazard analysis, understanding the uncertainty of the prediction of the ground-motion amplitude for a specific site owing to a specific source is important. In this study, the variability of the acceleration response spectra of single-path ground motion was evaluated using record pairs obtained from two earthquakes at the same site with the same magnitude, location, and focal mechanism, recorded by high-density strong-motion observation networks in Japan. The natural log standard deviations of the single-path ground motions varied with the period and were distributed in the range of approximately 0.3–0.5. Even if an empirical ground-motion prediction model that accurately models the characteristics of single-path ground motions could be developed, avoiding this variability in the prediction is difficult. The standard deviation of the within-event residuals was smaller at larger distances, and the period of the maximum standard deviation tended to increase as the earthquake magnitude increased. These features may be attributed to differences in the source characteristics of each earthquake. These findings will be useful for the development of advanced empirical ground-motion models and for improving the accuracy of seismic hazard analysis.

Machine Learning-Based Classification for Rapid Seismic Damage Assessment of Buildings at a Regional Scale

ABSTRACT The damage assessment of numerous buildings after the earthquake is still a challenge by traditional methods as it requires a significant amount of time and resources for carrying out building-by-building seismic damage assessment. This study presents the machine learning (ML)-based damage assessment of buildings after an earthquake. The applicability of the machine learning model will be limited considering only structural properties or ground motion characteristics. Thus, in this study, the applicability of different machine learning techniques is explored using real-world earthquake damage datasets considering both the structural properties and ground motion characteristics. Initially, the entire dataset is used to train the ML models to classify the building’s damage into five categories ranging from null to slight damage to collapse. Later, the dataset is divided into three traffic light damage tags: green, yellow, and red. The performance of the ML model to classify the building’s damage into three damage tags is found better than that of classifying it into five damage categories. This research aims to be beneficial in planning and decision-making for emergency response and recovery following an earthquake.

Dynamic Soil-Structure Interaction Through 2-D Site-Specific Response Analysis

Seismic response of structures involved soil-structure-interaction (SSI) that need to consider both inertial and kinematic interaction. Many underground SSI has been developed such as modelling the structures and soils as continuum with seismic load simplified as pseudo-static or static equivalent. More recent and more realistic SSI model consider non-linear time-history analysis in the form of 2-D site-specific response analysis (SSRA), in which both inertial and kinematic interaction in combination with non-linear soil model, as well as time-history ground-motions are simulated. This paper presents simplified pseudo-static soil-structure interaction finite-element (FE) response of underground box-station structure under prescribed maximum strain displacement as resulted from 1-D site-specific response analysis under various ground-motions characteristics of subduction and shallow crustal earthquakes. More complex model of SSI system of basement is also presented. This basement SSI model incorporates non-linear time-history analysis with dynamic soil properties considered through 2-D SSRA simulating seismic wave propagation from reference base-rock to ground surface. Various base-rock seismic ground-motions are simulated from results of de-aggregation analysis from probabilistic seismic hazard analysis considering both subduction and shallow crustal earthquakes scaled at various ground-motion periods. The analysis adopts dynamic soil model with non-linear modulus and damping using FLAC computer program.

Reliability of steel structures with Chevron bracing systems considering the performance-based seismic design philosophy

In this paper, the seismic performance and reliability of steel buildings with Chevron-Braced frames are studied integrating a novel probabilistic approach and the performance-based seismic design concept. The seismic response of models is extracted using response history analyses with the help the commercial software SAP2000. In this sense, three variables associated with the seismic response of the structure are studied: overall lateral displacement, rotation of connections, and inter-story drift. Those responses are evaluated by exciting the structure with eleven characteristic ground motions of the zone with respect to three performance levels: immediate occupancy, life safety, and collapse prevention. Once the seismic response is extracted for every performance level, the reliability of the models is calculated with respect to inter-story drift as described next. First, considering the seismic response in terms of inter-story drift for every ground motion, the associated histogram is constructed. Then, using 13 Probability Density Functions (PDFs), a Chi-square test is performed to identify the best-fitted PDF associated to the histogram of inter-story drift. Afterwards, with the best-fitted PDF of inter-story drift, the probability of failure and reliability index are extracted considering serviceability limits for every performance level. This represents a unique approach to extract the risk of structures subjected to ground motions associated to different performance levels. In addition to the structural reliability, a study about the cost of the structures with and without Chevron braces is developed, and then, it is documented the best option. Finally, based on the results reported in this paper, it is demonstrated that steel buildings with Chevron-braced frames present a better seismic performance than steel moment resisting frames without any bracing system. In summary, overall lateral drifts are reduced between 40 and 60% when Chevron braces are implemented in comparison to steel moment resisting frames without braces. On the other hand, if Chevron bracing systems are not used, i.e., in steel moment resisting frames, the inter-story drifts are about 300% higher than those of steel structures with Chevron braces. Hence, structural damages can be considerably reduced if Chevron-braced frames are implemented in steel structures that may be excited by characteristic ground motions of the zone where they are located.

