Category Archives: Earthquake

Istanbul: On the brink of an earthquake disaster

Istanbul is an ancient and beautiful city with a long history at the centre of major empires including the Roman, Byzantine, Latin and Ottoman. It is a city inundated with rich culture and history. In 2010 it was named a European Capital of Culture, which helped make it the world’s tenth most popular tourist destination. Home to over 11 million people, it is also one of the most populated cities in the world.

But this thriving and seemingly indestructible metropolis sits on a loaded spring: The North Anatolian Fault. The most active and earthquake prone fault system in Turkey, and the source of the 1999 magnitude 7.4 earthquake that killed nearly 18,00 people in the city of Izmit.

izmit
A building destroyed in the 199 Izmit earthquake. Wikimedia Commons

The North Anatolian Fault is about 1300km long running along the entire length of northern Turkey, from the Aegean Sea in the west to Lake Van in eastern Turkey.

Curiously, large earthquakes on the fault have tended to follow a successive sequence, i.e. an earthquake will often occur on the section of the fault adjacent to the last rupture. The current sequence started in 1939 with the magnitude 7.9 Erzincan earthquake, which killed over 30,000 people, and has been progressing to the west in a series of 8 large events.

Researchers in 1997 used this observation to successfully predict the location of the 1999 Izmit earthquake (if not the exact time). Worryingly the Izmit earthquake ruptured less than 100km to the east of Istanbul. Further work has led other researchers to predict a major earthquake, possibly another large magnitude 7.4, in the Istanbul region within the next 20 years!

Current westward progression of earthquakes along the North Anatolian Fault.

So what can we do? Firstly, we need to better understand the science behind the cause of earthquakes in this region. The FaultLab project based at the University of Leeds involves research on the the ground movements around the North Anatolian Fault during various stages of the earthquake cycle. A greater understanding of the fault system can be used in forecasting models to give a better idea of the seismic risk.

Secondly, more engineering work needs to be done to reinforce vulnerable buildings that would collapse in the event of ground shaking. In May 2012 the Turkish government passed a new Urban Transformation Law requiring all buildings that do not conform to current earthquake hazard and risk criteria to be demolished.

BamEq
Is it too late?

This effectively means nearly 6 million buildings throughout Turkey will be demolished over the next two decades! This massive project is expected to generate over USD 500 billion worth of construction industry over the next decade.

A new rail line that runs beneath the Bosphorus Straits and links the east and western parts of the city will be able to withstand shaking from a magnitude 9 earthquake.

The new airport terminal for the Sabiha Gokcen international airport that serves the city of Istanbul has also been built to withstand shaking from a magnitude 8 earthquake and importantly, remain operational afterwards. This is critical, as when a disaster does strike the airport will be one of the main entry points for international relief and aid.

But the key question is: will Turkey and Istanbul in particular be able to finish all its ambitious redevelopment plans before the next major earthquake?

I certainly hope so!

Ekbal

More information:
[1] Progressive failure on the North Anatolian fault since 1939 by earthquake stress triggering, 1997, Geophysical Journal International, v 128, pp 594-604
[2] Parsons, T., Shinji, T., Stein, R. S., Barka, A. A., Dietrich, J. H.; Heightened Odds of Large Earthquakes Near Istanbul: An Interaction-Based Probability Calculation, 2000, Science, v 288, pp 661-665
[3] http://www.invest.gov.tr/en-US/infocenter/news/Pages/220213-turkey-urban-transformation-project-foreign-investors.aspx

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Plight of the Bangladeshi

Lying on the floodplains of the mighty Ganges, Brahmaputra and Meghna rivers Bangladesh is a rich, fertile land. These giant river systems meet in the centre of the country and flow together into the Bay of Bengal which, at over 1600km wide, is the largest delta in the world.

Rising Sea Level

Bangladesh is often cited as one of the countries that will be most negatively affected by rising sea levels from human induced climate change. Two thirds of the country lies less than 5m above of sea level. With vast regions to the south much less than a 1m above sea level. The Intergovernmental Panel on Climate Change (IPCC) claims that just 1m rise in sea level could directly expose nearly 14 million people and result in potentially 17% land loss in southern Bangladesh.

