Extreme responses of sea-crossing bridges subjected to offshore ground motion and correlated extreme wind and wave

Empirical Attenuation relationship for Peak Ground Horizontal Acceleration for North-East Himalaya

New probabilistic strong seismic ground motion maps of Canada are derived by applying the “Cornell-McGuire” method to 32 earthquake source zones in Canada and adjacent regions. Peak horizontal acceleration and peak horizontal velocity are mapped to depict strong ground motion in the frequency ranges near 5 Hz and near 1 Hz, respectively.Some earthquake source zones are well defined on the basis of both tectonics and average seismicity rates, but a lack of understanding of the near-field effects of the large earthquakes prohibits accurate estimates of ground motion in their vicinity. Some source zones have no known large-scale crustal features or zones of weakness that can explain the seismicity and must, therefore, be defined simply as concentrations of seismic activity with no geological or geophysical controls on the boundaries. Other source zones lack information on low-magnitude seismicity that would be representative of longer periods of time.A significant source of uncertainty in the ground motion estimates is introduced by the uncertainty in strong ground motion attenuation relations, particularly in the near-field of large earthquakes and particularly in eastern Canada where no strong motion data are available for earthquakes larger than magnitude 5. Valid estimates can be made of relative levels of probabilistic strong ground motion on a regional basis at moderate probabilities; however, the simple peak ground motion parameters are not sufficient for engineering design purposes in the immediate vicinity of large earthquakes.A comparison of the new probabilistic ground motion estimates at the Canada-United States border with equivalent estimates made in the United States reveals that peak acceleration contours match well in the British Columbia-Washington State, Yukon-Alaska, and Lake Ontario border regions. Canadian peak velocities are a factor of two higher near the British Columbia-Washington State border. Canadian peak accelerations are higher in the border regions of eastern Canada influenced by the Charlevoix zone, and in regions of the Alaska Panhandle-British Columbia border influenced by the active Queen Charlotte and Fairweather fault zones.The new ground motion estimates are used to produce new peak acceleration and peak velocity zoning maps to replace the 1970 (peak acceleration) zoning map in the National Building Code of Canada. The acceleration and velocity maps provide independent ground motion reference levels for small rigid structures and taller flexible structures, respectively. Compared to the 1970 map with four zones, the new maps with seven zones have a finer subdivision of zoning in moderate risk areas and additional zones in the high risk areas. A change in probability of exceedence from 0.01 per annum on the 1970 map to 10 per cent in 50 yr on the new maps, and the addition of velocity as a zoning parameter, have necessitated changes in the seismic design provisions. These revisions will be incorporated into the 1985 edition of the Code.

The site response to strong and weak ground motion depends largely on the subsurface conditions at the soil site for the two rock-soil station pairs studied. The first station pair consists of a soft-soil site (Treasure Island) and a sandstone and shale site (Yerba Buena Island). These stations recorded strong ground shaking from the Loma Prieta mainshock and weak ground motion from four aftershocks. The range of peak ground acceleration is from approximately 0.00006 to 0.07 g at the rock site. Compared to the rock site, the strong ground motion at the soft-soil site is amplified by a factor of about 3 over a frequency range from 0.5 to 2.0 Hz. The amplification is much higher for weak motion and suggests a dependence on signal amplitude. For example, near 1 Hz, the site response shows an increasing amplification as magnitude (and the peak velocity at the rock site) decreases. For events of local magnitude 7.0, 4.3, 4.1, 3.5, and 3.3, the maximum soil-site amplifications are 4, 12, 17, 19, and 25, respectively. A second station pair consisting of a stiff-soil site (Gilroy #2) and a sandstone site (Gilroy #1) was also studied with contrasting results. These two stations recorded strong ground shaking from the 1979 Coyote Lake, 1984 Morgan Hill, and 1989 Loma Prieta mainshocks. Weak ground motion was recorded at these stations after the Loma Prieta mainshock. The range of peak ground acceleration is from 0.006 to 0.43 g at the rock site. Unlike the results for the soft-soil study above, the estimated stiff-soil site responses are not significantly different for strong and weak motion from 0.5 to 2.0 Hz. Near 0.7 Hz, the stiff-soil site responses range from 2.5 to 4.5 for strong ground shaking from three mainshocks and from 1.5 to 4.0 for weak ground shaking from thirteen aftershocks.

