Category Archives: Events

Remote sensing of cross-border quakes

Rich

Post by Richard Walters, Research Fellow at the University of Leeds with COMET and the Earthquakes without Frontiers project (r.j.walters@leeds.ac.uk)

 

Active faults and the devastating earthquakes they can trigger do not respect political borders. Whilst the recent earthquakes in Nepal did most damage to the mountain kingdom itself, hundreds of people were also killed or injured in neighbouring China, India and Bangladesh.

The region’s history tells a similar story – the three countries’ earthquake records over the last 500 years are intertwined by shared proximity to the Himalayan mountain belt and its underlying megathrust fault.

Ways of improving resilience to earthquake hazard also need to transcend political boundaries, bringing together scientists and policymakers from the affected countries to share knowledge, experience and ideas.

This principle has led to the Earthquakes without Frontiers (EwF) partnership – a diverse group of natural and social scientists from around the UK. Led by James Jackson of both COMET and the University of Cambridge, EwF is a 5-year initiative funded by NERC and ESRC (the Natural Environment and Economic and Social Research Councils) under the Improving Resilience to Natural Hazards programme.

As well as COMET, the partnership includes researchers from Cambridge, Durham, Hull, Leeds, Northumbria and Oxford Universities, the British Geological Survey, the Overseas Development Institute and Durham’s Institute of Hazard, Risk and Resilience.

The project focuses on three broad regions – China, the Himalayan mountain front (Nepal and Northern India) and Central Asia (Kazakhstan and Kyrgyzstan) – with the key objective of furthering knowledge on earthquakes and landslides in the continental interiors.

Much of this involves using remotely sensed data which complements the project’s cross-border approach. EwF scientists use digital topography and multispectral and optical imagery to research landslide hazard and map active faults, alongside satellite radar to measure the warping of the Earth’s crust and steady interseismic motions as faults build up stress before the next seismic event.

All of this contributes to a wider programme of social and natural scientific research with scientists in the partner countries, as well as being used to run workshops and training events for young international scientists.

Crucially, this knowledge exchange extends to countries dealing with similar hazards – the same types of fault that threaten vast regions in China also cause earthquakes in Italy, and lessons learnt about Iranian faults can inform work on hazard in Kazakhstan and vice versa.  As such, EwF brings together scientists from many countries to share knowledge and experience across an even wider network, culminating in the annual EwF partnership meetings, the most recent of which was held in Kathmandu in April 2015.

When a huge Mw7.8 earthquake struck Nepal on the 25th April, it came as a double blow to all within EwF. Nepal is not only one of our focus areas, but many of the UK team also had been in Kathmandu just one week before the earthquake, working and living alongside Nepali colleagues and friends.

The International Charter for Space and Major Disasters was invoked just 3 hours after the earthquake, and over the following few days, space agencies hurriedly tasked their satellites to acquire new imagery over Nepal. We all felt strongly that we should put our combined experience to good use in the immediate aftermath of the Nepal earthquake, and dashed to obtain satellite imagery of the area.  In the weeks since we have been working to analyse this imagery in order to aid both disaster relief efforts and hazard re-evaluation.

Figure 1: Satellite radar interferogram of the 25 April 2015 Mw7.8 Nepal Earthquake. The coloured fringes represent contours of ground motion towards the satellite, at intervals of 8.5 cm. Image credit: Pablo Gonzalez, University of Leeds, EwF, LiCS; SAR data provided by the European Space Agency
Figure 1: Satellite radar interferogram of the 25 April 2015 Mw7.8 Nepal Earthquake. The coloured fringes represent contours of ground motion towards the satellite, at intervals of 8.5 cm. Image credit: Pablo Gonzalez, University of Leeds, EwF, LiCS; SAR data provided by the European Space Agency

EwF researchers, along with colleagues at the University of Leeds, used data from the European Space Agency’s Sentinel-1A satellite to measure how the ground was permanently warped by the earthquake.  This was greatly assisted by COMET’s new automated processing facility, designed to cope with the vast amount of data from the Sentinel-1 satellites, which helped to produce some of the first radar interferograms of the Nepal earthquake.  These mapped how the ground was warped along a 170 km stretch of the fault, moving by up to ~1.4 m near Kathmandu.

We are now modelling the data to understand how the fault slipped at depth, establish the relationship with the large Mw 7.3 aftershock on the 12th May, and gauge how these events may have stressed the surrounding regions, making them more likely to fail in future.

At the same time, EwF scientists at Durham University and the British Geological Survey have been using high-resolution optical and multispectral imagery to map landslides in the region.  We have identified around 3,600 landslides that were either triggered or reactivated by the earthquake, using the maps to show where rivers are likely to be dammed and roads blocked. This has also highlighted the need to plan for the monsoon season which may reactivate or trigger even more deadly landslides.

Figure 2: Landslide map. Colour scale shows landslide intensity, with blue ~ 1 landslide/km2 and red ~29 landslides/km2. ( http://ewf.nerc.ac.uk/2015/05/28/nepal-updated-28-may-landslide-inventory-following-25-april-nepal-earthquake/) Image credit: University of Durham, EwF, BGS.  Satellite data have been provided via the International Charter for Space and Major Disasters and freely available online viewers: WorldView @ Digital Globe; USGS LandSat8; Bhuvan RS2; Astrium Imagery; Google Crisis.  Vector data: OSM. Digital Elevation Model: ASTER
Figure 2: Landslide map. Colour scale shows landslide intensity, with blue ~ 1 landslide/km2 and red ~29 landslides/km2. ( http://ewf.nerc.ac.uk/2015/05/28/nepal-updated-28-may-landslide-inventory-following-25-april-nepal-earthquake/) Image credit: University of Durham, EwF, BGS.  Satellite data have been provided via the International Charter for Space and Major Disasters and freely available online viewers: WorldView @ Digital Globe; USGS LandSat8; Bhuvan RS2; Astrium Imagery; Google Crisis.  Vector data: OSM. Digital Elevation Model: ASTER

Over the coming months, EwF researchers will continue to work on these topics as well as the many more questions raised by the Nepal earthquake. We hope that the lessons learned from this terrible event will bring us one step closer to improving resilience to future earthquakes, not just for Nepal and the countries across its borders, but for all earthquake-prone countries.

This is an abridged version of an article that appears in the current newsletter of the Geological Remote Sensing Group

 

 

Tectonics from above: recent advances in the use of high-resolution topography and imagery

RAS Specialist Discussion Meeting: Royal Astronomical Society, Burlington House, Piccadilly, London
13th March 2015 | Download the programme |

**Specialist Discussion Meeting open to all**

Organisers: Richard Walker (University of Oxford), James Hollingsworth (Arup), Ed Nissen (Colorado School of Mines) and Barry Parsons (University of Oxford)

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Topography is one of the most important geophysical observations that can be made at the Earth’s surface. Recent advances in topographic measurements have significantly improved the spatial resolutions available to earth scientists. Combining new high-resolution topography with high-resolution imagery allows Earth’s surface to be explored in a virtual environment, and comparison of pre- and post-event datasets allows the retrieval of 3D earthquake deformation fields.

The meeting aims to expose to a wider audience the new data sets and methods of analysis for measuring continental topography and surface displacements, and provide a forum for discussion of new tectonic applications of high-resolution topography and imagery.