Floods

Most of the country receives on average more than 2.5m of rainfall a year, 80% of which falls in about 4 months during the peak monsoon season, resulting in large annual floods. The flood waters bring nutrient rich clays and silts from the high Himalayas and deposit them on the river floodplains. These rich soils produce bountiful harvests of rice and other crops. Unsurprisingly, farming is the most common profession.

bangladesh_flood_NASA
A flooded street. Source: NASA

However floods, once welcomed by farmers and their families are now harbingers of disaster. Human induced climate change has resulted in more erratic monsoon weather patterns with often larger than normal volumes of water being delivered in shorter time intervals. The resulting floods have had devastating effects on the Bangladeshi people. In 2012 three large floods hit the country in swift succession between the months of July and September directly affecting more than 5 million people. These are now a common annual occurrence.

Cyclones

Bangladesh is also subject to annual tropical cyclones, storm surges and tornadoes. Some of the worst natural disasters in recorded history were results of cyclonic storms in the Bengal region. Among them, the 1970 Bhola cyclone which claimed over 500,000 lives! Worryingly new research into the impacts of climate change has shown that large cyclonic storms will become a more common occurrence in the years and decades to come.

Earthquakes

The foothills of the great Himalayan mountain belt has historically been the location of many large earthquakes. Earthquakes in the continent tend to be more infrequent compared to regions such as Japan and California. However this makes them more unpredictable and often unexpected. But when one does occur it can result in significant ground shaking. The 1897 magnitude 8.1 and 1950 magnitude 8.7 Assam earthquakes were two of the biggest to hit the region in recent times. The current building stock in Bangladesh is poorly built and most are not built to withstand ground shaking in an earthquake. The collapse of poorly built buildings is the greatest hazard during an earthquake.

Dhaka_Savar_Building_Collapse_W.Commons-rijans_edited
The Savar building collapse near Dhaka Bangladesh, which killed 1129 garment factory workers. Source: Wikimedia Commons

So what can we as earth scientists do?

Bangladesh has a population of over 160 million and among the highest population density of any country in the world. With the majority of the country built on river floodplains combined with widespread corruption and ignorance a large earthquake could quite possibly result in the greatest natural calamity to have ever hit the country!

Bangladesh needs to increase its resilience if its people are to survive the multitude of natural hazards they face. Earth scientists are well placed to understand the risks involved from these hazards and can play a key role in all aspects of building a resilient infrastructure.

Climate science research is ongoing and needs to continue to better understand the affect human induced climate is having and will have on the annual monsoon. This knowledge needs to be translated into rainfall variation and flooding potentials and communicated with the people who need this information. The socio-economic issues of a rising sea level needs to be addressed and plans put in place to allow big cities to efficiently absorb and cater for migrants moving away from hazard prone coastal regions. Hydro-geologists and geochemists are helping to find sustainable clean, arsenic free water sources for drinking and farming. Seismologists and earthquake scientists are working to better understand the seismic risk in the Himalayan foothills; produce more accurate hazard maps and importantly identify the active faults within the region.

These are to name but a few of the ways earth scientists can get involved. I believe it is our moral duty to translate the practical aspects of our science into real benefits for people.

Ekbal

More information:
[1] http://www.ipcc.ch/ipccreports/tar/wg2/index.phpidp=446
[2] http://www.guardian.co.uk/global-development/2013/jan/23/bangladesh-floods-harbingers-disaster
[3] http://reliefweb.int/disaster/fl-2012-000106bgd
[4] http://en.wikipedia.org/wiki/List_of_Bangladesh_tropical_cyclones
[5] http://en.banglapedia.org/index.php?title=Main_Page

North Korea’s nuclear test detected on seismographs

North Korea’s nuclear test today created a magnitude 5.1 earthquake equivalent seismic signal and has been measured on seismographs around the world.

More info: http://ds.iris.edu/ds/nodes/dmc/specialevents/2016/01/05/2016-north-korean-nuclear-test

NKorea4comparison_IRIS
Seismic recordings of vertical ground motion. (Andy Frassetto, IRIS)

Corruption and earthquake hazards

Earthquakes are caused by the sudden release of energy stored on fractures in the Earth’s crust called faults. Every year they are responsible for thousands of fatalities around the world.

For this post I’d like to focus on the role of corruption in the building industry and its impact on lives lost in earthquakes. The global construction industry was worth $8.7 trillion in 2012[3] and is recognised as being the most corrupt segment of the global economy[1].

Corruption in this industry takes the form of using inadequate and/or insufficient building materials, bribes to inspectors and civil authorities, substandard assembly methods and the inappropriate siting of buildings. Spontaneous building collapses even without earthquakes, such as the 2013 Savar factory collapse in Bangladesh, which killed 1129 people, are a stark reminder of the consequences of construction oversight and a terrifying view into what could happen if there is an earthquake in these regions.

