Earthquake Shaking Research Articles

Analytical formulation describing the behaviour of URM walls seismically strengthened using timber strong-backs

Unreinforced masonry structures are vulnerable to seismic actions and frequently exhibit partial or global out-of-plane wall collapse when subjected to large intensity earthquake shaking. The installation of timber strong-backs connected to the masonry surface with mechanical fasteners is a reversible and effective strengthening solution that considerably improves the out-of-plane response of masonry walls. An analytical formulation is presented that enables the out-of-plane behaviour of unreinforced masonry walls seismically retrofitted with timber strong-backs to be described, with limit analysis theorems being utilised to establish the lateral capacity curve and the demands on the masonry wall, on the timber strong-backs, and on the fastener components of the retrofitted walls, thereby enabling the design of retrofit interventions. These analytical predictions were validated using experimentally derived data from five full-scale masonry wall tests and were also compared with simulations obtained from a numerical model developed using the software SAP2000 and adopting a simplified micro-modelling approach. Analytically derived load actions were consistent with experimental values (errors < 5 %) and were compatible with the numerical deformation results (errors < 10 %). The expected performance of various retrofitted wall configurations is then reported as support for general considerations regarding the retrofit solution.

Behavior of RC Buildings Located on Hill Slopes under Earthquake Shaking

Behavior of RC Buildings Located on Hill Slopes under Earthquake Shaking

Dynamic model of the UC San Diego NHERI six‐degree‐of‐freedom large high‐performance outdoor shake table

AbstractThe UC San Diego large high‐performance outdoor shake table (LHPOST), which was commissioned on October 1, 2004 as a shared‐use experimental facility of the National Science Foundation (NSF) Network for Earthquake Engineering Simulation (NEES) program, was upgraded from its original one degree‐of‐freedom (LHPOST) to a six‐degree‐of‐freedom configuration (LHPOST6) between October 2019 and April 2022. A mechanics‐based numerical model of the LHPOST6 able to capture the dynamics of the upgraded 6‐DOF shake table system under bare table condition is presented in this paper. The model includes: (i) a rigid body kinematic model that relates the platen motion to the motions of the components attached to the platen, (ii) a hydraulic dynamic model that calculates the hydraulic actuator forces based on all fourth‐stage servovalve spool positions, (iii) a hold‐down strut model that determines the pull‐down forces produced by the three hold‐down struts, (iv) Bouc‐Wen models utilized to represent the dissipative forces in the shake table system, and (v) a rigid body dynamic model borrowed from robotic analysis governing the translational and rotational motions of the platen subjected to the forces from the various components attached to the platen. Extensive validation against experimental data shows excellent agreement for tri‐axial and six‐axial earthquake shake table tests. This validated model can be coupled with finite element models of test specimens to study the interaction between the shake table system and the specimens, and it offers potential for enhancing motion tracking performance through off‐line controller tuning or advanced control algorithm development.

Seismic site characterization baseline data for microzonation and site response analysis of Otuasega Town, Bayelsa State, Niger Delta region of Nigeria

This study presents the findings of a comprehensive geotechnical and seismic site investigation conducted at Otuasega Town located in Bayelsa State within the Niger Delta region of Nigeria. Subsurface exploration involved advancing 10 boreholes to 30 m depth using hollow stem auger drilling. Continuous disturbed and undisturbed soil sampling was performed at 1.5 m intervals for detailed geotechnical testing. Laboratory tests on the recovered soil samples established the index properties, classification, densities and consistency limits of the stratified deposits. The subsurface profile comprised alternating layers of clay, silt and sand typical of deltaic sediments, with the clay fractions exhibiting medium to high plasticity. Shear wave velocity (Vs) profiling using Multichannel Analysis of Surface Waves (WASW) techniques categorised the site predominantly as Site Class C and D based on international standards. The Standard Penetration Test (SPT) N-values ranged from 5 to 10, indicating soft normally consolidated clay conditions typical of the Niger Delta region. Predictive empirical models developed from the field and lab data showed strong correlations for estimating key geotechnical parameters such as SPT blow count, Vs and liquefaction resistance. Ground response analyses using the Vs and SPT data indicated significant site amplification potential, with peak ground accelerations up to 1.5 times the bedrock motion. Liquefaction analysis based on the empirical SPT-based methods revealed a high potential for liquefaction in the sandy layers, especially under strong earthquake shaking. The study characterized the complex sedimentology and provided baseline information for seismic microzonation and site-specific ground response analyses to advance understanding of geohazards in this delta environment.

