22 results for Bradley, B.A., Conference poster

  • A generalized conditional intensity measure approach and holistic ground motion selection

    Bradley, B.A. (2010)

    Conference poster
    University of Canterbury Library

    The rigorous selection of ground motions is an important consideration in a seismic risk assessment as it provides the link between seismic hazard (seismology) and seismic response (earthquake engineering). Despite the fact that many studies have highlighted the differences between the uniform hazard spectrum (UHS) and individual earthquake scenarios, the UHS is still the primary method by which ground motion records are selected and scaled. The conditional mean spectrum (CMS) is one alternative to the UHS for ground motion selection which provides the mean response spectral ordinates conditioned on the occurrence of a specific value of a single spectral period, and is directly linked to probabilistic seismic hazard analysis (PSHA). There are however several limitations in the use of the CMS for ground motion selection, which primarily stem from the fact that spectral accelerations provide only a partial picture of the true character of a ground motion. Based on the identified limitations of the CMS the objective of this work was to develop what is referred to as a generalised conditional intensity measure (GCIM) approach, which allows for the construction of the conditional distribution of any ground motion intensity measure. A holistic method of ground motion selection was also developed based on the comparison of the empirical distribution of a ground motion suite and the GCIM distributions.

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  • Strong ground motions observed in the 22 February 2011 Christchurch earthquake

    Bradley, B.A.; Cubrinovski, M. (2011)

    Conference poster
    University of Canterbury Library

    Poster listed as B-055

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  • Seismic sustainability assessment of structural systems: A preliminary case study

    Yeow, T.; MacRae, G.A.; Dhakal, R.P.; Bradley, B.A. (2012)

    Conference poster
    University of Canterbury Library

    The University of Canterbury has initialized a research program focusing on the seismic sustainability of structures. As part of this program, the relative seismic sustainability of various structures will be assessed to identify those with the highest sustainability for the Christchurch rebuild and general use in New Zealand. This preliminary case study assesses one reinforced concrete (RC) frame structure and one RC wall structure. The scenario loss is evaluated for two earthquake records considering direct losses only in order to explain and illustrate the methodology.

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  • Ground motion selection for seismic response analysis

    Bradley, B.A. (2010)

    Conference poster
    University of Canterbury Library

    Poster 47

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  • Hybrid broadband simulations of the 2010-2011 Canterbury earthquakes

    Razafindrakoto, H.N.T.; Bradley, B.A.; Thomson, E.M.; Graves, R.W. (2015)

    Conference poster
    University of Canterbury Library

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  • Characterization of dynamic soil properties and stratigraphy at Heathcote Valley, New Zealand, for simulation of 3D valley effects

    Jeong, S.; Bradley, B.A.; McGann, C.R.; DePascale, G. (2014)

    Conference poster
    University of Canterbury Library

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  • What new liquefaction can teach us about old earthquakes: Evaluating the efficacy of paleoliquefaction analytics using modern analogs

    Maurer, B.W.; Green, R.A.; Bradley, B.A.; Cubrinovski, M. (2014)

    Conference poster
    University of Canterbury Library

    Paleoliquefaction back-analyses can be very accurate if earthquake source location & mechanism are known. Accurate analysis is more difficult if source location is unknown, but index Ef enables more intelligent estimate of causative earthquake’s location and magnitude. Framework using site-specific geotechnical analysis shown to be effective and proposed for use in paleoliquefaction studies worldwide.

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  • Applicability of foreign ground motion prediction equations for New Zealand active shallow crustal earthquakes

    Bradley, B.A. (2010)

