Strong Earthquake Ground Motion Research Articles

George Housner: A Personal Remembrance (1910–2008)

George W. Housner, C F Braun Professor of Engineering, Emeritus, died after a short illness on November 10, 2008, just a few weeks before his 98th birthday. He was in the retirement home in Pasadena where he had lived for several years. For all of us who knew George, this marked the end of an era. Few people have guided and nurtured a field the way George led earthquake engineering over a period of several decades. He had a profound effect on many people and will long be remembered. His impact was so pervasive that he had earned the title of the ‘Father of Earthquake Engineering’. This article records some of my thoughts about this remarkable man.

Influences of subsurface geological structure neighboring geological repository on earthquake motion of the site

AbstractAccording to recent seismic observation records, there are some cases where unexpectedly large seismic motion was observed deep underground and that was larger than at the surface. The factors influencing such phenomena are assumed to be deep geological structures with topographic irregularity, velocity structure and non-linearity of subsurface layers. These factors should be taken into account in the earthquake-resistant design of a geological repository. The influence of a deep underground geological structure with topographic irregularity on ground motion has been studied and it has been confirmed that such a structure have a significant impact on ground motion and the constructive interference of waves may result in strong earthquake ground motion in the vicinity of a structural boundary deep underground.

Probabilistic Empirical Green's Function Method in Ground Motion Simulation

Problem statement: The Empirical Green's Function method is used to synthesize strong ground motion time histories.In previous simulation processes parameters were taken deterministically. Approach: In this study, the probabilistic consideration for some of these parameters was inserted to the process. For implementing this method a computer program was developed in GIS. GIS abilities for storing and processing geographic data is used to make Strong Ground motion simulation more convenient. Results: The 2003 Bam Earthquake strong ground motions were used for the simulation. Also for considering the probabilistic parameters the Logic Tree method is used. Conclusions/Recommendations: Probability distribution of peak ground acceleration and spectral acceleration are presented as the results of probabilistic simulation.

Attenuation relations of peak ground acceleration and velocity in the Southern Dead Sea Transform region

Using the recorded earthquake strong ground motion, the attenuation of peak ground acceleration (PGA) and peak ground velocity (PGV) are derived in the southern Dead Sea Transform region. The expected values of strong motion parameters from future earthquakes are estimated from attenuation equations, which are determined by regression analysis on real accelerograms. In this study, the method of Joyner and Boor [Bull Seismol Soc Am 71(6):2011–2038, 1981] was selected to produce the attenuation model for the southern Dead Sea Transform region. The dataset for PGA consists of 57 recordings from 30 earthquakes and for PGV 26 recordings from 19 earthquakes. The attenuation relations developed in this study are proposed as replacement for former probabilistic relations that have been used for a variety of earthquake engineering applications. The comparison between the derived PGA relations from this study with the former relations clearly shows significant lower values than the other relations.

A stochastic ground motion model with separable temporal and spectral nonstationarities

AbstractA fully nonstationary stochastic model for strong earthquake ground motion is developed. The model employs filtering of a discretized white‐noise process. Nonstationarity is achieved by modulating the intensity and varying the filter properties in time. The formulation has the important advantage of separating the temporal and spectral nonstationary characteristics of the process, thereby allowing flexibility and ease in modeling and parameter estimation. The model is fitted to target ground motions by matching a set of statistical characteristics, including the mean‐square intensity, the cumulative mean number of zero‐level up‐crossings and a measure of the bandwidth, all expressed as functions of time. Post‐processing by a second filter assures zero residual velocity and displacement, and improves the match to response spectral ordinates for long periods. Copyright © 2008 John Wiley & Sons, Ltd.

Estimation of Strong Ground Motions in Southwest Western Australia with a Combined Green's Function and Stochastic Approach

As only a very limited number of earthquake strong ground motion records are available in southwest Western Australia (SWWA), it is difficult to derive a reliable and unbiased strong ground motion attenuation model based on these data. To overcome this, in this study a combined approach is used to simulate ground motions. First, the stochastic approach is used to simulate ground motion time histories at various epicentral distances from small earthquake events. Then, the Green's function method, with the stochastically simulated time histories as input, is used to generate large event ground motion time histories. Comparing the Fourier spectra of the simulated motions with the recorded motions of a ML6.2 event in Cadoux in June 1979 and a ML5.5 event in Meckering in January 1990, provides good evidence in support of this method. This approach is then used to simulate a series of ground motion time histories from earthquakes of varying magnitudes and distances. From the regression analyses of these simulated data, the attenuation relations of peak ground acceleration (PGA), peak ground velocity (PGV), and response spectrum of ground motions on rock site in SWWA are derived.