Ground motion characteristics of the 2015 central Nepal (Gorkha-Dolakha) Earthquake and 2023 SE Turkey Earthquake doublets

The Alpine-Himalayan orogenic belt, the well-identified seismically active region in the world, has been evidenced by the occurrence of recent two devastating earthquake doublets in 2015 in central Nepal (MW 7.8 and MW 7.3) and in 2023 in southeastern Turkey(MW 7.8 and MW 7.5). In this study, seismic ground motion characteristics of two damaging earthquakes namely the 2015 central Nepal earthquake doublet that occurred in the central Himalaya and the 2023 southeastern Turkey earthquake doublet that occurred in the eastern Mediterranean has been investigated. The observed strong-motion recordings indicate that the peak ground acceleration (PGA) values are about 152.61–154.96 cm/s2 of the 2015 central Nepal earthquake doublet at KATNP station and about 451.834–842.924 cm/s2 of the 2023 southeastern Turkey earthquake doublet at station 3137. The seismic ground motion of both the 2015 central Nepal and the 2023 SE Turkey earthquakes doublet shows that the 2015 central Nepal doublet produced much lower peak ground acceleration than the 2023 southeastern Turkey earthquake doublet.

Regional offshore ground motion prediction model from a referenced empirical approach: A case study in the Japan Trench area

With increasing resource exploitation and engineering construction offshore, the seismic safety of offshore structures has received attention from researchers and designers, and an offshore ground motion prediction model (GMPM) can be used to estimate the possible earthquake response of structures and provide the foundation for seismic fortification of structures. Because there are few strong motion records recorded by offshore stations, there are insufficient empirical data in the magnitude-distance range to directly develop a GMPM using empirical regression techniques. To develop a reliable GMPM for data-poor offshore regions, we used a referenced empirical approach based on an onshore empirical prediction model. We collected 2605 records from 138 crustal earthquake events, 2669 records from 125 slab earthquake events and 5693 records from 267 interface earthquake events recorded by S-net stations. We used the existing Japanese onshore GMPM as a reference model. Then, we analyzed the residuals of the reference model for offshore data and calculated its adjustment factors. Finally, we developed a GMPM for the Japan Trench area and compared it with the existing onshore models. The proposed model fit the data subsets at hypocentral distances of 20–300 km reasonably well. There were different spectral accelerations (SAs) for different source types, with considerably larger SAs for short periods of offshore motions from crustal events than for the motions from the other two types, and the difference becomes more obvious with the increase of magnitude. At short periods, the SAs of the offshore motions from slab events were slightly larger than those of the motions from the interface events. The discrepancy of the offshore and onshore GMPM was significant, and the peak ground accelerations (PGAs) and SAs of the offshore ground motions were apparently greater than those of onshore ground motions of the same magnitude and distance. The offshore GMPM established by the reference empirical approach contribute to studying the characteristics of offshore strong ground motions, and this approach can be applied to data-poor regions.

Conditionally Simulated Spatial Non-Stationary Earthquake Accelerograms Using Wavelet Packets

ABSTRACT For regional hazard analysis or engineering applications, it is necessary to simulate a group of correlated ground motions containing information from given recordings. A new method is presented to conditionally generate ground motions at unobserved points using actual recordings in this localized region. This method is based on an extension of the traditional conditional simulation using a wavelet packet. Utilizing the advantages of wavelet-packet transformation, the time and frequency characteristics of ground motions are effectively identified. Besides by decomposing the signal into non-overlapping sub-frequency bands, it is possible to conditionally simulating stationary, space-time, and Gaussian random fields. These simulated motions are consistent with the actual recordings in terms of temporal variations in the frequency domain and its design spectrum, and their coherence functions satisfy the target coherence values. Two numerical examples have been provided to illustrate the capability of the proposed method: the simulation of ensembles of earthquake accelerograms using actual recordings and blind tests in SMART-1 array.

