Tag Archives: seismic hazard

When continents collide

Since 1900, 35 earthquakes worldwide have each killed at least 10,000 people. Of these, 26 were in the Alpine-Himalayan seismic belt – a broad “crumple zone” where the African, Arabian and Indian tectonic plates collide with Europe and Asia. Most of these deadly earthquakes were caused by the rupture of faults that had not previously been identified.

Tim Wright is Professor of Satellite Geodesy at the University of Leeds and Director of the Centre for the Observation and Modelling of Earthquakes, Volcanoes and Tectonics (COMET). His work has been at the forefront of developing the use of satellite radar for measuring tectonic and volcanic deformation.

Below is a lecture presented by Tim at the Geological Society talking about his work trying to understand the nature of seismic hazard within the Alpine-Himalayan region.

Massive earthquake threat lurking beneath Bangladesh

A megathrust fault could be lurking underneath Bangladesh, India and Myanmar, exposing one of the most densely populated regions in the world to the risk of a large earthquake, according to new research published in Nature Geoscience.

A new GPS study measuring tiny ground movements since 2003 in the south Asia region has found strong evidence suggesting that a large tectonic fault beneath Bangladesh and east India is seismically active.

Steckler_el2016
The new active fault beneath Bangladesh. Image from original paper, Steckler et al. 2016

The team, consisting of scientists from the USA, Singapore and Bangladesh, calculate that the megathrust fault could be accumulating strain energy at rates of about 15 mm per year.

Importantly, the researchers believe that the fault is “stuck” and has been storing energy for more than 400 years without a major earthquake; since the Mughal conquest of Bengal and the establishment of Dhaka as the Bangladeshi capital in the 1600s.

An earthquake occurs when the stresses become large enough that it causes the fault to break and releases all the stored energy. The 400 years of energy accumulation at 15 mm per year could result in a devastating magnitude 9 earthquake, similar in size to the Japanese quake that destroyed huge sections of the country’s northeastern coast in 2011.  Such an event would have enormous consequences for more than 140 million people living within 100km of the megathrust in Bangladesh and India.

Steckler_el2016_2
Earthquake hazard and vulnerable populations in Bangladesh and India. Source: Steckler et al. 2016

The tectonic activity of south Asia is a consequence of the collision of the Indian subcontinent with Asia, a process that began nearly 50 million years ago and is still occurring today. This monumental collision resulted in the uplifting of Tibet and the formation of the Himalayan mountain range. Over millions of years these mountains have been slowly eroded and deposited their rich soils onto the Bangladeshi plains by a network of giant rivers. The thick sediments have made the Bangladeshi plains some of the most agriculturally productive in the world.

While the sediments can take up some of the energy along the newly proposed fault, they’re not especially stable, particularly around the rapidly developed eastern outskirts of Dhaka. If a major earthquake strikes, the sediments could even amplify the seismic waves, causing further destruction.

“Dhaka’s basically like building a city on a bowl of Jell-O [jelly],” says Steckler, lead author of the new study, implying that even small earthquake shaking could be amplified by the sediments.

The Savar building collapse in 2013, which resulted in over 1100 deaths, showed the world that building codes in Bangladesh are not strictly enforced. If buildings are collapsing on their own, it is a terrifying prospect to consider what would happen during an earthquake. The lack of preparedness is clear and it is essential for the Bangladeshi government to make long-term changes to promote greater seismic awareness and stricter enforcement of building codes.

More information:
[1] The original paper: http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo2760.html

The 2016 Ecuador Earthquake

by Camilla Watson

An earthquake of magnitude 7.8 occurred in Ecuador on the 16th April this year. With the current death toll at 654 and another 58 still missing, this is one of the most devastating disasters South America has seen in modern times. Although the earthquake epicentre was in a relatively sparsely populated area, according to the US Geological Survey the focus was shallow at 19.2km (12 miles) and located 27km (17 miles) from Muisne off the west coast of northern Ecuador, meaning the effects were stronger than expected upon the Earth’s surface.

Ecuador_quake
Ground shaking from the magnitude 7.8 Ecuador earthquake. Source: USGS

The main initiator of earthquakes is tectonic plate movement. This particular earthquake was caused by a shallow thrust fault on or near the boundary between the Nazca and South American tectonic plates (USGS, 2016). In real terms, this means the Nazca plate is sliding beneath the South American plate, and the build-up of energy due to friction is realised in one sudden slip, causing the earthquake and its aftershocks (Wald, 2009).  Similar systems have caused some of the strongest earthquakes in the world, including the 1960 Chile earthquake of magnitude 9.5 – the largest ever recorded. Due to the presence of the subduction zone, this particular area within Ecuador is known to be prone to earthquakes, with many of the quakes occurring at 0-70km depths beneath the Earth’s surface. This often causes the consequences to be more devastating. The subduction system is also responsible for the formation of the Andes, the longest mountain chain in the world, and the high levels of volcanism within the area (USGS, 2016).

Scientists have been speculating as to whether the 2016 Ecuador earthquake was linked to the magnitude 7.0 Japan earthquake that occurred the day before, on the 15th April, with a shallow focus at 10km depth (Byrd, 2016). The idea behind this is something known as ‘remote triggering’, whereby a magnitude 6.5 earthquake in Japan would have caused slip along the boundaries of the tectonic plates on the other side of the Pacific Ocean, which triggered the tremors that made up the earthquake (Brown, 2016). However, this may also be chance due to both localities being situated on the Ring of Fire, an area known to be extremely tectonically active. Research so far shows no evidence for remotely triggered earthquakes to reach magnitudes above 5, making this particular situation between Ecuador and Japan either the first recorded case of its kind, or a coincidence. However, there has not yet been enough time for thorough research, but many earth scientists will now be focusing on the possibilities of using this information to help us to forecast and prepare for earthquakes in the future.

References:
[1] D. Byrd, (2016), Powerful earthquakes in Japan and Ecuador, EarthSky, [Online], Accessed 25/04/2016: http://earthsky.org/earth/powerful-earthquakes-japan-ecuador-april-2016
[2] E.K. Brown, (2016), Are the Japanese and Ecuador earthquakes related?, The Conversation, [Online], Accessed 25/04/2016: http://phys.org/news/2016-04-japanese-ecuador-earthquakes.html
[3] Fox News, (2016), Death toll in the powerful Ecuador Earthquake rises to 654, Fox News, [Online], Accessed 25/04/2016: http://www.foxnews.com/world/2016/04/24/death-toll-in-powerful-ecuador-earthquake-rises-to-654.html
[4] L. Wald (2009), The Science of Earthquakes, The Green Frog News, USGS, [Online], Accessed 25/04/2016: http://earthquake.usgs.gov/learn/kids/eqscience.php
[5] USGS, (2016), M7.8 – 27km SSE of Muisne, Ecaudor, United States Geological Survey (USGS), [Online], Accessed 25/04/2016: http://earthquake.usgs.gov/earthquakes/eventpage/us20005j32#general


Camilla_WatsonCamilla is a 3rd year undergraduate student in the School of Earth and Environment at the University of Leeds. She likes to combine her passion for travel with her love of geology. Check out her blog at: www.geologyandme.weebly.com

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

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

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’.

 

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

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