Brendon A. Bradley

National Seismic Hazard Model for New Zealand: 2010 Update

A team of earthquake geologists, seismologists, and engineering seis- mologists has collectively produced an update of the national probabilistic seismic hazard (PSH) model for New Zealand (National Seismic Hazard Model, or NSHM). The new NSHM supersedes the earlier NSHM published in 2002 and used as the hazard basis for the New Zealand Loadings Standard and numerous other end-user applica- tions. The new NSHM incorporates a fault source model that has been updated with over 200 new onshore and offshore fault sources and utilizes new New Zealand-based and international scaling relationships for the parameterization of the faults. The dis- tributed seismicity model has also been updated to include post-1997 seismicity data, a new seismicity regionalization, and improved methodology for calculation of the seismicity parameters. Probabilistic seismic hazard maps produced from the new NSHM show a similar pattern of hazard to the earlier model at the national scale, but there are some significant reductions and increases in hazard at the regional scale. The national-scale differences between the new and earlier NSHM appear less than those seen between much earlier national models, indicating that some degree of consis- tency has been achieved in the national-scale pattern of hazard estimates, at least for return periods of 475 years and greater. Online Material: Table of fault source parameters for the 2010 national seismic- hazard model.

Recurrent liquefaction in Christchurch, New Zealand, during the Canterbury earthquake sequence

Continuous observational monitoring of a study site in eastern Christchurch, New Zealand, following the 2010 M w 7.1 Darfi eld earthquake has recorded ten distinct liquefaction episodes in the mainshock‐aftershock sequence. Three nearby accelerometers allow calibration between the geological expressions of liquefaction and the intensity of earthquake-induced surface ground motion at the site. Sand blow formation was generated by M w 5.2‐7.1 earthquakes with M w 7.5‐normalized peak ground accelerations (PGA 7.5 ) of ≥ 0.057 g (acceleration due to gravity). Silt drapes between successive sand blow deposits provide markers for delineating distinct liquefaction-inducing earthquakes in the geologic record. However, erosion quickly modifi es the surface of sand blows into alluvial and aeolian forms that complicate geologic diagnosis. The two feeder-dike generations identifi ed in subsurface investigations signifi cantly underrepresent the number of liquefaction-inducing earthquakes due to extensive dike reactivation. New constitutive equations enable PGA 7.5 variations to be estimated from the thickness and areal extent of sand blows.

Ground Motion and Seismic Source Aspects of the Canterbury Earthquake Sequence

This paper provides an overview of the ground motion and seismic source aspects of the Canterbury earthquake sequence. Common reported attributes among the largest earthquakes in this sequence are complex ruptures, large displacements per unit fault length, and high stress drops. The Darfield earthquake produced an approximately 30 km surface rupture in the Canterbury Plains with dextral surface displacements of several meters, and a subordinate amount of vertical displacement, impacting residential structures, agricultural land, and river channels. The dense set of strong ground motions recorded in the near-source region of all the major events in the sequence provides significant insight into the spatial variability in ground motion characteristics, as well as the significance of directivity, basin-generated surface waves, and nonlinear local site effects. The ground motion amplitudes in the 22 February 2011 earthquake, in particular, produced horizontal ground motion amplitudes in the Central Business District (CBD) well above those specified for the design of conventional structures.

Correlation of Significant Duration with Amplitude and Cumulative Intensity Measures and Its Use in Ground Motion Selection

This manuscript examines, and develops parametric equations for, the correlation of significant duration with several amplitude- and cumulative-based ground motion intensity measures. The correlations are determined using ground motions from active shallow crustal earthquakes in the Next Generation Attenuation database, and recently developed ground motion prediction equations. It is found that significant durations tend to be negatively correlated with high-frequency amplitude-based intensity measures, weakly negatively correlated with moderate-frequency amplitude-based intensity measures, and weakly positively correlated with low-frequency amplitude-based intensity measures and cumulative absolute velocity. Particular attenuation is given to the physical interpretation of the observed correlations, which can largely be explained as a result of: (a) the 5–75% significant duration ( ) representing approximately the duration of body wave arrivals; and (b) the limited amount of energy contained in a ground motion time history. Finally, the practical application of the developed correlation equations in determining conditional distributions of ground motion duration for use in ground motion selection is demonstrated.

Empirical Correlations between Peak Ground Velocity and Spectrum-Based Intensity Measures

Empirical correlation equations between peak ground velocity (PGV) and several spectrum-based ground motion intensity measures are developed. The intensity measures examined in particular were: peak ground acceleration (PGA), 5% damped pseudo-spectral acceleration (SA), acceleration spectrum intensity (ASI), and spectrum intensity (SI). The computed correlations were obtained using ground motions from active shallow crustal earthquakes and four ground motion prediction equations. Results indicate that PGV is strongly correlated (i.e., a correlation coefficient of ρ = 0.89 ) with SI, moderately correlated with medium to long-period SA (i.e., ρ ≈ 0.8 for vibration periods 0.5-3.0 seconds), and also moderately correlated with short period SA, PGA and ASI ( ρ ≈ 0. 7 − 0. 73 ). A simple example is used to illustrate one possible application of the developed correlation equations for ground motion selection.