Strong ground motion characteristics observed in the 13 June 2011 Mw6.0 Christchurch, New Zealand earthquake

This paper describes earthquake criteria for platforms in the Gulf of Alaska. The effects of strong earthquake ground motions are determined by the dynamic response characteristics of the soils and attached structures. The design of the structures to resist extreme wave loadings has an important influence on these characteristics. Introduction The offshore industry is on the threshold of a significant challenge - the timely, safe, and economic development of the Gulf of Alaska oil and gas reserves. This area is swept frequently by severe storms that generate waves and currents rivaling those of the North Sea and North Atlantic. In addition, the area is bordered by the earth's most active seismic zone, the Circum-Pacific Belt. Some of the world's largest recorded earthquakes have occurred on the perimeter of the Gulf of Alaska. perimeter of the Gulf of Alaska. This paper focuses primarily on the second major environmental loading threat - earthquakes. Using concepts, background, and data presented at the Seventh Annual Offshore Technology Conference, this technology is synthesized in the framework of a reliability analysis to help define earthquake ground-motion criteria for pile-supported drilling and production platforms. Summary 1. Depending primarily on location and type of soilfoundation condition, elastic design level earthquake motions producing peak effective ground velocities in the range of 50 to 70 cm/sec (20 to 28 in./sec) are indicated. To produce the desired level of loading and superstructure-foundation characteristics, a design wave height of approximately 120 ft is suggested along with the application of API RP 2A member-sizing guidelines. These results are applicable to the type of platform, design procedure, and analytical models used in this study. Design criteria are intended to be platform-system, strength-determining parameters. In an environment like the Gulf of Alaska, where there may be multiple environmental threats that produce loadings of comparable magnitudes, design criteria for one threat should not be selected without explicit consideration of other threats. 2. The potential force effects developed by severe ground motions on pile-supported platforms are very different from those caused by intense wave and current action. While loading patterns may be similar, one loading system fundamentally is force-limited (earthquakes) and the other is load-unlimited (wave and currents). As earthquake ground-motion intensity increases, the amount of transmitted load is limited by the ability of the foundation elements and soils to transmit that energy to the platform. In contrast, as wave-current action increases, the platform. In contrast, as wave-current action increases, the amount of imposed load essentially is unlimited. 3. Two fundamental efforts are identified that should be a focus of engineering research in this general area of technology. First, strong ground motions should be recorded at offshore sites in the Gulf of Alaska. Such records could be used to determine the applicability of attenuation and local soilgeology modulation relationships that describe the effects of distant earthquakes on a given location. No measurements have been made of strong ground motions offshore. JPT P. 325

Earthquake response of a base-isolated bridge subjected to strong near-fault ground motion

