Peak Ground Displacement Research Articles

Bi-normalized Newmark–Hall spectra for seismic design and assessment

A bi-normalized Newmark–Hall response spectrum is presented for seismic design and assessment of structures. The period axis is normalized with respect to a characteristic period relating only to peak ground-motion parameters. The amplification factors are determined through a statistical analysis by normalizing spectral pseudo-acceleration, spectral pseudo-velocity, and spectral displacement, relative to peak ground acceleration, peak ground velocity, and peak ground displacement, respectively, in the low-, intermediate-, and high-period ranges, which do not need to be prescribed prior to normalization. A total of 671 three-component accelerograms are selected from the New Zealand Strong Motion Database for the statistical analysis. The relationship between peak ground-motion parameters is studied, enabling the construction of a design spectrum from either a given design scenario earthquake, or a code-specified peak ground acceleration value.

Quantifying the out-of-plane response of unreinforced masonry walls subjected to relative support motion

TThe supports of out-of-plane loaded unreinforced masonry walls in buildings are subjected to a motion that is filtered and amplified by the building structure and, in some cases, can be significantly different from the ground motion. Moreover, because these walls span one or several storeys, their top and bottom supports are subjected to motions that differ in phase and amplitude. In state-of-the-art assessment procedures for the out-of-plane stability of masonry walls any effect of a relative support motion is neglected. The objective of this paper is to study the effect of the relative support motion on the response of out-of-plane loaded vertically-spanning unreinforced masonry walls. The acceleration capacity of the walls is investigated by means of a discrete element model representative of different wall configurations. A set of ground motions covering a wide range of peak ground acceleration and peak ground displacement is used as input to the simulations. The relative motion between the wall supports is included in the model in a systematic way: firstly, through a motion that is non-synchronous but of equal amplitude; secondly, through a motion that is synchronous but of different amplitude. The effect of the relative support motion is studied on different wall configurations where the elastic modulus of masonry, the wall height-to-thickness ratio, the wall effective thickness and the overburden at the top wall are varied. The study shows that, because of the relative support motion, the acceleration capacity of the walls can drop by 20% and, in the cases where the overburden is high, by more than 50%.

Development of declustered processed earthquake accelerogram database for the Iranian Plateau: including near-field record categorization

In this paper, a comprehensive accelerogram database of the Iranian plateau containing 3585 data with all three components is gathered. The raw data are processed by the wavelet-based denoising method, and results are compared with the contaminated data. All the data are classified into mainshock and aftershock categories using the time and spatial window method. Afterward, the data are categorized into the pulse-like and non-pulse-like events based on the detection of velocity pulse in any of horizontal and/or vertical directions. Eventually, among 3585 data, the ones with an average shear wave velocity of top 30 m of subsurface soil profile are selected and their important ground motion parameters such as peak ground acceleration, velocity, and displacement, Arias intensity, ground motion duration, and acceleration response spectra are studied. It is observed that the intensity of vertical component of the accelerograms is almost at the same level as the strong horizontal direction or even more, in some cases. Near-field events cause more severe responses than far-field earthquakes. Generally, the mainshocks responses are slightly tougher than the aftershocks. By comparing the acceleration response spectra of the accelerograms with the ones obtained from the building design codes, the necessity of revising the existing standard spectra is revealed for considering the effects of mainshocks, aftershocks, near-field effects, as well as separate vertical component of the ground motions directly. Finally, the presented database, as a powerful tool, will give an interesting opportunity to the scientists and engineers who are enthusiastic to work on the Iranian plateau accelerograms.