Evaluation of the Liquefaction Potential Index for Assessing Liquefaction Hazard in Christchurch, New Zealand

AbstractWhile the liquefaction potential index (LPI) has been used to characterize liquefaction hazards worldwide, calibration of LPI to observed liquefaction severity is limited, and the efficacy of the LPI framework and accuracy of derivative liquefaction hazard maps are thus uncertain. Herein, utilizing cone penetration test soundings from nearly 1,200 sites, in conjunction with field observations following the Darfield and Christchurch, New Zealand, earthquakes, this study evaluates the performance of LPI in predicting the occurrence and severity of surficial liquefaction manifestations. It was found that LPI is generally effective in predicting moderate-to-severe liquefaction manifestations, but its utility diminishes for predicting less severe manifestations. Additionally, it was found that LPI should be used with caution in locations susceptible to lateral spreading, because LPI may inconsistently predict its occurrence. A relationship between overpredictions of liquefaction severity and profiles h...

Select Liquefaction Case Histories from the 2010–2011 Canterbury Earthquake Sequence

The 2010–2011 Canterbury earthquake sequence began with the 4 September 2010, Mw7.1 Darfield earthquake and includes up to ten events that induced liquefaction. Most notably, widespread liquefaction was induced by the Darfield and Mw6.2 Christchurch earthquakes. The combination of well-documented liquefaction response during multiple events, densely recorded ground motions for the events, and detailed subsurface characterization provides an unprecedented opportunity to add well-documented case histories to the liquefaction database. This paper presents and applies 50 high-quality cone penetration test (CPT) liquefaction case histories to evaluate three commonly used, deterministic, CPT-based simplified liquefaction evaluation procedures. While all the procedures predicted the majority of the cases correctly, the procedure proposed by Idriss and Boulanger (2008) results in the lowest error index for the case histories analyzed, thus indicating better predictions of the observed liquefaction response.

Empirical correlations between cumulative absolute velocity and amplitude-based ground motion intensity measures

Empirical correlation equations are developed between cumulative absolute velocity (CAV) and other common ground motion intensity measures, namely, peak ground acceleration (PGA), peak ground velocity (PGV), 5% damped pseudo spectral acceleration (SA), acceleration spectrum intensity (ASI), spectrum intensity (SI), and displacement spectrum intensity (DSI). It is found that, for a given earthquake rupture, CAV has the strongest correlation with high and moderate frequency intensity measures (IMs), that is, ASI, PGA, PGV and high-frequency SA, and to a lesser extent with low frequency IMs (DSI and low-frequency SA). The largest positive correlations of approximately 0.7 however are not high in an absolute sense, a result of the cumulative nature of CAV. The equations allow estimation of the joint distribution of these intensity measures for a given earthquake rupture, enabling the inclusion of CAV, and its benefit as a cumulative intensity measure, in seismic hazard analysis, ground motion selection, and seismic response analysis.

Epistemic Uncertainties in Component Fragility Functions

This paper is concerned with the inclusion of epistemic uncertainties in component fragility functions used in performance-based earthquake engineering. Conventionally fragility functions, defining the probability of incurring at least a specified level of damage for a given level of seismic demand, are defined by a mean and standard deviation and assumed to have a lognormal distribution. However, there exist many uncertainties in the development of such fragility functions. The sources of epistemic uncertainty in fragility functions, their consideration, combination, and propagation are presented and discussed. Two empirical fragility functions presented in literature are used to illustrate the epistemic uncertainty in the fragility function parameters due to the finite size of the datasets. These examples and the associated discussions illustrate that the magnitude of epistemic uncertainties are significant and there are clear benefits of the consideration of epistemic uncertainties pertaining to the documentation, quality assurance, implementation, and updating of fragility functions. Epistemic uncertainties should therefore always be addressed in future fragility functions developed for use in seismic performance assessment.

High-Force-to-Volume Seismic Dissipators Embedded in a Jointed Precast Concrete Frame

An experimental and computational study of an 80-percent scale precast concrete 3D beam-column joint subassembly designed with high force-to-volume (HF2V) dampers and damage-protected rocking connections is presented. A prestress system is implemented using high-alloy high-strength unbonded thread-bars through the beams and columns. The thread-bars are posttensioned and supplemental energy dissipation is provided by internally mounted lead-extrusion dampers. A multilevel seismic performance assessment (MSPA) is conducted considering three performance objectives related to occupant protection and collapse prevention. First, bidirectional quasi-static cyclic tests characterise the specimen’s performance. Results are used in a 3D nonlinear incremental dynamic analysis (IDA), to select critical earthquakes for further bidirectional experimental tests. Thus, quasi-earthquake displacement tests are performed by using the computationally predicted seismic demands corresponding to these ground motions. Resulting ...