59 Estimation of strong seismic ground motions

Recent earthquakes, such as the 1985 Michoacan earthquake, the 1989 Loma Prieta earthquake, the 1994 Northridge earthquake, and the 1995 Kobe earthquake provided new experimental data on the soil behavior in strong ground motion, in particular, on the liquefaction phenomena, and discussions on the nonlinearity of soil behavior were induced (Lomnitz et al., 1995; Aguirre & Irikura, 1997; Field et al., 1997; O'Connell, 1999, etc.).Though nonlinear elastic properties of soils were studied in multiple laboratory experiments, and valuable laboratory experimental data are accumulated sometimes, this is not sufficient for understanding the soil behavior in situ, because soils often represent multicomponent systems containing water, air, gases, etc., and strong ground motion can induce movement and redistribution of these components, i.e., changes in the properties of the soils.Experimental data on the soil behavior in strong motion in situ are still few, fragmental, and non-representative; and accumulation of these data is important for improving our understanding of soil behavior in strong motion.In strong ground motion Hooke's law does not hold for subsurface soils, i.e., soils should be taken as nonlinear systems transforming incident seismic signals into movement on the surface.For studying nonlinear properties of systems, effective methods are developed in system analysis, so-called nonlinear system identification technique, based on the determination of higher-order impulse characteristics of the systems.An output of a nonlinear system is represented as the Volterra-Wiener series, i.e., a sum of the response of a linear system to the input signal and a number of nonlinear corrections, which are due to quadratic, cubic nonlinearity, and nonlinearities of higher (the 4-th, 5-th, etc.) orders.If we know the input and output of a nonlinear system, we can judge regarding the types and quantitative characteristics of the system nonlinearity (Marmarelis & Marmarelis, 1978).Nonlinear identification of soils in various geotechnical conditions seems to be promising, because it allows a better understanding of the behavior of soils and structures in strong ground motion.However, to apply methods of system analysis to studying nonlinear properties of soils, knowledge of stress-strain relations in the soil layers in strong motions is required.In this section, a method of estimation of nonlinear stress-strain relations in soils in strong ground motion is proposed based on vertical array data.Numerous methods and programs developed for calculating the ground response in strong motion in various conditions do not allow estimation of stress-strain relations in soil layers in situ.Moreover, in cases of strong nonlinearity, there often remains some disagreement www.intechopen.comEarthquake Research and Analysis -New Frontiers in Seismology 256 between the observed and simulated records.As is known, equivalent linear models (SHAKE, QUAD-4, FEADAM, LUSH, FLUSH) are not applicable for calculation of such complex phenomena as soil liquefaction.Programs DESRA (Lee & Finn, 1978), TARA and their modifications (Finn et al., 1986; Finn & Yogendrakumar, 1989) allow determination of the possible level of the pore pressure and the possibility of liquefaction, and they can be applied for the analysis of soil behavior after liquefaction.Changes in the pore pressure are related to the volumetric deformations in soils in drained conditions, and one-dimensional diffusion is included in the algorithm.Programs DYSAC2, DYNAFLOW, and SWANDYNE are considered to provide the best results (Arulanandan et al., 1995).Equations of motion of the liquid and solid phases are related to the equation of conservation of matter.Generation and dissipation of the pore pressure are connected with the deformation of the solid matrix due to the Biot equations (Biot, 1956).However, in every case simplifications and assumptions are applied, concerning the medium properties, as well as the mechanisms of the processes, therefore, any uncertainties and mistakes in modeling lead to an improper calculation of the soil movement.At the same time, records of strong ground motion provided by seismic vertical arrays allow estimation of stress-strain relations in soil layers in situ.This chapter describes the method of estimation of stress-strain relations developed by Pavlenko & Irikura (2003) and its application to 1995 Kobe, 2000 Tottori, and 1999 Chi-Chi earthquakes.The method allows us to trace temporal changes in the stress-strain relations.Since the estimates are based only on real measurements, they are free of theoretical approximations and physical assumptions concerning mechanisms of processes arising in the medium in strong ground motion. Estimation of nonlinear time-dependent soil behavior in strong ground motion based on vertical array dataVertical array records of the 1995 Kobe earthquake were processed for three recording sites, Port-Island, SGK, and TKS.Distances to the closest point on the fault line are 2 km, 6 km, and 16 km, respectively.Figure 2.1 shows the locations of the sites, the major principal axes, and the epicenters of the main shock and aftershocks summarized by Disaster Prevention Research Institute of Kyoto University.At Port Island, the vertical array contains four three-component accelerometers, installed at GL-0 m, GL-16 m, GL-32 m, and GL-83 m; the arrays at SGK and TKS sites consist of three three-component devices at GL-0 m, GL-24.9 m, and GL-97 m, and GL-0 m, GL-25 m, and GL-100 m, respectively (Fig. 2.2).We checked the directional drifts of the accelerometers by calculating the horizontal orbits of the long-period particle motions for the main shock and the aftershocks at different depths at the three sites.At Port Island, N19 o W rotation at GL-83 m was detected and corrected; at SGK site, a reverse of NS component and N6 o W rotation at GL-24.9 m and a reverse of NS component and N34 o E rotation at GL-97 m were detected and corrected.At TKS site, N23 o W rotation at GL-25 m and N9 o E rotation at GL-100 m were detected and corrected.All these corrections agree with the conclusions of other authors.The materials at the three sites are similar to one another: reclaimed soil, clays, sands, and gravel (Fig. 2.2).The profiling data at Port Island used for nonlinear simulation were taken from (Aguirre & Irikura, 1997).Shear wave velocity, shear modulus degradation, and maximum shear strain at SGK and TKS sites were taken from Soeda et al. (1999).These data were used to calculate the shear stress in failure  max and the low-strain shear modulus G max in different layers, following Seed et al. (1984) and Sun et al. (1988).P-wave velocities, when www.intechopen.com

