Aftershocks hit Papua New Guinea as it recovers from a remote major earthquake

Sabin Zahirovic, University of Sydney; Gilles Brocard, University of Sydney; John Connell, University of Sydney, and Romain Beucher, University of Melbourne

Another powerful aftershock hit Papua New Guinea this weekend as the recovery effort continues following February’s deadly magnitude 7.5 earthquake, with many thousands of people dependent on humanitarian aid.

Aid organisations such as CARE Australia and UNICEF are still seeking donations. The Australian government has sent medical staff and other support to help.

Some have criticised the PNG government’s efforts as “too slow”.

Read more:
The science of landslides, and why they’re so devastating in PNG

But the earthquake highlights the challenge for emerging economies like PNG in deploying relief efforts into remote areas to deal with natural disasters.

And the same geological features that make PNG a rich source of mineral deposits are also part of its earthquake problem.

The earthquake hits

The February earthquake struck the western Highlands provinces of the Pacific island nation, and a series of aftershocks, including several of magnitude 6 or more, continued to shake the region during the following weeks.

Although parts of PNG are particularly earthquake-prone (especially in the north and the islands, along the plate boundary), February’s earthquake was quite exceptional.

It occurred in a usually less active part of the plate boundary and was remarkably powerful when compared with the short (modern) instrumental earthquake record. The strength and frequency of the aftershocks has posed an additional threat to local populations and key economic infrastructure.

On average 10-20 major earthquakes (magnitudes 7 and greater) occur on Earth every year. Most of them occur far from densely populated regions, such that only a few draw media attention.

The mountainous regions of New Guinea, known as the fold and thrust belt, have been geologically active for millions of years. But the long recurrence interval of major earthquakes (every few centuries) combined with the short period of the instrument records (just a few decades) gives us the false impression that seismicity is uncommon in this region.

The February earthquake occurred due to the activation of a major fault system in the forested foothills, between the Papuan highlands to the north and the Fly River lowlands to the south.

Australia collides

The Papuan highlands have risen due to the collision between the Australian and Caroline/Pacific tectonic plates over the past five million years.

An animation of Australia’s tectonic journey as it broke away from Gondwana more than 100 million years ago. (Credit: Sabin Zahirovic)

Despite this collision, the Australian plate continues to move at about 7 cm a year to the northeast, in geological terms a quite remarkable speed, leading to a build-up of strain in the continental crust.

Much of this strain is released at the plate boundary along northern New Guinea, usually with more frequent but less powerful swarms of earthquakes. It is this motion, driven by the churning interior of our planet, that leads to major adjustments to the GPS datum and reference coordinates for the entire Australian continent.

But few people are aware that this very motion of the Australian continent is what causes the seismic and volcanic activity in New Guinea and parts of Southeast Asia.

As Australia moves northward, the entire New Guinea margin acts as a bulldozer, collecting Pacific islands, seamounts and other topographic features. New Guinea represents the leading edge of the advancing Australian continent, which causes continental crust to fold and crumple over a broad region.

This is a well-known process in plate tectonics, where the oceanic plates are known to behave quite rigidly, whereas the continental regions tend to deform over broader diffuse boundaries that resemble plasticine over geological timeframes.

When continents are squeezed during tectonic collisions, the crust crumples and folds over geological timescales. (Credit: Romain Beucher)

But the continental deformation process results in poorly defined (often due to the thick tropical vegetation cover) and intermittently active fault systems in the continent.

Over the duration of mountain building in the past five million years, the areas of highest deformation have shifted across the range. Today most of the deformation in PNG takes place north of the mountainous area, where it generates a lot of earthquakes.

Underground riches at risk

Some substantial crumpling of the continental crust still occurs across the southern foothills. The folding and thrusting has generated geologically young folds, within which a large part of PNG’s gas and oil wealth has accumulated.

The intense tectonic activity has also led to the enrichment of mineral resources, including mines sourcing gold, copper, silver, nickel, cobalt and a suite of other ore types.