Prediction and sensitivity analysis of embankment dam settlement under earthquake loading using gene expression programming

ABSTRACT A correct understanding of dams’ dynamic behaviour can help improve structures’ design and safety. The settlement of earth dams caused by earthquake shaking can induce instability and destruction. Using white-box machine learning techniques, including gene expression programming (GEP), a numerical relationship has been tried to estimate the settlement of earth dams under different types of earthquake loading, so that this relationship can be used in the design of earth dams. The main input parameters used in this research include the ratio of the yield acceleration of the dam to the maximum horizontal acceleration of the earthquake (ay/amax), the ratio of the fundamental period of the dam to the predominant period of the earthquake (Td/Tp), the magnitude of the earthquake (Mw) and the settlement ratio (S/H) earth dam as the output parameter. The R, MAE, and RMSE values for the proposed relationship in the research were equal to 0.85, 0.058, and 0.127, respectively. The measurement of statistical parameters shows the acceptable accuracy of the GEP method in predicting S/H. However, developing a database containing other effective parameters can be considered for future research.

Experimental study on seismic behavior of reinforced concrete exterior beam-column joints under varying axial load

The majority of low-cycle loading tests on reinforced concrete (RC) beam-column joints were currently conducted under constant axial loads. During earthquake shaking, the axial load on the joints fluctuates due to the overturning moment and vertical ground vibration. Particularly in exterior beam-column joints, where beam shear occurs on only one side, the range of axial load variation is significantly larger. To elucidate the impact of varying axial loads on the seismic performance of exterior beam-column joints, low-cycle loading tests were conducted on four groups of full-size beam-column subassemblage specimens. Two identical specimens from each group underwent low-cycle loading tests with constant and varying axial loads, respectively. Based on the experimental findings, this paper examines the differences in cyclic behaviors among comparison specimens, focusing on damage characteristics, joint shear strength, stiffness degradation, displacement ductility, and longitudinal bar slip. The study suggests that compared to specimens subjected to constant axial loads, the comparison specimens exhibit variations in load-carrying capacity corresponding to the fluctuations in axial load. Furthermore, varying axial loads accelerate post-peak stiffness and strength degradation, leading to reduced ductility. Additionally, specimens in one of the comparison groups exhibited different failure models when subjected to varying axial loads and constant axial loads, specifically beam failure and joint failure, respectively. Numerical simulations of the corresponding beam-column subassemblages were conducted on the Opensees platform to elucidate how the two axial loading methods affect the transformation of failure modes. A subsequent parametric study focusing on the axial compression ratio was performed to further explore the impact of varying axial loads on the seismic behavior of beam-column joints.

From alert to action: earthquake early warning and deaf communities

Earthquake early warning (EEW) alerts may give people valuable seconds to take protective action, such as drop, cover and hold on, before earthquake shaking starts. In order for individuals to take protective action, they need to receive the alert, understand the alert message, and have enough contextual knowledge to take appropriate protective action. Deaf and hard of hearing (DHH+) persons do not have equitable access to earthquake information, warning systems, training, and participation in disaster decision-making at all levels. Despite international policies for emergency alerts to be accessible to people with disabilities, there are no research publications that specifically address the effectiveness of EEW alerts for DHH+ communities. Missed notifications and misunderstandings about elements of the EEW alert message can delay the response time of DHH+ persons. Furthermore, unequal access to earthquake drills and preparedness information can leave DHH+ persons with insufficient context to take protective action when receiving alerts. The existing gaps in effectiveness of the EEW alerts stem from language inequities for DHH+ persons in our schools, workplaces and families, which we analyze by applying linguistic anthropological and sociolinguistic frameworks to examine the nexus of DHH+ communities’ languages and EEW messaging. To advance language equity in EEW alerting, inclusion of DHH+ communities can improve messaging and reduce misunderstandings so that DHH+ persons can quickly take protective action when they receive an alert.