Imaging the graben structure in the deep basin with a microtremor profile crossing the Yinchuan City

Microtremor studies were originated in Japan and have gained broader recognition in studying the site effect in earthquake strong ground motion. In recent years, microtremors have also been used in investigating the subsurface structures of a basin. There are also many reports of using array observation to invert the crustal structure; it is particularly popular in Japan. However, to our knowledge, there has been no report on using the spectral ratios between the horizontal components of a microtremor relative to the vertical component, H/V, to deduce the basin's structure, whose thickness could reach a few kilometres, through dense microtremor observation independently. This paper reports the results from a microtremor observation profile crossing the Yinchuan City to study the crustal structure of the Yinchuan Basin, which is the west border of the Ordos block. This basin is a continent graben-basin. The sedimentary layer is very deep; the Quaternary alone is reaching 1600 m. We used the long-period velocity seismometer in this study. The auto-correlation function analysis is used to get the H/V spectral ratio, and to investigate the crustal structure based on the fundamental frequency obtained from the H/V spectra. We have used two methods to verify the computation results. The first one is to compare the crustal structure results with those obtained from seismic explorations. The two results are highly consistent. The second method is to compare the theoretical prediction of the microtremor characteristics using the deduced basin model with real observations. It is shown that it is practical and economical to use densely distributed single-point microtremor observations to study the basal structure of deep basins with decent precision.

Sustainable urban development and geophysics

Sustainable urban development and geophysics

Book Review of “On Strong Motion Seismology” (in Japanese) written and edited by Hiroaki Yamanaka, published by University of Tokyo Press

This book is a work for general readers, straight-forwardly treating the theme of "strong earthquake ground motion" directly causing disaster and explaining how to cope. Eartquake ground motion is generally said to cause earthquake disasters and the degree of ground motion is determined both by the magnitude of the earthquake and the distance from its epicenter. In reality, however, things are not so simple. In the 2003 Tokachi Offshore Earthquake, for example, shaking at a relatively long 10-second period resonated at the characteristic frequency of oil tanks, triggering sloshing and causing large fires. In the 1995 Southern Hyogo Prefecture Earthquake (the Great Hanshin-Awaji Earthquake Disaster), for another example, a long narrow belt of disaster confirmed where damage to collapsed building was especially significant because only ground within this belt quaked more intensely than elsewhere.

Source differentiation, modeling and simulating strong-motion data from Iran

For designing a structure to withstand the effects of strong earthquake ground motions, it is necessary to characterize the type of motion that probably affects the structure. The strong-motion accelerograms contain numerous data regarding the source, path, and receiver. Variables such as the Richter magnitude, hypocenter depth, duration of the event, and focal mechanism relate to the source. The soil parameter and distance to epicenter, relate to the path. The application of autoregressive moving average (ARMA) process in modeling an earthquake accelerogram of three different regions of Iran reveals a formulation, which relates the physical variables via a regression analysis. In order to generate time history data of a probable future earthquake, it is recommended to use the regression equations for a specific type of earthquake focal mechanism if the future earthquake mechanism and physical variables are known; otherwise, regional equations are more suitable.

Experimental Stiffness and Seismic Response of Pallet-Type Steel Storage Rack Connectors

The down-aisle lateral load-resisting systems of pallet-type steel storage racks are typically moment frames utilizing special beam-to-column moment-resisting connections. Both the stability and seismic response of racks are strongly influenced by the rotational stiffness developed by the beam-to-column connectors. The behavior of these connectors is poorly known, and consequently there is significant uncertainty as to proper values of connector stiffness and strength to use in design. This paper presents the results of down-aisle shake table tests performed on steel pallet-type storage racks fabricated from hot-rolled sections and incorporating four different bolted beam-to-column connectors. The main objectives of the tests were to determine appropriate static load connector rotational stiffness values from measured dynamic characteristics of storage racks under low amplitude vibrations, and to evaluate their response under quasi-static conditions as well as under strong earthquake ground motions. The e...

