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Earthquake research could improve seismic forecasts

The timing and size of three deadly earthquakes that struck Italy in 2016 may have been pre-determined, according to new research published in Earth and Planetary Science Letters that could improve future earthquake forecasts.

Credit: L.Gregory

A joint British-Italian team of geologists and seismologists have shown that the clustering of the three quakes might have been caused by the arrangement of a cross-cutting network of underground faults.

The findings show that although all three earthquakes occurred on the same major fault, several smaller faults prevented a single massive earthquake from occurring instead and also acted as pathways for naturally occurring fluids that triggered later earthquakes.

The cluster of three earthquakes, termed a “seismic sequence” by seismologists, each had magnitudes greater than six and killed more than 300 people in Italy’s Apennine mountains between 24 August and 30 October 2016.

Earthquake sequences

The research, led by COMET scientist Richard Walters from Durham University, comes on the second anniversary of the start of the earthquake sequence.

The researchers say the findings could have wider implications for the study of seismic hazards, enabling scientists to better understand potential earthquake sequences following a quake.

Dr Walters said: “These results address a long-standing mystery in earthquake science – why a major fault system sometimes fails in a single large earthquake that ruptures its entire length, versus failing in multiple smaller earthquakes drawn-out over months or years.

“Our results imply that even though we couldn’t have predicted when the earthquake sequence would start, once it got going, both the size and timing of the major earthquakes may have been pre-determined by the arrangement of faults at depth.

“This is all information we could hypothetically know before the event, and therefore, this could be a hugely important avenue for improving future earthquake forecasts.”

Location of survey site at rupture across a road near Castelluccio. The rupture occurred during the third earthquake in the seismic sequence and gives researchers a record of the deformation. Credit: L.Gregory

Thousands of aftershocks

Dr Walters and the team used satellite data to estimate which part of the fault failed in each earthquake, and compared this pattern with the location and timing of thousands of tiny aftershocks throughout the seismic sequence.

They found that intersections of small faults with the main fault system separated each of the three largest earthquakes, strongly suggesting these intersections stop the growth of each earthquake and prevent the faults failing in a single large event.

In addition, the scientists also found that after the first earthquake, thousands of aftershocks crept northwards along these same fault intersections at a rate of around 100 metres per day, in a manner consistent with naturally occurring water and gas being pumped along the faults by the first earthquake on 24 August, 2016.

The second earthquake, on the 26 October, occurred exactly when these fluids reached its location, therefore controlling the relative timing of failure.

Dr Walters added: “It was a big surprise that these relatively small faults were having such a huge influence over the whole sequence.

“They stop the first earthquake in its tracks, and then they channel the fluids that start the sequence up again months later. No-one’s ever seen this before.”

Seismic hazard

Co-author and COMET associate Dr Laura Gregory from the University of Leeds said it was important to understand whether or not a fault fails in a seismic sequence, and that the team’s results were only made possible by combining a varied array of different datasets.

Dr Gregory said: “A seismic sequence has vastly different implications for seismic hazard compared to a single large earthquake. If the faults in Italy in 2016 had failed together in one big event, the impact on the local population would have been much worse.

“This is the first time we’ve ever had this quality of modern data over one of these earthquake sequences, and bringing together a range of specialists was key for unpicking how the earthquakes related to one another.

“I was scrambling over the mountainside immediately after each earthquake with British and Italian colleagues, measuring the metre-high cliffs that had suddenly formed. Meanwhile, other members of our team were analysing data from seismometers stationed around the world, or were mapping the tiny bending of the ground around the faults using satellites orbiting the planet at 500 miles altitude.”

The research was partly supported by both COMET and a NERC Urgency Grant.

 

 

Tamsin Mather receives 2018 Rosalind Franklin Award from Royal Society

COMET Oxford’s Professor Tamsin Mather is the latest recipient of the Royal Society’s Rosalind Franklin Award, recognising her achievements in volcanology as well as her ability to engage with the public about her research.

The award is made to an individual for an outstanding contribution to any area of Science, Technology, Engineering and Mathematics (STEM) and to support the promotion of women in STEM.

Tamsin will receive a silver gilt medal at her Award Lecture in October 2018.  Congratulations Tamsin from all of your COMET colleagues.

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 COMET 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-west towards Istanbul.