Dhaka_Savar_Building_Collapse_W.Commons-rijans_edited
The Savar building collapse near Dhaka Bangladesh, which killed 1129 garment factory workers. Source: Wikimedia Commons

The 1999 Izmit earthquake (magnitude 7.4) in Turkey resulted in around 18,00 deaths. After the earthquake, inspectors found that nearly half of all the structures within the damage zone had failed to comply with building regulations[1].

Nicholas Ambraseys and Roger Bilham calculated that almost 83% of all deaths from building collapse in earthquakes in the last 3 decades occurred in countries that are poor and anomalously corrupt[4].

Corruption by itself is dangerous but when combined with poverty, it is disastrous. Corruption, poverty and ignorance essentially become indistinguishable for many low income countries. And even if corrupt practices are eliminated these countries will have inherited a building stock that is of poor quality and prone to failure in the next earthquake.

corruption_kills_v2
A pertinent quote from the famous Charles Richter in his 1970 retirement speech.

However, it’s not all bad news. There are some great examples of how reconstruction can happen under correct management and regulations to improve resilience to earthquakes and other natural hazards. For example, in 2012 the Turkish government passed the Law on the Regeneration of Areas Under Disaster Risk. Under these new guidelines all buildings that are not up to current earthquake risk standards will be demolished and rebuilt.

The reconstruction of the Macedonian capital of Skopje after it was destroyed in an earthquake in 1963 is another great example. Not only was all the infrastructure rebuilt to be earthquake-resistant, the city planners also ensured that the river Vardar was re-routed in order to control future flooding[5].

Achievements on this scale requires strong governance and management, and transparent national and local administration. With the rapid growth of cities into so-called megacities (>10 million population), often in high earthquake risk regions, this is even more important. We have yet to have an earthquake that has killed a million people. But at the rate these cities are growing under limited to no management, such an event might not be too far in the future.

More Information:
[1] Global Corruption Report 2005: Corruption in construction and post-conflict reconstruction, Transparency International
[2] Global Construction 2020: A Global Forecast for the construction industry over the next decade to 2020. (2010)
[3] Global Construction 2025:  A Global Forecast for the construction industry to 2025. (2013)
[4] Ambraseys, N. & Bilham, R., 2011
[5] Vladimir B. Ladinski 2010

Seismic hazard to seismic disaster

How does a seismic hazard turn into a seismic disaster? Professor Iain Stewart explains in the ‘Anatomy of an Earthquake’.

 

How do we measure earthquake strain energy?

I was asked a very interesting question on one of my recent LinkedIn posts that I thought deserved a slightly detailed answer. Here’s the question:

QuestionAnd here’s my answer:

Hi David. Firstly, this is not a basic question at all. In fact, it’s one that is of considerable importance. Your question has two parts and I’ll address them individually.

How do we measure strain energy released in earthquakes?

The main way we do this is by measuring how much the ground moves in an earthquake, this can be done with high precision GPS instruments on the ground or from space based satellite measurements.

Here’s an example from the giant Tohoku earthquake, that struck Japan in 2011, of what we can do with GPS instruments. Each little arrow is a GPS station and it records how much the ground moved during the earthquake.

We can use these kind of measurements to calculate how much the ground has moved all along the fault and at depth during an earthquake. Once we have the full displacement of the fault we can relate that directly to the stress drop and strain release.

How do we measure strain energy being stored on faults?

A similar method is used to determine strain stored on a fault. The ground very slowly warps itself around a locked fault in the decades to centuries before an earthquake.

Here’s an animated model of what I mean (might need a screen refresh to play it). Imagine looking down onto the ground from above with the top half of the earth moving to the right and the bottom moving to the left.

strain_accummulation2
The warping of the ground before an earthquake. Source: Philip England

If we can measure the degree of warping before the earthquake, again by using GPS and satellites, we can relate that to the strain energy getting stored on the fault. Here represented by the different colours, with red being the area of highest strain storage.

I hope that helps to answer your question!

Ekbal

Earthquake risk in the Himalaya

By Victoria Stevens

Earthquakes have not been releasing energy as fast as the energy has been building up along the Himalayan arc. Meaning that there could be a giant earthquake in the region placing millions at risk.

