Strong Seismic Motion Research Articles

Tsunami hazard evaluation of river embankment structures incorporating their vulnerability to seismic strong motion

Development of coastal areas in Japan for various land uses since the 1960s has contributed to industrial upgrades and improved the efficiency of transportation networks. However, there are concerns about the vulnerability of developments on alluvial plains and reclaimed lands to geological events, like ground subsidence due to liquefaction during large earthquakes. Realistic assessment of earthquake and tsunami hazards and evaluation of possible countermeasures require accurate estimation of the amount of subsidence that can be expected from liquefaction at coastal and riverside sites supporting various structures. In this study, to evaluate the amount a river embankment structure might be expected to settle as a result of strong motion from an assumed Nankai Trough great earthquake, we conducted a numerical simulation using the soil–water coupled finite deformation analysis code GEOASIA. We then investigated the effect of the estimated embankment subsidence on tsunami inundation, which was simulated by using nonlinear shallow-water equations and a grid spacing as fine as 3.3 m. The influence of urban structures on the inundated area was taken into account by using a structure-embedded elevation model (SEM). The results showed that subsidence of river embankments and the collapse of parapet walls on top of them would increase both the depth and area of inundation caused by a tsunami triggered by a Nankai Trough scenario earthquake. Our findings underscore the importance of evaluating not only earthquake resistance but also vulnerability of coastal and riverside structures to strong motion in tsunami hazard analyses. Furthermore, the importance of tsunami inundation analysis using a SEM for predicting the behavior of tsunami flotsam in urban areas was demonstrated.

Vertical seismic response of end-bearing piles in nearly saturated soil

This paper presents a study on the effect of the degree of saturation of the foundation soil on the vertical seismic response of end-bearing piles subjected to P-waves. The research focuses on nearly saturated soil, where the air phase is not continuous and air bubbles are dissolved in the pore water, and thus can be treated as two-phase material. The response of the two-phase soil–pile system is quantified by means of a rigorous coupled hydromechanical model, which is based on Biot’s theory for poroelastic media and treats the air bubbles–pore water mixture as a homogeneous fluid obeying Boyle’s law. Numerical results are used to illustrate the influence of the degree of saturation of the soil layer on the seismic strong motion transferred to the pile head, i.e., the capacity of piles to filter seismic wave energy. This work bridges the gap between single-phase and two-phase saturated soil models, which predict profoundly different pile head displacements at incident wave frequencies of practical interest, and elucidates the mechanisms that lead to these differences.

Predominant Frequency in Near-Field Strong Ground Motion by Analysis of Displacement Response Spectra

A literature review on the spectral content of seismic ground motion indicates that a clear predominant frequency in earthquakes is very difficult to define. Here, it is considered that this has been so because the usual seismic record or response quantity is always employed: acceleration. In this work, an attempt is made to define a single predominant frequency for strong seismic ground motion in the near field with a different idea. It is considered that this is possible if the concentration is on displacement rather than on ordinary acceleration. In particular, relative displacement response spectra will be studied, instead of the common acceleration one, and the existence of clear and neat maximum spectral displacements around, statistically, a single and general proposed predominant frequency will be investigated for a set of twenty very strong (magnitude larger than 6.5 MW) world events.

Assessment of seismic inelastic displacement profiles of steel MRFs by means of modal behavior factors

A new method for the estimation of inelastic displacements of steel moment resisting frames (MRFs) under strong seismic ground motions is presented. The method comes as an extension of previous work of the authors from reinforced concrete to steel MRFs. Key-elements of the present method are the modal behavior (strength reduction) factors, accounting for the first four modes of significance. These factors are expressed in terms of natural period, interstorey drift ratio and/or plastic rotation, soil type and performance level. These factors are multiplied by the corresponding elastic modal displacements to generate the inelastic modal displacement profile. Eventually, the inelastic displacements can be calculated after combining the modal responses through any combination rule (e.g. SRSS). The results of the presented method are compared with that of the well-known equal displacement rule and three others and attested through nonlinear time history analyses.

