Category Archives: Earth Observation

Turkish fault reveals seismic steadiness

Satellite data has shed new light on seismic hazard in one of the world’s most deadly earthquake zones.

Published today in Nature Communications, the study describes how tectonic strain builds up along Turkey’s North Anatolian Fault at a remarkably steady rate.

This means that present-day measurements can not only reflect past and future strain accumulation, but also provide vital information on events still to come.

The strain, which builds up as Turkey is squeezed between three major tectonic plates, has caused almost the entire length of the fault to rupture since 1939 in a series of major earthquakes gradually migrating east to west towards Istanbul.

NAF_strain
Surface velocities along Turkey’s North Anatolian Fault (past ruptures shown in purple/yellow) alongside westward progression of earthquakes since 1939

Led by Ekbal Hussain, the team used satellite images from the European Space Agency’s Envisat mission to identify tiny ground movements at earthquake locations along the fault.

Dr Hussain explained: “Because we know so much about the fault’s recent history, we could look at the strain build up at specific places knowing how much time had passed since the last earthquake.”

The 600-plus satellite images, taken between 2002 and 2010, provided insights into the equivalent of 250 years of the fault’s earthquake repeat cycle.

Remarkably, apart from the ten years immediately after an earthquake, strain rates levelled out at about 0.5 microstrain per year, equivalent to 50mm over a 100km region, regardless of where or when the last earthquake took place.

Dr Hussain added: “This means that the strain rates we measure over the short term can also reflect what’s happening in the longer term, telling us how much energy is being stored on the fault that could eventually be released in an earthquake.”

Until the satellite era, it was difficult to get a clear picture of how strain built up on the fault.  Now, satellites like Envisat, alongside the newer Sentinel-1 mission, can detect ground movements of less than a millimetre, indicating how and where strain is accumulating.

The findings suggest that some existing hazard assessment models, which presume that strain rates vary over time, need to be rethought.  This is especially true for regions where there are long gaps between earthquakes, such as the Himalayas.

Co-author Professor Tim Wright said: “Discovering this consistent strain accumulation will help us to reassess how we model seismic hazards, as well as improving understanding of the earthquake cycle worldwide.”

[1] The full paper is: Hussain et al. (2018) Constant strain accumulation rate between major earthquakes on the North Anatolian Fault, Nature Communications
[2] Lead author Ekbal Hussain is now a Remote Sensing Geoscientist at the British Geological Survey

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Review: New Views

New_Views_A_Bonnett

Disclaimer: I was sent a copy of this book to review.

Working professionally as a remote sensing scientist it is perhaps no surprise that I’m lover of maps and data. And so I was very excited to read New Views, a beautiful book full of fascinating maps and cartographic visualisations depicting global data in all its visual glory.

Created by Alastair Bonnett, Professor of Social Geography at Newcastle University, it is worth noting that many of the maps and/or the data behind them are the creation of other scientists and organisations, including NASA and various bodies of the United Nations. In each case Alastair declares the source of the data, often with  a quote or two from the original creators as well as some fascinating insights gleamed from the visualisations.

The book broadly cover three main topics: Land, Air and Sea, Humans and Animals, and Globalisation. The fifty maps are illustrated with highly visual and extremely informative data, which gives a global perspective to events like asteroid strikes, fire activity, religious diversity and critically endangered languages. My favourite was the global energy flux, which depicts the abundant energy infrastructure of the power hungry West with the growing energy fluxes in the booming countries of East Asia; while the dark expanses of the African continent illustrate the energy access and development challenges of the region.

So this book isn’t purely a collection of maps, it is a vivid illustration of global wealth inequality, of health disparities, of economic development, and environmental treasures. The global perspective they offer show us that we live in a highly diverse and unequal world, and only through such visualisations can we appreciate the global nature of our influence and our impact on the world.

The book ends with a mention, that delighted the map nerd in me, of the various map projections used in the book. It would have been great to learn why the author chose to use certain projections in his visualisations but alas, we shall never know!

‘Give me an atlas over a guidebook any day, for there is no more poetic book in the world.’ – Judith Schalansky

Earth’s Changing Surface water

Scientists have used satellite observations to study how the distribution of land and water on the Earth’s surface has changed over the last 30 years.

They found that the Earth’s surface has gained 115,000 sq km of water of extra water bodies and 173,000 sq km of water has now become land. The study is published in Nature Climate Change.

The interactive Aqua Monitor was developed by the Deltares Research Institute in the Netherlands. It is the first global-scale tool that shows, with a 30 metre resolution, where water has been transformed into land and vice-versa.

Tibet
New lakes – seen in blue – are appearing on the Tibetan Plateau. Image: Deltares Aqua Monitor

The largest increase in water has been on the Tibetan Plateau, where increased water from melting glaciers are creating huge new lakes.

A rise in the number of dams built over the last 30 years has also increased the number of inland water bodies. Using the satellite data, the team were able to identify previously unreported constructions in Myanmar and North Korea.

The Aral Sea, which lies between Kazakhstan and Uzbekistan, has seen the the greatest conversion of water into land. Formerly one of the four largest lakes in the world, the Aral Sea has been steadily shrinking since the 1960s after the rivers that fed it were diverted by Soviet irrigation projects.

Aral_Sea
The Aral Sea has almost completely dried out. Green here shows the area of water that has converted to land. Image: Deltares Aqua Monitor

There have also been striking changes along our coastlines. The largest coastal water to land change is the construction of Palm Island and adjacent islands along the coast of Dubai. Many countries have shaped and extended their coastlines by land reclamation, including almost the entire coastline of eastern China from the Yellow Sea all the way down to Hong Kong.

Big data at everyone’s fingertips
Universally-available analytics for big satellite data may have major implications for monitoring capacity. At the very local scale, members of the general public can now make assessments without expert assistance if their houses are threatened by coastal erosion. At the regional scale, countries can monitor their water body changes and assess flooding impacts and strategy for disaster risk reduction.

Jaap Kwadijk, the Deltares scientific director: “This has never been done before. So it is difficult to imagine all the new applications that will be made using this tool. But the tool can be used by everybody and so I am sure multiple applications will emerge in the next few years”.

Original Paper: http://www.nature.com/nclimate/journal/v6/n9/full/nclimate3111.html

 

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.

Satellite radar vision

How are radar satellites revolutionising our understanding of Earth processes and allowing us to respond to extreme weather events and natural disasters?