Distribution of the aftershocks magnitude 4+ since the main quake (as of April 9, 2018). The size and colour (small to large, yellow to red) indicate aftershock magnitude and D+ the number of days after main shock. The white shaded ellipse represents the area of greatest slip during the main shock. Green diamonds represent the main gas fields.
USGS/Gilles Brocard, Author provided

It is this tectonic activity that determines the delicate interplay of economic benefits from raw materials, and the often-devastating and usually-unpredictable effects of natural disasters on society.

Although the February earthquake occurred at the very heart of one of the largest and newest gas fields in the country, the industrial installations, at the highest international standards, have not suffered major damage from the tremors.

But the ongoing disaster triggered a temporary halt in gas extraction, as the facilities require inspections and repairs. Unfortunately, and unusually, the earthquakes have struck in some of the most remote parts of the country.

Coping with disaster

Hela province is one of the poorest in PNG and its people are unprepared and ill-equipped to deal with a disaster of this scale. As many as half a million people were reported to be affected by the earthquake. At least 145 people reported killed.

Read more:
Five active volcanoes on my Asia Pacific ‘Ring of Fire’ watch-list right now

The Highlands Highway, the one real road into the region, was badly damaged and this is the major source of food and medicines. Many feeder roads have gone.

Papua New Guineans are resilient but it is likely that more external assistance will be needed to ensure that a physical disaster does not become a greater human tragedy.

Even so the full extent of the disaster has still to be revealed, while aftershocks continue to trigger secondary hazards including major landslides that have isolated a large number of communities.

The ConversationNot only are local communities facing the immediate hazards of further earthquakes and landslides, they face a protracted and costly recovery ahead.

Sabin Zahirovic, Postdoctoral Research Associate, University of Sydney; Gilles Brocard, Post doctoral associate, University of Sydney; John Connell, Professor of Human Geography, University of Sydney, and Romain Beucher, Postdoctoral Research Associate in Computational Geodynamics, University of Melbourne

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


Nepal earthquake reconstruction won’t succeed until the vulnerability of survivors is addressed

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More than 600,000 buildings were fully damaged in the 2015 earthquake in Nepal.
Jason von Meding, Author provided

Jason von Meding, University of Newcastle; Hari Darshan Shrestha; Humayun Kabir, University of Dhaka, and Iftekhar Ahmed, University of Newcastle

In April 2015 the Gorkha earthquake brought Nepal’s vulnerability sharply into focus. Alongside massive damage to the built environment, the terrible impact on the people of Nepal sent shockwaves around the world.

Despite good intentions to rebuild Nepal to be more resilient, 30 months on little progress has been made. Of more than 400,000 homes that were earmarked for reconstruction, only 12% have been rebuilt. Little of the US$4.4 billion in aid pledged for reconstruction has been disbursed.

The Nepali government instituted a reconstruction program in October 2015 that identifies beneficiaries and entitles them to three instalments of compensation. The payments are dependent on progress and building code compliance. Those who do not own land are locked out of reconstruction support.

Read more: The science behind the Nepal earthquake

Nepal has robust building codes, developed over recent years. Serious efforts to implement the codes predate the Gorkha earthquake.

Unfortunately, despite such efforts, there are still more than five million existing buildings standing after the earthquake that are not to code. Many of these are “informal” and built by traditional masons. There is also a large stock of old, dilapidated buildings. These buildings will be a particular risk in Nepal when future earthquakes strike.

Widespread retrofitting would protect lives and property in the future. Strictly speaking, all new buildings must meet the code – something difficult to monitor and enforce. Forcing people into compliance also has drawbacks: it can lead people to bypass it by unlawful means, and can be particularly onerous for the poor.

Nepal needs a strategy for “safe building” that is acutely aware of the resource inequalities and other social impediments that block progress on code compliance.

Many people live in informal homes in Nepal.
Ifte Ahmed

Housing typology and quality in Nepal

Of the more than 600,000 buildings that were fully damaged by the earthquake, most predated building codes and were built from stone and mud. The death toll of around 9,000 was lower than may have been expected, considering the number of buildings destroyed. By contrast, the 2010 Haiti earthquake is estimated to have claimed more than 300,000 lives while fewer than 300,000 buildings were fully damaged.