    Conference poster
    University of Canterbury Library

    The number of instrumental ground motion records in New Zealand (NZ) has increased significantly in recent years due to an increase in the number and quality of seismometer throughout NZ. Figure 1 provides a comparison between NGA ground motion database and the NZ database developed as part of this study. Despite this increase in instrumental data, it can be seen clearly in Figure 1 that there is a lack of empirical records from large magnitude events observed at near-source distances. This is even more clear in Figure 2, which plots the cumulative number of records exceeding specific PGA values in the NZ ground motion database. There are only a total of 66 ground motion records which have PGA values above 0.1g (28 crustal, 11 interface, and 27 slab). Furthermore, the maximum PGA values recorded are 0.39g, 0.31g, and 0.28g for crustal, interface, and slab events, respectively. This lack of ground motion records from large magnitude nearsource records, which typically dominate seismic hazard analyses, makes it difficult to develop robust ground motion prediction equations used in seismic hazard analysis based on NZ data alone. In this study an alternative approach to empirical ground motion prediction equation development was taken. Firstly, the applicability of various foreign ground motion prediction equations (derived using plentiful data) to NZ were considered. The consideration was based on both the dependence of the inter- and intra-event residuals as a function of several predictor variables, and also the general predictor variable scaling of the various models. Secondly, the model exhibiting the best applicability to NZ was modified based on theoretical and empirically-driven considerations to better represent the NZ data.

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  • Evaluation of Liquefaction Potential Index (LPI) for Assessing Liquefaction Hazard: A Case Study in Christchurch, New Zealand

    Maurer, B.; Green, R.; Cubrinovski, M.; Bradley, B.A. (2013)

    Conference poster
    University of Canterbury Library

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  • Considering rupture directivity in selecting ground motion ensembles for seismic response analysis in the near-fault region

    Tarbali, K.; Bradley, B.A. (2015)

    Conference poster
    University of Canterbury Library

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  • 3D Canterbury Velocity Model (CantVM) – Version 1.0

    Bradley, B.A.; Lee, R.L.; Thomson, E.M.; Ghisetti, F.; McGann, C.R.; Pettinga, J.; Hughes, M.W. (2015)

    Conference poster
    University of Canterbury Library

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  • 1D Nonlinear site response prediction: Analysis of residuals at a large number of Kik-Net vertical seismometer arrays

    Kaklamanos, J.; Bradley, B.A. (2015)