The Response of Sandy and Clayey Soils to Weak and Strong Seismic Motions

The Response of Sandy and Clayey Soils to Weak and Strong Seismic Motions

Seismic response of elevated RC tanks equipped with the seesaw system

This paper investigates the effectiveness of the seesaw system when applied to elevated tanks in order to mitigate their seismic response to strong seismic motions. In particular, non-linear time-history analyses (NLTH) are conducted on an elevated steel frame reinforced concrete tank (RC), equipped with the seesaw system. Both the horizontal and vertical components of a set of seismic motions are used for the NLTH analysis, whereas two cases of water height within the RC tank are assumed. A rigid or flexible foundation of the RC tank is considered in order to assess the effects of soil-structure interaction (SSI). The seismic response indices monitored are the drift ratio and the residual drift ratio of the tank, the maximum moments of the tank wall, the maximum force of the members of the seesaw system and the exhibition of plastic hinges to the ends of the columns of the steel frame. From the results obtained it is concluded that a properly detailed seesaw system can be a good solution in improving the seismic behavior of elevated RC tanks.

Response of Sandy and Clayey Soils to Weak And Strong Seismic Loading

The response of sandy and clayey near-surface soils representing the classes of noncohesive and cohesive soils to seismic loading of various intensities is analyzed from the in situ data —from the records by vertical groups of the Japanese nationwide KiK-net strong motion seismograph network. For the analysis, out of a total of ~800 stations, we selected five stations with near-surface sandy soils and five stations with near-surface clayey soils, most purely represented in the upper layers. Using the method (Pavlenko and Irikura, 2003), we have constructed and analyzed the models of strong ground motion behavior for “sandy” and “clayey” stations, showing the distributions of earthquake-induced stresses and strains in the soil layers. Close estimates of the amplification of seismic waves in sands and clays at weak seismic ground motion and close stress-strain relationships characterizing the behavior of the near-surface soils at moderate seismic ground motion are obtained. The liquefaction of sandy soils under strong shaking (the 2011 Tohoku earthquake with Мw ~ 9.0) is analyzed. The effects of the extended seismic sources (directivity of their radiation pattern) on the behavior of sandy and clayey soils and the amplification of seismic waves in these soils is studied. Differences in the behavior of sandy and clayey soils are noted only at strong seismic motions: liquefaction in sandy soils is possible if the groundwater level is on the order of a few meters from the surface, while in clayey soils there is no liquefaction.

Reliability assessment for hybrid solar tower under near-fault pulse-like ground motions using Kriging surrogate and subset simulation

Concentrated solar towers are commonly designed as high-rise hybrid structures, which exhibit properties of non-uniform mass and rigidity along the height of the tower, and consequently are vulnerable to strong seismic ground motions. This study presents a comprehensive analysis of the seismic performance of a hybrid solar tower, which is one of the tallest hybrid solar towers in the world. The hybrid solar tower includes a reinforced concrete tube at the bottom and a steel-truss tube at the top and is subjected to near-fault pulse-like ground motions. A simulation technique that utilizes the stochastic point-source model and a velocity pulse model was introduced to generate stochastic pulse-like ground motions. The stochastic response of the hybrid solar tower to near-fault pulse-like ground motions was computed to estimate the tower’s reliability. To enhance the efficiency of reliability estimation, an algorithm combining the Kriging surrogate and subset simulation (K-SS) was presented. The aggregate response of the tower was found to be significantly more damaging over the border of the reinforced concrete tube and the steel-truss tube than below the border. The study found that the hybrid solar tower has a reliability of 90.53% when subjected to stochastic near-fault pulse-like ground motions with a peak ground acceleration of 0.62 g. The findings of this study contribute to the understanding of the seismic performance of high-rise hybrid solar towers under near-fault pulse-like ground motions.