Canonical Correlation Analysis of Selecting Optimal Ground Motion Intensity Measures for Bridges

The correlation between ground motion intensity measures (IMs) and that between component seismic demand parameters (DPs) have significant effects on the seismic demand of bridges. A canonical correlation analysis method was introduced to consider the two types of correlations in the optimal selection of IMs for probabilistic seismic demand analysis of bridges. A group of 100 ground motion-bridge samples were generated with the bin approach and Latin hypercube sampling method, to quantify the uncertainties of earthquakes and bridges. With the nonlinear time history analysis, the overall correlation between IMs and DPs was established (IMs and DPs were respectively treated as a whole), meanwhile the correlation between IMs and that between DPs were considered. The optimal IM was selected and verified with the criteria of efficiency, proficiency and sufficiency. The canonical correlation analysis reduced the complexity and limitation of simple correlation analysis used for all pairs of correlations between each of the IMs and each of the DPs. The combined peak IM of PGA (the peak ground acceleration), PGV (the peak ground velocity), PGD (the peak ground displacement) and combined root mean square IM of aRMS, vRMS, and dRMS were proved to be the optimal IMs and more appropriate in the probabilistic seismic demand analysis of normal girder bridges.

Suitable intensity measure for probabilistic seismic risk assessment of non-ductile Australian reinforced concrete buildings

This study investigates the suitability of various intensity measures for conducting probabilistic seismic risk assessment of low- to mid-rise non-ductile reinforced concrete buildings with various plan configurations located in low-to-moderate seismic regions. Probabilistic seismic demand models are developed by conducting three-dimensional nonlinear time history analyses. The building response is defined to be dependent on component response and interstorey drift limits. In total the suitability of eleven intensity measures is evaluated by examining five criteria: efficiency, practicality, proficiency, sufficiency, and hazard computability. Based on the first four criteria it is identified that peak ground velocity, peak ground displacement, and maximum spectral displacement response are the most suitable intensity measures. Hazard computability is then utilised to select the optimum intensity measure for a hazard model in accordance with the Australian standards.

Simulation method of ground motion matching for multiple targets and effects of fitting parameter variation on the distribution of PGD

When generating spectrum-compatible artificial ground motion in engineering practices, the effect of the variation in fitting parameters on the distribution of the peak ground displacement (PGD) has not yet drawn enough attention. In this study, a method for simulating ground motion matching for multiple targets is developed. In this method, a frequency-dependent amplitude envelope function with statistical parameters is introduced to simulate the nonstationarity of the frequency in earthquake ground motion. Then, several groups of time-history acceleration with different temporal and spectral nonstationarities were generated to analyze the effect of nonstationary parameter variations on the distribution of PGD. The following conclusions are drawn from the results: (1) In the simulation of spectrum-compatible artificial ground motion, if the acceleration time-history is generated with random initial phases, the corresponding PGD distribution is quite discrete and an uncertain number of PGD values lower than the limit value are observed. Nevertheless, the mean values of PGD always meet the requirement in every group. (2) If the nonstationary frequencies of the ground motion are taken into account when fitting the target spectrum, the corresponding PGD values will increase. A correlation analysis shows that the change in the mean and the dispersion values, from before the frequencies are controlled to after, correlates with the modal parameters of the predominant frequencies. (3) Extending the maximum period of the target spectrum will increase the corresponding PGD value and, simultaneously, decrease the PGD dispersion. Finally, in order to control the PGD effectively, the ground motion simulation method suggested in this study was revised to target a specified PGD. This novel method can generate ground motion that satisfies not only the required precision of the target spectrum, peak ground acceleration (PGA), and nonstationarity characteristics of the ground motion but also meets the required limit of the PGD, improving engineering practices.

Peak Ground Displacement Saturates Exactly When Expected: Implications for Earthquake Early Warning

AbstractThe scaling of rupture properties with magnitude is of critical importance to earthquake early warning systems that rely on source characterization using limited snapshots of waveform data. ShakeAlert, a prototype earthquake early warning system that is being developed for the western United States, provides real‐time estimates of earthquake magnitude based on P wave peak ground displacements measured at stations triggered by the event. The algorithms used in ShakeAlert assume that the displacement measurements at each station are statistically independent and that there exists a linear and time‐independent relation between log peak ground displacement and earthquake magnitude. Here we challenge this basic assumption using the largest data set assembled for this purpose to date: a comprehensive database of more than 140,000 vertical‐component waveforms from M4.5 to M9 earthquakes occurring near Japan from 1997 through 2018 and recorded by the K‐NET and KiK‐net strong‐motion networks. By analyzing the time evolution of P wave peak ground displacements for these earthquakes, we show that there is a break, or saturation, in the magnitude‐displacement scaling that depends on the length of the measurement time window. We demonstrate that the magnitude at which this saturation occurs is well‐explained by a simple and nondeterministic model of earthquake rupture growth. We then use the predictions of this saturation model to develop a Bayesian framework for estimating posterior uncertainties in real‐time magnitude estimates.