AN INTELLIGENT ISOLATION SYSTEM BASED-ON LONG SHORT-TERM MEMORY MODULE MODEL FOR GROUND MOTION CHARACTERISTICS PREDICTION

An intelligent control system based on a semi-active variable stiffness isolation system and the Long Short-Term Memory (LSTM) is proposed in this study. In the field of semi-active control, the design of control laws relies on the measurement and feedback of the structural response when an earthquake occurs. The optimal control parameters should be determined in real time to achieve the performance-oriented control target by identifying the ground motion characteristics, which have a great influence on the control performance in the early stage. To deploy the optimal control parameters, a LSTM-based module for predicting ground motion characteristics is first proposed. In addition, a sensitivity analysis using the world-wide ground motion database is also conducted, and the representative cases are selected to optimize the fuzzy inference surface for the Leverage-type Stiffness Controllable Isolation System (LSCIS). Numerical simulation indicates, by using the proposed GA-LSTM control system, prominent effect of suppressing the isolation displacement and superstructure acceleration for near-fault and far-field ground motions can be achieved respectively. Series of shaking table tests was also conducted to verify the actual control performance of the proposed system. Both numerical and experimental results have demonstrated that the proposed intelligent control system has high efficiency and reliability to protect the structures from earthquakes of all types of ground motion characteristics.

Wavelet packets-based simulation of non-stationary multivariate ground motions

This study proposes a novel approach to simulate non-stationary multivariate earthquake accelerograms for the seismic analysis of extended structures. This approach is based on an extension of the traditional stochastic decomposition technique applied to the wavelet packet theory using the spectral representation method. Using the advantages of a wavelet packet to identify the time and frequency characteristics of ground motion effectively, the generated recordings successfully reflected the non-stationarity in both the time and frequency domains. Accordingly, the spatial correlation trend was consistent with the selected coherence function. Compared to the ground motions observed using the traditional method, the proposed approach was exemplified by simulating ensembles of ground motions at three points spaced 200 m apart. The multivariate ground motions simulated by different methods were applied as multi-support excitations for the dynamic time–history analysis of a 190 m continuous rigid-frame box girder bridge. Notable variations in structural response were observed when considering the non-stationarity of the frequency domain, contrasting with the cases where it was not taken into account. This study provides an effective approach for generating non-stationary multivariate earthquake accelerograms, which is of great significance for structural response analysis in engineering applications.

Permanent displacement characteristics of landslides taking into consideration the frequency and energy behaviour of historical seismic ground motions

Landslides often occur along motorways in earthquake-prone areas, leading to casualties and the loss of property. Most previous studies have applied the simplified Newmark method to assess landslide susceptibility at a regional scale, ignoring the characteristics of local ground motions. In this study, we investigated permanent displacement characteristics of three potential landslide areas along the Dayong Expressway using the rigorous Newmark method that considers the frequency and energy characteristics of historical seismic waves. First, the frequency characteristics of historical earthquakes in the study areas were analysed using the fast Fourier transform method and were adopted as input ground motions in calculating the Newmark displacement. Next, the critical accelerations of the three study areas were computed. Parameters such as the elevation, soil layer thickness and soil strength that are required for critical acceleration calculations were obtained using high-precision ( c. 3 cm) unmanned aerial vehicle mapping technology, drilling operations and laboratory tests. Finally, the Newmark displacement was calculated and the landslide susceptibility of the study areas was evaluated. The results showed that the predominant frequency of historical seismic waves in the study areas was 0.38–3.36 Hz, indicating low-frequency characteristics. The results also indicated that the frequency and energy characteristics of the seismic ground motions significantly influenced the Newmark displacement. The maximum Newmark displacement under different waveforms at Damieju ranged from 2 to 18 cm. Under the most dangerous conditions, all three areas showed a potential for landslides. The maximum Newmark displacement positively correlated with the energy of the predominant frequency. The large-energy and low-frequency characteristics of the seismic wave correspond to a large displacement. The simplified Newmark method when used in regional landslide susceptibility analysis did not reflect this effect and may be unsuitable to determine the size of landslides.