Development of Seismic microzonation for Rancaekek Sub-District using microtremor method

Abstract Rancaekek sub-district located in the Bandung Regency is geologically characterized by soft and loose sediment layers such as clays, silts, and sands associated with the old Bandung Lake. Due to the existence of the Sesar Lembang Fault, the Rancaekek area is also vulnerable to seismic disasters. To provide knowledge on seismic vulnerability, therefore, a seismic microzonation study was conducted at 25 locations in the Rancaekek area using the microtremor method. Based on the available microtremor measurement data, the seismic vulnerability of the Rancaekek sub-district varies from one area to another. Amongst other areas Northern part of Bojongloa, Northern part of Rancaekek Wetan and Northern part of Jelegong areas are the most vulnerable to seismic damage because these areas have low dominant frequencies with medium amplification zones, and low Vs30 values ranging from 90 to 127 m/s. Thus, any building and infrastructure development in these areas should follow the national building code to reduce damage due to earthquake shaking.

Seismically induced deformations of layered slopes with non-unique and non-planar slip surfaces

Earthquake-induced deformation is prevalently used to evaluate the seismic performance of slopes, often assumed to occur along a predefined single slip surface. This paper presents a new limit equilibrium method combining with Newmark sliding block analysis for calculating the seismic displacement of layered slopes with non-unique and non-planar slip surfaces. The determination of the most and subsequent critical slip surfaces during the earthquake shaking is discussed with an emphasis on the coupling effects between the shallow and deep failures. The approach is validated by the results from numerical simulation and the shaking table model test of layered slopes. Comparison analyses are also performed for the predictions of seismic displacement from the developed and previous sliding-block models. It is found that the seismic sliding deformation at the first slip surface significantly affects the evolution and sliding deformation of the subsequent slip surface. For the considered example of layered slope, a second slip surface at deeper location passing through the slope toe is identified, and a coupled variation is observed for the sliding displacement along the two slip surfaces. These features are not well predicted from the available sliding-block models. The developed model can capture the interaction between the non-unique slip surfaces and the geometry effect of the non-planar slip surfaces.

The Geomechanics of the Dangkhar Landslide, Himachal Pradesh, India

The Dangkhar Landslide is an extremely large landslide located in the Spiti Valley of Himachal Pradesh, India. The landslide is situated in a remote high mountain desert within the Tethys Himalaya at elevations between 3400 m and 5600 m. It is amongst the five largest continental landslides on earth, covering an area of approximately 54 km2 and having an estimated volume of 15–20 km3. Geomechanical evaluations based on the block theory indicate that the Dangkhar Landslide formed as a result of unfavorable combinations of structural geological features and complex surface morphology. A massive kinematically removable block is created by a regional synclinal flexure that is crosscut and kinematically liberated by bounding side valleys. Three-dimensional block kinematics are necessary to permit the release of the giant block and its sliding along the synclinal flexure. Pseudostatic slope stability sensitivity analyses incorporating estimates of site seismicity and shear strength parameters suggest that earthquake shaking could have triggered instability if the static factor of safety was less than or in the range of about 1.5–1.9. Considering the glacial history of the region, ice debuttressing represents an additional potential triggering mechanism.