Vertical floor spectra in low- and mid-rise elastic RC moment resisting frame buildings

To examine how floor spectral accelerations affect the design force of flexible Non-Structural Components (NSCs), the present study discusses the estimation of floor response spectra resulting from strong vertical seismic motion. 3-, 6-, 9- and 12-storey reinforced concrete buildings with moderately ductile moment-resisting frame systems, designed in accordance with the National Building Code of Canada [25] were selected for this research. 65 sets of historical records relating to 31 severe earthquakes from across the world were used to analyze the linear behavior of these structures. A constant amplification of the Vertical Floor Spectral Acceleration (FSAV) was observed along the building height. This amplification was noticeably elevated for slab nodes, especially at the center of the interior slab and in shorter buildings. Furthermore, the vertical component of the earthquake had a greater impact at shorter periods, since the maximum vertical acceleration occurred at periods lasting less than 0.35 sec. Finally, equations to estimate FSAV corresponding to the input vertical ground acceleration were proposed for typical code-conforming RC frame buildings.

Effect of subterranean levels on the dynamic response of RC-MRF buildings

The dynamic response of reinforced concrete moment resisting frame (RC-MRF) building structures is mostly altered by the substructure system such as the type of foundations and features of subterranean levels, as well as subsurface soil conditions. The majority of low-to high-rise buildings, in urban areas, are designed with one or multi-level subterranean levels for parking and other services. However, many designers overlooked incorporating these subterranean levels and soils in the seismic resistance analysis assuming that the building is fixed at the ground surface. The present study assessed the effect of the subterranean levels on the dynamic response of RC-MRF buildings. Several two-dimensional (2D) nonlinear finite element seismic response analyses were carried out in ABAQUS software for medium-rise buildings without and with one to multi-level subterranean levels resting on a deep homogenous soft soil profile under the effect of strong seismic input motion. It was observed that the subterranean levels considerably alter the dynamic characteristics and demands of the building structures. Hence, explicitly incorporating the subterranean components and foundation soil during the seismic resistance design of building structures is important.

Distribution feature and development characteristics of geohazards in Wudu district, Gansu province, Northwest China

BackgroundThe study area located at southeast Gansu, China, has long been afflicted by the intense occurrence of geohazards. The study area is characterized by interleaving terrain of precipitous mountains and valley basins, abundant precipitation, and complicated geological setting. In this work, 1144 geohazards including 759 landslides, 281 debris flows, and 104 collapse were presented and their types were categorized in detail. Then, the distribution of geohazards were analyzed and the controlling role of hazard-inducing environment and triggering factors on geohazards were preliminary presented.ResultsIn this work, correlation analysis between geohazards and geological, topographical, and geomorphological context was conducted. Concave slopes with height smaller than 200 m and slope gradient between 21° and 40° is the favorable topographic feature for landslide occurrence and the predominant slope aspects of landslides are southwest, south, west, and southeast. Collapse generally occurs in slope with gradient larger than 45°. Valleys with valley gradient less than 400‰, valley height between 100 and 500 m, and watershed area of 1–10 km2 register the largest percentage and the most favorable slope gradient for the supply of solid source at the debris flow source area is 25°–45°. The preferable strata for geohazards (landslide, collapse and debris flow) are Middle and upper Pleistocene loess, Holocene diluvium, Silurian phyllite and slate, Neogene mudstone, and Devonian schist and gneiss, and most geohazards occurred in tectonic erosional middle altitude mountain, tectonic erosional high-middle altitude mountain, tectonic erosional-diluvial planation surface. In addition, the controlling role of triggering factors, i.e., precipitation, earthquake, and human engineering activity was discussed and described in this work.ConclusionGeohazards in the study area are synthetically controlled by the hazard-inducing environment and triggering factors. The complicated sliding-prone strata and steep topography resulted from strong tectonic movement provides a favorable basis for the development and formation of geohazards. Heavy rainfall, strong seismic motion, and human engineering activity are the main triggering factors for geohazard occurrence.

