Misko Cubrinovski

The Mw 6.2 Christchurch earthquake of February 2011: preliminary report

Abstract A moment magnitude (Mw) 6.2 earthquake struck beneath the outer suburbs of Christchurch, New Zealands second largest city, on 22 February 2011 local time. The Christchurch earthquake was the deadliest in New Zealand since the 1931 Mw 7.8 Hawkes Bay earthquake and the most expensive in New Zealands recorded history. The effects of the earthquake on the regions population and infrastructure were severe including 181 fatalities, widespread building damage, liquefaction and landslides. The Christchurch earthquake was an aftershock of the Mw 7.1 Darfield Earthquake of September 2010, occurring towards the eastern edge of the aftershock zone. This was a low recurrence earthquake for New Zealand and occurred on a fault unrecognised prior to the Darfield event. Geodetic and seismological source models show that oblique-reverse slip occurred along a northeast–southwest-striking fault dipping southeast at c. 69°, with maximum slip at 3–4 km depth. Ground motions during the earthquake were unusually large at near-source distances for an earthquake of its size, registering up to 2.2 g (vertical) and 1.7 g (horizontal) near the epicentre and up to 0.8 g (vertical) and 0.7 g (horizontal) in the city centre. Acceleration response spectra exceeded 2500 yr building design codes and estimates based on standard New Zealand models. The earthquake was associated with high apparent stress indicative of a strong fault. Furthermore, rupture in an updip direction towards Christchurch likely led to strong directivity effects in the city. Site effects including long period amplification and near-surface effects also contributed to the severity of ground motions.

Earthquake Response of Underground Pipeline Networks in Christchurch, NZ

This paper explores key aspects of underground pipeline network response to the Canterbury earthquake sequence in Christchurch, New Zealand, including the response of the water and wastewater distribution systems to the MW6.2 22 February 2011 and MW6.0 13 June 2011 earthquakes, and the response of the gas distribution system to the MW7.1 4 September 2010 earthquake, as well as the 22 February and 13 June events. Repair rates, expressed as repairs/km, for different types of pipelines are evaluated relative to (1) the spatial distribution of peak ground velocity outside liquefaction areas and (2) the differential ground surface settlement and lateral ground strain within areas affected by liquefaction, calculated from high-resolution LiDAR survey data acquired before and after each main seismic event. The excellent performance of the gas distribution network is the result of highly ductile polyethylene pipelines. Lessons learned regarding the earthquake performance of underground lifeline systems are summarized.

Assessment of Liquefaction-Induced Land Damage for Residential Christchurch

Christchurch, New Zealand, experienced four major earthquakes (Mw 5.9 to 7.1) since 4 September 2010 that triggered localized to widespread liquefaction. Liquefaction caused significant damage to residential foundations due to ground subsidence, ground failure, and lateral spreading. This paper describes the land damage assessment process for Christchurch, including the collection and processing of extensive data and observations related to liquefaction, the characterization of liquefaction effects on land performance, and the quantification of losses for insurance compensation purposes. The paper also examines the effectiveness of several existing liquefaction vulnerability parameters and a new parameter developed through this research, Liquefaction Severity Number (LSN), in explaining the observed liquefaction-induced damage in residential areas of Christchurch using results from 11,500 cone penetration tests (CPTs) as well as a robust regional groundwater model.

Lateral spreading and its impacts in urban areas in the 2010–2011 Christchurch earthquakes

Abstract In the 4 September 2010 (M W=7.1) and 22 February 2011 (M W=6.2) earthquakes, widespread liquefaction and lateral spreading occurred throughout Christchurch and the town of Kaiapoi. The severe soil liquefaction and lateral spreading in particular caused extensive and heavy damage to residential buildings, Christchurch business district (CBD) buildings, bridges and water supply and wastewater systems of Christchurch. After the earthquake, comprehensive field investigations and inspections were conducted to document the liquefaction-induced land damage and lateral spreading displacements and their impact on buildings and infrastructure. The results of ground surveying measurements of lateral spreads at approximately 120 locations along the Avon River, Kaiapoi River and streams in the affected area reveal permanent lateral ground displacements at the banks of up to 2–3 m that progressed inland as far as 200–250 m from the waterway, causing significant damage to structures located within the spreading zone. Different features and magnitudes of spreading were identified, which were often affected by a complex interplay of ground conditions, topography, meandering river geometry and local depositional environment. The spreading was characterised by very large and highly non-uniform ground deformation causing stretching of building foundations and the buildings themselves. Road bridges suffered a characteristic spreading-induced damage mechanism including back-rotation of the abutments associated with deck pinning and damage at the top of the abutment piles. The wastewater system of Christchurch was hit particularly hard by the liquefaction and lateral spreading, and approximately 60% of the damaged pipes of the potable water system were located in areas of severe liquefaction and lateral spreading.