    Conference poster
    University of Canterbury Library

    Site response models are frequently used in engineering practice to predict surficial ground motions based on a site-specific soil profile and input motions, and site response predictions are especially important for large strains and accelerations, which have a greater damage potential. To characterize nonlinear soil behavior at large strains, a number of constitutive soil models have been developed. However, the application of fully nonlinear time-domain site response analyses remains limited in practice, with the equivalent-linear site response approximation to nonlinear soil behavior, using frequency-domain programs such as SHAKE (Schnabel et al., 1972), still the most common approach. For a particular project, engineering practitioners are therefore faced with the challenge of selecting the appropriate level of model complexity (e.g., equivalent-linear vs. nonlinear). While previous validation studies have attempted to quantify the levels of ground motion for which nonlinear site response analyses are necessary (e.g., Assimaki et al., 2008; Kwok et al., 2008; Kim and Hashash, 2013; Kaklamanos et al., 2015), the assessment of fully nonlinear site response models is often limited to a relatively small number of sites and ground motions. In this study, one-dimensional (1D) total-stress nonlinear, equivalent linear, and linear site response predictions are calculated using an unprecedented number of sites and ground motions, allowing for more statistically significant conclusions to be drawn than in prior studies. This study uses Japan’s comprehensive Kiban-Kyoshin network of vertical seismometer arrays (Aoi et al., 2000), in particular, 5626 ground motions at 114 KiK-net sites are utilized, with 239 ground motions having PGA > 0.3g. Site response predictions are calculated using the program DEEPSOIL (Hashash et al., 2011), and SHAKE for the nonlinear, and equivalent linear analyses, respectively; based on the P- and S- wave velocity profiles, and soil types provided on the KiK-Net database. The Zhang et al. (2005) modulus-reduction and damping curves are used in the equivalent-linear analyses and as the target curves for the nonlinear analyses. This study builds upon prior work (Kaklamanos et al., 2013) in which linear and equivalentlinear site response analyses (but not nonlinear analyses) were performed at 100 KiK-net sites using 3720 ground motions, allowing for broad conclusions on the uncertainty of linear and equivalent-linear site response models. With the large database of nonlinear site response model predictions in the current study, the predictive capabilities of fully nonlinear total-stress site response models relative to linear and equivalent-linear models are assessed. The model residuals assessed in this study are those of the 5%-damped pseudo-acceleration response spectra, calculated as ln(PSAobs) – ln(PSApred), where PSAobs and PSApred are the observed and predicted spectral accelerations at a given period, respectively. From analyzing the trends of the model residuals versus the maximum shear strain in the soil profile, Kaklamanos et al. (2013) concluded that the equivalent-linear model becomes inaccurate when strains exceed 0.1 to 0.4%. In the current study, we find that the model residuals of the equivalent-linear and nonlinear site response models generally do not deviate from each other significantly at large shear strains. For shear strains greater than 0.5% at short spectral periods, both the equivalent-linear and nonlinear model residual plots slope upwards, indicating that these models tend to underpredict large-strain ground motions. However, the nonlinear model residuals do not slope upward as significantly at some spectral periods (for example, for spectral 1 accelerations at T = 0.1 s). Furthermore, the scatter in the equivalent-linear model residuals is greater than that of the nonlinear model residuals at large shear strains, suggesting that the equivalent-linear site response model is less precise at large shear strains. In the aggregate, the linear, equivalent-linear, and nonlinear model biases and standard deviations can be calculated across all sites and ground motions using mixed-effects regression on the model residuals. Comparisons of the model biases and standard deviations indicate that all 1D site response models (linear, equivalent-linear, and nonlinear) are biased towards underprediction of ground motions at short spectral periods, where nonlinear effects are strongest. However, the equivalent-linear and nonlinear model biases are smaller than the linear model bias. The persistent model biases suggest that: (1) many of these sites may experience a breakdown in the 1D site-response assumptions; and/or (2) the site investigation data provided on KiK-net (i.e. velocity profiles and broad soil type) may be over-simplified. With respect to the first point, in particular, the underlying assumptions of 1D site response may have to be addressed in order to make notable prediction improvements, perhaps by incorporation of three-dimensional soil constitutive response and incident ground motion effects. Based on the inter-site residuals, we have also identified some “interesting” sites at which all 1D site response models most strongly overpredict or underpredict ground motions: ISKH05 and KOCH05 are characterized by the strongest underpredictions, and HYGH07, IWTH07, and WKYH01 are characterized by the strongest overpredictions (at different vibration periods, however). Because these site-specific biases are consistent across all 1D site response models, the 1D site response assumption is likely not valid at these sites. Although the nonlinear site response models are shown to offer an improvement over equivalent-linear models, the remaining trends in the nonlinear model residuals suggest that other factors—such as three-dimensional effects—have a significant impact on site response behavior.

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  • Systematic ground motion observations in the Canterbury earthquakes

    Bradley, B.A. (2013)

    Conference poster
    University of Canterbury Library

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  • OpenSHA implementation of the GCIM approach for ground motion selection

    Bradley, B.A. (2010)

    Conference poster
    University of Canterbury Library

    Ground motion selection is known to be an important step in seismic hazard and risk assessment. There have been numerous procedures proposed for selecting ground motions ranging from somewhat ad-hoc guidelines specified in seismic design codes to more rigorous approaches which have found favour in the research-community, but are not yet applied routinely in earthquake engineering practice. The most common method (often specified in seismic design codes) for selecting ground motion records for use in seismic response analysis is based on their "fit" to a Uniform Hazard Spectrum (UHS). This is despite the fact that many studies have highlighted the differences between the UHS and individual earthquake scenarios, and therefore its inappropriateness for use in ground motion selection. The reluctance of the earthquake engineering profession to depart from UHS-based selection of ground motions is arguably because of its simplicity to implement relative to methodologies with sounder theoretical bases. To this end, the aim of the present work was to implement a recently developed Generalised Conditional Intensity Measure (GCIM) approach for ground motion selection (Bradley, 2010) into the open-source seismic hazard analysis software OpenSHA (Field et al. 2003).

