What happened in the New Zealand earthquake? And is the supermoon to blame?

Earthquake damage to State Highway One, near Ohau Point on the South Island's east coast. Image: AFP/Getty.

At least two people have died in the magnitide 7.5 earthquake that struck New Zealand’s South Island early on Monday, local time. Preliminary modelling suggests that the earthquake was caused by a rupture of a northeast-striking fault that projects to the surface offshore. But this may be a complex event, involving several faults on the South Island.

The northern part of the South Island straddles the boundary between the Pacific and Australian tectonic plates. The jostling between these plates pushes up rocks that create mountains including the southern Alps and the beautiful Seaward Kaikoura Range, one of New Zealand’s most rapidly uplifting mountain ranges.

The plate motion forces the oceanic crust of the Pacific plate beneath the Australian plate on thrust faults, and also causes the plates to slide laterally with respect to one another on strike-slip faults. The region affected by the recent earthquake has been one of the most seismically active in New Zealand over the past few years, including earthquakes that occurred as part of the Cook Strait earthquake sequence in 2013. It is likely that these sequences are related given their close spatial and temporal association.

What slipped during the earthquake?

The preliminary analysis strongly suggests that most of the energy release during this earthquake was sourced from the rupture of a roughly 200km-long fault system. This fault system is aligned northeast and dips to the northwest, beneath the northern part of the South Island. It coincides roughly with the subduction thrust in this area.

The potential for large earthquakes on the subduction fault in the lower North Island and upper South Island of New Zealand was recently highlighted by GNS Science, New Zealand’s geological survey. It published evidence for two similar events in the Blenheim area roughly 520-470 years ago, and 880-800 years ago.

Given its setting, this latest earthquake may be structurally complex, involving a mixture of plate boundary thrusting, lateral slip on strike-slip faults, and thrusting within the Pacific plate close to the epicentre, some 15km northeast of Culverden. The largest aftershocks suggest a mixture of thrusting and strike-slip movements.

The damage caused by the earthquake

 

Earthquake damage to State Highway One and the parallel railway tracks near Ohau Point on the South Island's east coast. Image: AFP/Getty.

 

Because the fault system was large, and the earthquake apparently started at the southwest end of the fault and propagated to the northeast, the seismic energy was released over a period of up to two minutes.

Large earthquakes produce more long period wave energy than smaller events. The 2011 Christchurch earthquake contained a lot of high-frequency energy and very strong ground accelerations, exposing more than 300,000 people to very strong to intense ground shaking.

In contrast, this recent earthquake was manifested in Christchurch as lower-frequency rolling, and due to the sparse population density in the earthquake region, roughly 3,000 people in the upper South Island experienced strong ground shaking equivalent to the Christchurch earthquake.

Reports are emerging of at least one major fracture in the ground surface that could be related to strike-slip faulting in the Clarence region. More traces may yet be found given the complexity of the earthquake. Tide gauge analysis will help to understand if a similar trace offshore caused the tsunami.

The earthquake has also triggered liquefaction in coastal areas and in susceptible sediments, and landsliding of up to a million cubic metres along steep susceptible cliffs in the northern South Island.

There are reports of extensive road damage including in the area between Hanmer Springs and Culverden, much of State Highway 1 and even Wellington, on the North Island. Most of this damage is probably caused by strong ground shaking, which causes weak ground to move en masse and has resulted in numerous slips and road closures in the central and northern South Island.


Earthquakes, aftershocks and the pull of the moon

Given the earthquake happened on the eve of a supermoon full moon, wthe closest the Earth has come to a full moon will be since 1948, it wasn’t long before some tried to make a connection. But the tidal triggering of earthquakes has been investigated since the 19th century and remains a challenging and controversial field.

Small amplitude and large wavelength tidal deformations of the Earth due to motions of the sun and moon influence stresses in Earth’s lithosphere.

It is possible that, for active faults that are imminently close to brittle failure, small tidal force perturbations could be enough to advance rupture relative to the earthquake cycle, or to allow a propagating rupture to travel further than it might otherwise have done.

But the specific time, magnitude and location of this or any other large earthquake has not been successfully predicted in the short-term using tidal stresses or any other possible precursory phenomenon. Deliberately vague predictions that provide no specific information about the precise location and magnitude of a future earthquake are not predictions at all. Rather, these are hedged bets that get media air time due to the romantic misinterpretation that they were valid predictions.

 

Damage at the Waiau Lodge Hotel, in Waiau, 120 kms north of Christchurch. Image: AFP/Getty.

Most earthquake scientists, including those that research tidal triggering of earthquakes, highlight the importance of preparedness over attempts at prediction when it comes to public safety. To this end, GNS Science uses a system of operational earthquake forecasts to communicate earthquake risk to concerned New Zealand residents during an aftershock sequence such as we are now entering.

These forecasts are based on earthquake physics and statistical seismology. The current operational forecast indicates an 80 per cent probability of:

A normal aftershock sequence that is spread over the next few months. Felt aftershocks (e.g. M>5) would occur from the M7.5 epicentre near Culverden, right up along the Kaikoura coastline to Cape Campbell over the next few weeks and months.