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...

Liquefaction Effects on Buildings in the Central Business District of Christchurch

The Canterbury earthquake sequence provides an exceptional opportunity to investigate the effects of varying degrees of liquefaction on the built environment. Many multistory buildings in the Central Business District were heavily damaged by liquefaction-induced ground movements during the Christchurch earthquake, but not by other earthquakes (e.g., the Darfield and June 2011 events). Cone penetration test (CPT)–based liquefaction triggering evaluations were conservative. The conservatism in the liquefaction triggering assessments led to post-liquefaction ground settlement estimates that were generally similar for the large events in the earthquake sequence, whereas significant ground settlements and building damage in the CBD were only observed for the Christchurch earthquake. Moreover, the liquefaction-induced ground settlement procedures do not capture important shear-induced deformation mechanisms and the effects of ground loss due to sediment ejecta. Performance-based earthquake engineering requires improved procedures to capture the differing levels of performance observed in Christchurch.

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.

Initial shear modulus of sandy soils and equivalent granular void ratio

The small strain/initial shear modulus, GO , for clean sands has been extensively studied over the last few decades, and it is generally accepted that GO is a function of the effective mean stress, p′ and void ratio, e. However, natural sandy soils often contain some fines (particle size ≤ 75 μm) and systematic studies on the effect of fines on GO are relatively limited. Two different approaches for capturing the effects of fines on GO have been reported. However, both approaches assumed that the GO values for a range of fines content specific to the sand and fines type are known in advance, and thus they cannot be used as predictive tools. This paper presents an alternative approach for evaluation of GO based on the equivalent granular void ratio, e*. Unlike earlier attempts, the proposed method does not rely on back-analysis and e* can be calculated from e and other conventional grading properties of sandy soils. The proposed approach approximately leads to a single relationship between GO and (e*, p′) irrespective of fines content. Thus, it provides a framework for estimating GO at different fines content from data on clean sand.

Performance of Bridges in Liquefied Deposits during the 2010–2011 Christchurch, New Zealand, Earthquakes

AbstractThe performance of road bridges undergoing liquefaction in the foundation soils and substantial lateral spreading during the 2010–2011 Christchurch earthquakes is discussed in this paper. Three, well-documented case studies are presented in detail to illustrate the performance of bridges and their typical damage associated with lateral spreading. The short-span bridges on pile foundations have a very stiff superstructure (deck), which was a key factor in the seismic response of the bridges. It led to a characteristic deformation mechanism for all bridges involving lateral spreading-deck pinning-abutment backrotation with consequent damage to the abutment piles and slumping of the approaches. Overall, road bridges performed relatively well in the 2010–2011 earthquakes compared to other engineering structures, despite the high seismic demands including substantial liquefaction and large kinematic and inertial loads due to spreading and strong ground shaking, respectively.

Strength and Deformational Characteristics of Foamed Bitumen Mixes under Suboptimal Conditions

The effects of foamed bitumen contents on the strength and deformational behavior of foamed bitumen mixes used for road pavements is very complex and not fully understood yet. While some writers report an increase in strength using one type of laboratory test, other writers report either only a small increase or even a decrease in strength using other types of tests, thus detracting foamed bitumen from being implemented as a cold-recycling technique for road pavement rehabilitation. This paper presents a laboratory study carried out on a specific granular material from New Zealand containing 1% cement and different foamed bitumen contents using indirect tensile strength (ITS), monotonic load triaxial (MLT), and repeat load triaxial (RLT) tests. The curing procedure, loading regime, and moisture contents were selected to simulate construction practice and suboptimal conditions normally found in New Zealand pavements. The results from these tests showed that an increase in foamed bitumen content up to an “o...