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

Led by COMET PhD student Ekbal Hussain[1], 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 and could eventually be released in an earthquake.”

Istanbul, straddling the Bosphorus Strait at the centre of the picture, and the surrounding area in northwestern Turkey captured by Envisat.  Turkey’s location makes it vulnerable to earthquakes, with the North Anatolian fault lying just 15 km south of Istanbul. Credit: ESA

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 and COMET Director 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.”

The full paper is: Hussain et al. (2018) Constant strain accumulation rate between major earthquakes on the North Anatolian Fault, Nature Communications, doi:10.1038/s41467-018-03739-2

[1] Now Remote Sensing Scientist at BGS Keyworth.  Dr Hussain is available for comment (ekhuss@bgs.ac.uk).

COMET honoured by Royal Astronomical Society

COMET’s achievements in Earth observation and modelling have been recognised by the Royal Astronomical Society (RAS) in their latest round of awards.

The 2018 RAS Group Achievement Award in Geophysics acknowledges COMET’s success in using satellite and ground-based observations and geophysical modelling to study earthquakes, volcanoes and tectonics across the globe.

COMET Director Tim Wright said: “We are delighted that our collective achievements have been recognised by the RAS in this way.  It’s particularly rewarding to receive an honour for the full breadth and depth of COMET’s research.”

In granting the award, the RAS highlighted COMET’s contributions to satellite geodesy, particularly Synthetic Aperture Radar Interferometry (InSAR), which has significantly improved COMET’s ability to respond to tectonic events.  Notably, COMET’s InSAR capabilities allowed rapid and in-depth investigations into the 2016 Amatrice, Italy and Kaikoura, New Zealand earthquakes.

Sentinel-1 interferogram of the ground deformation around Amatrice, Italy due to the 24 August 2016 earthquake.

Professor Wright added: “In both cases, we used InSAR to reveal the surprising complexity of the underlying faults, helping us to interpret the events and improve seismic hazard models.”

The launch of LiCSAR, COMET’s automated processing system, in December 2016 represented a major forward step in managing the vast amounts of data generated by the Sentinel-1 constellation, part of the EU’s Copernicus programme.  LiCSAR is enabling scientists to study specific earthquakes and eruptions as well as longer-term records of tectonic strain and ground deformation around volcanoes – including potential signs of eruption.

The service is already providing high-resolution deformation data for the entire Alpine-Himalayan seismic belt, where most of the planet’s deadly earthquakes occur, and will be expanded to provide global coverage of the tectonic belts over the next few years.

LiCSAR, the COMET-LiCS Sentinel-1 InSAR portal

COMET is also using automated Sentinel-1 data alongside other techniques to monitor deformation at over 900 volcanoes worldwide, including regions with hazardous volcanoes that have no ground-based monitoring in place.  The ultimate goal is to monitor all active land volcanoes, around 1,300 in total.

Elsewhere in COMET, satellite imagery is being combined with topographic data and fieldwork to create a database of active faults in the Tien Shan, a region of high seismic hazard in northern Central Asia.  Working with international partners, this is creating a robust regional model of strain accumulation and release that can be used in hazard management.

Atmospheric studies are also central to COMET’s work.  The satellite-borne Infrared Atmospheric Sounding Instrument (IASI) is being used to monitor volcanic ash and SO2 emissions such as those from Holuhraun (Iceland), whose eruption in 2014-15 was a major source of SO2 emissions.  Holuhraun’s remoteness made it difficult to monitor the volcano from the ground, especially during the harsh Icelandic winter, but using IASI data, COMET was able to provide insights into both the volcano’s behaviour and its environmental impacts.  The same approach has now been extended to other remote volcanoes such as Kamchatka (Russia) and Tungurahua (Ecuador).

Elevated levels of SO2 frequently identified using IASI measurements at volcanoes in Ecuador (a,b) and Kamchatka, Russia (c,d)

These are just a few aspects of COMET’s work, carried out by researchers across the UK as part of national and international collaborations.  At the same time, COMET is supporting a vibrant community of around 80 research students, working on topics ranging from monitoring volcano deformation to modelling earthquake sequences.   There is a strong commitment to developing the next generation of researchers, with COMET providing bespoke training to both members and the wider community on interpreting InSAR and GPS data to better understand geohazards and achieve scientific goals.

