Effects of the probability of pulse-like ground motions on landslide susceptibility assessment in near-fault areas

Earthquake-induced strong near-fault ground motion is typically accompanied by largevelocity pulse-like component,which causes serious damage to slopes and buildings.Although not all near-fault ground motions contain a pulse-like component,it is important to consider this factor in regional earthquake-induced landslide susceptibility assessment.In the present study,we considered the probability of the observed pulse-like ground motion at each site(PP)in the region of an earthquake as one of the conditioning factors for landslide susceptibility assessment.A subset of the area affected by the 1994Mw6.7 Northridge earthquake in California was examined.To explore and verify the effects of PP on landslide susceptibility assessment,seven models were established,consisting of six identical influencing factors(elevation,slope gradient,aspect,distance to drainage,distance to roads,and geology)and one or two factors characterizing the intensity of the earthquake(distance to fault,peak ground acceleration,peak ground velocity,and PP)in logistic regression analysis.The results showed that the model considering PP performed better in susceptibility assessment,with an area under the receiver operating characteristic curve value of 0.956.Based on the results of relative importance analysis,the contribution of the PP value to earthquakeinduced landslide susceptibility was ranked fourth after the slope gradient,elevation,and lithology.The prediction performance of the model considering the pulse-like effect was better than that reported previously.A logistic regression model that considers the pulse-like effect can be applied in disaster prevention,mitigation,and construction planning in near-fault areas.

Identification of pulse-like ground motions using artificial neural network

For more than 20 years,the concept of near-fault pulse-like ground motion has been a topic of great interest due to its distinct characteristics,particularly due to directivity or fling effects,which are hugely influenced by the rupture mechanism.These unexpected characteristics,along with their effective frequency,energy rate,and damage indices,create a near-fault,pulse-like ground motion capable of causing severe damage to structures.One of the most common approaches for identifying these ground motions is done by conducting wavelet decomposition of the ground motion time history to extract a pulse signal and eventually categorize an earthquake by comparing the original signal to the residual one.However,to overcome the intensive calculations required in this approach,this study proposes using artificial neural networks to identify pulse-like ground motions through classification to predict their pulse period by means of regression analysis.Furthermore,the study is intended to evaluate the reliability and accuracy of various artificial neural networks in identifying pulse-like ground motions and predicting their pulse periods.In general,the results of the study have shown that the artificial neural network can identify pulse-like earthquakes and reliably predict their pulse period.

Relative energy zero ratio-based approach for identifying pulse-like ground motions

Pulse-like ground motions are capable of inflicting significant damage to structures. Efficient classification of pulse-like ground motion is of great importance when performing the seismic assessment in near-fault regions. In this study, a new method for identifying the velocity pulses is proposed, based on different trends of two parameters: the short-time energy and the short-time zero crossing rate of a ground motion record. A new pulse indicator, the relative energy zero ratio(REZR), is defined to qualitatively identify pulse-like features. The threshold for pulse-like ground motions is derived and compared with two other identification methods through statistical analysis. The proposed procedure not only shows good accuracy and efficiency when identifying pulse-like ground motions but also exhibits good performance for classifying records with high-frequency noise and discontinuous pulses. The REZR method does not require a waveform formula to express and fit the potential velocity pulses;it is a purely signal-based classification method. Finally, the proposed procedure is used to evaluate the contribution of pulse-like motions to the total input energy of a seismic record, which dramatically increases the seismic damage potential.

Intensity measures for the seismic response evaluation of buried steel pipelines under near-field pulse-like ground motions

Ground-motion Intensity Measures (IMs) are used to quantify the strength of ground motions and evaluate the response of structures. IMs act as a link between seismic demand and seismic hazard analysis and therefore, have a key role in performance-based earthquake engineering. Many studies have been carried out on the determination of suitable IMs in terms of effi ciency, suffi ciency and scaling robustness. The majority of these investigations focused on ordinary structures such as buildings and bridges, and only a few were about buried pipelines. In the current study, the optimal IMs for predicting the seismic demand of continuous buried steel pipelines under near-fi eld pulse-like ground motion records is investigated. Incremental dynamic analysis is performed using twenty ground motion records. Using the results of the regression analysis, the optimality of 23 potential IMs are studied. It is concluded that specifi c energy density (SED) followed by VSI[ω1(PGD+RMSd )] are the optimal IMs based on effi ciency, suffi ciency and scaling robustness for seismic response evaluation of buried pipelines under near-fi eld ground motions.