A new study of the 2000 km long Main Himalaya Thrust, the largest earthquake generating fault in the Himalaya, has revealed that large quakes could occur in any location along the Himalayan arc.

Unlike in subduction zones, where some patches of the fault are moving, or ‘creeping’ at a constant speed, in the Himalaya we don’t see any creeping patches. This means that the fault is fully ‘locked’, i.e. strain energy is building up most of the time. This energy is released suddenly during earthquakes. Because there are no creeping patches, there are no barriers to rupture, which means once an earthquake has started, it could rupture a very long way along the fault without anything to limit its size.

The degree of 'locking' on the Main Himalayan Thrust. Where the fault is red, its fully locked and white where its not locked. Source: Stevens and Avouac 2015
The degree of ‘locking’ on the Main Himalayan Thrust. Where the fault is red, its fully locked and white where its not locked. Source: Stevens and Avouac 2015

The study shows that the pattern of coupling, i.e. the degree of fault locking, has been stationary with time. From the coupling pattern, the rate of moment build-up can be found. This is how much energy is building up each year, and is also the amount that needs to be released in earthquakes if all the energy is released seismically.

Earthquakes have not been releasing energy as fast as the energy has been building up, so we may expect very large earthquakes in this region in the future. Studies of ancient earthquakes have shown that quakes approaching magnitude 9 have occurred previously in both the western and eastern halves of the Himalayas. It is not impossible that these giant earthquakes could occur again.

night_lights
Night lights show large population densities living in the shadows of the Himalaya.

This has important implications for seismic hazard in the region. The population living in the Himalayas has increased dramatically in the past few decades, and most buildings are not resistant to large shaking caused by earthquakes. As we saw with the recent devastating April Gorkha-Nepal earthquake, the Himalayan countries prone to earthquakes are not yet prepared to meet all the challenges this natural hazards present.

Read the full journal article titled: Interseismic coupling on the main Himalayan thrust

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Victoria Stevens is a PhD graduate student at the California Institute of Technology (Caltech).

Balancing rocks and the earthquake detectives

Scientists have solved a mystery as to why precariously balanced rocks near the San Andreas Fault have never been toppled over by earthquakes.

During large earthquakes shaking of the ground causes unstable structures, both natural and man-made, to collapse in a wide region around the source of the quake. This high shaking zone can be anything from a few kilometres to hundreds of kilometres depending on the size of the earthquake.

Nick Hinze / Nevada Bureau of Mines & Geology
Nick Hinze / Nevada Bureau of Mines & Geology

It’s long been an intriguing mystery as to why many so called “precariously balanced rocks” are found in close proximity to one of the most active earthquake generating structures in the United States: the San Andreas Fault. Some of these rocks have been balanced for thousands of years. During which there might have 50 -100 earthquakes in the area.

A decade long study by US scientists, measuring and cataloguing balancing rocks along with computer modelling reveal that interactions between the San Andreas Fault and the neighbouring San Jacinto Fault may be the answer to the mystery.

The researchers believe that precariously balanced rocks have survived because interaction between the two faults has weakened earthquake ground shaking near them.

“These faults influence each other, and it looks like sometimes they have probably ruptured together in the past,” said lead author Lisa Grant Ludwig. “We can’t say so for sure, but that’s what our data point toward, and it’s an important possibility that we should think about in doing our earthquake planning.”

The scientists have realised that these rocks could provide a check for seismic hazard maps, and give long-term indications of ground shaking.

“”They are kind of natural seismoscopes – but you have to read them indirectly.”

More information:
[1] Press release – http://news.uci.edu/press-releases/precariously-balanced-rocks-provide-clues-for-unearthing-underground-fault-connections
[2] Journal article – http://srl.geoscienceworld.org/content/early/2015/07/31/0220140239.extract

Earthquake liquefaction causes ground to open and close

The 2011 magnitude 9 earthquake in Japan was one of the largest earthquakes ever measured. Strong shaking and the consequent tsunami caused the death of nearly 18,000 people.

Strong vibrations in earthquakes can cause soil particles in the ground to jiggle about and lose contact with each other. If there is a lot of water within the ground the shaking causes soil to behave more like a liquid than a solid. This process is called liquefaction.

Footage taken by an American tourist shows dynamic movements of the ground during the Japan earthquake. The changing pressures caused by the soil movement can force water out of the ground and form moving cracks on the surface.

Note that this is not ground movements caused by the actual shaking in the earthquake, but by secondary soil movements.