Seismic Design and Performances of Frame Structures Connected to a Strongback System and Equipped with Different Configurations of Supplemental Viscous Dampers

The paper investigates the dynamic behavior of structural systems obtained by connecting a moment-resisting frame structure with a vertical rigid truss pinned at the base, known in literature as “strongback,” and equipped with added fluid-viscous dampers. The strongback, designed in order to remain in the elastic field under strong seismic ground motion, acts as a mast by imposing to the structure a linear lateral deformed shape. By regularizing the lateral drift profile of the structure, the strongback limits undesired effects such as weak-storey mechanisms, damage concentration and residual drifts. In addition, when supplemental dampers are inserted in the structure, a considerable amount of energy can be dissipated, thus reducing the peak seismic response. The aim of the work is twofold: i) to provide analytical formulations for the preliminary design of added dampers based on the Generalized Single Degree Of Freedom (GSDOF) concept, and ii) to evaluate the increase in energy dissipation capabilities for selected dampers configurations thanks to the presence of the strongback. The formulas are developed for different configurations of added viscous dampers: dampers inserted within the frame between all or selected consecutive storeys (inter-storey placement) and dampers located at the base of the strongback to realize a rigid “dissipative tower.” The effectiveness of the dampers configurations is evaluated through dynamic time-history analyses.

FinDerS(+): Real-Time Earthquake Slip Profiles and Magnitudes Estimated from Backprojected Displacement with Consideration of Fault Source Maturity Gradient

The Finite-Fault Rupture Detector (FinDer) algorithm computes rapid line-source rupture models from high-frequency seismic acceleration amplitudes (PGA). In this paper, we propose two extensions to FinDer, called FinDerS and FinDerS+, which have the advantage of taking into account a geological property of the source fault, its structural maturity, as well as its relation to the earthquake slip distribution. These two new algorithms calculate real-time earthquake slip profiles by backprojecting seismic and/or geodetic displacement amplitudes onto the FinDer line-source. This backprojection is based on a general empirical equation established in previous work that relates dynamic peak ground displacement (PGD) at the stations to on-fault coseismic slip. While FinDerS projects PGD onto the current FinDer line-source, FinDerS+ allows the rupture to grow beyond the current model extent to predict future rupture evolution. For an informed interpolation and smoothing of the estimated slip values, FinDerS and FinDerS+ both employ a generic empirical function that has been shown to relate the along-strike gradient of structural maturity of the ruptured fault, the earthquake slip distribution, and the rupture length. Therefore, while FinDer derives magnitudes from a relatively uncertain and general empirical rupture length-magnitude relations, FinDerS and FinDerS+ provide alternate and better informed magnitude estimates using the mean slip of the profiles derived from the integration of fault source maturity. The two new algorithms can incorporate both seismic strong-motion and geodetic displacement data. In order to recover PGD from strong-motion instruments, we double-integrate and high-pass filter (>0.075 Hz) the seismic acceleration records. Together, the three algorithms exploit the full spectrum of ground-motions, including high frequencies to derive a source fault model (FinDer) and low frequencies to determine the static offsets along this model (FinDerS and FinDerS+). We test the three algorithms for the 2019 MW7.1 Ridgecrest (California), 2016 MW7.0 Kumamoto (Japan), and 2008 MW7.9 Wenchuan (China) earthquakes. Conclusively, low-frequency PGD data and integration of the fault maturity gradient do not speed-up calculations for these events, but provide additional information on slip distribution and final rupture length, as well as alternative estimates of magnitudes that can be useful to check for consistency across the algorithm suite. The FinDer algorithms systematically outperform previously established real-time PGD-based magnitude estimates in terms of speed and accuracy. The resulting slip distributions can be useful for improved ground-motion prediction given the observed relationship between seismic radiation and fault maturity.