Predicting the principal strong ground motion parameters: A deep learning approach

In this research, new models are developed to estimate the three principal time-domain parameters of seismic ground motion. A novel deep learning (DL) approach coupled with artificial neural network (ANN), namely deep neural network (DNN) is employed for predicting the strong ground motion parameters such as peak ground acceleration (PGA), peak ground velocity (PGV) and peak ground displacement (PGD). This robust technique that has extended the applications of conventional neural networks improves learning of complicated and nonlinear features via increasing the number of layers as well as the neurons in each layer. The proposed models are constructed upon the NGA-West2 database provided by PEER (Pacific Earthquake Engineering Research Center). This database is more comprehensive than NGA-West1 which was mainly considered for developing previous artificial intelligence-based prediction models. Therefore, the new models are more reliable and can be used for wider ranges of predictors. The DNN attenuation models yield accurate estimates of the site PGA, PGV and PGD based on earthquake magnitude, rake angle, source to site distance and soil shear wave velocity. In addition, it is shown that the developed models, with correlation coefficients of 0.902, 0.899 and 0.911 (for PGA, PGV and PGD respectively), outperform the existing soft computing models. Furthermore, the average values of error measures such as MAE, MAPE and RMSE for PGA, PGV and PGD equal to 0.456, 0.758 and 0.581 compare favorably with those of previous models.

Fling Effects from Near‐Source Strong‐Motion Records: Insights from the 2016 Mw 6.5 Norcia, Central Italy, Earthquake

We propose a semiautomatic processing scheme (extended BASeline Correction [eBASCO]) for recovering the tectonic fling from near-source records. The method, based on a piecewise linear detrend of the strong-motion (SM) recordings, is applied to reconstruct the ground displacement field of the 30 October 2016 M w 6.5 earthquake in central Italy. The robustness of the results is checked against geodetic measurements, remote sensing data, ground-motion simulations, and existing empirical models for fling amplitude. The outcomes of eBASCO are analyzed with the goal of testing its capability to preserve long-period content in near-source SM recordings affected by tectonic fling, different from standard processing schemes based on bandpass filtering. Comparison of peak ground displacements, peak ground velocities, and spectral displacements shows that long-period ground motion recorded over and in proximity of the fault can be underestimated by standard processing. Spectral displacement ordinates can diverge up to the 25% for periods longer than 5 s when an appropriate baseline correction is made.

Seismic response of the subway station due to a specific active fault

In this paper, seismic response of a subway station structure was analyzed using a fault-structure system, which was performed in a two-step process. First, the strong ground motions induced by the specific active fault were synthesized using the revised empirical Green’s function (EGF) method at a geologic-length scale. Then, the synthesized seismic waves were used as the input seismic excitations for the dynamic response analysis of a subway station structure at an engineering-length scale. The maximum story drift deformation was calculated by finite element methods. The calculated results indicate that the maximum story drift angles of the subway station have a linear correlation with the peak ground displacements, which are different from the surface structures. Correlation between maximum story drift angles and the flexibility ratio were discussed at last. The results show that subway stations with smaller flexibility ratio suffer smaller story drift deformation. For underground structures with small flexibility ratio, the decreasing of frictional coefficients of the interfaces between the underground structure and the surrounding soil would decrease the maximum story drift deformation.

