Matthew W. Hughes

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.

Increased sediment transport via bioturbation at the last glacial-interglacial transition

Global sedimentation rates increased during the Quaternary due to frequent landscape adjustment to climatic oscillations. Although high rates of sediment transport are commonly associated with glacial conditions in mountainous terrain, the infl uence of climate and vegetation on geomorphic response is poorly constrained outside of glaciated settings. Along a low-gradient (<30%) hillslope-valley transect on a moderately dissected, loess-mantled fl uvial terrace in the Charwell Basin, New Zealand, we coupled records of colluvial infi lling and vegetation change (via phytoliths) to show that late Pleistocene sediment fl ux was ~0.0012 m 3 m ‐1 a ‐1 under a shrubland/grassland mosaic and Holocene sediment fl ux was ~0.0022 m 3 m ‐1 a ‐1 under forest. This near doubling through the last glacial-interglacial transition appears to refl ect increased bioturbation and downslope soil transport associated with a forest ecosystem. Such an increase in sediment transport contrasts with a contemporaneous decrease inferred for adjacent steep, landslide-prone catchments, suggesting that geomorphic response to climate change is heavily modulated by biology, topography, and geological substrate. Our fi ndings appear to contradict the commonly cited notion that forest colonization universally stabilizes soils and suppresses erosion. Instead, over long time scales, bioturbation associated with forests may increase transport along gentle portions of the landscape not subject to slope instability or erosion by overland fl ow.

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.

Geometry and growth kinematics of salt pillows in the southern North Sea

Abstract Low-amplitude salt pillow structures can potentially reveal important details of the physical behaviour of salt and overburden from their growth histories. This is because the initial characteristic wavelengths are likely to be preserved, beds are more easily traceable across the tops of the structures, and original salt thicknesses can be accurately estimated. For these reasons, a detailed analysis of depth-converted seismic data was undertaken to gain insight into the formation, growth and spatial distribution of salt pillows in the southern North Sea basin (around Quadrant 44). This area contains a Permian Zechstein salt interval which has undergone widespread halokinesis to the pillow stage since Triassic times, but with the main movement during the Tertiary, perhaps due to inversion. The wavelength of the pillows decreases northwards from over 24 to 1 km, and estimated original salt thickness also decreases northwards from 1300 to 800 m, and there is a strong positive relationship between salt thickness and pillow wavelength. Pillows appear to be spaced at a characteristic wavelength, as they are not directly related to faults and the wavelength varies smoothly through the area. However, there is a strong alignment of some pillows parallel with the underlying NW-SE fault trend, suggesting that their axis of elongation was controlled by faulting. Average vertical growth rates of the pillows vary from 40 m/Ma in the north to less than 10 m/Ma in the central part of the area, measured over vertical distances up to 1250 m. Most of the growth occurred in the Tertiary, although a few pillows initiated in the Triassic in the north of the area. The northern pillows appear to have slowed or even stopped growing during the Jurassic and Cretaceous, and then restarted in the Tertiary. Assuming Rayleigh-Taylor instability controlled the initial pillow wavelengths and using the calculated original salt/overburden thicknesses ratios, the viscosity ratio between the overburden and the salt can be estimated across the area, and was found to vary from 6000 to less than 100. The pillows which moved earliest had the lowest inferred viscosity ratios, which is probably because the sediments were less lithified at the time of movement.

The sinking city: Earthquakes increase flood hazard in Christchurch, New Zealand

Airborne light detection and ranging (LiDAR) data were acquired over the coastal city of Christchurch, New Zealand, prior to and throughout the 2010 to 2011 Canterbury Earthquake Sequence. Differencing of preand post-earthquake LiDAR data reveals land surface and waterway deformation due to seismic shaking and tectonic displacements above blind faults. Shaking caused floodplain subsidence in excess of 0.5 to 1 m along tidal stretches of the two main urban rivers, greatly enhancing the spatial extent and severity of inundation hazards posed by 100-year floods, storm surges, and sea-level rise. Additional shaking effects included river channel narrowing and shallowing, due primarily to liquefaction, and lateral spreading and sedimentation, which further increased flood hazard. Differential tectonic movement and associated narrowing of downstream river channels decreased channel gradients and volumetric capacities and increased upstream flood hazards. Flood mitigation along the large regional Waimakariri River north of Christchurch may have, paradoxically, increased the long-term flood hazard in the city by halting long-term aggradation of the alluvial plain upon which Christchurch is situated. Our findings highlight the potential for moderate magnitude (MW 6–7) earthquakes to cause major topographic changes that influence flood hazard in coastal settings.

Tsunami runup and tide-gauge observations from the 14 November 2016 M7.8 Kaikōura earthquake, New Zealand

The 2016 Mw 7.8 Kaikōura earthquake was one of the largest earthquakes in New Zealand’s historical record, and it generated the most significant local source tsunami to affect New Zealand since 1947. There are many unusual features of this earthquake from a tsunami perspective: the epicentre was well inland of the coast, multiple faults were involved in the rupture, and the greatest tsunami damage to residential property was far from the source. In this paper, we summarise the tectonic setting and the historical and geological evidence for past tsunamis on this coast, then present tsunami tide gauge and runup field observations of the tsunami that followed the Kaikōura earthquake. For the size of the tsunami, as inferred from the measured heights, the impact of this event was relatively modest, and we discuss the reasons for this which include: the state of the tide at the time of the earthquake, the degree of co-seismic uplift, and the nature of the coastal environment in the tsunami source region.

Spreading-Induced Damage to Short-Span Bridges in Christchurch, New Zealand

This paper discusses the performance of road bridges during the 2010–2011 Canterbury earthquakes and focuses on the response of bridges in liquefying soils undergoing lateral spreading. A characteristic spreading-induced mechanism for short-span bridges with rigid superstructures is presented and explored using four well-documented case studies. A series of pseudo-static analyses are then used to investigate the observed response of the bridges and their pile foundations in particular. Deformations and damage to the piles are evaluated and correlated with the spreading displacements, and key factors controlling the pile response and the development of the spreading-induced damage mechanism are identified.

Mapping surface liquefaction caused by the September 2010 and February 2011 Canterbury earthquakes: a digital dataset

ABSTRACT We present maps and digital data of the surface manifestation of liquefaction for the two major events during the 2010–2011 Canterbury earthquake sequence, the 2010 Darfield and the 2011 Christchurch earthquakes, in order to show liquefaction extent. Maps include detailed interpretation of aerial photograph mosaics and satellite images captured immediately following each event, and incorporate ground-based surveys of liquefaction occurrences. Evidence of liquefaction includes predominantly silt to fine sand and/or water ejected to the ground surface, and the presence of lateral spreading cracks (with or without ejected sediment). Liquefaction appears to be related to recent alluvial systems, and is more prevalent adjacent to existing waterways and in abandoned stream channels, where young, normally consolidated and poorly compacted sediments are water-saturated. The digital data are available for download in standard geographic information system (GIS) formats, and should provide a reference for future regional scale liquefaction studies.