Pulses in ground motions identified through surface partial matching and their impact on seismic rocking consequence

In seismology and earthquake engineering,it is fundamental to identify and characterize the pulse-like features in pulse-type ground motions.To capture the pulses that dominate structural responses,this study establishes congruence and shift relationships between response spectrum surfaces.A similarity search between spectrum surfaces,supplemented with a similarity search in time series,has been applied to characterize the pulse-like features in pulse-type ground motions.The identified pulses are tested in predicting the rocking consequences of slender rectangular blocks under the original ground motions.Generally,the prediction is promising for the majority of the ground motions where the dominant pulse is correctly identified.

Pulse-like ground motion observed during the 6 February 2023 M_(W)7.8 Pazarcık Earthquake(Kahramanmaraş,SE Türkiye)

In this study,we analyzed 100 three-component strong ground motion records observed within 200 km of the causative fault of the 6 February 2023 M_(W)7.8 Pazarcık(Kahramanmaraş)Earthquake in SE Türkiye.The wavelet method was utilized to identify and analyze the characteristics of pulse-like ground motions in the near-fault region,while considering the uncertainty of the pulse orientation during the analysis.Our investigation focused on the effects of the focal mechanism and rupture process on the spatial distribution,pulse orientation,and maximum pulse direction of the observed pulse-like ground motion.We also analyzed the amplitude and period of the observed ground pulses and the effect of long-period amplification on the ground motion response spectra.Our results indicated the following:(1)A total of 21 typical ground velocity pulses were observed during this earthquake,exhibiting complex characteristics due to the influence of the strike-slip mechanism and rupture directivity.Most ground pulses(17 out of 21)were recorded within 20 km of the fault,in a wide range of orientations,including normal and parallel to the fault direction.The waveforms exhibited unidirectional features,indicating the effects of left-lateral fault slip.Distinct pulses observed more than 20 km from the fault were mainly oriented normal to the fault.The waveforms were bidirectional with double-or multi-round trips as a result of rupture directivity.(2)The amplitudes of the observed pulses ranged from 30.5 to 220.0 cm/s,with the largest peak velocity of 220.0 cm/s observed at Station 3138.The pulse periods ranged from 2.3 to 14.5 s,with the longest pulse period of 14.5 s observed at Station 3116.The amplitude and period of the pulses observed during this earthquake were comparable to those of similar-magnitude global earthquakes.The amplitude of the pulses decreased significantly with increasing fault distance,whereas the pulse period was not significantly affected by the fault distance.(3)Compared with non-pulse records,the velocity pulse records had a pronounced amplification effect on the acceleration response spectra near the pulse period,with factors ranging from 2.1 to 5.8.The larger velocity pulses also significantly amplified the velocity response spectra,particularly over the long periods.This significant amplification effect of the pulses on the response spectra leads to empirical models underestimating the long-period earthquake ground motion.

Evaluation of underground blast-induced ground motions through nearsurface low-velocity geological layers

Surface ground motion produced by underground blasts is significantly influenced by near-surface geological conditions.However,near-surface low-propagation velocity layers were always ignored in past analyses of ground motions due to their thin thickness.With the rising concern about surface ground motions produced by the ascendant scale and frequentness of underground excavation and mining,close attention is gradually paid to ground blast vibrations.Therefore,systemic experiments were conducted and took seven months in an underground mine to clarify the variation of motion from underground rock to surface ground.The attenuation of surface ground peak particle velocities(PPVs)is compared to that in underground rock,and horizontal amplitudes are compared to vertical amplitudes.Differences between bedrock and surface ground vibrations are analyzed to illustrate the site effect of near-surface lower-propagation velocity layers.One-dimensional site response analysis is employed to quantify the influence of different geological profiles on surface ground vibrations.The experimental data and site response analysis allowed the following conclusions:(1)geological site effects mainly produce decreasing dominant frequency(DF)of surface ground vibrations;(2)the site amplification effect of blast vibration needs to be characterized by peak particle displacement(PPD);(3)shear waves(S-waves)begin to dominate and surface Rayleigh waves(R-waves)develop as blast-induced ground vibrations travel upward through rock and lower-velocity layers to the surface.The comparison of response relative displacement to a critical value is best to assess the potential for cracking on surface structures.