Method to identify if torsional mode of a building is its first mode

Torsionally flexible buildings (that have torsional mode as fundamental mode) twist during earthquake shaking, and may collapse partially or completely depending upon the direction and level of shaking. The problem is aggravated when the building is torsionally unsymmetrical. Some design codes (like Eurocode, Indian Code) explicitly prohibit the design of such buildings. This paper presents a simple approximate method to identify torsionally flexible RC Moment Frame and RC Structural Wall buildings at the initial proportioning stage itself without carrying out a detailed structural analysis. It is possible to identify whether or not the first mode is torsional mode of a building (i.e., torsionally flexible building) if Natural Period Ratio τ&gt;1 by modelling the building with rigid diaphragm and distribution of mass &amp; stiffness along the height of building, and estimating: (1) radius of gyration of rotational mass rm of each floor plan geometry by lumping the masses of slabs, beams and all vertical elements at each nodes, (2) radius of gyration of twisting stiffness rKθ of all vertical elements using their translational and torsional stiffnesses (considering flexibility of adjoining beams and vertical elements accounting for both flexural and shear deformations), and (iv) τ (=rm/rKθ). The method is validated with 3D Modal Analysis (using τ =Tθ/T, where Tθ is Uncoupled Torsional Natural Period and T Uncoupled Translational Natural Period) of hypothetical buildings using a commercial structural analysis software. Also, parameters are identified that lead to τ&gt;1, and solutions suggested to avoid torsional flexibility in buildings. Further, the method helps identify vertical stiffness irregularity in buildings. Draft provisions are suggested for inclusion in seismic codes. Also, poor performance of multi-storey building (with τ&gt;1) is demonstrated using nonlinear static and nonlinear time history analyses.

Overturning resistant capacities of rocking frames with supplemental vibration control devices under pulse-type excitations

Rocking structures are vulnerable to overturn under earthquake shaking. It is necessary to reduce the overturning probability of rocking structures. Recently, inerters were proposed to control the vibrations of rocking columns, and it was found that the structure equipped with inerter has reduced probability of overturning. However, inerter does not have capacity to dissipate energy, its control performance is believed able to be enhanced once being used in conjunction with dampers. Therefore, this paper approaches rocking structural vibration control from two directions: by applying supplemental inertia and applying supplemental damping to the structure. To this end, inerter, clutched-inerter and viscous damper are selected as control devices, and two combined scenarios are also considered, with configuration Ⅰ consisting of an inerter and a viscous damper in parallel and configuration Ⅱ consisting of a clutched-inerter and a viscous damper in parallel. The analytical models of a rocking frame with supplemental control devices in variable positions are presented and the equations of motion for each model are derived. In addition, the maximum coefficient of restitution of the rocking frame with supplemental control device is derived based on the angular momentum-impulse theorem. The effects and applicable conditions of the considered devices are evaluated by means of assessing the overturning resistances, maximum responses and fragility curves of rocking frames under different conditions. The results show that, with appropriate damping coefficient and apparent mass of the inerter, the combined configurations Ⅰ and Ⅱ provide better control effectiveness than the cases with inerter, clutched-inerter or viscous damper applied individually.

Threshold of Keulegan–Carpenter instability within a 6 × 6 rod bundle

The literature is rich in fluid–structure interaction studies of a single rod in oscillating fluid (or the reciprocate), however, there is a dearth of experimental data for rod bundle oscillation, particularly if the bundle is in a confined environment. The presence of the fluid surrounding the moving solid is modeled with force coefficients such as inertial and drag. In case of small amplitudes oscillating flow, these force coefficients depend non-linearly on the Keulegan–Carpenter number KC. The dependence present different regimes, separated by threshold KC numbers. At different regimes correspond different fluid dynamics, hence different force coefficients. The aim of this paper is to experimentally investigate the fluid dynamic for a rod bundle oscillating in a stagnant fluid. The velocity fields have been measured with Particle Image Velocimetry (PIV). Both the rod bundle and the fluid have the same refractive index, which allow to measure the velocity fields within the rod bundle in an non intrusive manner. The bundle is hosted in a double tank, immersed in a refractive index matched solution and placed on an earthquake shake table. The shake table sets the bundle into motion along a single direction.Data enable the identification of a threshold effect in the fluid response to the oscillating assembly. This threshold effect is due to the formation of vortexes in the fluid. Data show a clear trend on how the development of turbulence occurs firstly inside the rod assembly and then in the bypass between the assembly and the tank wall. The experimental results indicate the presence of a viscous boundary layer developed along the rod, above the threshold KC. The results presented in this paper represent a step forward the comprehension of the damping effect induced by the fluid at different oscillating amplitudes and frequencies, due to different KC regimes.