Reversible ground motion-to-intensity conversion equations based on the EMS-98 scale

The relation between observed macroseismic intensities and recorded ground motion parameters is a matter of interest in earthquake engineering, and it has been widely discussed in literature in the past. Several relationships already exist, correlating macroseismic intensity and peak ground motion parameters (i.e. PGA, PGV or PGD, respectively peak ground acceleration, velocity and displacement). However, most of these formulations are based on Mercalli-Cancani-Sieberg (MCS) scale, developed using regional databases and difficult to be applied at large scale. In this research, new formulations are proposed that correlate European Macroseismic Scale (EMS-98) with ground shaking parameters (PGMs), Arias intensity and Housner intensity. An initial PGM/EMS-98 intensity dataset was assembled for this scope, collecting 610 data pairs of observations, from 35 different Italian seismic events derived from the Parametric Catalogue of Italian Earthquakes (CPTI15) and the Italian Accelerometric Archive (ITACA), subsequently filtered considering only tectonic events and data pairs with site – station distances lower than 3 km. The resulting final dataset of 220 data pairs from 22 earthquakes was thus used to obtain regression relationships, finally compared with existing models based on the Modified Mercalli (MM) scale and MCS scale.

Attenuation of fourier amplitude and pseudo relative velocity spectra due to local earthquakes in the national capital region of India

In this paper we present attenuation of spectral amplitudes of strong earthquake ground motion in the National Capital Region (NCR) of India that surrounds and includes the National Capital Territory (NCT) of Delhi. In this region, because of the small volume of seismogenic zone in the shallow crust and the coincidence of this volume with a network of recording strong-motion stations, it is possible to determine the amplitude attenuation and scaling equations along the wave paths in this well-defined shallow geological environment. Similar to the Northeastern region of India, the basement in the NCR zone also comprises the Precambrian metamorphic rocks of the peninsular shield. The frequency-dependent attenuation function for the NCR is therefore obtained by assuming the applicability of the dependence on magnitude and site-condition parameters for the local earthquakes in Northeast India. The validity of the empirical scaling equations thus developed has been established by comparing the estimates of seismic moment and peak ground displacement from long-period extensions and the estimates of seismic wave energy and peak ground acceleration from short-period extensions of the empirical spectra with the expected theoretical trend or recorded values of the same parameters. The presented scaling relations for Fourier (FS) and pseudo relative velocity (PSV) spectra can be considered to provide a sound basis for macro- and micro-zoning specific to the highly risk-prone Delhi region.

A Global Database of Strong‐Motion Displacement GNSS Recordings and an Example Application to PGD Scaling

Displacement waveforms derived from Global Navigation Satellite System (GNSS) data have become more commonly used by seismologists in the past 15 yrs. Unlike strong‐motion accelerometer recordings that are affected by baseline offsets during very strong shaking, GNSS data record displacement with fidelity down to 0 Hz. Unfortunately, fully processed GNSS waveform data are still scarce because of limited public availability and the highly technical nature of GNSS processing. In an effort to further the use and adoption of high‐rate (HR) GNSS for earthquake seismology, ground‐motion studies, and structural monitoring applications, we describe and make available a database of fully curated HR‐GNSS displacement waveforms for significant earthquakes. We include data from HR‐GNSS networks at near‐source to regional distances (1–1000 km) for 29 earthquakes between M_w 6.0 and 9.0 worldwide. As a demonstration of the utility of this dataset, we model the magnitude scaling properties of peak ground displacements (PGDs) for these events. In addition to tripling the number of earthquakes used in previous PGD scaling studies, the number of data points over a range of distances and magnitudes is dramatically increased. The data are made available as a compressed archive with the article.

Copula-based earthquake early warning decision-making strategy

This paper presents a new copula-based earthquake early warning (EEW) decision-making strategy, aiming to characterize missed-alarm and false-alarm probabilities for an on-site EEW and determine an optimum threshold at which EEW should be set off with the lowest missed-alarm and false-alarm probabilities combined. On the basis of an existing PD3-PGV (PD3: peak ground displacement within the first three seconds after P-wave arrives; PGV: peak ground velocity) on-site EEW, the analysis shows that a copula model consisting of the Lognormal distribution, Weibull distribution, and Frank copula can satisfactorily model the PD3-PGV joint probability distribution. Accordingly, the optimum PD3 triggering thresholds for different PGV warning thresholds from 5 to 35 cm/s are presented for future references in the use of the PD3-PGV on-site EEW with maximum reliability.