Near-fault directivity pulse-like ground motion effect on high-speed railway bridge

The vehicle-track-bridge(VTB)element was used to investigate how a high-speed railway bridge reacted when it was subjected to near-fault directivity pulse-like ground motions.Based on the PEER NAG Strong Ground Motion Database,the spatial analysis model of a vehicle-bridge system was developed,the VTB element was derived to simulate the interaction of train and bridge,and the elasto-plastic seismic responses of the bridge were calculated.The calculation results show that girder and pier top displacement,and bending moment of the pier base increase subjected to near-fault directivity pulse-like ground motion compared to far-field earthquakes,and the greater deformation responses in near-fault shaking are associated with fewer reversed cycles of loading.The hysteretic characteristics of the pier subjected to a near-fault directivity pulse-like earthquake should be explicitly expressed as the bending moment-rotation relationship of the pier base,which is characterized by the centrally strengthened hysteretic cycles at some point of the loading time-history curve.The results show that there is an amplification of the vertical deflection in the girder's mid-span owing to the high vertical ground motion.In light of these findings,the effect of the vertical ground motion should be used to adjust the unconservative amplification constant 2/3 of the vertical-to-horizontal peak ground motion ratio in the seismic design of bridge.

Seismic fragility analysis of clay-pile-pier systems considering the optimization of ground motion intensity measures

The performance of clay-pile-pier system under earthquake shaking was comprehensively examined via three-dimensional finite element analyses,in which the complex stress-strain relationships of a clay and piled pier system were depicted by a hyperbolic-hysteretic and an equivalent elastoplastic model,respectively.One hundred twenty ground motions with varying peak accelerations were considered,along with the variations in bridge superstructure mass and pile flexural rigidity.Comprehensive comparison studies suggested that peak pile-cap acceleration and peak pile-cap velocity are the optimal ground motion intensity measures for seismic responses of the pier and the pile,respectively.Furthermore,based on two optimal ground motion intensity measures and using curvature ductility to quantify different damage states,seismic fragility analyses were performed.The pier generally had no evident damage except when the bridge girder mass was equal to 960 t,which seemed to be comparatively insensitive to the varying pile flexural rigidity.In comparison,the pile was found to be more vulnerable to seismic damage and its failure probabilities tended to clearly reduce with the increment of pile flexural rigidity,while the influence of the bridge girder mass was relatively minor.

Dominant pulse simulation of near fault ground motions

In this study, a new mathematical model is developed composed of two parts, including harmonic and polynomial expressions for simulating the dominant velocity pulse of near fault ground motions. Based on a proposed velocity function, the corresponding expressions for the ground acceleration and displacement time histories are also derived. The proposed model is then fitted using some selected pulse-like near fault ground motions in the Next Generation Attenuation （NGA） project library. The new model is not only simple in form but also simulates the long-period portion of actual velocity near fault records with a high level of precision. It is shown that the proposed model-based elastic response spectra are compatible with the near fault records in the neighborhood of the prevailing frequency of the pulse. The results indicate that the proposed model adequately simulates the components of the time histories. Finally, the energy of the proposed pulse was compared with the energy of the actual record to confirm the compatibility.

Traveling wave effect on the seismic response of a steel arch bridge subjected to near fault ground motions

In the 1990s, several major earthquakes occurred throughout the world, with a common observation that near fault ground motion （NFGM） characteristics had a distinct impact on causing damage to civil engineering structures that could not be predicted by using far field ground motions. Since then, seismic responses of structures under NFGMs have been extensively examined, with most of the studies focusing on structures with relatively short fundamental periods, where the traveling wave effect does not need to be considered. However, for long span bridges, especially arch bridges, the traveling wave （only time delay considered） effect may be very distinct and is therefore important. In this paper, the results from a case study on the seismic response of a steel arch bridge under selected NFGMs is presented by considering the traveling wave effect with variable apparent velocities. The effects of fling step and long period pulses of NFGMs on the seismic responses of the arch bridge are also discussed.

