The Iranian and Pakistani coast is rapidly urbanising. It's at risk of a tsunami

Iranian holidaymakers enjoy the Gulf resort of Kish in November 2016. Image: Getty.

That tsunamis can cause death and devastation has become painfully clear over the past two decades. On Boxing Day, 2004, a magnitude 9 earthquake off the coast of Sumatra caused waves several metres high to devastate the Indian Ocean – killing more than 230,000 people in 14 countries. In 2011, another magnitude 9 earthquake, this time off Japan, produced waves up to 20 metres in height, flooding the Fukushima nuclear reactor. It killed more than 15,000 people. The Conversation

A new study, published in Geophysical Journal International, by my colleagues and me suggests that a 1,000km long fault at the northern end of the Arabian Sea may pose a similar threat.

The Makran, as the southern coastal region of Iran and Pakistan is known, is a subduction zone. In such regions, one of the Earth’s tectonic plates is dragged beneath another, forming a giant fault known as a “megathrust”. As the plates move past each other, they can get stuck, causing stress to build up. At some point the stress becomes high enough that the megathrust breaks in an earthquake.

This was exactly what caused the Sumatra 2004 and Tohoku 2011 earthquakes. When a megathrust moves suddenly, the whole seafloor is offset and the water has to move out of the way over a huge area. This sets off waves with particular characteristics that can cross entire oceans: tsunamis. The phenomenon, along with their potentially large size, makes subduction zone earthquakes particularly dangerous.

The Makran region. Image: adapted from NASA photo.

But just because a part of a subduction zone produces earthquakes doesn’t mean that the whole megathrust can move in one go. We often see that stress builds up at different rates on different parts of the fault, with some parts sliding smoothly past each other. How much of a megathrust can move in one go is important because it determines the size of the resulting earthquake. The amount that the Makran megathrust can move in earthquakes has been a longstanding question, but the hostile climate and challenging politics of the region have made research there difficult.


We know that the eastern part of the Makran megathrust (in Pakistan) can produce large earthquakes. A magnitude 8.1 quake off the coast of western Pakistan in 1945 caused a tsunami which killed about 300 people along the coasts of Pakistan and Oman. There have been several smaller earthquakes on the megathrust since, including a magnitude 6 in February this year.

If the western part of the Makran (in Iran) also produces earthquakes – and the whole Makran megathrust were to move in one go – it could produce a magnitude 9 earthquake, similar to those in Sumatra and Tohoku.

However, we have never actually recorded a subduction earthquake in this part of Makran. In fact, there are only records of one candidate quake from 1483 – and the actual location of this is disputed. But it’s important to keep in mind that just because we haven’t seen an earthquake doesn’t mean that there couldn’t be one – particularly since the intervals between earthquakes are often hundreds or thousands of years. Historically, not many people have lived in the remote Iranian Makran, a desert which killed Alexander the Great’s army. So earthquakes might simply not have been documented.

GPS data

We used new data to look for tell-tale signs of a possible earthquake. Imagine a piece of paper on a table. If you hold one end and push the other end towards it, the paper crumples up and the distance between the two ends gets shorter. If you let go, the paper flattens out. The fixed end is like a megathrust which is stuck. Indeed, if the Arabian plate is stuck, and stress is building up, southern Iran will be squeezed and shortened. We can look for evidence of this shortening by using a more accurate version of the GPS systems found in smartphones. My coauthors from the National Cartographic Centre in Iran have set up a network of GPS stations to measure how fast different parts of Iran are moving relative to Arabia.

We found that the velocities fit with Iran being shortened near the coast, suggesting that stress is indeed building up – and meaning there could be a large subduction earthquake in the future. This fits with recent work looking at large boulders along the coast of Oman, thought to have been deposited by tsunamis. The locations of these boulders suggest that the tsunami which brought them there would need to have come from a subduction earthquake, either in western Makran or along the entire subduction zone – including Pakistan. These boulders were probably deposited in the last 5,000 years, but we can’t know for sure.

The 2004 Sumatra tsunami strikes Ao Nang, Thailand. Image: David Rydevik/wikipedia.