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  • A 3D seismic velocity model for Canterbury, New Zealand for broadband ground motion simulation

    Lee, R.L.; Bradley, B.A.; Pettinga, J.R.; Hughes, M.; Graves, R.W. (2013)

    Conference poster
    University of Canterbury Library

    his poster presents the ongoing development of a 3D Canterbury seismic velocity model which will be used in physics-based hybrid broadband ground motion simulation of the 2010-2011 Canterbury earthquakes. Velocity models must sufficiently represent critical aspects of the crustal structure over multiple length scales which will influence the results of the simulations. As a result, numerous sources of data are utilized in order to provide adequate resolution where necessary. Figure 2: (a) Seismic reflection line showing P-wave velocities and significant geologic horizons (Barnes et al. 2011), and (b) Shear wave profiles at 10 locations (Stokoe et al. 2013). Figure 4: Cross sections of the current version of the Canterbury velocity model to depths of 10km as shown in Figure 1: (a) at a constant latitude value of -43.6˚, and (b) at a constant longitude value of 172.64˚. 3. Ground Surface and Geologic Horizon Models Figure 3: (a) Ground surface model derived from numerous available digital elevation models, and (b) Base of the Quaternary sediments derived from structural contours and seismic reflection line elevations. The Canterbury region has a unique and complex geology which likely has a significant impact on strong ground motions, in particular the deep and loose deposits of the Canterbury basin. The Canterbury basin has several implications on seismic wave phenomena such as long period ground motion amplification and wave guide effects. Using a realistic 3D seismic velocity model in physics-based ground motion simulation will implicitly account for such effects and the resultant simulated ground motions can be studied to gain a fundamental understanding of the salient ground motion phenomena which occurred during the Canterbury earthquakes, and the potential for repeat occurrences in the Canterbury region. Figure 1 shows the current model domain as a rectangular area between Lat=[-43.2˚,-44.0˚], and Lon=[171.5˚,173.0˚]. This essentially spans the area between the foot of the Southern Alps in the North West to Banks Peninsula in the East. Currently the model extends to a depth of 50km below sea level.

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  • Sensitivity of predicted liquefaction-induced lateral displacements from the 2010 Darfield and 2011 Christchurch earthquakes

    Robinson, K.; Cubrinovski, M.; Bradley, B.A. (2013)

    Conference poster
    University of Canterbury Library

    Liquefaction-induced lateral spreading in Christchurch and surrounding suburbs during the recent Canterbury Earthquake Sequence (2010-2011) caused significant damage to structures and lifelines located in close proximity to streams and rivers. Simplified methods used in current engineering practice for predicting lateral ground displacements exhibit a high degree of epistemic uncertainty, but provide ‘order of magnitude’ estimates to appraise the hazard. We wish to compare model predictions to field measurements in order to assess the model’s capabilities and limitations with respect to Christchurch conditions. The analysis presented focuses on the widely-used empirical model of Youd et al. (2002), developed based on multi-linear regression (MLR) of case history data from lateral spreading occurrence in Japan and the US. Two issues arising from the application of this model to Christchurch were considered: • Small data set of Standard Penetration Test (SPT) and soil gradation indices (fines content FC, and mean grain size, D50) required for input. We attempt to use widely available CPT data with site specific correlations to FC and D50. • Uncertainty associated with the model input parameters and their influence on predicted displacements. This has been investigated for a specific location through a sensitivity analysis.

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  • A comparison of ground motions and first-hand experience of the 2011 Mw6.3 Christchurch, New Zealand and 2011 Mw9.0 Tohoku, Japan earthquakes

    Bradley, B.A. (2013)