Direct use of peak ground motion parameters for the estimation of inelastic displacement ratio of SDOF systems subjected to repeated far fault ground motions

This study is aimed at developing statistical equations to estimate the inelastic displacement ratio of singledegree-of-freedom systems subjected to far fault repeated earthquakes. In the study, peak ground motion parameters are used to define the scatter of the original data. The ratio of peak ground acceleration to peak ground velocity, and peak ground velocity of the ground motion records and structural parameters such as period of vibration and lateral strength ratio are used in the proposed equations. For the development of the equations, nonlinear time history analyses of single-degree-offreedom systems are conducted. Then, the results are used in a multivariate regression procedure. The equations are verified by comparing the estimated results with the calculated results. The average error and coefficient of variation of the proposed equations are presented. The analyses results revealed that the direct use of peak ground motion parameters for the estimation of inelastic displacement ratio significantly reduced the scatter in the original data and yielded accurate results. From the comparative results it is also observed that results obtained using equations specific to peak ground velocity or peak ground acceleration to peak ground velocity ratio are similar.

Simulation of spatially correlated earthquake ground motions for engineering purposes

A new model to simulate spatially correlated earthquake ground motions is developed. In the model, the main factors that characterize three distinct effects of spatial variability, namely, the incoherency effect, the wave-passage effect and the site-response effect, are taken into account, and corresponding terms/parameters are incorporated into the well known model of uniform ground motions. Some of these terms/parameters can be determined by the root operation, and others can be calculated directly. The proposed model is first verified theoretically, and examples of ground motion simulations are provided as a further illustration. It is proven that the ensemble expected value and the ensemble auto-/cross-spectral density functions of the simulated ground motions are identical to the target spectral density functions. The proposed model can also be used to simulate other correlated stochastic processes, such as wave and wind loads.

Simulation of multi-support depth-varying earthquake ground motions within heterogeneous onshore and offshore sites

This paper presents a novel approach to model and simulate the multi-support depth-varying seismic motions（MDSMs） within heterogeneous offshore and onshore sites.Based on 1 D wave propagation theory,the three-dimensional ground motion transfer functions on the surface or within an offshore or onshore site are derived by considering the effects of seawater and porous soils on the propagation of seismic P waves.Moreover,the depth-varying and spatial variation properties of seismic ground motions are considered in the ground motion simulation.Using the obtained transfer functions at any locations within a site,the offshore or onshore depth-varying seismic motions are stochastically simulated based on the spectral representation method（SRM）.The traditional approaches for simulating spatially varying ground motions are improved and extended to generate MDSMs within multiple offshore and onshore sites.The simulation results show that the PSD functions and coherency losses of the generated MDSMs are compatible with respective target values,which fully validates the effectiveness of the proposed simulation method.The synthesized MDSMs can provide strong support for the precise seismic response prediction and performance-based design of both offshore and onshore large-span engineering structures.

Representation of near-fault pulse-type ground motions

Near-fault ground motions with long-period pulses have been identified as critical in the design of structures. To aid in the representation of this special type of motion, eight simple pulses that characterize the effects of either the flingstep or forward-directivity are considered. Relationships between pulse amplitudes and velocity pulse period for different pulses are discussed. Representative ratios and peak acceleration amplification can exhibit distinctive features depending on variations in pulse duration, amplitude and the selected acceleration pulse shape. Additionally, response spectral characteristics for the equivalent pulses are identified and compared in terms of fixed PGA and PGV, respectively. Response spectra are strongly affected by the duration of pulses and the shape of the basic pulses. Finally, dynamic time history response features of a damped SDOF system subjected to pulse excitations are examined. These special aspects of pulse waveforms and their response spectra should be taken into account in the estimation of ground motions for a project site close to a fault.