This is a hazard that people need to be aware of, particularly those living in coastal regions around the Arabian Sea. Rapid urbanisation along the Omani and Pakistani coasts in recent years has increased the population exposed to earthquakes and tsunamis in the Makran. Karachi, at the eastern end of the subduction zone, is now a megacity and home to around 25m people. Much of Muscat, the Omani capital, is less than 10 metres above sea level, making it vulnerable to tsunamis. The port of Gwadar in Pakistan, which was badly damaged in a 1945 earthquake, is also undergoing massive development.

To help protect these people, and make sure that they are properly prepared, we need to understand this hazard better. Education and early warning are both key – exercises testing the Indian Ocean Tsunami Warning System are a step in the right direction, especially if they engage the public.

At the moment, we can only say that a large earthquake in the Makran is consistent with the limited data which we have available. By continuing to work with scientists in Iran and Pakistan to make more measurements I hope that in the future we will have a much better idea of what to expect from this subduction zone.

Camilla Penney is a PhD Candidate in geophysics at the University of Cambridge.

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

 
 
 
 

Brexit is an opportunity for cities to take back control

Leeds Town Hall. Image: Getty.

The Labour leader of Leeds City Council on the future of Britain’s cities.

As the negotiations about the shape of the UK’s exit from the EU continue, Britain’s most economically powerful cities outside London are arguing that the UK can be made stronger for Brexit – by allowing cities to “take back control” of service provision though new powers and freedoms

Core Cites UK, the representative voice of the cities at the centre of the ten largest economic areas outside London, has just launched an updated version of our green paper, ‘Invest Reform Trust’. The document calls for radical but deliverable proposals to allow cities to prepare for Brexit by boosting their productivity, and helping to rebalance the economy by supporting inclusive economic growth across the UK.

Despite representing areas responsible for a quarter of the UK’s economy and nearly a third of exports, city leaders have played little part in the development of the government’s approach to Brexit. Cities want a dialogue with the government on their Brexit plans and a new settlement which sees power passing from central government to local communities.

To help us deliver a Brexit that works for the UK’s cities, we are opening a dialogue with the EU Commission’s Chief Negotiator Michel Barnier to share our views of the Brexit process and what our cities want to achieve.

Most of the changes the Core Cities want to see can already be delivered by the UK. To address the fact that the productivity of UK cities lags behind competitors, we need to think differently and begin to address the structural problems in our economy before Brexit.

International evidence shows that cities which have the most control over taxes raised in their area tend to be the most productive.  The UK is significantly out of step with international competitors in the power given to cities and we are one of the most centralised countries in the world.  


Boosting the productivity of the UK’s Core Cities to the UK national average would increase the country’s national income by £70-£90bn a year. This would be a critical boost to the UK’s post-Brexit economic success.

Our green paper is clear that one-size fits all policy solutions simply can’t deal with the complexities of 21st century Britain. We need a place-based approach that looks at challenges and solutions in a different way, focused on the particular needs of local communities and local economies.

For example, our Core Cities face levels of unemployment higher than the national average, but also face shortages of skilled workers.  We need a more localised approach to skills, education and employment support with greater involvement from local democratic and business leaderships to deliver the skills to support growth in each area.

The UK will only make a success of Brexit if we are able to increase our international trade. Evidence shows city to city networks play an important role in boosting international trade.  The green paper calls for a new partnership with the Department of International trade to develop an Urban Trade programme across the UK’s cities and give cities more of a role in international trade missions.

To deliver economic growth that includes all areas of the UK, we also need to invest in our infrastructure. Not just our physical infrastructure of roads, rail telecommunications and so forth, but also our health, education and care infrastructure, ensuring that we are able to unlock the potential of our core assets, our people.

Whether you think that Brexit is a positive or a negative thing for the UK, it is clear that the process will be a challenging one.  Cities have a key role to play in delivering a good Brexit: one that sees local communities empowered and economic prosperity across all areas of the UK.

Cllr Judith Blake is leader of Leeds City Council.