Selection of earthquake records for the non-uniform excitation of bridges

Currently, there is no research effort on the efficient selection of earthquake records for the non-uniform excitation of bridges. The present investigation addresses this topic. Initially, the physics of the bridge response to asynchronous seismic excitations are illustrated. Next, two basic criteria are presented to provide insight into the selection of reference ground motions for the simulation of asynchronous excitations. The first criterion is the ratio of the zero-crossings of the reference ground displacement time series (n) to the total duration of the ground shaking (t), which can be evaluated by visual inspection of the displacement time series, and the second is the peak ground displacement. The former criterion is an indicator of the degree of sensitivity of the simulated displacement time series at various separation distances to the loss of coherency, and the numerical results of the present study indicate that the simulated waveforms of earthquake displacements with n/t greater than unity are highly dependent on coherency, i.e. become significantly modified by coherency, and, consequently, are more crucial for the pseudo-static response of bridges subjected to asynchronous seismic excitations. The latter criterion is also directly related to the magnitude of the pseudo-static force induced in the bridge structure. Finally, a brief discussion on the selection strategy of earthquake records for the seismic assessment of bridges is provided.

Seismic performance and fragility functions of a 3D steel-concrete composite structure made of high-strength steel

This paper provides insight into a probabilistic seismic demand analysis of a steel-concrete composite structure made of a novel type of high-strength steel moment resisting frame, to be used either in a seismic risk assessment or a fully probabilistic Performance-Based Earthquake Engineering (PBEE) framework. The application of the PBEE methodology with a full probabilistic character is able to rigorously evaluate the seismic risk to which a structure may be exposed, as well as to quantify economic losses, including both direct -repair, reconstruction costs, etc.- and indirect costs -downtimes, etc.-. In this respect, the knowledge of seismic fragility functions is paramount. Moreover, due to the dynamic complexity of the examined structure caused by irregularity in elevation and different lateral-force resisting systems in the two main directions -moment resisting frames (MRFs) and concrete shear walls- the seismic behaviour is not straightforward to foresee. Therefore, two separate 2D analyses along the building main directions may not suffice to identify the actual dynamic response and, consequently, a 3D comprehensive probabilistic seismic demand analysis was performed by taking into account the earthquake incident angle. In order to exploit the inherent overstrength of non-dissipative members, consistently with the capacity design philosophy, the structure, that is a representative example of a realistic office building, is characterised by a newly-conceived type of moment resisting frame made of high-strength steel circular columns filled of concrete and of mild steel beams. In this respect, a nonlinear 3D FE model was developed and calibrated on experimental tests performed on both beam-to-column and column-base joints that formed MRFs. A multiple incremental dynamic analysis (MIDA) was then performed with two groups of bespoke accelerograms characterised, on one hand, by large magnitude and large distance and, on the other hand, by near-source effects. The earthquake incidence angle was also considered and, to decrease the number of simulations, the accelerogram-incident angle pairs were selected by means of the Latin hypercube sampling (LHS) method. The relevant seismic analyses highlighted the need to include the incident angle to better characterise its dynamic behaviour. Hence, the seismic fragility functions were built both for damage and collapse limit states considering both the maximum interstorey drift ratio as engineering demand parameter and different intensity measures as well as the incident angle randomness. The results showed that peak ground displacement entails a more efficient probabilistic model because the dominant structural dynamic behaviour was governed by MRFs characterised by fairly long periods.

Discrete element simulation of the dynamic response of a dip slope under shaking table tests

A dip slope contains weak planes in the same dip direction along the slope face. In this study, a discrete element simulation was implemented to investigate the behavior of a dip slope under shaking table tests. The simulated dip slope model was first verified by testing under different horizontal excitations. Then, the influence of the slope angle and dynamic force on the deformation characteristics of the dip slopes was explored. The simulations provide detailed descriptions of the deformation processes and potential sliding mechanisms associated with the dip slopes. The results of this study are summarized as follows: (1) Two types of slope sliding, namely differential and complete, were recognized. The model with a dip angle lower than 20° was more stable, and differential sliding developed gradually during external excitation. In the model with a dip angle higher than 20°, the external excitation easily triggered complete sliding. (2) For threshold slope angles higher than 20°, the behavior of the dip slope model changed from deformation to sliding, and the displacement within the models increased with increasing slope angle. (3) An increase in frequency led to a decrease in the trigger time for slope sliding. In addition, the slope angle was negatively correlated with the triggering time for sliding. (4) The amplification factor of peak ground displacement (PGD) increased as the slope angle increased. The amplification factors corresponding to low excitation frequencies were considerably lower than those for high excitation frequencies. In contrast to the trends for PGD, the amplification factor of peak ground acceleration (PGA) decreased as the slope angle increased.