Moving forward, COMET remains committed to providing open data on earthquakes, tectonics and volcanoes to support scientists worldwide, and providing greater insight into how the Earth is deforming.

Professor Wright summarised: “This honour from RAS is a great reward for the efforts being made across the COMET family to improve our understanding of earthquakes and volcanoes.  The aim now is to continue to make ground-breaking progress that also benefits the communities and decision makers managing these geohazards as part of daily life.”

Notes

  1. The NERC-funded UK Centre for Observation and Modelling of Earthquakes, Volcanoes and Tectonics (COMET) provides national capability in the observation and modelling of tectonic and volcanic hazards. COMET delivers services, facilities, data and long-term research to produce world-leading science that can help the UK and others to prepare for, and respond rapidly to, earthquakes and eruptions.  Further information can be found at http://comet.nerc.ac.uk.
  2. COMET was founded in 2002, rapidly becoming a world-leading centre for the integrated exploitation of Earth Observation and ground-based data with geophysical models for research into geohazards. From 2008 to 2014, COMET formed a theme within the National Centre for Earth Observation (NCEO). Since 2014, COMET has worked in partnership with the British Geological Survey (BGS).
  3. COMET is currently distributed across nine UK academic institutions: the universities of Bristol, Cambridge, Durham, Leeds, Liverpool, Newcastle, Oxford and Reading and University College London. A full membership list can be found at http://comet.nerc.ac.uk/whos-who/.
  4. The Royal Astronomical Society (ras.org.uk) was founded in 1820 to encourage and promote the study of geophysics as well as astronomy and solar-system science. The Group Award recognises outstanding achievement by large consortia in any branch of astronomy or geophysics.  The full citation for COMET’s award can be found via the RAS website.
  5. LiCSAR, the COMET-LiCS Sentinel-1 InSAR portal can be found at http://comet.nerc.ac.uk/COMET-LiCS-portal. LiCSAR is funded by NERC via COMET (COME30001), the Looking inside the Continents from Space large grant (NE/K011006/1), and the Earthquakes without Frontiers project (NE/J01978X/1).

Juliet Biggs receives 2017 AGU Geodesy Section Award

COMET scientist Juliet Biggs will receive the 2017 Geodesy Section Award at this year’s American Geophysical Union (AGU) Fall Meeting, to be held 11–15 December in New Orleans.Juliet Biggs, recipient of the 2017 Geodesy Section Award.The award recognises Juliet’s outstanding contributions to the field of satellite geodesy for understanding both active volcanism and faulting.

On receiving the award, she said: “Many of the previous AGU Geodesy Section Award winners have been role models for me personally, and seeing my name among them is truly humbling.”

You can read the full article on the AGU’s Eos website.

Researchers track sneaky Eastern Rift emissions

COMET researchers at the University of Oxford have estimated the total carbon emissions emanating from the Eastern Rift – the eastern branch of the East African Rift, a zone near the horn of East Africa where the crust stretches and splits.

A hot spring bubbling with carbon dioxide in Ethiopia near the Main Ethiopian Rift. Credit: Jonathan Hunt

The new study published in Geochemistry, Geophysics, Geosystems, led by COMET PhD student Jonathan Hunt, working alongside Tamsin Mather and David Pyle as well as colleagues from Oxford and Addis Ababa University, Ethiopia, extrapolates from soil carbon dioxide surveys to estimate that the Eastern Rift emits somewhere between 3.9 and 32.7 million metric tons (Mt) of carbon dioxide each year.

The research demonstrates how, even near some seemingly inactive volcanoes, carbon dioxide from melted rock seeps out through cracks in the surrounding crust.

You can read more about the study on the Deep Carbon Observatory website.

The full reference is: Hunt JA, Zafu A, Mather TA, Pyle DM, Barry PH (2017) Spatially variable CO2 degassing in the Main Ethiopian Rift: Implications for magma storage, volatile transport and rift-related emissionsGeochemistry, Geophysics, Geosystems doi: 10.1002/2017GC006975

 

Permafrost dynamics in the remote Canadian Arctic revealed by high-resolution topographic measurements

Pablo J Gonzalez is a COMET researcher at the University of Liverpool.  He is currently (August 2017) carrying out a field campaign in the Canadian Arctic funded by the NERC British Arctic Office under the UK-Canada bursaries project Ice-landforms characterization due to permafrost dynamics around the Pingo National Landmark, Tuktoyaktuk, Northwest Territories, Canada.