GRAPES: Earthquake Early Warning by Passing Seismic Vectors Through the Grapevine

AbstractEstimating an earthquake's magnitude and location may not be necessary to predict shaking in real time; instead, wavefield‐based approaches predict shaking with few assumptions about the seismic source. Here, we introduce GRAph Prediction of Earthquake Shaking (GRAPES), a deep learning model trained to characterize and propagate earthquake shaking across a seismic network. We show that GRAPES’ internal activations, which we call “seismic vectors”, correspond to the arrival of distinct seismic phases. GRAPES builds upon recent deep learning models applied to earthquake early warning by allowing for continuous ground motion prediction with seismic networks of all sizes. While trained on earthquakes recorded in Japan, we show that GRAPES, without modification, outperforms the ShakeAlert earthquake early warning system on the 2019 M7.1 Ridgecrest, CA earthquake.

Why do seismic hazard models worldwide appear to overpredict historical intensity observations?

Probabilistic seismic hazard assessments (PSHAs) provide the scientific basis for building codes to reduce damage from earthquakes. Despite their substantial impact, little is known about how well PSHA predicts actual shaking. Recent PSHA for California, Japan, Italy, Nepal, and France appear to consistently overpredict historically observed earthquake shaking intensities. Numerical simulations show that observed shaking is equally likely to be above or below predictions. This result from independently developed models and datasets in different countries and tectonic settings indicates possible systematic bias in the hazard models, the observations, or both. Analysis of possible causes shows that much of the discrepancy is due to a subtle and rarely considered issue: the conversion equations used in comparing the models-which forecast shaking as peak ground acceleration or velocity-and observations-parameterizations of qualitative shaking reports. Historical shaking reports fill a crucial data gap, but more research is warranted on how qualitative observations relate to instrumental shaking measures for earthquakes.

Exploring the Use of Orientation-Independent Inelastic Spectral Displacements in the Seismic Assessment of Bridges

ABSTRACT Seismic intensity measures (IMs) provide a link between the seismic hazard and the dynamic response of structures subjected to earthquake shaking. The spectral acceleration at the first and usually dominant vibration mode, Sa(T 1), is a popular choice for building structures. Meanwhile, the IM selection for bridges is non-trivial since they do not typically possess a single dominant mode. Even for ordinary bridges with a dominant mode, the behavior can change significantly in each principal direction through the activation, or yielding, of its different components. This study examines the performance of a novel IM that incorporates ground motion directionality and structure non-linearity in this context: the nn th percentile of all rotation angles of the inelastic spectral displacement, Sd i,RotDnn. This evaluation is carried out within the context of an ordinary bridge structure and is compared with other conventional IMs used in regional risk assessment of bridges. The case study bridge utilized is a highway overcrossing located in California with two spans and a continuous prestressed reinforced concrete box girder deck section. A large ground motion set was selected from the NGA-West2 database, and incremental dynamic analysis was carried out on the structure to assess the IM performance to characterize collapse. The results indicate that Sd i,RotDnn performs very well compared to other IMs for the bridge structure and could be a prudent choice to characterize inelastic response of bridges with several possible mechanisms in different principal directions. Also, using the RotD50 definition, typically used in ground motion models, showed a 17.3% increase in efficiency compared to RotD100 definition typically used in engineering practice.

Damping‐dependent correlations between horizontal‐horizontal, horizontal‐vertical, and vertical‐vertical pairs of spectral accelerations