Attenuation of strong earthquake ground motion – II: Dependence on geology along the wave paths from the Burmese subduction zone to northeastern India

This paper presents another example of event-specific, region-specific attenuation equations for strong earthquake ground motion through essentially the same geological region defined by geometrically constrained ray paths. The current study describes strong motion wave attenuation from deep earthquakes in the Burmese subduction zone, as recorded by strong motion accelerographs in northeastern India. The accompanying empirical scaling equations to determine the Fourier and pseudo-relative velocity (PSV) spectra for the same events are also presented. To demonstrate the validity of the long-period extension of the above spectra, independent estimates of peak ground displacement from recorded accelerograms and estimates of the seismic moment from distant recordings of earthquakes are shown to be in good agreement with the extended spectral amplitudes. The validity of a short-period extension has been tested by comparing the values of pseudo acceleration spectral amplitudes at short periods with the recorded peak ground accelerations. Presented Fourier and PSV spectra can thus be considered to provide a sound basis for macro- and micro-zoning specific to the highly seismic regions of northeastern India.

An algorithm developed in Matlab for the automatic selection of cut-off frequencies, in the correction of strong motion data

Strong motion recordings are the key in many earthquake engineering applications and are also fundamental for seismic design. The present study focuses on the automated correction of accelerograms, analog and digital. The main feature of the proposed algorithm is the automatic selection for the cut-off frequencies based on a minimum spectral value in a predefined frequency bandwidth, instead of the typical signal-to-noise approach. The algorithm follows the basic steps of the correction procedure (instrument correction, baseline correction and appropriate filtering). Besides the corrected time histories, Peak Ground Acceleration, Peak Ground Velocity, Peak Ground Displacement values and the corrected Fourier Spectra are also calculated as well as the response spectra. The algorithm is written in Matlab environment, is fast enough and can be used for batch processing or in real-time applications. In addition, the possibility to also perform a signal-to-noise ratio is added as well as to perform causal or acausal filtering. The algorithm has been tested in six significant earthquakes (Kozani-Grevena 1995, Aigio 1995, Athens 1999, Lefkada 2003 and Kefalonia 2014) of the Greek territory with analog and digital accelerograms.

Ground Motion Simulation for Earthquakes in Sumatran Region

The present study aims at developing a model for simulating ground motion for earthquakes in the Sumatran region where one of the most devastating earthquakes took place in 2004 with a moment magnitude (M w ) of 9.1. With advancements in instrumentation, the three-dimensional material properties, topography and bathymetry of the region are available in the global database. These parameters are used as inputs in Spectral Finite Element Method to simulate ground motions. The model is first validated with the IGCAR broadband velocity data for 2012 M w 8.6 Sumatra Earthquake. Due to favourable comparison, our model is also used to generate ground displacement characteristics of M w 9.1 event. The source uncertainties are accounted by using three finite fault slip models available in the global database. The simulated time histories showed that the ground motion is sensitive to input slip models. The peak ground displacement (PGD) and ground residual displacement (GRD) in both horizontal and vertical directions are presented as contour plots. PGD obtained from various slip models in the epicentral region is of the order of 14–22 m in horizontal direction and 7–16 m in vertical direction. GRD in the epicentral region is of the order of 6–17 m in East–West (E–W) 4–17 m in the North–South (N–S) directions. The vertical uplift obtained from various slip models is around 2–8 m. The developed model can be used to simulate ground motion time histories, which can be further used in hazard analysis, tsunami simulations, etc.