Permafrost dynamics, related to ice aggradation and thawing, are effective climatic indicators.  Pingos (conical ice-cored hills, Fig. 1) concentrate large amounts of ice near the surface and, hence are highly sensitive systems to environmental changes.

Figure 1. Pingo National Landmark is a unique area with a high density of ice-landforms in Canada, hosting around 10% of pingos in the world. Credit: Wikipedia

Thus, the morphology and dynamics of pingos can be used to monitor regional effects of climate change over wide regions in the Arctic. However, we can identify two main difficulties in using pingos for environmental monitoring:

  1. The relationship of pingo morphology with its origin and permafrost conditions has not been established quantitatively.
  2. Monitoring pingo dynamics (growth, stability or collapse) has not been possible due to their small size (<300 m) and remote locations.

In this project, we aim to increase our understanding of pingo dynamics to fully exploit their potential as climate indicators. Here, we will apply novel methods to retrieve high spatial resolution (1-m) and very-high precision (<1m) topography based on satellite and drone technology.

The essential field work (late August 2017) is being carried out in collaboration with scientists from the Canada Centre for Remote Sensing, Natural Resources Canada (Dr. Yu Zhang and Dr. Sergey Samsonov), who are currently working in the area under the Polar Knowledge Canada project “Monitoring Land Surface and Permafrost Conditions along the Inuvik-Tuktoyaktuk Highway Corridor”.

This UK-Canada project will establish, for the first time, new and unique morphometric descriptions of a large number of pingos; conduct an exploratory analysis to establish links between current morphology with respect to genetics (origin), environmental conditions and stage of evolution; and unequivocally demonstrate the systematic decline, stability or growth of pingos in Tuktoyaktuk (Fig. 2), which could be linked to current climate change in the Western Canadian Arctic.

Figure 2. Location of Tuktoyaktuk, Northwestern Territories, Canada. Credit: Google Maps

 

Sentinel-1 satellites reveal pre-event movements and source areas of the Maoxian landslides, China

At about 5:38am local time on 24 June 2017 (21:38 on 23 June 2017 UTC), a massive landslide struck Xinmo Village, Maoxian County, Sichuan Province in China. Sichuan province is prone to earthquakes, including the 2008 Mw 7.9 Wenchuan earthquake that killed over 70,000 people, as well as the 1933 Mw 7.3 Diexi earthquake with a death toll of up to 9300.

Authorities have confirmed that the Maoxian landslide was triggered by heavy rain. The Maoxian landslide swept 64 homes in Xinmo village, blocking a 2km section of river and burying 1,600 meters of road. The collapsed rubble was estimated to be about eight million cubic meters (Figure 1a). Three days later (on 27 June 2017), a second landslide hit Xinmo Village; almost in the same time, another landslide occurred in Shidaguan Town, 20km away from Xinmo Village (Figure 1b).

Figure 1. The Maoxian landslides: (a) Xinmo Village (24 June 2017 local time); (b) Shidaguan  Town (27 June 2017 local time)

As part of the ESA’s Copernicus Program, the Sentinel-1 mission comprises a constellation of two polar-orbiting satellites, operating day and night performing C-band synthetic aperture radar imaging in all-weather conditions. Sentinel-1 images acquired before and after events such as landslides, earthquakes or volcanoes offer information on the extent and surface displacements of affected areas, which can be used for damage and future hazard assessment.

A joint team from Newcastle University (UK), Chengdu University of Technology, Tongji University, China Academy of Space Technology and Wuhan University (China) have been racing against time to respond these two events by combining ESA’s Sentinel-1, Chinese Gaofen-2/3 with field observations.

“Sentinel-1 acquired a post-event image thirteen and half hours after the Xinmo event, and provided us the first interferogram for the Xinmo landslide.” said Professor Zhenhong Li, Professor of Imaging Geodesy at Newcastle University, “This first Sentinel-1 interferogram, together with its corresponding coherence and amplitude maps, not only helped us identify the source area of this massive landslide, but also assisted with mapping the landslide boundary (Figure 2).”