Seismic performance of isolated curved steel viaducts equipped with deck unseating prevention cable restrainers

This paper presents an in-depth analysis to evaluate the efficiency of using cable restrainers connecting isolated and non-isolated spans for preventing unseating of curved steel viaducts. For this purpose, the overall three-dimensional non-linear bridge response is examined in detail under the action of strong earthquake ground motions. The expected seismic vulnerability of bridge structures with curved deck geometries has been demonstrated, providing a refined estimation of seismic demands on most critical bridge components. The advantage of using a precise three-dimensional model has revealed the concentration of large seismic forces on specific steel bearing supports and cable restrainer units that greatly increase their failure possibility. Moreover, the unbalanced distribution of pounding forces found across the expansion joint is able to cause local damage to colliding girders and transmit high impact forces to bearing supports. In general, restrainers perform effectively to minimize the possibility of deck unseating and reduce the pounding forces at the expansion joint. Special attention should be paid to the non-linear bridge dynamic response in order to avoid failure of restrainers and ensure the adequate proportioning of the cables according to the characteristics of isolation bearings.

Tilts in Strong Ground Motion

Most instruments used in seismological practice to record ground mo- tion are pendulum seismographs, velocigraphs, or accelerographs. In most cases it is assumed that seismic instruments are only sensitive to the translational motion of the instrument's base. In this study the full equation of pendulum motion, including the inputs of rotations and tilts, is considered. It is shown that tilting the accelerograph's base can severely impact its response to the ground motion. The method of tilt evaluation using uncorrected strong-motion accelerograms was first suggested by Graizer (1989), and later tested in several laboratory experiments with different strong-motion instruments. The method is based on the difference in the tilt sensi- tivity of the horizontal and vertical pendulums. The method was applied to many of the strongest records of the Mw 6.7 Northridge earthquake of 1994. Examples are shown when relatively large tilts of up to a few degrees occurred during strong earthquake ground motion. Residual tilt extracted from the strong-motion record at the Pacoima Dam-Upper Left Abutment reached 3.1 in N45E direction, and was a result of local earthquake-induced tilting due to high-amplitude shaking. This value is in agreement with the residual tilt measured by using electronic level a few days after the earthquake. The method was applied to the building records from the North- ridge earthquake. According to the estimates, residual tilt reached 2.6 on the ground floor of the 12-story Hotel in Ventura. Processing of most of the strongest records of the Northridge earthquake shows that tilts, if happened, were within the error of the method, or less than about 0.5.

Selection of the appropriate methodology for the deterministic seismic hazard assessment on the territory of the Republic of Serbia

This paper presents a discussion regarding the most common approaches to the deterministic seismic hazard analysis, as well as their relation with the probabilistic hazard analysis. Different methodologies for estimation of the strong earthquake ground motion at a site of interest on the territory of the Republic of Serbia are also discussed. When generation of the synthetic ground motion time histories on the territory of the Republic of Serbia is concerned, a method developed by Trifunac and his associates is suggested having in mind that this approach uses only those input parameters that can be easily and accurately defined while at the same time being able to model all properties of strong earthquake ground motion that are presently known as well as to consider the probabilistic nature of earthquake occurrence.

The case for seismic superiority of well‐engineered tall buildings

AbstractThe objective of this paper is to bring the lingering debate over whether more rigid or more flexible buildings fare better during major earthquakes to an end. Historical data, design experience, and ground motions obtained from simulation of a magnitude 7·1 blind fault rupture directly below downtown Los Angeles are utilized in this study. Assuming the same level of attention to design, detailing, and construction workmanship is applied to buildings of all heights resulting in well‐engineered buildings, the results indicate that well‐engineered tall buildings are substantially safer than shorter, stiffer, buildings when subjected to strong earthquake ground motions. This is true even in the case of strong ground motions containing significant directivity and near‐source velocity pulses. Copyright © 2005 John Wiley & Sons, Ltd.