Read more: Two years after the earthquake, why has Nepal failed to recover?

Traditional building knowledge is clearly a valuable asset in determining how to save lives in an earthquake – but technical advances have been made that must now be integrated during reconstruction. The five million buildings that survived the earthquake require urgent retrofitting.

In Nepal, 80% of human settlement is often referred to as “informal”. These are households that are not in compliance with building norms and planning regulations. This can be a measure of marginalisation and can bring spatial segregation and discriminatory treatment.

In addition, Nepal is rapidly urbanising. The temptation in urban areas is to build higher, but in a country like Nepal this could have fatal consequences in an earthquake. Local engineers fear mass casualties if heavy, reinforced concrete structures (as are being widely built) collapse in the future.

Why has reconstruction stalled?

Rebuilding has been slowed by a range of technical, social and political challenges.
Jason von Meding

The government housing grant is available in three instalments on the basis of progress; Rs50,000 (US$477) upon signing an agreement; Rs150,000 (US$1,437) after completion up to plinth level; and Rs100,000 (US$958) upon completion of the structure.

More than 400,000 households entered into an agreement, but so far only 12% have completed the program.

The National Reconstruction Authority (NRA) undertook a lengthy consultation period in the name of building back better. Development of a building code compliance process and a catalogue on rural housing took 18 months to produce and disseminate.

By the time guidance was finally available, many beneficiaries had spent the first instalment on other priorities – many of those affected struggle to provide for the basic needs of their families.

Due to the remoteness of many reconstruction properties in the mountainous terrain, checking for compliance is a major challenge. In addition to the delays in establishing a suitable mechanism, the NRA has been unable to provide enough technical experts in remote, rural areas to implement their own policy.

Read more: What can tourists do to help, not hinder, Nepal’s quake recovery?

Safe, affordable and high quality construction is possible

Safe building is inherently difficult in a developing country like Nepal. For many people, putting food on the table is a daily struggle. Investing in earthquake-resistant housing measures is simply not within reach.

Some in Nepal are forced to live in buildings that could fall down at any time.
Jason von Meding

In such situations, people are forced to accept acute risk in the course of just surviving. This includes living in buildings that might fall down at any time. In Nepal, people have continued with life since the 2015 earthquake and have reoccupied dangerous premises.

Beyond simply improving the effectiveness of building code enforcement, it’s important we don’t neglect social and economic aspects of the dilemma in Nepal. While affordability is critical, quality is achievable by adapting Indigenous building techniques. If safe building is valued, people would voluntarily comply with codes and regulations.

The ConversationThe potential for change will be wasted if we fail to understand and address the chronic vulnerability of people recovering from this disaster. Not everyone has the same access to opportunities and resources – so better codes and regulations only go so far.

Jason von Meding, Senior Lecturer in Disaster Risk Reduction, University of Newcastle; Hari Darshan Shrestha, Associate professor Disaster Management and structural Engineering; Humayun Kabir, Professor, DRR expert, University of Dhaka, and Iftekhar Ahmed, Senior Lecturer, University of Newcastle

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

New Zealand’s Alpine Fault reveals extreme underground heat and fluid pressure

File 20170517 24350 bor3lx
The drilling project at New Zealand’s Alpine Fault is the first to investigate a major fault that is due to rupture in a big earthquake in coming decades.
John Townend/Victoria University of Wellington, CC BY-SA

Rupert Sutherland, Victoria University of Wellington

An international team that drilled almost a kilometre deep into New Zealand’s Alpine Fault, which is expected to rupture in a major earthquake in the next decades, has found extremely hot temperatures and high fluid pressures. The Conversation

Our findings, published today in Nature, describe these surprising underground conditions. They have broad implications for understanding what happens in the buildup to a major earthquake, and may represent the discovery of a new type of geothermal energy resource.