We have been conducting seismic hazard assessment for Japan under the guidance of the Headquarters for Earthquake Research Promotion of Japan since the 1995 Hyogo-ken Nanbu Earthquake, and have made National Seismic Hazard Maps for Japan for use in estimating strong ground motion caused by future earthquakes. This special issue reviews the results of these efforts. Such work includes the development of seismic hazard assessment methodology for Japan, highly accurate prediction techniques for strong seismic ground motion and modeling underground structures for evaluating strong ground motion. Related research on utilization initiatives and risk assessment based on hazard information has also been conducted. An open Web system – the Japan Seismic Hazard Information Station (J-SHIS) – has even been developed to provide information interactively. The 2011 Mw9.0 Great East Japan Earthquake was the largest such event recorded in the history of Japan. This megathrust earthquake was not considered in National Seismic Hazard Maps for Japan. But efforts toward revising seismic hazard assessment in Japan are progressing based on lessons learned from this earthquake. Hazard assessment is currently being reviewed in relation to the large earthquakes anticipated to occur in the near future based in the Sagami Trough and the Nankai Trough in the waters of offshore Japan. This assessment, which considers earthquakes larger than those assumed to have occurred in the past, is being reviewed as of this writing. In light of these pressing circumstances, studies are now being implemented to evaluate the long-period ground motion accompanying these large earthquakes. The knowledge that has been cultivated in Japan in terms of seismic hazard assessment has reached a high level, and it is important to expand such knowledge both internationally and domestically. This is just one of the reasons that efforts here in Japan are being made to help improve the level of seismic hazard assessment in the Asian region and throughout the entire world. It is expected that this special issue will help contribute to the further development of strong ground motion prediction and seismic hazard assessment now and in the future. Finally, I extend our sincere thanks to all of the contributors and reviewers involved with these articles.

The current study examined the effectiveness of considering the nonlinear behavior of lead rubber bearings (LRBs) on the response of seismically isolated bridges. Also, the effect of the vertical component of the strong ground motion on the critical buckling capacity of LRBs was studied. 3D modeling of a seismically isolated bridge with nonlinear time history analysis under near-fault ground motion was applied. The results showed lack of consideration of the cavitation, post-cavitation and strength degradation behavior in tension and force softening under compression produces a large axial force and small axial displacement in LRBs and axial force-deformation appears to be perfectly linear. The results revealed that the average maximum base shear force in the bridge piers increased by 116% and 29.8% in the longitudinal and transverse direction respectively in comparison with the simple modeling. It also increased the average maximum displacement of bridge pier about 113% in the longitudinal direction and 31% in the transverse direction. Simplifying the LRBs modeling led to produces smaller stress and base shear forces of the bridge columns relative to actual conditions. Since the AASHTO regulation requires a seismically isolated bridge substructure to remain in the linear range, so in the bridges with a simplified model of LRBs, the nonlinear behavior of some columns of isolated bridges will be ignored under strong near-fault ground motion.

This thesis describes an investigation of the attenuation of strong earthquake ground motion in the 0. 4 to 16 Hz frequency band during the M=6.4, February 9, 1971, San Fernando, California earthquake. It is found that Fourier amplitudes of ground acceleration decay according to a simple expression incorporating a geometric spreading term, and a material attenuation term with constant specific attenuation Q. The scatter in the amplitude data about an expected level given by the simple decay expression is nearly constant with respect to both frequency and focal distance. Fourier amplitudes of acceleration corrected to a reference hypocentral distance agree well with those determined by a two-parameter source model of the San Fernando earthquake. Focusing of energy to the south by the southward propagating rupture is observed at frequencies below 8 Hz. The propagation of rupture was incoherent with respect to higher frequency components. The relationship between intensity of ground motion and site geology is examined. It is found that while, -in general, sedimentary sites were accelerated more strongly than basement rock sites, no clear difference could be found between sedimentary sites classified as soft by Trifunac and Brady (1975) (generally recent alluvium) and those classified as having medium soil stiffness, generally consisting of older alluvium and sedimentary rock. The difference between amplitudes recorded on basement rock and sediments is more complex. In general, smoothed amplitude spectra from accelerograms recorded on basement rock are lower than smoothed amplitudes at corresponding sedimentary sites. However, basement site spectra show marked isolated peaks, as high as those from sedimentary sites at similar distances. This is attributed to the focusing effects of the irregular topography normally accompanying basement rock outcrops. In the frequency band considered, it is concluded that for the purposes of aseismic design of structures no discrimination should be made between the intensity of ground motion expected on basement rock, sedimentary rock, and coarse-grained alluvium typical of Southern California. The agreement between the recorded strong motion amplitudes and those predicted by a simple two-parameter source model suggests that the model can be used for the assessment of strong ground motion to be used in design procedures. A procedure for estimating design earthquakes using the source model and the amplitude decay expression is presented.