Figure 2. The Xinmo landslide: (a) the first Sentinel-1 interferogram (20170612-20170624);  (b) UAV imagery. Note: (1) Red lines represent the landslide boundary derived from InSAR observations; (2) Yellow lines indicate relatively stable areas; and (3) Green and while circles imply the source area of this massive landslide.

“More importantly, through the analysis of the archived Sentinel-1 data, we found that pre-event movements exhibited in the source area during the period from 14 May to 19 June 2017 for the Xinmo event.”

GIF

Pre-event signals are even clearer for the Shidaguan landslide, suggesting it had been sliding for a while.

GIF

“It is well known that landslides are hard to predict” said Professor Qiang Xu, Geologist with Chengdu University of Technology, “This study convincingly demonstrates that InSAR can be used to detect and map active landslides, which is a great achievement.”

After presenting the joint research findings in the Dragon-4 symposium at Copenhagen on 27 June 2017, Professor Deren Li, Academician of Chinese Academy of Sciences (CAS) and Chinese Academy of Engineering (CAE) at Wuhan University concluded, “This joint effort suggests that landslide Early Warning System (EWS) might be encouraging. There are a range of factors we should consider for EWS, such as real time, automatic, spatial and temporal resolutions, and data uncertainty.”

 

Intrusive activity at Cerro Azul Volcano, Galápagos Islands (Ecuador)

Cerro Azul is the southernmost active volcano on Isabela Island, Galápagos (Ecuador). On 18-19 March 2017, seismic activity increased on the SE flank of the volcano.

On the same day, the Instituto Geofisico Escuela Politécnica National (IGEPN), the organisation responsible for the monitoring of Ecuadorian volcanoes, issued a warning for a possible imminent eruption.

The recorded seismicity was composed of volcano tectonic (VT) earthquakes, consistent with processes of rock fracturing, with the majority of the events having magnitude ranging between 2.4 and 3.  There were also sporadic events with magnitude up to 3.6 (see the second activity update released by IGEPN on 24 March).

The Sentinel-1 satellite acquired synthetic aperture radar data on 7  and 8 of March, prior to the onset of the seismic activity, and on 19 and 20 March, once seismicity started to exceed background levels both in terms of number of earthquakes and of energy release.

Applying SAR interferometric techniques (e.g. InSAR) showed significant deformation (up to 14 cm) in the region affected by the seismic swarm. More specifically, the InSAR data shows uplift at the southeastern flank of the volcano and contemporary subsidence centered at the summit of the volcano.

Sentinel-1 interferogram showing deformation caused by the magmatic intrusion as of 20 March 2017. Each color fringe corresponds to ~2.8 cm of displacement in the direction between the ground and the satellite.

COMET researcher Marco Bagnardi, working with the IGEPN, carried out a preliminary analysis of the InSAR data and observed that the deformation (at least as of 20 March 2017) can be explained by the intrusion of a 20-40 million cubic meters sill at a depth of ~5 km beneath the surface of the volcano.

Modelling results from the inversion of InSAR data. The proposed model is composed of a horizontal sill intrusion at ~5 km depth (black rectangle) fed by a deflating source at ~6 km depth (black star).

Such intrusion is likely to be fed by a 6 km deep reservoir, cantered beneath the summit of the volcano. The location of the intrusion well matches the location of the seismicity recorded by IGEPN.

Earthquake locations between 13 and 25 March 2017. Credit: IGEPN “Informe Especial Cerro Azul No. 2 – 2017”.

Marco Bagnardi said: “Within ten hours from receiving the warning from IGEPN, we were able to get hold of the most recent Sentinel-1 data for the area, process them to form differential interferograms, invert the data to infer the source of the observed deformation, and pass on the information to our Ecuadorian colleagues.”

The seismic activity seems to be continuing today.  IGEPN is currently proposing two possible scenarios for the evolution of this episode of volcanic unrest:

  • the intrusion could reach the surface and feed an effusive eruption in the coming days or weeks, as happened in 1998 and 2008; or
  • seismic activity and deformation could return to background level without the eruption of magma at the surface.

The next Sentinel-1 acquisitions will be on 1 and 2 April.  They will hopefully shed more light on the nature of the magmatic intrusion and on its evolution since 20 March.