Seismic forces building up

The Alpine Fault is one of the world’s major plate boundaries and New Zealand’s most hazardous earthquake-generating fault. It runs for 650 kilometres along the spine of New Zealand’s South Island and we know that it ruptures on average every 300 years, producing an earthquake of about magnitude 8.

The last time the Alpine Fault did this was in 1717, when it shunted land horizontally by eight metres and uplifted the mountains a couple of metres. It is expected to rupture in a major earthquake in the next few decades and, even though this may not happen in the next 30 years or even 100 years, we know that the fault is at the end of its seismic cycle.

Other projects around the world have drilled into major faults, but usually just after a major earthquake. The Deep Fault Drilling Project, which involved more than 100 scientists from 12 countries, gave us an opportunity to take a close look at a fault as it builds up to its next rupture. It is the first time this has ever been done on a major fault that is due to fail in coming decades.

Drilling into New Zealand’s most hazardous fault.

Hot water at depth

We drilled two holes and during our second attempt made it to 893 metres deep. As we drilled deeper, the temperature increased rapidly, at a rate of about 15 degrees Celsius per 100 metres in depth. This is much higher than the normal rate of about 3°C per 100m in depth. At a depth of 630 metres, the water at the bottom of the drill hole was hot enough to boil, if it had been allowed to rise to the surface. The high pressures at depth stop it from boiling.

The hottest boreholes on Earth are mostly found in volcanic regions. We discovered a geothermal gradient – a measure of how fast temperature increases with depth – that is similar to the hottest geothermal energy boreholes drilled into volcanoes of the central North Island; but there are no volcanoes near the Alpine Fault.

How does it get so hot

There are two processes we think explain the extreme underground conditions at our drill site. An earthquake on the Alpine Fault has two geological effects: mountains are pushed higher and the shaking breaks up rocks.

During an earthquake and over time, the fractured rocks come down in landslides and rivers carry them to the sea. This limits how high the mountains can get. This process has operated for millions of years, with the height of the mountains staying about the same. Eventually, hot rocks from great depth (about 30 kilometres deep, at 550°C) were transported to the surface quickly enough (on geological time scales) that they did not have time to fully cool. Heat is transported from depth by the rock movement.

The other process that helps explain our findings is the rock fracturing, which allows rain water and snow melt to percolate downwards into the mountains so fast that it can move heat towards the valley, where water wells up and discharges. The flow needs to be fast enough so that the heat is not lost along the way, just as a water pipe in your home moves heat from a hot water cylinder to your bath before having time to cool. Water flowing through the rock concentrates heat and raises fluid pressure beneath the valleys.

The hot, high-pressure water beneath the valleys is mostly invisible at the surface, because it mixes with shallow, cold groundwater that flows to a depth of about 50 metres at our drill site. However, most of the valleys in the region where we drilled have a few warm springs that hint at this deeper source of hot water.

Better modelling of future hazards

The unexpected results of our research are important beyond New Zealand. Other faults around the world that we know are similar to the Alpine Fault may also have extreme conditions that have never been investigated.

Perhaps most significantly, we can now describe and estimate conditions on a geological fault that will rupture in an earthquake. This will help us to develop better computer models of earthquake rupture. It may also help us to explain how some types of geology (for example certain types of gold mineralisation) have formed as a result of similar conditions in ancient earthquakes.

Economic benefits

The extreme underground conditions we discovered may result in substantial economic benefits for New Zealand by providing a sustainable and clean geothermal energy resource that could be used by industry and local communities. We expect that similar hot geothermal conditions exist in other nearby valleys, and maybe in some other places in the world that are geologically similar to western New Zealand.

More drilling and measurements are needed to establish the scale of this local resource, its possible uses, and if it is safe to develop.

Rupert Sutherland, Professor of tectonics and geophysics, Victoria University of Wellington

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

What happened in New Zealand’s magnitude 7.5 earthquake

Brendan Duffy, University of Melbourne and Mark Quigley, University of Melbourne

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

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, and the closest the Earth and 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.

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% 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%) 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, Lecturer in Applied Geoscience, University of Melbourne and Mark Quigley, Associate professor, University of Melbourne

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