This aftershock sequence will probably (98 per cent) include several large aftershocks: some greater than magnitude 6 have already occurred. And, for each magnitude 6 aftershock we expect 10 more magnitude 5 aftershocks over the coming days and weeks.The Conversation

Brendan Duffy is a lecturer in applied geoscience, and Mark Quigley an associate professor, at the University of Melbourne.

This article was originally published on The Conversation. Read the original article.

 
 
 
 

To transform Australia’s cities, it should scrap its car parks

A Sydney car park from above. Image: Getty.

Parking may seem like a “pedestrian” topic (pun intended). However, parking is of increasing importance in metropolitan areas worldwide. On average, motor vehicles are parked 95 per cent of the time. Yet most transport analysis focuses on vehicles when they are moving.

Substantial amounts of land and buildings are set aside to accommodate “immobile” vehicles. In Australia, Brisbane provides 25,633 parking spaces in the CBD, Sydney 28,939 and Melbourne 41,687. In high-demand areas, car parks can cost far more than the vehicle itself.

However, parking is not just an Australian problem. By some estimates, 30,000 square kilometres of land is devoted to parking in Europe and 27,000 km² in the US. This parking takes up a large part of city space, much of it highly valued, centrally located land.

Traditionally, transport planners believed that generous parking allocations provided substantial benefits to users. In reality, excessive parking is known to adversely affect both transport and land use. These impacts, along with recent land-use, socioeconomic and technological trends, are prompting cities to start asking some important questions about parking.

Australian planners must engage with emerging trends to help cities work out the best way to reclaim and repurpose parking space in ways that enhance efficiency and liveability while minimising disruption.

Here we chart likely challenges and opportunities created by these trends over coming decades.

Key trends affecting parking space in cities. Image: author provided.

Land use

All Australian cities have policies to encourage densification, consolidation and infill development in their centres. In conjunction, some cities are setting maximum limits on parking to prevent it taking over valuable inner-city properties.

Transit-oriented development (TOD) has also become popular, at least on paper. This is another form of urban consolidation around transit nodes and corridors. It is known to benefit from high-quality urban design, “walkability”, “cyclability” and a mix of functions.

These developments mean that people who live in CBDs, inner-ring suburbs and near public transport stops will use cars less. Consequently, demand for parking will decrease.

Some non-TOD suburbs are trying to replicate inner-city features as well. For example, some suburban shopping centres have introduced paid parking. This is a significant shift from previous eras, when malls guaranteed ample free parking.

Suburbanites who lack easy public transport access will continue to rely on cars. But rather than driving all the way to a CBD, commuters will increasingly opt for park-and-ride at suburban stations, thereby increasing demand for park-and-ride lots at public transport interchanges. However, excessive capacity might hurt rather than help patronage.


Social trends

In addition to land use, several social trends will affect the need for parking.

First, young people are delaying getting drivers’ licences because driving is culturally less important to them than in previous generations.

Second, people of all ages are moving from outer suburbs to inner cities. For many, this means less driving because walking, cycling and public transport are more convenient in inner cities.

 

inally, the emergence of Uber, Lyft and vehicle-sharing arrangements means that people are not buying cars. Research suggests that each car-sharing vehicle removes nine to 13 individually owned vehicles from the road.

Together, these trends point to a reduced need for parking because there will be fewer cars overall.

Technology

The importance of technology in parking is rising – paving the way for “smarter” parking.

The emergence of a host of smartphone apps, such as ParkMe, Kerb, ParkHound and ParkWhiz, has begun to reshape the parking landscape. For the first time, users can identify and reserve parking according to price and location before starting their journeys.

Apps also make available a host of car parks that previously went unused – such as spaces in a residential driveway. This is because there was no mechanism for letting people know these were available.

In addition, smart pricing programs, such as SFPark in San Francisco, periodically adjust meter and garage pricing to match demand. This encourages drivers to park in underused areas and garages and reduces demand in overused areas.

The advent of autonomous vehicles promises to have dramatic impacts on transport and land use, including parking.

According to one school of thought, mobility services will own most autonomous vehicles, rather than individuals, due to insurance and liability issues. If this happens, far fewer vehicles and parking spaces will be needed as most will be “in motion” rather than parked most of the time.

More space for people and places

The Tikku (Finnish for ‘stick’), by architect Marco Casagrande, is a house with a footprint of just 2.5x5m, the size of a car parking space. Image: Casagrande Laboratory.

The next decade promises much change as emerging land-use, socioeconomic and technological trends reshape the need for, and use of, parking. Cities will devote less space to parking and more space to people and places.

Parking lanes will likely be repurposed as cycling lanes, shared streets, parklets, community gardens and even housing. Concrete parking lots, and faceless garages will likely be converted to much-needed residential, commercial and light industrial use.

The ConversationBy transforming parking, much urban land can turn from wasteland into vibrant activity space.

Dorina Pojani, Lecturer in Urban Planning, The University of Queensland; Iderlina Mateo-Babiano, Senior Lecturer in Urban Planning, University of Melbourne; Jonathan Corcoran, Professor, School of Earth and Environmental Sciences, The University of Queensland, and Neil Sipe, Professor of Urban and Regional Planning, The University of Queensland

This article was originally published on The Conversation. Read the original article.