Optimal single concave sliding device properties for isolated multi-span continuous deck bridges depending on the ground motion characteristics

The present study investigates the analysis of the optimal friction coefficient with respect to the seismic performance of isolated multi-span continuous deck bridges, equipped with single concave friction pendulum (FPS) isolators. A six-degree-of-freedom system is used to model the structural system and the FPS friction property is described by means of a law that considers the dependency on the velocity. The equations of motions have been implemented in nondimensional form by considering the peak ground acceleration-to-velocity ratio (PGA/PGV) and the peak ground acceleration (PGA) as ground motion parameters for two different sets of seismic records: near-fault and far-field inputs. In addition, different bridge models are considered for various parameters (i.e., pier period, deck period, friction coefficient and mass of the structural system). The results show the effectiveness of the PGA/PGV ratio within the proposed nondimensionalization together with the existence of an optimum value of the friction coefficient that minimizes the nondimensional response of the pier. At the end, a linear regression expression is presented with the aim to compute the optimal value of the normalized friction coefficient as a function of the deck period and PGA/PGV ratio, which can be used in the preliminary phase to design the FPS bearings. Additionally, a multivariate non-linear regression expression is also provided to evaluate the pier response.

Influence of near-fault ground motion characteristics and the relative geographical positioning of sites on the seismic response of RC structures

PurposeThe objective of the study is to examine the response of reinforced concrete (RC) structures subjected to Near-Fault Ground Motions (NFGM) and highlight the importance of considering various factors including the influence of the relative geographical position of near-fault sites that can affect the structural response during an earthquake.Design/methodology/approachIn this paper, the response of a four-storey RC building subjected to NFGMs with varied characteristics like hanging wall and footwall in conjunction with directivity and the effect of pulse-like ground motions with rupture direction are investigated to understand the combined influence of these factors on the behavior of the structure. Furthermore, the capacity and demand of the structural element are investigated for computing the performance ratio.FindingsResults from this study indicate that the most unfavorable combinations for structural damage due to near-fault ground motion are the hanging wall with forward rupture, the fault normal component of ground motions, and pulse-like ground motions with forward directivity.Originality/valueThe results from this study provide valuable insight into the response of RC structures subjected to NFGM and highlight the importance of considering various factors that can affect the structural response during an earthquake. Moreover, the computation of capacity and demand of the critical beam indicates exceedance of desired limits, resulting in the early deterioration of the structural elements. Finally, the analytical analysis from the present study confirms that the hanging wall with forward ruptures, pulse-like motions, and fling steps are the most unfavorable combinations for seismic structural damage.

A Machine-Learning-Based Software for the Simulation of Regional Characteristic Ground Motion

Ground-motion simulations provide input time history data required for designing and assessing structures; however, the simulations conducted by the currently available tools only match the design spectrum without verifying if the statistical characteristics of the spectrum and duration are satisfied. A ground-motion simulation software was developed to resolve these issues. The developed software employs machine learning methods to match the amplitude, spectrum, and duration features of the target region. Principal component analysis is employed to extract features from the actual ground-motion database to detect characteristic ground motions and predict the target acceleration amplitude, response spectrum, and duration, based on the response spectrum and duration prediction equations. The results show that the simulated ground motion can match the amplitude, spectrum, and duration characteristics well. Therefore, the simulated ground motion can provide more reasonable input for the structure. Moreover, the developed software provides visualization functions that enable the user to determine the target area and obtain the amplitude field intuitively.

Sustainable and resilient seismic design of reinforced concrete frames with rocking isolation on spread footings

The rapidly evolving climate change together with the urgent need of modern societies for resilience against catastrophic threats set the sustainable and resilient seismic design of reinforced concrete (RC) structures as a priority. Rocking isolation of RC frames resting on spread footings has been proven numerically and experimentally to offer superior seismic performance with reduced seismic demands in the superstructure. At the same time, rocking footings do not require special construction solutions and can be readily implemented in the current state of practice. To exploit these benefits, the present study, for first time, utilizes rocking footings in the optimum design of RC frames for high seismic resilience and reduced environmental impact. This is achieved by incorporating a resilient seismic design methodology into a numerical optimization procedure that is aiming to minimize embodied carbon. Applications of the proposed approach show that the carbon footprint of RC frames can be reduced by 40% due to rocking isolation on spread footings. The benefits become more important as the level of seismic hazard increases. It is also found that the environmental benefits of rocking footings for RC frames are rather insensitive to the characteristics of ground motions and the uncertainties of soil properties.