Scientists collaborating through the UK Natural Environment Research Council’s Centre for the Observation and Modelling of Earthquakes, Volcanoes and Tectonics (COMET), used Sentinel-1A’s special capabilities to analyse the quake in California's Napa Valley.
‘Synthetic aperture radar interferometry’ is a technique where two or more satellite radar images of the same area are combined to detect large-scale surface changes. Small changes on the ground modify the reflected radar signal and lead to rainbow-coloured fringes in the ‘interferogram’.
Yngvar Larsen from Norway’s Northern Research Institute and Petar Marinkovic from PPO.labs in the Netherlands processed this new interferogram from two images: one that Sentinel-1A acquired on 7 August, the day the satellite reached its operational orbit, and another captured on 31 August.
It clearly confirms that part of the West Napa Fault system was responsible for the 6.0 earthquake that rocked California’s wine-producing region. However, the fault had not been identified as being particularly hazardous prior to the quake that hit on 24 August.
Importantly, the extent of the ground deformation in the interferogram shows that the fault slip continues further north than the extent of the rupture mapped at the surface.
Sharp lines in the interferogram show minor movements on other faults, such as the part of the West Napa Fault system that crosses Napa airport.
COMET Director, Tim Wright, from University of Leeds said, “This successful demonstration of Sentinel-1A marks the beginning of a new era for our ability to map earthquakes from space.
“COMET scientists are building a system that will provide these results routinely for all continental earthquakes, as well as mapping the slow warping of the ground surface that leads to earthquakes.”
Prof. Andy Hooper, also at the University of Leeds, added, “This satellite represents a sea change in the way we will be able to monitor catastrophic events such as earthquakes and volcanic eruptions in the future, due to its systematic observation strategy.”
Austin Elliott, a PhD student at the University of California Davis, one of the team mapping the earthquake rupture on the ground, said, “The data from satellites are invaluable for completely identifying the surface break of the earthquake – deformation maps from satellite imagery guide us to places where rupture has not yet been mapped.”
Although Sentinel-1A is still being commissioned, ESA was able to respond specifically to the incident and provide data rapidly to the science team.
Betlem Rosich-Tell, ESA’s Project Manager for the Copernicus Sentinel-1 Payload Data Ground Segment, noted, “I’m very pleased to see that the dedication from the various Sentinel-1 ground segment teams, both at ESA and at industry, meant that we could react to an emergency at this early stage in the mission and provide an ‘out-of-the-box utilisation’ of Sentinel-1A data.
“The Sentinel-1 ground segment is designed to fully exploit the potential of the mission by acquiring, processing and delivering a huge amount of high-quality data products in a timely manner for both operational and scientific applications.”
Sentinel-1A passes over the same spot on the ground every 12 days. However, once its identical twin, Sentinel-1B, is launched in 2016, this will be cut to just six days, so that changes can be mapped even faster.
1. Sentinel-1 carries an advanced synthetic aperture radar that works in several specialised modes to provide detailed imagery for Europe’s Copernicus programme. These data will be used for applications such as monitoring the oceans, including shipping lanes, sea ice and oil spills. It also provides data to map changing land cover, ground deformation, ice shelves and glaciers, and can be used to help emergency response when disasters such as floods strike and to support humanitarian relief efforts at times of crisis. Image copyright ESA/ATG medialab
2. The biggest earthquake in 25 years struck California’s Napa Valley in the early hours of 24 August 2014. By processing two Sentinel-1A images, which were acquired on 7 August and 31 August 2014 over this wine-producing region, an interferogram was generated. The two round shapes around Napa valley, which are visible in the central part of the image show how the ground moved during the quake. Deformation on the ground causes phase changes in radar signals that appear as the rainbow-coloured patterns. Each colour cycle corresponds to a deformation of 28 mm deformation. The maximum deformation is more than 10 cm, and an area of about 30x30 km was affected significantly. Interferograms like these are being used by scientists on the ground to help them map the surface rupture and model the earthquake. This interferogram very clearly shows the fault that caused the earthquake, which had not been identified as being particularly hazardous prior to the event. Despite this interferogram being computed with images acquired in the satellite’s ‘stripmap mode’, which is not going to be the default mode when operational, this result demonstrates the capability of Sentinel-1A and marks the beginning of a new era for our ability to map earthquakes from space. Image copyright Copernicus data (2014)/ESA/PPO.labs/Norut/COMET-SEOM Insarap study
3. Fault damage in the suburbs west of Napa, California from the 6.0 magnitude earthquake that struck on 24 August. The fault rupture ran through homes and across roads, buckling the tarmac surface and pavements, resulting in damage expected to cost hundreds of millions of dollars. Photo copyright A. Elliott–UC Davis
Source: European Space Agency (www.esa.int)
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