Study on equivalent velocity pulse of nearfault ground motions

Near-fault strong ground motions that resulted in serious structural damage are characterized by directivity effect and pulse-type motion. Large-amplitude and long-period pulses are contained in the velocity time-history traces of near-fault pulse-type records. A reasonable model of equivalent velocity pulse is proposed on the basis of the ex- isted models in this paper to simplify the calculation and analysis. Based on the large amount of collected near-fault strong earthquakes records, the parameters describing equivalent velocity pulse model such as pulse period, pulse intensity and number of predominant pulses are studied, and comparison is made with the results obtained by others models. The proposed model is contributive to the seismic design for structures in near-fault areas.

Engineering characteristics of near-fault vertical ground motions and their effect on the seismic response of bridges

A wide variety of near-fault strong ground motion records were collected from various tectonic environments worldwide and were used to study the peak value ratio and response spectrum ratio of the vertical to horizontal component of ground motion, focusing on the effect of earthquake magnitude, site conditions, pulse duration, and statistical component. The results show that both the peak value ratio and response spectrum ratio are larger than the 2/3 value prescribed in existing seismic codes, and the relationship between the vertical and horizontal ground motions is comparatively intricate. In addition, the effect of the near-fault ground motions on bridge performance is analyzed, considering both the material nonlinear characteristics and the P-A effect.

Study on inelastic displacement ratio spectra for near-fault pulse-type ground motions

In displacement-based seismic design, inelastic displacement ratio spectra （IDRS） are particularly useful for estimating the maximum lateral inelastic displacement demand of a nonlinear SDOF system from the maximum elastic displacement demand of its counterpart linear elastic SDOF system. In this study, the characteristics of IDRS for near-fault pulse-type ground motions are investigated based on a great number of earthquake ground motions. The influence of site conditions, ratio of peak ground velocity （PGV） to peak ground acceleration （PGA）, the PGV, and the maximum incremental velocity （MIV） on IDRS are also evaluated. The results indicate that the effect of near-fault ground motions on IDRS are significant only at periods between 0.2 s - 1.5 s, where the amplification can approach 20%. The PGV/PGA ratio has the most significant influence on IDRS among the parameters considered. It is also found that site conditions only slightly affect the IDRS.

Near-fault ground motions with prominent acceleration pulses:pulse characteristics and ductility demand

Major earthquakes of last 15 years （e.g., Northridge 1994, Kobe 1995 and Chi-Chi 1999） have shown that many near-fault ground motions possess prominent acceleration pulses. Some of the prominent ground acceleration pulses are related to large ground velocity pulses, others are caused by mechanisms that are totally different from those causing the velocity pulses or fling steps. Various efforts to model acceleration pulses have been reported in the literature. In this paper, research results from a recent study of acceleration pulse prominent ground motions and an analysis of structural damage induced by acceleration pulses are summarized. The main results of the study include： （1） temporal characteristics of acceleration pulses; （2） ductility demand spectrum of simple acceleration pulses with respect to equivalent classes of dynamic systems and pulse characteristic parameters; and （3） estimation of fundamental period change under the excitation of strong acceleration pulses. By using the acceleration pulse induced linear acceleration spectrum and the ductility demand spectrum, a simple procedure has been developed to estimate the ductility demand and the fundamental period change of a reinforced concrete （RC） structure under the impact of a strong acceleration pulse.

Approximation approach to the SRM based on root decomposition in the simulation of spatially varying ground motions

The spectral representation method （SRM） is widely used to simulate spatially varying ground motions. This study focuses on the approximation approach to the SRM based on root decomposition, which can improve the efficiency of the simulation. The accuracy of the approximation approach may be affected by three factors： matrix for decomposition, distribution of frequency interpolation nodes and elements for interpolation. The influence of these factors on the accuracy of this approach is examined and the following conclusions are drawn. The SRM based on the root decomposition of the lagged coherency matrix exhibits greater accuracy than the SRM based on the root decomposition of the cross spectral matrix. The equal energy distribution of frequency interpolation nodes proposed in this study is more effective than the counter pith with an equal spacing. Elements for interpolation do not have much of an effect on the accuracy, so interpolation of the elements of the decomposed matrix is recommended because it is less complicated from a computational efficiency perspective.