AbstractCorrelation coefficients for 5%‐damped spectral accelerations (SAs) of horizontal ground‐motion components have been extensively studied and applied in probabilistic seismic analysis using vector‐valued intensity measures (IMs). Such correlations are, however, not sufficient for structures with different damping ratios under multidirectional earthquake shakings. This paper presents a comprehensive study on the correlations between horizontal‐horizontal (H‐H), horizontal‐vertical (H‐V), and vertical‐vertical (V‐V) pairs of SAs for different damping ratios based on the NGA‐West2 ground motion database. The correlations of SAs with peak ground acceleration (PGA) and peak ground velocity (PGV) are also investigated. The uncertainty in correlations is measured by integrating the bootstrap method into the logic‐tree framework. Comparative results indicate that the correlation coefficients generally increase for IMs of larger damping ratios. The relative difference between the damping‐dependent and conventional 5%‐damped correlation coefficients can be notable, reaching 100% and 35% in the SA‐SA and SA‐PGV (or PGA) pairs, respectively. Based on the empirical correlation results, an artificial neural network is utilized to develop parametric models of the correlations and the executive files for implementing these models are provided. The ANN‐aided damping‐dependent correlation models developed can be considered as a generalization of the conventional 5%‐damped correlation models, and may serve as useful tool in applications such as ground‐motion selection and vector‐valued probabilistic seismic risk assessment for structure systems.

Distribusi Kerentanan Seismik di Wilayah Pusat Kota Surabaya

Surabaya is the second major city of Indonesia and the economic capital of eastern Indonesia. The city’s central area is the governmental center of East Java Province. This area is traversed by the Surabaya section of the Kendeng Fault which could potentially generate a maximum M6.5 earthquake. The East Java megathrust zone also threatens this area with a potential maximum magnitude of M8.9 earthquake. The rock geology of this region is dominated by soft alluvial soil which could amplify earthquake shaking. This study aims to identify the distribution of seismic vulnerability index in Surabaya’s central area. Therefore, microtremor measurements were carried out at 61 points in this area. The results were then analyzed using the Horizontal to Vertical Spectral Ratio (HVSR) method to determine the amplification factor values and seismic vulnerability index. The results of the HVSR analysis show that the amplification factor value and seismic vulnerability index are in the low to medium category ranging from 0.8370 - 3.8298 and 0.6041 - 14.6268, respectively. The distribution of the results shows that the northern area is more vulnerable than the southern part. This is verified by the geological conditions of the northern part which is dominated by alluvial soil.

Modeling protective action decision-making in earthquakes by using explainable machine learning and video data

Earthquakes pose substantial threats to communities worldwide. Understanding how people respond to the fast-changing environment during earthquakes is crucial for reducing risks and saving lives. This study aims to study people’s protective action decision-making in earthquakes by leveraging explainable machine learning and video data. Specifically, this study first collected real-world CCTV footage and video postings from social media platforms, and then identified and annotated changes in the environment and people’s behavioral responses during the M7.1 2018 Anchorage earthquake. By using the fully annotated video data, we applied XGBoost, a widely-used machine learning method, to model and forecast people’s protective actions (e.g., drop and cover, hold on, and evacuate) during the earthquake. Then, explainable machine learning techniques were used to reveal the complex, nonlinear relationships between different factors and people’s choices of protective actions. Modeling results confirm that social and environmental cues played critical roles in affecting the probability of different protective actions. Certain factors, such as the earthquake shaking intensity and number of people shown in the environment, displayed evident nonlinear relationships with the probability of choosing to evacuate. These findings can help emergency managers and policymakers design more effective protective action recommendations during earthquakes.

Liquefaction potential analysis based on standard penetration test data at irrigation canals in Sibowi Area-Central Sulawesi Province

A phenomenon in which non-cohesive soil in saturated conditions loses its carrying capacity owing to the reduced stiffness and strength of the soil during earthquake shaking or rapid loading is called liquefaction. This occurs under the structure and can cause damage during earthquakes. In this study, we estimated the possibility of liquefaction in the main irrigation canals in the Sibowi area of Central Sulawesi Province, considering that the soil type in this area is sandy. Liquefaction analysis uses a simplified procedure using Standard Penetration Test data to obtain the Safety Factor and estimate the potential level of liquefaction using the Liquid Potential Index (LPI) method. According to the analysis, with the 7.5 Mw earthquake and groundwater levels observed, most of the soil layer below the irrigation canals still has liquefaction potential at 15 m to 19.5 m. The LPI result that 5 (five) out of 10 (ten) boreholes have the potential for liquefaction in low to moderate categories, and the boreholes that have liquefaction potential have groundwater depths between 14 and 16 m.