We simulate the strong ground motion of 1999 Chi‐Chi, Taiwan earthquake (Mw = 7.6) by considering a three‐dimensional source rupture model in a full waveform three‐dimensional wave propagation study. The strong ground motion records during the 1999 Chi‐Chi earthquake show various characteristics at different sites in Taiwan. We adopt a three‐dimensional source model derived from an inversion study with identical path effects as considered in this three‐dimensional forward study. Comparisons between the simulation results and observed waveforms from dense island‐wide strong motion stations demonstrate that the fault geometry, lateral velocity variation, and complex source rupture process greatly influence the distribution of strong ground shaking. The simulation has reproduced the heavy damage area that is mainly concentrated in the hanging wall, especially close to the surface break of the Chelungpu fault. The source directivity effect is also reproduced and shows serious shaking along the northward rupture direction. Low‐velocity material in the shallow part of the Western Plain is found to generate significantly amplified ground motions. In the Central Range, the shaking is relatively weak owing to the energy radiation characteristics of a low‐angle thrust of the Chelungpu faulting system. The wavefield is then amplified by a high‐velocity gradient under the Coastal Range. Our simulation results in the frequency range of 0.01–0.5 Hz give good agreement with the extensive strong motion observations of the Chi‐Chi earthquake. We find that adequate source representation, good three‐dimensional crustal velocity structures, and careful numerical work are necessary to make the ground motion prediction feasible.

Success of earthquake resistant design practices critically depends on how accurately the future ground motion can be determined at a desired site. But very limited recorded data are available about ground motion in India for engineers to rely upon. To identify the needs of engineers, under such circumstances, in estimating ground motion time histories, this article presents a detailed review of literature on modeling and synthesis of strong ground motion data. In particular, modeling of seismic sources and earth medium, analytical and empirical Green’s functions approaches for ground motion simulation, stochastic models for strong motion and ground motion relations are covered. These models can be used to generate realistic near-field and far-field ground motion in regions lacking strong motion data. Numerical examples are shown for illustration by taking Kutch earthquake-2001 as a case study.

How to select the adequate real strong earthquake ground motion for seismic analysis and design of structures is an essential problem in earthquake engineering research and practice. In the paper the concept of the severest design ground motion is proposed and a method is developed for comparing the severity of the recorded strong ground motions. By using this method the severest earthquake ground motions are selected out as seismic inputs to the structures to be designed from a database that consists of more than five thousand significant strong ground motion records collected over the world. The selected severest ground motions are very likely to be able to drive the structures to their critical response and thereby result in the highest damage potential. It is noted that for different structures with different predominant natural periods and at different sites where structures are located the severest design ground motions are usually different. Finally, two examples are illustrated to demonstrate the rationality of the concept and the reliability of the selected design motion.

Computer simulation was used to study the nature of the strong ground motion near a strike-slip fault. The faulting process was modeled by stress release with fixed rupture velocity in a uniform elastic half-space or layered half-space. The fourth-order 3-D finite-difference method with staggered grids was employed to compute both ground motions and slip histories on the fault. The fault rupture was assumed to start from a point and propagate circularly with 0.8 times shear-wave velocity. In the present paper, we focused on the spatial pattern of ground velocity vectors, i.e., the direction of strong motions. In the case of bilateral rupture propagation, the strong fault parallel ground motion appeared near the center of the fault. The fault normal motions of ground velocity appeared near the edges of the fault. In the case of unilateral rupture, the fault parallel motion appeared near the starting point however, the amplitude was lower than that for the bilateral rupture case. The fault normal motion was predominant near the terminal point of the rupture. The results were applied to the earthquake damage data, especially the directions that simple bodies overturned and wooden houses collapsed, caused by the 1927 Tango, the 1930 Kita-Izu, and the 1948 Fukui earthquakes. The spatial distributions of the direction data were found to reflect the strong ground motions generated from the earthquake source process.