FUZZY PATTERN CLASSIFICATION OF STRONG GROUND MOTION RECORDS

Classification of earthquake strong ground motion (SGM) records is performed using fuzzy pattern recognition to exploit knowledge in the data that is utilised in a genetic algorithm (GA) search and scaling program. SGM records are historically treated as “fingerprints” of certain event magnitude and mechanism of faulting systems recorded at different distances on different soil types. Therefore, databases of SGM records of today present data of complex nature in high dimensions (many of the dimensions—or SGM parameters in time and frequency domain—are presently available from different archives). In this study, simple ground motion parameters were used but were combined and scaled nonlinearly such that the physical properties of the data could be preserved while reducing its dimensionality. The processed data was then analysed using fuzzy c-means (FCM) clustering method to explore the possibility of meaningfully representing earthquake SGM data in lower dimensions through finding subsets of mathematically similar vectors in a benchmark database. This representation can be used in practical applications and has a direct influence on the processes of synthesising ground motion records, identifying unknown ground motion parameters (e.g. soil type in this study), improving the quality of matching SGM records to design target spectra, and in rule generalisation for response. The results showed that the stochastic behaviour of earthquake ground motion records can be accurately simplified by having only a few of motion parameters. The very same parameters may also be utilised to derive unknown characteristics of the motion when the classification task on “training” records is performed carefully. The clusters are valid and stable in time and frequency domain and are meaningful even with respect to seismological features that were not included in the classification task.

THE USE OF SIMPLE PULSES TO ESTIMATE INELASTIC RESPONSE SPECTRA

Inelastic response spectra are estimated for elasto-plastic SDOF systems subjected to strong earthquake ground motions by applying the strength reduction factors determined for a simple pulse to the elastic response spectrum of the ground motion. This approach relies upon similarities in the strength reduction factors computed for earthquake ground motions and for short duration pulses. The accuracy of the estimated inelastic spectra obtained using 24 simple pulse waveforms is assessed in order to identify subsets of just several pulse waveforms that are suited for this purpose. Based upon the ground motions and pulses investigated, this approach appears to be equally applicable to short and long duration ground motions and those having near-fault forward directivity features.

Seismic response of steel frames under repeated earthquake ground motions

Seismic sequences characterized by the repetition of medium–strong earthquake ground motions occurring at short time one after the other were observed in many parts of the world. The paper investigates the effects produced by these events on steel structures. Single-degree-of-freedom (SDOF) systems with elastic–plastic laws, moment resistant frames with rigid and semi-rigid joints, and a concentrically braced steel frame have been analysed under seismic sequences. Both the SDOF systems and steel frames are characterized by a significant damage accumulation with respect to only one event. According to the approach where, for damage control limit state verifications, the seismic analysis of a non-linear system is performed through an elastic analysis by using the q-factor, a reduction in the q-factor is hence proposed. This reduction in the behaviour factor should be considered in earthquake-prone regions, where the repetition of seismic events may have a high probability of occurrence.

Near Real-Time Mapping of Peak Ground Acceleration and Peak Ground Velocity Following a Strong Earthquake

During a disastrous earthquake, the early assessment and timely reporting of the peak ground acceleration (PGA) and peak ground velocity (PGV) maps will be crucial in an effective emergency response operation. In this study, we first derive an empirical relationship between M L and M W. The PGA and PGV attenuation relationships are deduced with data from the Taiwan Strong Motion Instrumentation Program (TSMIP) and the Taiwan Rapid Earthquake Information Release System (TREIRS). Site corrections of the attenuation relationships for shallow and large earthquakes in Taiwan region are also obtained. Peak values of earthquake strong ground motion can be well determined in Taiwan as soon as the earthquake location is determined, and magnitudes are calculated by the TREIRS. This peak ground motion value information can be immediately turned into the calculated PGA and PGV maps that can be issued within two minutes of the earthquake origin time. During any disastrous earthquake, these maps are found to be very useful for immediate seismic damage assessment and dispatching of emergency response missions. Manuscript received 1 December 2000.

Characterization of Earthquake Strong Ground Motion

Some underwater landslides are triggered by strong ground motions caused by earthquakes. This paper reviews current concepts and trends in the characterization of strong ground motion. Improved empirical ground motion models have been derived from a strong motion data set that has grown markedly over the past decade. However, these empirical models have a large degree of uncertainty because the magnitude-distance-soil category parameterization of these models often oversimplifies reality. This reflects the fact that other conditions that are known to have an important influence on strong ground motions, such as near-fault rupture directivity effects, crustal waveguide effects, and basin response effects, are not treated as parameters of these simple models. Numerical ground motion models based on seismological theory that include these additional effects have been developed and extensively validated against recorded ground motions, and used to estimate the ground motions of past earthquakes and predict the ground motions of future scenario earthquakes.