Dynamic Process and Mechanism of the Catastrophic Taihongcun Landslide Triggered by the 2008 Wenchuan Earthquake Based on Field Investigations and Discrete Element Method Simulations

The Taihongcun landslide, which was a remarkable geological disaster triggered by the 2008 Wenchuan earthquake, had a volume of about 2 × 106 m3 and killed about 23 people. Through detailed field investigations, basic information of topography, geological structure and stratigraphy for the landslide were acquired and key kinetic characteristics of the landslide were identified. On the basis of filed investigations, 2D numerical models with discrete element method (DEM) were established to simulate the kinematics and failure process of the landslide. To ensure the validity of the dynamic calculations, the free-field boundary condition was developed and introduced intro the DEM models. According to filed investigations and DEM simulations, the dynamic processes of the Taihongcun landslide can be divided into four phases: fragmentation, projection motion, scraping, and granular debris flow and accumulation. In addition, the parameter analysis showed that the particle bond strength had a significant influence on the runout distance and landslide debris morphology. Finally, the possible mechanism of the Taihongcun landslide was determined: a rock mass of poor quality provided the lithological basis for this landslide formation; a joint set J1 in the back scarp and a weak interlayer of carbonaceous slate and shale between the upper sliding mass and the bedrock formed the rupture boundaries of the upper source area; a strong seismic ground motion was the external excitation that triggered the destructive landslide event; additionally, hypermobility was caused by the high elevation and topographical conditions of the landslide.

Seismic response analysis for Romanian extra-carpathian sedimentary areas

The seismic response of the ground motion is analysed using processed recordings and related spectral characteristics. The analysis is carried out for few representative different sites, with different geological local conditions. Data used are recordings from the last strongest seismic events (1986, August 30, Mw = 7.1, 1990, May 30, Mw = 6.9 and 1990, May 31, Mw=6.4). The approach used herein to assess the particular features of the seismic effects could open a new perspective in microzoning and risk studies. In the context of Vrancea-intermediate depth seismicity, whose effects are encountered at long epicentral distances, the choice of these sites is fully justified. Therefore the paper intends to focus on the particularities in the site effects that occur due to the sedimentary deposits’ oscillation under strong seismic ground motion for different areas. The spectral amplification factors are introduced in order to have a quantitative representation with respect to the variability of site effects.

Shaking table test on the seismic response of the portal section in soft and hard rock junction.

Tunnel portal sections located in the soft-hard rock junction are vulnerable to the strong earthquake motions in seismically active regions. The main objective of this paper is to investigate the seismic response of tunnel portals located in the soft-hard rock junction. Taking the Baiyunding tunnel in northeast China as a background, a shaking table test with a geometric scaling ratio of 1:30 was built. Details of test setup and procedures are introduced first and then the test results are presented. The discussion of the results is based on the peak ground acceleration (PGA), the longitudinal, the contact stress, and the safety factor. The results show that the soft section of the soft-hard rock junction suffers remarkable damages under strong seismic motions, while the hard rock section is less affected by earthquakes. The increasing soft rock range causes a rise of the forced displacement of tunnel linings, which, together with the seismic inertia force, leads to the increase of the contact stress of the linings, and ultimately resulting in the deterioration of the tunnel seismic safety. To mitigate the seismic damage of tunnel portals in the soft-hard rock junction, rock grouting, bolt support, and other effective reinforced methods should be considered in the seismic design of the soft section.