    Conference poster
    University of Canterbury Library

    This poster provides a comparison between the strong ground motions observed in the 22 February 2011 Mw6.3 Christchurch earthquake with those observed in Tokyo during the 11 March 2011 Mw9.0 Tohoku earthquake. The destuction resulting from both of these events has been well documented, although tsunami was the principal cause of damage in the latter event, and less attention has been devoted to the impact of earthquake-induced ground motions. Despite Tokyo being located over 100km from the nearest part of the causative rupture, the ground motions observed from the Tohoku earthquake were significant enough to cause structural damage and also significant liquefaction to loose reclaimed soils in Tokyo Bay. The author was fortunate enough (from the perspective of an earthquake engineer) to experience first-hand both of these events. Following the Tohoku event, the athor conducted various ground motion analyses and reconniassance of the Urayasu region in Tokyo Bay affected by liquefaction in collaboration with Prof. Kenji Ishihara. This conference is therefore a fitting opportunity in which to discuss some of authors insights obtained as a result of this first hand knowledge. Figure 1 illustrates the ground motions recorded in the Christchurch CBD in the 22 February 2011 and 4 September 2010 earthquakes, with that recorded in Tokyo Bay in the 11 March 2011 Tohoku earthquake. It is evident that these three ground motions vary widely in their amplitude and duration. The CBGS ground motion from the 22 February 2011 event has a very large amplitude (nearly 0.6g) and short duration (approx. 10s of intense shaking), as a result of the causal Mw6.3 rupture at short distance (Rrup=4km). The CBGS ground motion from the 4 September 2010 earthquake has a longer duration (approx. 30s of intense shaking), but reduced acceleration amplitude, as a result of the causal Mw7.1 rupture at a short-to-moderate distance (Rrup=14km). Finally, the Urayasu ground motion in Tokyo bay during the 11 March 2011 Tohoku earthquake exhibits an acceleration amplitude similar to the 4 September 2010 CBGS ground motion, but a significantly larger duration (approx 150s of intense shaking). Clearly, these three different ground motions will affect structures and soils in different ways depending on the vibration characteristics of the structures/soil, and the potential for strength and stiffness degradation due to cumulative effects. Figure 2 provides a comparison between the arias intensities of the several ground motion records from the three different events. It can be seen that the arias intensities of the ground motions in the Christchurch CBD from the 22 February 2011 earthquake (which is on average AI=2.5m/s) is approximately twice that from the 4 September 2010 earthquake (average AI≈1.25). This is consistent with a factor of approximately 1.6 obtained by Cubrinovski et al. (2011) using the stress-based (i.e.PGA-MSF) approach of liquefaction triggering. It can also be seen that the arias intensity of the ground motions recorded in Tokyo during the 2011 Tohoku earthquake are larger than ground motions in the Christchurch CBD from the 4 September 2011 earthquake, but smaller than those of the 22 February 2011 earthquake. Based on the arias intensity liquefaction triggering approach it can therefore be concluded that the ground motion severity, in terms of liquefaction potential, for the Tokyo ground motions is between those ground motions in Christchurch CBD from the 4 September 2010 and 22 February 2011 events.

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  • Shallow shear wave velocity characterization of the urban Christchurch, New Zealand region

    McGann, C.R.; Bradley, B.A.; Cubrinovski, M. (2014)

    Conference poster
    University of Canterbury Library

    This poster provides a summary of the development of a 3D shallow (z 15,000 logs as of 01/01/2014). In particular, the 3D model provides shear wave velocities for the surficial Springston Formation, Christchurch Formation, and Riccarton gravel layers which generally comprise the upper 40m in the Christchurch urban area. Point-estimates are provided on a 200m-by- 200m grid from which interpolation to other locations can be performed. This model has applications for future site characterization and numerical modeling efforts via maps of timeaveraged Vs over specific depths (e.g. Vs30, Vs10) and via the identification of typical Vs profiles for different regions and soil behaviour types within Christchurch. In addition, the Vs model can be used to constrain the near-surface velocities for the 3D seismic velocity model of the Canterbury basin (Lee et al. 2014) currently being developed for the purpose of broadband ground motion simulation.

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  • Low frequency (f=1Hz) ground motion simulations of 10 events in the 2010-2011 Canterbury earthquake sequence

    Bradley, B.A.; Graves, R.W. (2014)

    Conference poster
    University of Canterbury Library

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  • A 3D seismic velocity model for Canterbury, New Zealand for broadband ground motion simulation

    Lee, R.L.; Bradley, B.A.; Ghisetti, F.; Pettinga, J.R.; Hughes, M.W.; Thomson, E.M. (2014)

    Conference poster
    University of Canterbury Library

    This poster presents the on-going development of a new 3D seismic velocity model of Canterbury, New Zealand. The intention of the model is to provide the 3D crustal structure in the region at multiple length scales for seismic wave propagation simulations, both broadband ground motion and more localized shallow site response analyses.

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