Seismic Performance of Deposit Slopes with Underlying Bedrock before and after Reinforcement by Stabilizing Piles

The seismic performance of stabilizing piles used to reinforce underlying bedrock in a deposit slope is a complex soil–structure interaction problem. Two centrifuge shaking table model testswere conducted to ascertain the dynamic responses of the underlying bedrock deposit slopes without and with the use of stabilizing piles during an earthquake. Multi-stage seismic waves with various peak accelerations were applied from the bottom of each model. The differencesin the response accelerations between the deposit and bedrock increase significantly with the increase in amplitude of the input seismic waves. The presence of the rock-socketed stabilizing piles can bridge the uncoordinated movement of the bedrock and the overlying deposit to some extent. The resultant force arising from a distributed load increment on the piles caused by an earthquake is mainly concentrated in the upper part. With increases in the peak ground acceleration of the input motion, the resistance of the bedrock in front of the stabilizing piles increases and the peak resistance under the bedrock surface of the stabilizing piles gradually moves downwards.This finding indicates that the strong seismic motion significantly changes the embedded working state of the stabilizing pile.

A Review: The Tectonic Perspective and seismic response of Darbandikhan Dam Stability and potential solutions

Darbandikhan dam is a rockfill dam constructed northwest of Iraq in the early sixties. Even though the dam is located in a mountain zone with high seismic influence, the dam was not designed to resist a high seismic motion. This study is a review of Darbandikhan dam current situation and the possible factors of its potential failure. The dam can be regarded as a vulnerable condition. Due to the unstable geologic formations and the existence of limestone and anhydrite which can impact the dam stability. On the other hand, rainfall dwindling and the temperature rising affected the hydrological system in the area. Climate change causes drought, desertification followed by a flood in a very short period. Therefore, the dam reservoir elevation has been diminished due to the reduction of the inflow. The dam has experienced a strong seismic motion in November 2017, it causes serious fissures on the dam road, failure on the left side slope and rocks toppling. The sliding of soil and the falling rocks in the dam lake when the earthquake hit the dam location, lead to clay accumulation which has prevented the gates to be opened. Serious and fast maintenance have to be implemented to fix the landslides and dam safety against earthquakes.

Role of strong motion duration on seismic responses of high concrete faced rockfill dams

This study investigates the role of strong seismic motions on the dynamic responses of high CFRDs through elastoplastic analysis. Damage measures (DMs) including vertical and horizontal displacements, plastic shear strain, as well as a face-slab damage index are selected to gauge the deformation, stability of the dam slope and the anti-seepage ability of the face slab, respectively. The selected DMs are key to the safety of high CFRDs. A group of 35 as-recorded ground motions with a wide range of durations are modified to conform to a 5% damped target spectrum are used as input motions for dynamic analysis. A comprehensive understanding of the effects of ground motion duration is obtained through a tri-fold analysis of the ground motion records, the nonlinear dynamic response of CFRDs and the statistics of the results. The definitions of significant duration, bracketed duration and uniform duration, each with consideration to two different thresholds, are selected to characterize strong motion durations. The results suggests that significant duration is the most useful indicator for seismic assessment of high CFRDs and for evaluating the effects of the duration of an earthquake on the integrity of high CFRDs.

SPH-DEM simulations of saturated granular soils liquefaction incorporating particles of irregular shape

A coupled smoothed particle hydrodynamics (SPH) and discrete element method (DEM) scheme is presented herein to investigate liquefaction of saturated granular deposits during strong seismic ground motions. Irregular-shaped solid particles in the form of polyhedral blocks are utilized to represent soil grains using DEM. In SPH, the fluid domain is discretized into distinct particles carrying local properties of the fluid. Therefore, the presented approach is a fully particle-based technique ideal for handling free-surface and moving boundary problems. The phase coupling is achieved through local averaging techniques and well-established semi-empirical relations quantifying fluid-particle interaction. Level and mildly sloped deposits were subjected to seismic ground motions introduced into the system through the base wall. The results of the performed simulations suggest that both deposits liquefied during strong base excitation due to the contraction of pore spaces leading to large increases in the excess pore fluid pressure that in turn results in significant loss of interparticle contacts and degradation of soil strength and stiffness. In addition, the sloping deposit experienced large lateral displacements, especially, at the shallow soil layers which completely liquefied during the seismic loading.